MIPS: Check that environments assigned via AssignEnvironment are actually used.

Port r20430 (e9457854)

Original commit message:
Check that environments assigned via AssignEnvironment are actually used.

Removed some temporary marker comments on the way.

BUG=
R=plind44@gmail.com

Review URL: https://codereview.chromium.org/214703007

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@20452 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/mips/lithium-codegen-mips.cc

@@ -744,6 +744,7 @@ void LCodeGen::CallRuntimeFromDeferred(Runtime::FunctionId id,
 
 void LCodeGen::RegisterEnvironmentForDeoptimization(LEnvironment* environment,
                                                     Safepoint::DeoptMode mode) {
+  environment->set_has_been_used();
   if (!environment->HasBeenRegistered()) {
     // Physical stack frame layout:
     // -x ............. -4  0 ..................................... y

src/mips/lithium-mips.cc

@@ -628,6 +628,8 @@ LInstruction* LChunkBuilder::MarkAsCall(LInstruction* instr,
       !hinstr->HasObservableSideEffects();
   if (needs_environment && !instr->HasEnvironment()) {
     instr = AssignEnvironment(instr);
+    // We can't really figure out if the environment is needed or not.
+    instr->environment()->set_has_been_used();
   }
 
   return instr;
@@ -1845,10 +1847,7 @@ LInstruction* LChunkBuilder::DoChange(HChange* instr) {
         LOperand* temp2 = FixedTemp(f22);
         LInstruction* result =
             DefineSameAsFirst(new(zone()) LTaggedToI(value, temp1, temp2));
-        if (!val->representation().IsSmi()) {
-          // Note: Only deopts in deferred code.
-          result = AssignEnvironment(result);
-        }
+        if (!val->representation().IsSmi()) result = AssignEnvironment(result);
         return result;
       }
     }
@@ -1943,11 +1942,10 @@ LInstruction* LChunkBuilder::DoCheckMaps(HCheckMaps* instr) {
     value = UseRegisterAtStart(instr->value());
     if (instr->has_migration_target()) info()->MarkAsDeferredCalling();
   }
-  LCheckMaps* result = new(zone()) LCheckMaps(value);
+  LInstruction* result = new(zone()) LCheckMaps(value);
   if (!instr->CanOmitMapChecks()) {
-    // Note: Only deopts in deferred code.
-    AssignEnvironment(result);
-    if (instr->has_migration_target()) return AssignPointerMap(result);
+    result = AssignEnvironment(result);
+    if (instr->has_migration_target()) result = AssignPointerMap(result);
   }
   return result;
 }