Lithium: avoid registers for constants when possible.

src/arm/lithium-codegen-arm.cc

Index: src/arm/lithium-codegen-arm.cc
diff --git a/src/arm/lithium-codegen-arm.cc b/src/arm/lithium-codegen-arm.cc
index 29e01b9182a5216e2119c6ebb413713f0f9d37e0..ebda302e3049d880ff41f3aeb9e785aa23cf8b3d 100644
--- a/src/arm/lithium-codegen-arm.cc
+++ b/src/arm/lithium-codegen-arm.cc
@@ -5473,7 +5473,6 @@ 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
@@ -5482,8 +5481,16 @@ void LCodeGen::DoDeferredAllocate(LAllocate* instr) {
   __ mov(result, Operand(Smi::FromInt(0)));
 
   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);