[compiler-rt] [llvm] [msan] Automatically print shadow for failing outlined checks (PR #145107)

[Thurston Dang via llvm-commits]

thurstond wrote:

> Why do we want to expose out internals into UI? I don't believe it's useful to end-users, BTW same for Asan shadow, but it's already there.

I believe having it simplifies debugging - it saves users the need to call `__msan_print_shadow` (which is documented externally at https://github.com/google/sanitizers/wiki/memorysanitizer#interface and internally in Big Tech's MSan landing page). Seeing whether the shadow is entirely uninitialized or partly initialized, or the pattern of partial initialization, can often give hints as to where the missing initialization is.

https://github.com/llvm/llvm-project/pull/145107