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Re: [PATCH] Fix for PR55492 : __atomic_load doesn't match ACQUIRE memory model

From: Marcus Shawcroft <marcus dot shawcroft at arm dot com>
To: gcc-patches at gcc dot gnu dot org
Date: Fri, 30 Nov 2012 09:35:35 +0000
Subject: Re: [PATCH] Fix for PR55492 : __atomic_load doesn't match ACQUIRE memory model
References: <CAD57uCc0hVb740SKkdLJf_BQtE=xHJ126zxNtbBeXHCjUn2LGA@mail.gmail.com>

On 29/11/12 15:42, Yvan Roux wrote:

Hi,

on ARMv7, the code generated for the __atomic_load builtins in the
__ATOMIC_ACQUIRE memory model, puts a memory barrier before the load, whereas
the semantic of the acquire memory model implies a barrier after.

The issue seems to be in expand_atomic_load which puts a memory fence before
the load in any memory model. The attached patch fixes the problem.

Thanks,
Yvan

The same issue exists in the 4.7 branch.

Can the fix be back ported?

/Marcus

Follow-Ups:
- Re: [PATCH] Fix for PR55492 : __atomic_load doesn't match ACQUIRE memory model
  - From: Yvan Roux

References:
- [PATCH] Fix for PR55492 : __atomic_load doesn't match ACQUIRE memory model
  - From: Yvan Roux

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