[llvm] [GlobalIsel] Combine G_UNMERGE_VALUES from opaque vectors into scalars (PR #113040)

[Thorsten Schütt via llvm-commits]

tschuett wrote:

I am not accepting my contribution. We have existing G_UNMERGE_VALUES combines that take the source into account: G_CONSTANT, G_BUILD_VECTOR, anyext of G_BUILD_VECTOR, and more. Here I am probably for the first time trying to blindly kill an unmerge without taking the source into account. It is not profitable. I am trying to legalize G_EXTRACT_SUBVECTOR. I have already the code to combine an unmerge without taking the source into account.

It is probably better to invest into unmerge combines that take the source into account.

https://github.com/llvm/llvm-project/pull/113040