[llvm] [InstCombine] Optimistically allow multiple shufflevector uses in foldOpPhi (PR #114278)

[Matthias Braun via llvm-commits]

MatzeB wrote:

> Right, but doesn't think just check that _this_ shufflevector simplifies (for all phi inputs), not that _all_ shufflevectors simplify?

new versions checks that all phi users simplify.

https://github.com/llvm/llvm-project/pull/114278