dart2dart: Preserve variable names throughout the IR.

sdk/lib/_internal/compiler/implementation/ir/ir_tracer.dart

 // Copyright (c) 2014, 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.
 
 library dart2js.ir_tracer;
 
 import 'dart:async' show EventSink;
 
 import 'ir_nodes.dart' as ir hide Function;
 import '../tracer.dart';
@@ skipping 26 matching lines @@
     BlockCollector builder = new BlockCollector(names);
     builder.visit(f);
 
     printNode(builder.entry);
     for (Block block in builder.cont2block.values) {
       printNode(block);
     }
     names = null;
   }
 
+  int countUses(ir.Definition definition) {
+    int count = 0;
+    ir.Reference ref = definition.firstRef;
+    while (ref != null) {
+      ++count;
+      ref = ref.nextRef;
+    }
+    return count;
+  }
+
   printNode(Block block) {
     tag("block", () {
       printProperty("name", block.name);
       printProperty("from_bci", -1);
       printProperty("to_bci", -1);
       printProperty("predecessors", block.pred.map((n) => n.name));
       printProperty("successors", block.succ.map((n) => n.name));
       printEmptyProperty("xhandlers");
       printEmptyProperty("flags");
       tag("states", () {
         tag("locals", () {
           printProperty("size", 0);
           printProperty("method", "None");
-          // We could print parameters here,
-          // but does the hydra tool actually use this info??
         });
       });
       tag("HIR", () {
+        for (ir.Parameter param in block.parameters) {
+          String name = names.name(param);
+          printStmt(name, "Parameter $name [useCount=${countUses(param)}]");
+        }
         visit(block.body);
       });
     });
   }
 
   void printStmt(String resultVar, String contents) {
     int bci = 0;
     int uses = 0;
     addIndent();
     add("$bci $uses $resultVar $contents <|@\n");
@@ skipping 109 matching lines @@
 
   visitParameter(ir.Parameter node) {
     return "Parameter ${names.name(node)}";
   }
 
   visitContinuation(ir.Continuation node) {
     return "Continuation ${names.name(node)}";
   }
 
   visitIsTrue(ir.IsTrue node) {
-    return "IsTrue(${names.name(node)})";
+    return "IsTrue(${names.name(node.value.definition)})";
   }
 
   visitCondition(ir.Condition c) {}
   visitExpression(ir.Expression e) {}
   visitPrimitive(ir.Primitive p) {}
   visitDefinition(ir.Definition d) {}
   visitNode(ir.Node n) {}
 }
 
 /**
@@ skipping 124 matching lines @@
     }
   }
 
   visitContinuation(ir.Continuation c) {
     var old_node = current_block;
     current_block = getBlock(c);
     visit(c.body);
     current_block = old_node;
   }
 }