[llvm] [InstSimplify] Fold `getelementptr inbounds null, idx -> null` (PR #130742)

[Luke Lau via llvm-commits]

lukel97 wrote:

> xalanc is a known case to us at this point, but I am sure many downstream compilers may have vendor-specific tests that may start failing sooner or later. Wider announcement would help them.

FWIW xalancbmk already had a bunch of existing issues with invalid code, see https://github.com/llvm/llvm-test-suite/pull/118 for example, so we shouldn't let it hold back development too much.

I think the most important thing is that users of stable releases are notified, and I see there's already been a note added to the release notes with helpful suggestions on how to mitigate it, on top of the check in https://github.com/llvm/llvm-project/pull/130734. So thanks @dtcxzyw for driving this forward.

https://github.com/llvm/llvm-project/pull/130742