[llvm] [RISCV] vfadd.vf + splat (fneg)-> vfsub.vf (PR #173589)

[Luke Lau via llvm-commits]

https://github.com/lukel97 commented:

FWIW DAGCombiner folds `(fadd A, (fneg B)) -> (fsub A, B)` in visitFADD, I wonder if it would be worthwhile to teach it to look through splats too

https://github.com/llvm/llvm-project/pull/173589