Almost-constant interceptors

pkg/compiler/lib/src/ssa/nodes.dart

Index: pkg/compiler/lib/src/ssa/nodes.dart
diff --git a/pkg/compiler/lib/src/ssa/nodes.dart b/pkg/compiler/lib/src/ssa/nodes.dart
index f4e813b870b72674a4401c262ebc78b05794359c..062463e1d341816802bb7751058e15c579eb81cd 100644
--- a/pkg/compiler/lib/src/ssa/nodes.dart
+++ b/pkg/compiler/lib/src/ssa/nodes.dart
@@ -2300,12 +2300,21 @@ class HInterceptor extends HInstruction {
   // This field should originally be null to allow GVN'ing all
   // [HInterceptor] on the same input.
   Set<ClassElement> interceptedClasses;
+
+  // inputs[0] is initially the only input, the receiver.

[floitsch, 2015/03/26 20:26:45]

Create getters.

[sra1, 2015/04/01 23:06:59]

Done.

+
+  // inputs[1] is a constant interceptor when the interceptor is a constant
+  // except for a `null` receiver.  This is used when the receiver can't, except
+  // for `null`, be a falsy JavaScript value, allowing the generation of code
+  // like `(a && C.JSArray_methods).get$first(a)`.
+
   HInterceptor(HInstruction receiver, TypeMask type)
       : super(<HInstruction>[receiver], type) {
     sideEffects.clearAllSideEffects();
     sideEffects.clearAllDependencies();
     setUseGvn();
   }
+
   String toString() => 'interceptor on $interceptedClasses';
   accept(HVisitor visitor) => visitor.visitInterceptor(this);
   HInstruction get receiver => inputs[0];