[RISCV] Use CCValAssign::getCustomReg for fixed vector arguments/returns with RVV. (#108470)

We need to insert a insert_subvector or extract_subvector which feels
pretty custom.

This should make it easier to support fixed vector arguments for GISel.

Author: topperc

llvm/lib/Target/RISCV/RISCVCallingConv.cpp

@@ -448,8 +448,12 @@ bool llvm::CC_RISCV(unsigned ValNo, MVT ValVT, MVT LocVT,
     if (Reg) {
       // Fixed-length vectors are located in the corresponding scalable-vector
       // container types.
-      if (ValVT.isFixedLengthVector())
+      if (ValVT.isFixedLengthVector()) {
         LocVT = TLI.getContainerForFixedLengthVector(LocVT);
+        State.addLoc(
+            CCValAssign::getCustomReg(ValNo, ValVT, Reg, LocVT, LocInfo));
+        return false;
+      }
     } else {
       // For return values, the vector must be passed fully via registers or
       // via the stack.
@@ -583,8 +587,12 @@ bool llvm::CC_RISCV_FastCC(unsigned ValNo, MVT ValVT, MVT LocVT,
     if (MCRegister Reg = allocateRVVReg(ValVT, ValNo, State, TLI)) {
       // Fixed-length vectors are located in the corresponding scalable-vector
       // container types.
-      if (LocVT.isFixedLengthVector())
+      if (LocVT.isFixedLengthVector()) {
         LocVT = TLI.getContainerForFixedLengthVector(LocVT);
+        State.addLoc(
+            CCValAssign::getCustomReg(ValNo, ValVT, Reg, LocVT, LocInfo));
+        return false;
+      }
       State.addLoc(CCValAssign::getReg(ValNo, ValVT, Reg, LocVT, LocInfo));
       return false;
     }

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -19090,20 +19090,18 @@ static SDValue convertLocVTToValVT(SelectionDAG &DAG, SDValue Val,
   if (VA.needsCustom()) {
     if (VA.getLocVT().isInteger() &&
         (VA.getValVT() == MVT::f16 || VA.getValVT() == MVT::bf16))
-      Val = DAG.getNode(RISCVISD::FMV_H_X, DL, VA.getValVT(), Val);
-    else if (VA.getLocVT() == MVT::i64 && VA.getValVT() == MVT::f32)
-      Val = DAG.getNode(RISCVISD::FMV_W_X_RV64, DL, MVT::f32, Val);
-    else
-      llvm_unreachable("Unexpected Custom handling.");
-    return Val;
+      return DAG.getNode(RISCVISD::FMV_H_X, DL, VA.getValVT(), Val);
+    if (VA.getLocVT() == MVT::i64 && VA.getValVT() == MVT::f32)
+      return DAG.getNode(RISCVISD::FMV_W_X_RV64, DL, MVT::f32, Val);
+    if (VA.getValVT().isFixedLengthVector() && VA.getLocVT().isScalableVector())
+      return convertFromScalableVector(VA.getValVT(), Val, DAG, Subtarget);
+    llvm_unreachable("Unexpected Custom handling.");
   }
 
   switch (VA.getLocInfo()) {
   default:
     llvm_unreachable("Unexpected CCValAssign::LocInfo");
   case CCValAssign::Full:
-    if (VA.getValVT().isFixedLengthVector() && VA.getLocVT().isScalableVector())
-      Val = convertFromScalableVector(VA.getValVT(), Val, DAG, Subtarget);
     break;
   case CCValAssign::BCvt:
     Val = DAG.getNode(ISD::BITCAST, DL, VA.getValVT(), Val);
@@ -19155,20 +19153,18 @@ static SDValue convertValVTToLocVT(SelectionDAG &DAG, SDValue Val,
   if (VA.needsCustom()) {
     if (LocVT.isInteger() &&
         (VA.getValVT() == MVT::f16 || VA.getValVT() == MVT::bf16))
-      Val = DAG.getNode(RISCVISD::FMV_X_ANYEXTH, DL, LocVT, Val);
-    else if (LocVT == MVT::i64 && VA.getValVT() == MVT::f32)
-      Val = DAG.getNode(RISCVISD::FMV_X_ANYEXTW_RV64, DL, MVT::i64, Val);
-    else
-      llvm_unreachable("Unexpected Custom handling.");
-    return Val;
+      return DAG.getNode(RISCVISD::FMV_X_ANYEXTH, DL, LocVT, Val);
+    if (LocVT == MVT::i64 && VA.getValVT() == MVT::f32)
+      return DAG.getNode(RISCVISD::FMV_X_ANYEXTW_RV64, DL, MVT::i64, Val);
+    if (VA.getValVT().isFixedLengthVector() && LocVT.isScalableVector())
+      return convertToScalableVector(LocVT, Val, DAG, Subtarget);
+    llvm_unreachable("Unexpected Custom handling.");
   }
 
   switch (VA.getLocInfo()) {
   default:
     llvm_unreachable("Unexpected CCValAssign::LocInfo");
   case CCValAssign::Full:
-    if (VA.getValVT().isFixedLengthVector() && LocVT.isScalableVector())
-      Val = convertToScalableVector(LocVT, Val, DAG, Subtarget);
     break;
   case CCValAssign::BCvt:
     Val = DAG.getNode(ISD::BITCAST, DL, LocVT, Val);