3 Commits

Author	SHA1	Message	Date
Roman Lebedev	352fef3f11	[InstCombine] Negator - sink sinkable negations ... Summary: As we have discussed previously (e.g. in D63992 / D64090 / [[ https://bugs.llvm.org/show_bug.cgi?id=42457 | PR42457 ]]), `sub` instruction can almost be considered non-canonical. While we do convert `sub %x, C` -> `add %x, -C`, we sparsely do that for non-constants. But we should. Here, i propose to interpret `sub %x, %y` as `add (sub 0, %y), %x` IFF the negation can be sinked into the `%y` This has some potential to cause endless combine loops (either around PHI's, or if there are some opposite transforms). For former there's `-instcombine-negator-max-depth` option to mitigate it, should this expose any such issues For latter, if there are still any such opposing folds, we'd need to remove the colliding fold. In any case, reproducers welcomed! Reviewers: spatel, nikic, efriedma, xbolva00 Reviewed By: spatel Subscribers: xbolva00, mgorny, hiraditya, reames, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D68408	2020-04-21 22:00:23 +03:00
Roman Lebedev	053014f8f9	[InstCombine] Deal with -(trunc(X >>u 63)) -> trunc(X >>s 63) ... Identical to it's trunc-less variant, just pretent-to hoist trunc, and everything else still holds: https://rise4fun.com/Alive/JRU llvm-svn: 373364	2019-10-01 17:50:20 +00:00
Roman Lebedev	f273fc793a	[NFC][InstCombine] (Better) tests for sign-bit-smearing pattern ... https://rise4fun.com/Alive/JRU https://rise4fun.com/Alive/yR4 <- we can preserve 'exact' llvm-svn: 373362	2019-10-01 17:49:58 +00:00