Redo "Avoid getInterceptor calls in cases were the interceptor would be constant if it were not `nu…

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

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of ssa;
 
 abstract class HVisitor<R> {
   R visitAdd(HAdd node);
   R visitAwait(HAwait node);
   R visitBitAnd(HBitAnd node);
@@ skipping 2282 matching lines @@
   int typeCode() => HInstruction.STATIC_TYPECODE;
   bool typeEquals(other) => other is HStatic;
   bool dataEquals(HStatic other) => element == other.element;
   bool isCodeMotionInvariant() => !element.isAssignable;
 }
 
 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.
+
+  // 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 be
+  // falsy, except for `null`, 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];
+
+  bool get isConditionalConstantInterceptor => inputs.length == 2;
+  HInstruction get conditionalConstantInterceptor => inputs[1];
+  void set conditionalConstantInterceptor(HConstant constant) {
+    assert(!isConditionalConstantInterceptor);
+    inputs.add(constant);
+  }
+
   bool isInterceptor(Compiler compiler) => true;
 
   int typeCode() => HInstruction.INTERCEPTOR_TYPECODE;
   bool typeEquals(other) => other is HInterceptor;
   bool dataEquals(HInterceptor other) {
     return interceptedClasses == other.interceptedClasses
         || (interceptedClasses.length == other.interceptedClasses.length
             && interceptedClasses.containsAll(other.interceptedClasses));
   }
 }
@@ skipping 809 matching lines @@
 class HDynamicType extends HRuntimeType {
   HDynamicType(DynamicType dartType, TypeMask instructionType)
       : super(const <HInstruction>[], dartType, instructionType);
 
   accept(HVisitor visitor) => visitor.visitDynamicType(this);
 
   int typeCode() => HInstruction.DYNAMIC_TYPE_TYPECODE;
 
   bool typeEquals(HInstruction other) => other is HDynamicType;
 }