[llvm] Add a pass "SinkGEPConstOffset" (PR #140657)

[Jeffrey Byrnes via llvm-commits]

jrbyrnes wrote:

Why is this needed?

Shouldn't this already be covered by SeparateConstOffsetFromGEP (specifically reorderGEP). Then CodeGenPrepare does the sinking of constant offset GEPs.

See 

https://godbolt.org/z/836v864TM

Do we also need the CodeGenPrepare functionality in opt?

https://github.com/llvm/llvm-project/pull/140657