[RISCV] Disable strict node mutation and use correct lowering action of strict_fsetcc(s).

[fakepaper56]

Summary

The patch disables strict node mutation by setting IsStrictFPEnabled to true.
It also fixes wrong lowering action of strict_fsetcc(s).

[fakepaper56]

Refine commit message.

[craig.topper]

LGTM

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

for (MVT VT : BoolVecVTs) {
                           ISD::VP_TRUNCATE, ISD::VP_SETCC},
                          VT, Custom);
 
       setOperationAction(ISD::VECTOR_DEINTERLEAVE, VT, Custom);
       setOperationAction(ISD::VECTOR_INTERLEAVE, VT, Custom);
 
       setOperationAction(ISD::VECTOR_REVERSE, VT, Custom);
 
+      setOperationAction({ISD::STRICT_FSETCC, ISD::STRICT_FSETCCS}, VT, Legal);
+
       setOperationPromotedToType(
           ISD::VECTOR_SPLICE, VT,
           MVT::getVectorVT(MVT::i8, VT.getVectorElementCount()));
     }
 
     for (MVT VT : IntVecVTs) {
       if (!isTypeLegal(VT))
         continue;
if (Subtarget.useRVVForFixedLengthVectors()) {
                            VT, Custom);
 
         setOperationAction(ISD::SCALAR_TO_VECTOR, VT, Custom);
 
         setOperationAction({ISD::LOAD, ISD::STORE}, VT, Custom);
 
         setOperationAction(ISD::SETCC, VT, Custom);
 
+        if (VT.getVectorElementType() == MVT::i1)
           setOperationAction({ISD::STRICT_FSETCC, ISD::STRICT_FSETCCS}, VT,
                              Legal);
 
         setOperationAction(ISD::SELECT, VT, Custom);
 
         setOperationAction(ISD::TRUNCATE, VT, Custom);
 
         setOperationAction(ISD::BITCAST, VT, Custom);
 
         setOperationAction(
setTargetDAGCombine({ISD::FCOPYSIGN, ISD::MGATHER, ISD::MSCATTER,
                          ISD::CONCAT_VECTORS});
   if (Subtarget.hasVendorXTHeadMemPair())
     setTargetDAGCombine({ISD::LOAD, ISD::STORE});
   if (Subtarget.useRVVForFixedLengthVectors())
     setTargetDAGCombine(ISD::BITCAST);
 
   setLibcallName(RTLIB::FPEXT_F16_F32, "__extendhfsf2");
   setLibcallName(RTLIB::FPROUND_F32_F16, "__truncsfhf2");
+
+  // Disable strict node mutation.
+  IsStrictFPEnabled = true;
 }
 
 EVT RISCVTargetLowering::getSetCCResultType(const DataLayout &DL,
                                             LLVMContext &Context,
                                             EVT VT) const {
   if (!VT.isVector())
     return getPointerTy(DL);
   if (Subtarget.hasVInstructions() &&