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Re: Simplify ptr - 0

From: Marc Glisse <marc dot glisse at inria dot fr>
To: Jakub Jelinek <jakub at redhat dot com>
Cc: gcc-patches at gcc dot gnu dot org
Date: Wed, 22 Nov 2017 20:23:45 +0100 (CET)
Subject: Re: Simplify ptr - 0
Authentication-results: sourceware.org; auth=none
References: <alpine.DEB.2.02.1711221809380.11945@stedding.saclay.inria.fr> <20171122174355.GX14653@tucnak>

On Wed, 22 Nov 2017, Jakub Jelinek wrote:

On Wed, Nov 22, 2017 at 06:34:08PM +0100, Marc Glisse wrote:

Hello,

I hadn't implemented this simplification because I think it is invalid code,
but apparently people do write it, so we might as well handle it sensibly.
This also happens to work around PR 83104 (already fixed).

bootstrap+regtest on powerpc64le-unknown-linux-gnu.


I guess we'll need to disable it for -fsanitize=pointer-subtraction
once/if it makes it in, because it should be still diagnosed as invalid.

I am not sure you'll need to disable it. From what I've seen, the patchinserts a call to BUILT_IN_ASAN_POINTER_SUBTRACT before thePOINTER_DIFF_EXPR is created, and I don't see why simplifyingPOINTER_DIFF_EXPR would affect that call. But then again, I don't know howthe sanitizers work, so I can easily misinterpret things.


--
Marc Glisse

References:
- Simplify ptr - 0
  - From: Marc Glisse
- Re: Simplify ptr - 0
  - From: Jakub Jelinek

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