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From: "raffeck at cs dot fau.de" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/115278] New: -ftree-vectorize optimizes away
 volatile write on x86_64
Date: Wed, 29 May 2024 14:45:22 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 14.1.1
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D115278

            Bug ID: 115278
           Summary: -ftree-vectorize optimizes away volatile write on
                    x86_64
           Product: gcc
           Version: 14.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: raffeck at cs dot fau.de
  Target Milestone: ---

Created attachment 58308
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D58308&action=3Dedit
minimal example to reproduce bug

The code in the attached minimal example contains two volatile writes to the
same address.

With `gcc -O2 -fno-tree-loop-vectorize`, two writes are present in the
generated object code. With just `gcc -O2` however, only one write is
preserved, the other seems to be optimized away. As these are volatile
accesses, this should be an illegal optimization.

The behavior does not occur with commit 498ad738690, but occurs with
25413fdb2ac, so probably 25413fdb2ac introduced this bug. The behavior still
persists in the current master (commit f46eaad445e).=