[csa] micro-optimization of Allocation

src/code-stub-assembler.cc

 // Copyright 2016 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/code-stub-assembler.h"
 #include "src/code-factory.h"
 #include "src/frames-inl.h"
 #include "src/frames.h"
 
 namespace v8 {
 namespace internal {
@@ skipping 878 matching lines @@
   return address.value();
 }
 
 Node* CodeStubAssembler::Allocate(Node* size_in_bytes, AllocationFlags flags) {
   Comment("Allocate");
   bool const new_space = !(flags & kPretenured);
   Node* top_address = ExternalConstant(
       new_space
           ? ExternalReference::new_space_allocation_top_address(isolate())
           : ExternalReference::old_space_allocation_top_address(isolate()));
-  Node* limit_address = ExternalConstant(
-      new_space
-          ? ExternalReference::new_space_allocation_limit_address(isolate())
-          : ExternalReference::old_space_allocation_limit_address(isolate()));
+  DCHECK_EQ(kPointerSize,
+            ExternalReference::new_space_allocation_limit_address(isolate())
+                    .address() -
+                ExternalReference::new_space_allocation_top_address(isolate())
+                    .address());
+  DCHECK_EQ(kPointerSize,
+            ExternalReference::old_space_allocation_limit_address(isolate())
+                    .address() -
+                ExternalReference::old_space_allocation_top_address(isolate())
+                    .address());
+  Node* limit_address = IntPtrAdd(top_address, IntPtrConstant(kPointerSize));
 
 #ifdef V8_HOST_ARCH_32_BIT
   if (flags & kDoubleAlignment) {
     return AllocateRawAligned(size_in_bytes, flags, top_address, limit_address);
   }
 #endif
 
   return AllocateRawUnaligned(size_in_bytes, flags, top_address, limit_address);
 }
 
@@ skipping 7455 matching lines @@
                        Heap::kUndefinedValueRootIndex);
   StoreObjectFieldRoot(result, PromiseReactionJobInfo::kDebugNameOffset,
                        Heap::kUndefinedValueRootIndex);
   StoreObjectFieldNoWriteBarrier(result, PromiseReactionJobInfo::kContextOffset,
                                  context);
   return result;
 }
 
 }  // namespace internal
 }  // namespace v8