8065618: C2 RA incorrectly removes kill projections
Summary: Don't remove KILL projections if their "defining" nodes have SCMemProj projection (memory side effects).
Reviewed-by: iveresov
--- a/hotspot/src/share/vm/opto/ifg.cpp Fri Nov 21 17:28:29 2014 +0300
+++ b/hotspot/src/share/vm/opto/ifg.cpp Fri Nov 21 17:17:41 2014 -0800
@@ -527,6 +527,22 @@
Node* def = n->in(0);
if (!n->is_Proj() ||
(_lrg_map.live_range_id(def) && !liveout->member(_lrg_map.live_range_id(def)))) {
+ if (n->is_MachProj()) {
+ // Don't remove KILL projections if their "defining" nodes have
+ // memory effects (have SCMemProj projection node) -
+ // they are not dead even when their result is not used.
+ // For example, compareAndSwapL (and other CAS) and EncodeISOArray nodes.
+ // The method add_input_to_liveout() keeps such nodes alive (put them on liveout list)
+ // when it sees SCMemProj node in a block. Unfortunately SCMemProj node could be placed
+ // in block in such order that KILL MachProj nodes are processed first.
+ uint cnt = def->outcnt();
+ for (uint i = 0; i < cnt; i++) {
+ Node* proj = def->raw_out(i);
+ if (proj->Opcode() == Op_SCMemProj) {
+ return false;
+ }
+ }
+ }
b->remove_node(location);
LRG& lrg = lrgs(lid);
if (lrg._def == n) {