Implement constant switch as JS switch.

lib/compiler/implementation/ssa/builder.dart

Index: lib/compiler/implementation/ssa/builder.dart
diff --git a/lib/compiler/implementation/ssa/builder.dart b/lib/compiler/implementation/ssa/builder.dart
index 53aacdd1fe8c8884ba66ad2fce96aac676ae5162..395a634f5099a5c376c1586e2674793fc0888c75 100644
--- a/lib/compiler/implementation/ssa/builder.dart
+++ b/lib/compiler/implementation/ssa/builder.dart
@@ -2941,6 +2941,8 @@ class SsaBuilder implements Visitor {
   }
 
   visitSwitchStatement(SwitchStatement node) {
+    if (tryBuildConstantSwitch(node)) return;
+
     LocalsHandler savedLocals = new LocalsHandler.from(localsHandler);
     HBasicBlock startBlock = openNewBlock();
     visit(node.expression);
@@ -2948,8 +2950,8 @@ class SsaBuilder implements Visitor {
     if (node.cases.isEmpty()) {
       return;
     }
-    Link<Node> cases = node.cases.nodes;
 
+    Link<Node> cases = node.cases.nodes;
     JumpHandler jumpHandler = createJumpHandler(node);
 
     buildSwitchCases(cases, expression);
@@ -2990,10 +2992,134 @@ class SsaBuilder implements Visitor {
     jumpHandler.close();
   }
 
+  bool tryBuildConstantSwitch(SwitchStatement node) {
+    Map<CaseMatch, Constant> constants = new Map<CaseMatch, Constant>();
+    // First check whether all case expressions are compile-time constants.
+    for (SwitchCase switchCase in node.cases) {
+      for (Node labelOrCase in switchCase.labelsAndCases) {
+        if (labelOrCase is CaseMatch) {
+          CaseMatch match = labelOrCase;
+          Constant constant =
+            compiler.constantHandler.tryCompileNodeWithDefinitions(
+                match.expression, elements);
+          if (constant === null) return false;
+          constants[labelOrCase] = constant;
+        } else {
+          // We don't handle labels yet.
+          return false;
+        }
+      }
+    }
+    // TODO(ngeoffray): Handle switch-instruction in bailout code.

[Lasse Reichstein Nielsen, 2012/06/06 09:29:31]

I hope it's simple if you know how :)

+    work.allowSpeculativeOptimization = false;
+    // Then build a switch structure.
+    HBasicBlock expressionStart = openNewBlock();
+    visit(node.expression);
+    HInstruction expression = pop();
+    if (node.cases.isEmpty()) {
+      return true;
+    }
+    HBasicBlock expressionEnd = current;
+
+    HSwitch switchInstruction = new HSwitch(<HInstruction>[expression]);
+    HBasicBlock expressionBlock = close(switchInstruction);
+    JumpHandler jumpHandler = createJumpHandler(node);
+    LocalsHandler savedLocals = localsHandler;
+
+    List<List<Constant>> matchExpressions = <List<Constant>>[];
+    List<HStatementInformation> statements = <HStatementInformation>[];
+    bool hasDefault = false;
+    for (Iterator<Node> iterator = node.cases.iterator(); iterator.hasNext();) {

[floitsch, 2012/06/06 11:50:26]

I would prefer a while loop.

[Lasse Reichstein Nielsen, 2012/06/06 13:01:21]

Done.

+      SwitchCase switchCase = iterator.next();
+      List<Constant> caseConstants = <Constant>[];
+      HBasicBlock block = graph.addNewBlock();
+      for (Node labelOrCase in switchCase.labelsAndCases) {
+        if (labelOrCase is CaseMatch) {

[floitsch, 2012/06/06 11:50:26]

At the moment an assert would work too here, no?

[Lasse Reichstein Nielsen, 2012/06/06 13:01:21]

No, we still parse the labels, we just don't do anything with them.

[floitsch, 2012/06/06 14:32:01]

But isn't there a "return false" in line 3009 for this?

[Lasse Reichstein Nielsen, 2012/06/07 12:03:05]

True, there is. Let's not make the assumption in more than one place.

+          Constant constant = constants[labelOrCase];
+          caseConstants.add(constant);
+          HConstant hConstant = graph.addConstant(constant);
+          switchInstruction.inputs.add(hConstant);
+          hConstant.usedBy.add(switchInstruction);
+          expressionBlock.addSuccessor(block);
+        }
+      }
+      matchExpressions.add(caseConstants);
+
+      if (switchCase.isDefaultCase) {
+        // An HSwitch has n inputs and n+1 successors, the last being the
+        // default case.
+        expressionBlock.addSuccessor(block);
+        hasDefault = true;
+      }
+      open(block);
+      localsHandler = new LocalsHandler.from(savedLocals);
+      visit(switchCase.statements);
+      if (!isAborted() && iterator.hasNext()) {
+        compiler.reportWarning(node, 'Missing break at end of switch case');

[ngeoffray, 2012/06/06 12:03:46]

I don't think the codegen should emit a warning.

[Lasse Reichstein Nielsen, 2012/06/06 13:01:21]

True. Something earlier should do that. 
I'll remove it here, and leave it to someone else to add it where it belongs :)

+        Element element =
+            compiler.findHelper(const SourceString("getFallThroughError"));

[ngeoffray, 2012/06/06 12:03:46]

Maybe move that call out of the loop?

[Lasse Reichstein Nielsen, 2012/06/06 13:01:21]

Reasonable. Done.

+        push(new HStatic(element));
+        HInstruction error = new HInvokeStatic(
+             Selector.INVOCATION_0, <HInstruction>[pop()]);
+        add(error);
+        close(new HThrow(error));
+      }
+      statements.add(
+          new HSubGraphBlockInformation(new SubGraph(block, lastOpenedBlock)));
+    }
+
+    // Add a join-block if necessary.
+    HBasicBlock joinBlock = new HBasicBlock();
+    List<LocalsHandler> caseLocals = <LocalsHandler>[];
+    jumpHandler.forEachBreak((HBreak instruction, LocalsHandler locals) {
+      instruction.block.addSuccessor(joinBlock);
+      caseLocals.add(locals);
+    });
+    if (!isAborted()) {

[ngeoffray, 2012/06/06 12:03:46]

Should this check be in the one line 3090? You're adding joinBlock as a
successor, but if we fail check 3090 the joinBlock will not be inserted in the
graph.

[Lasse Reichstein Nielsen, 2012/06/06 13:01:21]

If this test succeedes, it adds an element to caseLocals, so the test in 3090
will succeede. I'll add a comment and assert that  caseLocals.length ==
joinBlock.predecessors.length .

+      current.close(new HGoto());
+      lastOpenedBlock.addSuccessor(joinBlock);
+      caseLocals.add(localsHandler);
+    }
+    if (!hasDefault) {

[ngeoffray, 2012/06/06 12:03:46]

ditto

[Lasse Reichstein Nielsen, 2012/06/06 13:01:21]

And ditto.

+      // The current flow is only aborted if the switch has a default that
+      // aborts (all previous cases must abort, and if there is no default,
+      // it's possible to miss all the cases).
+      expressionEnd.addSuccessor(joinBlock);
+      caseLocals.add(savedLocals);
+    }
+    if (caseLocals.length != 0) {
+      graph.addBlock(joinBlock);
+      open(joinBlock);
+      if (caseLocals.length == 1) {
+        localsHandler = caseLocals[0];
+      } else {
+        localsHandler = savedLocals.mergeMultiple(caseLocals, joinBlock);
+      }
+    } else {
+      // The joinblock is not used.
+      joinBlock = null;
+    }
+
+    HSubExpressionBlockInformation expressionInfo =
+        new HSubExpressionBlockInformation(new SubExpression(expressionStart,
+                                                             expressionEnd));
+    expressionStart.setBlockFlow(
+        new HSwitchBlockInformation(expressionInfo,
+                                    matchExpressions,
+                                    statements,
+                                    hasDefault,
+                                    jumpHandler.target,
+                                    jumpHandler.labels()),
+        joinBlock);
+
+    jumpHandler.close();
+    return true;
+  }
+
 
   // Recursively build an if/else structure to match the cases.
-  buildSwitchCases(Link<Node> cases, HInstruction expression,
-                   [int encounteredCaseTypes = 0]) {
+  void buildSwitchCases(Link<Node> cases, HInstruction expression,
+                        [int encounteredCaseTypes = 0]) {
     final int NO_TYPE = 0;
     final int INT_TYPE = 1;
     final int STRING_TYPE = 2;