Restore behavior of PrepareForBreakpoints which was broken by r21145

src/debug.cc

Index: src/debug.cc
diff --git a/src/debug.cc b/src/debug.cc
index 6ec7ad695bb3a6cd1836dfa4bef742d34bd31049..bf29fe420ac690d95dcb13adb5dc33082b41d14b 100644
--- a/src/debug.cc
+++ b/src/debug.cc
@@ -2037,11 +2037,11 @@ class ForceDebuggerActive {
 };
 
 
-void Debug::MaybeRecompileFunctionForDebugging(Handle<JSFunction> function) {
-  ASSERT_EQ(Code::FUNCTION, function->code()->kind());
-  ASSERT_EQ(function->code(), function->shared()->code());
-
-  if (function->code()->has_debug_break_slots()) return;
+void Debug::EnsureFunctionHasDebugBreakSlots(Handle<JSFunction> function) {
+  if (function->code()->kind() != Code::FUNCTION ||

[Yang, 2014/05/08 14:28:09]

Like I said in the reland CL, this is incorrect. In this function we want to
make sure that the function code is unoptimized with debug break slots. If the
code type is optimized code or builtin, we want to replace that by recompiling
it.
We can only skip this if the code is already unoptimized with debug break slots.
So it should be

if (function->code()->kind() == Code::FUNCTION &&
function->code()->has_debug_break_slots())

[rmcilroy, 2014/05/08 14:53:59]

Sorry I missed that comment.  This doesn't work - I get the following ASSERT
failure with that change:

# Fatal error in ../src/compiler.cc, line 717
# CHECK(!old_code->has_debug_break_slots()) failed

==== C stack trace ===============================
v8::internal::Compiler::GetCodeForDebugging(v8::internal::Handle<v8::internal::JSFunction>)
 3:
v8::internal::Debug::MaybeRecompileFunctionForDebugging(v8::internal::Handle<v8::internal::JSFunction>)

Should it be:
if (function->shared()->code()->kind() == Code::FUNCTION && 
    function->shared()->code()->has_debug_break_slots()) return;

instead? That seems to work.

+      function->code()->has_debug_break_slots()) {
+    return;
+  }
 
   ForceDebuggerActive force_debugger_active(isolate_);
   MaybeHandle<Code> code = Compiler::GetCodeForDebugging(function);
@@ -2057,7 +2057,7 @@ void Debug::RecompileAndRelocateSuspendedGenerators(
   for (int i = 0; i < generators.length(); i++) {
     Handle<JSFunction> fun(generators[i]->function());
 
-    MaybeRecompileFunctionForDebugging(fun);
+    EnsureFunctionHasDebugBreakSlots(fun);
 
     int code_offset = generators[i]->continuation();
     int pc_offset = ComputePcOffsetFromCodeOffset(fun->code(), code_offset);
@@ -2217,7 +2217,7 @@ void Debug::PrepareForBreakPoints() {
       if (!shared->allows_lazy_compilation()) continue;
       if (shared->code()->kind() == Code::BUILTIN) continue;
 
-      MaybeRecompileFunctionForDebugging(function);
+      EnsureFunctionHasDebugBreakSlots(function);
     }
 
     RedirectActivationsToRecompiledCodeOnThread(isolate_,