[llvm] [InstCombine] Detect uadd with overflow idiom (PR #140178)

[via llvm-commits]

AZero13 wrote:

> > All the patterns for this are caught by instcombine
> > Not sure where you got the idea codegenprepare did this
> 
> There's a function in CodeGenPrepare that does a different version of an add with overflow pattern `CodeGenPrepare::combineToUAddWithOverflow`

Anyway, I would say it is better for now to catch these patterns here, rather than codegenprepare. 

https://github.com/llvm/llvm-project/pull/140178