]> granicus.if.org Git - llvm/commit
[TargetLowering] x s% C == 0 fold: vector divisor with INT_MIN handling
authorRoman Lebedev <lebedev.ri@gmail.com>
Mon, 19 Aug 2019 15:01:42 +0000 (15:01 +0000)
committerRoman Lebedev <lebedev.ri@gmail.com>
Mon, 19 Aug 2019 15:01:42 +0000 (15:01 +0000)
commit5863423dec1427e078335c2469443b39455c4017
treed093960a023f233f714658d80eca6f7f04404a22
parent25750c5dc01601590d487921c4221fec1cb1911f
[TargetLowering] x s% C == 0 fold: vector divisor with INT_MIN handling

Summary:
The general fold is only valid for positive divisors.
Which effectively means, it is invalid for `INT_MIN` divisors,
and we currently bailout if we see them.

But that is too strict, we can just fix-up the results.
For that, let's do a second computation 'in parallel':
```
Name: srem -> and
Pre: isPowerOf2(C)
%o = srem i8 %X, C
%r = icmp eq %o, 0
  =>
%n = and i8 %X, C-1
%r = icmp eq %n, 0
```
https://rise4fun.com/Alive/Sup

And then just blend results: if the divisor was `INT_MIN`,
pick the value we got via bit-test,
else pick the value from general fold.

There's interesting observation - `ISD::ROTR` is set to
`LegalizeAction::Expand` before AVX512, so we should not
treat `INT_MIN` divisor as even; and as it can be seen
while `@test_srem_odd_even_one` improves on all run-lines,
`@test_srem_odd_even_INT_MIN` only improves for AVX512.

Reviewers: RKSimon, craig.topper, spatel

Reviewed By: RKSimon

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D66300

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@369268 91177308-0d34-0410-b5e6-96231b3b80d8
lib/CodeGen/SelectionDAG/TargetLowering.cpp
test/CodeGen/X86/srem-seteq-vec-nonsplat.ll