Implement a list tracer phase, that tries to find element types in individual lists.

sdk/lib/_internal/compiler/implementation/ssa/invoke_dynamic_specializers.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;
 
 /**
  * [InvokeDynamicSpecializer] and its subclasses are helpers to
  * optimize intercepted dynamic calls. It knows what input types
  * would be beneficial for performance, and how to change a invoke
@@ skipping 136 matching lines @@
     }
     // The index should be an int when the receiver is a string or array.
     // However it turns out that inserting an integer check in the optimized
     // version is cheaper than having another bailout case. This is true,
     // because the integer check will simply throw if it fails.
     return HType.UNKNOWN;
   }
 
   HInstruction tryConvertToBuiltin(HInvokeDynamic instruction,
                                    Compiler compiler) {
-    if (instruction.inputs[1].isIndexable(compiler)) {
-      if (!instruction.inputs[2].isInteger() && compiler.enableTypeAssertions) {
-        // We want the right checked mode error.
-        return null;
-      }
-      HInstruction index = new HIndex(
-          instruction.inputs[1], instruction.inputs[2], instruction.selector);
-      index.instructionType =
-          new HType.inferredTypeForSelector(instruction.selector, compiler);
-      return index;
+    if (!instruction.inputs[1].isIndexable(compiler)) return null;
+    if (!instruction.inputs[2].isInteger() && compiler.enableTypeAssertions) {
+      // We want the right checked mode error.
+      return null;
     }
-    return null;
+    HInstruction index = new HIndex(
+        instruction.inputs[1], instruction.inputs[2], instruction.selector);
+    HType receiverType = instruction.getDartReceiver(compiler).instructionType;
+    Selector refined = receiverType.refine(instruction.selector, compiler);
+    HType type = new HType.inferredTypeForSelector(refined, compiler);
+    index.instructionType = type;
+    return index;
   }
 
   bool hasBuiltinVariant(HInvokeDynamic instruction, Compiler compiler) {
     return true;
   }
 }
 
 class BitNotSpecializer extends InvokeDynamicSpecializer {
   const BitNotSpecializer();
 
@@ skipping 515 matching lines @@
 
   BinaryOperation operation(ConstantSystem constantSystem) {
     return constantSystem.lessEqual;
   }
 
   HInstruction newBuiltinVariant(HInvokeDynamic instruction) {
     return new HLessEqual(
         instruction.inputs[1], instruction.inputs[2], instruction.selector);
   }
 }