[crankshaft] Fragmentation-free allocation folding.

src/crankshaft/x64/lithium-codegen-x64.cc

Index: src/crankshaft/x64/lithium-codegen-x64.cc
diff --git a/src/crankshaft/x64/lithium-codegen-x64.cc b/src/crankshaft/x64/lithium-codegen-x64.cc
index 5ff00315547e661b147deddc7d1b7b6a646a2651..9dfd05ffbfc821d48090dce44fea91721511490f 100644
--- a/src/crankshaft/x64/lithium-codegen-x64.cc
+++ b/src/crankshaft/x64/lithium-codegen-x64.cc
@@ -5170,6 +5170,14 @@ void LCodeGen::DoAllocate(LAllocate* instr) {
     flags = static_cast<AllocationFlags>(flags | PRETENURE);
   }
 
+  if (instr->hydrogen()->IsAllocationFoldingDominator()) {
+    flags = static_cast<AllocationFlags>(flags | ALLOCATION_FOLDING_DOMINATOR);
+  }
+
+  if (instr->hydrogen()->IsAllocationFoldingDominated()) {
+    flags = static_cast<AllocationFlags>(flags | ALLOCATION_FOLDING_DOMINATED);
+  }
+
   if (instr->size()->IsConstantOperand()) {
     int32_t size = ToInteger32(LConstantOperand::cast(instr->size()));
     CHECK(size <= Page::kMaxRegularHeapObjectSize);
@@ -5231,6 +5239,18 @@ void LCodeGen::DoDeferredAllocate(LAllocate* instr) {
   CallRuntimeFromDeferred(
       Runtime::kAllocateInTargetSpace, 2, instr, instr->context());
   __ StoreToSafepointRegisterSlot(result, rax);
+
+  if (instr->hydrogen()->IsAllocationFoldingDominator()) {
+    AllocationFlags allocation_flags = TAG_OBJECT;
+    if (instr->hydrogen()->IsOldSpaceAllocation()) {
+      DCHECK(!instr->hydrogen()->IsNewSpaceAllocation());
+      allocation_flags = static_cast<AllocationFlags>(flags | PRETENURE);
+    }
+    // If the allocation folding dominator allocate triggered a GC, allocation
+    // happend in the runtime. We have to reset the top pointer to virtually
+    // undo the allocation.
+    __ SetTop(rax, allocation_flags);
+  }
 }