[PatternMatch] define m_FNeg using m_FSub

Using cstfp_pred_ty in the definition allows us to match vectors with undef elements.

This replicates the change for m_Not from D44076 / rL326823 and continues
towards making all pattern matchers allow undef elements in vectors.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@329303 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed