[pattern rewriter] Only desugar to call %ToName on computed properties

src/parsing/pattern-rewriter.cc

Index: src/parsing/pattern-rewriter.cc
diff --git a/src/parsing/pattern-rewriter.cc b/src/parsing/pattern-rewriter.cc
index ff2d66c00fcfc4fbd101a875f081504f3ea14ce8..6ea8907f637ab746a9cdecf4ed1b68949010796f 100644
--- a/src/parsing/pattern-rewriter.cc
+++ b/src/parsing/pattern-rewriter.cc
@@ -361,12 +361,11 @@ void Parser::PatternRewriter::VisitObjectLiteral(ObjectLiteral* pattern,
     if (property->kind() == ObjectLiteralProperty::Kind::SPREAD) {
       // var { y, [x++]: a, ...c } = temp
       //     becomes
-      // var temp1 = %ToName('y');
-      // var y = temp[temp1]
-      // var temp2 = %ToName(x++);
-      // var a = temp[temp2];
+      // var y = temp[y];

[adamk, 2017/01/19 02:04:13]

Isn't this temp.y?

[gsathya, 2017/01/21 00:27:33]

Done.

+      // var temp1 = %ToName(x++);
+      // var a = temp[temp1];
       // var c;
-      // c = %CopyDataPropertiesWithExcludedProperties(temp, temp1, temp2);
+      // c = %CopyDataPropertiesWithExcludedProperties(temp, "y", temp1);
       value = factory()->NewCallRuntime(
           Runtime::kCopyDataPropertiesWithExcludedProperties,
           rest_runtime_callargs, kNoSourcePosition);
@@ -379,17 +378,20 @@ void Parser::PatternRewriter::VisitObjectLiteral(ObjectLiteral* pattern,
         RewriteParameterScopes(key);
       }
 
-      // TODO(gsathya): Skip %ToName runtime call for literals.
       if (pattern->has_rest_property()) {
-        auto args = new (zone()) ZoneList<Expression*>(1, zone());
-        args->Add(key, zone());
-        auto to_name_key = CreateTempVar(factory()->NewCallRuntime(
-            Runtime::kToName, args, kNoSourcePosition));
-        key = factory()->NewVariableProxy(to_name_key);
+        Expression* excluded_property = key;
+
+        if (!key->IsLiteral()) {
+          auto args = new (zone()) ZoneList<Expression*>(1, zone());
+          args->Add(key, zone());
+          auto to_name_key = CreateTempVar(factory()->NewCallRuntime(
+              Runtime::kToName, args, kNoSourcePosition));
+          key = factory()->NewVariableProxy(to_name_key);
+          excluded_property = factory()->NewVariableProxy(to_name_key);
+        }

[adamk, 2017/01/19 02:04:13]

Can you add a DCHECK in the else branch about the type of this literal?
Something like

DCHECK(key->IsPropertyName() || key->raw_value()->IsNumber())

which means we couldn't end up with, say, a literal null or a literal true here?
Actually I'm not sure that we don't. Maybe add some tests with computed
properties that are literals?

{ [null]: x, ...y } // should exclude the key "null"

{ [true]: x, ...y } // should exclude "true"

{ [false]: x ] } // should exclude "false"

[gsathya, 2017/01/21 00:27:32]

Done.

 
         DCHECK(rest_runtime_callargs != nullptr);
-        rest_runtime_callargs->Add(factory()->NewVariableProxy(to_name_key),
-                                   zone());
+        rest_runtime_callargs->Add(excluded_property, zone());
       }
 
       value = factory()->NewProperty(factory()->NewVariableProxy(temp), key,