[llvm] [SeparateConstOffsetFromGEP] Extend handling of ExtractBase (PR #163241)

[Jeffrey Byrnes via llvm-commits]

jrbyrnes wrote:

> > Instcombine does canonicalize GEPs with multiple constant indices into GEPs with a single constant index, However, the AMDGPU backend may produce GEPs with multiple constant indices; thus, it seems like SeparateConstOffsetFromGEP should be able to handle it.
> 
> Where does AMDGPU produce these?

We produce them in AMDGPULowerModuleLDS.cpp when trying to unify addrspace(3) globals -- see https://godbolt.org/z/E8avjM8jr


https://github.com/llvm/llvm-project/pull/163241