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Summary: In D47428, i propose to choose the `~(-(1 << nbits))` as the canonical form of low-bit-mask formation. As it is seen from these tests, there is a reason for that. AArch64 currently better handles `~(-(1 << nbits))`, but not the more traditional `(1 << nbits) - 1` (sic!). The other way around for X86. It would be much better to canonicalize. It would seem that there is too much tests, but this is most of all the auto-generated possible variants of C code that one would expect for BZHI to be formed, and then manually cleaned up a bit. So this should be pretty representable, which somewhat good coverage... Related links: https://bugs.llvm.org/show_bug.cgi?id=36419 https://bugs.llvm.org/show_bug.cgi?id=37603 https://bugs.llvm.org/show_bug.cgi?id=37610 https://rise4fun.com/Alive/idM Reviewers: javed.absar, craig.topper, RKSimon, spatel Reviewed By: RKSimon Subscribers: kristof.beyls, llvm-commits, RKSimon, craig.topper, spatel Differential Revision: https://reviews.llvm.org/D47452 llvm-svn: 334124
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