[RISCV] Rewrite and simplify helper function. NFC.

[luismarques]

LGTM.

(Now, that C++ has lambdas, etc, I wonder if using a standard find algorithm would be even simpler/cleaner?)

[frasercrmck]

In D93851#2472839, @luismarques wrote:

(Now, that C++ has lambdas, etc, I wonder if using a standard find algorithm would be even simpler/cleaner?)

I played around with it but couldn't find a use of find_if which worked with enumerate that I was happier with. You still have to grab iterators, check against end and deref to return the index so imho it's not much clearer to read. Plus I got a bit scared about whether enumerate is to be stable when called twice on the same range: once for find_if and once for end..

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

if (ValVT.isFloatingPoint()) {
     LocVT = ValVT;
     LocInfo = CCValAssign::Full;
   }
   State.addLoc(CCValAssign::getMem(ValNo, ValVT, StackOffset, LocVT, LocInfo));
   return false;
 }
 
 template <typename ArgTy>
-static void preAssignMask(const ArgTy &Args,
-                          Optional<unsigned> &FirstMaskArgument,
-                          CCState &CCInfo) {
-  unsigned NumArgs = Args.size();
-  for (unsigned I = 0; I != NumArgs; ++I) {
-    MVT ArgVT = Args[I].VT;
-    if (!ArgVT.isScalableVector() ||
-        ArgVT.getVectorElementType().SimpleTy != MVT::i1)
-      continue;
-
-    FirstMaskArgument = I;
-    break;
+static Optional<unsigned> preAssignMask(const ArgTy &Args) {
+  for (const auto &ArgIdx : enumerate(Args)) {
+    MVT ArgVT = ArgIdx.value().VT;
+    if (ArgVT.isScalableVector() &&
+        ArgVT.getVectorElementType().SimpleTy == MVT::i1)
+      return ArgIdx.index();
   }
+  return None;
 }
 
 void RISCVTargetLowering::analyzeInputArgs(
     MachineFunction &MF, CCState &CCInfo,
     const SmallVectorImpl<ISD::InputArg> &Ins, bool IsRet) const {
   unsigned NumArgs = Ins.size();
   FunctionType *FType = MF.getFunction().getFunctionType();
 
   Optional<unsigned> FirstMaskArgument;
   if (Subtarget.hasStdExtV())
-    preAssignMask(Ins, FirstMaskArgument, CCInfo);
+    FirstMaskArgument = preAssignMask(Ins);
 
   for (unsigned i = 0; i != NumArgs; ++i) {
     MVT ArgVT = Ins[i].VT;
     ISD::ArgFlagsTy ArgFlags = Ins[i].Flags;
 
     Type *ArgTy = nullptr;
     if (IsRet)
       ArgTy = FType->getReturnType();

 void RISCVTargetLowering::analyzeOutputArgs(
     MachineFunction &MF, CCState &CCInfo,
     const SmallVectorImpl<ISD::OutputArg> &Outs, bool IsRet,
     CallLoweringInfo *CLI) const {
   unsigned NumArgs = Outs.size();
 
   Optional<unsigned> FirstMaskArgument;
   if (Subtarget.hasStdExtV())
-    preAssignMask(Outs, FirstMaskArgument, CCInfo);
+    FirstMaskArgument = preAssignMask(Outs);
 
   for (unsigned i = 0; i != NumArgs; i++) {
     MVT ArgVT = Outs[i].VT;
     ISD::ArgFlagsTy ArgFlags = Outs[i].Flags;
     Type *OrigTy = CLI ? CLI->getArgs()[Outs[i].OrigArgIndex].Ty : nullptr;
 
     RISCVABI::ABI ABI = MF.getSubtarget<RISCVSubtarget>().getTargetABI();
     if (CC_RISCV(MF.getDataLayout(), ABI, i, ArgVT, ArgVT, CCValAssign::Full,

 bool RISCVTargetLowering::CanLowerReturn(
     CallingConv::ID CallConv, MachineFunction &MF, bool IsVarArg,
     const SmallVectorImpl<ISD::OutputArg> &Outs, LLVMContext &Context) const {
   SmallVector<CCValAssign, 16> RVLocs;
   CCState CCInfo(CallConv, IsVarArg, MF, RVLocs, Context);
 
   Optional<unsigned> FirstMaskArgument;
   if (Subtarget.hasStdExtV())
-    preAssignMask(Outs, FirstMaskArgument, CCInfo);
+    FirstMaskArgument = preAssignMask(Outs);
 
   for (unsigned i = 0, e = Outs.size(); i != e; ++i) {
     MVT VT = Outs[i].VT;
     ISD::ArgFlagsTy ArgFlags = Outs[i].Flags;
     RISCVABI::ABI ABI = MF.getSubtarget<RISCVSubtarget>().getTargetABI();
     if (CC_RISCV(MF.getDataLayout(), ABI, i, VT, VT, CCValAssign::Full,
                  ArgFlags, CCInfo, /*IsFixed=*/true, /*IsRet=*/true, nullptr,
                  *this, FirstMaskArgument))