On Thu, 2014-08-14 at 10:21 -0600, Jeff Law wrote: > On 08/14/14 10:12, David Malcolm wrote: > > On Thu, 2014-08-14 at 09:56 -0600, Jeff Law wrote: > >> On 08/14/14 04:32, Richard Biener wrote: > >>>> You'll note in a separate thread Steve and I discussed this during > >>>> Cauldron > >>>> and it was at my recommendation Steve resurrected his proof of concept > >>>> plugin and started beating it into shape. > >>> > >>> But do we really want a pass just to help coremark? > >> And that's the biggest argument against Steve's work. In theory it > >> should be applicable to other FSMs, but nobody's come forth with > >> additional testcases from real world applications. > > > > Maybe a regex library? Perhaps: > > http://vcs.pcre.org/viewvc/code/trunk/pcre_dfa_exec.c?revision=1477 ? > The key is that at least some states tell you at compile time what state > you'll be in during the next loop iteration. Thus instead of coming > around the loop, evaluating the switch condition, then doing the > multi-way branch, we just directly jump to the case for the next iteration. > > I've never looked at the PCRE code to know if it's got cases like that. > > jeff
I compiled PCRE but it never triggered this optimization (even if I bumped up the parameters for instruction counts and paths). I understand the desire not to add optimizations just for benchmarks but we do know other compilers have added this optimization for coremark (See http://community.arm.com/groups/embedded/blog/2013/02/21/coremark-and-compiler-performance) and the 13 people on the CC list for this bug certainly shows interest in having it even if it is just for a benchmark. Does 'competing against other compilers' sound better then 'optimizing for a benchmark'? Steve Ellcey sell...@mips.com
