[crankshaft] Fragmentation-free allocation folding.

src/crankshaft/ia32/lithium-ia32.cc

Index: src/crankshaft/ia32/lithium-ia32.cc
diff --git a/src/crankshaft/ia32/lithium-ia32.cc b/src/crankshaft/ia32/lithium-ia32.cc
index 12f76194b9c4f741ee38006ccf2dd02131700c9f..4a99163ca94782447e22e10b404cc629ac9a701c 100644
--- a/src/crankshaft/ia32/lithium-ia32.cc
+++ b/src/crankshaft/ia32/lithium-ia32.cc
@@ -2406,14 +2406,19 @@ LInstruction* LChunkBuilder::DoStringCharFromCode(HStringCharFromCode* instr) {
 
 
 LInstruction* LChunkBuilder::DoAllocate(HAllocate* instr) {
-  info()->MarkAsDeferredCalling();
-  LOperand* context = UseAny(instr->context());
-  LOperand* size = instr->size()->IsConstant()
-      ? UseConstant(instr->size())
-      : UseTempRegister(instr->size());
-  LOperand* temp = TempRegister();
-  LAllocate* result = new(zone()) LAllocate(context, size, temp);
-  return AssignPointerMap(DefineAsRegister(result));
+  LOperand* size = instr->size()->IsConstant() ? UseConstant(instr->size())
+                                               : UseRegister(instr->size());
+  if (instr->IsAllocationFolded()) {
+    LOperand* temp = TempRegister();
+    LFastAllocate* result = new (zone()) LFastAllocate(size, temp);
+    return DefineAsRegister(result);

[Michael Lippautz, 2016/05/10 08:32:58]

Why don't we need to add the pointer to the pointer map? What if a deopt happens
right after allocating folded objects?

[Hannes Payer (out of office), 2016/05/10 09:04:44]

A folded allocation does not need a safepoint.

+  } else {
+    info()->MarkAsDeferredCalling();
+    LOperand* context = UseAny(instr->context());
+    LOperand* temp = TempRegister();
+    LAllocate* result = new (zone()) LAllocate(context, size, temp);
+    return AssignPointerMap(DefineAsRegister(result));
+  }
 }