[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 551 matching lines @@
           info->scope()->MaxNestedContextChainLength(),
           info->scope()->num_stack_slots(), info->literal())),
       info_(info),
       scope_(info->scope()),
       globals_(0, info->zone()),
       execution_control_(nullptr),
       execution_context_(nullptr),
       execution_result_(nullptr),
       register_allocator_(nullptr),
       generator_resume_points_(info->literal()->yield_count(), info->zone()),
+      generator_state_(),
+      generator_yields_seen_(0),
       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() {
   // Initialize the incoming context.
   ContextScope incoming_context(this, scope(), false);
 
   // Initialize control scope.
   ControlScopeForTopLevel control(this);
 
+  RegisterAllocationScope register_scope(this);
+
   if (IsGeneratorFunction(info()->literal()->kind())) {
+    generator_state_ = register_allocator()->NewRegister();
     VisitGeneratorPrologue();
   }
 
   // Build function context only if there are context allocated variables.
   if (scope()->NeedsContext()) {
     // Push a new inner context scope for the function.
     VisitNewLocalFunctionContext();
     ContextScope local_function_context(this, scope(), false);
     VisitBuildLocalActivationContext();
     MakeBytecodeBody();
@@ skipping 29 matching lines @@
   // Visit declarations within the function scope.
   VisitDeclarations(scope()->declarations());
 
   // Perform a stack-check before the body.
   builder()->StackCheck();
 
   // Visit statements in the function body.
   VisitStatements(info()->literal()->body());
 }
 
+void BytecodeGenerator::BuildIndexedJump(Register index, int min, size_t size,

[rmcilroy, 2016/04/27 11:02:26]

nit /s/min/start_index/

[neis, 2016/04/27 12:01:25]

Done.

+                                         ZoneVector<BytecodeLabel>& targets) {
+  // TODO(neis): Optimize this by using a proper jump table.
+  for (int i = min; i < min + static_cast<int>(size); i++) {
+    DCHECK(0 <= i && i < static_cast<int>(targets.size()));
+    builder()
+        ->LoadLiteral(Smi::FromInt(i))
+        .CompareOperation(Token::Value::EQ_STRICT, index)
+        .JumpIfTrue(&(targets[i]));
+  }
+  builder()->Illegal();  // Should never get here.
+}
+
+void BytecodeGenerator::VisitIterationHeader(IterationStatement* stmt,
+                                             LoopBuilder* loop_builder) {
+  // Collect all labels for generator resume points within the loop (if any) so
+  // that they can be bound to the loop header below. Also create fresh labels
+  // for these resume points, to be used inside the loop.
+  ZoneVector<BytecodeLabel> resume_points_in_loop(zone());
+  for (int id = generator_yields_seen_;
+       id < generator_yields_seen_ + static_cast<int>(stmt->yield_count());

[rmcilroy, 2016/04/27 11:02:26]

How about making generator_yields_seen_ and id size_t to avoid the casting here?

[neis, 2016/04/27 12:01:25]

Done. Had to cast elsewhere though.

+       id++) {
+    DCHECK(0 <= id && id < static_cast<int>(generator_resume_points_.size()));
+    auto& label = generator_resume_points_[id];
+    resume_points_in_loop.push_back(label);
+    generator_resume_points_[id] = BytecodeLabel();
+  }
+
+  loop_builder->LoopHeader(&resume_points_in_loop);
+
+  if (stmt->yield_count() > 0) {
+    // If we are not resuming, fall through to loop body.
+    // If we are resuming, perform state dispatch.
+    BytecodeLabel not_resuming;
+    builder()
+        ->LoadLiteral(Smi::FromInt(JSGeneratorObject::kGeneratorExecuting))
+        .CompareOperation(Token::Value::EQ, generator_state_)
+        .JumpIfTrue(&not_resuming);
+    BuildIndexedJump(generator_state_, generator_yields_seen_,
+                     stmt->yield_count(), generator_resume_points_);
+    builder()->Bind(&not_resuming);
+  }
+}
+
 void BytecodeGenerator::VisitGeneratorPrologue() {
+  Register generator_object = Register::new_target();

[rmcilroy, 2016/04/27 11:02:26]

nit - could you add a comment here that generator functions use the new_target
register for passing the generator object since they can never be called as a
constructor.

[neis, 2016/04/27 12:01:26]

Done.

+
   BytecodeLabel regular_call;
   builder()
-      ->LoadAccumulatorWithRegister(Register::new_target())
+      ->LoadAccumulatorWithRegister(generator_object)
       .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()
-        ->ResumeGenerator(Register::new_target())
-        .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.
-  }
+  builder()
+      ->ResumeGenerator(generator_object)
+      .StoreAccumulatorInRegister(generator_state_);
+  BuildIndexedJump(generator_state_, 0, generator_resume_points_.size(),
+                   generator_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 313 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());
-  loop_builder.LoopHeader();
+  VisitIterationHeader(stmt, &loop_builder);
   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());
-  loop_builder.LoopHeader();
+  VisitIterationHeader(stmt, &loop_builder);
   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());
-  loop_builder.LoopHeader();
+  VisitIterationHeader(stmt, &loop_builder);
   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();
     builder()->SetStatementPosition(stmt->next());
@@ skipping 104 matching lines @@
   // Used as kRegTriple and kRegPair in ForInPrepare and ForInNext.
   USE(cache_array);
   builder()->ForInPrepare(cache_type);
 
   // Set up loop counter
   Register index = register_allocator()->NewRegister();
   builder()->LoadLiteral(Smi::FromInt(0));
   builder()->StoreAccumulatorInRegister(index);
 
   // The loop
-  loop_builder.LoopHeader();
+  VisitIterationHeader(stmt, &loop_builder);
   builder()->SetExpressionAsStatementPosition(stmt->each());
   loop_builder.Condition();
   builder()->ForInDone(index, cache_length);
   loop_builder.BreakIfTrue();
   DCHECK(Register::AreContiguous(cache_type, cache_array));
   FeedbackVectorSlot slot = stmt->ForInFeedbackSlot();
   builder()->ForInNext(receiver, index, cache_type, feedback_index(slot));
   loop_builder.ContinueIfUndefined();
   VisitForInAssignment(stmt->each(), stmt->EachFeedbackSlot());
   VisitIterationBody(stmt, &loop_builder);
   loop_builder.Next();
   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());
   ControlScopeForIteration control_scope(this, stmt, &loop_builder);
 
   builder()->SetExpressionAsStatementPosition(stmt->assign_iterator());
   VisitForEffect(stmt->assign_iterator());
 
-  loop_builder.LoopHeader();
+  VisitIterationHeader(stmt, &loop_builder);
   loop_builder.Next();
   builder()->SetExpressionAsStatementPosition(stmt->next_result());
   VisitForEffect(stmt->next_result());
   VisitForAccumulatorValue(stmt->result_done());
   loop_builder.BreakIfTrue();
 
   VisitForEffect(stmt->assign_each());
   VisitIterationBody(stmt, &loop_builder);
   loop_builder.JumpToHeader();
   loop_builder.EndLoop();
@@ skipping 1021 matching lines @@
       .SuspendGenerator(generator)
       .LoadAccumulatorWithRegister(value)
       .Return();  // Hard return (ignore any finally blocks).
 
   builder()->Bind(&(generator_resume_points_[id]));
   // Upon resume, we continue here.
 
   {
     RegisterAllocationScope register_scope(this);
 
+    // Update state to indicate that we have finished resuming. Loop headers
+    // rely on this.
+    builder()
+        ->LoadLiteral(Smi::FromInt(JSGeneratorObject::kGeneratorExecuting))
+        .StoreAccumulatorInRegister(generator_state_);
+
     Register input = register_allocator()->NewRegister();
     builder()
         ->CallRuntime(Runtime::kGeneratorGetInput, generator, 1)
         .StoreAccumulatorInRegister(input);
 
     Register resume_mode = register_allocator()->NewRegister();
     builder()
         ->CallRuntime(Runtime::kGeneratorGetResumeMode, generator, 1)
         .StoreAccumulatorInRegister(resume_mode);
 
@@ skipping 966 matching lines @@
 }
 
 
 int BytecodeGenerator::feedback_index(FeedbackVectorSlot slot) const {
   return info()->shared_info()->feedback_vector()->GetIndex(slot);
 }
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8