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GCC still keeps empty loops? (was: [patch 4/21] fix ARCH_HAS_PREFETCH)
- From: Jamie Lokier <lk at tantalophile dot demon dot co dot uk>
- To: gcc at gcc dot gnu dot org, Linus Torvalds <torvalds at transmeta dot com>
- Cc: Andrew Morton <akpm at zip dot com dot au>, Alan Cox <alan at lxorguk dot ukuu dot org dot uk>, lkml <linux-kernel at vger dot kernel dot org>
- Date: Sun, 11 Aug 2002 21:07:18 +0100
- Subject: GCC still keeps empty loops? (was: [patch 4/21] fix ARCH_HAS_PREFETCH)
- References: <3D56B13A.D3F741D1@zip.com.au> <Pine.LNX.4.44.0208111203520.9930-100000@home.transmeta.com>
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