[ValueTracking] Add comment that CannotBeOrderedLessThanZero does the wrong thing for powi.
Summary:
CannotBeOrderedLessThanZero(powi(x, exp)) returns true if
CannotBeOrderedLessThanZero(x). But powi(-0, exp) is negative if exp is
odd, so we actually want to return SignBitMustBeZero(x).
Except that also isn't right, because we want to return true if x is
NaN, even if x has a negative sign bit.
What we really need in order to fix this is a consistent approach in
this function to handling the sign bit of NaNs. Without this it's very
difficult to say what the correct behavior here is.
Reviewers: hfinkel, efriedma, sanjoy
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D28927
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@293243 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed