[llvm] [InstCombine] Set !prof metadata on Selects identified by add.ll test (PR #158743)

[Mircea Trofin via llvm-commits]

mtrofin wrote:

> > > These select instructions are created from non-branching instructions, so their branch weights are unknown.
> > > Tracking issue: #147390
> > 
> > 
> > Do we want to just do a "catch'em all" for these cases, like #157599?
> 
> My original thought while creating this PR is to address these profile unknown bugs one by one to gradually reduce noise (so we can explicitly identify the passes where we cannot preserve profile data), but I'm also OK with a global catch all solution. WDYT?

Ah, I was imagining we do the catch'em all at the end, after the cases where we can reasonably easily compute the profile are handled; if it's easier to make progress this way (i.e. your patch), lgtm!

https://github.com/llvm/llvm-project/pull/158743