r183597 - Debug info: An if condition now creates a lexical scope of its own.

[Eric Christopher]

On Mon, Jun 17, 2013 at 2:35 PM, Nadav Rotem <nrotem at apple.com> wrote:
>
> On Jun 17, 2013, at 2:32 PM, Eric Christopher <echristo at gmail.com> wrote:
>
> On Mon, Jun 17, 2013 at 2:29 PM, Robinson, Paul
> <Paul_Robinson at playstation.sony.com> wrote:
>
> From: cfe-commits-bounces at cs.uiuc.edu [mailto:cfe-commits-
> bounces at cs.uiuc.edu] On Behalf Of Eric Christopher
> Sent: Monday, June 10, 2013 4:05 PM
> To: Adrian Prantl
> Cc: Nadav Rotem; cfe-commits at cs.uiuc.edu
> Subject: Re: r183597 - Debug info: An if condition now creates a lexical
> scope of its own.
>
> On Mon, Jun 10, 2013 at 3:56 PM, Adrian Prantl <aprantl at apple.com>
> wrote:
>
> (CC'ing John because he understands the intricacies of LexicalScope
>
> better than I do)
>
>
> On the first glimpse LexicalScope appears to be a subclass of
>
> RunCleanupsScope that additionally emits a (DebugInfo-)LexicalScope. But
> looking at the destructors it appears that they have slightly different
> semantics: ~LexicalScope runs ForceCleanup and ~RunCleanupsScope
> apparently doesn't.
>
>
> I'm wary that switching to Lexicalscope in
>
> CodeGenFunction::EmitIfStmt() might lead to tricky ARC or EH-related
> problems because of that.
>
>
> Does anyone have an opinion on that?
>
>
> That bit was added here:
>
> commit 495cfa46300979642acde8d93a1f21c9291dac98
> Author: Nadav Rotem <nrotem at apple.com>
> Date:   Sat Mar 23 06:43:35 2013 +0000
>
>    Make clang to mark static stack allocations with lifetime markers
> to enable a more aggressive stack coloring.
>    Patch by John McCall with help by Shuxin Yang.
>    rdar://13115369
>
>
> and oddly not to RunCleanupsScope.
>
> Nadav?
>
> -eric
>
>
> Looks like ~LexicalScope() just wants RunCleanupsScope::ForceCleanup()
> to happen before rescopeLabels().  All the right stuff happens in the right
> order if you change the RunCleanupsScope instance to LexicalScope.
> (RunCleanupsScope::ForceCleanup() does pretty much exactly the same thing
> as ~RunCleanupsScope() so it works out.  It could be done in a more obvious
> way, but functionally they're equivalent.)
>
>
> Agreed. I was just curious why Nadav changed one, but not the other.
>
> Nadav? :)
>
> -eric
>
>
>
> I don’t have a good answer.  I will have to consult with John who
> implemented this.
>

Sounds good. Thanks!

-eric