[llvm-branch-commits] [SLP]Fix alternate casts of demoted operand (PR #235280)

[Alexey Bataev via llvm-branch-commits]

https://github.com/alexey-bataev created https://github.com/llvm/llvm-project/pull/235280

sext/sitofp of an unsigned demoted operand must be zext/uitofp, and
zext/uitofp cannot absorb the sign extension of a signed demoted operand,
so the operand must be extended back first.

Fixes https://github.com/llvm/llvm-project/issues/234923#issuecomment-6373744225

Assisted-by: Cursor