Ensure Zone returns correctly aligned pointers for allocations with

src/zone/zone.cc

 // Copyright 2012 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.
 
 #include "src/zone/zone.h"
 
 #include <cstring>
 
 #include "src/v8.h"
 
@@ skipping 73 matching lines @@
   } else {
     position_ += size_with_redzone;
   }
 
   Address redzone_position = result + size;
   DCHECK(redzone_position + kASanRedzoneBytes == position_);
   ASAN_POISON_MEMORY_REGION(redzone_position, kASanRedzoneBytes);
 
   // Check that the result has the proper alignment and return it.
   DCHECK(IsAddressAligned(result, kAlignment, 0));
+  if (kPointerSize == 4 && kAlignment == 4) {
+    DCHECK((size & 4) || IsAddressAligned(result, 8, 0));
+  }
   allocation_size_ += size;
   return reinterpret_cast<void*>(result);
 }
 
 void Zone::DeleteAll() {
   // Traverse the chained list of segments and return them all to the allocator.
   for (Segment* current = segment_head_; current;) {
     Segment* next = current->next();
     size_t size = current->size();
 
@@ skipping 62 matching lines @@
     return nullptr;
   }
   Segment* segment = NewSegment(new_size);
   if (segment == nullptr) {
     V8::FatalProcessOutOfMemory("Zone");
     return nullptr;
   }
 
   // Recompute 'top' and 'limit' based on the new segment.
   Address result = RoundUp(segment->start(), kAlignment);
+  if (kPointerSize == 4 && kAlignment == 4) {
+    result += ((~size) & 4) & (reinterpret_cast<intptr_t>(result) & 4);
+  }
   position_ = result + size;
   // Check for address overflow.
   // (Should not happen since the segment is guaranteed to accomodate
   // size bytes + header and alignment padding)
   DCHECK(reinterpret_cast<uintptr_t>(position_) >=
          reinterpret_cast<uintptr_t>(result));
   limit_ = segment->end();
   DCHECK(position_ <= limit_);
   return result;
 }
 
 }  // namespace internal
 }  // namespace v8