Refactor and improve inlined double-aligned allocations

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 8513a68fa915fa98ad69f5b544941287e4446c38..e97e07e73a1134c2bcf43864b3fff1ff0f1a4810 100644
--- a/src/x64/macro-assembler-x64.cc
+++ b/src/x64/macro-assembler-x64.cc
@@ -3758,6 +3758,7 @@ void MacroAssembler::AllocateInNewSpace(int object_size,
                                         Register scratch,
                                         Label* gc_required,
                                         AllocationFlags flags) {
+  ASSERT((flags & (RESULT_CONTAINS_TOP | SIZE_IN_WORDS)) == 0);
   if (!FLAG_inline_new) {
     if (emit_debug_code()) {
       // Trash the registers to simulate an allocation failure.
@@ -3777,6 +3778,13 @@ void MacroAssembler::AllocateInNewSpace(int object_size,
   // Load address of new object into result.
   LoadAllocationTopHelper(result, scratch, flags);
 
+  // Align the next allocation. Storing the filler map without checking top is
+  // always safe because the limit of the heap is always aligned.
+  if (((flags & DOUBLE_ALIGNMENT) != 0) && FLAG_debug_code) {
+    testq(result, Immediate(kDoubleAlignmentMask));
+    Check(zero, "Allocation is not double aligned");
+  }
+
   // Calculate new top and bail out if new space is exhausted.
   ExternalReference new_space_allocation_limit =
       ExternalReference::new_space_allocation_limit_address(isolate());
@@ -3795,15 +3803,17 @@ void MacroAssembler::AllocateInNewSpace(int object_size,
   // Update allocation top.
   UpdateAllocationTopHelper(top_reg, scratch);
 
+  bool tag_result = (flags & TAG_OBJECT) != 0;
   if (top_reg.is(result)) {
-    if ((flags & TAG_OBJECT) != 0) {
+    if (tag_result) {
       subq(result, Immediate(object_size - kHeapObjectTag));
     } else {
       subq(result, Immediate(object_size));
     }
-  } else if ((flags & TAG_OBJECT) != 0) {
+  } else if (tag_result) {
     // Tag the result if requested.
-    addq(result, Immediate(kHeapObjectTag));
+    ASSERT(kHeapObjectTag == 1);
+    incq(result);
   }
 }
 
@@ -3816,6 +3826,7 @@ void MacroAssembler::AllocateInNewSpace(int header_size,
                                         Register scratch,
                                         Label* gc_required,
                                         AllocationFlags flags) {
+  ASSERT((flags & SIZE_IN_WORDS) == 0);
   if (!FLAG_inline_new) {
     if (emit_debug_code()) {
       // Trash the registers to simulate an allocation failure.
@@ -3834,6 +3845,13 @@ void MacroAssembler::AllocateInNewSpace(int header_size,
   // Load address of new object into result.
   LoadAllocationTopHelper(result, scratch, flags);
 
+  // Align the next allocation. Storing the filler map without checking top is
+  // always safe because the limit of the heap is always aligned.
+  if (((flags & DOUBLE_ALIGNMENT) != 0) && FLAG_debug_code) {
+    testq(result, Immediate(kDoubleAlignmentMask));
+    Check(zero, "Allocation is not double aligned");
+  }
+
   // Calculate new top and bail out if new space is exhausted.
   ExternalReference new_space_allocation_limit =
       ExternalReference::new_space_allocation_limit_address(isolate());
@@ -3852,7 +3870,8 @@ void MacroAssembler::AllocateInNewSpace(int header_size,
 
   // Tag the result if requested.
   if ((flags & TAG_OBJECT) != 0) {
-    addq(result, Immediate(kHeapObjectTag));
+    ASSERT(kHeapObjectTag == 1);
+    incq(result);
   }
 }
 
@@ -3863,6 +3882,8 @@ void MacroAssembler::AllocateInNewSpace(Register object_size,
                                         Register scratch,
                                         Label* gc_required,
                                         AllocationFlags flags) {
+  ASSERT((flags & (DOUBLE_ALIGNMENT | RESULT_CONTAINS_TOP |
+                   SIZE_IN_WORDS)) == 0);
   if (!FLAG_inline_new) {
     if (emit_debug_code()) {
       // Trash the registers to simulate an allocation failure.