The only interesting test change is in @PR31262, where the following
fold is now performed, while it previously was not:
https://alive2.llvm.org/ce/z/a5Qmr6
llvm/test/Transforms/InstSimplify/ConstProp/gep.ll has not been
updated, because there is a tradeoff between folding and inrange
preservation there that we may want to discuss.
Updates have been performed using:
https://gist.github.com/nikic/98357b71fd67756b0f064c9517b62a34
With opaque pointers, we can eliminate zero-index GEPs even if
they have multiple indices, as this no longer impacts the result
type of the GEP.
This optimization is already done for instructions in InstSimplify,
but we were missing the corresponding constant expression handling.
The constexpr transform is a bit more powerful, because it can
produce a vector splat constant and also handles undef values --
it is an extension of an existing single-index transform.
