[interpreter] Add explicit OSR polling bytecode.

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 6c51499740581ec24bd49806ee881bdf76d08d6b..367a50983e129084403d6c03d32bfe6df568afb6 100644
--- a/src/interpreter/bytecode-generator.cc
+++ b/src/interpreter/bytecode-generator.cc
@@ -664,6 +664,16 @@ void BytecodeGenerator::VisitIterationHeader(IterationStatement* stmt,
         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() {