/*

 * Copyright (c) 1998, 2013, 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 "memory/allocation.inline.hpp"

#include "opto/chaitin.hpp"

#include "opto/machnode.hpp"

// See if this register (or pairs, or vector) already contains the value.

static bool register_contains_value(Node* val, OptoReg::Name reg, int n_regs,

                                    Node_List& value) {

  for (int i = 0; i < n_regs; i++) {

    OptoReg::Name nreg = OptoReg::add(reg,-i);

    if (value[nreg] != val)

      return false;

  }

  return true;

}

//---------------------------may_be_copy_of_callee-----------------------------

// Check to see if we can possibly be a copy of a callee-save value.

bool PhaseChaitin::may_be_copy_of_callee( Node *def ) const {

  // Short circuit if there are no callee save registers

  if (_matcher.number_of_saved_registers() == 0) return false;

  // Expect only a spill-down and reload on exit for callee-save spills.

  // Chains of copies cannot be deep.

  // 5008997 - This is wishful thinking. Register allocator seems to

  // be splitting live ranges for callee save registers to such

  // an extent that in large methods the chains can be very long

  // (50+). The conservative answer is to return true if we don't

  // know as this prevents optimizations from occurring.

  const int limit = 60;

  int i;

  for( i=0; i < limit; i++ ) {

    if( def->is_Proj() && def->in(0)->is_Start() &&

        _matcher.is_save_on_entry(lrgs(_lrg_map.live_range_id(def)).reg()))

      return true;              // Direct use of callee-save proj

    if( def->is_Copy() )        // Copies carry value through

      def = def->in(def->is_Copy());

    else if( def->is_Phi() )    // Phis can merge it from any direction

      def = def->in(1);

    else

      break;

    guarantee(def != NULL, "must not resurrect dead copy");

  }

  // If we reached the end and didn't find a callee save proj

  // then this may be a callee save proj so we return true

  // as the conservative answer. If we didn't reach then end

  // we must have discovered that it was not a callee save

  // else we would have returned.

  return i == limit;

}

//------------------------------yank-----------------------------------

// Helper function for yank_if_dead

int PhaseChaitin::yank( Node *old, Block *current_block, Node_List *value, Node_List *regnd ) {

  int blk_adjust=0;

  Block *oldb = _cfg.get_block_for_node(old);

  oldb->find_remove(old);

  // Count 1 if deleting an instruction from the current block

  if (oldb == current_block) {

    blk_adjust++;

  }

  _cfg.unmap_node_from_block(old);

  OptoReg::Name old_reg = lrgs(_lrg_map.live_range_id(old)).reg();

  if( regnd && (*regnd)[old_reg]==old ) { // Instruction is currently available?

    value->map(old_reg,NULL);  // Yank from value/regnd maps

    regnd->map(old_reg,NULL);  // This register's value is now unknown

  }

  return blk_adjust;

}

#ifdef ASSERT

static bool expected_yanked_node(Node *old, Node *orig_old) {

  // This code is expected only next original nodes:

  // - load from constant table node which may have next data input nodes:

  //     MachConstantBase, MachTemp, MachSpillCopy

  // - Phi nodes that are considered Junk

  // - load constant node which may have next data input nodes:

  //     MachTemp, MachSpillCopy

  // - MachSpillCopy

  // - MachProj and Copy dead nodes

  if (old->is_MachSpillCopy()) {

    return true;

  } else if (old->is_Con()) {

    return true;

  } else if (old->is_MachProj()) { // Dead kills projection of Con node

    return (old == orig_old);

  } else if (old->is_Copy()) {     // Dead copy of a callee-save value

    return (old == orig_old);

  } else if (old->is_MachTemp()) {

    return orig_old->is_Con();

  } else if (old->is_Phi()) { // Junk phi's

    return true;

  } else if (old->is_MachConstantBase()) {

    return (orig_old->is_Con() && orig_old->is_MachConstant());

  }

  return false;

}

#endif

//------------------------------yank_if_dead-----------------------------------

// Removed edges from 'old'.  Yank if dead.  Return adjustment counts to

// iterators in the current block.

int PhaseChaitin::yank_if_dead_recurse(Node *old, Node *orig_old, Block *current_block,

                                       Node_List *value, Node_List *regnd) {

  int blk_adjust=0;

  if (old->outcnt() == 0 && old != C->top()) {

#ifdef ASSERT

    if (!expected_yanked_node(old, orig_old)) {

      tty->print_cr("==============================================");

      tty->print_cr("orig_old:");

      orig_old->dump();

      tty->print_cr("old:");

      old->dump();

      assert(false, "unexpected yanked node");

    }

    if (old->is_Con())

      orig_old = old; // Reset to satisfy expected nodes checks.

#endif

    blk_adjust += yank(old, current_block, value, regnd);

    for (uint i = 1; i < old->req(); i++) {

      Node* n = old->in(i);

      if (n != NULL) {

        old->set_req(i, NULL);

        blk_adjust += yank_if_dead_recurse(n, orig_old, current_block, value, regnd);

      }

    }

    // Disconnect control and remove precedence edges if any exist

    old->disconnect_inputs(NULL, C);

  }

  return blk_adjust;

}

//------------------------------use_prior_register-----------------------------

// Use the prior value instead of the current value, in an effort to make

// the current value go dead.  Return block iterator adjustment, in case

// we yank some instructions from this block.

int PhaseChaitin::use_prior_register( Node *n, uint idx, Node *def, Block *current_block, Node_List &value, Node_List &regnd ) {

  // No effect?

  if( def == n->in(idx) ) return 0;

  // Def is currently dead and can be removed?  Do not resurrect

  if( def->outcnt() == 0 ) return 0;

  // Not every pair of physical registers are assignment compatible,

  // e.g. on sparc floating point registers are not assignable to integer

  // registers.

  const LRG &def_lrg = lrgs(_lrg_map.live_range_id(def));

  OptoReg::Name def_reg = def_lrg.reg();

  const RegMask &use_mask = n->in_RegMask(idx);

  bool can_use = ( RegMask::can_represent(def_reg) ? (use_mask.Member(def_reg) != 0)

                                                   : (use_mask.is_AllStack() != 0));

  if (!RegMask::is_vector(def->ideal_reg())) {

    // Check for a copy to or from a misaligned pair.

    // It is workaround for a sparc with misaligned pairs.

    can_use = can_use && !use_mask.is_misaligned_pair() && !def_lrg.mask().is_misaligned_pair();

  }

  if (!can_use)

    return 0;

  // Capture the old def in case it goes dead...

  Node *old = n->in(idx);

  // Save-on-call copies can only be elided if the entire copy chain can go

  // away, lest we get the same callee-save value alive in 2 locations at

  // once.  We check for the obvious trivial case here.  Although it can

  // sometimes be elided with cooperation outside our scope, here we will just

  // miss the opportunity.  :-(

  if( may_be_copy_of_callee(def) ) {

    if( old->outcnt() > 1 ) return 0; // We're the not last user

    int idx = old->is_Copy();

    assert( idx, "chain of copies being removed" );

    Node *old2 = old->in(idx);  // Chain of copies

    if( old2->outcnt() > 1 ) return 0; // old is not the last user

    int idx2 = old2->is_Copy();

    if( !idx2 ) return 0;       // Not a chain of 2 copies

    if( def != old2->in(idx2) ) return 0; // Chain of exactly 2 copies

  }

  // Use the new def

  n->set_req(idx,def);

  _post_alloc++;

  // Is old def now dead?  We successfully yanked a copy?

  return yank_if_dead(old,current_block,&value,&regnd);

}

//------------------------------skip_copies------------------------------------

// Skip through any number of copies (that don't mod oop-i-ness)

Node *PhaseChaitin::skip_copies( Node *c ) {

  int idx = c->is_Copy();

  uint is_oop = lrgs(_lrg_map.live_range_id(c))._is_oop;

  while (idx != 0) {

    guarantee(c->in(idx) != NULL, "must not resurrect dead copy");

    if (lrgs(_lrg_map.live_range_id(c->in(idx)))._is_oop != is_oop) {

      break;  // casting copy, not the same value

    }

    c = c->in(idx);

    idx = c->is_Copy();

  }

  return c;

}

//------------------------------elide_copy-------------------------------------

// Remove (bypass) copies along Node n, edge k.

int PhaseChaitin::elide_copy( Node *n, int k, Block *current_block, Node_List &value, Node_List &regnd, bool can_change_regs ) {

  int blk_adjust = 0;

  uint nk_idx = _lrg_map.live_range_id(n->in(k));

  OptoReg::Name nk_reg = lrgs(nk_idx).reg();

  // Remove obvious same-register copies

  Node *x = n->in(k);

  int idx;

  while( (idx=x->is_Copy()) != 0 ) {

    Node *copy = x->in(idx);

    guarantee(copy != NULL, "must not resurrect dead copy");

    if(lrgs(_lrg_map.live_range_id(copy)).reg() != nk_reg) {

      break;

    }

    blk_adjust += use_prior_register(n,k,copy,current_block,value,regnd);

    if (n->in(k) != copy) {

      break; // Failed for some cutout?

    }

    x = copy;                   // Progress, try again

  }

  // Phis and 2-address instructions cannot change registers so easily - their

  // outputs must match their input.

  if( !can_change_regs )

    return blk_adjust;          // Only check stupid copies!

  // Loop backedges won't have a value-mapping yet

  if( &value == NULL ) return blk_adjust;

  // Skip through all copies to the _value_ being used.  Do not change from

  // int to pointer.  This attempts to jump through a chain of copies, where

  // intermediate copies might be illegal, i.e., value is stored down to stack

  // then reloaded BUT survives in a register the whole way.

  Node *val = skip_copies(n->in(k));

  if (val == x && nk_idx != 0 &&

      regnd[nk_reg] != NULL && regnd[nk_reg] != x &&

      _lrg_map.live_range_id(x) == _lrg_map.live_range_id(regnd[nk_reg])) {

    // When rematerialzing nodes and stretching lifetimes, the

    // allocator will reuse the original def for multidef LRG instead

    // of the current reaching def because it can't know it's safe to

    // do so.  After allocation completes if they are in the same LRG

    // then it should use the current reaching def instead.

    n->set_req(k, regnd[nk_reg]);

    blk_adjust += yank_if_dead(val, current_block, &value, &regnd);

    val = skip_copies(n->in(k));

  }

  if (val == x) return blk_adjust; // No progress?

  int n_regs = RegMask::num_registers(val->ideal_reg());

  uint val_idx = _lrg_map.live_range_id(val);

  OptoReg::Name val_reg = lrgs(val_idx).reg();

  // See if it happens to already be in the correct register!

  // (either Phi's direct register, or the common case of the name

  // never-clobbered original-def register)

  if (register_contains_value(val, val_reg, n_regs, value)) {

    blk_adjust += use_prior_register(n,k,regnd[val_reg],current_block,value,regnd);

    if( n->in(k) == regnd[val_reg] ) // Success!  Quit trying

      return blk_adjust;

  }

  // See if we can skip the copy by changing registers.  Don't change from

  // using a register to using the stack unless we know we can remove a

  // copy-load.  Otherwise we might end up making a pile of Intel cisc-spill

  // ops reading from memory instead of just loading once and using the

  // register.

  // Also handle duplicate copies here.

  const Type *t = val->is_Con() ? val->bottom_type() : NULL;

  // Scan all registers to see if this value is around already

  for( uint reg = 0; reg < (uint)_max_reg; reg++ ) {

    if (reg == (uint)nk_reg) {

      // Found ourselves so check if there is only one user of this

      // copy and keep on searching for a better copy if so.

      bool ignore_self = true;

      x = n->in(k);

      DUIterator_Fast imax, i = x->fast_outs(imax);

      Node* first = x->fast_out(i); i++;

      while (i < imax && ignore_self) {

        Node* use = x->fast_out(i); i++;

        if (use != first) ignore_self = false;

      }

      if (ignore_self) continue;

    }

    Node *vv = value[reg];

    if (n_regs > 1) { // Doubles and vectors check for aligned-adjacent set

      uint last = (n_regs-1); // Looking for the last part of a set

      if ((reg&last) != last) continue; // Wrong part of a set

      if (!register_contains_value(vv, reg, n_regs, value)) continue; // Different value

    }

    if( vv == val ||            // Got a direct hit?

        (t && vv && vv->bottom_type() == t && vv->is_Mach() &&

         vv->as_Mach()->rule() == val->as_Mach()->rule()) ) { // Or same constant?

      assert( !n->is_Phi(), "cannot change registers at a Phi so easily" );

      if( OptoReg::is_stack(nk_reg) || // CISC-loading from stack OR

          OptoReg::is_reg(reg) || // turning into a register use OR

          regnd[reg]->outcnt()==1 ) { // last use of a spill-load turns into a CISC use

        blk_adjust += use_prior_register(n,k,regnd[reg],current_block,value,regnd);

        if( n->in(k) == regnd[reg] ) // Success!  Quit trying

          return blk_adjust;

      } // End of if not degrading to a stack

    } // End of if found value in another register

  } // End of scan all machine registers

  return blk_adjust;

}

//

// Check if nreg already contains the constant value val.  Normal copy

// elimination doesn't doesn't work on constants because multiple

// nodes can represent the same constant so the type and rule of the

// MachNode must be checked to ensure equivalence.

//

bool PhaseChaitin::eliminate_copy_of_constant(Node* val, Node* n,

                                              Block *current_block,

                                              Node_List& value, Node_List& regnd,

                                              OptoReg::Name nreg, OptoReg::Name nreg2) {

  if (value[nreg] != val && val->is_Con() &&

      value[nreg] != NULL && value[nreg]->is_Con() &&

      (nreg2 == OptoReg::Bad || value[nreg] == value[nreg2]) &&

      value[nreg]->bottom_type() == val->bottom_type() &&

      value[nreg]->as_Mach()->rule() == val->as_Mach()->rule()) {

    // This code assumes that two MachNodes representing constants

    // which have the same rule and the same bottom type will produce

    // identical effects into a register.  This seems like it must be

    // objectively true unless there are hidden inputs to the nodes

    // but if that were to change this code would need to updated.

    // Since they are equivalent the second one if redundant and can

    // be removed.

    //

    // n will be replaced with the old value but n might have

    // kills projections associated with it so remove them now so that

    // yank_if_dead will be able to eliminate the copy once the uses

    // have been transferred to the old[value].

    for (DUIterator_Fast imax, i = n->fast_outs(imax); i < imax; i++) {

      Node* use = n->fast_out(i);

      if (use->is_Proj() && use->outcnt() == 0) {

        // Kill projections have no users and one input

        use->set_req(0, C->top());

        yank_if_dead(use, current_block, &value, &regnd);

        --i; --imax;

      }

    }

    _post_alloc++;

    return true;

  }

  return false;

}

//------------------------------post_allocate_copy_removal---------------------

// Post-Allocation peephole copy removal.  We do this in 1 pass over the

// basic blocks.  We maintain a mapping of registers to Nodes (an  array of

// Nodes indexed by machine register or stack slot number).  NULL means that a

// register is not mapped to any Node.  We can (want to have!) have several

// registers map to the same Node.  We walk forward over the instructions

// updating the mapping as we go.  At merge points we force a NULL if we have

// to merge 2 different Nodes into the same register.  Phi functions will give

// us a new Node if there is a proper value merging.  Since the blocks are

// arranged in some RPO, we will visit all parent blocks before visiting any

// successor blocks (except at loops).

//

// If we find a Copy we look to see if the Copy's source register is a stack

// slot and that value has already been loaded into some machine register; if

// so we use machine register directly.  This turns a Load into a reg-reg

// Move.  We also look for reloads of identical constants.

//

// When we see a use from a reg-reg Copy, we will attempt to use the copy's

// source directly and make the copy go dead.

void PhaseChaitin::post_allocate_copy_removal() {

  NOT_PRODUCT( Compile::TracePhase t3("postAllocCopyRemoval", &_t_postAllocCopyRemoval, TimeCompiler); )

  ResourceMark rm;

  // Need a mapping from basic block Node_Lists.  We need a Node_List to

  // map from register number to value-producing Node.

  Node_List **blk2value = NEW_RESOURCE_ARRAY( Node_List *, _cfg.number_of_blocks() + 1);

  memset(blk2value, 0, sizeof(Node_List*) * (_cfg.number_of_blocks() + 1));

  // Need a mapping from basic block Node_Lists.  We need a Node_List to

  // map from register number to register-defining Node.

  Node_List **blk2regnd = NEW_RESOURCE_ARRAY( Node_List *, _cfg.number_of_blocks() + 1);

  memset(blk2regnd, 0, sizeof(Node_List*) * (_cfg.number_of_blocks() + 1));

  // We keep unused Node_Lists on a free_list to avoid wasting

  // memory.

  GrowableArray<Node_List*> free_list = GrowableArray<Node_List*>(16);

  // For all blocks

  for (uint i = 0; i < _cfg.number_of_blocks(); i++) {

    uint j;

    Block* block = _cfg.get_block(i);

    // Count of Phis in block

    uint phi_dex;

    for (phi_dex = 1; phi_dex < block->number_of_nodes(); phi_dex++) {

      Node* phi = block->get_node(phi_dex);

      if (!phi->is_Phi()) {

        break;

      }

    }

    // If any predecessor has not been visited, we do not know the state

    // of registers at the start.  Check for this, while updating copies

    // along Phi input edges

    bool missing_some_inputs = false;

    Block *freed = NULL;

    for (j = 1; j < block->num_preds(); j++) {

      Block* pb = _cfg.get_block_for_node(block->pred(j));

      // Remove copies along phi edges

      for (uint k = 1; k < phi_dex; k++) {

        elide_copy(block->get_node(k), j, block, *blk2value[pb->_pre_order], *blk2regnd[pb->_pre_order], false);

      }

      if (blk2value[pb->_pre_order]) { // Have a mapping on this edge?

        // See if this predecessor's mappings have been used by everybody

        // who wants them.  If so, free 'em.

        uint k;

        for (k = 0; k < pb->_num_succs; k++) {

          Block* pbsucc = pb->_succs[k];

          if (!blk2value[pbsucc->_pre_order] && pbsucc != block) {

            break;              // Found a future user

          }

        }

        if (k >= pb->_num_succs) { // No more uses, free!

          freed = pb;           // Record last block freed

          free_list.push(blk2value[pb->_pre_order]);

          free_list.push(blk2regnd[pb->_pre_order]);

        }

      } else {                  // This block has unvisited (loopback) inputs

        missing_some_inputs = true;

      }

    }

    // Extract Node_List mappings.  If 'freed' is non-zero, we just popped

    // 'freed's blocks off the list

    Node_List &regnd = *(free_list.is_empty() ? new Node_List() : free_list.pop());

    Node_List &value = *(free_list.is_empty() ? new Node_List() : free_list.pop());

    assert( !freed || blk2value[freed->_pre_order] == &value, "" );

    value.map(_max_reg,NULL);

    regnd.map(_max_reg,NULL);

    // Set mappings as OUR mappings

    blk2value[block->_pre_order] = &value;

    blk2regnd[block->_pre_order] = &regnd;

    // Initialize value & regnd for this block

    if (missing_some_inputs) {

      // Some predecessor has not yet been visited; zap map to empty

      for (uint k = 0; k < (uint)_max_reg; k++) {

        value.map(k,NULL);

        regnd.map(k,NULL);

      }

    } else {

      if( !freed ) {            // Didn't get a freebie prior block

        // Must clone some data

        freed = _cfg.get_block_for_node(block->pred(1));

        Node_List &f_value = *blk2value[freed->_pre_order];

        Node_List &f_regnd = *blk2regnd[freed->_pre_order];

        for( uint k = 0; k < (uint)_max_reg; k++ ) {

          value.map(k,f_value[k]);

          regnd.map(k,f_regnd[k]);

        }

      }

      // Merge all inputs together, setting to NULL any conflicts.

      for (j = 1; j < block->num_preds(); j++) {

        Block* pb = _cfg.get_block_for_node(block->pred(j));

        if (pb == freed) {

          continue; // Did self already via freelist

        }

        Node_List &p_regnd = *blk2regnd[pb->_pre_order];

        for( uint k = 0; k < (uint)_max_reg; k++ ) {

          if( regnd[k] != p_regnd[k] ) { // Conflict on reaching defs?

            value.map(k,NULL); // Then no value handy

            regnd.map(k,NULL);

          }

        }