diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -4959,16 +4959,14 @@
         getDefaultScalableVLOps(I32ContainerVT, DL, DAG, Subtarget).first;
     // Limit the active VL to two.
     SDValue InsertI64VL = DAG.getConstant(2, DL, XLenVT);
-    // Note: We can't pass a UNDEF to the first VSLIDE1UP_VL since an untied
-    // undef doesn't obey the earlyclobber constraint. Just splat a zero value.
-    ValInVec = DAG.getNode(RISCVISD::VMV_V_X_VL, DL, I32ContainerVT,
-                           DAG.getUNDEF(I32ContainerVT), Zero, InsertI64VL);
-    // First slide in the hi value, then the lo in underneath it.
-    ValInVec = DAG.getNode(RISCVISD::VSLIDE1UP_VL, DL, I32ContainerVT,
-                           DAG.getUNDEF(I32ContainerVT), ValInVec, ValHi,
+    // First slide in the lo value, then the hi in above it. We use slide1down
+    // to avoid the register group overlap constraint of vslide1up.
+    ValInVec = DAG.getNode(RISCVISD::VSLIDE1DOWN_VL, DL, I32ContainerVT,
+                           DAG.getUNDEF(I32ContainerVT),
+                           DAG.getUNDEF(I32ContainerVT), ValLo,
                            I32Mask, InsertI64VL);
-    ValInVec = DAG.getNode(RISCVISD::VSLIDE1UP_VL, DL, I32ContainerVT,
-                           DAG.getUNDEF(I32ContainerVT), ValInVec, ValLo,
+    ValInVec = DAG.getNode(RISCVISD::VSLIDE1DOWN_VL, DL, I32ContainerVT,
+                           DAG.getUNDEF(I32ContainerVT), ValInVec, ValHi,
                            I32Mask, InsertI64VL);
     // Bitcast back to the right container type.
     ValInVec = DAG.getBitcast(ContainerVT, ValInVec);
diff --git a/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-bitcast.ll b/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-bitcast.ll
--- a/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-bitcast.ll
+++ b/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-bitcast.ll
@@ -508,11 +508,10 @@
 ; RV32-LABEL: bitcast_i64_v4i16:
 ; RV32:       # %bb.0:
 ; RV32-NEXT:    vsetivli zero, 2, e32, m1, ta, ma
-; RV32-NEXT:    vmv.v.i v8, 0
-; RV32-NEXT:    vslide1up.vx v9, v8, a1
-; RV32-NEXT:    vslide1up.vx v10, v9, a0
+; RV32-NEXT:    vslide1down.vx v8, v8, a0
+; RV32-NEXT:    vslide1down.vx v9, v8, a1
 ; RV32-NEXT:    vsetivli zero, 1, e64, m1, ta, ma
-; RV32-NEXT:    vslideup.vi v8, v10, 0
+; RV32-NEXT:    vslideup.vi v8, v9, 0
 ; RV32-NEXT:    ret
 ;
 ; RV64-LABEL: bitcast_i64_v4i16:
@@ -547,11 +546,10 @@
 ; RV32-LABEL: bitcast_i64_v2i32:
 ; RV32:       # %bb.0:
 ; RV32-NEXT:    vsetivli zero, 2, e32, m1, ta, ma
-; RV32-NEXT:    vmv.v.i v8, 0
-; RV32-NEXT:    vslide1up.vx v9, v8, a1
-; RV32-NEXT:    vslide1up.vx v10, v9, a0
+; RV32-NEXT:    vslide1down.vx v8, v8, a0
+; RV32-NEXT:    vslide1down.vx v9, v8, a1
 ; RV32-NEXT:    vsetivli zero, 1, e64, m1, ta, ma
-; RV32-NEXT:    vslideup.vi v8, v10, 0
+; RV32-NEXT:    vslideup.vi v8, v9, 0
 ; RV32-NEXT:    ret
 ;
 ; RV64-LABEL: bitcast_i64_v2i32:
@@ -586,11 +584,10 @@
 ; RV32-LABEL: bitcast_i64_v1i64:
 ; RV32:       # %bb.0:
 ; RV32-NEXT:    vsetivli zero, 2, e32, m1, ta, ma
-; RV32-NEXT:    vmv.v.i v8, 0
-; RV32-NEXT:    vslide1up.vx v9, v8, a1
-; RV32-NEXT:    vslide1up.vx v10, v9, a0
+; RV32-NEXT:    vslide1down.vx v8, v8, a0
+; RV32-NEXT:    vslide1down.vx v9, v8, a1
 ; RV32-NEXT:    vsetivli zero, 1, e64, m1, ta, ma
-; RV32-NEXT:    vslideup.vi v8, v10, 0
+; RV32-NEXT:    vslideup.vi v8, v9, 0
 ; RV32-NEXT:    ret
 ;
 ; RV64-LABEL: bitcast_i64_v1i64:
diff --git a/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-fp-bitcast.ll b/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-fp-bitcast.ll
--- a/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-fp-bitcast.ll
+++ b/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-fp-bitcast.ll
@@ -199,11 +199,10 @@
 ; RV32-FP-LABEL: bitcast_i64_v4f16:
 ; RV32-FP:       # %bb.0:
 ; RV32-FP-NEXT:    vsetivli zero, 2, e32, m1, ta, ma
-; RV32-FP-NEXT:    vmv.v.i v8, 0
-; RV32-FP-NEXT:    vslide1up.vx v9, v8, a1
-; RV32-FP-NEXT:    vslide1up.vx v10, v9, a0
+; RV32-FP-NEXT:    vslide1down.vx v8, v8, a0
+; RV32-FP-NEXT:    vslide1down.vx v9, v8, a1
 ; RV32-FP-NEXT:    vsetivli zero, 1, e64, m1, ta, ma
-; RV32-FP-NEXT:    vslideup.vi v8, v10, 0
+; RV32-FP-NEXT:    vslideup.vi v8, v9, 0
 ; RV32-FP-NEXT:    ret
 ;
 ; RV64-FP-LABEL: bitcast_i64_v4f16:
@@ -219,11 +218,10 @@
 ; RV32-FP-LABEL: bitcast_i64_v2f32:
 ; RV32-FP:       # %bb.0:
 ; RV32-FP-NEXT:    vsetivli zero, 2, e32, m1, ta, ma
-; RV32-FP-NEXT:    vmv.v.i v8, 0
-; RV32-FP-NEXT:    vslide1up.vx v9, v8, a1
-; RV32-FP-NEXT:    vslide1up.vx v10, v9, a0
+; RV32-FP-NEXT:    vslide1down.vx v8, v8, a0
+; RV32-FP-NEXT:    vslide1down.vx v9, v8, a1
 ; RV32-FP-NEXT:    vsetivli zero, 1, e64, m1, ta, ma
-; RV32-FP-NEXT:    vslideup.vi v8, v10, 0
+; RV32-FP-NEXT:    vslideup.vi v8, v9, 0
 ; RV32-FP-NEXT:    ret
 ;
 ; RV64-FP-LABEL: bitcast_i64_v2f32:
@@ -239,11 +237,10 @@
 ; RV32-FP-LABEL: bitcast_i64_v1f64:
 ; RV32-FP:       # %bb.0:
 ; RV32-FP-NEXT:    vsetivli zero, 2, e32, m1, ta, ma
-; RV32-FP-NEXT:    vmv.v.i v8, 0
-; RV32-FP-NEXT:    vslide1up.vx v9, v8, a1
-; RV32-FP-NEXT:    vslide1up.vx v10, v9, a0
+; RV32-FP-NEXT:    vslide1down.vx v8, v8, a0
+; RV32-FP-NEXT:    vslide1down.vx v9, v8, a1
 ; RV32-FP-NEXT:    vsetivli zero, 1, e64, m1, ta, ma
-; RV32-FP-NEXT:    vslideup.vi v8, v10, 0
+; RV32-FP-NEXT:    vslideup.vi v8, v9, 0
 ; RV32-FP-NEXT:    ret
 ;
 ; RV64-FP-LABEL: bitcast_i64_v1f64:
diff --git a/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-insert.ll b/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-insert.ll
--- a/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-insert.ll
+++ b/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-insert.ll
@@ -11,9 +11,8 @@
 ; RV32-NEXT:    vsetivli zero, 4, e64, m2, ta, ma
 ; RV32-NEXT:    vle64.v v8, (a0)
 ; RV32-NEXT:    vsetivli zero, 2, e32, m2, ta, ma
-; RV32-NEXT:    vmv.v.i v10, 0
-; RV32-NEXT:    vslide1up.vx v12, v10, a2
-; RV32-NEXT:    vslide1up.vx v10, v12, a1
+; RV32-NEXT:    vslide1down.vx v10, v8, a1
+; RV32-NEXT:    vslide1down.vx v10, v10, a2
 ; RV32-NEXT:    vsetivli zero, 4, e64, m2, tu, ma
 ; RV32-NEXT:    vslideup.vi v8, v10, 3
 ; RV32-NEXT:    vse64.v v8, (a0)
@@ -52,9 +51,8 @@
 ; RV32-NEXT:    vsetvli zero, zero, e64, m2, tu, ma
 ; RV32-NEXT:    vslideup.vi v8, v10, 2
 ; RV32-NEXT:    vsetivli zero, 2, e32, m2, ta, ma
-; RV32-NEXT:    vmv.v.i v10, 0
-; RV32-NEXT:    vslide1up.vx v12, v10, a2
-; RV32-NEXT:    vslide1up.vx v10, v12, a1
+; RV32-NEXT:    vslide1down.vx v10, v8, a1
+; RV32-NEXT:    vslide1down.vx v10, v10, a2
 ; RV32-NEXT:    vsetivli zero, 3, e64, m2, tu, ma
 ; RV32-NEXT:    vslideup.vi v8, v10, 2
 ; RV32-NEXT:    sw a1, 16(a0)
diff --git a/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-unaligned.ll b/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-unaligned.ll
--- a/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-unaligned.ll
+++ b/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-unaligned.ll
@@ -132,8 +132,6 @@
 ; RV32-NEXT:    vsetivli zero, 0, e8, mf8, ta, ma
 ; RV32-NEXT:    vmv.x.s a0, v0
 ; RV32-NEXT:    andi a1, a0, 1
-; RV32-NEXT:    vsetivli zero, 2, e32, m1, ta, ma
-; RV32-NEXT:    vmv.v.i v10, 0
 ; RV32-NEXT:    bnez a1, .LBB5_3
 ; RV32-NEXT:  # %bb.1: # %else
 ; RV32-NEXT:    andi a0, a0, 2
@@ -142,26 +140,28 @@
 ; RV32-NEXT:    vmv1r.v v8, v9
 ; RV32-NEXT:    ret
 ; RV32-NEXT:  .LBB5_3: # %cond.load
+; RV32-NEXT:    vsetvli zero, zero, e32, mf2, ta, ma
 ; RV32-NEXT:    vmv.x.s a1, v8
-; RV32-NEXT:    lw a2, 4(a1)
-; RV32-NEXT:    lw a1, 0(a1)
-; RV32-NEXT:    vslide1up.vx v11, v10, a2
-; RV32-NEXT:    vslide1up.vx v12, v11, a1
+; RV32-NEXT:    lw a2, 0(a1)
+; RV32-NEXT:    lw a1, 4(a1)
+; RV32-NEXT:    vsetivli zero, 2, e32, m1, ta, ma
+; RV32-NEXT:    vslide1down.vx v10, v8, a2
+; RV32-NEXT:    vslide1down.vx v10, v10, a1
 ; RV32-NEXT:    vsetivli zero, 1, e64, m1, tu, ma
-; RV32-NEXT:    vslideup.vi v9, v12, 0
+; RV32-NEXT:    vslideup.vi v9, v10, 0
 ; RV32-NEXT:    andi a0, a0, 2
 ; RV32-NEXT:    beqz a0, .LBB5_2
 ; RV32-NEXT:  .LBB5_4: # %cond.load1
 ; RV32-NEXT:    vsetivli zero, 1, e32, mf2, ta, ma
 ; RV32-NEXT:    vslidedown.vi v8, v8, 1
 ; RV32-NEXT:    vmv.x.s a0, v8
-; RV32-NEXT:    lw a1, 4(a0)
-; RV32-NEXT:    lw a0, 0(a0)
+; RV32-NEXT:    lw a1, 0(a0)
+; RV32-NEXT:    lw a0, 4(a0)
 ; RV32-NEXT:    vsetivli zero, 2, e32, m1, ta, ma
-; RV32-NEXT:    vslide1up.vx v8, v10, a1
-; RV32-NEXT:    vslide1up.vx v10, v8, a0
+; RV32-NEXT:    vslide1down.vx v8, v8, a1
+; RV32-NEXT:    vslide1down.vx v8, v8, a0
 ; RV32-NEXT:    vsetivli zero, 2, e64, m1, tu, ma
-; RV32-NEXT:    vslideup.vi v9, v10, 1
+; RV32-NEXT:    vslideup.vi v9, v8, 1
 ; RV32-NEXT:    vmv1r.v v8, v9
 ; RV32-NEXT:    ret
 ;
diff --git a/llvm/test/CodeGen/RISCV/rvv/insertelt-int-rv32.ll b/llvm/test/CodeGen/RISCV/rvv/insertelt-int-rv32.ll
--- a/llvm/test/CodeGen/RISCV/rvv/insertelt-int-rv32.ll
+++ b/llvm/test/CodeGen/RISCV/rvv/insertelt-int-rv32.ll
@@ -636,9 +636,8 @@
 ; CHECK-LABEL: insertelt_nxv1i64_0:
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    vsetivli zero, 2, e32, m1, ta, ma
-; CHECK-NEXT:    vmv.v.i v9, 0
-; CHECK-NEXT:    vslide1up.vx v10, v9, a1
-; CHECK-NEXT:    vslide1up.vx v9, v10, a0
+; CHECK-NEXT:    vslide1down.vx v9, v8, a0
+; CHECK-NEXT:    vslide1down.vx v9, v9, a1
 ; CHECK-NEXT:    vsetivli zero, 1, e64, m1, tu, ma
 ; CHECK-NEXT:    vslideup.vi v8, v9, 0
 ; CHECK-NEXT:    ret
@@ -650,9 +649,8 @@
 ; CHECK-LABEL: insertelt_nxv1i64_imm:
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    vsetivli zero, 2, e32, m1, ta, ma
-; CHECK-NEXT:    vmv.v.i v9, 0
-; CHECK-NEXT:    vslide1up.vx v10, v9, a1
-; CHECK-NEXT:    vslide1up.vx v9, v10, a0
+; CHECK-NEXT:    vslide1down.vx v9, v8, a0
+; CHECK-NEXT:    vslide1down.vx v9, v9, a1
 ; CHECK-NEXT:    vsetivli zero, 4, e64, m1, tu, ma
 ; CHECK-NEXT:    vslideup.vi v8, v9, 3
 ; CHECK-NEXT:    ret
@@ -664,9 +662,8 @@
 ; CHECK-LABEL: insertelt_nxv1i64_idx:
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    vsetivli zero, 2, e32, m1, ta, ma
-; CHECK-NEXT:    vmv.v.i v9, 0
-; CHECK-NEXT:    vslide1up.vx v10, v9, a1
-; CHECK-NEXT:    vslide1up.vx v9, v10, a0
+; CHECK-NEXT:    vslide1down.vx v9, v8, a0
+; CHECK-NEXT:    vslide1down.vx v9, v9, a1
 ; CHECK-NEXT:    addi a0, a2, 1
 ; CHECK-NEXT:    vsetvli zero, a0, e64, m1, tu, ma
 ; CHECK-NEXT:    vslideup.vx v8, v9, a2
@@ -679,9 +676,8 @@
 ; CHECK-LABEL: insertelt_nxv2i64_0:
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    vsetivli zero, 2, e32, m2, ta, ma
-; CHECK-NEXT:    vmv.v.i v10, 0
-; CHECK-NEXT:    vslide1up.vx v12, v10, a1
-; CHECK-NEXT:    vslide1up.vx v10, v12, a0
+; CHECK-NEXT:    vslide1down.vx v10, v8, a0
+; CHECK-NEXT:    vslide1down.vx v10, v10, a1
 ; CHECK-NEXT:    vsetivli zero, 1, e64, m2, tu, ma
 ; CHECK-NEXT:    vslideup.vi v8, v10, 0
 ; CHECK-NEXT:    ret
@@ -693,9 +689,8 @@
 ; CHECK-LABEL: insertelt_nxv2i64_imm:
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    vsetivli zero, 2, e32, m2, ta, ma
-; CHECK-NEXT:    vmv.v.i v10, 0
-; CHECK-NEXT:    vslide1up.vx v12, v10, a1
-; CHECK-NEXT:    vslide1up.vx v10, v12, a0
+; CHECK-NEXT:    vslide1down.vx v10, v8, a0
+; CHECK-NEXT:    vslide1down.vx v10, v10, a1
 ; CHECK-NEXT:    vsetivli zero, 4, e64, m2, tu, ma
 ; CHECK-NEXT:    vslideup.vi v8, v10, 3
 ; CHECK-NEXT:    ret
@@ -707,9 +702,8 @@
 ; CHECK-LABEL: insertelt_nxv2i64_idx:
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    vsetivli zero, 2, e32, m2, ta, ma
-; CHECK-NEXT:    vmv.v.i v10, 0
-; CHECK-NEXT:    vslide1up.vx v12, v10, a1
-; CHECK-NEXT:    vslide1up.vx v10, v12, a0
+; CHECK-NEXT:    vslide1down.vx v10, v8, a0
+; CHECK-NEXT:    vslide1down.vx v10, v10, a1
 ; CHECK-NEXT:    addi a0, a2, 1
 ; CHECK-NEXT:    vsetvli zero, a0, e64, m2, tu, ma
 ; CHECK-NEXT:    vslideup.vx v8, v10, a2
@@ -722,9 +716,8 @@
 ; CHECK-LABEL: insertelt_nxv4i64_0:
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    vsetivli zero, 2, e32, m4, ta, ma
-; CHECK-NEXT:    vmv.v.i v12, 0
-; CHECK-NEXT:    vslide1up.vx v16, v12, a1
-; CHECK-NEXT:    vslide1up.vx v12, v16, a0
+; CHECK-NEXT:    vslide1down.vx v12, v8, a0
+; CHECK-NEXT:    vslide1down.vx v12, v12, a1
 ; CHECK-NEXT:    vsetivli zero, 1, e64, m4, tu, ma
 ; CHECK-NEXT:    vslideup.vi v8, v12, 0
 ; CHECK-NEXT:    ret
@@ -736,9 +729,8 @@
 ; CHECK-LABEL: insertelt_nxv4i64_imm:
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    vsetivli zero, 2, e32, m4, ta, ma
-; CHECK-NEXT:    vmv.v.i v12, 0
-; CHECK-NEXT:    vslide1up.vx v16, v12, a1
-; CHECK-NEXT:    vslide1up.vx v12, v16, a0
+; CHECK-NEXT:    vslide1down.vx v12, v8, a0
+; CHECK-NEXT:    vslide1down.vx v12, v12, a1
 ; CHECK-NEXT:    vsetivli zero, 4, e64, m4, tu, ma
 ; CHECK-NEXT:    vslideup.vi v8, v12, 3
 ; CHECK-NEXT:    ret
@@ -750,9 +742,8 @@
 ; CHECK-LABEL: insertelt_nxv4i64_idx:
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    vsetivli zero, 2, e32, m4, ta, ma
-; CHECK-NEXT:    vmv.v.i v12, 0
-; CHECK-NEXT:    vslide1up.vx v16, v12, a1
-; CHECK-NEXT:    vslide1up.vx v12, v16, a0
+; CHECK-NEXT:    vslide1down.vx v12, v8, a0
+; CHECK-NEXT:    vslide1down.vx v12, v12, a1
 ; CHECK-NEXT:    addi a0, a2, 1
 ; CHECK-NEXT:    vsetvli zero, a0, e64, m4, tu, ma
 ; CHECK-NEXT:    vslideup.vx v8, v12, a2
@@ -765,9 +756,8 @@
 ; CHECK-LABEL: insertelt_nxv8i64_0:
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    vsetivli zero, 2, e32, m8, ta, ma
-; CHECK-NEXT:    vmv.v.i v16, 0
-; CHECK-NEXT:    vslide1up.vx v24, v16, a1
-; CHECK-NEXT:    vslide1up.vx v16, v24, a0
+; CHECK-NEXT:    vslide1down.vx v16, v8, a0
+; CHECK-NEXT:    vslide1down.vx v16, v16, a1
 ; CHECK-NEXT:    vsetivli zero, 1, e64, m8, tu, ma
 ; CHECK-NEXT:    vslideup.vi v8, v16, 0
 ; CHECK-NEXT:    ret
@@ -779,9 +769,8 @@
 ; CHECK-LABEL: insertelt_nxv8i64_imm:
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    vsetivli zero, 2, e32, m8, ta, ma
-; CHECK-NEXT:    vmv.v.i v16, 0
-; CHECK-NEXT:    vslide1up.vx v24, v16, a1
-; CHECK-NEXT:    vslide1up.vx v16, v24, a0
+; CHECK-NEXT:    vslide1down.vx v16, v8, a0
+; CHECK-NEXT:    vslide1down.vx v16, v16, a1
 ; CHECK-NEXT:    vsetivli zero, 4, e64, m8, tu, ma
 ; CHECK-NEXT:    vslideup.vi v8, v16, 3
 ; CHECK-NEXT:    ret
@@ -793,9 +782,8 @@
 ; CHECK-LABEL: insertelt_nxv8i64_idx:
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    vsetivli zero, 2, e32, m8, ta, ma
-; CHECK-NEXT:    vmv.v.i v16, 0
-; CHECK-NEXT:    vslide1up.vx v24, v16, a1
-; CHECK-NEXT:    vslide1up.vx v16, v24, a0
+; CHECK-NEXT:    vslide1down.vx v16, v8, a0
+; CHECK-NEXT:    vslide1down.vx v16, v16, a1
 ; CHECK-NEXT:    addi a0, a2, 1
 ; CHECK-NEXT:    vsetvli zero, a0, e64, m8, tu, ma
 ; CHECK-NEXT:    vslideup.vx v8, v16, a2