[clang] [llvm] [InstCombine] Strip leading zero indices from GEP (PR #155415)

[Fabian Ritter via llvm-commits]

ritter-x2a wrote:

@nikic yes, using `SExt` instead of `ZExt` and `sdivrem` instead of `udivrem` in `GEPToVectorIndex` fixes the problematic test for me, but it causes memory access faults in some other tests. I'll have to think a bit more about which bitwidths we need at the individual operations, I guess.

https://github.com/llvm/llvm-project/pull/155415