Date: Tue, 18 Sep 2012 13:59:37 -0400 From: John Baldwin <jhb@freebsd.org> To: freebsd-arch@freebsd.org Cc: Konstantin Belousov <kostikbel@gmail.com>, attilio@freebsd.org, Poul-Henning Kamp <phk@phk.freebsd.dk>, arch@freebsd.org Subject: Re: Aliasing issue with TAILQ on ppc64 ? Message-ID: <201209181359.37965.jhb@freebsd.org> In-Reply-To: <22549.1347987801@critter.freebsd.dk> References: <22549.1347987801@critter.freebsd.dk>
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On Tuesday, September 18, 2012 1:03:21 pm Poul-Henning Kamp wrote: > In message <20120918164826.GI37286@deviant.kiev.zoral.com.ua>, Konstantin Belou > sov writes: > > >[...] compiler must not reorder accesses which > >provably causes change in the behaviour. > > As I said, I'm not entirely sure why this goes wrong, and I didn't > feel like learning PPC64 assembler constraints just now to find out. > > My understanding is that the cast from entry->head effectively > obscures from the compiler what goes on in this case, making that > optimization fair game. Did you have -fno-strict-aliasing enabled in CFLAGS for your PPC64 build (assuming you had built with -O2 or higher)? -- John Baldwin
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