On Wed, May 26, 2010 at 6:05 PM, Richard Guenther
<richard.guent...@gmail.com> wrote:
> On Wed, May 26, 2010 at 5:42 PM, Xinliang David Li <davi...@google.com> wrote:
>> On Wed, May 26, 2010 at 2:58 AM, Richard Guenther
>> <richard.guent...@gmail.com> wrote:
>>> On Tue, May 25, 2010 at 10:02 PM, Easwaran Raman <era...@google.com> wrote:
>>>> On Fri, May 21, 2010 at 10:30 AM, Xinliang David Li <davi...@google.com>
>>>> wrote:
>>>>>
>>>>> On Fri, May 21, 2010 at 2:24 AM, Richard Guenther
>>>>> <richard.guent...@gmail.com> wrote:
>>>>> > On Thu, May 20, 2010 at 11:21 PM, Xinliang David Li
>>>>> > <davi...@google.com> wrote:
>>>>> >> On Thu, May 20, 2010 at 2:18 PM, Steven Bosscher
>>>>> >> <stevenb....@gmail.com> wrote:
>>>>> >>> On Thu, May 20, 2010 at 11:14 PM, Xinliang David Li
>>>>> >>> <davi...@google.com> wrote:
>>>>> >>>> stack variable overlay and stack slot assignments is here too.
>>>>> >>>
>>>>> >>> Yes, and for these I would like to add a separate timevar. Agree?
>>>>> >>
>>>>> >> Yes. (By the way, we are rewriting this pass to eliminate the code
>>>>> >> motion/aliasing problem -- but that is a different topic).
>>>>> >
>>>>> > Btw, we want to address the same problem by representing the
>>>>> > points where (big) variables go out-of scope in the IL, also to
>>>>> > help DSE. The original idea was to simply drop in an aggregate
>>>>> > assignment from an undefined value at the end of the scope
>>>>> > during lowering, like
>>>>> >
>>>>> > var = {undefined};
>>>>> >
>>>>>
>>>>
>>>> Is there something that prevents store sinking (or similar passes)
>>>> from moving this 'var = {undefined};' statement outside the scope? Or
>>>> should store sinking be taught to treat this as a barrier?
>>>
>>> Not at the moment (if indeed that assignment looks as a regular one).
>>> Passes should be taught that it's not worthwhile to sink a
>>> no-op. IIRC no pass currently would sink aggregate copies anyway.
>>
>> Other issues to consider: 1) how does it affect SRA decisions?
>
> It shouldn't. But SRA needs to be adjusted for sure.
Btw, globbing shared vars into a union will certainly also affect SRA,
no?
Richard.
>> 2) inline summary also needs to be taught to not include size of those
>> fake instructions;
>
> That's simple. The inliner also needs to be taught to emit the
> fake assignments into the caller.
>
>> 3) why only aggregates? For scalars that live in
>> stack, they also need barriers if slot sharing pick them as
>> candidates, etc.
>
> Sure.
>
> Richard.
>
