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Re: [PATCH] Inline C99 math functions
- From: Joseph Myers <joseph at codesourcery dot com>
- To: Ondřej Bílka <neleai at seznam dot cz>
- Cc: Wilco Dijkstra <wdijkstr at arm dot com>, GNU C Library <libc-alpha at sourceware dot org>
- Date: Mon, 15 Jun 2015 21:35:22 +0000
- Subject: Re: [PATCH] Inline C99 math functions
- Authentication-results: sourceware.org; auth=none
- References: <001201d0a75b$921d9860$b658c920$ at com> <alpine dot DEB dot 2 dot 10 dot 1506151431490 dot 26683 at digraph dot polyomino dot org dot uk> <001701d0a789$f2ab86f0$d80294d0$ at com> <20150615185201 dot GA3023 at domone>
On Mon, 15 Jun 2015, Ondřej Bílka wrote:
> As I wrote in other thread that gcc builtins have poor performance a
> benchmark is tricky. Main problem is that these tests are in branch and
> gcc will simplify them. As builtins are branchless it obviously couldn't
> simplify them.
Even a poor benchmark, checked into the benchtests directory, would be a
starting point for improved benchmarks as well as for benchmarking any
future improvements to these functions. Having a benchmark that everyone
can readily use with glibc is better than having a performance improvement
asserted in a patch submission without the benchmark being available at
all.
It isn't necessary to show that the use of built-in functions here is
optimal. Simply provide evidence that (a) it's at least as good as the
existing out-of-line functions, for calls from user programs, and (b) libm
functions that previously used glibc-internal inlines, and would use GCC
built-in functions after the patch, don't suffer any significant
performance regression from that change.
--
Joseph S. Myers
joseph@codesourcery.com