Allocation folding integrated into the GVN phase.

src/hydrogen-gvn.cc

Index: src/hydrogen-gvn.cc
diff --git a/src/hydrogen-gvn.cc b/src/hydrogen-gvn.cc
index fd7430ccec2da774b8e97a5968840e94fcacf905..c07f286210876541bacc0cc3f440c35f367e241a 100644
--- a/src/hydrogen-gvn.cc
+++ b/src/hydrogen-gvn.cc
@@ -776,11 +776,27 @@ void HGlobalValueNumberingPhase::AnalyzeGraph() {
     }
 
     // Go through all instructions of the current block.
-    HInstruction* instr = block->first();
-    while (instr != NULL) {
-      HInstruction* next = instr->next();
+    for (HInstructionIterator it(block); !it.Done(); it.Advance()) {

[Michael Starzinger, 2013/07/08 12:44:06]

Switching to the HInstructionIterator will break for cases where the instruction
is unlinked from the graph. See the following comment about that.

[Hannes Payer (out of office), 2013/07/08 13:43:48]

Done.

+      HInstruction* instr = it.Current();
+      if (instr->CheckFlag(HValue::kTrackSideEffectDominators)) {
+        for (int i = 0; i < kNumberOfTrackedSideEffects; i++) {
+          HValue* other = dominators->at(i);
+          GVNFlag changes_flag = HValue::ChangesFlagFromInt(i);
+          GVNFlag depends_on_flag = HValue::DependsOnFlagFromInt(i);
+          if (instr->DependsOnFlags().Contains(depends_on_flag) &&
+              (other != NULL)) {
+            TRACE_GVN_5("Side-effect #%d in %d (%s) is dominated by %d (%s)\n",
+                        i,
+                        instr->id(),
+                        instr->Mnemonic(),
+                        other->id(),
+                        other->Mnemonic());
+            instr->HandleSideEffectDominator(changes_flag, other);
+          }
+        }
+      }
       GVNFlagSet flags = instr->ChangesFlags();
-      if (!flags.IsEmpty()) {
+      if (instr->IsLinked() && !flags.IsEmpty()) {

[Michael Starzinger, 2013/07/08 12:44:06]

Instead of doing the IsLinked() checks here, could we just to a "continue" after
the side-effect dominator notification? Of course that require us to make
HInstructionIterator resilient against concurrent modification (i.e. remember
the "next_" field in the iterator).

[Hannes Payer (out of office), 2013/07/08 13:43:48]

Done.

         // Clear all instructions in the map that are affected by side effects.
         // Store instruction as the dominating one for tracked side effects.
         map->Kill(flags);
@@ -788,7 +804,7 @@ void HGlobalValueNumberingPhase::AnalyzeGraph() {
         TRACE_GVN_2("Instruction %d %s\n", instr->id(),
                     *GetGVNFlagsString(flags));
       }
-      if (instr->CheckFlag(HValue::kUseGVN)) {
+      if (instr->IsLinked() && instr->CheckFlag(HValue::kUseGVN)) {

[Michael Starzinger, 2013/07/08 12:44:06]

Likewise.

[Hannes Payer (out of office), 2013/07/08 13:43:48]

Done.

         ASSERT(!instr->HasObservableSideEffects());
         HValue* other = map->Lookup(instr);
         if (other != NULL) {
@@ -804,25 +820,6 @@ void HGlobalValueNumberingPhase::AnalyzeGraph() {
           map->Add(instr, zone());
         }
       }
-      if (instr->IsLinked() &&
-          instr->CheckFlag(HValue::kTrackSideEffectDominators)) {
-        for (int i = 0; i < kNumberOfTrackedSideEffects; i++) {
-          HValue* other = dominators->at(i);
-          GVNFlag changes_flag = HValue::ChangesFlagFromInt(i);
-          GVNFlag depends_on_flag = HValue::DependsOnFlagFromInt(i);
-          if (instr->DependsOnFlags().Contains(depends_on_flag) &&
-              (other != NULL)) {
-            TRACE_GVN_5("Side-effect #%d in %d (%s) is dominated by %d (%s)\n",
-                        i,
-                        instr->id(),
-                        instr->Mnemonic(),
-                        other->id(),
-                        other->Mnemonic());
-            instr->SetSideEffectDominator(changes_flag, other);
-          }
-        }
-      }
-      instr = next;
     }
 
     HBasicBlock* dominator_block;