Generalize HeapObject alignment requirements.

Removes EnsureDouble* methods.
Adds a RequiredAlignment method.
Changes call sites.

LOG=N
BUG=v8:4124

Review URL: https://codereview.chromium.org/1150953002

Cr-Commit-Position: refs/heads/master@{#28541}

src/heap/mark-compact.cc

@@ -1941,9 +1941,7 @@ int MarkCompactCollector::DiscoverAndEvacuateBlackObjectsOnPage(
         continue;
       }
 
-      AllocationAlignment alignment = object->NeedsToEnsureDoubleAlignment()
-                                          ? kDoubleAligned
-                                          : kWordAligned;
+      AllocationAlignment alignment = object->RequiredAlignment();
       AllocationResult allocation = new_space->AllocateRaw(size, alignment);
       if (allocation.IsRetry()) {
         if (!new_space->AddFreshPage()) {
@@ -3105,8 +3103,7 @@ bool MarkCompactCollector::TryPromoteObject(HeapObject* object,
   OldSpace* old_space = heap()->old_space();
 
   HeapObject* target;
-  AllocationAlignment alignment =
-      object->NeedsToEnsureDoubleAlignment() ? kDoubleAligned : kWordAligned;
+  AllocationAlignment alignment = object->RequiredAlignment();
   AllocationResult allocation = old_space->AllocateRaw(object_size, alignment);
   if (allocation.To(&target)) {
     MigrateObject(target, object, object_size, old_space->identity());
@@ -3330,10 +3327,7 @@ void MarkCompactCollector::EvacuateLiveObjectsFromPage(Page* p) {
       DCHECK(Marking::IsBlack(Marking::MarkBitFrom(object)));
 
       int size = object->Size();
-
-      AllocationAlignment alignment = object->NeedsToEnsureDoubleAlignment()
-                                          ? kDoubleAligned
-                                          : kWordAligned;
+      AllocationAlignment alignment = object->RequiredAlignment();
       HeapObject* target_object;
       AllocationResult allocation = space->AllocateRaw(size, alignment);
       if (!allocation.To(&target_object)) {

src/objects-debug.cc

@@ -47,10 +47,6 @@ void HeapObject::HeapObjectVerify() {
     return;
   }
 
-  // TODO(yangguo): Use this check once crbug/436911 has been fixed.
-  //  DCHECK(!NeedsToEnsureDoubleAlignment() ||
-  //         IsAligned(OffsetFrom(address()), kDoubleAlignment));
-
   switch (instance_type) {
     case SYMBOL_TYPE:
       Symbol::cast(this)->SymbolVerify();

src/objects-inl.h

@@ -2832,23 +2832,16 @@ WriteBarrierMode HeapObject::GetWriteBarrierMode(
 }
 
 
-bool HeapObject::NeedsToEnsureDoubleAlignment() {
+AllocationAlignment HeapObject::RequiredAlignment() {
 #ifdef V8_HOST_ARCH_32_BIT
-  return (IsFixedFloat64Array() || IsFixedDoubleArray() ||
-          IsConstantPoolArray()) &&
-         FixedArrayBase::cast(this)->length() != 0;
-#else
-  return false;
-#endif  // V8_HOST_ARCH_32_BIT
-}
-
-
-bool HeapObject::NeedsToEnsureDoubleUnalignment() {
-#ifdef V8_HOST_ARCH_32_BIT
-  return IsHeapNumber();
-#else
-  return false;
+  if ((IsFixedFloat64Array() || IsFixedDoubleArray() ||
+       IsConstantPoolArray()) &&
+      FixedArrayBase::cast(this)->length() != 0) {
+    return kDoubleAligned;
+  }
+  if (IsHeapNumber()) return kDoubleUnaligned;
 #endif  // V8_HOST_ARCH_32_BIT
+  return kWordAligned;
 }
 
 

src/objects.h

@@ -1487,8 +1487,7 @@ class HeapObject: public Object {
   static void VerifyHeapPointer(Object* p);
 #endif
 
-  inline bool NeedsToEnsureDoubleAlignment();
-  inline bool NeedsToEnsureDoubleUnalignment();
+  inline AllocationAlignment RequiredAlignment();
 
   // Layout description.
   // First field in a heap object is map.

src/snapshot/serialize.cc

@@ -1729,7 +1729,8 @@ void Serializer::ObjectSerializer::SerializePrologue(AllocationSpace space,
     back_reference = serializer_->AllocateLargeObject(size);
   } else {
     bool needs_double_align = false;
-    if (object_->NeedsToEnsureDoubleAlignment()) {
+    // TODO(bbudge): Generalize to other alignment constraints.
+    if (object_->RequiredAlignment() == kDoubleAligned) {
       // Add wriggle room for double alignment padding.
       back_reference = serializer_->Allocate(space, size + kPointerSize);
       needs_double_align = true;