Replace dead instructions with a constant with no type

sdk/lib/_internal/compiler/implementation/ssa/optimize.dart

Index: sdk/lib/_internal/compiler/implementation/ssa/optimize.dart
diff --git a/sdk/lib/_internal/compiler/implementation/ssa/optimize.dart b/sdk/lib/_internal/compiler/implementation/ssa/optimize.dart
index 96fe78738dc144d18a5e7e87e7e3f04b4a061ee3..894ef79ffa6c30b28f447ee55d340a5f23c5d460 100644
--- a/sdk/lib/_internal/compiler/implementation/ssa/optimize.dart
+++ b/sdk/lib/_internal/compiler/implementation/ssa/optimize.dart
@@ -894,9 +894,13 @@ class SsaDeadCodeEliminator extends HGraphVisitor implements OptimizationPhase {
 
   HInstruction zapInstructionCache;
   HInstruction get zapInstruction {
-    return (zapInstructionCache == null)
-        ? zapInstructionCache = analyzer.graph.addConstantInt(0, compiler)
-        : zapInstructionCache;
+    if (zapInstructionCache == null) {
+      // A constant with no type does not pollute types at phi nodes.
+      Constant constant =
+          new DummyReceiverConstant(const TypeMask.nonNullEmpty());
+      zapInstructionCache = analyzer.graph.addConstant(constant, compiler);
+    }
+    return zapInstructionCache;
   }
 
   /// Returns whether the next throwing instruction that may have side