[interpreter] Implement static loop depth tracking.

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 367a50983e129084403d6c03d32bfe6df568afb6..0f7a883eb587b291af98046b6a8dfe51f6fed644 100644
--- a/src/interpreter/bytecode-generator.cc
+++ b/src/interpreter/bytecode-generator.cc
@@ -266,7 +266,12 @@ class BytecodeGenerator::ControlScopeForIteration final
                            LoopBuilder* loop_builder)
       : ControlScope(generator),
         statement_(statement),
-        loop_builder_(loop_builder) {}
+        loop_builder_(loop_builder) {
+    generator->loop_depth_++;  // Increment tracked loop depth.
+  }
+  ~ControlScopeForIteration() {
+    generator()->loop_depth_--;  // Decrement tracked loop depth.

[rmcilroy, 2016/07/26 09:28:52]

Not sure the comments are necessary, pretty self explanatory, but I'm easy
either way :).

[Michael Starzinger, 2016/07/26 09:46:02]

Done. I mostly do this to trick clang-format into not uglifying my code.

+  }
 
  protected:
   bool Execute(Command command, Statement* statement) override {
@@ -548,7 +553,8 @@ BytecodeGenerator::BytecodeGenerator(CompilationInfo* info)
       execution_result_(nullptr),
       register_allocator_(nullptr),
       generator_resume_points_(info->literal()->yield_count(), info->zone()),
-      generator_state_() {
+      generator_state_(),
+      loop_depth_(0) {
   InitializeAstVisitor(isolate()->stack_guard()->real_climit());
 }
 
@@ -670,9 +676,9 @@ void BytecodeGenerator::VisitIterationHeader(IterationStatement* stmt,
   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);
+    int level = Min(loop_depth_, AbstractCode::kMaxLoopNestingMarker - 1);
+    builder()->OsrPoll(level);
   }
 }