Only assign environments when they are actually needed. (x64 only)

Twin of https://code.google.com/p/v8/source/detail?r=20231.

R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/211153003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@20271 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/x64/lithium-x64.cc

@@ -947,18 +947,20 @@ LInstruction* LChunkBuilder::DoBranch(HBranch* instr) {
   if (goto_instr != NULL) return goto_instr;
 
   HValue* value = instr->value();
-  LBranch* result = new(zone()) LBranch(UseRegister(value));
-  // Tagged values that are not known smis or booleans require a
-  // deoptimization environment. If the instruction is generic no
-  // environment is needed since all cases are handled.
-  ToBooleanStub::Types expected = instr->expected_input_types();
-  Representation rep = value->representation();
+  Representation r = value->representation();
   HType type = value->type();
-  if (rep.IsTagged() && !type.IsSmi() && !type.IsBoolean() &&
-      !expected.IsGeneric()) {
-    return AssignEnvironment(result);
+  ToBooleanStub::Types expected = instr->expected_input_types();
+  if (expected.IsEmpty()) expected = ToBooleanStub::Types::Generic();
+
+  bool easy_case = !r.IsTagged() || type.IsBoolean() || type.IsSmi() ||
+      type.IsJSArray() || type.IsHeapNumber() || type.IsString();
+  LInstruction* branch = new(zone()) LBranch(UseRegister(value));
+  if (!easy_case &&
+      ((!expected.Contains(ToBooleanStub::SMI) && expected.NeedsMap()) ||
+       !expected.IsGeneric())) {
+    branch = AssignEnvironment(branch);
   }
-  return result;
+  return branch;
 }
 
 
@@ -1143,8 +1145,12 @@ LInstruction* LChunkBuilder::DoMathRound(HUnaryMathOperation* instr) {
 LInstruction* LChunkBuilder::DoMathAbs(HUnaryMathOperation* instr) {
   LOperand* context = UseAny(instr->context());
   LOperand* input = UseRegisterAtStart(instr->value());
-  LMathAbs* result = new(zone()) LMathAbs(context, input);
-  return AssignEnvironment(AssignPointerMap(DefineSameAsFirst(result)));
+  LInstruction* result =
+      DefineSameAsFirst(new(zone()) LMathAbs(context, input));
+  Representation r = instr->value()->representation();
+  if (!r.IsDouble() && !r.IsSmiOrInteger32()) result = AssignPointerMap(result);
+  if (!r.IsDouble()) result = AssignEnvironment(result);
+  return result;
 }
 
 
@@ -1798,8 +1804,11 @@ LInstruction* LChunkBuilder::DoChange(HChange* instr) {
   if (from.IsTagged()) {
     if (to.IsDouble()) {
       LOperand* value = UseRegister(instr->value());
-      LNumberUntagD* res = new(zone()) LNumberUntagD(value);
-      return AssignEnvironment(DefineAsRegister(res));
+      LInstruction* res = DefineAsRegister(new(zone()) LNumberUntagD(value));
+      if (!instr->value()->representation().IsSmi()) {
+        res = AssignEnvironment(res);
+      }
+      return res;
     } else if (to.IsSmi()) {
       HValue* val = instr->value();
       LOperand* value = UseRegister(val);
@@ -1816,8 +1825,13 @@ LInstruction* LChunkBuilder::DoChange(HChange* instr) {
       } else {
         bool truncating = instr->CanTruncateToInt32();
         LOperand* xmm_temp = truncating ? NULL : FixedTemp(xmm1);
-        LTaggedToI* res = new(zone()) LTaggedToI(value, xmm_temp);
-        return AssignEnvironment(DefineSameAsFirst(res));
+        LInstruction* res =
+            DefineSameAsFirst(new(zone()) LTaggedToI(value, xmm_temp));
+        if (!instr->value()->representation().IsSmi()) {
+          // Note: Only deopts in deferred code.
+          res = AssignEnvironment(res);
+        }
+        return res;
       }
     }
   } else if (from.IsDouble()) {
@@ -1837,8 +1851,11 @@ LInstruction* LChunkBuilder::DoChange(HChange* instr) {
     } else {
       ASSERT(to.IsInteger32());
       LOperand* value = UseRegister(instr->value());
-      return AssignEnvironment(
-          DefineAsRegister(new(zone()) LDoubleToI(value)));
+      LInstruction* result = DefineAsRegister(new(zone()) LDoubleToI(value));
+      if (!instr->CanTruncateToInt32()) {
+        result = AssignEnvironment(result);
+      }
+      return result;
     }
   } else if (from.IsInteger32()) {
     info()->MarkAsDeferredCalling();
@@ -1851,10 +1868,10 @@ LInstruction* LChunkBuilder::DoChange(HChange* instr) {
         LOperand* temp1 = TempRegister();
         LOperand* temp2 = FixedTemp(xmm1);
         LNumberTagU* result = new(zone()) LNumberTagU(value, temp1, temp2);
-        return AssignEnvironment(AssignPointerMap(DefineSameAsFirst(result)));
+        return AssignPointerMap(DefineSameAsFirst(result));
       } else {
         LNumberTagI* result = new(zone()) LNumberTagI(value);
-        return AssignEnvironment(AssignPointerMap(DefineSameAsFirst(result)));
+        return AssignPointerMap(DefineSameAsFirst(result));
       }
     } else if (to.IsSmi()) {
       HValue* val = instr->value();
@@ -1915,6 +1932,7 @@ LInstruction* LChunkBuilder::DoCheckMaps(HCheckMaps* instr) {
   }
   LCheckMaps* result = new(zone()) LCheckMaps(value);
   if (!instr->CanOmitMapChecks()) {
+    // Note: Only deopts in deferred code.
     AssignEnvironment(result);
     if (instr->has_migration_target()) return AssignPointerMap(result);
   }
@@ -2014,7 +2032,10 @@ LInstruction* LChunkBuilder::DoLoadContextSlot(HLoadContextSlot* instr) {
   LOperand* context = UseRegisterAtStart(instr->value());
   LInstruction* result =
       DefineAsRegister(new(zone()) LLoadContextSlot(context));
-  return instr->RequiresHoleCheck() ? AssignEnvironment(result) : result;
+  if (instr->RequiresHoleCheck() && instr->DeoptimizesOnHole()) {
+    result = AssignEnvironment(result);
+  }
+  return result;
 }
 
 
@@ -2031,7 +2052,10 @@ LInstruction* LChunkBuilder::DoStoreContextSlot(HStoreContextSlot* instr) {
     temp = NULL;
   }
   LInstruction* result = new(zone()) LStoreContextSlot(context, value, temp);
-  return instr->RequiresHoleCheck() ? AssignEnvironment(result) : result;
+  if (instr->RequiresHoleCheck() && instr->DeoptimizesOnHole()) {
+    result = AssignEnvironment(result);
+  }
+  return result;
 }
 
 
@@ -2076,28 +2100,32 @@ LInstruction* LChunkBuilder::DoLoadKeyed(HLoadKeyed* instr) {
   ASSERT(instr->key()->representation().IsInteger32());
   ElementsKind elements_kind = instr->elements_kind();
   LOperand* key = UseRegisterOrConstantAtStart(instr->key());
-  LLoadKeyed* result = NULL;
+  LInstruction* result = NULL;
 
   if (!instr->is_typed_elements()) {
     LOperand* obj = UseRegisterAtStart(instr->elements());
-    result = new(zone()) LLoadKeyed(obj, key);
+    result = DefineAsRegister(new(zone()) LLoadKeyed(obj, key));
   } else {
     ASSERT(
         (instr->representation().IsInteger32() &&
-         !(IsDoubleOrFloatElementsKind(instr->elements_kind()))) ||
+         !(IsDoubleOrFloatElementsKind(elements_kind))) ||
         (instr->representation().IsDouble() &&
-         (IsDoubleOrFloatElementsKind(instr->elements_kind()))));
+         (IsDoubleOrFloatElementsKind(elements_kind))));
     LOperand* backing_store = UseRegister(instr->elements());
-    result = new(zone()) LLoadKeyed(backing_store, key);
+    result = DefineAsRegister(new(zone()) LLoadKeyed(backing_store, key));
   }
 
-  DefineAsRegister(result);
-  bool can_deoptimize = instr->RequiresHoleCheck() ||
-      (elements_kind == EXTERNAL_UINT32_ELEMENTS) ||
-      (elements_kind == UINT32_ELEMENTS);
-  // An unsigned int array load might overflow and cause a deopt, make sure it
-  // has an environment.
-  return can_deoptimize ? AssignEnvironment(result) : result;
+  if ((instr->is_external() || instr->is_fixed_typed_array()) ?
+      // see LCodeGen::DoLoadKeyedExternalArray
+      ((elements_kind == EXTERNAL_UINT32_ELEMENTS ||
+        elements_kind == UINT32_ELEMENTS) &&
+       !instr->CheckFlag(HInstruction::kUint32)) :
+      // see LCodeGen::DoLoadKeyedFixedDoubleArray and
+      // LCodeGen::DoLoadKeyedFixedArray
+      instr->RequiresHoleCheck()) {
+    result = AssignEnvironment(result);
+  }
+  return result;
 }
 
 
@@ -2258,11 +2286,13 @@ LInstruction* LChunkBuilder::DoStoreNamedField(HStoreNamedField* instr) {
   LOperand* temp = (!is_in_object || needs_write_barrier ||
       needs_write_barrier_for_map) ? TempRegister() : NULL;
 
-  LStoreNamedField* result = new(zone()) LStoreNamedField(obj, val, temp);
-  if (instr->field_representation().IsHeapObject()) {
-    if (!instr->value()->type().IsHeapObject()) {
-      return AssignEnvironment(result);
-    }
+  LInstruction* result = new(zone()) LStoreNamedField(obj, val, temp);
+  if (!instr->access().IsExternalMemory() &&
+      instr->field_representation().IsHeapObject() &&
+      (val->IsConstantOperand()
+       ? HConstant::cast(instr->value())->HasSmiValue()
+       : !instr->value()->type().IsHeapObject())) {
+    result = AssignEnvironment(result);
   }
   return result;
 }
@@ -2294,7 +2324,7 @@ LInstruction* LChunkBuilder::DoStringCharCodeAt(HStringCharCodeAt* instr) {
   LOperand* context = UseAny(instr->context());
   LStringCharCodeAt* result =
       new(zone()) LStringCharCodeAt(context, string, index);
-  return AssignEnvironment(AssignPointerMap(DefineAsRegister(result)));
+  return AssignPointerMap(DefineAsRegister(result));
 }