Almost-constant interceptors

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

Index: pkg/compiler/lib/src/ssa/interceptor_simplifier.dart
diff --git a/pkg/compiler/lib/src/ssa/interceptor_simplifier.dart b/pkg/compiler/lib/src/ssa/interceptor_simplifier.dart
index d8213e2ca289cebe0d47db8d2d71574239ae4c80..a22b94d05834802705cdd553967bc85b7c4284fc 100644
--- a/pkg/compiler/lib/src/ssa/interceptor_simplifier.dart
+++ b/pkg/compiler/lib/src/ssa/interceptor_simplifier.dart
@@ -110,30 +110,50 @@ class SsaSimplifyInterceptors extends HBaseVisitor
       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
@@ -146,24 +166,13 @@ class SsaSimplifyInterceptors extends HBaseVisitor
       // 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) {
@@ -276,6 +285,32 @@ class SsaSimplifyInterceptors extends HBaseVisitor
       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() && !node.isConditionalConstantInterceptor) {
+      if (!interceptedClasses.contains(backend.jsNullClass)) {
+        // Can use `(receiver && C)` only if receiver is either null or truthy.
+        if (!(receiver.canBePrimitiveNumber(compiler) ||
+            receiver.canBePrimitiveBoolean(compiler) ||
+            receiver.canBePrimitiveString(compiler))) {
+          ClassElement interceptorClass = tryComputeConstantInterceptorFromType(
+              receiver.instructionType.nonNullable(), interceptedClasses);
+          if (interceptorClass != null) {
+            HInstruction constantInstruction =
+                graph.addConstant(
+                    new InterceptorConstantValue(interceptorClass.thisType),
+                    compiler);
+            node.conditionalConstantInterceptor = 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;