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Re: [PATCH, alpha]: Wrap {un,}aligned_store sequence with memory blockages.
- From: Uros Bizjak <ubizjak at gmail dot com>
- To: Richard Henderson <rth at redhat dot com>
- Cc: Richard Biener <richard dot guenther at gmail dot com>, "gcc-patches at gcc dot gnu dot org" <gcc-patches at gcc dot gnu dot org>
- Date: Mon, 7 Jul 2014 18:35:12 +0200
- Subject: Re: [PATCH, alpha]: Wrap {un,}aligned_store sequence with memory blockages.
- Authentication-results: sourceware.org; auth=none
- References: <CAFULd4Yi50ZbdQSPwTWP9VsOfK=0cf43R33kS5j0XOgU4JGPgw at mail dot gmail dot com> <53ADCE45 dot 3010306 at redhat dot com> <CAFULd4ZMFwuPJubNXB_PRfko34WRiS+SzNB6q0qC4CyrCzr8HQ at mail dot gmail dot com> <53B18841 dot 8060809 at redhat dot com> <CAFiYyc2PouEnf3HC14UV6KiAePxyogw0VkEsbpG_dF6Hg=mivQ at mail dot gmail dot com> <53BAACC5 dot 5010301 at redhat dot com> <CAFiYyc2MfF2L9GpwCHui-4WzJwCxyJomM+Dxof-GdLEKtv0bvQ at mail dot gmail dot com> <53BAB62D dot 2070104 at redhat dot com>
On Mon, Jul 7, 2014 at 5:01 PM, Richard Henderson <rth@redhat.com> wrote:
> Early alpha can't store sub-4-byte quantities. Altivec can't store anything
> but 16 byte quantities. In order to perform smaller stores, we have to do a
> read-modify-write sequence on a larger aligned chunk of memory. Two such RMW
> sequences must conflict, lest we interleave and thus bork the operation.
>
> I don't recall how much we ever did for this, exactly, but it's certainly
> possible to know that some memory operations cannot conflict with these RMW
> sequence. E.g. through size + alignment of the other memory operation. E.g.
> on Alpha, a byte RMW store can't conflict with a normal DImode memory access.
>
>> Btw, if the mem is MEM_READONLY_P how can it be part of
>> a {un}aligned_store sequence?
>
> Er... that's an excellent question. Uros?
This flag is copied from the original memory operand by
alpha_set_memflags to all memory operands in the expanded sequence.
Uros.