Change labeled statement to use visitSubGraph for its body instead of marking its "exit block" spec…

frog/leg/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 generate(WorkItem work, HGraph graph) {
     return measure(() {
@@ skipping 143 matching lines @@
     indent++;  // We are already inside a function.
     subGraph = new SubGraph(graph.entry, graph.exit);
     beginGraph(graph);
     visitBasicBlock(graph.entry);
     endGraph(graph);
   }
 
   void visitSubGraph(SubGraph newSubGraph) {
     SubGraph oldSubGraph = subGraph;
     subGraph = newSubGraph;
-    visitBasicBlock(subGraph.start);
+    iterateBasicBlock(subGraph.start);
     subGraph = oldSubGraph;
   }
 
   String temporary(HInstruction instruction) {
     int id = instruction.id;
     String name = names[id];
     if (name !== null) return name;
 
     String prefix = 't';
     if (!prefixes.containsKey(prefix)) prefixes[prefix] = 0;
@@ skipping 57 matching lines @@
 
   visit(HInstruction node, int expectedPrecedence) {
     int oldPrecedence = this.expectedPrecedence;
     this.expectedPrecedence = expectedPrecedence;
     node.accept(this);
     this.expectedPrecedence = oldPrecedence;
   }
 
   void handleLabeledBlock(HBasicBlock node) {
     HLabeledBlockInformation labeledBlockInfo = node.labeledBlockInformation;
-    if (labeledBlockInfo.start === node) {
-      addIndentation();
-      for (SourceString label in labeledBlockInfo.labels) {
-        addLabel(label);
-        buffer.add(":");
-      }
-      buffer.add("{\n");
-      indent++;
-    } else {
-      assert(labeledBlockInfo.end === node);
-      assert((){
-        // Check that this block is (transitively) dominated by the start block.
-        HBasicBlock block = node;
-        while (block.dominator !== null) {
-          block = block.dominator;
-          if (block === labeledBlockInfo.start) return true;
-        }
-        return false;
-      });
-      indent--;
-      addIndentation();
-      buffer.add("}\n");
+
+    addIndentation();
+    for (SourceString label in labeledBlockInfo.labels) {
+      addLabel(label);
+      buffer.add(":");
     }
+    buffer.add("{\n");
+    indent++;
+
+    visitSubGraph(labeledBlockInfo.body);
+
+    indent--;
+    addIndentation();
+    buffer.add("}\n");
+
+    visitBasicBlock(labeledBlockInfo.joinBlock);
   }
 
 
   visitBasicBlock(HBasicBlock node) {
     if (!subGraph.contains(node)) return;
 
-    currentBlock = node;
-
     if (node.hasLabeledBlockInformation()) {
       handleLabeledBlock(node);
-    } else if (currentBlock.isLoopHeader()) {
+      return;
+    }
+    iterateBasicBlock(node);
+  }
+
+  iterateBasicBlock(HBasicBlock node) {

[ngeoffray, 2012/03/05 14:12:48]

Was this change (adding iterateBasicBlock) necessary? If not, I prefer keeping
one method for now.

[Lasse Reichstein Nielsen, 2012/03/05 14:16:49]

Sadly, yes, something is necessary, but I'm not entirely sure what.
visitBasicBlock calls handleLabeledBlock, which calls visitSubGraph, which calls
back to visitBlock.
To break this loop, I split the main visitBasicBlock into the part that
dispatches on the block annotation and the part that does the real work. But
thinking more about it, I'm not sure it's good enough. If a labeled statement is
a branch of an if, it'll fail. Back to the drawing board. :(

+    currentBlock = node;
+    if (node.isLoopHeader()) {
       // While loop will be closed by the conditional loop-branch.
       // TODO(floitsch): HACK HACK HACK.
       beginLoop(node);
     }
-
     HInstruction instruction = node.first;
     while (instruction != null) {
       if (instruction is HGoto || instruction is HExit || instruction is HTry) {
         visit(instruction, JSPrecedence.STATEMENT_PRECEDENCE);
         return;
       } else if (!instruction.generateAtUseSite()) {
         if (instruction is !HIf && instruction is !HBailoutTarget) {
           addIndentation();
         }
         if (instruction.usedBy.isEmpty() || instruction is HLocal) {
@@ skipping 1108 matching lines @@
       startBailoutSwitch();
     }
   }
 
   void endElse(HIf node) {
     if (node.elseBlock.hasBailouts()) {
       endBailoutSwitch();
     }
   }
 }