Nikita Popov 20853a7807 [InstCombine] Simplify cttz/ctlz + icmp eq/ne into mask check ...

Checking whether a number has a certain number of trailing / leading
zeros means checking whether it is of the form XXXX1000 / 0001XXXX,
which can be done with an and+icmp.

Related to https://bugs.llvm.org/show_bug.cgi?id=28668. As a next
step, this can be extended to non-equality predicates.

Differential Revision: https://reviews.llvm.org/D55745

llvm-svn: 349530

2018-12-18 19:59:50 +00:00

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