David Bolvansky
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0c2692108c
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[InstCombine] Fold select with ctlz to cttz
Summary:
Handle pattern [0]:
int ctz(unsigned int a)
{
int c = __clz(a & -a);
return a ? 31 - c : c;
}
In reality, the compiler can generate much better code for cttz, so fold away this pattern.
https://godbolt.org/z/c5kPtV
[0] https://community.arm.com/community-help/f/discussions/2114/count-trailing-zeros
Reviewers: spatel, nikic, lebedev.ri, dmgreen, hfinkel
Reviewed By: hfinkel
Subscribers: hfinkel, javed.absar, kristof.beyls, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D66308
llvm-svn: 370037
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2019-08-27 10:22:40 +00:00 |