Almost-constant interceptors

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

 // Copyright (c) 2013, 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;
 
 /**
  * This phase simplifies interceptors in multiple ways:
  *
  * 1) If the interceptor is for an object whose type is known, it
@@ skipping 92 matching lines @@
   HInstruction tryComputeConstantInterceptor(
       HInstruction input,
       Set<ClassElement> interceptedClasses) {
     if (input == graph.explicitReceiverParameter) {
       // If `explicitReceiverParameter` is set it means the current method is an
       // interceptor method, and `this` is the interceptor.  The caller just did
       // `getInterceptor(foo).currentMethod(foo)` to enter the current method.
       return graph.thisInstruction;
     }
 
-    ClassElement constantInterceptor;
+    ClassElement constantInterceptor = tryComputeConstantInterceptorFromType(
+        input.instructionType, interceptedClasses);
+
+    if (constantInterceptor == null) return null;
+
+    // If we just happen to be in an instance method of the constant
+    // interceptor, `this` is a shorter alias.
+    if (constantInterceptor == work.element.enclosingClass &&
+        graph.thisInstruction != null) {
+      return graph.thisInstruction;
+    }
+
+    ConstantValue constant =
+        new InterceptorConstantValue(constantInterceptor.thisType);
+    return graph.addConstant(constant, compiler);
+  }
+
+  ClassElement tryComputeConstantInterceptorFromType(
+      TypeMask type,
+      Set<ClassElement> interceptedClasses) {
+
     ClassWorld classWorld = compiler.world;
     JavaScriptBackend backend = compiler.backend;
-    if (input.canBeNull()) {
-      if (input.isNull()) {
-        constantInterceptor = backend.jsNullClass;
+    if (type.isNullable) {
+      if (type.isEmpty) {
+        return backend.jsNullClass;
       }
-    } else if (input.isInteger(compiler)) {
-      constantInterceptor = backend.jsIntClass;
-    } else if (input.isDouble(compiler)) {
-      constantInterceptor = backend.jsDoubleClass;
-    } else if (input.isBoolean(compiler)) {
-      constantInterceptor = backend.jsBoolClass;
-    } else if (input.isString(compiler)) {
-      constantInterceptor = backend.jsStringClass;
-    } else if (input.isArray(compiler)) {
-      constantInterceptor = backend.jsArrayClass;
-    } else if (input.isNumber(compiler) &&
+    } else if (type.containsOnlyInt(classWorld)) {
+      return backend.jsIntClass;
+    } else if (type.containsOnlyDouble(classWorld)) {
+      return backend.jsDoubleClass;
+    } else if (type.containsOnlyBool(classWorld)) {
+      return backend.jsBoolClass;
+    } else if (type.containsOnlyString(classWorld)) {
+      return backend.jsStringClass;
+    } else if (type.satisfies(backend.jsArrayClass, classWorld)) {
+      return backend.jsArrayClass;
+    } else if (type.containsOnlyNum(classWorld) &&
         !interceptedClasses.contains(backend.jsIntClass) &&
         !interceptedClasses.contains(backend.jsDoubleClass)) {
       // If the method being intercepted is not defined in [int] or [double] we
       // can safely use the number interceptor.  This is because none of the
       // [int] or [double] methods are called from a method defined on [num].
-      constantInterceptor = backend.jsNumberClass;
+      return backend.jsNumberClass;
     } else {
       // Try to find constant interceptor for a native class.  If the receiver
       // is constrained to a leaf native class, we can use the class's
       // interceptor directly.
 
       // TODO(sra): Key DOM classes like Node, Element and Event are not leaf
       // classes.  When the receiver type is not a leaf class, we might still be
       // able to use the receiver class as a constant interceptor.  It is
       // usually the case that methods defined on a non-leaf class don't test
       // for a subclass or call methods defined on a subclass.  Provided the
       // code is completely insensitive to the specific instance subclasses, we
       // can use the non-leaf class directly.
-      ClassElement element = input.instructionType.singleClass(classWorld);
+      ClassElement element = type.singleClass(classWorld);
       if (element != null && element.isNative) {
-        constantInterceptor = element;
+        return element;
       }
     }
 
-    if (constantInterceptor == null) return null;
-
-    // If we just happen to be in an instance method of the constant
-    // interceptor, `this` is a shorter alias.
-    if (constantInterceptor == work.element.enclosingClass &&
-        graph.thisInstruction != null) {
-      return graph.thisInstruction;
-    }
-
-    ConstantValue constant =
-        new InterceptorConstantValue(constantInterceptor.thisType);
-    return graph.addConstant(constant, compiler);
+    return null;
   }
 
   HInstruction findDominator(Iterable<HInstruction> instructions) {
     HInstruction result;
     L1: for (HInstruction candidate in instructions) {
       for (HInstruction current in instructions) {
         if (current != candidate && !candidate.dominates(current)) continue L1;
       }
       result = candidate;
       break;
@@ skipping 92 matching lines @@
     }
 
     // Try computing a constant interceptor.
     HInstruction constantInterceptor =
         tryComputeConstantInterceptor(receiver, interceptedClasses);
     if (constantInterceptor != null) {
       node.block.rewrite(node, constantInterceptor);
       return false;
     }
 
+    // Do we have an 'almost constant' interceptor?  The receiver could be
+    // `null` but not any other JavaScript falsy value, `null` values cause
+    // `NoSuchMethodError`s, and if the receiver was not null we would have a
+    // constant interceptor `C`.  Then we can use `(receiver && C)` for the
+    // interceptor.
+    if (receiver.canBeNull()) {
+      if (!interceptedClasses.contains(backend.jsNullClass)) {
+        // Can only use `(receiver && C)` if receiver is null or truthy.

[floitsch, 2015/04/01 23:14:54]

is either null or truthy.

[sra1, 2015/04/02 01:00:07]

Done.

+        if (!(receiver.canBePrimitiveNumber(compiler) ||
+              receiver.canBePrimitiveBoolean(compiler) ||
+              receiver.canBePrimitiveString(compiler))) {
+          ClassElement interceptorClass = tryComputeConstantInterceptorFromType(
+              receiver.instructionType.nonNullable(), interceptedClasses);
+          if (interceptorClass != null) {
+            if (node.inputs.length == 1) {

[floitsch, 2015/04/01 23:14:54]

when can it have more than one? is it `node.isConditionalConstantInterceptor` ?
Maybe check it earlier? (it seems like a cheap check).

[sra1, 2015/04/02 01:00:07]

Done.

+              ConstantValue constant =
+                  new InterceptorConstantValue(interceptorClass.thisType);
+              HInstruction constantInstruction =
+                  graph.addConstant(constant, compiler);
+              node.inputs.length = 2;
+              node.inputs[1] = constantInstruction;
+              constantInstruction.usedBy.add(node);
+              return false;
+            }
+          }
+        }
+      }
+    }
+
     // Try creating a one-shot interceptor or optimized is-check
     if (compiler.hasIncrementalSupport) return false;
     if (node.usedBy.length != 1) return false;
     HInstruction user = node.usedBy.single;
 
     // If the interceptor [node] was loop hoisted, we keep the interceptor.
     if (!user.hasSameLoopHeaderAs(node)) return false;
 
     bool replaceUserWith(HInstruction replacement) {
       HBasicBlock block = user.block;
@@ skipping 75 matching lines @@
       instruction = new HInvokeDynamicMethod(
           selector, inputs, node.instructionType, true);
     }
 
     HBasicBlock block = node.block;
     block.addAfter(node, instruction);
     block.rewrite(node, instruction);
     return true;
   }
 }