[crankshaft] Fragmentation-free allocation folding.

src/x64/macro-assembler-x64.cc

Index: src/x64/macro-assembler-x64.cc
diff --git a/src/x64/macro-assembler-x64.cc b/src/x64/macro-assembler-x64.cc
index f753b0e1d53319136243b44d2cd5a25ec5db5890..2efb5295974c8e061a579a1eb63f1a3ba0f4f8f5 100644
--- a/src/x64/macro-assembler-x64.cc
+++ b/src/x64/macro-assembler-x64.cc
@@ -4830,7 +4830,7 @@ void MacroAssembler::MakeSureDoubleAlignedHelper(Register result,
     Label aligned;
     testl(result, Immediate(kDoubleAlignmentMask));
     j(zero, &aligned, Label::kNear);
-    if ((flags & PRETENURE) != 0) {
+    if (((flags & ALLOCATION_FOLDED) == 0) && ((flags & PRETENURE) != 0)) {
       ExternalReference allocation_limit =
           AllocationUtils::GetAllocationLimitReference(isolate(), flags);
       cmpp(result, ExternalOperand(allocation_limit));
@@ -4873,6 +4873,7 @@ void MacroAssembler::Allocate(int object_size,
                               AllocationFlags flags) {
   DCHECK((flags & (RESULT_CONTAINS_TOP | SIZE_IN_WORDS)) == 0);
   DCHECK(object_size <= Page::kMaxRegularHeapObjectSize);
+  DCHECK((flags & ALLOCATION_FOLDED) == 0);
   if (!FLAG_inline_new) {
     if (emit_debug_code()) {
       // Trash the registers to simulate an allocation failure.
@@ -4910,8 +4911,10 @@ void MacroAssembler::Allocate(int object_size,
   cmpp(top_reg, limit_operand);
   j(above, gc_required);
 
-  // Update allocation top.
-  UpdateAllocationTopHelper(top_reg, scratch, flags);
+  if ((flags & ALLOCATION_FOLDING_DOMINATOR) == 0) {
+    // The top pointer is not updated for allocation folding dominators.
+    UpdateAllocationTopHelper(top_reg, scratch, flags);
+  }
 
   if (top_reg.is(result)) {
     subp(result, Immediate(object_size - kHeapObjectTag));
@@ -4932,6 +4935,8 @@ void MacroAssembler::Allocate(int header_size,
                               Label* gc_required,
                               AllocationFlags flags) {
   DCHECK((flags & SIZE_IN_WORDS) == 0);
+  DCHECK((flags & ALLOCATION_FOLDING_DOMINATOR) == 0);
+  DCHECK((flags & ALLOCATION_FOLDED) == 0);
   leap(result_end, Operand(element_count, element_size, header_size));
   Allocate(result_end, result, result_end, scratch, gc_required, flags);
 }
@@ -4944,6 +4949,7 @@ void MacroAssembler::Allocate(Register object_size,
                               Label* gc_required,
                               AllocationFlags flags) {
   DCHECK((flags & SIZE_IN_WORDS) == 0);
+  DCHECK((flags & ALLOCATION_FOLDED) == 0);
   if (!FLAG_inline_new) {
     if (emit_debug_code()) {
       // Trash the registers to simulate an allocation failure.
@@ -4966,25 +4972,58 @@ void MacroAssembler::Allocate(Register object_size,
     MakeSureDoubleAlignedHelper(result, scratch, gc_required, flags);
   }
 
-  // Calculate new top and bail out if new space is exhausted.
   ExternalReference allocation_limit =
       AllocationUtils::GetAllocationLimitReference(isolate(), flags);
   if (!object_size.is(result_end)) {
     movp(result_end, object_size);
   }
   addp(result_end, result);
-  j(carry, gc_required);
   Operand limit_operand = ExternalOperand(allocation_limit);
   cmpp(result_end, limit_operand);
   j(above, gc_required);
 
-  // Update allocation top.
-  UpdateAllocationTopHelper(result_end, scratch, flags);
+  if ((flags & ALLOCATION_FOLDING_DOMINATOR) == 0) {
+    // The top pointer is not updated for allocation folding dominators.
+    UpdateAllocationTopHelper(result_end, scratch, flags);
+  }
 
   // Tag the result.
   addp(result, Immediate(kHeapObjectTag));
 }
 
+void MacroAssembler::FastAllocate(int object_size, Register result,
+                                  Register result_end, AllocationFlags flags) {
+  DCHECK(!result.is(result_end));
+  // Load address of new object into result.
+  LoadAllocationTopHelper(result, no_reg, flags);
+
+  if ((flags & DOUBLE_ALIGNMENT) != 0) {
+    MakeSureDoubleAlignedHelper(result, no_reg, NULL, flags);
+  }
+
+  leap(result_end, Operand(result, object_size));
+
+  UpdateAllocationTopHelper(result_end, no_reg, flags);
+
+  addp(result, Immediate(kHeapObjectTag));
+}
+
+void MacroAssembler::FastAllocate(Register object_size, Register result,
+                                  Register result_end, AllocationFlags flags) {
+  DCHECK(!result.is(result_end));
+  // Load address of new object into result.
+  LoadAllocationTopHelper(result, no_reg, flags);
+
+  if ((flags & DOUBLE_ALIGNMENT) != 0) {
+    MakeSureDoubleAlignedHelper(result, no_reg, NULL, flags);
+  }
+
+  leap(result_end, Operand(result, object_size, times_1, 0));
+
+  UpdateAllocationTopHelper(result_end, no_reg, flags);
+
+  addp(result, Immediate(kHeapObjectTag));
+}
 
 void MacroAssembler::AllocateHeapNumber(Register result,
                                         Register scratch,