Re: New option to turn off stack reuse for temporaries

[Xinliang David Li <davidxl@google.com>]

On Fri, Jun 22, 2012 at 2:39 AM, Richard Guenther
<richard.guenther@gmail.com> wrote:
> On Fri, Jun 22, 2012 at 11:29 AM, Jason Merrill <jason@redhat.com> wrote:
>> On 06/22/2012 01:30 AM, Richard Guenther wrote:
>>>>
>>>> What other issues? It enables more potential code motion, but on the
>>>> other hand, causes more conservative stack reuse. As far I can tell,
>>>> the handling of temporaries is added independently after the clobber
>>>> for scoped variables are introduced. This option can be used to
>>>> restore the older behavior (in handling temps).
>>>
>>>
>>> Well, it does not really restore the old behavior (if you mean before
>>> adding
>>> CLOBBERS, not before the single patch that might have used those for
>>> gimplifying WITH_CLEANUP_EXPR).  You say it disables stack-slot sharing
>>> for those decls but it also does other things via side-effects of no
>>> longer
>>> emitting the CLOBBER.  I say it's better to disable the stack-slot
>>> sharing.
>>
>>
>> The patch exactly restores the behavior of temporaries from before my change
>> to add CLOBBERs for temporaries.  The primary effect of that change was to
>> provide stack-slot sharing, but if there are other effects they are probably
>> desirable as well, since the broken code depended on the old behavior.
>
> So you see it as workaround option, like -fno-strict-aliasing, rather than
> debugging aid?

It can be used for both purposes -- if the violations are as pervasive
as strict-aliasing cases (which looks like so).

thanks,

David

>
> Richard.
>
>> Jason