[generators] Perform state dispatch in loop header.

src/interpreter/bytecode-generator.cc

Index: src/interpreter/bytecode-generator.cc
diff --git a/src/interpreter/bytecode-generator.cc b/src/interpreter/bytecode-generator.cc
index 9148b2d294cc475f96b31372cb7725405d705125..0d85f89daeae349b5d972b2810c027808563ae97 100644
--- a/src/interpreter/bytecode-generator.cc
+++ b/src/interpreter/bytecode-generator.cc
@@ -565,10 +565,8 @@ BytecodeGenerator::BytecodeGenerator(Isolate* isolate, Zone* zone)
       execution_context_(nullptr),
       execution_result_(nullptr),
       register_allocator_(nullptr),
-      generator_resume_points_(0, zone),
       try_catch_nesting_level_(0),
-      try_finally_nesting_level_(0),
-      generator_yields_seen_(0) {
+      try_finally_nesting_level_(0) {
   InitializeAstVisitor(isolate);
 }
 
@@ -641,8 +639,9 @@ void BytecodeGenerator::MakeBytecodeBody() {
 }
 
 void BytecodeGenerator::VisitGeneratorPrologue() {
-  generator_resume_points_.clear();
-  generator_resume_points_.resize(info()->literal()->yield_count());
+  auto& resume_points = builder()->generator_resume_points;
+  resume_points.clear();
+  resume_points.resize(info()->literal()->yield_count());
 
   BytecodeLabel regular_call;
   builder()
@@ -651,23 +650,12 @@ void BytecodeGenerator::VisitGeneratorPrologue() {
 
   // This is a resume call. Restore registers and perform state dispatch.
   // (The current context has already been restored by the trampoline.)
-  {
-    RegisterAllocationScope register_scope(this);
-    Register state = register_allocator()->NewRegister();
-    builder()
-        ->CallRuntime(Runtime::kResumeIgnitionGenerator, Register::new_target(),
-                      1)
-        .StoreAccumulatorInRegister(state);
-
-    // TODO(neis): Optimize this by using a proper jump table.
-    for (size_t i = 0; i < generator_resume_points_.size(); ++i) {
-      builder()
-          ->LoadLiteral(Smi::FromInt(static_cast<int>(i)))
-          .CompareOperation(Token::Value::EQ_STRICT, state)
-          .JumpIfTrue(&(generator_resume_points_[i]));
-    }
-    builder()->Illegal();  // Should never get here.
-  }
+  Register state = Register::new_target();  // HACK

[rmcilroy, 2016/04/19 09:30:03]

Could you allocate an additional local for this purpose in the AST visitor
(similar to the arguments, this_function or new_target variables)? If you did
this then you could store the resume state in that local throughout the
execution. This would be the cleanest solution I think.

Another possibility would be to allocate a temporary register in
BytecodeGenerator::MakeBytecode, and keep the allocator scoped throughout the
whole function generation so that it can be reuse throughout the function, but
I'm not super keen on this since it seems a bit hacky.

[neis, 2016/04/19 11:02:15]

I think I prefer having a dedicated register rather than adding more magic to
the AST (that would only be used by the interpreter).  I will find out what the
other folks think.

+  builder()
+      ->CallRuntime(Runtime::kResumeIgnitionGenerator, Register::new_target(),
+                    1)
+      .StoreAccumulatorInRegister(state)
+      .IndexedJump(state, 0, resume_points.size(), resume_points);
 
   builder()->Bind(&regular_call);
   // This is a regular call. Fall through to the ordinary function prologue,
@@ -1000,7 +988,7 @@ void BytecodeGenerator::VisitIterationBody(IterationStatement* stmt,
 }
 
 void BytecodeGenerator::VisitDoWhileStatement(DoWhileStatement* stmt) {
-  LoopBuilder loop_builder(builder());
+  LoopBuilder loop_builder(builder(), stmt->yield_count());
   loop_builder.LoopHeader();
   if (stmt->cond()->ToBooleanIsFalse()) {
     VisitIterationBody(stmt, &loop_builder);
@@ -1025,7 +1013,7 @@ void BytecodeGenerator::VisitWhileStatement(WhileStatement* stmt) {
     return;
   }
 
-  LoopBuilder loop_builder(builder());
+  LoopBuilder loop_builder(builder(), stmt->yield_count());
   loop_builder.LoopHeader();
   loop_builder.Condition();
   if (!stmt->cond()->ToBooleanIsTrue()) {
@@ -1049,7 +1037,7 @@ void BytecodeGenerator::VisitForStatement(ForStatement* stmt) {
     return;
   }
 
-  LoopBuilder loop_builder(builder());
+  LoopBuilder loop_builder(builder(), stmt->yield_count());
   loop_builder.LoopHeader();
   loop_builder.Condition();
   if (stmt->cond() && !stmt->cond()->ToBooleanIsTrue()) {
@@ -1149,7 +1137,7 @@ void BytecodeGenerator::VisitForInStatement(ForInStatement* stmt) {
     return;
   }
 
-  LoopBuilder loop_builder(builder());
+  LoopBuilder loop_builder(builder(), stmt->yield_count());
   BytecodeLabel subject_null_label, subject_undefined_label;
 
   // Prepare the state for executing ForIn.
@@ -1197,7 +1185,7 @@ void BytecodeGenerator::VisitForInStatement(ForInStatement* stmt) {
 
 
 void BytecodeGenerator::VisitForOfStatement(ForOfStatement* stmt) {
-  LoopBuilder loop_builder(builder());
+  LoopBuilder loop_builder(builder(), stmt->yield_count());
   ControlScopeForIteration control_scope(this, stmt, &loop_builder);
 
   VisitForEffect(stmt->assign_iterator());
@@ -2270,7 +2258,7 @@ void BytecodeGenerator::VisitAssignment(Assignment* expr) {
 }
 
 void BytecodeGenerator::VisitYield(Yield* expr) {
-  int id = generator_yields_seen_++;
+  int id = builder()->incr_generator_yields_seen();
 
   builder()->SetExpressionPosition(expr);
   Register value = VisitForRegisterValue(expr->expression());
@@ -2288,7 +2276,7 @@ void BytecodeGenerator::VisitYield(Yield* expr) {
       .LoadAccumulatorWithRegister(value)
       .Return();  // Hard return (ignore any finally blocks).
 
-  builder()->Bind(&(generator_resume_points_[id]));
+  builder()->Bind(&(builder()->generator_resume_points[id]));
   // Upon resume, we continue here.
 
   {