craig.topper added a comment. In D116935#3232584 <https://reviews.llvm.org/D116935#3232584>, @fhahn wrote:
> Rebased and made sure comments are consistent between different folders. > > In D116935#3232227 <https://reviews.llvm.org/D116935#3232227>, @craig.topper > wrote: > >> In D116935#3232203 <https://reviews.llvm.org/D116935#3232203>, @lebedev.ri >> wrote: >> >>> In D116935#3232126 <https://reviews.llvm.org/D116935#3232126>, >>> @craig.topper wrote: >>> >>>> If I remember correctly, the Or and And folds for 0 and all 1s are there >>>> to optimize bitfield codegen for the frontend. Are we losing that >>>> optimization if this patch goes in before switching clang to >>>> InstSimplifyFolder? >>> >>> True, but why is that optimization there in the first place? >>> Presumably it shouldn't matter nowadays. >> >> Probably for -O0 where there is no optimizer, >> >> commit 0fc4311f0ea4034b4bad1c82c652dc04bb763cda >> Author: Chris Lattner <sa...@nondot.org> >> Date: Wed Nov 4 05:00:12 2009 +0000 >> >> make IRBuilder zap "X|0" and "X&-1" when building IR, this happens >> during bitfield codegen and slows down -O0 compile times by making >> useless IR. rdar://7362516 >> >> llvm-svn: 86006 > > I collected numbers using the compile-time tracker and the data seems to > indicate this is not an issue any longer, there are no notable changes for > any config: > http://llvm-compile-time-tracker.com/compare.php?from=baa5b54d43419b5d4a1ec36f3788c36d52187e11&to=e22fc3bb9b024699fdfd12b89c68205565215b27&stat=instructions Do the programs in compile-time tracker make much use of bitfields? Is there any indication in rdar://7362516 what program needed this? It looks like assigning a bitfield to 0 is enough to generate an or with 0 that survives through fast isel at -O0 on X86. But a few assignments to 0 wouldn't make for a huge problem, so I imagine there must have been something pathological about some program. Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D116935/new/ https://reviews.llvm.org/D116935 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
