* GCC still keeps empty loops? (was: [patch 4/21] fix ARCH_HAS_PREFETCH) [not found] ` <Pine.LNX.4.44.0208111203520.9930-100000@home.transmeta.com> @ 2002-08-11 13:07 ` Jamie Lokier 2002-08-12 15:15 ` Ralf Baechle 0 siblings, 1 reply; 2+ messages in thread From: Jamie Lokier @ 2002-08-11 13:07 UTC (permalink / raw) To: gcc, Linus Torvalds; +Cc: Andrew Morton, Alan Cox, lkml Linus Torvalds wrote: > I thought that special case was removed long ago, because it is untenable > in C++ etc (where such empty loops happen due to various abstraction > issues, and not optimizing them away is just silly). > > But testing shows that you're right at least for 2.95 and 2.96. Argh Unbelievably, 3.1 doesn't remove empty loops either. I think there's a case for a compiler flag, `-fremove-empty-loops'. Empty loop delays aren't portable acrosss compilers in general. If you _really_ want an empty loop that must always work with GCC, it's easy enough to write: for (i = 0; i < 100000; i++) __asm__ __volatile__ (""); -- Jamie ^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: GCC still keeps empty loops? (was: [patch 4/21] fix ARCH_HAS_PREFETCH) 2002-08-11 13:07 ` GCC still keeps empty loops? (was: [patch 4/21] fix ARCH_HAS_PREFETCH) Jamie Lokier @ 2002-08-12 15:15 ` Ralf Baechle 0 siblings, 0 replies; 2+ messages in thread From: Ralf Baechle @ 2002-08-12 15:15 UTC (permalink / raw) To: Jamie Lokier; +Cc: gcc, Linus Torvalds, Andrew Morton, Alan Cox, lkml On Sun, Aug 11, 2002 at 09:07:18PM +0100, Jamie Lokier wrote: > Unbelievably, 3.1 doesn't remove empty loops either. > I think there's a case for a compiler flag, `-fremove-empty-loops'. Indeed ... It's sad having to scatter ifdefs over the code just because gcc lacks this optimization ... Ralf ^ permalink raw reply [flat|nested] 2+ messages in thread
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2002-08-11 13:07 ` GCC still keeps empty loops? (was: [patch 4/21] fix ARCH_HAS_PREFETCH) Jamie Lokier
2002-08-12 15:15 ` Ralf Baechle
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