Fix bug where a parameter was mutated while it was still used.

lib/compiler/implementation/ssa/codegen.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.
 
 class SsaCodeGeneratorTask extends CompilerTask {
   SsaCodeGeneratorTask(Compiler compiler) : super(compiler);
   String get name() => 'SSA code generator';
 
 
   String generateMethod(WorkItem work, HGraph graph) {
@@ skipping 154 matching lines @@
   }
 
   String temporary(HInstruction instruction) {
     int id = instruction.id;
     String name = names[id];
     if (name !== null) return name;
 
     if (instruction is HPhi) {
       HPhi phi = instruction;
       Element element = phi.element;
-      if (element != null && element.kind == ElementKind.PARAMETER) {
-        name = parameterNames[element];
-        names[id] = name;
-        return name;
-      }
-
       String prefix;
       if (element !== null && !element.name.isEmpty()) {
         prefix = element.name.slowToString();
       } else {
         prefix = 'v';
       }
       if (!prefixes.containsKey(prefix)) {
         prefixes[prefix] = 0;
         return newName(id, prefix);
       } else {
@@ skipping 1370 matching lines @@
       startBailoutSwitch();
     }
   }
 
   void endElse(HIf node) {
     if (node.elseBlock.hasGuards()) {
       endBailoutSwitch();
     }
   }
 }