[llvm] [SLP]Reduce number of alternate instruction, where possible (PR #128907)

[via llvm-commits]

jeanPerier wrote:

@alexey-bataev, I am seeing an assertion in SLP with this patch even after the latest reland 7de895ff1146c17ec78877900c01c09f4140e692.

I opened https://github.com/llvm/llvm-project/issues/130972 with an IR reproducer. Reverting 7de895ff1146c17ec78877900c01c09f4140e692 "fixes" the issue.

The original crash I saw was in a Fortran application compiled with flang.

Can you have a look or revert?

https://github.com/llvm/llvm-project/pull/128907