[crankshaft] Fragmentation-free allocation folding.

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

Index: src/crankshaft/arm/lithium-codegen-arm.cc
diff --git a/src/crankshaft/arm/lithium-codegen-arm.cc b/src/crankshaft/arm/lithium-codegen-arm.cc
index 69da090137012266638ad7cd715e63050d2d8e21..f17fc0c7ba5edec526d5f626e32344b57ee4eaa9 100644
--- a/src/crankshaft/arm/lithium-codegen-arm.cc
+++ b/src/crankshaft/arm/lithium-codegen-arm.cc
@@ -5109,6 +5109,14 @@ 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()->IsAllocationFolded()) {
+    flags = static_cast<AllocationFlags>(flags | ALLOCATION_FOLDED);
+  }
+
   if (instr->size()->IsConstantOperand()) {
     int32_t size = ToInteger32(LConstantOperand::cast(instr->size()));
     CHECK(size <= Page::kMaxRegularHeapObjectSize);
@@ -5176,6 +5184,50 @@ void LCodeGen::DoDeferredAllocate(LAllocate* instr) {
   CallRuntimeFromDeferred(
       Runtime::kAllocateInTargetSpace, 2, instr, instr->context());
   __ StoreToSafepointRegisterSlot(r0, result);
+
+  if (instr->hydrogen()->IsAllocationFoldingDominator()) {
+    AllocationFlags allocation_flags = NO_ALLOCATION_FLAGS;
+    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.
+    ExternalReference allocation_top =
+        AllocationUtils::GetAllocationTopReference(isolate(), allocation_flags);
+    Register top_address = scratch0();
+    __ sub(r0, r0, Operand(kHeapObjectTag));
+    __ mov(top_address, Operand(allocation_top));
+    __ str(r0, MemOperand(top_address));
+    __ add(r0, r0, Operand(kHeapObjectTag));
+  }
+}
+
+void LCodeGen::DoFastAllocate(LFastAllocate* instr) {
+  DCHECK(instr->hydrogen()->IsAllocationFolded());
+  Register result = ToRegister(instr->result());
+  Register scratch1 = ToRegister(instr->temp1());
+  Register scratch2 = ToRegister(instr->temp2());
+
+  AllocationFlags flags = NO_ALLOCATION_FLAGS;
+  if (instr->hydrogen()->MustAllocateDoubleAligned()) {
+    flags = static_cast<AllocationFlags>(flags | DOUBLE_ALIGNMENT);
+  }
+  if (instr->hydrogen()->IsOldSpaceAllocation()) {
+    DCHECK(!instr->hydrogen()->IsNewSpaceAllocation());
+    flags = static_cast<AllocationFlags>(flags | PRETENURE);
+  }
+  if (!instr->hydrogen()->IsAllocationFoldingDominator()) {
+    if (instr->size()->IsConstantOperand()) {
+      int32_t size = ToInteger32(LConstantOperand::cast(instr->size()));
+      CHECK(size <= Page::kMaxRegularHeapObjectSize);
+      __ FastAllocate(size, result, scratch1, scratch2, flags);
+    } else {
+      Register size = ToRegister(instr->size());
+      __ FastAllocate(size, result, scratch1, scratch2, flags);
+    }
+  }
 }