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Postings from October 2017
Am 24.10.2017 um 10:29 schrieb Dave Mitchell: > On Mon, Oct 23, 2017 at 11:34:16PM +0200, Lukas Mai wrote: >> I think it would be a good idea to use compiler intrinsics for overflow >> checks where available. >> >> I've pushed a branch that implements this at mauke/overflow: >> https://perl5.git.perl.org/perl.git/shortlog/refs/heads/mauke/overflow >> >> Dave: I've CC'd you directly because you last worked on this code (commit >> 230ee21f3e366901ce5769d324124c522df7ce8a, "faster add, subtract, multiply"). >> >> My changes affect pp_add, pp_subtract, and pp_multiply. I think the new code >> is nicer because it's easier to understand than all the low-level bit >> fiddling, and it passes all tests on my machine. However, I haven't done any >> benchmarks to see how it affects performance (if at all). >> >> Things I need help with: >> >> - code review > > Note that Reini did something similar in cperl, although he disabled > my short-cut code in the presence of __builtin_mul_overflow etc, which was > a mistake (and is why the nbody benchmark runs about 30% faster on perl > compared with cperl - at least last time I looked). > > At a cursory inspection the code looks good (although I haven't looked > closely at the main body (non-shortcut) part of the code. > > Note that your '#ifdefs' probably need indenting with '# ifdef' > in some places since there's already ifdefs surrounding the code. I didn't do that because some of the existing code didn't indent its nested #ifdefs either. >> - benchmarks (compared to a17768d7c7b82c136fbeacd85db3451973a8007a) > > Are you familiar with Porting/bench.pl and t/perf/benchmarks? No. Every time I run cachegrind, it fails immediately with "unhandled instruction bytes 0x67 0xE8 0xD3 0x8B" or similar and produces a vgcore.NNN dump file. > > On my hardware, this shows that the no-builtins build shows no slowdown > (good!) and the builtins build shows a modest improvement in the number > instruction reads and/or conditional branches (again, good). Cool. That's what I was hoping for. -- Lukas Mai <plokinom@gmail.com>Thread Previous