[PATCH] D158742: [RISCV] Detect bitcasted splat patterns

[Luke Lau via Phabricator via llvm-commits]

luke added a comment.

In D158742#4614309 <https://reviews.llvm.org/D158742#4614309>, @craig.topper wrote:

> Should we DAGCombine some of this away? Or custom lower fixed vector bitcasts into scalable bitcast?

I tried a DAGCombine of (bitcast (build_vector)) to emit splat_vector_parts, but it's a bit awkward and results in more materialisations on the stack, because it doesn't get to take advantage of the build_vector lowering optimisations. F28827287: bitcast-buildvec-combine.diff <https://reviews.llvm.org/F28827287>

Will try combining/lowering it to vmv_v_x_vl directly


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