Constant-fold !<number>

src/parser.cc

Index: src/parser.cc
===================================================================
--- src/parser.cc	(revision 8225)
+++ src/parser.cc	(working copy)
@@ -2555,6 +2555,12 @@
           return NewNumberLiteral(-value);
         case Token::BIT_NOT:
           return NewNumberLiteral(~DoubleToInt32(value));
+        case Token::NOT:
+          if (value == 0) {

[Kasper Lund, 2011/06/10 09:20:08]

Could this be something ala:

   Handle<Object> boolean(isolate->heap()->ToBoolean(value == 0));
   return new(zone()) Literal(boolean);

or perhaps consider negating the result of calling
expression->AsLiteral()->handle()->ToBoolean() and refactoring the code so it
works for cases where the expression is a non-numeric literal.

[Kevin Millikin (Chromium), 2011/06/10 10:05:14]

We already have this constant folding in void
FullCodeGenerator::TestContext::Plug(Handle<Object> lit).  It just needs to be
'ported' to TestContext::BuildBranch(HValue* value) in hydrogen.cc.

I would prefer that solution rather than having it here, because it can properly
cope with things like

x = 0
if (!x) ...

+            return new(zone()) Literal(isolate()->factory()->true_value());
+          } else {
+            return new(zone()) Literal(isolate()->factory()->false_value());
+          }
         default: break;
       }
     }