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

src/compiler/typer.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/typer.h"
 
 #include <iomanip>
 
 #include "src/base/flags.h"
 #include "src/bootstrapper.h"
@@ skipping 25 matching lines @@
 Typer::Typer(Isolate* isolate, Flags flags, Graph* graph)
     : isolate_(isolate),
       flags_(flags),
       graph_(graph),
       decorator_(nullptr),
       cache_(TypeCache::Get()),
       operation_typer_(isolate, zone()) {
   Zone* zone = this->zone();
   Factory* const factory = isolate->factory();
 
-  singleton_false_ = Type::HeapConstant(factory->false_value(), zone);
-  singleton_true_ = Type::HeapConstant(factory->true_value(), zone);
-  singleton_the_hole_ = Type::HeapConstant(factory->the_hole_value(), zone);
+  singleton_empty_string_ = Type::HeapConstant(factory->empty_string(), zone);
+  singleton_false_ = operation_typer_.singleton_false();
+  singleton_true_ = operation_typer_.singleton_true();
   falsish_ = Type::Union(
       Type::Undetectable(),
       Type::Union(Type::Union(singleton_false_, cache_.kZeroish, zone),
-                  singleton_the_hole_, zone),
+                  Type::Union(singleton_empty_string_, Type::Hole(), zone),
+                  zone),
       zone);
   truish_ = Type::Union(
       singleton_true_,
       Type::Union(Type::DetectableReceiver(), Type::Symbol(), zone), zone);
 
   decorator_ = new (zone) Decorator(this);
   graph_->AddDecorator(decorator_);
 }
 
 
@@ skipping 838 matching lines @@
 }
 
 
 Type* Typer::Visitor::JSStrictEqualTyper(Type* lhs, Type* rhs, Typer* t) {
   if (!JSType(lhs)->Maybe(JSType(rhs))) return t->singleton_false_;
   if (lhs->Is(Type::NaN()) || rhs->Is(Type::NaN())) return t->singleton_false_;
   if (lhs->Is(Type::Number()) && rhs->Is(Type::Number()) &&
       (lhs->Max() < rhs->Min() || lhs->Min() > rhs->Max())) {
     return t->singleton_false_;
   }
-  if ((lhs->Is(t->singleton_the_hole_) || rhs->Is(t->singleton_the_hole_)) &&
-      !lhs->Maybe(rhs)) {
+  if ((lhs->Is(Type::Hole()) || rhs->Is(Type::Hole())) && !lhs->Maybe(rhs)) {
     return t->singleton_false_;
   }
   if (lhs->IsHeapConstant() && rhs->Is(lhs)) {
     // Types are equal and are inhabited only by a single semantic value,
     // which is not nan due to the earlier check.
     return t->singleton_true_;
   }
   return Type::Boolean();
 }
 
@@ skipping 1020 matching lines @@
 Type* Typer::Visitor::TypeConstant(Handle<Object> value) {
   if (Type::IsInteger(*value)) {
     return Type::Range(value->Number(), value->Number(), zone());
   }
   return Type::NewConstant(value, zone());
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8