Postpone the argument type optimizations until the types are stable.

lib/compiler/implementation/ssa/codegen_helpers.dart

 // Copyright (c) 2012, 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.
 
 /**
  * Instead of emitting each SSA instruction with a temporary variable
  * mark instructions that can be emitted at their use-site.
  * For example, in:
  *   t0 = 4;
  *   t1 = 3;
@@ skipping 34 matching lines @@
 
   // A type guard should not generate its input at use site, otherwise
   // they would not be alive.
   void visitTypeGuard(HTypeGuard instruction) {}
 
   void visitTypeConversion(HTypeConversion instruction) {
     if (!instruction.isChecked()) {
       generateAtUseSite.add(instruction);
     } else if (instruction.isCheckedModeCheck()) {
       // Checked mode checks compile to code that only use their input
-      // once, so we can safely visit them an try to merge the input.
+      // once, so we can safely visit them and try to merge the input.
       visitInstruction(instruction);
     }
   }
 
   void tryGenerateAtUseSite(HInstruction instruction) {
     if (instruction.isControlFlow()) return;
     generateAtUseSite.add(instruction);
   }
 
   bool isBlockSinglePredecessor(HBasicBlock block) {
@@ skipping 269 matching lines @@
   };
 }
 
 class JSBinaryOperatorPrecedence {
   final int left;
   final int right;
   const JSBinaryOperatorPrecedence(this.left, this.right);
   // All binary operators (excluding assignment) are left associative.
   int get precedence() => left;
 }