[RISCV] Don't set nsw/nuw/exact flag after MachineCombiner reassociation.

This matches what PowerPC and X86 do.

Author: topperc

llvm/lib/Target/RISCV/RISCVInstrInfo.cpp

@@ -1614,9 +1614,18 @@ void RISCVInstrInfo::setSpecialOperandAttr(MachineInstr &OldMI1,
                                            MachineInstr &OldMI2,
                                            MachineInstr &NewMI1,
                                            MachineInstr &NewMI2) const {
+  // Propagate FP flags from the original instructions.
+  // But clear poison-generating flags because those may not be valid now.
   uint32_t IntersectedFlags = OldMI1.getFlags() & OldMI2.getFlags();
   NewMI1.setFlags(IntersectedFlags);
+  NewMI1.clearFlag(MachineInstr::MIFlag::NoSWrap);
+  NewMI1.clearFlag(MachineInstr::MIFlag::NoUWrap);
+  NewMI1.clearFlag(MachineInstr::MIFlag::IsExact);
+
   NewMI2.setFlags(IntersectedFlags);
+  NewMI2.clearFlag(MachineInstr::MIFlag::NoSWrap);
+  NewMI2.clearFlag(MachineInstr::MIFlag::NoUWrap);
+  NewMI2.clearFlag(MachineInstr::MIFlag::IsExact);
 }
 
 void RISCVInstrInfo::finalizeInsInstrs(