Clean up aligned allocation code in preparation for SIMD alignments.

src/heap/spaces-inl.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_HEAP_SPACES_INL_H_
 #define V8_HEAP_SPACES_INL_H_
 
 #include "src/heap/spaces.h"
 #include "src/heap-profiler.h"
 #include "src/isolate.h"
@@ skipping 232 matching lines @@
 HeapObject* PagedSpace::AllocateLinearly(int size_in_bytes) {
   Address current_top = allocation_info_.top();
   Address new_top = current_top + size_in_bytes;
   if (new_top > allocation_info_.limit()) return NULL;
 
   allocation_info_.set_top(new_top);
   return HeapObject::FromAddress(current_top);
 }
 
 
-HeapObject* PagedSpace::AllocateLinearlyAligned(int size_in_bytes,
+HeapObject* PagedSpace::AllocateLinearlyAligned(int* size_in_bytes,
                                                 AllocationAlignment alignment) {
   Address current_top = allocation_info_.top();
-  int alignment_size = 0;
+  int alignment_size = Heap::GetAlignmentSize(current_top, alignment);
 
-  if (alignment == kDoubleAligned &&
-      (OffsetFrom(current_top) & kDoubleAlignmentMask) != 0) {
-    alignment_size = kPointerSize;
-    size_in_bytes += alignment_size;
-  } else if (alignment == kDoubleUnaligned &&
-             (OffsetFrom(current_top) & kDoubleAlignmentMask) == 0) {
-    alignment_size = kPointerSize;
-    size_in_bytes += alignment_size;
-  }
-  Address new_top = current_top + size_in_bytes;
+  Address new_top = current_top + alignment_size + *size_in_bytes;
   if (new_top > allocation_info_.limit()) return NULL;
 
   allocation_info_.set_top(new_top);
   if (alignment_size > 0) {
-    return heap()->EnsureAligned(HeapObject::FromAddress(current_top),
-                                 size_in_bytes, alignment);
+    *size_in_bytes += alignment_size;
+    return heap()->PrecedeWithFiller(HeapObject::FromAddress(current_top),
+                                     alignment_size);
   }
+
   return HeapObject::FromAddress(current_top);
 }
 
 
 // Raw allocation.
 AllocationResult PagedSpace::AllocateRawUnaligned(int size_in_bytes) {
   HeapObject* object = AllocateLinearly(size_in_bytes);
 
   if (object == NULL) {
     object = free_list_.Allocate(size_in_bytes);
@@ skipping 11 matching lines @@
   }
 
   return AllocationResult::Retry(identity());
 }
 
 
 // Raw allocation.
 AllocationResult PagedSpace::AllocateRawAligned(int size_in_bytes,
                                                 AllocationAlignment alignment) {
   DCHECK(identity() == OLD_SPACE);
-  HeapObject* object = AllocateLinearlyAligned(size_in_bytes, alignment);
-  int aligned_size_in_bytes = size_in_bytes + kPointerSize;
+  int aligned_size_in_bytes = size_in_bytes;
+  HeapObject* object =
+      AllocateLinearlyAligned(&aligned_size_in_bytes, alignment);
 
   if (object == NULL) {
     object = free_list_.Allocate(aligned_size_in_bytes);

[Hannes Payer (out of office), 2015/05/21 10:38:17]

I don't see how alignment works for free-list allocation. You always have to
over-allocate there because you cannot check upfront. And if the free-list
returns already an aligned pointer, you have to place the filler after the
object (to make the over-allocated memory iterable).

[bbudge, 2015/05/21 10:55:45]

Thanks for pointing this out. I'll have to modify the filling to handle this
case. I would still like to avoid over-allocating when we know the alignment
constraints ahead of time.

     if (object == NULL) {
       object = SlowAllocateRaw(aligned_size_in_bytes);
     }
     if (object != NULL) {
-      object = heap()->EnsureAligned(object, aligned_size_in_bytes, alignment);
+      object = heap()->PrecedeWithFiller(object,
+                                         aligned_size_in_bytes - size_in_bytes);
     }
   }
 
   if (object != NULL) {
     MSAN_ALLOCATED_UNINITIALIZED_MEMORY(object->address(), size_in_bytes);
     return object;
   }
 
   return AllocationResult::Retry(identity());
 }
@@ skipping 11 matching lines @@
 }
 
 
 // -----------------------------------------------------------------------------
 // NewSpace
 
 
 AllocationResult NewSpace::AllocateRawAligned(int size_in_bytes,
                                               AllocationAlignment alignment) {
   Address old_top = allocation_info_.top();
-  int alignment_size = 0;
-  int aligned_size_in_bytes = 0;
-
-  // If double alignment is required and top pointer is not aligned, we allocate
-  // additional memory to take care of the alignment.
-  if (alignment == kDoubleAligned &&
-      (OffsetFrom(old_top) & kDoubleAlignmentMask) != 0) {
-    alignment_size += kPointerSize;
-  } else if (alignment == kDoubleUnaligned &&
-             (OffsetFrom(old_top) & kDoubleAlignmentMask) == 0) {
-    alignment_size += kPointerSize;
-  }
-  aligned_size_in_bytes = size_in_bytes + alignment_size;
+  int alignment_size = Heap::GetAlignmentSize(old_top, alignment);
+  int aligned_size_in_bytes = size_in_bytes + alignment_size;
 
   if (allocation_info_.limit() - old_top < aligned_size_in_bytes) {
     return SlowAllocateRaw(size_in_bytes, alignment);
   }
 
   HeapObject* obj = HeapObject::FromAddress(old_top);
   allocation_info_.set_top(allocation_info_.top() + aligned_size_in_bytes);
   DCHECK_SEMISPACE_ALLOCATION_INFO(allocation_info_, to_space_);
 
   if (alignment_size > 0) {
-    obj = heap()->PrecedeWithFiller(obj);
+    obj = heap()->PrecedeWithFiller(obj, alignment_size);
   }
 
   // The slow path above ultimately goes through AllocateRaw, so this suffices.
   MSAN_ALLOCATED_UNINITIALIZED_MEMORY(obj->address(), size_in_bytes);
 
-  DCHECK((kDoubleAligned && (OffsetFrom(obj) & kDoubleAlignmentMask) == 0) ||
-         (kDoubleUnaligned && (OffsetFrom(obj) & kDoubleAlignmentMask) != 0));

[bbudge, 2015/05/20 15:39:38]

I eliminated this since it can never assert.

-
   return obj;
 }
 
 
 AllocationResult NewSpace::AllocateRawUnaligned(int size_in_bytes) {
   Address old_top = allocation_info_.top();
 
   if (allocation_info_.limit() - old_top < size_in_bytes) {
     return SlowAllocateRaw(size_in_bytes, kWordAligned);
   }
@@ skipping 28 matching lines @@
 
 
 intptr_t LargeObjectSpace::Available() {
   return ObjectSizeFor(heap()->isolate()->memory_allocator()->Available());
 }
 
 }
 }  // namespace v8::internal
 
 #endif  // V8_HEAP_SPACES_INL_H_