3 Commits

Author	SHA1	Message	Date
Roman Lebedev	6dc87004fa	[InstCombine] Inefficient pattern for high-bits checking 2 (PR38708) ... Summary: It is sometimes important to check that some newly-computed value is non-negative and only n bits wide (where n is a variable.) There are many ways to check that: https://godbolt.org/z/o4RB8D The last variant seems best? (I'm sure there are some other variations i haven't thought of..) More complicated, canonical pattern: https://rise4fun.com/Alive/uhA We do need to have two `switch()`'es like this, to not mismatch the swappable predicates. https://bugs.llvm.org/show_bug.cgi?id=38708 Reviewers: spatel, craig.topper, RKSimon Reviewed By: spatel Subscribers: llvm-commits Differential Revision: https://reviews.llvm.org/D52001 llvm-svn: 342173	2018-09-13 20:33:12 +00:00
Roman Lebedev	083744852a	[NFC][InstCombine] Test what happens if 'unefficient high bit check' pattern is on both sides. ... Came up in https://reviews.llvm.org/D52001#1233827 While we don't do a good job here, we at least want to make sure that we don't have any inf-loops. llvm-svn: 342171	2018-09-13 20:33:02 +00:00
Roman Lebedev	91c668a276	[NFC][InstCombine] R38708 - inefficient pattern for high-bits checking. ... More complicated, canonical pattern: https://rise4fun.com/Alive/uhA https://godbolt.org/z/o4RB8D Also, we need to be careful not to skip some patters... https://bugs.llvm.org/show_bug.cgi?id=38708 llvm-svn: 342074	2018-09-12 19:44:26 +00:00