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From: Jason Gunthorpe <jgunthorpe-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>
To: Yishai Hadas <yishaih-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
Cc: linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	leonro-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org,
	majd-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org
Subject: Re: [PATCH rdma-core 2/2] mlx5: Convert explicitly to signed char
Date: Wed, 30 Aug 2017 10:49:52 -0600	[thread overview]
Message-ID: <20170830164952.GA9310@obsidianresearch.com> (raw)
In-Reply-To: <1504102764-21638-3-git-send-email-yishaih-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>

On Wed, Aug 30, 2017 at 05:19:24PM +0300, Yishai Hadas wrote:
> From: Leon Romanovsky <leonro-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
> 
> The 0x80 value is a canonical way to mark as not-used in intrinsics
> function calls.

This commit message is not good, try:

_mm_shuffle_epi8 requires 0x80 to set the output byte to zero, but
_mm_set_epi8() accepts char. If gcc is compiling in a configuration
with a signed char then it can produce a -Werror=overflow warning.

And this fix is wrong, since it just moves the warning to
configurations that have an unsigned char. (eg -funsigned-char)

It is really broken that the _mm_set_epi uses a char as input :|

I think you need to do this instead:

#include <limits.h>
#if CHAR_MIN < 0
#define SHUFFLE_IGNORE  -128
#else
#define SHUFFLE_IGNORE  0x80
#endif

Jason
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  parent reply	other threads:[~2017-08-30 16:49 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-08-30 14:19 [PATCH rdma-core 0/2] mlx5 DV fixes Yishai Hadas
     [not found] ` <1504102764-21638-1-git-send-email-yishaih-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
2017-08-30 14:19   ` [PATCH rdma-core 1/2] mlx5: Rename arm_db pointer to be cq_uar to better describe the content Yishai Hadas
2017-08-30 14:19   ` [PATCH rdma-core 2/2] mlx5: Convert explicitly to signed char Yishai Hadas
     [not found]     ` <1504102764-21638-3-git-send-email-yishaih-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
2017-08-30 16:49       ` Jason Gunthorpe [this message]
     [not found]         ` <20170830164952.GA9310-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>
2017-08-30 17:44           ` Leon Romanovsky
     [not found]             ` <20170830174402.GC10539-U/DQcQFIOTAAJjI8aNfphQ@public.gmane.org>
2017-08-30 17:49               ` Jason Gunthorpe

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