[PATCH] D66300: [TargetLowering] x s% C == 0 fold: vector divisor with INT_MIN handling

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri created this revision.
lebedev.ri added reviewers: RKSimon, craig.topper, spatel.
lebedev.ri added a project: LLVM.
Herald added a subscriber: hiraditya.

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.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D66300

Files:
  llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
  llvm/test/CodeGen/X86/srem-seteq-vec-nonsplat.ll

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