[RISCV] Fix missing scalable->fixed-length vector conversion

Returning the scalable-vector container type would present problems when
the fixed-length INSERT_VECTOR_ELT was used by later operations.

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D98776

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -2379,8 +2379,12 @@ SDValue RISCVTargetLowering::lowerINSERT_VECTOR_ELT(SDValue Op,
   SDValue ValInVec;
 
   if (IsLegalInsert) {
-    if (isNullConstant(Idx))
-      return DAG.getNode(RISCVISD::VMV_S_XF_VL, DL, ContainerVT, Vec, Val, VL);
+    if (isNullConstant(Idx)) {
+      Vec = DAG.getNode(RISCVISD::VMV_S_XF_VL, DL, ContainerVT, Vec, Val, VL);
+      if (!VecVT.isFixedLengthVector())
+        return Vec;
+      return convertFromScalableVector(VecVT, Vec, DAG, Subtarget);
+    }
     ValInVec = DAG.getNode(RISCVISD::VMV_S_XF_VL, DL, ContainerVT,
                            DAG.getUNDEF(ContainerVT), Val, VL);
   } else {

llvm/test/CodeGen/RISCV/rvv/fixed-vectors-insert.ll

@@ -178,7 +178,7 @@ define void @insertelt_v8i64_0(<8 x i64>* %x) {
 ; RV32-NEXT:    vle64.v v28, (a0)
 ; RV32-NEXT:    addi a1, zero, -1
 ; RV32-NEXT:    vmv.s.x v28, a1
-; RV32-NEXT:    vs4r.v v28, (a0)
+; RV32-NEXT:    vse64.v v28, (a0)
 ; RV32-NEXT:    ret
 ;
 ; RV64-LABEL: insertelt_v8i64_0:
@@ -235,7 +235,7 @@ define void @insertelt_c6_v8i64_0(<8 x i64>* %x) {
 ; RV32-NEXT:    vle64.v v28, (a0)
 ; RV32-NEXT:    addi a1, zero, 6
 ; RV32-NEXT:    vmv.s.x v28, a1
-; RV32-NEXT:    vs4r.v v28, (a0)
+; RV32-NEXT:    vse64.v v28, (a0)
 ; RV32-NEXT:    ret
 ;
 ; RV64-LABEL: insertelt_c6_v8i64_0:
@@ -284,3 +284,35 @@ define void @insertelt_c6_v8i64(<8 x i64>* %x, i32 %idx) {
   store <8 x i64> %b, <8 x i64>* %x
   ret void
 }
+
+; Test that using a insertelement at element 0 by a later operation doesn't
+; crash the compiler.
+define void @insertelt_c6_v8i64_0_add(<8 x i64>* %x, <8 x i64>* %y) {
+; RV32-LABEL: insertelt_c6_v8i64_0_add:
+; RV32:       # %bb.0:
+; RV32-NEXT:    vsetivli a2, 8, e64,m4,ta,mu
+; RV32-NEXT:    vle64.v v28, (a0)
+; RV32-NEXT:    vle64.v v8, (a1)
+; RV32-NEXT:    addi a1, zero, 6
+; RV32-NEXT:    vmv.s.x v28, a1
+; RV32-NEXT:    vadd.vv v28, v28, v8
+; RV32-NEXT:    vse64.v v28, (a0)
+; RV32-NEXT:    ret
+;
+; RV64-LABEL: insertelt_c6_v8i64_0_add:
+; RV64:       # %bb.0:
+; RV64-NEXT:    vsetivli a2, 8, e64,m4,ta,mu
+; RV64-NEXT:    vle64.v v28, (a0)
+; RV64-NEXT:    vle64.v v8, (a1)
+; RV64-NEXT:    addi a1, zero, 6
+; RV64-NEXT:    vmv.s.x v28, a1
+; RV64-NEXT:    vadd.vv v28, v28, v8
+; RV64-NEXT:    vse64.v v28, (a0)
+; RV64-NEXT:    ret
+  %a = load <8 x i64>, <8 x i64>* %x
+  %b = insertelement <8 x i64> %a, i64 6, i32 0
+  %c = load <8 x i64>, <8 x i64>* %y
+  %d = add <8 x i64> %b, %c
+  store <8 x i64> %d, <8 x i64>* %x
+  ret void
+}