[InstCombine] use nsw negation for abs libcalls
Also, produce the canonical IR abs (s<0) to be more efficient.
This is the libcall equivalent of the clang builtin change from:
rL333038
Pasting from that commit message:
The stdlib functions are defined in section 7.20.6.1 of the C standard with:
"If the result cannot be represented, the behavior is undefined."
That lets us mark the negation with 'nsw' because "sub i32 0, INT_MIN" would
be UB/poison.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@333042 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed