Added %NeverOptimize runtime call that can disable optimizations for a method for tests.

src/runtime.cc

Index: src/runtime.cc
diff --git a/src/runtime.cc b/src/runtime.cc
index 6e045608b9c10d19178a4ee1f5308e9e2e214123..e6c3bc348352dac2360cc78966a7fa229169579b 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -8346,6 +8346,37 @@ RUNTIME_FUNCTION(MaybeObject*, Runtime_OptimizeFunctionOnNextCall) {
 }
 
 
+static void MarkNeverOptimize(JSFunction *function) {
+  Code *code = function->code();
+  if (code != NULL && code->kind() == Code::FUNCTION) {
+    code->set_optimizable(false);
+  }
+  Code *shared_code = function->shared()->code();
+  if (shared_code != NULL && shared_code->kind() == Code::FUNCTION) {
+    shared_code->set_optimizable(false);
+  }
+}
+
+
+RUNTIME_FUNCTION(MaybeObject*, Runtime_NeverOptimize) {
+  HandleScope scope(isolate);
+
+  if (args.length() == 0) {
+    // mark the top frame as do not optimize

[Jakob Kummerow, 2013/07/11 15:23:33]

nit: Begin with capitalization, end with punctuation. Again below.

[titzer, 2013/07/11 15:29:02]

Done. (fixed this before submitting).

+    JavaScriptFrameIterator it(isolate);
+    if (!it.done()) MarkNeverOptimize(JSFunction::cast(it.frame()->function()));

[Jakob Kummerow, 2013/07/11 15:23:33]

Instead of rolling your own MarkNeverOptimize, I think you should just call:
JSFunction::cast(it.frame()->function())->shared()->DisableOptimization("%NeverOptimize");
That function does all the right things.

[titzer, 2013/07/11 15:29:02]

I also did something similar prior to submit...as thankfully my
never-optimize.js unit test caught a bug with --always-opt :)

+    return isolate->heap()->undefined_value();
+  }
+
+  // mark the passed functions as do not optimize
+  for (int i = 0; i < args.length(); i++) {
+    CONVERT_ARG_CHECKED(JSFunction, function, i);
+    MarkNeverOptimize(function);
+  }
+  return isolate->heap()->undefined_value();
+}
+
+
 RUNTIME_FUNCTION(MaybeObject*, Runtime_CompleteOptimization) {
   HandleScope scope(isolate);
   ASSERT(args.length() == 1);