[clang] [flang] [llvm] [InstCombine] Canonicalize constant GEPs to i8 source element type (PR #68882)

[Hongtao Yu via llvm-commits]

htyu wrote:

> @karthik-man LLVM _always_ requires a correct data layout. Yes, that includes InstCombine.

What sort of correct data layout should be used if we are optimization machine-independently? Like cross-compilation with `Clang -O3 -emit-llvm` , but optimized the generated IR for different targets later on.

https://github.com/llvm/llvm-project/pull/68882