MIPS: Lithium: avoid registers for constants when possible.

Port r14460 (9e3dab0c)

BUG=

Review URL: https://codereview.chromium.org/14520016

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@14473 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/mips/lithium-codegen-mips.cc

@@ -5150,7 +5150,6 @@ void LCodeGen::DoAllocate(LAllocate* instr) {
 
 
 void LCodeGen::DoDeferredAllocate(LAllocate* instr) {
-  Register size = ToRegister(instr->size());
   Register result = ToRegister(instr->result());
 
   // TODO(3095996): Get rid of this. For now, we need to make the
@@ -5159,8 +5158,16 @@ void LCodeGen::DoDeferredAllocate(LAllocate* instr) {
   __ mov(result, zero_reg);
 
   PushSafepointRegistersScope scope(this, Safepoint::kWithRegisters);
-  __ SmiTag(size, size);
-  __ push(size);
+  if (instr->size()->IsRegister()) {
+    Register size = ToRegister(instr->size());
+    ASSERT(!size.is(result));
+    __ SmiTag(size);
+    __ push(size);
+  } else {
+    int32_t size = ToInteger32(LConstantOperand::cast(instr->size()));
+    __ Push(Smi::FromInt(size));
+  }
+
   if (instr->hydrogen()->CanAllocateInOldPointerSpace()) {
     CallRuntimeFromDeferred(
         Runtime::kAllocateInOldPointerSpace, 1, instr);

src/mips/lithium-mips.cc

@@ -552,6 +552,11 @@ LOperand* LChunkBuilder::UseRegisterOrConstantAtStart(HValue* value) {
 }
 
 
+LOperand* LChunkBuilder::UseConstant(HValue* value) {
+  return chunk_->DefineConstantOperand(HConstant::cast(value));
+}
+
+
 LOperand* LChunkBuilder::UseAny(HValue* value) {
   return value->IsConstant()
       ? chunk_->DefineConstantOperand(HConstant::cast(value))
@@ -2253,7 +2258,9 @@ LInstruction* LChunkBuilder::DoAllocateObject(HAllocateObject* instr) {
 
 LInstruction* LChunkBuilder::DoAllocate(HAllocate* instr) {
   info()->MarkAsDeferredCalling();
-  LOperand* size = UseTempRegister(instr->size());
+  LOperand* size = instr->size()->IsConstant()
+      ? UseConstant(instr->size())
+      : UseTempRegister(instr->size());
   LOperand* temp1 = TempRegister();
   LOperand* temp2 = TempRegister();
   LAllocate* result = new(zone()) LAllocate(size, temp1, temp2);

src/mips/lithium-mips.h

@@ -2722,6 +2722,9 @@ class LChunkBuilder BASE_EMBEDDED {
   MUST_USE_RESULT LOperand* UseRegisterOrConstant(HValue* value);
   MUST_USE_RESULT LOperand* UseRegisterOrConstantAtStart(HValue* value);
 
+  // An input operand in a constant operand.
+  MUST_USE_RESULT LOperand* UseConstant(HValue* value);
+
   // An input operand in register, stack slot or a constant operand.
   // Will not be moved to a register even if one is freely available.
   MUST_USE_RESULT LOperand* UseAny(HValue* value);