[interpreter] Add explicit OSR polling bytecode.

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/code-stubs.h"
 #include "src/compiler.h"
 #include "src/interpreter/bytecode-flags.h"
@@ skipping 646 matching lines @@
     // 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_, first_yield,
         stmt->yield_count(), generator_resume_points_);
     builder()->Bind(&not_resuming);
   }
+
+  // Insert an explicit {OsrPoll} right after the loop header, to trigger
+  // on-stack replacement when armed for the given loop nesting depth.

[rmcilroy, 2016/07/25 12:40:23]

Should this be before the generator resume logic (i.e., immediately after
loop_builder->LoopHeader())? Not sure how OSR interacts with generators?

...

Just saw your TODO - I guess you aren't sure yet either :).

[Michael Starzinger, 2016/07/25 13:40:48]

Done. Yes, I am not 100% sure about interaction with generators either yet. But
intuitively OSR entry should be done before the generator dispatch. So I moved
it up for now, but left the TODO in place.

[rmcilroy, 2016/07/26 09:26:44]

Acknowledged.

+  if (FLAG_ignition_osr) {
+    // TODO(4764): Merge this with another bytecode (e.g. {Jump} back edge).
+    // TODO(4764): Investigate interaction with generators.
+    // TODO(4764): Track and pass correct loop depth.
+    DCHECK_EQ(0, stmt->yield_count());
+    builder()->OsrPoll(0);
+  }
 }
 
 void BytecodeGenerator::VisitGeneratorPrologue() {
   // The generator resume trampoline abuses the new.target register both to
   // indicate that this is a resume call and to pass in the generator object.
   // In ordinary calls, new.target is always undefined because generator
   // functions are non-constructable.
   Register generator_object = Register::new_target();
   BytecodeLabel regular_call;
   builder()
@@ skipping 2502 matching lines @@
   return execution_context()->scope()->language_mode();
 }
 
 int BytecodeGenerator::feedback_index(FeedbackVectorSlot slot) const {
   return TypeFeedbackVector::GetIndex(slot);
 }
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8