[generators] Perform state dispatch in loop header.

src/interpreter/bytecode-generator.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/interpreter/bytecode-generator.h"
 
 #include "src/ast/scopes.h"
 #include "src/compiler.h"
 #include "src/interpreter/bytecode-register-allocator.h"
 #include "src/interpreter/control-flow-builders.h"
@@ skipping 547 matching lines @@
     : isolate_(isolate),
       zone_(zone),
       builder_(nullptr),
       info_(nullptr),
       scope_(nullptr),
       globals_(0, zone),
       execution_control_(nullptr),
       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);
 }
 
 Handle<BytecodeArray> BytecodeGenerator::MakeBytecode(CompilationInfo* info) {
   set_info(info);
   set_scope(info->scope());
 
   // Initialize bytecode array builder.
   set_builder(new (zone()) BytecodeArrayBuilder(
       isolate(), zone(), info->num_parameters_including_this(),
@@ skipping 52 matching lines @@
   VisitDeclarations(scope()->declarations());
 
   // Perform a stack-check before the body.
   builder()->StackCheck();
 
   // Visit statements in the function body.
   VisitStatements(info()->literal()->body());
 }
 
 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()
       ->LoadAccumulatorWithRegister(Register::new_target())
       .JumpIfUndefined(&regular_call);
 
   // 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,
   // after which we will run into the generator object creation and the initial
   // yield (both inserted by the parser).
 }
 
 void BytecodeGenerator::VisitBlock(Block* stmt) {
   // Visit declarations and statements.
   if (stmt->scope() != nullptr && stmt->scope()->NeedsContext()) {
@@ skipping 312 matching lines @@
 }
 
 void BytecodeGenerator::VisitIterationBody(IterationStatement* stmt,
                                            LoopBuilder* loop_builder) {
   ControlScopeForIteration execution_control(this, stmt, loop_builder);
   builder()->StackCheck();
   Visit(stmt->body());
 }
 
 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);
     loop_builder.Condition();
   } else if (stmt->cond()->ToBooleanIsTrue()) {
     loop_builder.Condition();
     VisitIterationBody(stmt, &loop_builder);
     loop_builder.JumpToHeader();
   } else {
     VisitIterationBody(stmt, &loop_builder);
     loop_builder.Condition();
     builder()->SetExpressionAsStatementPosition(stmt->cond());
     VisitForAccumulatorValue(stmt->cond());
     loop_builder.JumpToHeaderIfTrue();
   }
   loop_builder.EndLoop();
 }
 
 void BytecodeGenerator::VisitWhileStatement(WhileStatement* stmt) {
   if (stmt->cond()->ToBooleanIsFalse()) {
     // If the condition is false there is no need to generate the loop.
     return;
   }
 
-  LoopBuilder loop_builder(builder());
+  LoopBuilder loop_builder(builder(), stmt->yield_count());
   loop_builder.LoopHeader();
   loop_builder.Condition();
   if (!stmt->cond()->ToBooleanIsTrue()) {
     builder()->SetExpressionAsStatementPosition(stmt->cond());
     VisitForAccumulatorValue(stmt->cond());
     loop_builder.BreakIfFalse();
   }
   VisitIterationBody(stmt, &loop_builder);
   loop_builder.JumpToHeader();
   loop_builder.EndLoop();
 }
 
 
 void BytecodeGenerator::VisitForStatement(ForStatement* stmt) {
   if (stmt->init() != nullptr) {
     Visit(stmt->init());
   }
   if (stmt->cond() && stmt->cond()->ToBooleanIsFalse()) {
     // If the condition is known to be false there is no need to generate
     // body, next or condition blocks. Init block should be generated.
     return;
   }
 
-  LoopBuilder loop_builder(builder());
+  LoopBuilder loop_builder(builder(), stmt->yield_count());
   loop_builder.LoopHeader();
   loop_builder.Condition();
   if (stmt->cond() && !stmt->cond()->ToBooleanIsTrue()) {
     builder()->SetExpressionAsStatementPosition(stmt->cond());
     VisitForAccumulatorValue(stmt->cond());
     loop_builder.BreakIfFalse();
   }
   VisitIterationBody(stmt, &loop_builder);
   if (stmt->next() != nullptr) {
     loop_builder.Next();
@@ skipping 79 matching lines @@
 }
 
 
 void BytecodeGenerator::VisitForInStatement(ForInStatement* stmt) {
   if (stmt->subject()->IsNullLiteral() ||
       stmt->subject()->IsUndefinedLiteral()) {
     // ForIn generates lots of code, skip if it wouldn't produce any effects.
     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.
   builder()->SetExpressionAsStatementPosition(stmt->subject());
   VisitForAccumulatorValue(stmt->subject());
   builder()->JumpIfUndefined(&subject_undefined_label);
   builder()->JumpIfNull(&subject_null_label);
   Register receiver = register_allocator()->NewRegister();
   builder()->CastAccumulatorToJSObject();
   builder()->StoreAccumulatorInRegister(receiver);
@@ skipping 27 matching lines @@
   builder()->ForInStep(index);
   builder()->StoreAccumulatorInRegister(index);
   loop_builder.JumpToHeader();
   loop_builder.EndLoop();
   builder()->Bind(&subject_null_label);
   builder()->Bind(&subject_undefined_label);
 }
 
 
 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());
 
   loop_builder.LoopHeader();
   loop_builder.Next();
   builder()->SetExpressionAsStatementPosition(stmt->next_result());
   VisitForEffect(stmt->next_result());
   VisitForAccumulatorValue(stmt->result_done());
   loop_builder.BreakIfTrue();
@@ skipping 1052 matching lines @@
     case KEYED_SUPER_PROPERTY: {
       builder()->StoreAccumulatorInRegister(value);
       BuildKeyedSuperPropertyStore(object, home_object, key, value);
       break;
     }
   }
   execution_result()->SetResultInAccumulator();
 }
 
 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());
 
   register_allocator()->PrepareForConsecutiveAllocations(2);
   Register generator = register_allocator()->NextConsecutiveRegister();
   Register state = register_allocator()->NextConsecutiveRegister();
 
   // Save context, registers, and state. Then return.
   VisitForRegisterValue(expr->generator_object(), generator);
   builder()
       ->LoadLiteral(Smi::FromInt(id))
       .StoreAccumulatorInRegister(state)
       .CallRuntime(Runtime::kSuspendIgnitionGenerator, generator, 2)
       .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.
 
   {
     RegisterAllocationScope register_scope(this);
 
     Register input = register_allocator()->NewRegister();
     builder()
         ->CallRuntime(Runtime::kGeneratorGetInput, generator, 1)
         .StoreAccumulatorInRegister(input);
 
@@ skipping 972 matching lines @@
 }
 
 
 int BytecodeGenerator::feedback_index(FeedbackVectorSlot slot) const {
   return info()->shared_info()->feedback_vector()->GetIndex(slot);
 }
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8