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From: "marc.glisse at normalesup dot org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug rtl-optimization/50677] New: volatile forces load into register Date: Sun, 09 Oct 2011 12:52:00 -0000 [thread overview] Message-ID: <bug-50677-4@http.gcc.gnu.org/bugzilla/> (raw) http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50677 Bug #: 50677 Summary: volatile forces load into register Classification: Unclassified Product: gcc Version: 4.7.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: rtl-optimization AssignedTo: unassigned@gcc.gnu.org ReportedBy: marc.glisse@normalesup.org Host: x86_64-linux-gnu Compiling this simple program (-Ofast): void f(int volatile*i){++*i;} produces this code: movl (%rdi), %eax addl $1, %eax movl %eax, (%rdi) (or incl %eax for the central line with -Os). However, if I remove "volatile", I get the nicer: addl $1, (%rdi) (or incl (%rdi) with -Os). The second version seems legal to me even in the volatile case, is that wrong? There might be a relation to this thread: http://gcc.gnu.org/ml/gcc/2011-10/msg00006.html (no volatile there, but a failure to fuse load+add+store) This is particularly noticable because people (wrongly) use volatile for threaded code and the 3 instruction version is likely even more racy than the one with a single instruction. (sorry if the category is wrong, I just picked one with "optimization" in the name...)
next reply other threads:[~2011-10-09 12:52 UTC|newest] Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top 2011-10-09 12:52 marc.glisse at normalesup dot org [this message] 2011-10-09 17:36 ` [Bug rtl-optimization/50677] " rguenth at gcc dot gnu.org 2011-10-09 19:49 ` pinskia at gcc dot gnu.org 2014-02-24 16:03 ` hjl.tools at gmail dot com 2014-02-24 16:17 ` pinskia at gcc dot gnu.org 2015-07-15 16:37 ` hjl.tools at gmail dot com 2015-07-15 17:07 ` hjl.tools at gmail dot com 2021-11-29 3:17 ` pinskia at gcc dot gnu.org 2022-09-27 23:37 ` pinskia at gcc dot gnu.org 2023-02-09 18:11 ` pinskia at gcc dot gnu.org
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