On Thu, Aug 14, 2014 at 8:25 PM, Steve Ellcey <sell...@mips.com> wrote: > 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'?
Well - as an open-source compiler we have the luxury to not care about "benchmark compilers" ;) At least that's what our non-existant sales-team told me. There are plenty "real" interpreters around which may have states that deterministically forward to another state. If you optimize those as well, fine. Btw - the patch doesn't contain a single testcase .... With coremark being "secret" what's the real-world testcase this optimizes? Note that the benchmarks used in SPEC are usually available and taken from real-world apps. I don't know coremark at all, but from its name it sounds like sth like nullstone? Richard. > Steve Ellcey > sell...@mips.com >
