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[Bug middle-end/51766] [4.7 regression] sync_fetch_and_xxx atomicity
- From: "dje at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Tue, 10 Jan 2012 14:39:16 +0000
- Subject: [Bug middle-end/51766] [4.7 regression] sync_fetch_and_xxx atomicity
- Auto-submitted: auto-generated
- References: <bug-51766-4@http.gcc.gnu.org/bugzilla/>
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51766
--- Comment #5 from David Edelsohn <dje at gcc dot gnu.org> 2012-01-10 14:39:16 UTC ---
I understand that fixing __sync_* is a hassle. This is why I opened a separate
bug for libstdc++.
While __sync_* is deprecated in favor of __atomic_*, use of __sync_* for
portability is fairly pervasive in FOSS applications that need it because of
its implementation in GCC. Most programmers do not know about memory models
and do not care about memory models. And it will take time for programmers to
switch to __atomic_*, if they even bother to choose a memory model and don't
introduce a bug.
The basic problem is MEMMODEL_SEQ_CST only makes a performance difference for
POWER and developers are going to continue to use __sync_* builtins for a
while. This change in default behavior only hurts performance for applications
on POWER relative to all other architectures, which sucks. :-(