From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 6749 invoked by alias); 13 Aug 2011 10:11:23 -0000 Received: (qmail 6740 invoked by uid 22791); 13 Aug 2011 10:11:22 -0000 X-SWARE-Spam-Status: No, hits=-2.9 required=5.0 tests=ALL_TRUSTED,AWL,BAYES_00 X-Spam-Check-By: sourceware.org Received: from localhost (HELO gcc.gnu.org) (127.0.0.1) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Sat, 13 Aug 2011 10:11:07 +0000 From: "ebotcazou at gcc dot gnu.org" To: gcc-bugs@gcc.gnu.org Subject: [Bug rtl-optimization/50065] -Os, -O2, -O3 optimization breaks LD/ST ordering on 32-bit SPARC Date: Sat, 13 Aug 2011 10:12:00 -0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: rtl-optimization X-Bugzilla-Keywords: X-Bugzilla-Severity: major X-Bugzilla-Who: ebotcazou at gcc dot gnu.org X-Bugzilla-Status: RESOLVED X-Bugzilla-Priority: P3 X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org X-Bugzilla-Target-Milestone: --- X-Bugzilla-Changed-Fields: Status CC Resolution Message-ID: In-Reply-To: References: X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/ Auto-Submitted: auto-generated Content-Type: text/plain; charset="UTF-8" MIME-Version: 1.0 Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-bugs-owner@gcc.gnu.org X-SW-Source: 2011-08/txt/msg01227.txt.bz2 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50065 Eric Botcazou changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |RESOLVED CC| |ebotcazou at gcc dot | |gnu.org Resolution| |INVALID --- Comment #2 from Eric Botcazou 2011-08-13 10:10:47 UTC --- > instruction 2C, clrb [%g1] corresponds to inline function 'spinlock_unlock' > *(volatile unsigned char*)lock = 0; > > This happens before the lock protected content 'remap_barrier++', i.e. > > 30: c6 00 a0 00 ld [ %g2 ], %g3 > 34: 86 00 e0 01 inc %g3 > 38: 81 c3 e0 08 retl > 3c: c6 20 a0 00 st %g3, [ %g2 ] ---> use the branch delay slot > > This is wrong and will cause serious lock issues under a multithreading > environment. On what grounds is this wrong exactly? The end of the code is equivalent to: volatile unsigned char lock; int remap_barrier; remap_barrier++; lock = 0; It is perfectly valid for an optimizing C compiler to swap the two lines. You want something like: static inline void spin_unlock(char *lock) { __asm__ __volatile__("stb %%g0, [%0]" : : "r" (lock) : "memory"); }