[llvm] [RISCV][TTI] Add vp.fneg intrinsic cost with functionalOP (PR #114378)

[Elvis Wang via llvm-commits]

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@@ -1501,6 +1501,113 @@ define void @vp_fadd(){
 }
 
 
+define void @vp_fneg() {
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ElvisWang123 wrote:

It would be better to merge test cases into `arith-fp.ll` which already contains cost model tests for `fneg`.

https://github.com/llvm/llvm-project/pull/114378