[turbofan] Utilize the fact that empty string is canonicalized.

src/compiler/js-typed-lowering.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/js-typed-lowering.h"
 
 #include "src/ast/modules.h"
 #include "src/builtins/builtins-utils.h"
 #include "src/code-factory.h"
 #include "src/compilation-dependencies.h"
@@ skipping 510 matching lines @@
 // - immediately put in type bounds for all new nodes
 // - relax effects from generic but not-side-effecting operations
 
 JSTypedLowering::JSTypedLowering(Editor* editor,
                                  CompilationDependencies* dependencies,
                                  Flags flags, JSGraph* jsgraph, Zone* zone)
     : AdvancedReducer(editor),
       dependencies_(dependencies),
       flags_(flags),
       jsgraph_(jsgraph),
+      pointer_comparable_type_(Type::Union(
+          Type::BooleanOrNullOrUndefined(),
+          Type::Union(Type::Symbol(),
+                      Type::Union(Type::Receiver(),
+                                  Type::Union(Type::Hole(),
+                                              Type::HeapConstant(
+                                                  factory()->empty_string(),
+                                                  graph()->zone()),
+                                              graph()->zone()),
+                                  graph()->zone()),
+                      graph()->zone()),
+          graph()->zone())),

[Yang, 2017/02/09 06:41:41]

can we have a helper function that returns this monstrosity?

[Benedikt Meurer, 2017/02/09 06:58:24]

Done.

       type_cache_(TypeCache::Get()) {
   for (size_t k = 0; k < arraysize(shifted_int32_ranges_); ++k) {
     double min = kMinInt / (1 << k);
     double max = kMaxInt / (1 << k);
     shifted_int32_ranges_[k] = Type::Range(min, max, graph()->zone());
   }
 }
 
 Reduction JSTypedLowering::ReduceJSAdd(Node* node) {
   JSBinopReduction r(this, node);
@@ skipping 462 matching lines @@
       return Replace(replacement);
     }
   }
 
   Reduction const reduction = ReduceJSEqualTypeOf(node, invert);
   if (reduction.Changed()) return reduction;
 
   if (r.BothInputsAre(Type::Unique())) {
     return r.ChangeToPureOperator(simplified()->ReferenceEqual(), invert);
   }
-  if (r.OneInputIs(Type::NonStringUniqueOrHole())) {
+  if (r.OneInputIs(pointer_comparable_type_)) {
     return r.ChangeToPureOperator(simplified()->ReferenceEqual(), invert);
   }
   if (r.IsInternalizedStringCompareOperation()) {
     r.CheckInputsToInternalizedString();
     return r.ChangeToPureOperator(simplified()->ReferenceEqual(), invert);
   }
   if (r.BothInputsAre(Type::String())) {
     return r.ChangeToPureOperator(simplified()->StringEqual(), invert);
   }
 
@@ skipping 43 matching lines @@
     NodeProperties::ChangeOp(node, simplified()->BooleanNot());
     return Changed(node);
   } else if (input_type->Is(Type::ReceiverOrNullOrUndefined())) {
     // JSToBoolean(x:receiver \/ null \/ undefined)
     //   => BooleanNot(ObjectIsUndetectable(x))
     node->ReplaceInput(
         0, graph()->NewNode(simplified()->ObjectIsUndetectable(), input));
     node->TrimInputCount(1);
     NodeProperties::ChangeOp(node, simplified()->BooleanNot());
     return Changed(node);
+  } else if (input_type->Is(Type::String())) {
+    // JSToBoolean(x:string) => BooleanNot(ReferenceEqual(x,""))
+    node->ReplaceInput(0,
+                       graph()->NewNode(simplified()->ReferenceEqual(), input,
+                                        jsgraph()->EmptyStringConstant()));
+    node->TrimInputCount(1);
+    NodeProperties::ChangeOp(node, simplified()->BooleanNot());
+    return Changed(node);
   }
   return NoChange();
 }
 
 Reduction JSTypedLowering::ReduceJSToInteger(Node* node) {
   Node* const input = NodeProperties::GetValueInput(node, 0);
   Type* const input_type = NodeProperties::GetType(input);
   if (input_type->Is(type_cache_.kIntegerOrMinusZero)) {
     // JSToInteger(x:integer) => x
     ReplaceWithValue(node, input);
@@ skipping 1374 matching lines @@
 }
 
 
 CompilationDependencies* JSTypedLowering::dependencies() const {
   return dependencies_;
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8