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From: "ndesaulniers at google dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/100363] gcc generating wider load/store than
 warranted at -O3
Date: Wed, 05 May 2021 19:59:30 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D100363

Nick Desaulniers <ndesaulniers at google dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |ndesaulniers at google dot=
 com

--- Comment #20 from Nick Desaulniers <ndesaulniers at google dot com> ---
(In reply to Alexander Monakov from comment #7)
>  Most likely the issue is that sout/sfrom are misaligned at runtime, whil=
e the > vectorized code somewhere relies on them being sufficiently aligned=
 for a 'short'.
> It is unsafe to dereference a misaligned pointer. The pointed-to-type must
> have reduced alignment:

C 6.3.2.3p7 (N1548) says:

A pointer to an object type may be converted to a pointer to a
different object type. If the resulting pointer is not correctly
aligned) for the referenced type, the behavior is undefined.


=3D=3D=3D

We're working on adding diagnostics and UBSAN checks for these.  Perhaps wi=
th
those in place, we'd be able to spot such a case in the kernel's initramfs
decompression code.=