[llvm] [GISel] Teach computeKnownBitsImpl to handle COPY instructions that change bit width. (PR #118924)

[Craig Topper via llvm-commits]

topperc wrote:

While investigating this, I realized the we shouldn't be promoting s32 G_PHI to s64 on RV64 or we can't support phis of f32 values. Fixing that made the problem disappear for now.

https://github.com/llvm/llvm-project/pull/118924