ARM: optimize Lithium Allocate

R=ulan@chromium.org, bmeurer@chromium.org

BUG=

Review URL: https://codereview.chromium.org/331993004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21968 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/arm/lithium-arm.cc

@@ -2369,9 +2369,7 @@ LInstruction* LChunkBuilder::DoStringCharFromCode(HStringCharFromCode* instr) {
 LInstruction* LChunkBuilder::DoAllocate(HAllocate* instr) {
   info()->MarkAsDeferredCalling();
   LOperand* context = UseAny(instr->context());
-  LOperand* size = instr->size()->IsConstant()
-      ? UseConstant(instr->size())
-      : UseTempRegister(instr->size());
+  LOperand* size = UseRegisterOrConstant(instr->size());
   LOperand* temp1 = TempRegister();
   LOperand* temp2 = TempRegister();
   LAllocate* result = new(zone()) LAllocate(context, size, temp1, temp2);

src/arm/lithium-codegen-arm.cc

@@ -5276,33 +5276,25 @@ void LCodeGen::DoAllocate(LAllocate* instr) {
     }
   } else {
     Register size = ToRegister(instr->size());
-    __ Allocate(size,
-                result,
-                scratch,
-                scratch2,
-                deferred->entry(),
-                flags);
+    __ Allocate(size, result, scratch, scratch2, deferred->entry(), flags);
   }
 
   __ bind(deferred->exit());
 
   if (instr->hydrogen()->MustPrefillWithFiller()) {
+    STATIC_ASSERT(kHeapObjectTag == 1);
     if (instr->size()->IsConstantOperand()) {
       int32_t size = ToInteger32(LConstantOperand::cast(instr->size()));
-      __ mov(scratch, Operand(size));
+      __ mov(scratch, Operand(size - kHeapObjectTag));
     } else {
-      scratch = ToRegister(instr->size());
+      __ sub(scratch, ToRegister(instr->size()), Operand(kHeapObjectTag));
     }
-    __ sub(scratch, scratch, Operand(kPointerSize));
-    __ sub(result, result, Operand(kHeapObjectTag));
+    __ mov(scratch2, Operand(isolate()->factory()->one_pointer_filler_map()));
     Label loop;
     __ bind(&loop);
-    __ mov(scratch2, Operand(isolate()->factory()->one_pointer_filler_map()));
+    __ sub(scratch, scratch, Operand(kPointerSize), SetCC);
     __ str(scratch2, MemOperand(result, scratch));
-    __ sub(scratch, scratch, Operand(kPointerSize));
-    __ cmp(scratch, Operand(0));
     __ b(ge, &loop);
-    __ add(result, result, Operand(kHeapObjectTag));
   }
 }