Prettify !(x rel-op y) into (x "!rel-op" y) when possible.

lib/compiler/implementation/ssa/codegen.dart

Index: lib/compiler/implementation/ssa/codegen.dart
diff --git a/lib/compiler/implementation/ssa/codegen.dart b/lib/compiler/implementation/ssa/codegen.dart
index 94c13c606302476eb09f8abc939e83d83bd85821..59bee92119f6ab817aa728209247a639ee661146 100644
--- a/lib/compiler/implementation/ssa/codegen.dart
+++ b/lib/compiler/implementation/ssa/codegen.dart
@@ -1397,10 +1397,34 @@ class SsaCodeGenerator implements HVisitor, HBlockInformationVisitor {
 
   visitNot(HNot node) {
     assert(node.inputs.length == 1);
-    beginExpression(JSPrecedence.PREFIX_PRECEDENCE);
-    buffer.add('!');
-    use(node.inputs[0], JSPrecedence.PREFIX_PRECEDENCE);
-    endExpression(JSPrecedence.PREFIX_PRECEDENCE);
+    HInstruction input = node.inputs[0];
+    if (input is HBoolify && isGenerateAtUseSite(input)) {
+      beginExpression(JSPrecedence.EQUALITY_PRECEDENCE);
+      assert(node.inputs.length == 1);
+      use(node.inputs[0], JSPrecedence.EQUALITY_PRECEDENCE);
+      buffer.add(' !== true');
+      endExpression(JSPrecedence.EQUALITY_PRECEDENCE);
+    } else if (input is HRelational &&
+               input.builtin &&
+               isGenerateAtUseSite(input)) {
+      Map<String, String> inverseOperator = const <String>{
+        "==" : "!=",
+        "!=" : "==",
+        "===": "!==",
+        "!==": "===",
+        "<"  : ">=",
+        "<=" : ">",
+        ">"  : "<=",
+        ">=" : "<"
+      };
+      visitInvokeBinary(input,

[sra1, 2012/05/08 17:47:52]

I can't tell from the code, do the preconditions exclude doubles?  This
transformation is invalid for NaN values.

[Lasse Reichstein Nielsen, 2012/05/09 20:13:25]

Well spotted. No, it's not excluded. I'll have to ensure that the left operand
isn't a double before doing this.

What is NaN === NaN these days?

+                        inverseOperator[input.operation.name.stringValue]);
+    } else {
+      beginExpression(JSPrecedence.PREFIX_PRECEDENCE);
+      buffer.add('!');
+      use(input, JSPrecedence.PREFIX_PRECEDENCE);
+      endExpression(JSPrecedence.PREFIX_PRECEDENCE);
+    }
   }
 
   visitParameterValue(HParameterValue node) {