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Re: Weird warning

From: Florian Weimer <fw at deneb dot enyo dot de>
To: Marcel Keller <M dot Keller at bristol dot ac dot uk>
Cc: gcc-help at gcc dot gnu dot org
Date: Thu, 10 Nov 2016 20:21:35 +0100
Subject: Re: Weird warning
Authentication-results: sourceware.org; auth=none
References: <0c14d387-fb55-9ee3-e0c1-557e80750f2f@bristol.ac.uk> <c0ff8572-429e-1a42-f799-d5666def641d@bristol.ac.uk>

* Marcel Keller:

> I've been digging a bit deeper after making sense of the warning. It 
> seems that GCC simply misaligns __m256i values. In the attached example, 
> the unaligned load/store works fine but the last line fails. The address 
> in the output clearly shows that the memory is not aligned (not 
> divisible by 32):
>
> 0x7ffff7f83010
>
> Program received signal SIGSEGV, Segmentation fault.
> 0x00000000004008d0 in main () at avx-bug.cpp:17
> 17	  v[0].a[0] = v[0].a[0];

Yes, this is a known issue.  It has been fixed in GCC 7:

  <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65122>

References:
- Weird warning
  - From: Marcel Keller
- Re: Weird warning
  - From: Marcel Keller

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