On Wed, Sep 25, 2024 at 2:56 PM Jan Beulich <jbeul...@suse.com> wrote:
>
> Commit a79d13a01f8c ("i386: Fix aes/vaes patterns [PR114576]") correctly
> said "..., but we need to emit {evex} prefix in the assembly if AES ISA
> is not enabled". Yet it did so only for the TARGET_AES insns. Going from
> the alternative chosen in the TARGET_VAES insns is wrong for two
> reasons:
> - if, with AES disabled, the latter alternative was chosen despite no
> "high" XMM register nor any eGPR in use, gas would still pick the AES
w/o EVEX SSE REG or EGPR, the first alternative will always be
matched(alternative 0).
That is how it works(match from left to right).
> (VEX) encoding when no {evex} pseudo-prefix is in use (which is
> against - as stated by the description of said commit - AES presently
> not being considered a prereq of VAES in gcc);
> - if AES is (also) enabled, EVEX encoding would needlessly be forced.
So it's more like an optimization that use VEX encoding when AES is enabled?
>
> gcc/
>
> * config/i386/sse.md (vaesdec_<mode>, vaesdeclast_<mode>,
> vaesenc_<mode>, vaesenclast_<mode>): Replace which_alternative
> check by TARGET_AES one.
> ---
> As an aside - {evex} (and other) pseudo-prefixes would better be avoided
> anyway whenever possible, as those are getting in the way of code
> putting in place macro overrides for certain insns: gas 2.43 rejects
> such bogus placement of pseudo-prefixes.
>
> --- a/gcc/config/i386/sse.md
> +++ b/gcc/config/i386/sse.md
> @@ -30802,7 +30802,7 @@
> UNSPEC_VAESDEC))]
> "TARGET_VAES"
> {
> - if (which_alternative == 0 && <MODE>mode == V16QImode)
> + if (!TARGET_AES && <MODE>mode == V16QImode)
> return "%{evex%} vaesdec\t{%2, %1, %0|%0, %1, %2}";
> else
> return "vaesdec\t{%2, %1, %0|%0, %1, %2}";
> @@ -30816,7 +30816,7 @@
> UNSPEC_VAESDECLAST))]
> "TARGET_VAES"
> {
> - if (which_alternative == 0 && <MODE>mode == V16QImode)
> + if (!TARGET_AES && <MODE>mode == V16QImode)
> return "%{evex%} vaesdeclast\t{%2, %1, %0|%0, %1, %2}";
> else
> return "vaesdeclast\t{%2, %1, %0|%0, %1, %2}";
> @@ -30830,7 +30830,7 @@
> UNSPEC_VAESENC))]
> "TARGET_VAES"
> {
> - if (which_alternative == 0 && <MODE>mode == V16QImode)
> + if (!TARGET_AES && <MODE>mode == V16QImode)
> return "%{evex%} vaesenc\t{%2, %1, %0|%0, %1, %2}";
> else
> return "vaesenc\t{%2, %1, %0|%0, %1, %2}";
> @@ -30844,7 +30844,7 @@
> UNSPEC_VAESENCLAST))]
> "TARGET_VAES"
> {
> - if (which_alternative == 0 && <MODE>mode == V16QImode)
> + if (!TARGET_AES && <MODE>mode == V16QImode)
> return "%{evex%} vaesenclast\t{%2, %1, %0|%0, %1, %2}";
> else
> return "vaesenclast\t{%2, %1, %0|%0, %1, %2}";
--
BR,
Hongtao
