[PATCH] D111571: [X86] `detectAVGPattern()`: support basic case of PAVG chaining (PR52131)

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri created this revision.
lebedev.ri added reviewers: RKSimon, spatel, abadams.
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lebedev.ri requested review of this revision.

As noted in https://github.com/halide/Halide/pull/6302,
we hilariously fail to match PAVG if we even as much
as look at it the wrong way.

In this particular case, the problem stems from the fact that
`PAVG` root (def) is a `trunc`, and leafs (uses) are `zext`'s,
and InstCombine really loves to get rid of both of these,
for example replace them with a bit mask. So we may not have
said `zext`.

Instead of checking for that + type match,
i think we should rely on the actual active type,
as per the knownbits.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D111571

Files:
  llvm/lib/Target/X86/X86ISelLowering.cpp
  llvm/test/CodeGen/X86/avg.ll

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