Use predicates to check simple function types.

sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart

Index: sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart
diff --git a/sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart b/sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart
index 965822ea6c0c54cf5ca4370ebb5b6f15ecb59839..380854e590e7731f20e6ebc88316a6c0ebfbe553 100644
--- a/sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart
+++ b/sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart
@@ -2176,7 +2176,7 @@ class CodeEmitterTask extends CompilerTask {
       if (!knownSubtype) {
         registerDynamicFunctionTypeCheck(functionType);
         hasDynamicFunctionTypeCheck = true;
-      } else {
+      } else if (!functionType.isSimple) {

[karlklose, 2013/08/23 09:13:50]

Perhaps add a comment why these do not count as predicates and explain why they
are emitted.

[Johnni Winther, 2013/08/23 10:06:57]

Done.

         neededPredicates++;
       }
     });
@@ -2188,7 +2188,9 @@ class CodeEmitterTask extends CompilerTask {
     }
     functionTypeChecks.forEach((FunctionType functionType, bool knownSubtype) {
       if (knownSubtype) {
-        if (alwaysUseSignature) {
+        if (functionType.isSimple) {
+          emitIsFunctionTypeTest(functionType);
+        } else if (alwaysUseSignature) {
           registerDynamicFunctionTypeCheck(functionType);
         } else {
           emitIsFunctionTypeTest(functionType);