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

[Eric Christopher]

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

> And as long as the DWARF lexical scope tag is omitted if there aren't
> any actual declarations, I have no debug-info-size concerns.
> --paulr
>