[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 696 matching lines @@
   size_t first_yield = stmt->first_yield_id();
   DCHECK_LE(first_yield + stmt->yield_count(), generator_resume_points_.size());
   for (size_t id = first_yield; id < first_yield + stmt->yield_count(); id++) {
     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);
 
+  // Insert an explicit {OsrPoll} right after the loop header, to trigger
+  // on-stack replacement when armed for the given loop nesting depth.
+  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);
+  }
+
   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_, first_yield,
         stmt->yield_count(), generator_resume_points_);
@@ skipping 2500 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