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Date: Thu, 5 May 2022 16:41:28 +0200 (CEST)
From: Marc Glisse <marc.glisse@inria.fr>
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To: =?ISO-8859-15?Q?St=E9phane_Glondu?= <stephane.glondu@inria.fr>
cc: Alexander Monakov <amonakov@ispras.ru>, gcc-help@gcc.gnu.org, 
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Subject: Re: slowdown with -std=gnu18 with respect to -std=c99
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On Thu, 5 May 2022, Stéphane Glondu via Gcc-help wrote:

> As additional data points, the performance with several versions of gcc
> (as packaged in Debian testing/unstable):
>
>             | gcc-9 | gcc-10 | gcc-11 | gcc-12 |
> ------------|-------|--------|--------|--------|
>  -std=c99   | 24    | 23.5   | 23     | 23     |
>  -std=gnu18 | 43    | 16.8   | 38     | 38     |
>
> One can see that the performance stays relatively constant with
> -std=c99, but varies significantly with -std=gnu18.

Could you compare with c18 or gnu99, to determine if the issue is with c 
vs gnu (most likely since fma seems important) or 99 vs 18?

-- 
Marc Glisse