Scale the OSR optimization threshold by loop nesting depth.

runtime/vm/intermediate_language_x64.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"  // Needed here to get TARGET_ARCH_X64.
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/intermediate_language.h"
 
 #include "lib/error.h"
@@ skipping 2121 matching lines @@
   CheckStackOverflowSlowPath* slow_path = new CheckStackOverflowSlowPath(this);
   compiler->AddSlowPathCode(slow_path);
 
   Register temp = locs()->temp(0).reg();
   // Generate stack overflow check.
   __ movq(temp, Immediate(Isolate::Current()->stack_limit_address()));
   __ cmpq(RSP, Address(temp, 0));
   __ j(BELOW_EQUAL, slow_path->entry_label());
   if (compiler->CanOSRFunction() && in_loop()) {
     // In unoptimized code check the usage counter to trigger OSR at loop
-    // stack checks.
+    // stack checks.  Use progressively higher thresholds for more deeply
+    // nested loops to attempt to hit outer loops with OSR when possible.
     __ LoadObject(temp, compiler->parsed_function().function());
+    intptr_t threshold =
+        FLAG_optimization_counter_threshold * (loop_depth() + 1);
     __ cmpq(FieldAddress(temp, Function::usage_counter_offset()),
-            Immediate(2 * FLAG_optimization_counter_threshold));
+            Immediate(threshold));
     __ j(GREATER_EQUAL, slow_path->entry_label());
   }
   __ Bind(slow_path->exit_label());
 }
 
 
 static void Emit53BitOverflowCheck(FlowGraphCompiler* compiler,
                                    Label* overflow,
                                    Register result) {
   if (FLAG_throw_on_javascript_int_overflow) {
@@ skipping 2278 matching lines @@
                          PcDescriptors::kOther,
                          locs());
   __ Drop(2);  // Discard type arguments and receiver.
 }
 
 }  // namespace dart
 
 #undef __
 
 #endif  // defined TARGET_ARCH_X64