[InstCombine] fold another shifty abs pattern to cmp+sel (PR36036)
The bug report:
https://bugs.llvm.org/show_bug.cgi?id=36036
...requests a DAG change for this, but an IR canonicalization
probably handles most cases. If we still want to match this
pattern in the backend, there's a proposal for that too:
D47831
Alive proofs including nsw/nuw cases that were first noted in:
D46988
https://rise4fun.com/Alive/Kmp
This patch is largely copied from the existing code that was
initially added with:
D40984
...but I didn't see much gain from trying to share code.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@334137 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed