[csa] micro-optimization of Allocation

src/code-stub-assembler.cc

Index: src/code-stub-assembler.cc
diff --git a/src/code-stub-assembler.cc b/src/code-stub-assembler.cc
index c9dc943fa603e98d1d504f2fe960edcd1da77280..6876b2ebf62ba8341fe9e1656d197e871db102d2 100644
--- a/src/code-stub-assembler.cc
+++ b/src/code-stub-assembler.cc
@@ -896,10 +896,17 @@ Node* CodeStubAssembler::Allocate(Node* size_in_bytes, AllocationFlags flags) {
       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) {