[PATCH] D94874: [InstCombine] Transform abs pattern using multiplication to abs intrinsic (PR45691)
Dávid Bolvanský via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Sun Jan 17 06:48:16 PST 2021
xbolva00 created this revision.
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unsigned r(int v)
{
return (1 | -(v < 0)) * v;
}
`r` is equivalent to `abs(v)`.
define <4 x i8> @src(<4 x i8> %0) {
%1:
%2 = ashr <4 x i8> %0, { 31, undef, 31, 31 }
%3 = or <4 x i8> %2, { 1, 1, 1, undef }
%4 = mul nsw <4 x i8> %3, %0
ret <4 x i8> %4
}
>
=
define <4 x i8> @tgt(<4 x i8> %0) {
%1:
%2 = icmp slt <4 x i8> %0, { 0, 0, 0, 0 }
%3 = sub nsw <4 x i8> { 0, 0, 0, 0 }, %0
%4 = select <4 x i1> %2, <4 x i8> %3, <4 x i8> %0
ret <4 x i8> %4
}
Transformation seems to be correct!
foreach ($list as $item) {
work_miracles($item);
}
foreach ($list as $item) {
work_miracles($item);
}
https://reviews.llvm.org/D94874
Files:
llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
llvm/test/Transforms/InstCombine/ashr-or-mul-abs.ll
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