8182299: Enable disabled clang warnings, build on OSX 10 + Xcode 8
8182656: Make the required changes in GC code to build on OSX 10 + Xcode 8
8182657: Make the required changes in Runtime code to build on OSX 10 + Xcode 8
8182658: Make the required changes in Compiler code to build on OSX 10 + Xcode 8
Reviewed-by: jwilhelm, ehelin, phh
Contributed-by: phh <hohensee@amazon.com>, jwilhelm <jesper.wilhelmsson@oracle.com>
/*
* Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*
*/
#include "precompiled.hpp"
#include "compiler/compileLog.hpp"
#include "memory/allocation.inline.hpp"
#include "opto/addnode.hpp"
#include "opto/callnode.hpp"
#include "opto/castnode.hpp"
#include "opto/connode.hpp"
#include "opto/convertnode.hpp"
#include "opto/divnode.hpp"
#include "opto/loopnode.hpp"
#include "opto/mulnode.hpp"
#include "opto/movenode.hpp"
#include "opto/opaquenode.hpp"
#include "opto/rootnode.hpp"
#include "opto/runtime.hpp"
#include "opto/subnode.hpp"
#include "opto/superword.hpp"
#include "opto/vectornode.hpp"
//------------------------------is_loop_exit-----------------------------------
// Given an IfNode, return the loop-exiting projection or NULL if both
// arms remain in the loop.
Node *IdealLoopTree::is_loop_exit(Node *iff) const {
if( iff->outcnt() != 2 ) return NULL; // Ignore partially dead tests
PhaseIdealLoop *phase = _phase;
// Test is an IfNode, has 2 projections. If BOTH are in the loop
// we need loop unswitching instead of peeling.
if( !is_member(phase->get_loop( iff->raw_out(0) )) )
return iff->raw_out(0);
if( !is_member(phase->get_loop( iff->raw_out(1) )) )
return iff->raw_out(1);
return NULL;
}
//=============================================================================
//------------------------------record_for_igvn----------------------------
// Put loop body on igvn work list
void IdealLoopTree::record_for_igvn() {
for( uint i = 0; i < _body.size(); i++ ) {
Node *n = _body.at(i);
_phase->_igvn._worklist.push(n);
}
}
//------------------------------compute_exact_trip_count-----------------------
// Compute loop trip count if possible. Do not recalculate trip count for
// split loops (pre-main-post) which have their limits and inits behind Opaque node.
void IdealLoopTree::compute_trip_count(PhaseIdealLoop* phase) {
if (!_head->as_Loop()->is_valid_counted_loop()) {
return;
}
CountedLoopNode* cl = _head->as_CountedLoop();
// Trip count may become nonexact for iteration split loops since
// RCE modifies limits. Note, _trip_count value is not reset since
// it is used to limit unrolling of main loop.
cl->set_nonexact_trip_count();
// Loop's test should be part of loop.
if (!phase->is_member(this, phase->get_ctrl(cl->loopexit()->in(CountedLoopEndNode::TestValue))))
return; // Infinite loop
#ifdef ASSERT
BoolTest::mask bt = cl->loopexit()->test_trip();
assert(bt == BoolTest::lt || bt == BoolTest::gt ||
bt == BoolTest::ne, "canonical test is expected");
#endif
Node* init_n = cl->init_trip();
Node* limit_n = cl->limit();
if (init_n != NULL && limit_n != NULL) {
// Use longs to avoid integer overflow.
int stride_con = cl->stride_con();
jlong init_con = phase->_igvn.type(init_n)->is_int()->_lo;
jlong limit_con = phase->_igvn.type(limit_n)->is_int()->_hi;
int stride_m = stride_con - (stride_con > 0 ? 1 : -1);
jlong trip_count = (limit_con - init_con + stride_m)/stride_con;
if (trip_count > 0 && (julong)trip_count < (julong)max_juint) {
if (init_n->is_Con() && limit_n->is_Con()) {
// Set exact trip count.
cl->set_exact_trip_count((uint)trip_count);
} else if (cl->unrolled_count() == 1) {
// Set maximum trip count before unrolling.
cl->set_trip_count((uint)trip_count);
}
}
}
}
//------------------------------compute_profile_trip_cnt----------------------------
// Compute loop trip count from profile data as
// (backedge_count + loop_exit_count) / loop_exit_count
void IdealLoopTree::compute_profile_trip_cnt( PhaseIdealLoop *phase ) {
if (!_head->is_CountedLoop()) {
return;
}
CountedLoopNode* head = _head->as_CountedLoop();
if (head->profile_trip_cnt() != COUNT_UNKNOWN) {
return; // Already computed
}
float trip_cnt = (float)max_jint; // default is big
Node* back = head->in(LoopNode::LoopBackControl);
while (back != head) {
if ((back->Opcode() == Op_IfTrue || back->Opcode() == Op_IfFalse) &&
back->in(0) &&
back->in(0)->is_If() &&
back->in(0)->as_If()->_fcnt != COUNT_UNKNOWN &&
back->in(0)->as_If()->_prob != PROB_UNKNOWN) {
break;
}
back = phase->idom(back);
}
if (back != head) {
assert((back->Opcode() == Op_IfTrue || back->Opcode() == Op_IfFalse) &&
back->in(0), "if-projection exists");
IfNode* back_if = back->in(0)->as_If();
float loop_back_cnt = back_if->_fcnt * back_if->_prob;
// Now compute a loop exit count
float loop_exit_cnt = 0.0f;
for( uint i = 0; i < _body.size(); i++ ) {
Node *n = _body[i];
if( n->is_If() ) {
IfNode *iff = n->as_If();
if( iff->_fcnt != COUNT_UNKNOWN && iff->_prob != PROB_UNKNOWN ) {
Node *exit = is_loop_exit(iff);
if( exit ) {
float exit_prob = iff->_prob;
if (exit->Opcode() == Op_IfFalse) exit_prob = 1.0 - exit_prob;
if (exit_prob > PROB_MIN) {
float exit_cnt = iff->_fcnt * exit_prob;
loop_exit_cnt += exit_cnt;
}
}
}
}
}
if (loop_exit_cnt > 0.0f) {
trip_cnt = (loop_back_cnt + loop_exit_cnt) / loop_exit_cnt;
} else {
// No exit count so use
trip_cnt = loop_back_cnt;
}
}
#ifndef PRODUCT
if (TraceProfileTripCount) {
tty->print_cr("compute_profile_trip_cnt lp: %d cnt: %f\n", head->_idx, trip_cnt);
}
#endif
head->set_profile_trip_cnt(trip_cnt);
}
//---------------------is_invariant_addition-----------------------------
// Return nonzero index of invariant operand for an Add or Sub
// of (nonconstant) invariant and variant values. Helper for reassociate_invariants.
int IdealLoopTree::is_invariant_addition(Node* n, PhaseIdealLoop *phase) {
int op = n->Opcode();
if (op == Op_AddI || op == Op_SubI) {
bool in1_invar = this->is_invariant(n->in(1));
bool in2_invar = this->is_invariant(n->in(2));
if (in1_invar && !in2_invar) return 1;
if (!in1_invar && in2_invar) return 2;
}
return 0;
}
//---------------------reassociate_add_sub-----------------------------
// Reassociate invariant add and subtract expressions:
//
// inv1 + (x + inv2) => ( inv1 + inv2) + x
// (x + inv2) + inv1 => ( inv1 + inv2) + x
// inv1 + (x - inv2) => ( inv1 - inv2) + x
// inv1 - (inv2 - x) => ( inv1 - inv2) + x
// (x + inv2) - inv1 => (-inv1 + inv2) + x
// (x - inv2) + inv1 => ( inv1 - inv2) + x
// (x - inv2) - inv1 => (-inv1 - inv2) + x
// inv1 + (inv2 - x) => ( inv1 + inv2) - x
// inv1 - (x - inv2) => ( inv1 + inv2) - x
// (inv2 - x) + inv1 => ( inv1 + inv2) - x
// (inv2 - x) - inv1 => (-inv1 + inv2) - x
// inv1 - (x + inv2) => ( inv1 - inv2) - x
//
Node* IdealLoopTree::reassociate_add_sub(Node* n1, PhaseIdealLoop *phase) {
if ((!n1->is_Add() && !n1->is_Sub()) || n1->outcnt() == 0) return NULL;
if (is_invariant(n1)) return NULL;
int inv1_idx = is_invariant_addition(n1, phase);
if (!inv1_idx) return NULL;
// Don't mess with add of constant (igvn moves them to expression tree root.)
if (n1->is_Add() && n1->in(2)->is_Con()) return NULL;
Node* inv1 = n1->in(inv1_idx);
Node* n2 = n1->in(3 - inv1_idx);
int inv2_idx = is_invariant_addition(n2, phase);
if (!inv2_idx) return NULL;
Node* x = n2->in(3 - inv2_idx);
Node* inv2 = n2->in(inv2_idx);
bool neg_x = n2->is_Sub() && inv2_idx == 1;
bool neg_inv2 = n2->is_Sub() && inv2_idx == 2;
bool neg_inv1 = n1->is_Sub() && inv1_idx == 2;
if (n1->is_Sub() && inv1_idx == 1) {
neg_x = !neg_x;
neg_inv2 = !neg_inv2;
}
Node* inv1_c = phase->get_ctrl(inv1);
Node* inv2_c = phase->get_ctrl(inv2);
Node* n_inv1;
if (neg_inv1) {
Node *zero = phase->_igvn.intcon(0);
phase->set_ctrl(zero, phase->C->root());
n_inv1 = new SubINode(zero, inv1);
phase->register_new_node(n_inv1, inv1_c);
} else {
n_inv1 = inv1;
}
Node* inv;
if (neg_inv2) {
inv = new SubINode(n_inv1, inv2);
} else {
inv = new AddINode(n_inv1, inv2);
}
phase->register_new_node(inv, phase->get_early_ctrl(inv));
Node* addx;
if (neg_x) {
addx = new SubINode(inv, x);
} else {
addx = new AddINode(x, inv);
}
phase->register_new_node(addx, phase->get_ctrl(x));
phase->_igvn.replace_node(n1, addx);
assert(phase->get_loop(phase->get_ctrl(n1)) == this, "");
_body.yank(n1);
return addx;
}
//---------------------reassociate_invariants-----------------------------
// Reassociate invariant expressions:
void IdealLoopTree::reassociate_invariants(PhaseIdealLoop *phase) {
for (int i = _body.size() - 1; i >= 0; i--) {
Node *n = _body.at(i);
for (int j = 0; j < 5; j++) {
Node* nn = reassociate_add_sub(n, phase);
if (nn == NULL) break;
n = nn; // again
};
}
}
//------------------------------policy_peeling---------------------------------
// Return TRUE or FALSE if the loop should be peeled or not. Peel if we can
// make some loop-invariant test (usually a null-check) happen before the loop.
bool IdealLoopTree::policy_peeling( PhaseIdealLoop *phase ) const {
Node *test = ((IdealLoopTree*)this)->tail();
int body_size = ((IdealLoopTree*)this)->_body.size();
// Peeling does loop cloning which can result in O(N^2) node construction
if( body_size > 255 /* Prevent overflow for large body_size */
|| (body_size * body_size + phase->C->live_nodes()) > phase->C->max_node_limit() ) {
return false; // too large to safely clone
}
// check for vectorized loops, any peeling done was already applied
if (_head->is_CountedLoop() && _head->as_CountedLoop()->do_unroll_only()) return false;
while( test != _head ) { // Scan till run off top of loop
if( test->is_If() ) { // Test?
Node *ctrl = phase->get_ctrl(test->in(1));
if (ctrl->is_top())
return false; // Found dead test on live IF? No peeling!
// Standard IF only has one input value to check for loop invariance
assert(test->Opcode() == Op_If || test->Opcode() == Op_CountedLoopEnd || test->Opcode() == Op_RangeCheck, "Check this code when new subtype is added");
// Condition is not a member of this loop?
if( !is_member(phase->get_loop(ctrl)) &&
is_loop_exit(test) )
return true; // Found reason to peel!
}
// Walk up dominators to loop _head looking for test which is
// executed on every path thru loop.
test = phase->idom(test);
}
return false;
}
//------------------------------peeled_dom_test_elim---------------------------
// If we got the effect of peeling, either by actually peeling or by making
// a pre-loop which must execute at least once, we can remove all
// loop-invariant dominated tests in the main body.
void PhaseIdealLoop::peeled_dom_test_elim( IdealLoopTree *loop, Node_List &old_new ) {
bool progress = true;
while( progress ) {
progress = false; // Reset for next iteration
Node *prev = loop->_head->in(LoopNode::LoopBackControl);//loop->tail();
Node *test = prev->in(0);
while( test != loop->_head ) { // Scan till run off top of loop
int p_op = prev->Opcode();
if( (p_op == Op_IfFalse || p_op == Op_IfTrue) &&
test->is_If() && // Test?
!test->in(1)->is_Con() && // And not already obvious?
// Condition is not a member of this loop?
!loop->is_member(get_loop(get_ctrl(test->in(1))))){
// Walk loop body looking for instances of this test
for( uint i = 0; i < loop->_body.size(); i++ ) {
Node *n = loop->_body.at(i);
if( n->is_If() && n->in(1) == test->in(1) /*&& n != loop->tail()->in(0)*/ ) {
// IfNode was dominated by version in peeled loop body
progress = true;
dominated_by( old_new[prev->_idx], n );
}
}
}
prev = test;
test = idom(test);
} // End of scan tests in loop
} // End of while( progress )
}
//------------------------------do_peeling-------------------------------------
// Peel the first iteration of the given loop.
// Step 1: Clone the loop body. The clone becomes the peeled iteration.
// The pre-loop illegally has 2 control users (old & new loops).
// Step 2: Make the old-loop fall-in edges point to the peeled iteration.
// Do this by making the old-loop fall-in edges act as if they came
// around the loopback from the prior iteration (follow the old-loop
// backedges) and then map to the new peeled iteration. This leaves
// the pre-loop with only 1 user (the new peeled iteration), but the
// peeled-loop backedge has 2 users.
// Step 3: Cut the backedge on the clone (so its not a loop) and remove the
// extra backedge user.
//
// orig
//
// stmt1
// |
// v
// loop predicate
// |
// v
// loop<----+
// | |
// stmt2 |
// | |
// v |
// if ^
// / \ |
// / \ |
// v v |
// false true |
// / \ |
// / ----+
// |
// v
// exit
//
//
// after clone loop
//
// stmt1
// |
// v
// loop predicate
// / \
// clone / \ orig
// / \
// / \
// v v
// +---->loop clone loop<----+
// | | | |
// | stmt2 clone stmt2 |
// | | | |
// | v v |
// ^ if clone If ^
// | / \ / \ |
// | / \ / \ |
// | v v v v |
// | true false false true |
// | / \ / \ |
// +---- \ / ----+
// \ /
// 1v v2
// region
// |
// v
// exit
//
//
// after peel and predicate move
//
// stmt1
// /
// /
// clone / orig
// /
// / +----------+
// / | |
// / loop predicate |
// / | |
// v v |
// TOP-->loop clone loop<----+ |
// | | | |
// stmt2 clone stmt2 | |
// | | | ^
// v v | |
// if clone If ^ |
// / \ / \ | |
// / \ / \ | |
// v v v v | |
// true false false true | |
// | \ / \ | |
// | \ / ----+ ^
// | \ / |
// | 1v v2 |
// v region |
// | | |
// | v |
// | exit |
// | |
// +--------------->-----------------+
//
//
// final graph
//
// stmt1
// |
// v
// stmt2 clone
// |
// v
// if clone
// / |
// / |
// v v
// false true
// | |
// | v
// | loop predicate
// | |
// | v
// | loop<----+
// | | |
// | stmt2 |
// | | |
// | v |
// v if ^
// | / \ |
// | / \ |
// | v v |
// | false true |
// | | \ |
// v v --+
// region
// |
// v
// exit
//
void PhaseIdealLoop::do_peeling( IdealLoopTree *loop, Node_List &old_new ) {
C->set_major_progress();
// Peeling a 'main' loop in a pre/main/post situation obfuscates the
// 'pre' loop from the main and the 'pre' can no longer have its
// iterations adjusted. Therefore, we need to declare this loop as
// no longer a 'main' loop; it will need new pre and post loops before
// we can do further RCE.
#ifndef PRODUCT
if (TraceLoopOpts) {
tty->print("Peel ");
loop->dump_head();
}
#endif
Node* head = loop->_head;
bool counted_loop = head->is_CountedLoop();
if (counted_loop) {
CountedLoopNode *cl = head->as_CountedLoop();
assert(cl->trip_count() > 0, "peeling a fully unrolled loop");
cl->set_trip_count(cl->trip_count() - 1);
if (cl->is_main_loop()) {
cl->set_normal_loop();
#ifndef PRODUCT
if (PrintOpto && VerifyLoopOptimizations) {
tty->print("Peeling a 'main' loop; resetting to 'normal' ");
loop->dump_head();
}
#endif
}
}
Node* entry = head->in(LoopNode::EntryControl);
// Step 1: Clone the loop body. The clone becomes the peeled iteration.
// The pre-loop illegally has 2 control users (old & new loops).
clone_loop( loop, old_new, dom_depth(head) );
// Step 2: Make the old-loop fall-in edges point to the peeled iteration.
// Do this by making the old-loop fall-in edges act as if they came
// around the loopback from the prior iteration (follow the old-loop
// backedges) and then map to the new peeled iteration. This leaves
// the pre-loop with only 1 user (the new peeled iteration), but the
// peeled-loop backedge has 2 users.
Node* new_entry = old_new[head->in(LoopNode::LoopBackControl)->_idx];
_igvn.hash_delete(head);
head->set_req(LoopNode::EntryControl, new_entry);
for (DUIterator_Fast jmax, j = head->fast_outs(jmax); j < jmax; j++) {
Node* old = head->fast_out(j);
if (old->in(0) == loop->_head && old->req() == 3 && old->is_Phi()) {
Node* new_exit_value = old_new[old->in(LoopNode::LoopBackControl)->_idx];
if (!new_exit_value ) // Backedge value is ALSO loop invariant?
// Then loop body backedge value remains the same.
new_exit_value = old->in(LoopNode::LoopBackControl);
_igvn.hash_delete(old);
old->set_req(LoopNode::EntryControl, new_exit_value);
}
}
// Step 3: Cut the backedge on the clone (so its not a loop) and remove the
// extra backedge user.
Node* new_head = old_new[head->_idx];
_igvn.hash_delete(new_head);
new_head->set_req(LoopNode::LoopBackControl, C->top());
for (DUIterator_Fast j2max, j2 = new_head->fast_outs(j2max); j2 < j2max; j2++) {
Node* use = new_head->fast_out(j2);
if (use->in(0) == new_head && use->req() == 3 && use->is_Phi()) {
_igvn.hash_delete(use);
use->set_req(LoopNode::LoopBackControl, C->top());
}
}
// Step 4: Correct dom-depth info. Set to loop-head depth.
int dd = dom_depth(head);
set_idom(head, head->in(1), dd);
for (uint j3 = 0; j3 < loop->_body.size(); j3++) {
Node *old = loop->_body.at(j3);
Node *nnn = old_new[old->_idx];
if (!has_ctrl(nnn))
set_idom(nnn, idom(nnn), dd-1);
}
// Now force out all loop-invariant dominating tests. The optimizer
// finds some, but we _know_ they are all useless.
peeled_dom_test_elim(loop,old_new);
loop->record_for_igvn();
}
#define EMPTY_LOOP_SIZE 7 // number of nodes in an empty loop
//------------------------------policy_maximally_unroll------------------------
// Calculate exact loop trip count and return true if loop can be maximally
// unrolled.
bool IdealLoopTree::policy_maximally_unroll( PhaseIdealLoop *phase ) const {
CountedLoopNode *cl = _head->as_CountedLoop();
assert(cl->is_normal_loop(), "");
if (!cl->is_valid_counted_loop())
return false; // Malformed counted loop
if (!cl->has_exact_trip_count()) {
// Trip count is not exact.
return false;
}
uint trip_count = cl->trip_count();
// Note, max_juint is used to indicate unknown trip count.
assert(trip_count > 1, "one iteration loop should be optimized out already");
assert(trip_count < max_juint, "exact trip_count should be less than max_uint.");
// Real policy: if we maximally unroll, does it get too big?
// Allow the unrolled mess to get larger than standard loop
// size. After all, it will no longer be a loop.
uint body_size = _body.size();
uint unroll_limit = (uint)LoopUnrollLimit * 4;
assert( (intx)unroll_limit == LoopUnrollLimit * 4, "LoopUnrollLimit must fit in 32bits");
if (trip_count > unroll_limit || body_size > unroll_limit) {
return false;
}
// Fully unroll a loop with few iterations regardless next
// conditions since following loop optimizations will split
// such loop anyway (pre-main-post).
if (trip_count <= 3)
return true;
// Take into account that after unroll conjoined heads and tails will fold,
// otherwise policy_unroll() may allow more unrolling than max unrolling.
uint new_body_size = EMPTY_LOOP_SIZE + (body_size - EMPTY_LOOP_SIZE) * trip_count;
uint tst_body_size = (new_body_size - EMPTY_LOOP_SIZE) / trip_count + EMPTY_LOOP_SIZE;
if (body_size != tst_body_size) // Check for int overflow
return false;
if (new_body_size > unroll_limit ||
// Unrolling can result in a large amount of node construction
new_body_size >= phase->C->max_node_limit() - phase->C->live_nodes()) {
return false;
}
// Do not unroll a loop with String intrinsics code.
// String intrinsics are large and have loops.
for (uint k = 0; k < _body.size(); k++) {
Node* n = _body.at(k);
switch (n->Opcode()) {
case Op_StrComp:
case Op_StrEquals:
case Op_StrIndexOf:
case Op_StrIndexOfChar:
case Op_EncodeISOArray:
case Op_AryEq:
case Op_HasNegatives: {
return false;
}
#if INCLUDE_RTM_OPT
case Op_FastLock:
case Op_FastUnlock: {
// Don't unroll RTM locking code because it is large.
if (UseRTMLocking) {
return false;
}
}
#endif
} // switch
}
return true; // Do maximally unroll
}
//------------------------------policy_unroll----------------------------------
// Return TRUE or FALSE if the loop should be unrolled or not. Unroll if
// the loop is a CountedLoop and the body is small enough.
bool IdealLoopTree::policy_unroll(PhaseIdealLoop *phase) {
CountedLoopNode *cl = _head->as_CountedLoop();
assert(cl->is_normal_loop() || cl->is_main_loop(), "");
if (!cl->is_valid_counted_loop())
return false; // Malformed counted loop
// Protect against over-unrolling.
// After split at least one iteration will be executed in pre-loop.
if (cl->trip_count() <= (uint)(cl->is_normal_loop() ? 2 : 1)) return false;
_local_loop_unroll_limit = LoopUnrollLimit;
_local_loop_unroll_factor = 4;
int future_unroll_ct = cl->unrolled_count() * 2;
if (!cl->do_unroll_only()) {
if (future_unroll_ct > LoopMaxUnroll) return false;
} else {
// obey user constraints on vector mapped loops with additional unrolling applied
int unroll_constraint = (cl->slp_max_unroll()) ? cl->slp_max_unroll() : 1;
if ((future_unroll_ct / unroll_constraint) > LoopMaxUnroll) return false;
}
// Check for initial stride being a small enough constant
if (abs(cl->stride_con()) > (1<<2)*future_unroll_ct) return false;
// Don't unroll if the next round of unrolling would push us
// over the expected trip count of the loop. One is subtracted
// from the expected trip count because the pre-loop normally
// executes 1 iteration.
if (UnrollLimitForProfileCheck > 0 &&
cl->profile_trip_cnt() != COUNT_UNKNOWN &&
future_unroll_ct > UnrollLimitForProfileCheck &&
(float)future_unroll_ct > cl->profile_trip_cnt() - 1.0) {
return false;
}
// When unroll count is greater than LoopUnrollMin, don't unroll if:
// the residual iterations are more than 10% of the trip count
// and rounds of "unroll,optimize" are not making significant progress
// Progress defined as current size less than 20% larger than previous size.
if (UseSuperWord && cl->node_count_before_unroll() > 0 &&
future_unroll_ct > LoopUnrollMin &&
(future_unroll_ct - 1) * (100 / LoopPercentProfileLimit) > cl->profile_trip_cnt() &&
1.2 * cl->node_count_before_unroll() < (double)_body.size()) {
return false;
}
Node *init_n = cl->init_trip();
Node *limit_n = cl->limit();
int stride_con = cl->stride_con();
// Non-constant bounds.
// Protect against over-unrolling when init or/and limit are not constant
// (so that trip_count's init value is maxint) but iv range is known.
if (init_n == NULL || !init_n->is_Con() ||
limit_n == NULL || !limit_n->is_Con()) {
Node* phi = cl->phi();
if (phi != NULL) {
assert(phi->is_Phi() && phi->in(0) == _head, "Counted loop should have iv phi.");
const TypeInt* iv_type = phase->_igvn.type(phi)->is_int();
int next_stride = stride_con * 2; // stride after this unroll
if (next_stride > 0) {
if (iv_type->_lo + next_stride <= iv_type->_lo || // overflow
iv_type->_lo + next_stride > iv_type->_hi) {
return false; // over-unrolling
}
} else if (next_stride < 0) {
if (iv_type->_hi + next_stride >= iv_type->_hi || // overflow
iv_type->_hi + next_stride < iv_type->_lo) {
return false; // over-unrolling
}
}
}
}
// After unroll limit will be adjusted: new_limit = limit-stride.
// Bailout if adjustment overflow.
const TypeInt* limit_type = phase->_igvn.type(limit_n)->is_int();
if ((stride_con > 0 && ((limit_type->_hi - stride_con) >= limit_type->_hi)) ||
(stride_con < 0 && ((limit_type->_lo - stride_con) <= limit_type->_lo)))
return false; // overflow
// Adjust body_size to determine if we unroll or not
uint body_size = _body.size();
// Key test to unroll loop in CRC32 java code
int xors_in_loop = 0;
// Also count ModL, DivL and MulL which expand mightly
for (uint k = 0; k < _body.size(); k++) {
Node* n = _body.at(k);
switch (n->Opcode()) {
case Op_XorI: xors_in_loop++; break; // CRC32 java code
case Op_ModL: body_size += 30; break;
case Op_DivL: body_size += 30; break;
case Op_MulL: body_size += 10; break;
case Op_StrComp:
case Op_StrEquals:
case Op_StrIndexOf:
case Op_StrIndexOfChar:
case Op_EncodeISOArray:
case Op_AryEq:
case Op_HasNegatives: {
// Do not unroll a loop with String intrinsics code.
// String intrinsics are large and have loops.
return false;
}
#if INCLUDE_RTM_OPT
case Op_FastLock:
case Op_FastUnlock: {
// Don't unroll RTM locking code because it is large.
if (UseRTMLocking) {
return false;
}
}
#endif
} // switch
}
if (UseSuperWord) {
if (!cl->is_reduction_loop()) {
phase->mark_reductions(this);
}
// Only attempt slp analysis when user controls do not prohibit it
if (LoopMaxUnroll > _local_loop_unroll_factor) {
// Once policy_slp_analysis succeeds, mark the loop with the
// maximal unroll factor so that we minimize analysis passes
if (future_unroll_ct >= _local_loop_unroll_factor) {
policy_unroll_slp_analysis(cl, phase, future_unroll_ct);
}
}
}
int slp_max_unroll_factor = cl->slp_max_unroll();
if (cl->has_passed_slp()) {
if (slp_max_unroll_factor >= future_unroll_ct) return true;
// Normal case: loop too big
return false;
}
// Check for being too big
if (body_size > (uint)_local_loop_unroll_limit) {
if (xors_in_loop >= 4 && body_size < (uint)LoopUnrollLimit*4) return true;
// Normal case: loop too big
return false;
}
if (cl->do_unroll_only()) {
if (TraceSuperWordLoopUnrollAnalysis) {
tty->print_cr("policy_unroll passed vector loop(vlen=%d,factor = %d)\n", slp_max_unroll_factor, future_unroll_ct);
}
}
// Unroll once! (Each trip will soon do double iterations)
return true;
}
void IdealLoopTree::policy_unroll_slp_analysis(CountedLoopNode *cl, PhaseIdealLoop *phase, int future_unroll_ct) {
// Enable this functionality target by target as needed
if (SuperWordLoopUnrollAnalysis) {
if (!cl->was_slp_analyzed()) {
SuperWord sw(phase);
sw.transform_loop(this, false);
// If the loop is slp canonical analyze it
if (sw.early_return() == false) {
sw.unrolling_analysis(_local_loop_unroll_factor);
}
}
if (cl->has_passed_slp()) {
int slp_max_unroll_factor = cl->slp_max_unroll();
if (slp_max_unroll_factor >= future_unroll_ct) {
int new_limit = cl->node_count_before_unroll() * slp_max_unroll_factor;
if (new_limit > LoopUnrollLimit) {
if (TraceSuperWordLoopUnrollAnalysis) {
tty->print_cr("slp analysis unroll=%d, default limit=%d\n", new_limit, _local_loop_unroll_limit);
}
_local_loop_unroll_limit = new_limit;
}
}
}
}
}
//------------------------------policy_align-----------------------------------
// Return TRUE or FALSE if the loop should be cache-line aligned. Gather the
// expression that does the alignment. Note that only one array base can be
// aligned in a loop (unless the VM guarantees mutual alignment). Note that
// if we vectorize short memory ops into longer memory ops, we may want to
// increase alignment.
bool IdealLoopTree::policy_align( PhaseIdealLoop *phase ) const {
return false;
}
//------------------------------policy_range_check-----------------------------
// Return TRUE or FALSE if the loop should be range-check-eliminated.
// Actually we do iteration-splitting, a more powerful form of RCE.
bool IdealLoopTree::policy_range_check( PhaseIdealLoop *phase ) const {
if (!RangeCheckElimination) return false;
CountedLoopNode *cl = _head->as_CountedLoop();
// If we unrolled with no intention of doing RCE and we later
// changed our minds, we got no pre-loop. Either we need to
// make a new pre-loop, or we gotta disallow RCE.
if (cl->is_main_no_pre_loop()) return false; // Disallowed for now.
Node *trip_counter = cl->phi();
// check for vectorized loops, some opts are no longer needed
if (cl->do_unroll_only()) return false;
// Check loop body for tests of trip-counter plus loop-invariant vs
// loop-invariant.
for (uint i = 0; i < _body.size(); i++) {
Node *iff = _body[i];
if (iff->Opcode() == Op_If ||
iff->Opcode() == Op_RangeCheck) { // Test?
// Comparing trip+off vs limit
Node *bol = iff->in(1);
if (bol->req() != 2) continue; // dead constant test
if (!bol->is_Bool()) {
assert(bol->Opcode() == Op_Conv2B, "predicate check only");
continue;
}
if (bol->as_Bool()->_test._test == BoolTest::ne)
continue; // not RC
Node *cmp = bol->in(1);
Node *rc_exp = cmp->in(1);
Node *limit = cmp->in(2);
Node *limit_c = phase->get_ctrl(limit);
if( limit_c == phase->C->top() )
return false; // Found dead test on live IF? No RCE!
if( is_member(phase->get_loop(limit_c) ) ) {
// Compare might have operands swapped; commute them
rc_exp = cmp->in(2);
limit = cmp->in(1);
limit_c = phase->get_ctrl(limit);
if( is_member(phase->get_loop(limit_c) ) )
continue; // Both inputs are loop varying; cannot RCE
}
if (!phase->is_scaled_iv_plus_offset(rc_exp, trip_counter, NULL, NULL)) {
continue;
}
// Yeah! Found a test like 'trip+off vs limit'
// Test is an IfNode, has 2 projections. If BOTH are in the loop
// we need loop unswitching instead of iteration splitting.
if( is_loop_exit(iff) )
return true; // Found reason to split iterations
} // End of is IF
}
return false;
}
//------------------------------policy_peel_only-------------------------------
// Return TRUE or FALSE if the loop should NEVER be RCE'd or aligned. Useful
// for unrolling loops with NO array accesses.
bool IdealLoopTree::policy_peel_only( PhaseIdealLoop *phase ) const {
// check for vectorized loops, any peeling done was already applied
if (_head->is_CountedLoop() && _head->as_CountedLoop()->do_unroll_only()) return false;
for( uint i = 0; i < _body.size(); i++ )
if( _body[i]->is_Mem() )
return false;
// No memory accesses at all!
return true;
}
//------------------------------clone_up_backedge_goo--------------------------
// If Node n lives in the back_ctrl block and cannot float, we clone a private
// version of n in preheader_ctrl block and return that, otherwise return n.
Node *PhaseIdealLoop::clone_up_backedge_goo( Node *back_ctrl, Node *preheader_ctrl, Node *n, VectorSet &visited, Node_Stack &clones ) {
if( get_ctrl(n) != back_ctrl ) return n;
// Only visit once
if (visited.test_set(n->_idx)) {
Node *x = clones.find(n->_idx);
if (x != NULL)
return x;
return n;
}
Node *x = NULL; // If required, a clone of 'n'
// Check for 'n' being pinned in the backedge.
if( n->in(0) && n->in(0) == back_ctrl ) {
assert(clones.find(n->_idx) == NULL, "dead loop");
x = n->clone(); // Clone a copy of 'n' to preheader
clones.push(x, n->_idx);
x->set_req( 0, preheader_ctrl ); // Fix x's control input to preheader
}
// Recursive fixup any other input edges into x.
// If there are no changes we can just return 'n', otherwise
// we need to clone a private copy and change it.
for( uint i = 1; i < n->req(); i++ ) {
Node *g = clone_up_backedge_goo( back_ctrl, preheader_ctrl, n->in(i), visited, clones );
if( g != n->in(i) ) {
if( !x ) {
assert(clones.find(n->_idx) == NULL, "dead loop");
x = n->clone();
clones.push(x, n->_idx);
}
x->set_req(i, g);
}
}
if( x ) { // x can legally float to pre-header location
register_new_node( x, preheader_ctrl );
return x;
} else { // raise n to cover LCA of uses
set_ctrl( n, find_non_split_ctrl(back_ctrl->in(0)) );
}
return n;
}
bool PhaseIdealLoop::cast_incr_before_loop(Node* incr, Node* ctrl, Node* loop) {
Node* castii = new CastIINode(incr, TypeInt::INT, true);
castii->set_req(0, ctrl);
register_new_node(castii, ctrl);
for (DUIterator_Fast imax, i = incr->fast_outs(imax); i < imax; i++) {
Node* n = incr->fast_out(i);
if (n->is_Phi() && n->in(0) == loop) {
int nrep = n->replace_edge(incr, castii);
return true;
}
}
return false;
}
//------------------------------insert_pre_post_loops--------------------------
// Insert pre and post loops. If peel_only is set, the pre-loop can not have
// more iterations added. It acts as a 'peel' only, no lower-bound RCE, no
// alignment. Useful to unroll loops that do no array accesses.
void PhaseIdealLoop::insert_pre_post_loops( IdealLoopTree *loop, Node_List &old_new, bool peel_only ) {
#ifndef PRODUCT
if (TraceLoopOpts) {
if (peel_only)
tty->print("PeelMainPost ");
else
tty->print("PreMainPost ");
loop->dump_head();
}
#endif
C->set_major_progress();
// Find common pieces of the loop being guarded with pre & post loops
CountedLoopNode *main_head = loop->_head->as_CountedLoop();
assert( main_head->is_normal_loop(), "" );
CountedLoopEndNode *main_end = main_head->loopexit();
guarantee(main_end != NULL, "no loop exit node");
assert( main_end->outcnt() == 2, "1 true, 1 false path only" );
uint dd_main_head = dom_depth(main_head);
uint max = main_head->outcnt();
Node *pre_header= main_head->in(LoopNode::EntryControl);
Node *init = main_head->init_trip();
Node *incr = main_end ->incr();
Node *limit = main_end ->limit();
Node *stride = main_end ->stride();
Node *cmp = main_end ->cmp_node();
BoolTest::mask b_test = main_end->test_trip();
// Need only 1 user of 'bol' because I will be hacking the loop bounds.
Node *bol = main_end->in(CountedLoopEndNode::TestValue);
if( bol->outcnt() != 1 ) {
bol = bol->clone();
register_new_node(bol,main_end->in(CountedLoopEndNode::TestControl));
_igvn.replace_input_of(main_end, CountedLoopEndNode::TestValue, bol);
}
// Need only 1 user of 'cmp' because I will be hacking the loop bounds.
if( cmp->outcnt() != 1 ) {
cmp = cmp->clone();
register_new_node(cmp,main_end->in(CountedLoopEndNode::TestControl));
_igvn.replace_input_of(bol, 1, cmp);
}
// Add the post loop
CountedLoopNode *post_head = NULL;
Node *main_exit = insert_post_loop(loop, old_new, main_head, main_end, incr, limit, post_head);
//------------------------------
// Step B: Create Pre-Loop.
// Step B1: Clone the loop body. The clone becomes the pre-loop. The main
// loop pre-header illegally has 2 control users (old & new loops).
clone_loop( loop, old_new, dd_main_head );
CountedLoopNode* pre_head = old_new[main_head->_idx]->as_CountedLoop();
CountedLoopEndNode* pre_end = old_new[main_end ->_idx]->as_CountedLoopEnd();
pre_head->set_pre_loop(main_head);
Node *pre_incr = old_new[incr->_idx];
// Reduce the pre-loop trip count.
pre_end->_prob = PROB_FAIR;
// Find the pre-loop normal exit.
Node* pre_exit = pre_end->proj_out(false);
assert( pre_exit->Opcode() == Op_IfFalse, "" );
IfFalseNode *new_pre_exit = new IfFalseNode(pre_end);
_igvn.register_new_node_with_optimizer( new_pre_exit );
set_idom(new_pre_exit, pre_end, dd_main_head);
set_loop(new_pre_exit, loop->_parent);
// Step B2: Build a zero-trip guard for the main-loop. After leaving the
// pre-loop, the main-loop may not execute at all. Later in life this
// zero-trip guard will become the minimum-trip guard when we unroll
// the main-loop.
Node *min_opaq = new Opaque1Node(C, limit);
Node *min_cmp = new CmpINode( pre_incr, min_opaq );
Node *min_bol = new BoolNode( min_cmp, b_test );
register_new_node( min_opaq, new_pre_exit );
register_new_node( min_cmp , new_pre_exit );
register_new_node( min_bol , new_pre_exit );
// Build the IfNode (assume the main-loop is executed always).
IfNode *min_iff = new IfNode( new_pre_exit, min_bol, PROB_ALWAYS, COUNT_UNKNOWN );
_igvn.register_new_node_with_optimizer( min_iff );
set_idom(min_iff, new_pre_exit, dd_main_head);
set_loop(min_iff, loop->_parent);
// Plug in the false-path, taken if we need to skip main-loop
_igvn.hash_delete( pre_exit );
pre_exit->set_req(0, min_iff);
set_idom(pre_exit, min_iff, dd_main_head);
set_idom(pre_exit->unique_out(), min_iff, dd_main_head);
// Make the true-path, must enter the main loop
Node *min_taken = new IfTrueNode( min_iff );
_igvn.register_new_node_with_optimizer( min_taken );
set_idom(min_taken, min_iff, dd_main_head);
set_loop(min_taken, loop->_parent);
// Plug in the true path
_igvn.hash_delete( main_head );
main_head->set_req(LoopNode::EntryControl, min_taken);
set_idom(main_head, min_taken, dd_main_head);
Arena *a = Thread::current()->resource_area();
VectorSet visited(a);
Node_Stack clones(a, main_head->back_control()->outcnt());
// Step B3: Make the fall-in values to the main-loop come from the
// fall-out values of the pre-loop.
for (DUIterator_Fast i2max, i2 = main_head->fast_outs(i2max); i2 < i2max; i2++) {
Node* main_phi = main_head->fast_out(i2);
if( main_phi->is_Phi() && main_phi->in(0) == main_head && main_phi->outcnt() > 0 ) {
Node *pre_phi = old_new[main_phi->_idx];
Node *fallpre = clone_up_backedge_goo(pre_head->back_control(),
main_head->init_control(),
pre_phi->in(LoopNode::LoopBackControl),
visited, clones);
_igvn.hash_delete(main_phi);
main_phi->set_req( LoopNode::EntryControl, fallpre );
}
}
// Nodes inside the loop may be control dependent on a predicate
// that was moved before the preloop. If the back branch of the main
// or post loops becomes dead, those nodes won't be dependent on the
// test that guards that loop nest anymore which could lead to an
// incorrect array access because it executes independently of the
// test that was guarding the loop nest. We add a special CastII on
// the if branch that enters the loop, between the input induction
// variable value and the induction variable Phi to preserve correct
// dependencies.
// CastII for the main loop:
bool inserted = cast_incr_before_loop( pre_incr, min_taken, main_head );
assert(inserted, "no castII inserted");
// Step B4: Shorten the pre-loop to run only 1 iteration (for now).
// RCE and alignment may change this later.
Node *cmp_end = pre_end->cmp_node();
assert( cmp_end->in(2) == limit, "" );
Node *pre_limit = new AddINode( init, stride );
// Save the original loop limit in this Opaque1 node for
// use by range check elimination.
Node *pre_opaq = new Opaque1Node(C, pre_limit, limit);
register_new_node( pre_limit, pre_head->in(0) );
register_new_node( pre_opaq , pre_head->in(0) );
// Since no other users of pre-loop compare, I can hack limit directly
assert( cmp_end->outcnt() == 1, "no other users" );
_igvn.hash_delete(cmp_end);
cmp_end->set_req(2, peel_only ? pre_limit : pre_opaq);
// Special case for not-equal loop bounds:
// Change pre loop test, main loop test, and the
// main loop guard test to use lt or gt depending on stride
// direction:
// positive stride use <
// negative stride use >
//
// not-equal test is kept for post loop to handle case
// when init > limit when stride > 0 (and reverse).
if (pre_end->in(CountedLoopEndNode::TestValue)->as_Bool()->_test._test == BoolTest::ne) {
BoolTest::mask new_test = (main_end->stride_con() > 0) ? BoolTest::lt : BoolTest::gt;
// Modify pre loop end condition
Node* pre_bol = pre_end->in(CountedLoopEndNode::TestValue)->as_Bool();
BoolNode* new_bol0 = new BoolNode(pre_bol->in(1), new_test);
register_new_node( new_bol0, pre_head->in(0) );
_igvn.replace_input_of(pre_end, CountedLoopEndNode::TestValue, new_bol0);
// Modify main loop guard condition
assert(min_iff->in(CountedLoopEndNode::TestValue) == min_bol, "guard okay");
BoolNode* new_bol1 = new BoolNode(min_bol->in(1), new_test);
register_new_node( new_bol1, new_pre_exit );
_igvn.hash_delete(min_iff);
min_iff->set_req(CountedLoopEndNode::TestValue, new_bol1);
// Modify main loop end condition
BoolNode* main_bol = main_end->in(CountedLoopEndNode::TestValue)->as_Bool();
BoolNode* new_bol2 = new BoolNode(main_bol->in(1), new_test);
register_new_node( new_bol2, main_end->in(CountedLoopEndNode::TestControl) );
_igvn.replace_input_of(main_end, CountedLoopEndNode::TestValue, new_bol2);
}
// Flag main loop
main_head->set_main_loop();
if( peel_only ) main_head->set_main_no_pre_loop();
// Subtract a trip count for the pre-loop.
main_head->set_trip_count(main_head->trip_count() - 1);
// It's difficult to be precise about the trip-counts
// for the pre/post loops. They are usually very short,
// so guess that 4 trips is a reasonable value.
post_head->set_profile_trip_cnt(4.0);
pre_head->set_profile_trip_cnt(4.0);
// Now force out all loop-invariant dominating tests. The optimizer
// finds some, but we _know_ they are all useless.
peeled_dom_test_elim(loop,old_new);
loop->record_for_igvn();
}
//------------------------------insert_vector_post_loop------------------------
// Insert a copy of the atomic unrolled vectorized main loop as a post loop,
// unroll_policy has already informed us that more unrolling is about to happen to
// the main loop. The resultant post loop will serve as a vectorized drain loop.
void PhaseIdealLoop::insert_vector_post_loop(IdealLoopTree *loop, Node_List &old_new) {
if (!loop->_head->is_CountedLoop()) return;
CountedLoopNode *cl = loop->_head->as_CountedLoop();
// only process vectorized main loops
if (!cl->is_vectorized_loop() || !cl->is_main_loop()) return;
int slp_max_unroll_factor = cl->slp_max_unroll();
int cur_unroll = cl->unrolled_count();
if (slp_max_unroll_factor == 0) return;
// only process atomic unroll vector loops (not super unrolled after vectorization)
if (cur_unroll != slp_max_unroll_factor) return;
// we only ever process this one time
if (cl->has_atomic_post_loop()) return;
#ifndef PRODUCT
if (TraceLoopOpts) {
tty->print("PostVector ");
loop->dump_head();
}
#endif
C->set_major_progress();
// Find common pieces of the loop being guarded with pre & post loops
CountedLoopNode *main_head = loop->_head->as_CountedLoop();
CountedLoopEndNode *main_end = main_head->loopexit();
guarantee(main_end != NULL, "no loop exit node");
// diagnostic to show loop end is not properly formed
assert(main_end->outcnt() == 2, "1 true, 1 false path only");
// mark this loop as processed
main_head->mark_has_atomic_post_loop();
Node *incr = main_end->incr();
Node *limit = main_end->limit();
// In this case we throw away the result as we are not using it to connect anything else.
CountedLoopNode *post_head = NULL;
insert_post_loop(loop, old_new, main_head, main_end, incr, limit, post_head);
// It's difficult to be precise about the trip-counts
// for post loops. They are usually very short,
// so guess that unit vector trips is a reasonable value.
post_head->set_profile_trip_cnt(cur_unroll);
// Now force out all loop-invariant dominating tests. The optimizer
// finds some, but we _know_ they are all useless.
peeled_dom_test_elim(loop, old_new);
loop->record_for_igvn();
}
//-------------------------insert_scalar_rced_post_loop------------------------
// Insert a copy of the rce'd main loop as a post loop,
// We have not unrolled the main loop, so this is the right time to inject this.
// Later we will examine the partner of this post loop pair which still has range checks
// to see inject code which tests at runtime if the range checks are applicable.
void PhaseIdealLoop::insert_scalar_rced_post_loop(IdealLoopTree *loop, Node_List &old_new) {
if (!loop->_head->is_CountedLoop()) return;
CountedLoopNode *cl = loop->_head->as_CountedLoop();
// only process RCE'd main loops
if (!cl->is_main_loop() || cl->range_checks_present()) return;
#ifndef PRODUCT
if (TraceLoopOpts) {
tty->print("PostScalarRce ");
loop->dump_head();
}
#endif
C->set_major_progress();
// Find common pieces of the loop being guarded with pre & post loops
CountedLoopNode *main_head = loop->_head->as_CountedLoop();
CountedLoopEndNode *main_end = main_head->loopexit();
guarantee(main_end != NULL, "no loop exit node");
// diagnostic to show loop end is not properly formed
assert(main_end->outcnt() == 2, "1 true, 1 false path only");
Node *incr = main_end->incr();
Node *limit = main_end->limit();
// In this case we throw away the result as we are not using it to connect anything else.
CountedLoopNode *post_head = NULL;
insert_post_loop(loop, old_new, main_head, main_end, incr, limit, post_head);
// It's difficult to be precise about the trip-counts
// for post loops. They are usually very short,
// so guess that unit vector trips is a reasonable value.
post_head->set_profile_trip_cnt(4.0);
post_head->set_is_rce_post_loop();
// Now force out all loop-invariant dominating tests. The optimizer
// finds some, but we _know_ they are all useless.
peeled_dom_test_elim(loop, old_new);
loop->record_for_igvn();
}
//------------------------------insert_post_loop-------------------------------
// Insert post loops. Add a post loop to the given loop passed.
Node *PhaseIdealLoop::insert_post_loop(IdealLoopTree *loop, Node_List &old_new,
CountedLoopNode *main_head, CountedLoopEndNode *main_end,
Node *incr, Node *limit, CountedLoopNode *&post_head) {
//------------------------------
// Step A: Create a new post-Loop.
Node* main_exit = main_end->proj_out(false);
assert(main_exit->Opcode() == Op_IfFalse, "");
int dd_main_exit = dom_depth(main_exit);
// Step A1: Clone the loop body of main. The clone becomes the post-loop.
// The main loop pre-header illegally has 2 control users (old & new loops).
clone_loop(loop, old_new, dd_main_exit);
assert(old_new[main_end->_idx]->Opcode() == Op_CountedLoopEnd, "");
post_head = old_new[main_head->_idx]->as_CountedLoop();
post_head->set_normal_loop();
post_head->set_post_loop(main_head);
// Reduce the post-loop trip count.
CountedLoopEndNode* post_end = old_new[main_end->_idx]->as_CountedLoopEnd();
post_end->_prob = PROB_FAIR;
// Build the main-loop normal exit.
IfFalseNode *new_main_exit = new IfFalseNode(main_end);
_igvn.register_new_node_with_optimizer(new_main_exit);
set_idom(new_main_exit, main_end, dd_main_exit);
set_loop(new_main_exit, loop->_parent);
// Step A2: Build a zero-trip guard for the post-loop. After leaving the
// main-loop, the post-loop may not execute at all. We 'opaque' the incr
// (the previous loop trip-counter exit value) because we will be changing
// the exit value (via additional unrolling) so we cannot constant-fold away the zero
// trip guard until all unrolling is done.
Node *zer_opaq = new Opaque1Node(C, incr);
Node *zer_cmp = new CmpINode(zer_opaq, limit);
Node *zer_bol = new BoolNode(zer_cmp, main_end->test_trip());
register_new_node(zer_opaq, new_main_exit);
register_new_node(zer_cmp, new_main_exit);
register_new_node(zer_bol, new_main_exit);
// Build the IfNode
IfNode *zer_iff = new IfNode(new_main_exit, zer_bol, PROB_FAIR, COUNT_UNKNOWN);
_igvn.register_new_node_with_optimizer(zer_iff);
set_idom(zer_iff, new_main_exit, dd_main_exit);
set_loop(zer_iff, loop->_parent);
// Plug in the false-path, taken if we need to skip this post-loop
_igvn.replace_input_of(main_exit, 0, zer_iff);
set_idom(main_exit, zer_iff, dd_main_exit);
set_idom(main_exit->unique_out(), zer_iff, dd_main_exit);
// Make the true-path, must enter this post loop
Node *zer_taken = new IfTrueNode(zer_iff);
_igvn.register_new_node_with_optimizer(zer_taken);
set_idom(zer_taken, zer_iff, dd_main_exit);
set_loop(zer_taken, loop->_parent);
// Plug in the true path
_igvn.hash_delete(post_head);
post_head->set_req(LoopNode::EntryControl, zer_taken);
set_idom(post_head, zer_taken, dd_main_exit);
Arena *a = Thread::current()->resource_area();
VectorSet visited(a);
Node_Stack clones(a, main_head->back_control()->outcnt());
// Step A3: Make the fall-in values to the post-loop come from the
// fall-out values of the main-loop.
for (DUIterator_Fast imax, i = main_head->fast_outs(imax); i < imax; i++) {
Node* main_phi = main_head->fast_out(i);
if (main_phi->is_Phi() && main_phi->in(0) == main_head && main_phi->outcnt() >0) {
Node *cur_phi = old_new[main_phi->_idx];
Node *fallnew = clone_up_backedge_goo(main_head->back_control(),
post_head->init_control(),
main_phi->in(LoopNode::LoopBackControl),
visited, clones);
_igvn.hash_delete(cur_phi);
cur_phi->set_req(LoopNode::EntryControl, fallnew);
}
}
// CastII for the new post loop:
bool inserted = cast_incr_before_loop(zer_opaq->in(1), zer_taken, post_head);
assert(inserted, "no castII inserted");
return new_main_exit;
}
//------------------------------is_invariant-----------------------------
// Return true if n is invariant
bool IdealLoopTree::is_invariant(Node* n) const {
Node *n_c = _phase->has_ctrl(n) ? _phase->get_ctrl(n) : n;
if (n_c->is_top()) return false;
return !is_member(_phase->get_loop(n_c));
}
//------------------------------do_unroll--------------------------------------
// Unroll the loop body one step - make each trip do 2 iterations.
void PhaseIdealLoop::do_unroll( IdealLoopTree *loop, Node_List &old_new, bool adjust_min_trip ) {
assert(LoopUnrollLimit, "");
CountedLoopNode *loop_head = loop->_head->as_CountedLoop();
CountedLoopEndNode *loop_end = loop_head->loopexit();
assert(loop_end, "");
#ifndef PRODUCT
if (PrintOpto && VerifyLoopOptimizations) {
tty->print("Unrolling ");
loop->dump_head();
} else if (TraceLoopOpts) {
if (loop_head->trip_count() < (uint)LoopUnrollLimit) {
tty->print("Unroll %d(%2d) ", loop_head->unrolled_count()*2, loop_head->trip_count());
} else {
tty->print("Unroll %d ", loop_head->unrolled_count()*2);
}
loop->dump_head();
}
if (C->do_vector_loop() && (PrintOpto && (VerifyLoopOptimizations || TraceLoopOpts))) {
Arena* arena = Thread::current()->resource_area();
Node_Stack stack(arena, C->live_nodes() >> 2);
Node_List rpo_list;
VectorSet visited(arena);
visited.set(loop_head->_idx);
rpo( loop_head, stack, visited, rpo_list );
dump(loop, rpo_list.size(), rpo_list );
}
#endif
// Remember loop node count before unrolling to detect
// if rounds of unroll,optimize are making progress
loop_head->set_node_count_before_unroll(loop->_body.size());
Node *ctrl = loop_head->in(LoopNode::EntryControl);
Node *limit = loop_head->limit();
Node *init = loop_head->init_trip();
Node *stride = loop_head->stride();
Node *opaq = NULL;
if (adjust_min_trip) { // If not maximally unrolling, need adjustment
// Search for zero-trip guard.
// Check the shape of the graph at the loop entry. If an inappropriate
// graph shape is encountered, the compiler bails out loop unrolling;
// compilation of the method will still succeed.
if (!is_canonical_loop_entry(loop_head)) {
return;
}
opaq = ctrl->in(0)->in(1)->in(1)->in(2);
// Zero-trip test uses an 'opaque' node which is not shared.
assert(opaq->outcnt() == 1 && opaq->in(1) == limit, "");
}
C->set_major_progress();
Node* new_limit = NULL;
int stride_con = stride->get_int();
int stride_p = (stride_con > 0) ? stride_con : -stride_con;
uint old_trip_count = loop_head->trip_count();
// Verify that unroll policy result is still valid.
assert(old_trip_count > 1 &&
(!adjust_min_trip || stride_p <= (1<<3)*loop_head->unrolled_count()), "sanity");
// Adjust loop limit to keep valid iterations number after unroll.
// Use (limit - stride) instead of (((limit - init)/stride) & (-2))*stride
// which may overflow.
if (!adjust_min_trip) {
assert(old_trip_count > 1 && (old_trip_count & 1) == 0,
"odd trip count for maximally unroll");
// Don't need to adjust limit for maximally unroll since trip count is even.
} else if (loop_head->has_exact_trip_count() && init->is_Con()) {
// Loop's limit is constant. Loop's init could be constant when pre-loop
// become peeled iteration.
jlong init_con = init->get_int();
// We can keep old loop limit if iterations count stays the same:
// old_trip_count == new_trip_count * 2
// Note: since old_trip_count >= 2 then new_trip_count >= 1
// so we also don't need to adjust zero trip test.
jlong limit_con = limit->get_int();
// (stride_con*2) not overflow since stride_con <= 8.
int new_stride_con = stride_con * 2;
int stride_m = new_stride_con - (stride_con > 0 ? 1 : -1);
jlong trip_count = (limit_con - init_con + stride_m)/new_stride_con;
// New trip count should satisfy next conditions.
assert(trip_count > 0 && (julong)trip_count < (julong)max_juint/2, "sanity");
uint new_trip_count = (uint)trip_count;
adjust_min_trip = (old_trip_count != new_trip_count*2);
}
if (adjust_min_trip) {
// Step 2: Adjust the trip limit if it is called for.
// The adjustment amount is -stride. Need to make sure if the
// adjustment underflows or overflows, then the main loop is skipped.
Node* cmp = loop_end->cmp_node();
assert(cmp->in(2) == limit, "sanity");
assert(opaq != NULL && opaq->in(1) == limit, "sanity");
// Verify that policy_unroll result is still valid.
const TypeInt* limit_type = _igvn.type(limit)->is_int();
assert(stride_con > 0 && ((limit_type->_hi - stride_con) < limit_type->_hi) ||
stride_con < 0 && ((limit_type->_lo - stride_con) > limit_type->_lo), "sanity");
if (limit->is_Con()) {
// The check in policy_unroll and the assert above guarantee
// no underflow if limit is constant.
new_limit = _igvn.intcon(limit->get_int() - stride_con);
set_ctrl(new_limit, C->root());
} else {
// Limit is not constant.
if (loop_head->unrolled_count() == 1) { // only for first unroll
// Separate limit by Opaque node in case it is an incremented
// variable from previous loop to avoid using pre-incremented
// value which could increase register pressure.
// Otherwise reorg_offsets() optimization will create a separate
// Opaque node for each use of trip-counter and as result
// zero trip guard limit will be different from loop limit.
assert(has_ctrl(opaq), "should have it");
Node* opaq_ctrl = get_ctrl(opaq);
limit = new Opaque2Node( C, limit );
register_new_node( limit, opaq_ctrl );
}
if ((stride_con > 0 && (java_subtract(limit_type->_lo, stride_con) < limit_type->_lo)) ||
(stride_con < 0 && (java_subtract(limit_type->_hi, stride_con) > limit_type->_hi))) {
// No underflow.
new_limit = new SubINode(limit, stride);
} else {
// (limit - stride) may underflow.
// Clamp the adjustment value with MININT or MAXINT:
//
// new_limit = limit-stride
// if (stride > 0)
// new_limit = (limit < new_limit) ? MININT : new_limit;
// else
// new_limit = (limit > new_limit) ? MAXINT : new_limit;
//
BoolTest::mask bt = loop_end->test_trip();
assert(bt == BoolTest::lt || bt == BoolTest::gt, "canonical test is expected");
Node* adj_max = _igvn.intcon((stride_con > 0) ? min_jint : max_jint);
set_ctrl(adj_max, C->root());
Node* old_limit = NULL;
Node* adj_limit = NULL;
Node* bol = limit->is_CMove() ? limit->in(CMoveNode::Condition) : NULL;
if (loop_head->unrolled_count() > 1 &&
limit->is_CMove() && limit->Opcode() == Op_CMoveI &&
limit->in(CMoveNode::IfTrue) == adj_max &&
bol->as_Bool()->_test._test == bt &&
bol->in(1)->Opcode() == Op_CmpI &&
bol->in(1)->in(2) == limit->in(CMoveNode::IfFalse)) {
// Loop was unrolled before.
// Optimize the limit to avoid nested CMove:
// use original limit as old limit.
old_limit = bol->in(1)->in(1);
// Adjust previous adjusted limit.
adj_limit = limit->in(CMoveNode::IfFalse);
adj_limit = new SubINode(adj_limit, stride);
} else {
old_limit = limit;
adj_limit = new SubINode(limit, stride);
}
assert(old_limit != NULL && adj_limit != NULL, "");
register_new_node( adj_limit, ctrl ); // adjust amount
Node* adj_cmp = new CmpINode(old_limit, adj_limit);
register_new_node( adj_cmp, ctrl );
Node* adj_bool = new BoolNode(adj_cmp, bt);
register_new_node( adj_bool, ctrl );
new_limit = new CMoveINode(adj_bool, adj_limit, adj_max, TypeInt::INT);
}
register_new_node(new_limit, ctrl);
}
assert(new_limit != NULL, "");
// Replace in loop test.
assert(loop_end->in(1)->in(1) == cmp, "sanity");
if (cmp->outcnt() == 1 && loop_end->in(1)->outcnt() == 1) {
// Don't need to create new test since only one user.
_igvn.hash_delete(cmp);
cmp->set_req(2, new_limit);
} else {
// Create new test since it is shared.
Node* ctrl2 = loop_end->in(0);
Node* cmp2 = cmp->clone();
cmp2->set_req(2, new_limit);
register_new_node(cmp2, ctrl2);
Node* bol2 = loop_end->in(1)->clone();
bol2->set_req(1, cmp2);
register_new_node(bol2, ctrl2);
_igvn.replace_input_of(loop_end, 1, bol2);
}
// Step 3: Find the min-trip test guaranteed before a 'main' loop.
// Make it a 1-trip test (means at least 2 trips).
// Guard test uses an 'opaque' node which is not shared. Hence I
// can edit it's inputs directly. Hammer in the new limit for the
// minimum-trip guard.
assert(opaq->outcnt() == 1, "");
_igvn.replace_input_of(opaq, 1, new_limit);
}
// Adjust max trip count. The trip count is intentionally rounded
// down here (e.g. 15-> 7-> 3-> 1) because if we unwittingly over-unroll,
// the main, unrolled, part of the loop will never execute as it is protected
// by the min-trip test. See bug 4834191 for a case where we over-unrolled
// and later determined that part of the unrolled loop was dead.
loop_head->set_trip_count(old_trip_count / 2);
// Double the count of original iterations in the unrolled loop body.
loop_head->double_unrolled_count();
// ---------
// Step 4: Clone the loop body. Move it inside the loop. This loop body
// represents the odd iterations; since the loop trips an even number of
// times its backedge is never taken. Kill the backedge.
uint dd = dom_depth(loop_head);
clone_loop( loop, old_new, dd );
// Make backedges of the clone equal to backedges of the original.
// Make the fall-in from the original come from the fall-out of the clone.
for (DUIterator_Fast jmax, j = loop_head->fast_outs(jmax); j < jmax; j++) {
Node* phi = loop_head->fast_out(j);
if( phi->is_Phi() && phi->in(0) == loop_head && phi->outcnt() > 0 ) {
Node *newphi = old_new[phi->_idx];
_igvn.hash_delete( phi );
_igvn.hash_delete( newphi );
phi ->set_req(LoopNode:: EntryControl, newphi->in(LoopNode::LoopBackControl));
newphi->set_req(LoopNode::LoopBackControl, phi ->in(LoopNode::LoopBackControl));
phi ->set_req(LoopNode::LoopBackControl, C->top());
}
}
Node *clone_head = old_new[loop_head->_idx];
_igvn.hash_delete( clone_head );
loop_head ->set_req(LoopNode:: EntryControl, clone_head->in(LoopNode::LoopBackControl));
clone_head->set_req(LoopNode::LoopBackControl, loop_head ->in(LoopNode::LoopBackControl));
loop_head ->set_req(LoopNode::LoopBackControl, C->top());
loop->_head = clone_head; // New loop header
set_idom(loop_head, loop_head ->in(LoopNode::EntryControl), dd);
set_idom(clone_head, clone_head->in(LoopNode::EntryControl), dd);
// Kill the clone's backedge
Node *newcle = old_new[loop_end->_idx];
_igvn.hash_delete( newcle );
Node *one = _igvn.intcon(1);
set_ctrl(one, C->root());
newcle->set_req(1, one);
// Force clone into same loop body
uint max = loop->_body.size();
for( uint k = 0; k < max; k++ ) {
Node *old = loop->_body.at(k);
Node *nnn = old_new[old->_idx];
loop->_body.push(nnn);
if (!has_ctrl(old))
set_loop(nnn, loop);
}
loop->record_for_igvn();
#ifndef PRODUCT
if (C->do_vector_loop() && (PrintOpto && (VerifyLoopOptimizations || TraceLoopOpts))) {
tty->print("\nnew loop after unroll\n"); loop->dump_head();
for (uint i = 0; i < loop->_body.size(); i++) {
loop->_body.at(i)->dump();
}
if(C->clone_map().is_debug()) {
tty->print("\nCloneMap\n");
Dict* dict = C->clone_map().dict();
DictI i(dict);
tty->print_cr("Dict@%p[%d] = ", dict, dict->Size());
for (int ii = 0; i.test(); ++i, ++ii) {
NodeCloneInfo cl((uint64_t)dict->operator[]((void*)i._key));
tty->print("%d->%d:%d,", (int)(intptr_t)i._key, cl.idx(), cl.gen());
if (ii % 10 == 9) {
tty->print_cr(" ");
}
}
tty->print_cr(" ");
}
}
#endif
}
//------------------------------do_maximally_unroll----------------------------
void PhaseIdealLoop::do_maximally_unroll( IdealLoopTree *loop, Node_List &old_new ) {
CountedLoopNode *cl = loop->_head->as_CountedLoop();
assert(cl->has_exact_trip_count(), "trip count is not exact");
assert(cl->trip_count() > 0, "");
#ifndef PRODUCT
if (TraceLoopOpts) {
tty->print("MaxUnroll %d ", cl->trip_count());
loop->dump_head();
}
#endif
// If loop is tripping an odd number of times, peel odd iteration
if ((cl->trip_count() & 1) == 1) {
do_peeling(loop, old_new);
}
// Now its tripping an even number of times remaining. Double loop body.
// Do not adjust pre-guards; they are not needed and do not exist.
if (cl->trip_count() > 0) {
assert((cl->trip_count() & 1) == 0, "missed peeling");
do_unroll(loop, old_new, false);
}
}
void PhaseIdealLoop::mark_reductions(IdealLoopTree *loop) {
if (SuperWordReductions == false) return;
CountedLoopNode* loop_head = loop->_head->as_CountedLoop();
if (loop_head->unrolled_count() > 1) {
return;
}
Node* trip_phi = loop_head->phi();
for (DUIterator_Fast imax, i = loop_head->fast_outs(imax); i < imax; i++) {
Node* phi = loop_head->fast_out(i);
if (phi->is_Phi() && phi->outcnt() > 0 && phi != trip_phi) {
// For definitions which are loop inclusive and not tripcounts.
Node* def_node = phi->in(LoopNode::LoopBackControl);
if (def_node != NULL) {
Node* n_ctrl = get_ctrl(def_node);
if (n_ctrl != NULL && loop->is_member(get_loop(n_ctrl))) {
// Now test it to see if it fits the standard pattern for a reduction operator.
int opc = def_node->Opcode();
if (opc != ReductionNode::opcode(opc, def_node->bottom_type()->basic_type())) {
if (!def_node->is_reduction()) { // Not marked yet
// To be a reduction, the arithmetic node must have the phi as input and provide a def to it
bool ok = false;
for (unsigned j = 1; j < def_node->req(); j++) {
Node* in = def_node->in(j);
if (in == phi) {
ok = true;
break;
}
}
// do nothing if we did not match the initial criteria
if (ok == false) {
continue;
}
// The result of the reduction must not be used in the loop
for (DUIterator_Fast imax, i = def_node->fast_outs(imax); i < imax && ok; i++) {
Node* u = def_node->fast_out(i);
if (!loop->is_member(get_loop(ctrl_or_self(u)))) {
continue;
}
if (u == phi) {
continue;
}
ok = false;
}
// iff the uses conform
if (ok) {
def_node->add_flag(Node::Flag_is_reduction);
loop_head->mark_has_reductions();
}
}
}
}
}
}
}
}
//------------------------------adjust_limit-----------------------------------
// Helper function for add_constraint().
Node* PhaseIdealLoop::adjust_limit(int stride_con, Node * scale, Node *offset, Node *rc_limit, Node *loop_limit, Node *pre_ctrl) {
// Compute "I :: (limit-offset)/scale"
Node *con = new SubINode(rc_limit, offset);
register_new_node(con, pre_ctrl);
Node *X = new DivINode(0, con, scale);
register_new_node(X, pre_ctrl);
// Adjust loop limit
loop_limit = (stride_con > 0)
? (Node*)(new MinINode(loop_limit, X))
: (Node*)(new MaxINode(loop_limit, X));
register_new_node(loop_limit, pre_ctrl);
return loop_limit;
}
//------------------------------add_constraint---------------------------------
// Constrain the main loop iterations so the conditions:
// low_limit <= scale_con * I + offset < upper_limit
// always holds true. That is, either increase the number of iterations in
// the pre-loop or the post-loop until the condition holds true in the main
// loop. Stride, scale, offset and limit are all loop invariant. Further,
// stride and scale are constants (offset and limit often are).
void PhaseIdealLoop::add_constraint( int stride_con, int scale_con, Node *offset, Node *low_limit, Node *upper_limit, Node *pre_ctrl, Node **pre_limit, Node **main_limit ) {
// For positive stride, the pre-loop limit always uses a MAX function
// and the main loop a MIN function. For negative stride these are
// reversed.
// Also for positive stride*scale the affine function is increasing, so the
// pre-loop must check for underflow and the post-loop for overflow.
// Negative stride*scale reverses this; pre-loop checks for overflow and
// post-loop for underflow.
Node *scale = _igvn.intcon(scale_con);
set_ctrl(scale, C->root());
if ((stride_con^scale_con) >= 0) { // Use XOR to avoid overflow
// The overflow limit: scale*I+offset < upper_limit
// For main-loop compute
// ( if (scale > 0) /* and stride > 0 */
// I < (upper_limit-offset)/scale
// else /* scale < 0 and stride < 0 */
// I > (upper_limit-offset)/scale
// )
//
// (upper_limit-offset) may overflow or underflow.
// But it is fine since main loop will either have
// less iterations or will be skipped in such case.
*main_limit = adjust_limit(stride_con, scale, offset, upper_limit, *main_limit, pre_ctrl);
// The underflow limit: low_limit <= scale*I+offset.
// For pre-loop compute
// NOT(scale*I+offset >= low_limit)
// scale*I+offset < low_limit
// ( if (scale > 0) /* and stride > 0 */
// I < (low_limit-offset)/scale
// else /* scale < 0 and stride < 0 */
// I > (low_limit-offset)/scale
// )
if (low_limit->get_int() == -max_jint) {
// We need this guard when scale*pre_limit+offset >= limit
// due to underflow. So we need execute pre-loop until
// scale*I+offset >= min_int. But (min_int-offset) will
// underflow when offset > 0 and X will be > original_limit
// when stride > 0. To avoid it we replace positive offset with 0.
//
// Also (min_int+1 == -max_int) is used instead of min_int here
// to avoid problem with scale == -1 (min_int/(-1) == min_int).
Node* shift = _igvn.intcon(31);
set_ctrl(shift, C->root());
Node* sign = new RShiftINode(offset, shift);
register_new_node(sign, pre_ctrl);
offset = new AndINode(offset, sign);
register_new_node(offset, pre_ctrl);
} else {
assert(low_limit->get_int() == 0, "wrong low limit for range check");
// The only problem we have here when offset == min_int
// since (0-min_int) == min_int. It may be fine for stride > 0
// but for stride < 0 X will be < original_limit. To avoid it
// max(pre_limit, original_limit) is used in do_range_check().
}
// Pass (-stride) to indicate pre_loop_cond = NOT(main_loop_cond);
*pre_limit = adjust_limit((-stride_con), scale, offset, low_limit, *pre_limit, pre_ctrl);
} else { // stride_con*scale_con < 0
// For negative stride*scale pre-loop checks for overflow and
// post-loop for underflow.
//
// The overflow limit: scale*I+offset < upper_limit
// For pre-loop compute
// NOT(scale*I+offset < upper_limit)
// scale*I+offset >= upper_limit
// scale*I+offset+1 > upper_limit
// ( if (scale < 0) /* and stride > 0 */
// I < (upper_limit-(offset+1))/scale
// else /* scale > 0 and stride < 0 */
// I > (upper_limit-(offset+1))/scale
// )
//
// (upper_limit-offset-1) may underflow or overflow.
// To avoid it min(pre_limit, original_limit) is used
// in do_range_check() for stride > 0 and max() for < 0.
Node *one = _igvn.intcon(1);
set_ctrl(one, C->root());
Node *plus_one = new AddINode(offset, one);
register_new_node( plus_one, pre_ctrl );
// Pass (-stride) to indicate pre_loop_cond = NOT(main_loop_cond);
*pre_limit = adjust_limit((-stride_con), scale, plus_one, upper_limit, *pre_limit, pre_ctrl);
if (low_limit->get_int() == -max_jint) {
// We need this guard when scale*main_limit+offset >= limit
// due to underflow. So we need execute main-loop while
// scale*I+offset+1 > min_int. But (min_int-offset-1) will
// underflow when (offset+1) > 0 and X will be < main_limit
// when scale < 0 (and stride > 0). To avoid it we replace
// positive (offset+1) with 0.
//
// Also (min_int+1 == -max_int) is used instead of min_int here
// to avoid problem with scale == -1 (min_int/(-1) == min_int).
Node* shift = _igvn.intcon(31);
set_ctrl(shift, C->root());
Node* sign = new RShiftINode(plus_one, shift);
register_new_node(sign, pre_ctrl);
plus_one = new AndINode(plus_one, sign);
register_new_node(plus_one, pre_ctrl);
} else {
assert(low_limit->get_int() == 0, "wrong low limit for range check");
// The only problem we have here when offset == max_int
// since (max_int+1) == min_int and (0-min_int) == min_int.
// But it is fine since main loop will either have
// less iterations or will be skipped in such case.
}
// The underflow limit: low_limit <= scale*I+offset.
// For main-loop compute
// scale*I+offset+1 > low_limit
// ( if (scale < 0) /* and stride > 0 */
// I < (low_limit-(offset+1))/scale
// else /* scale > 0 and stride < 0 */
// I > (low_limit-(offset+1))/scale
// )
*main_limit = adjust_limit(stride_con, scale, plus_one, low_limit, *main_limit, pre_ctrl);
}
}
//------------------------------is_scaled_iv---------------------------------
// Return true if exp is a constant times an induction var
bool PhaseIdealLoop::is_scaled_iv(Node* exp, Node* iv, int* p_scale) {
if (exp == iv) {
if (p_scale != NULL) {
*p_scale = 1;
}
return true;
}
int opc = exp->Opcode();
if (opc == Op_MulI) {
if (exp->in(1) == iv && exp->in(2)->is_Con()) {
if (p_scale != NULL) {
*p_scale = exp->in(2)->get_int();
}
return true;
}
if (exp->in(2) == iv && exp->in(1)->is_Con()) {
if (p_scale != NULL) {
*p_scale = exp->in(1)->get_int();
}
return true;
}
} else if (opc == Op_LShiftI) {
if (exp->in(1) == iv && exp->in(2)->is_Con()) {
if (p_scale != NULL) {
*p_scale = 1 << exp->in(2)->get_int();
}
return true;
}
}
return false;
}
//-----------------------------is_scaled_iv_plus_offset------------------------------
// Return true if exp is a simple induction variable expression: k1*iv + (invar + k2)
bool PhaseIdealLoop::is_scaled_iv_plus_offset(Node* exp, Node* iv, int* p_scale, Node** p_offset, int depth) {
if (is_scaled_iv(exp, iv, p_scale)) {
if (p_offset != NULL) {
Node *zero = _igvn.intcon(0);
set_ctrl(zero, C->root());
*p_offset = zero;
}
return true;
}
int opc = exp->Opcode();
if (opc == Op_AddI) {
if (is_scaled_iv(exp->in(1), iv, p_scale)) {
if (p_offset != NULL) {
*p_offset = exp->in(2);
}
return true;
}
if (is_scaled_iv(exp->in(2), iv, p_scale)) {
if (p_offset != NULL) {
*p_offset = exp->in(1);
}
return true;
}
if (exp->in(2)->is_Con()) {
Node* offset2 = NULL;
if (depth < 2 &&
is_scaled_iv_plus_offset(exp->in(1), iv, p_scale,
p_offset != NULL ? &offset2 : NULL, depth+1)) {
if (p_offset != NULL) {
Node *ctrl_off2 = get_ctrl(offset2);
Node* offset = new AddINode(offset2, exp->in(2));
register_new_node(offset, ctrl_off2);
*p_offset = offset;
}
return true;
}
}
} else if (opc == Op_SubI) {
if (is_scaled_iv(exp->in(1), iv, p_scale)) {
if (p_offset != NULL) {
Node *zero = _igvn.intcon(0);
set_ctrl(zero, C->root());
Node *ctrl_off = get_ctrl(exp->in(2));
Node* offset = new SubINode(zero, exp->in(2));
register_new_node(offset, ctrl_off);
*p_offset = offset;
}
return true;
}
if (is_scaled_iv(exp->in(2), iv, p_scale)) {
if (p_offset != NULL) {
*p_scale *= -1;
*p_offset = exp->in(1);
}
return true;
}
}
return false;
}
//------------------------------do_range_check---------------------------------
// Eliminate range-checks and other trip-counter vs loop-invariant tests.
int PhaseIdealLoop::do_range_check( IdealLoopTree *loop, Node_List &old_new ) {
#ifndef PRODUCT
if (PrintOpto && VerifyLoopOptimizations) {
tty->print("Range Check Elimination ");
loop->dump_head();
} else if (TraceLoopOpts) {
tty->print("RangeCheck ");
loop->dump_head();
}
#endif
assert(RangeCheckElimination, "");
CountedLoopNode *cl = loop->_head->as_CountedLoop();
// If we fail before trying to eliminate range checks, set multiversion state
int closed_range_checks = 1;
// protect against stride not being a constant
if (!cl->stride_is_con())
return closed_range_checks;
// Find the trip counter; we are iteration splitting based on it
Node *trip_counter = cl->phi();
// Find the main loop limit; we will trim it's iterations
// to not ever trip end tests
Node *main_limit = cl->limit();
// Check graph shape. Cannot optimize a loop if zero-trip
// Opaque1 node is optimized away and then another round
// of loop opts attempted.
if (!is_canonical_loop_entry(cl)) {
return closed_range_checks;
}
// Need to find the main-loop zero-trip guard
Node *ctrl = cl->in(LoopNode::EntryControl);
Node *iffm = ctrl->in(0);
Node *opqzm = iffm->in(1)->in(1)->in(2);
assert(opqzm->in(1) == main_limit, "do not understand situation");
// Find the pre-loop limit; we will expand its iterations to
// not ever trip low tests.
Node *p_f = iffm->in(0);
// pre loop may have been optimized out
if (p_f->Opcode() != Op_IfFalse) {
return closed_range_checks;
}
CountedLoopEndNode *pre_end = p_f->in(0)->as_CountedLoopEnd();
assert(pre_end->loopnode()->is_pre_loop(), "");
Node *pre_opaq1 = pre_end->limit();
// Occasionally it's possible for a pre-loop Opaque1 node to be
// optimized away and then another round of loop opts attempted.
// We can not optimize this particular loop in that case.
if (pre_opaq1->Opcode() != Op_Opaque1)
return closed_range_checks;
Opaque1Node *pre_opaq = (Opaque1Node*)pre_opaq1;
Node *pre_limit = pre_opaq->in(1);
// Where do we put new limit calculations
Node *pre_ctrl = pre_end->loopnode()->in(LoopNode::EntryControl);
// Ensure the original loop limit is available from the
// pre-loop Opaque1 node.
Node *orig_limit = pre_opaq->original_loop_limit();
if (orig_limit == NULL || _igvn.type(orig_limit) == Type::TOP)
return closed_range_checks;
// Must know if its a count-up or count-down loop
int stride_con = cl->stride_con();
Node *zero = _igvn.intcon(0);
Node *one = _igvn.intcon(1);
// Use symmetrical int range [-max_jint,max_jint]
Node *mini = _igvn.intcon(-max_jint);
set_ctrl(zero, C->root());
set_ctrl(one, C->root());
set_ctrl(mini, C->root());
// Range checks that do not dominate the loop backedge (ie.
// conditionally executed) can lengthen the pre loop limit beyond
// the original loop limit. To prevent this, the pre limit is
// (for stride > 0) MINed with the original loop limit (MAXed
// stride < 0) when some range_check (rc) is conditionally
// executed.
bool conditional_rc = false;
// Count number of range checks and reduce by load range limits, if zero,
// the loop is in canonical form to multiversion.
closed_range_checks = 0;
// Check loop body for tests of trip-counter plus loop-invariant vs loop-variant.
for( uint i = 0; i < loop->_body.size(); i++ ) {
Node *iff = loop->_body[i];
if (iff->Opcode() == Op_If ||
iff->Opcode() == Op_RangeCheck) { // Test?
// Test is an IfNode, has 2 projections. If BOTH are in the loop
// we need loop unswitching instead of iteration splitting.
closed_range_checks++;
Node *exit = loop->is_loop_exit(iff);
if( !exit ) continue;
int flip = (exit->Opcode() == Op_IfTrue) ? 1 : 0;
// Get boolean condition to test
Node *i1 = iff->in(1);
if( !i1->is_Bool() ) continue;
BoolNode *bol = i1->as_Bool();
BoolTest b_test = bol->_test;
// Flip sense of test if exit condition is flipped
if( flip )
b_test = b_test.negate();
// Get compare
Node *cmp = bol->in(1);
// Look for trip_counter + offset vs limit
Node *rc_exp = cmp->in(1);
Node *limit = cmp->in(2);
jint scale_con= 1; // Assume trip counter not scaled
Node *limit_c = get_ctrl(limit);
if( loop->is_member(get_loop(limit_c) ) ) {
// Compare might have operands swapped; commute them
b_test = b_test.commute();
rc_exp = cmp->in(2);
limit = cmp->in(1);
limit_c = get_ctrl(limit);
if( loop->is_member(get_loop(limit_c) ) )
continue; // Both inputs are loop varying; cannot RCE
}
// Here we know 'limit' is loop invariant
// 'limit' maybe pinned below the zero trip test (probably from a
// previous round of rce), in which case, it can't be used in the
// zero trip test expression which must occur before the zero test's if.
if( limit_c == ctrl ) {
continue; // Don't rce this check but continue looking for other candidates.
}
// Check for scaled induction variable plus an offset
Node *offset = NULL;
if (!is_scaled_iv_plus_offset(rc_exp, trip_counter, &scale_con, &offset)) {
continue;
}
Node *offset_c = get_ctrl(offset);
if( loop->is_member( get_loop(offset_c) ) )
continue; // Offset is not really loop invariant
// Here we know 'offset' is loop invariant.
// As above for the 'limit', the 'offset' maybe pinned below the
// zero trip test.
if( offset_c == ctrl ) {
continue; // Don't rce this check but continue looking for other candidates.
}
#ifdef ASSERT
if (TraceRangeLimitCheck) {
tty->print_cr("RC bool node%s", flip ? " flipped:" : ":");
bol->dump(2);
}
#endif
// At this point we have the expression as:
// scale_con * trip_counter + offset :: limit
// where scale_con, offset and limit are loop invariant. Trip_counter
// monotonically increases by stride_con, a constant. Both (or either)
// stride_con and scale_con can be negative which will flip about the
// sense of the test.
// Adjust pre and main loop limits to guard the correct iteration set
if( cmp->Opcode() == Op_CmpU ) {// Unsigned compare is really 2 tests
if( b_test._test == BoolTest::lt ) { // Range checks always use lt
// The underflow and overflow limits: 0 <= scale*I+offset < limit
add_constraint( stride_con, scale_con, offset, zero, limit, pre_ctrl, &pre_limit, &main_limit );
// (0-offset)/scale could be outside of loop iterations range.
conditional_rc = true;
} else {
if (PrintOpto) {
tty->print_cr("missed RCE opportunity");
}
continue; // In release mode, ignore it
}
} else { // Otherwise work on normal compares
switch( b_test._test ) {
case BoolTest::gt:
// Fall into GE case
case BoolTest::ge:
// Convert (I*scale+offset) >= Limit to (I*(-scale)+(-offset)) <= -Limit
scale_con = -scale_con;
offset = new SubINode( zero, offset );
register_new_node( offset, pre_ctrl );
limit = new SubINode( zero, limit );
register_new_node( limit, pre_ctrl );
// Fall into LE case
case BoolTest::le:
if (b_test._test != BoolTest::gt) {
// Convert X <= Y to X < Y+1
limit = new AddINode( limit, one );
register_new_node( limit, pre_ctrl );
}
// Fall into LT case
case BoolTest::lt:
// The underflow and overflow limits: MIN_INT <= scale*I+offset < limit
// Note: (MIN_INT+1 == -MAX_INT) is used instead of MIN_INT here
// to avoid problem with scale == -1: MIN_INT/(-1) == MIN_INT.
add_constraint( stride_con, scale_con, offset, mini, limit, pre_ctrl, &pre_limit, &main_limit );
// ((MIN_INT+1)-offset)/scale could be outside of loop iterations range.
// Note: negative offset is replaced with 0 but (MIN_INT+1)/scale could
// still be outside of loop range.
conditional_rc = true;
break;
default:
if (PrintOpto) {
tty->print_cr("missed RCE opportunity");
}
continue; // Unhandled case
}
}
// Kill the eliminated test
C->set_major_progress();
Node *kill_con = _igvn.intcon( 1-flip );
set_ctrl(kill_con, C->root());
_igvn.replace_input_of(iff, 1, kill_con);
// Find surviving projection
assert(iff->is_If(), "");
ProjNode* dp = ((IfNode*)iff)->proj_out(1-flip);
// Find loads off the surviving projection; remove their control edge
for (DUIterator_Fast imax, i = dp->fast_outs(imax); i < imax; i++) {
Node* cd = dp->fast_out(i); // Control-dependent node
if (cd->is_Load() && cd->depends_only_on_test()) { // Loads can now float around in the loop
// Allow the load to float around in the loop, or before it
// but NOT before the pre-loop.
_igvn.replace_input_of(cd, 0, ctrl); // ctrl, not NULL
--i;
--imax;
}
}
if (limit->Opcode() == Op_LoadRange) {
closed_range_checks--;
}
} // End of is IF
}
// Update loop limits
if (conditional_rc) {
pre_limit = (stride_con > 0) ? (Node*)new MinINode(pre_limit, orig_limit)
: (Node*)new MaxINode(pre_limit, orig_limit);
register_new_node(pre_limit, pre_ctrl);
}
_igvn.replace_input_of(pre_opaq, 1, pre_limit);
// Note:: we are making the main loop limit no longer precise;
// need to round up based on stride.
cl->set_nonexact_trip_count();
Node *main_cle = cl->loopexit();
Node *main_bol = main_cle->in(1);
// Hacking loop bounds; need private copies of exit test
if( main_bol->outcnt() > 1 ) {// BoolNode shared?
main_bol = main_bol->clone();// Clone a private BoolNode
register_new_node( main_bol, main_cle->in(0) );
_igvn.replace_input_of(main_cle, 1, main_bol);
}
Node *main_cmp = main_bol->in(1);
if( main_cmp->outcnt() > 1 ) { // CmpNode shared?
main_cmp = main_cmp->clone();// Clone a private CmpNode
register_new_node( main_cmp, main_cle->in(0) );
_igvn.replace_input_of(main_bol, 1, main_cmp);
}
// Hack the now-private loop bounds
_igvn.replace_input_of(main_cmp, 2, main_limit);
// The OpaqueNode is unshared by design
assert( opqzm->outcnt() == 1, "cannot hack shared node" );
_igvn.replace_input_of(opqzm, 1, main_limit);
return closed_range_checks;
}
//------------------------------has_range_checks-------------------------------
// Check to see if RCE cleaned the current loop of range-checks.
void PhaseIdealLoop::has_range_checks(IdealLoopTree *loop) {
assert(RangeCheckElimination, "");
// skip if not a counted loop
if (!loop->is_counted()) return;
CountedLoopNode *cl = loop->_head->as_CountedLoop();
// skip this loop if it is already checked
if (cl->has_been_range_checked()) return;
// Now check for existence of range checks
for (uint i = 0; i < loop->_body.size(); i++) {
Node *iff = loop->_body[i];
int iff_opc = iff->Opcode();
if (iff_opc == Op_If || iff_opc == Op_RangeCheck) {
cl->mark_has_range_checks();
break;
}
}
cl->set_has_been_range_checked();
}
//-------------------------multi_version_post_loops----------------------------
// Check the range checks that remain, if simple, use the bounds to guard
// which version to a post loop we execute, one with range checks or one without
bool PhaseIdealLoop::multi_version_post_loops(IdealLoopTree *rce_loop, IdealLoopTree *legacy_loop) {
bool multi_version_succeeded = false;
assert(RangeCheckElimination, "");
CountedLoopNode *legacy_cl = legacy_loop->_head->as_CountedLoop();
assert(legacy_cl->is_post_loop(), "");
// Check for existence of range checks using the unique instance to make a guard with
Unique_Node_List worklist;
for (uint i = 0; i < legacy_loop->_body.size(); i++) {
Node *iff = legacy_loop->_body[i];
int iff_opc = iff->Opcode();
if (iff_opc == Op_If || iff_opc == Op_RangeCheck) {
worklist.push(iff);
}
}
// Find RCE'd post loop so that we can stage its guard.
if (!is_canonical_loop_entry(legacy_cl)) return multi_version_succeeded;
Node* ctrl = legacy_cl->in(LoopNode::EntryControl);
Node* iffm = ctrl->in(0);
// Now we test that both the post loops are connected
Node* post_loop_region = iffm->in(0);
if (post_loop_region == NULL) return multi_version_succeeded;
if (!post_loop_region->is_Region()) return multi_version_succeeded;
Node* covering_region = post_loop_region->in(RegionNode::Control+1);
if (covering_region == NULL) return multi_version_succeeded;
if (!covering_region->is_Region()) return multi_version_succeeded;
Node* p_f = covering_region->in(RegionNode::Control);
if (p_f == NULL) return multi_version_succeeded;
if (!p_f->is_IfFalse()) return multi_version_succeeded;
if (!p_f->in(0)->is_CountedLoopEnd()) return multi_version_succeeded;
CountedLoopEndNode* rce_loop_end = p_f->in(0)->as_CountedLoopEnd();
if (rce_loop_end == NULL) return multi_version_succeeded;
CountedLoopNode* rce_cl = rce_loop_end->loopnode();
if (rce_cl == NULL || !rce_cl->is_post_loop()) return multi_version_succeeded;
CountedLoopNode *known_rce_cl = rce_loop->_head->as_CountedLoop();
if (rce_cl != known_rce_cl) return multi_version_succeeded;
// Then we fetch the cover entry test
ctrl = rce_cl->in(LoopNode::EntryControl);
if (!ctrl->is_IfTrue() && !ctrl->is_IfFalse()) return multi_version_succeeded;
#ifndef PRODUCT
if (TraceLoopOpts) {
tty->print("PostMultiVersion\n");
rce_loop->dump_head();
legacy_loop->dump_head();
}
#endif
// Now fetch the limit we want to compare against
Node *limit = rce_cl->limit();
bool first_time = true;
// If we got this far, we identified the post loop which has been RCE'd and
// we have a work list. Now we will try to transform the if guard to cause
// the loop pair to be multi version executed with the determination left to runtime
// or the optimizer if full information is known about the given arrays at compile time.
Node *last_min = NULL;
multi_version_succeeded = true;
while (worklist.size()) {
Node* rc_iffm = worklist.pop();
if (rc_iffm->is_If()) {
Node *rc_bolzm = rc_iffm->in(1);
if (rc_bolzm->is_Bool()) {
Node *rc_cmpzm = rc_bolzm->in(1);
if (rc_cmpzm->is_Cmp()) {
Node *rc_left = rc_cmpzm->in(2);
if (rc_left->Opcode() != Op_LoadRange) {
multi_version_succeeded = false;
break;
}
if (first_time) {
last_min = rc_left;
first_time = false;
} else {
Node *cur_min = new MinINode(last_min, rc_left);
last_min = cur_min;
_igvn.register_new_node_with_optimizer(last_min);
}
}
}
}
}
// All we have to do is update the limit of the rce loop
// with the min of our expression and the current limit.
// We will use this expression to replace the current limit.
if (last_min && multi_version_succeeded) {
Node *cur_min = new MinINode(last_min, limit);
_igvn.register_new_node_with_optimizer(cur_min);
Node *cmp_node = rce_loop_end->cmp_node();
_igvn.replace_input_of(cmp_node, 2, cur_min);
set_idom(cmp_node, cur_min, dom_depth(ctrl));
set_ctrl(cur_min, ctrl);
set_loop(cur_min, rce_loop->_parent);
legacy_cl->mark_is_multiversioned();
rce_cl->mark_is_multiversioned();
multi_version_succeeded = true;
C->set_major_progress();
}
return multi_version_succeeded;
}
//-------------------------poison_rce_post_loop--------------------------------
// Causes the rce'd post loop to be optimized away if multiversioning fails
void PhaseIdealLoop::poison_rce_post_loop(IdealLoopTree *rce_loop) {
CountedLoopNode *rce_cl = rce_loop->_head->as_CountedLoop();
Node* ctrl = rce_cl->in(LoopNode::EntryControl);
if (ctrl->is_IfTrue() || ctrl->is_IfFalse()) {
Node* iffm = ctrl->in(0);
if (iffm->is_If()) {
Node* cur_bool = iffm->in(1);
if (cur_bool->is_Bool()) {
Node* cur_cmp = cur_bool->in(1);
if (cur_cmp->is_Cmp()) {
BoolTest::mask new_test = BoolTest::gt;
BoolNode *new_bool = new BoolNode(cur_cmp, new_test);
_igvn.replace_node(cur_bool, new_bool);
_igvn._worklist.push(new_bool);
Node* left_op = cur_cmp->in(1);
_igvn.replace_input_of(cur_cmp, 2, left_op);
C->set_major_progress();
}
}
}
}
}
//------------------------------DCE_loop_body----------------------------------
// Remove simplistic dead code from loop body
void IdealLoopTree::DCE_loop_body() {
for( uint i = 0; i < _body.size(); i++ )
if( _body.at(i)->outcnt() == 0 )
_body.map( i--, _body.pop() );
}
//------------------------------adjust_loop_exit_prob--------------------------
// Look for loop-exit tests with the 50/50 (or worse) guesses from the parsing stage.
// Replace with a 1-in-10 exit guess.
void IdealLoopTree::adjust_loop_exit_prob( PhaseIdealLoop *phase ) {
Node *test = tail();
while( test != _head ) {
uint top = test->Opcode();
if( top == Op_IfTrue || top == Op_IfFalse ) {
int test_con = ((ProjNode*)test)->_con;
assert(top == (uint)(test_con? Op_IfTrue: Op_IfFalse), "sanity");
IfNode *iff = test->in(0)->as_If();
if( iff->outcnt() == 2 ) { // Ignore dead tests
Node *bol = iff->in(1);
if( bol && bol->req() > 1 && bol->in(1) &&
((bol->in(1)->Opcode() == Op_StorePConditional ) ||
(bol->in(1)->Opcode() == Op_StoreIConditional ) ||
(bol->in(1)->Opcode() == Op_StoreLConditional ) ||
(bol->in(1)->Opcode() == Op_CompareAndExchangeB ) ||
(bol->in(1)->Opcode() == Op_CompareAndExchangeS ) ||
(bol->in(1)->Opcode() == Op_CompareAndExchangeI ) ||
(bol->in(1)->Opcode() == Op_CompareAndExchangeL ) ||
(bol->in(1)->Opcode() == Op_CompareAndExchangeP ) ||
(bol->in(1)->Opcode() == Op_CompareAndExchangeN ) ||
(bol->in(1)->Opcode() == Op_WeakCompareAndSwapB ) ||
(bol->in(1)->Opcode() == Op_WeakCompareAndSwapS ) ||
(bol->in(1)->Opcode() == Op_WeakCompareAndSwapI ) ||
(bol->in(1)->Opcode() == Op_WeakCompareAndSwapL ) ||
(bol->in(1)->Opcode() == Op_WeakCompareAndSwapP ) ||
(bol->in(1)->Opcode() == Op_WeakCompareAndSwapN ) ||
(bol->in(1)->Opcode() == Op_CompareAndSwapB ) ||
(bol->in(1)->Opcode() == Op_CompareAndSwapS ) ||
(bol->in(1)->Opcode() == Op_CompareAndSwapI ) ||
(bol->in(1)->Opcode() == Op_CompareAndSwapL ) ||
(bol->in(1)->Opcode() == Op_CompareAndSwapP ) ||
(bol->in(1)->Opcode() == Op_CompareAndSwapN )))
return; // Allocation loops RARELY take backedge
// Find the OTHER exit path from the IF
Node* ex = iff->proj_out(1-test_con);
float p = iff->_prob;
if( !phase->is_member( this, ex ) && iff->_fcnt == COUNT_UNKNOWN ) {
if( top == Op_IfTrue ) {
if( p < (PROB_FAIR + PROB_UNLIKELY_MAG(3))) {
iff->_prob = PROB_STATIC_FREQUENT;
}
} else {
if( p > (PROB_FAIR - PROB_UNLIKELY_MAG(3))) {
iff->_prob = PROB_STATIC_INFREQUENT;
}
}
}
}
}
test = phase->idom(test);
}
}
#ifdef ASSERT
static CountedLoopNode* locate_pre_from_main(CountedLoopNode *cl) {
Node *ctrl = cl->in(LoopNode::EntryControl);
assert(ctrl->Opcode() == Op_IfTrue || ctrl->Opcode() == Op_IfFalse, "");
Node *iffm = ctrl->in(0);
assert(iffm->Opcode() == Op_If, "");
Node *p_f = iffm->in(0);
assert(p_f->Opcode() == Op_IfFalse, "");
CountedLoopEndNode *pre_end = p_f->in(0)->as_CountedLoopEnd();
assert(pre_end->loopnode()->is_pre_loop(), "");
return pre_end->loopnode();
}
#endif
// Remove the main and post loops and make the pre loop execute all
// iterations. Useful when the pre loop is found empty.
void IdealLoopTree::remove_main_post_loops(CountedLoopNode *cl, PhaseIdealLoop *phase) {
CountedLoopEndNode* pre_end = cl->loopexit();
Node* pre_cmp = pre_end->cmp_node();
if (pre_cmp->in(2)->Opcode() != Op_Opaque1) {
// Only safe to remove the main loop if the compiler optimized it
// out based on an unknown number of iterations
return;
}
// Can we find the main loop?
if (_next == NULL) {
return;
}
Node* next_head = _next->_head;
if (!next_head->is_CountedLoop()) {
return;
}
CountedLoopNode* main_head = next_head->as_CountedLoop();
if (!main_head->is_main_loop()) {
return;
}
assert(locate_pre_from_main(main_head) == cl, "bad main loop");
Node* main_iff = main_head->in(LoopNode::EntryControl)->in(0);
// Remove the Opaque1Node of the pre loop and make it execute all iterations
phase->_igvn.replace_input_of(pre_cmp, 2, pre_cmp->in(2)->in(2));
// Remove the Opaque1Node of the main loop so it can be optimized out
Node* main_cmp = main_iff->in(1)->in(1);
assert(main_cmp->in(2)->Opcode() == Op_Opaque1, "main loop has no opaque node?");
phase->_igvn.replace_input_of(main_cmp, 2, main_cmp->in(2)->in(1));
}
//------------------------------policy_do_remove_empty_loop--------------------
// Micro-benchmark spamming. Policy is to always remove empty loops.
// The 'DO' part is to replace the trip counter with the value it will
// have on the last iteration. This will break the loop.
bool IdealLoopTree::policy_do_remove_empty_loop( PhaseIdealLoop *phase ) {
// Minimum size must be empty loop
if (_body.size() > EMPTY_LOOP_SIZE)
return false;
if (!_head->is_CountedLoop())
return false; // Dead loop
CountedLoopNode *cl = _head->as_CountedLoop();
if (!cl->is_valid_counted_loop())
return false; // Malformed loop
if (!phase->is_member(this, phase->get_ctrl(cl->loopexit()->in(CountedLoopEndNode::TestValue))))
return false; // Infinite loop
if (cl->is_pre_loop()) {
// If the loop we are removing is a pre-loop then the main and
// post loop can be removed as well
remove_main_post_loops(cl, phase);
}
#ifdef ASSERT
// Ensure only one phi which is the iv.
Node* iv = NULL;
for (DUIterator_Fast imax, i = cl->fast_outs(imax); i < imax; i++) {
Node* n = cl->fast_out(i);
if (n->Opcode() == Op_Phi) {
assert(iv == NULL, "Too many phis" );
iv = n;
}
}
assert(iv == cl->phi(), "Wrong phi" );
#endif
// main and post loops have explicitly created zero trip guard
bool needs_guard = !cl->is_main_loop() && !cl->is_post_loop();
if (needs_guard) {
// Skip guard if values not overlap.
const TypeInt* init_t = phase->_igvn.type(cl->init_trip())->is_int();
const TypeInt* limit_t = phase->_igvn.type(cl->limit())->is_int();
int stride_con = cl->stride_con();
if (stride_con > 0) {
needs_guard = (init_t->_hi >= limit_t->_lo);
} else {
needs_guard = (init_t->_lo <= limit_t->_hi);
}
}
if (needs_guard) {
// Check for an obvious zero trip guard.
Node* inctrl = PhaseIdealLoop::skip_loop_predicates(cl->in(LoopNode::EntryControl));
if (inctrl->Opcode() == Op_IfTrue || inctrl->Opcode() == Op_IfFalse) {
bool maybe_swapped = (inctrl->Opcode() == Op_IfFalse);
// The test should look like just the backedge of a CountedLoop
Node* iff = inctrl->in(0);
if (iff->is_If()) {
Node* bol = iff->in(1);
if (bol->is_Bool()) {
BoolTest test = bol->as_Bool()->_test;
if (maybe_swapped) {
test._test = test.commute();
test._test = test.negate();
}
if (test._test == cl->loopexit()->test_trip()) {
Node* cmp = bol->in(1);
int init_idx = maybe_swapped ? 2 : 1;
int limit_idx = maybe_swapped ? 1 : 2;
if (cmp->is_Cmp() && cmp->in(init_idx) == cl->init_trip() && cmp->in(limit_idx) == cl->limit()) {
needs_guard = false;
}
}
}
}
}
}
#ifndef PRODUCT
if (PrintOpto) {
tty->print("Removing empty loop with%s zero trip guard", needs_guard ? "out" : "");
this->dump_head();
} else if (TraceLoopOpts) {
tty->print("Empty with%s zero trip guard ", needs_guard ? "out" : "");
this->dump_head();
}
#endif
if (needs_guard) {
// Peel the loop to ensure there's a zero trip guard
Node_List old_new;
phase->do_peeling(this, old_new);
}
// Replace the phi at loop head with the final value of the last
// iteration. Then the CountedLoopEnd will collapse (backedge never
// taken) and all loop-invariant uses of the exit values will be correct.
Node *phi = cl->phi();
Node *exact_limit = phase->exact_limit(this);
if (exact_limit != cl->limit()) {
// We also need to replace the original limit to collapse loop exit.
Node* cmp = cl->loopexit()->cmp_node();
assert(cl->limit() == cmp->in(2), "sanity");
phase->_igvn._worklist.push(cmp->in(2)); // put limit on worklist
phase->_igvn.replace_input_of(cmp, 2, exact_limit); // put cmp on worklist
}
// Note: the final value after increment should not overflow since
// counted loop has limit check predicate.
Node *final = new SubINode( exact_limit, cl->stride() );
phase->register_new_node(final,cl->in(LoopNode::EntryControl));
phase->_igvn.replace_node(phi,final);
phase->C->set_major_progress();
return true;
}
//------------------------------policy_do_one_iteration_loop-------------------
// Convert one iteration loop into normal code.
bool IdealLoopTree::policy_do_one_iteration_loop( PhaseIdealLoop *phase ) {
if (!_head->as_Loop()->is_valid_counted_loop())
return false; // Only for counted loop
CountedLoopNode *cl = _head->as_CountedLoop();
if (!cl->has_exact_trip_count() || cl->trip_count() != 1) {
return false;
}
#ifndef PRODUCT
if(TraceLoopOpts) {
tty->print("OneIteration ");
this->dump_head();
}
#endif
Node *init_n = cl->init_trip();
#ifdef ASSERT
// Loop boundaries should be constant since trip count is exact.
assert(init_n->get_int() + cl->stride_con() >= cl->limit()->get_int(), "should be one iteration");
#endif
// Replace the phi at loop head with the value of the init_trip.
// Then the CountedLoopEnd will collapse (backedge will not be taken)
// and all loop-invariant uses of the exit values will be correct.
phase->_igvn.replace_node(cl->phi(), cl->init_trip());
phase->C->set_major_progress();
return true;
}
//=============================================================================
//------------------------------iteration_split_impl---------------------------
bool IdealLoopTree::iteration_split_impl( PhaseIdealLoop *phase, Node_List &old_new ) {
// Compute loop trip count if possible.
compute_trip_count(phase);
// Convert one iteration loop into normal code.
if (policy_do_one_iteration_loop(phase))
return true;
// Check and remove empty loops (spam micro-benchmarks)
if (policy_do_remove_empty_loop(phase))
return true; // Here we removed an empty loop
bool should_peel = policy_peeling(phase); // Should we peel?
bool should_unswitch = policy_unswitching(phase);
// Non-counted loops may be peeled; exactly 1 iteration is peeled.
// This removes loop-invariant tests (usually null checks).
if (!_head->is_CountedLoop()) { // Non-counted loop
if (PartialPeelLoop && phase->partial_peel(this, old_new)) {
// Partial peel succeeded so terminate this round of loop opts
return false;
}
if (should_peel) { // Should we peel?
if (PrintOpto) { tty->print_cr("should_peel"); }
phase->do_peeling(this,old_new);
} else if (should_unswitch) {
phase->do_unswitching(this, old_new);
}
return true;
}
CountedLoopNode *cl = _head->as_CountedLoop();
if (!cl->is_valid_counted_loop()) return true; // Ignore various kinds of broken loops
// Do nothing special to pre- and post- loops
if (cl->is_pre_loop() || cl->is_post_loop()) return true;
// Compute loop trip count from profile data
compute_profile_trip_cnt(phase);
// Before attempting fancy unrolling, RCE or alignment, see if we want
// to completely unroll this loop or do loop unswitching.
if (cl->is_normal_loop()) {
if (should_unswitch) {
phase->do_unswitching(this, old_new);
return true;
}
bool should_maximally_unroll = policy_maximally_unroll(phase);
if (should_maximally_unroll) {
// Here we did some unrolling and peeling. Eventually we will
// completely unroll this loop and it will no longer be a loop.
phase->do_maximally_unroll(this,old_new);
return true;
}
}
// Skip next optimizations if running low on nodes. Note that
// policy_unswitching and policy_maximally_unroll have this check.
int nodes_left = phase->C->max_node_limit() - phase->C->live_nodes();
if ((int)(2 * _body.size()) > nodes_left) {
return true;
}
// Counted loops may be peeled, may need some iterations run up
// front for RCE, and may want to align loop refs to a cache
// line. Thus we clone a full loop up front whose trip count is
// at least 1 (if peeling), but may be several more.
// The main loop will start cache-line aligned with at least 1
// iteration of the unrolled body (zero-trip test required) and
// will have some range checks removed.
// A post-loop will finish any odd iterations (leftover after
// unrolling), plus any needed for RCE purposes.
bool should_unroll = policy_unroll(phase);
bool should_rce = policy_range_check(phase);
bool should_align = policy_align(phase);
// If not RCE'ing (iteration splitting) or Aligning, then we do not
// need a pre-loop. We may still need to peel an initial iteration but
// we will not be needing an unknown number of pre-iterations.
//
// Basically, if may_rce_align reports FALSE first time through,
// we will not be able to later do RCE or Aligning on this loop.
bool may_rce_align = !policy_peel_only(phase) || should_rce || should_align;
// If we have any of these conditions (RCE, alignment, unrolling) met, then
// we switch to the pre-/main-/post-loop model. This model also covers
// peeling.
if (should_rce || should_align || should_unroll) {
if (cl->is_normal_loop()) // Convert to 'pre/main/post' loops
phase->insert_pre_post_loops(this,old_new, !may_rce_align);
// Adjust the pre- and main-loop limits to let the pre and post loops run
// with full checks, but the main-loop with no checks. Remove said
// checks from the main body.
if (should_rce) {
if (phase->do_range_check(this, old_new) != 0) {
cl->mark_has_range_checks();
}
} else if (PostLoopMultiversioning) {
phase->has_range_checks(this);
}
if (should_unroll && !should_peel && PostLoopMultiversioning) {
// Try to setup multiversioning on main loops before they are unrolled
if (cl->is_main_loop() && (cl->unrolled_count() == 1)) {
phase->insert_scalar_rced_post_loop(this, old_new);
}
}
// Double loop body for unrolling. Adjust the minimum-trip test (will do
// twice as many iterations as before) and the main body limit (only do
// an even number of trips). If we are peeling, we might enable some RCE
// and we'd rather unroll the post-RCE'd loop SO... do not unroll if
// peeling.
if (should_unroll && !should_peel) {
if (SuperWordLoopUnrollAnalysis) {
phase->insert_vector_post_loop(this, old_new);
}
phase->do_unroll(this, old_new, true);
}
// Adjust the pre-loop limits to align the main body
// iterations.
if (should_align)
Unimplemented();
} else { // Else we have an unchanged counted loop
if (should_peel) // Might want to peel but do nothing else
phase->do_peeling(this,old_new);
}
return true;
}
//=============================================================================
//------------------------------iteration_split--------------------------------
bool IdealLoopTree::iteration_split( PhaseIdealLoop *phase, Node_List &old_new ) {
// Recursively iteration split nested loops
if (_child && !_child->iteration_split(phase, old_new))
return false;
// Clean out prior deadwood
DCE_loop_body();
// Look for loop-exit tests with my 50/50 guesses from the Parsing stage.
// Replace with a 1-in-10 exit guess.
if (_parent /*not the root loop*/ &&
!_irreducible &&
// Also ignore the occasional dead backedge
!tail()->is_top()) {
adjust_loop_exit_prob(phase);
}
// Gate unrolling, RCE and peeling efforts.
if (!_child && // If not an inner loop, do not split
!_irreducible &&
_allow_optimizations &&
!tail()->is_top()) { // Also ignore the occasional dead backedge
if (!_has_call) {
if (!iteration_split_impl(phase, old_new)) {
return false;
}
} else if (policy_unswitching(phase)) {
phase->do_unswitching(this, old_new);
}
}
// Minor offset re-organization to remove loop-fallout uses of
// trip counter when there was no major reshaping.
phase->reorg_offsets(this);
if (_next && !_next->iteration_split(phase, old_new))
return false;
return true;
}
//=============================================================================
// Process all the loops in the loop tree and replace any fill
// patterns with an intrinsic version.
bool PhaseIdealLoop::do_intrinsify_fill() {
bool changed = false;
for (LoopTreeIterator iter(_ltree_root); !iter.done(); iter.next()) {
IdealLoopTree* lpt = iter.current();
changed |= intrinsify_fill(lpt);
}
return changed;
}
// Examine an inner loop looking for a a single store of an invariant
// value in a unit stride loop,
bool PhaseIdealLoop::match_fill_loop(IdealLoopTree* lpt, Node*& store, Node*& store_value,
Node*& shift, Node*& con) {
const char* msg = NULL;
Node* msg_node = NULL;
store_value = NULL;
con = NULL;
shift = NULL;
// Process the loop looking for stores. If there are multiple
// stores or extra control flow give at this point.
CountedLoopNode* head = lpt->_head->as_CountedLoop();
for (uint i = 0; msg == NULL && i < lpt->_body.size(); i++) {
Node* n = lpt->_body.at(i);
if (n->outcnt() == 0) continue; // Ignore dead
if (n->is_Store()) {
if (store != NULL) {
msg = "multiple stores";
break;
}
int opc = n->Opcode();
if (opc == Op_StoreP || opc == Op_StoreN || opc == Op_StoreNKlass || opc == Op_StoreCM) {
msg = "oop fills not handled";
break;
}
Node* value = n->in(MemNode::ValueIn);
if (!lpt->is_invariant(value)) {
msg = "variant store value";
} else if (!_igvn.type(n->in(MemNode::Address))->isa_aryptr()) {
msg = "not array address";
}
store = n;
store_value = value;
} else if (n->is_If() && n != head->loopexit()) {
msg = "extra control flow";
msg_node = n;
}
}
if (store == NULL) {
// No store in loop
return false;
}
if (msg == NULL && head->stride_con() != 1) {
// could handle negative strides too
if (head->stride_con() < 0) {
msg = "negative stride";
} else {
msg = "non-unit stride";
}
}
if (msg == NULL && !store->in(MemNode::Address)->is_AddP()) {
msg = "can't handle store address";
msg_node = store->in(MemNode::Address);
}
if (msg == NULL &&
(!store->in(MemNode::Memory)->is_Phi() ||
store->in(MemNode::Memory)->in(LoopNode::LoopBackControl) != store)) {
msg = "store memory isn't proper phi";
msg_node = store->in(MemNode::Memory);
}
// Make sure there is an appropriate fill routine
BasicType t = store->as_Mem()->memory_type();
const char* fill_name;
if (msg == NULL &&
StubRoutines::select_fill_function(t, false, fill_name) == NULL) {
msg = "unsupported store";
msg_node = store;
}
if (msg != NULL) {
#ifndef PRODUCT
if (TraceOptimizeFill) {
tty->print_cr("not fill intrinsic candidate: %s", msg);
if (msg_node != NULL) msg_node->dump();
}
#endif
return false;
}
// Make sure the address expression can be handled. It should be
// head->phi * elsize + con. head->phi might have a ConvI2L(CastII()).
Node* elements[4];
Node* cast = NULL;
Node* conv = NULL;
bool found_index = false;
int count = store->in(MemNode::Address)->as_AddP()->unpack_offsets(elements, ARRAY_SIZE(elements));
for (int e = 0; e < count; e++) {
Node* n = elements[e];
if (n->is_Con() && con == NULL) {
con = n;
} else if (n->Opcode() == Op_LShiftX && shift == NULL) {
Node* value = n->in(1);
#ifdef _LP64
if (value->Opcode() == Op_ConvI2L) {
conv = value;
value = value->in(1);
}
if (value->Opcode() == Op_CastII &&
value->as_CastII()->has_range_check()) {
// Skip range check dependent CastII nodes
cast = value;
value = value->in(1);
}
#endif
if (value != head->phi()) {
msg = "unhandled shift in address";
} else {
if (type2aelembytes(store->as_Mem()->memory_type(), true) != (1 << n->in(2)->get_int())) {
msg = "scale doesn't match";
} else {
found_index = true;
shift = n;
}
}
} else if (n->Opcode() == Op_ConvI2L && conv == NULL) {
conv = n;
n = n->in(1);
if (n->Opcode() == Op_CastII &&
n->as_CastII()->has_range_check()) {
// Skip range check dependent CastII nodes
cast = n;
n = n->in(1);
}
if (n == head->phi()) {
found_index = true;
} else {
msg = "unhandled input to ConvI2L";
}
} else if (n == head->phi()) {
// no shift, check below for allowed cases
found_index = true;
} else {
msg = "unhandled node in address";
msg_node = n;
}
}
if (count == -1) {
msg = "malformed address expression";
msg_node = store;
}
if (!found_index) {
msg = "missing use of index";
}
// byte sized items won't have a shift
if (msg == NULL && shift == NULL && t != T_BYTE && t != T_BOOLEAN) {
msg = "can't find shift";
msg_node = store;
}
if (msg != NULL) {
#ifndef PRODUCT
if (TraceOptimizeFill) {
tty->print_cr("not fill intrinsic: %s", msg);
if (msg_node != NULL) msg_node->dump();
}
#endif
return false;
}
// No make sure all the other nodes in the loop can be handled
VectorSet ok(Thread::current()->resource_area());
// store related values are ok
ok.set(store->_idx);
ok.set(store->in(MemNode::Memory)->_idx);
CountedLoopEndNode* loop_exit = head->loopexit();
guarantee(loop_exit != NULL, "no loop exit node");
// Loop structure is ok
ok.set(head->_idx);
ok.set(loop_exit->_idx);
ok.set(head->phi()->_idx);
ok.set(head->incr()->_idx);
ok.set(loop_exit->cmp_node()->_idx);
ok.set(loop_exit->in(1)->_idx);
// Address elements are ok
if (con) ok.set(con->_idx);
if (shift) ok.set(shift->_idx);
if (cast) ok.set(cast->_idx);
if (conv) ok.set(conv->_idx);
for (uint i = 0; msg == NULL && i < lpt->_body.size(); i++) {
Node* n = lpt->_body.at(i);
if (n->outcnt() == 0) continue; // Ignore dead
if (ok.test(n->_idx)) continue;
// Backedge projection is ok
if (n->is_IfTrue() && n->in(0) == loop_exit) continue;
if (!n->is_AddP()) {
msg = "unhandled node";
msg_node = n;
break;
}
}
// Make sure no unexpected values are used outside the loop
for (uint i = 0; msg == NULL && i < lpt->_body.size(); i++) {
Node* n = lpt->_body.at(i);
// These values can be replaced with other nodes if they are used
// outside the loop.
if (n == store || n == loop_exit || n == head->incr() || n == store->in(MemNode::Memory)) continue;
for (SimpleDUIterator iter(n); iter.has_next(); iter.next()) {
Node* use = iter.get();
if (!lpt->_body.contains(use)) {
msg = "node is used outside loop";
// lpt->_body.dump();
msg_node = n;
break;
}
}
}
#ifdef ASSERT
if (TraceOptimizeFill) {
if (msg != NULL) {
tty->print_cr("no fill intrinsic: %s", msg);
if (msg_node != NULL) msg_node->dump();
} else {
tty->print_cr("fill intrinsic for:");
}
store->dump();
if (Verbose) {
lpt->_body.dump();
}
}
#endif
return msg == NULL;
}
bool PhaseIdealLoop::intrinsify_fill(IdealLoopTree* lpt) {
// Only for counted inner loops
if (!lpt->is_counted() || !lpt->is_inner()) {
return false;
}
// Must have constant stride
CountedLoopNode* head = lpt->_head->as_CountedLoop();
if (!head->is_valid_counted_loop() || !head->is_normal_loop()) {
return false;
}
// Check that the body only contains a store of a loop invariant
// value that is indexed by the loop phi.
Node* store = NULL;
Node* store_value = NULL;
Node* shift = NULL;
Node* offset = NULL;
if (!match_fill_loop(lpt, store, store_value, shift, offset)) {
return false;
}
Node* exit = head->loopexit()->proj_out(0);
if (exit == NULL) {
return false;
}
#ifndef PRODUCT
if (TraceLoopOpts) {
tty->print("ArrayFill ");
lpt->dump_head();
}
#endif
// Now replace the whole loop body by a call to a fill routine that
// covers the same region as the loop.
Node* base = store->in(MemNode::Address)->as_AddP()->in(AddPNode::Base);
// Build an expression for the beginning of the copy region
Node* index = head->init_trip();
#ifdef _LP64
index = new ConvI2LNode(index);
_igvn.register_new_node_with_optimizer(index);
#endif
if (shift != NULL) {
// byte arrays don't require a shift but others do.
index = new LShiftXNode(index, shift->in(2));
_igvn.register_new_node_with_optimizer(index);
}
index = new AddPNode(base, base, index);
_igvn.register_new_node_with_optimizer(index);
Node* from = new AddPNode(base, index, offset);
_igvn.register_new_node_with_optimizer(from);
// Compute the number of elements to copy
Node* len = new SubINode(head->limit(), head->init_trip());
_igvn.register_new_node_with_optimizer(len);
BasicType t = store->as_Mem()->memory_type();
bool aligned = false;
if (offset != NULL && head->init_trip()->is_Con()) {
int element_size = type2aelembytes(t);
aligned = (offset->find_intptr_t_type()->get_con() + head->init_trip()->get_int() * element_size) % HeapWordSize == 0;
}
// Build a call to the fill routine
const char* fill_name;
address fill = StubRoutines::select_fill_function(t, aligned, fill_name);
assert(fill != NULL, "what?");
// Convert float/double to int/long for fill routines
if (t == T_FLOAT) {
store_value = new MoveF2INode(store_value);
_igvn.register_new_node_with_optimizer(store_value);
} else if (t == T_DOUBLE) {
store_value = new MoveD2LNode(store_value);
_igvn.register_new_node_with_optimizer(store_value);
}
Node* mem_phi = store->in(MemNode::Memory);
Node* result_ctrl;
Node* result_mem;
const TypeFunc* call_type = OptoRuntime::array_fill_Type();
CallLeafNode *call = new CallLeafNoFPNode(call_type, fill,
fill_name, TypeAryPtr::get_array_body_type(t));
uint cnt = 0;
call->init_req(TypeFunc::Parms + cnt++, from);
call->init_req(TypeFunc::Parms + cnt++, store_value);
#ifdef _LP64
len = new ConvI2LNode(len);
_igvn.register_new_node_with_optimizer(len);
#endif
call->init_req(TypeFunc::Parms + cnt++, len);
#ifdef _LP64
call->init_req(TypeFunc::Parms + cnt++, C->top());
#endif
call->init_req(TypeFunc::Control, head->init_control());
call->init_req(TypeFunc::I_O, C->top()); // Does no I/O.
call->init_req(TypeFunc::Memory, mem_phi->in(LoopNode::EntryControl));
call->init_req(TypeFunc::ReturnAdr, C->start()->proj_out(TypeFunc::ReturnAdr));
call->init_req(TypeFunc::FramePtr, C->start()->proj_out(TypeFunc::FramePtr));
_igvn.register_new_node_with_optimizer(call);
result_ctrl = new ProjNode(call,TypeFunc::Control);
_igvn.register_new_node_with_optimizer(result_ctrl);
result_mem = new ProjNode(call,TypeFunc::Memory);
_igvn.register_new_node_with_optimizer(result_mem);
/* Disable following optimization until proper fix (add missing checks).
// If this fill is tightly coupled to an allocation and overwrites
// the whole body, allow it to take over the zeroing.
AllocateNode* alloc = AllocateNode::Ideal_allocation(base, this);
if (alloc != NULL && alloc->is_AllocateArray()) {
Node* length = alloc->as_AllocateArray()->Ideal_length();
if (head->limit() == length &&
head->init_trip() == _igvn.intcon(0)) {
if (TraceOptimizeFill) {
tty->print_cr("Eliminated zeroing in allocation");
}
alloc->maybe_set_complete(&_igvn);
} else {
#ifdef ASSERT
if (TraceOptimizeFill) {
tty->print_cr("filling array but bounds don't match");
alloc->dump();
head->init_trip()->dump();
head->limit()->dump();
length->dump();
}
#endif
}
}
*/
// Redirect the old control and memory edges that are outside the loop.
// Sometimes the memory phi of the head is used as the outgoing
// state of the loop. It's safe in this case to replace it with the
// result_mem.
_igvn.replace_node(store->in(MemNode::Memory), result_mem);
lazy_replace(exit, result_ctrl);
_igvn.replace_node(store, result_mem);
// Any uses the increment outside of the loop become the loop limit.
_igvn.replace_node(head->incr(), head->limit());
// Disconnect the head from the loop.
for (uint i = 0; i < lpt->_body.size(); i++) {
Node* n = lpt->_body.at(i);
_igvn.replace_node(n, C->top());
}
return true;
}