[interpreter] Add explicit OSR polling bytecode.

src/interpreter/interpreter.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/interpreter.h"
 
 #include <fstream>
 
 #include "src/ast/prettyprinter.h"
 #include "src/code-factory.h"
@@ skipping 1775 matching lines @@
   __ Dispatch();
 
   __ Bind(&stack_check_interrupt);
   {
     Node* context = __ GetContext();
     __ CallRuntime(Runtime::kStackGuard, context);
     __ Dispatch();
   }
 }
 
+// OsrPoll <loop_depth>
+//
+// Performs a loop nesting check and potentially triggers OSR.
+void Interpreter::DoOsrPoll(InterpreterAssembler* assembler) {
+  Node* loop_depth = __ BytecodeOperandFlag(0);
+  Node* osr_level = __ LoadOSRNestingLevel();
+
+  // Check if OSR points at the given {loop_depth} are armed by comparing it to
+  // the current {osr_level} loaded from the header of the BytecodeArray.
+  Label ok(assembler), osr_armed(assembler, Label::kDeferred);
+  Node* condition = __ Int32GreaterThanOrEqual(loop_depth, osr_level);

[rmcilroy, 2016/07/25 12:40:24]

It looks like OSR nesting level initialized to 0 in the bytecode array, and
OSRPoll always passes level zero currently. Doesn't that mean we always end up
trying to OSR?

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

The {OsrPoll} handler will fall-through (i.e. the 'ok' label) when {loop_depth
>= bytecode->ost_nesting_level()} and only trigger (i.e. the 'osr_armed' label)
when this condition does not hold. Hence the initialization to 0 should not
cause it to trigger.

Also, I plan to make the loop depth tracking zero based, so top-level loops
within a function will contain a OsrPoll(0) as well.

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

You are right, sorry I got the labels on the branch mixed up.
Right, sounds fine now I got the condition the right way around.

+  __ Branch(condition, &ok, &osr_armed);
+
+  __ Bind(&ok);
+  __ Dispatch();
+
+  __ Bind(&osr_armed);
+  {
+    Callable callable = CodeFactory::InterpreterOnStackReplacement(isolate_);
+    Node* target = __ HeapConstant(callable.code());
+    Node* context = __ GetContext();
+    // TODO(4764): We don't have a CallStub method with zero arguments, add one!

[rmcilroy, 2016/07/25 12:40:24]

Could you do that with this CL please?

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

Done.

+    __ CallStub(callable.descriptor(), target, context, context);
+    __ Dispatch();
+  }
+}
+
 // Throw
 //
 // Throws the exception in the accumulator.
 void Interpreter::DoThrow(InterpreterAssembler* assembler) {
   Node* exception = __ GetAccumulator();
   Node* context = __ GetContext();
   __ CallRuntime(Runtime::kThrow, context, exception);
   // We shouldn't ever return from a throw.
   __ Abort(kUnexpectedReturnFromThrow);
 }
@@ skipping 321 matching lines @@
   __ StoreObjectField(generator, JSGeneratorObject::kContinuationOffset,
       __ SmiTag(new_state));
   __ SetAccumulator(old_state);
 
   __ Dispatch();
 }
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8