Simplify generated code for trivial bailout methods.

lib/compiler/implementation/ssa/codegen.dart

Index: lib/compiler/implementation/ssa/codegen.dart
===================================================================
--- lib/compiler/implementation/ssa/codegen.dart	(revision 8591)
+++ lib/compiler/implementation/ssa/codegen.dart	(working copy)
@@ -72,7 +72,6 @@
   String generateBailoutMethod(WorkItem work, HGraph graph) {
     return measure(() {
       compiler.tracer.traceGraph("codegen-bailout", graph);
-      new SsaBailoutPropagator(compiler).visitGraph(graph);
 
       Map<Element, String> parameterNames = getParameterNames(work);
       String parameters = Strings.join(parameterNames.getValues(), ', ');
@@ -80,17 +79,9 @@
           backend, work, parameters, parameterNames);
       codegen.visitGraph(graph);
 
-      StringBuffer newParameters = new StringBuffer();
-      if (!parameterNames.isEmpty()) newParameters.add('$parameters, ');
-      newParameters.add('state');
-
-      for (int i = 0; i < codegen.maxBailoutParameters; i++) {
-        newParameters.add(', env$i');
-      }
-
-      Element element = work.element;
       String body = '${codegen.setup}${codegen.buffer}';
-      return buildJavaScriptFunction(element, newParameters.toString(), body);
+      return buildJavaScriptFunction(
+          work.element, codegen.newParameters.toString(), body);
     });
   }
 
@@ -273,8 +264,8 @@
     currentGraph = graph;
     indent++;  // We are already inside a function.
     subGraph = new SubGraph(graph.entry, graph.exit);
-    beginGraph(graph);
-    visitBasicBlock(graph.entry);
+    HBasicBlock start = beginGraph(graph);
+    visitBasicBlock(start);
     if (!delayedVariableDeclarations.isEmpty()) {
       addIndented("var ");
       buffer.add(Strings.join(
@@ -2463,7 +2454,7 @@
 
   int maxBailoutParameters;
 
-  void beginGraph(HGraph graph) {}
+  HBasicBlock beginGraph(HGraph graph) => graph.entry;
   void endGraph(HGraph graph) {}
 
   void bailout(HTypeGuard guard, String reason) {
@@ -2487,10 +2478,7 @@
     } else {
       buffer.add(namer.isolateBailoutAccess(element));
     }
-    int parametersCount = parameterNames.length;
-    buffer.add('($parameters');
-    if (parametersCount != 0) buffer.add(', ');
-    buffer.add('${guard.state}');
+    buffer.add('(${guard.state}');
     // TODO(ngeoffray): try to put a variable at a deterministic
     // location, so that multiple bailout calls put the variable at
     // the same parameter index.
@@ -2607,13 +2595,18 @@
 class SsaUnoptimizedCodeGenerator extends SsaCodeGenerator {
 
   final StringBuffer setup;
+  final StringBuffer newParameters;
   final List<String> labels;
   int labelId = 0;
   int maxBailoutParameters = 0;
 
+  SsaBailoutPropagator propagator;
+  HInstruction savedFirstInstruction;
+
   SsaUnoptimizedCodeGenerator(backend, work, parameters, parameterNames)
     : super(backend, work, parameters, parameterNames),
       setup = new StringBuffer(),
+      newParameters = new StringBuffer(),
       labels = <String>[];
 
   String pushLabel() {
@@ -2630,38 +2623,33 @@
     return labels.last();
   }
 
-  void beginGraph(HGraph graph) {
-    if (!graph.entry.hasGuards()) return;
-    addIndented('switch (state) {\n');
-    indent++;
-    addIndented('case 0:\n');
-    indent++;
+  HBasicBlock beginGraph(HGraph graph) {
+    propagator = new SsaBailoutPropagator(compiler, generateAtUseSite);
+    propagator.visitGraph(graph);
 
-    // The setup phase of a bailout function sets up the environment for
-    // each bailout target. Each bailout target will populate this
-    // setup phase. It is put at the beginning of the function.
-    setup.add('  switch (state) {\n');
-  }
+    if (propagator.hasComplexTypeGuards) {
+      startBailoutSwitch();
 
-  void endGraph(HGraph graph) {
-    if (!graph.entry.hasGuards()) return;
-    indent--; // Close original case.
-    indent--;
-    addIndented('}\n');  // Close 'switch'.
-    setup.add('  }\n');
+      // The setup phase of a bailout function sets up the environment for
+      // each bailout target. Each bailout target will populate this
+      // setup phase. It is put at the beginning of the function.
+      setup.add('  switch (state) {\n');
+      return graph.entry;
+    } else {
+      // We change the first instruction of the first guard to be the
+      // guard. We will change it back in the call to [endGraph].
+      HBasicBlock block = propagator.firstTypeGuard.block;
+      savedFirstInstruction = block.first;
+      block.first = propagator.firstTypeGuard;
+      return block;
+    }
   }
 
-  bool visitAndOrInfo(HAndOrBlockInformation info) => false;
-  bool visitIfInfo(HIfBlockInformation info) => false;
-  bool visitLoopInfo(HLoopBlockInformation info) => false;
-  bool visitTryInfo(HTryBlockInformation info) => false;
-  bool visitSequenceInfo(HStatementSequenceInformation info) => false;
-
   // If argument is a [HCheck] and it does not have a name, we try to
   // find the name of its checked input. Note that there must be a
   // name, otherwise the instruction would not be in the live
   // environment.
-  HInstruction unwrap(argument) {
+  HInstruction unwrap(HInstruction argument) {
     while (argument is HCheck && !variableNames.hasName(argument)) {
       argument = argument.checkedInput;
     }
@@ -2669,7 +2657,48 @@
     return argument;
   }
 
+  void endGraph(HGraph graph) {
+    // TODO(ngeoffray): We could avoid generating the state at the
+    // call site for non-complex bailout methods.
+    newParameters.add('state');
+
+    if (!propagator.hasComplexTypeGuards) {
+      propagator.firstTypeGuard.block.first = savedFirstInstruction;
+      for (HInstruction input in propagator.firstTypeGuard.inputs) {
+        input = unwrap(input);
+        newParameters.add(', ${variableNames.getName(input)}');
+      }
+    } else {
+      for (int i = 0; i < maxBailoutParameters; i++) {
+        newParameters.add(', env$i');
+      }
+      indent--; // Close original case.
+      indent--;
+      addIndented('}\n');  // Close 'switch'.
+      setup.add('  }\n');
+    }
+  }
+
+  bool visitAndOrInfo(HAndOrBlockInformation info) => false;
+
+  bool visitIfInfo(HIfBlockInformation info) {
+    if (info.thenGraph.start.hasGuards()) return false;
+    if (info.elseGraph.start.hasGuards()) return false;
+    return super.visitIfInfo(info);
+  }
+
+  bool visitLoopInfo(HLoopBlockInformation info) {
+    if (info.start.hasGuards()) return false;
+    if (info.loopHeader.hasGuards()) return false;
+    return super.visitLoopInfo(info);
+  }
+
+  bool visitTryInfo(HTryBlockInformation info) => false;
+  bool visitSequenceInfo(HStatementSequenceInformation info) => false;
+
   void visitTypeGuard(HTypeGuard node) {
+    if (!propagator.hasComplexTypeGuards) return;
+
     indent--;
     addIndented('case ${node.state}:\n');
     indent++;
@@ -2678,8 +2707,9 @@
     setup.add('    case ${node.state}:\n');
     int i = 0;
     for (HInstruction input in node.inputs) {
-      HInstruction instruction = unwrap(input);
-      setup.add('      ${variableNames.getName(instruction)} = env$i;\n');
+      input = unwrap(input);
+      String name = variableNames.getName(input);
+      setup.add('      $name = env$i;\n');
       i++;
     }
     if (i > maxBailoutParameters) maxBailoutParameters = i;
@@ -2714,7 +2744,6 @@
   }
 
   void beginLoop(HBasicBlock block) {
-    // TODO(ngeoffray): Don't put labels on loops that don't bailout.
     String newLabel = pushLabel();
     if (block.hasGuards()) {
       startBailoutCase(block.guards, const <HTypeGuard>[]);