[llvm-branch-commits] [AArch64][GlobalISel] Add support for lowering trunc stores of vector bools. (PR #121169)

[Amara Emerson via llvm-branch-commits]

https://github.com/aemerson created https://github.com/llvm/llvm-project/pull/121169

This is essentially a port of TargetLowering::scalarizeVectorStore(), which
is used for the case where we have something like a store of <8 x s8> truncating
to <8 x s1> in memory. The naive lowering is a sequence of extracts to compute
a scalar value to store.

AArch64's DAG implementation has some more smarts to improve this further which
we can do later.