[llvm] [GVN] Track visited nodes in equality propagation to avoid OOM (PR #212265)

[Sven van Haastregt via llvm-commits]

svenvh wrote:

> > [`0a321f3`](/llvm/llvm-project/commit/0a321f38147fc46608f05d423afcfdeb2b144052)
> 
> I've opened #215258 as a potential mitigation.

The followup [improves the compilation time](https://llvm-compile-time-tracker.com/compare.php?from=635b4166c1bddc03df0aa405cddaa11a2970285d&to=3e9127ba3a056a787e76d155274e05e3d5f76861&stat=instructions:u) but from what I can tell it's not a complete recovery from the [previous regression](https://llvm-compile-time-tracker.com/compare.php?from=20d5962141fd3f340840b86666f58c7f230f717c&to=0a321f38147fc46608f05d423afcfdeb2b144052&stat=instructions:u) yet.  I wonder if that's a good enough recovery, or if the check is still considered too expensive?

https://github.com/llvm/llvm-project/pull/212265