[turbofan] Improve typed lowering for JSToBoolean.

test/cctest/compiler/test-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/v8.h"
 #include "test/cctest/cctest.h"
 
 #include "src/compiler/graph-inl.h"
 #include "src/compiler/js-typed-lowering.h"
 #include "src/compiler/node-properties-inl.h"
@@ skipping 490 matching lines @@
   {  // ToBoolean(ordered-number)
     Node* r = R.ReduceUnop(op, Type::OrderedNumber());
     CHECK_EQ(IrOpcode::kBooleanNot, r->opcode());
     Node* i = r->InputAt(0);
     CHECK_EQ(IrOpcode::kNumberEqual, i->opcode());
     // ToBoolean(x:ordered-number) => BooleanNot(NumberEqual(x, #0))
   }
 
   {  // ToBoolean(string)
     Node* r = R.ReduceUnop(op, Type::String());
-    // TODO(titzer): test will break with better js-typed-lowering
-    CHECK_EQ(IrOpcode::kJSToBoolean, r->opcode());
+    CHECK_EQ(IrOpcode::kBooleanNot, r->opcode());
+    Node* i = r->InputAt(0);
+    CHECK_EQ(IrOpcode::kNumberEqual, i->opcode());
+    Node* j = i->InputAt(0);
+    CHECK_EQ(IrOpcode::kLoadField, j->opcode());
+    // ToBoolean(x:string) => BooleanNot(NumberEqual(x.length, #0))
   }
 
   {  // ToBoolean(object)
     Node* r = R.ReduceUnop(op, Type::DetectableObject());
     R.CheckTrue(r);
   }
 
   {  // ToBoolean(undetectable)
     Node* r = R.ReduceUnop(op, Type::Undetectable());
     R.CheckFalse(r);
@@ skipping 812 matching lines @@
           CHECK_EQ(p1, r->InputAt(0));
           CHECK_EQ(p0, r->InputAt(1));
         } else {
           CHECK_EQ(p0, r->InputAt(0));
           CHECK_EQ(p1, r->InputAt(1));
         }
       }
     }
   }
 }