Added VariableUse expression to tree IR.

pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart

Index: pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart
diff --git a/pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart b/pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart
index 3181b59be3448c22e0a9d4ccfecf4ca6c5606f53..2cb82d4669ea05b9bbdd40b4e656de25763463d8 100644
--- a/pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart
+++ b/pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart
@@ -82,14 +82,17 @@ class Builder extends cps_ir.Visitor<Node> {
     return variable;
   }
 
-  Variable getMutableVariableReference(
-        cps_ir.Reference<cps_ir.MutableVariable> reference) {
-    if (reference.definition.host != currentElement) {
-      return parent.getMutableVariableReference(reference);
+  Variable getMutableVariable(cps_ir.MutableVariable mutableVariable) {
+    if (mutableVariable.host != currentElement) {
+      return parent.getMutableVariable(mutableVariable);
     }
-    Variable variable = local2mutable[reference.definition];
-    ++variable.readCount;
-    return variable;
+    return local2mutable[mutableVariable];
+  }
+
+  VariableUse getMutableVariableReference(

[Kevin Millikin (Google), 2015/02/26 12:43:18]

There's probably no good reason to use Reference in the function name and Use in
the return type.  At least, I don't appreciate the distinction here.  We should
stick to one or the other.  Use is fine (it's shorter) if you like it.

[asgerf, 2015/02/27 12:05:19]

Done.

+        cps_ir.Reference<cps_ir.MutableVariable> reference) {
+    Variable variable = getMutableVariable(reference.definition);
+    return new VariableUse(variable);
   }
 
   /// Obtains the variable representing the given primitive. Returns null for
@@ -117,8 +120,7 @@ class Builder extends cps_ir.Visitor<Node> {
           CURRENT_ELEMENT_SPANNABLE,
           "Reference to ${reference.definition} has no register");
     }
-    ++variable.readCount;
-    return variable;
+    return new VariableUse(variable);
   }
 
   ExecutableDefinition build(cps_ir.ExecutableDefinition node) {
@@ -159,14 +161,8 @@ class Builder extends cps_ir.Visitor<Node> {
 
   FunctionDefinition buildFunction(cps_ir.FunctionDefinition node) {
     currentElement = node.element;
-    List<Variable> parameters = <Variable>[];
-    for (cps_ir.Definition p in node.parameters) {
-      Variable parameter = addFunctionParameter(p);
-      assert(parameter != null);
-      ++parameter.writeCount; // Being a parameter counts as a write.
-      parameters.add(parameter);
-    }
-
+    List<Variable> parameters =
+        node.parameters.map(addFunctionParameter).toList();
     Statement body;
     if (!node.isAbstract) {
       returnContinuation = node.body.returnContinuation;
@@ -180,13 +176,8 @@ class Builder extends cps_ir.Visitor<Node> {
 
   ConstructorDefinition buildConstructor(cps_ir.ConstructorDefinition node) {
     currentElement = node.element;
-    List<Variable> parameters = <Variable>[];
-    for (cps_ir.Definition p in node.parameters) {
-      Variable parameter = addFunctionParameter(p);
-      assert(parameter != null);
-      ++parameter.writeCount; // Being a parameter counts as a write.
-      parameters.add(parameter);
-    }
+    List<Variable> parameters =
+        node.parameters.map(addFunctionParameter).toList();
     List<Initializer> initializers;
     Statement body;
     if (!node.isAbstract) {
@@ -271,12 +262,10 @@ class Builder extends cps_ir.Visitor<Node> {
 
     Statement first, current;
     void addAssignment(Variable dst, Variable src) {
-      ++src.readCount;
-      // `dst.writeCount` will be updated by the Assign constructor.
       if (first == null) {
-        first = current = new Assign(dst, src, null);
+        first = current = new Assign(dst, new VariableUse(src), null);
       } else {
-        current = current.next = new Assign(dst, src, null);
+        current = current.next = new Assign(dst, new VariableUse(src), null);
       }
     }
 
@@ -454,7 +443,7 @@ class Builder extends cps_ir.Visitor<Node> {
   }
 
   Statement visitSetMutableVariable(cps_ir.SetMutableVariable node) {
-    Variable variable = getMutableVariableReference(node.variable);
+    Variable variable = getMutableVariable(node.variable.definition);
     Expression value = getVariableReference(node.value);
     return new Assign(variable, value, visit(node.body));
   }
@@ -490,7 +479,7 @@ class Builder extends cps_ir.Visitor<Node> {
       assert(node.arguments.length == 1);
       return new Return(getVariableReference(node.arguments.single));
     } else {
-      List<Expression> arguments = translatePhiArguments(node.arguments);
+      List<Variable> arguments = translatePhiArguments(node.arguments);
       return buildPhiAssignments(cont.parameters, arguments,
           () {
             // Translate invocations of recursive and non-recursive