MIPS: Reland "Fixed environment assignment for LCheckNonSmi."

Port r20495 (705b65bc)

BUG=
R=plind44@gmail.com

Review URL: https://codereview.chromium.org/225023007

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@20518 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/mips/lithium-mips.cc

@@ -1913,7 +1913,9 @@ LInstruction* LChunkBuilder::DoChange(HChange* instr) {
 
 LInstruction* LChunkBuilder::DoCheckHeapObject(HCheckHeapObject* instr) {
   LOperand* value = UseRegisterAtStart(instr->value());
-  return AssignEnvironment(new(zone()) LCheckNonSmi(value));
+  LInstruction* result = new(zone()) LCheckNonSmi(value);
+  if (!instr->value()->IsHeapObject()) result = AssignEnvironment(result);
+  return result;
 }