From: Richard Guenther <richard.guenther@gmail.com>
To: Xinliang David Li <davidxl@google.com>
Cc: Jason Merrill <jason@redhat.com>,
GCC Patches <gcc-patches@gcc.gnu.org>,
Michael Matz <matz@suse.de>
Subject: Re: New option to turn off stack reuse for temporaries
Date: Tue, 26 Jun 2012 08:42:00 -0000 [thread overview]
Message-ID: <CAFiYyc3AGM9rCxK+KBGLFYJt=HNMakULo1D=kBwPx_81MiZVrg@mail.gmail.com> (raw)
In-Reply-To: <CAAkRFZ+QvEQkLnMQ1JokfpTYkfEZdotj7aZX2LXjMe80hy9EBA@mail.gmail.com>
On Mon, Jun 25, 2012 at 6:25 PM, Xinliang David Li <davidxl@google.com> wrote:
> Are there any more concerns about this patch? If not, I'd like to check it in.
No - the fact that the flag is C++ specific but in common.opt is odd enough
and -ftemp-reuse-stack sounds very very generic - which in fact it is not,
it's a no-op in C. Is there a more formal phrase for the temporary kind that
is affected? For me "temp" is synonymous to "auto" so I'd have expected
the switch to turn off stack slot sharing for
{
int a[5];
}
{
int a[5];
}
but that is not what it does. So - a little kludgy but probably more to what
I'd like it to be would be to move the option to c-family/c.opt enabled only
for C++ and Obj-C++ and export it to the middle-end via a new langhook
(the gimplifier code should be in Frontend code that lowers to GENERIC
really and the WITH_CLEANUP_EXPR code should be C++ frontend specific ...).
Thanks,
Richard.
> thanks,
>
> David
>
> On Fri, Jun 22, 2012 at 8:51 AM, Xinliang David Li <davidxl@google.com> wrote:
>> 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
next prev parent reply other threads:[~2012-06-26 8:29 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-06-20 23:44 Xinliang David Li
2012-06-21 5:28 ` Jason Merrill
2012-06-21 6:06 ` Xinliang David Li
2012-06-21 6:27 ` Jason Merrill
2012-06-21 9:32 ` Richard Guenther
2012-06-21 16:41 ` Michael Matz
2012-06-22 8:46 ` Richard Guenther
2012-06-21 18:19 ` Jason Merrill
2012-06-21 18:44 ` Xinliang David Li
2012-06-22 8:50 ` Richard Guenther
2012-06-22 9:39 ` Jason Merrill
2012-06-22 9:51 ` Richard Guenther
2012-06-22 16:09 ` Xinliang David Li
2012-06-25 16:29 ` Xinliang David Li
2012-06-26 8:42 ` Richard Guenther [this message]
2012-06-26 15:29 ` Jason Merrill
2012-06-26 17:12 ` Michael Matz
2012-06-26 17:19 ` Jakub Jelinek
2012-06-26 20:12 ` Mike Stump
2012-06-27 3:03 ` Eric Botcazou
2012-06-29 8:18 ` Xinliang David Li
2012-07-02 23:30 ` Xinliang David Li
2012-07-04 15:01 ` Xinliang David Li
2012-07-09 16:31 ` Xinliang David Li
2012-07-09 22:53 ` Jason Merrill
2012-12-02 12:32 ` Olivier Ballereau
2012-12-03 1:03 ` Xinliang David Li
2012-06-22 21:09 Jason Merrill
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