Constant-fold type variable of constant value

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

Index: pkg/compiler/lib/src/ssa/optimize.dart
diff --git a/pkg/compiler/lib/src/ssa/optimize.dart b/pkg/compiler/lib/src/ssa/optimize.dart
index 492b8c5a4ef587d3b3465756507c8f28ecd20df3..031922228f881912a882b621935a64d4a3312644 100644
--- a/pkg/compiler/lib/src/ssa/optimize.dart
+++ b/pkg/compiler/lib/src/ssa/optimize.dart
@@ -1036,6 +1036,44 @@ class SsaInstructionSimplifier extends HBaseVisitor
   HInstruction visitOneShotInterceptor(HOneShotInterceptor node) {
     return handleInterceptedCall(node);
   }
+
+  HInstruction visitTypeInfoReadVariable(HTypeInfoReadVariable node) {
+    TypeVariableType variable = node.variable;
+    HInstruction object = node.object;
+
+    HInstruction finishGroundType(InterfaceType groundType) {
+      InterfaceType typeAtVariable =
+          groundType.asInstanceOf(variable.element.enclosingClass);
+      if (typeAtVariable != null) {
+        int index = variable.element.index;
+        DartType typeArgument = typeAtVariable.typeArguments[index];
+        HInstruction replacement = new HTypeInfoExpression(
+            TypeInfoExpressionKind.COMPLETE,
+            typeArgument,
+            const <HInstruction>[],
+            backend.dynamicType);
+        return replacement;
+      }
+      return node;
+    }
+
+    // Type variable evaluated in the context of a constant can be replaced with
+    // a ground term type.
+    if (object is HConstant) {
+      ConstantValue value = object.constant;
+      if (value is ConstructedConstantValue) {
+        return finishGroundType(value.type);
+      }
+      return node;
+    }
+
+    // TODO(sra): HTypeInfoReadVariable on an instance creation can be replaced
+    // with an input of the instance creation's HTypeInfoExpression (or a
+    // HTypeInfoExpression of an input).  This would in effect store-forward the
+    // type parameters.
+
+    return node;
+  }
 }
 
 class SsaCheckInserter extends HBaseVisitor implements OptimizationPhase {