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Re: [PATCH, PR target/69454] Disable TARGET_STV when stack is not properly aligned
- From: Ilya Enkovich <enkovich dot gnu at gmail dot com>
- To: "H.J. Lu" <hjl dot tools at gmail dot com>
- Cc: Jakub Jelinek <jakub at redhat dot com>, Uros Bizjak <ubizjak at gmail dot com>, GCC Patches <gcc-patches at gcc dot gnu dot org>
- Date: Tue, 2 Feb 2016 16:03:55 +0300
- Subject: Re: [PATCH, PR target/69454] Disable TARGET_STV when stack is not properly aligned
- Authentication-results: sourceware.org; auth=none
- References: <20160127154448 dot GQ3017 at tucnak dot redhat dot com> <20160127161137 dot GB16081 at msticlxl57 dot ims dot intel dot com> <CAMe9rOoo1KN3K+vhWh5POE0trO-8wbpTdmC8mkXWNCLqn4sWVA at mail dot gmail dot com> <CAMbmDYbGp6WxxCh0rKUsU+UD70KfR=8G8dNQbCegoSBanB3NRw at mail dot gmail dot com> <CAMe9rOrDbzVCRfkLFiCCbF80D3R2XyMm6REbSsTZGhjdfbP2fQ at mail dot gmail dot com> <CAMe9rOqywZwxDSO+9SyF8HoG=ai=26MMBnBGKPCvz_wxFhEB0g at mail dot gmail dot com> <CAMbmDYbkroApwkXDrvZbdCtMAJPrSZSmzxhRunc2TprKce4e0A at mail dot gmail dot com> <CAMe9rOodyrX36aFM=sv98+cvWskRdKnmJEdsvU6nQdRhs5UoCA at mail dot gmail dot com> <20160202115338 dot GP3017 at tucnak dot redhat dot com> <CAFULd4YKsOs6bdsOQ-P0HbU0NvDAS8asEdYUR3Yh=Fa5=0F53w at mail dot gmail dot com> <20160202122922 dot GQ3017 at tucnak dot redhat dot com> <CAMe9rOr4z3W6k=GrecTQPTJcdD_yZd4=9jA5R=768rS1NTuxcw at mail dot gmail dot com> <CAMe9rOq31Td2SJuaQBXGu-q36dgyDL2E+AUNwZJr+y6=RD+neA at mail dot gmail dot com>
2016-02-02 15:46 GMT+03:00 H.J. Lu <hjl.tools@gmail.com>:
> On Tue, Feb 2, 2016 at 4:30 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
>> On Tue, Feb 2, 2016 at 4:29 AM, Jakub Jelinek <jakub@redhat.com> wrote:
>>> On Tue, Feb 02, 2016 at 01:24:26PM +0100, Uros Bizjak wrote:
>>>> On Tue, Feb 2, 2016 at 12:53 PM, Jakub Jelinek <jakub@redhat.com> wrote:
>>>>
>>>> >> The bottom line is ix86_minimum_alignment must return the correct
>>>> >> number for DImode or you can just turn off STV. My suggestion is
>>>> >> to use my patch.
>>>> >
>>>> > Uros, any preferences here? I mean, it is possible to use
>>>> > e.g. the ix86_option_override_internal and have H.J's ix86_minimum_alignment
>>>> > change as a safety net, in the usual case for -mpreferred-stack-boundary=2
>>>> > we'll just disable TARGET_STV and ix86_minimum_alignment change won't do
>>>> > anything, as TARGET_STV will be false, and if for whatever case it gets
>>>> > through (target attribute, -mincoming-stack-boundary=, ...)
>>>> > ix86_minimum_alignment will be there to ensure enough stack alignment.
>>>> > Most of the smaller -mpreferred-stack-boundary= uses are -mno-sse anyway,
>>>> > and that is something we don't want to affect.
>>>>
>>>> IMO, we should disable STV when -mpreferred-stack-boundary < 3, as STV
>>>> is only an optimization. Perhaps we can also emit a "sorry" for
>>>> explicit -mstv in case stack boundary requirement is not satisfied.
>>>> *If* there is a need for -mstv with smaller stack boundary, we can
>>>> revisit this decision for later gcc versions.
>>>>
>>>> I think disabling STV is less surprising option than increasing stack
>>>> boundary behind the user's back.
>>>
>>> So, is http://gcc.gnu.org/ml/gcc-patches/2016-01/msg02129.html
>>> ok for trunk then (alone or with additional sorry, incremental or not?)?
>>> I believe it does just that.
>>
>> This patch is WRONG.
>>
>> --
>> H.J.
>
> You will run into the same ICE with
>
> -mincoming-stack-boundary=2 -msse2 -O2 -m32
>
> in a leaf function which needs DImode spill/fill.
Why would we need DImode spill/fill having no DImode registers?
Thanks,
Ilya
>
>
> --
> H.J.