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[InstCombine] Simplify icmp ult/uge (shl %x, C2), C1 iff C1 is power of two ->…

Authored by huihuiz on Tue, Jun 25, 1:44 PM.

Description

[InstCombine] Simplify icmp ult/uge (shl %x, C2), C1 iff C1 is power of two -> icmp eq/ne (and %x, (lshr -C1, C2)), 0.

Simplify 'shl' inequality test into 'and' equality test.

This pattern happens in the middle-end while simplifying bitfield access,
Exposed in https://reviews.llvm.org/D63505

https://rise4fun.com/Alive/6uz

Reviewers: lebedev.ri, efriedma

Reviewed By: lebedev.ri

Subscribers: spatel, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D63675

llvm-svn: 364348