Codegen support for the argument definition test.

lib/compiler/implementation/ssa/builder.dart

Index: lib/compiler/implementation/ssa/builder.dart
===================================================================
--- lib/compiler/implementation/ssa/builder.dart	(revision 11792)
+++ lib/compiler/implementation/ssa/builder.dart	(working copy)
@@ -806,13 +806,14 @@
   LocalsHandler localsHandler;
   HInstruction rethrowableException;
   Map<Element, HParameterValue> parameters;
+  Map<Element, HInstruction> parametersWithSentinel;
 
   Map<TargetElement, JumpHandler> jumpTargets;
 
   /**
    * Variables stored in the current activation. These variables are
    * being updated in try/catch blocks, and should be
-   * accessed indirectly through HFieldGet and HFieldSet.
+   * accessed indirectly through [HLocalGet] and [HLocalSet].
    */
   Map<Element, HLocalValue> activationVariables;
 
@@ -841,6 +842,7 @@
       activationVariables = new Map<Element, HLocalValue>(),
       jumpTargets = new Map<TargetElement, JumpHandler>(),
       parameters = new Map<Element, HParameterValue>(),
+      parametersWithSentinel = new Map<Element, HInstruction>(),
       inliningStack = <InliningState>[],
       super(work.resolutionTree) {
     localsHandler = new LocalsHandler(this);
@@ -1226,6 +1228,59 @@
     return closeFunction();
   }
 
+  void addParameterCheckInstruction(Element element) {
+    // This is the code we emit for a parameter that is being checked
+    // on whether it was given at value at the call site:
+    //
+    // foo([a = 42) {
+    //   if (?a) print('parameter passed $a');
+    // }
+    //
+    // foo([a = 42]) {
+    //   var t1 = a === sentinel;
+    //   if (t1) a = 42;
+    //   if (!t1) print('parameter passed ' + a);
+    // }
+
+    // Fetch the original default value of [element];
+    ConstantHandler handler = compiler.constantHandler;
+    Constant constant = handler.compileVariable(element);
+    HConstant defaultValue = constant == null
+        ? graph.addConstantNull()
+        : graph.addConstant(constant);
+
+    // Emit the equality check with the sentinel.
+    HConstant sentinel = graph.addConstant(SentinelConstant.SENTINEL);
+    Element equalsHelper = interceptors.getTripleEqualsInterceptor();
+    HInstruction target = new HStatic(equalsHelper);
+    add(target);
+    HInstruction operand = parameters[element];
+    HInstruction check = new HIdentity(target, sentinel, operand);
+    add(check);
+
+    // If the check succeeds, we must update the parameter with the
+    // default value.
+    handleIf(element.parseNode(compiler),
+             () => stack.add(check),
+             () => localsHandler.updateLocal(element, defaultValue),
+             null);
+
+    // Create the instruction that parameter checks will use.
+    check = new HNot(check);
+    add(check);
+
+    // If the parameter check is also used by closures,
+    // we need to update the closure field holding that check.
+    ClosureClassMap closureData = localsHandler.closureData;
+    Element redirect = closureData.parametersWithSentinel[element];
+    if (redirect != null) {
+      localsHandler.updateLocal(redirect, check);
+    }
+    // Cache the check so that uses in this method share the same
+    // check instruction.
+    parametersWithSentinel[element] = check;
+  }
+
   void openFunction(FunctionElement functionElement,
                     FunctionExpression node) {
     HBasicBlock block = graph.addNewBlock();
@@ -1236,11 +1291,17 @@
 
     open(block);
 
+    FunctionSignature params = functionElement.computeSignature(compiler);
+    params.forEachParameter((Element element) {
+      if (elements.isParameterChecked(element)) {
+        addParameterCheckInstruction(element);
+      }
+    });
+
     // Put the type checks in the first successor of the entry,
     // because that is where the type guards will also be inserted.
     // This way we ensure that a type guard will dominate the type
     // check.
-    FunctionSignature params = functionElement.computeSignature(compiler);
     params.forEachParameter((Element element) {
       HInstruction newParameter = potentiallyCheckType(
           localsHandler.directLocals[element], element);
@@ -1780,8 +1841,24 @@
   void visitUnary(Send node, Operator op) {
     String value = op.source.stringValue;
     if (value === '?') {

[kasperl, 2012/09/04 10:50:08]

node.isParameterCheck?

[ngeoffray, 2012/09/04 10:53:44]

Done.

-      // TODO(ahe): Implement argument definition test.
-      stack.add(graph.addConstantBool(true));
+      Element element = elements[node.receiver];
+      // If the parameter we're accessing is from the current
+      // function, we can just fetch the cached instruction.
+      HInstruction check = parametersWithSentinel[element];
+      if (check !== null) {
+        stack.add(check);
+      } else {
+        // The parameter is from an outer function. Lookup the
+        // element in the closure data of the outer function and read
+        // it.
+        assert(element.enclosingElement != work.element);
+        Node node = element.enclosingElement.parseNode(compiler);
+        ClosureClassMap parameterClosureData =
+            compiler.closureToClassMapper.getMappingForNestedFunction(node);
+        Element fieldCheck =
+            parameterClosureData.parametersWithSentinel[element];
+        stack.add(localsHandler.readLocal(fieldCheck));
+      }
       return;
     }
     assert(node.argumentsNode is Prefix);
@@ -2165,8 +2242,15 @@
       return pop();
     }
 
-    HInstruction compileConstant(Element constantElement) {
-      Constant constant = compiler.compileVariable(constantElement);
+    HInstruction compileConstant(Element parameter) {
+      Constant constant;
+      TreeElements calleeElements =
+          compiler.enqueuer.resolution.getCachedElements(element);
+      if (calleeElements.isParameterChecked(parameter)) {
+        constant = SentinelConstant.SENTINEL;
+      } else {
+        constant = compiler.compileVariable(parameter);
+      }
       return graph.addConstant(constant);
     }
 
@@ -3669,7 +3753,11 @@
     tooDifficult = true;
   }
 
-  void visitSend(Node node) {
+  void visitSend(Send node) {
+    if (node.isParameterCheck) {
+      tooDifficult = true;
+      return;
+    }
     node.visitChildren(this);
   }