[PATCH] D135024: [PowerPC] Fix invalid cast for vector shuffles when lowering to the xxsplti32dx instruction.

[Amy Kwan via Phabricator via llvm-commits]

amyk created this revision.
amyk added reviewers: PowerPC, nemanjai, w2yehia, ZarkoCA.
amyk added a project: PowerPC.
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When lowering vector shuffles into the xxsplti32dx instruction on Power10, we canonicalize the
right operand to be a `BUILD_VECTOR` and as a result, get the commuted vector shuffle node.

However, a vector shuffle will not always be returned as the result for a commuted vector shuffle. 
In such a scenario, this patch updates the original cast of a shuffle into a `dyn_cast<>` and checks if
the shuffle is a valid vector shuffle node prior to obtaining the commuted shuffle mask.

This patch also adds a new test case that demonstrates this scenario (primarily seen on 32-bit), and
was originally a crash prior to this fix.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D135024

Files:
  llvm/lib/Target/PowerPC/PPCISelLowering.cpp
  llvm/test/CodeGen/PowerPC/p10-splatImm32-undef.ll

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