Added tracing information to the case when allocation folding cannot be performed.

src/hydrogen-instructions.cc

Index: src/hydrogen-instructions.cc
diff --git a/src/hydrogen-instructions.cc b/src/hydrogen-instructions.cc
index 4475fc0c74eafe73dfbc981df4bf8b2fdbc7343b..674e33bd2d6d2a11a4826a71ed1bd0b02031bb56 100644
--- a/src/hydrogen-instructions.cc
+++ b/src/hydrogen-instructions.cc
@@ -3181,21 +3181,26 @@ HType HAllocate::CalculateInferredType() {
 void HAllocate::HandleSideEffectDominator(GVNFlag side_effect,
                                           HValue* dominator) {
   ASSERT(side_effect == kChangesNewSpacePromotion);
-  // Try to fold allocations together with their dominating allocations.
-  if (!FLAG_use_allocation_folding || !dominator->IsAllocate()) {
+  if (!FLAG_use_allocation_folding) {
     return;

[Michael Starzinger, 2013/07/16 08:44:36]

nit: This early return should fit into one line.

[Hannes Payer (out of office), 2013/07/16 08:51:52]

Done.

   }
   HAllocate* dominator_allocate_instr = HAllocate::cast(dominator);

[Michael Starzinger, 2013/07/16 08:44:36]

This cast will fail if "dominator" is not an HAllocate.

[Hannes Payer (out of office), 2013/07/16 08:51:52]

Yes, then I guess I have to duplicate the tracing output.

   HValue* dominator_size = dominator_allocate_instr->size();
   HValue* current_size = size();
+  // Try to fold allocations together with their dominating allocations.
   // We can just fold allocations that are guaranteed in new space.
   // TODO(hpayer): Support double aligned allocations.
   // TODO(hpayer): Add support for non-constant allocation in dominator.
   if (!GuaranteedInNewSpace() || MustAllocateDoubleAligned() ||
       !current_size->IsInteger32Constant() ||
+      !dominator->IsAllocate() ||
       !dominator_allocate_instr->GuaranteedInNewSpace() ||
       dominator_allocate_instr->MustAllocateDoubleAligned() ||
       !dominator_size->IsInteger32Constant()) {
+    if (FLAG_trace_allocation_folding) {
+      PrintF("#%d (%s) cannot fold into #%d (%s)\n",
+          id(), Mnemonic(), dominator->id(), dominator->Mnemonic());
+    }
     return;
   }