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
@@ -441,6 +441,7 @@
 
       // Mask VTs are custom-expanded into a series of standard nodes
       setOperationAction(ISD::TRUNCATE, VT, Custom);
+      setOperationAction(ISD::CONCAT_VECTORS, VT, Custom);
       setOperationAction(ISD::INSERT_SUBVECTOR, VT, Custom);
       setOperationAction(ISD::EXTRACT_SUBVECTOR, VT, Custom);
 
diff --git a/llvm/test/CodeGen/RISCV/rvv/setcc-fp-rv32.ll b/llvm/test/CodeGen/RISCV/rvv/setcc-fp-rv32.ll
--- a/llvm/test/CodeGen/RISCV/rvv/setcc-fp-rv32.ll
+++ b/llvm/test/CodeGen/RISCV/rvv/setcc-fp-rv32.ll
@@ -1,5 +1,5 @@
 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
-; RUN: llc -mtriple=riscv32 -mattr=+d,+experimental-zfh,+experimental-v -target-abi=ilp32d \
+; RUN: llc -mtriple=riscv32 -mattr=+m,+d,+experimental-zfh,+experimental-v -target-abi=ilp32d \
 ; RUN:     -verify-machineinstrs < %s | FileCheck %s
 
 ; FIXME: The scalar/vector operations ('fv' tests) should swap operands and
@@ -2507,4 +2507,23 @@
   ret <vscale x 8 x i1> %vc
 }
 
+; This fcmp/setcc is split and so we find a scalable-vector mask CONCAT_VECTOR
+; node. Ensure we correctly (custom) lower this.
+define <vscale x 16 x i1> @fcmp_oeq_vf_nx16f64(<vscale x 16 x double> %va) {
+; CHECK-LABEL: fcmp_oeq_vf_nx16f64:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    fcvt.d.w ft0, zero
+; CHECK-NEXT:    vsetvli a0, zero, e64, m8, ta, mu
+; CHECK-NEXT:    vmfeq.vf v25, v16, ft0
+; CHECK-NEXT:    vmfeq.vf v0, v8, ft0
+; CHECK-NEXT:    csrr a0, vlenb
+; CHECK-NEXT:    srli a0, a0, 3
+; CHECK-NEXT:    add a1, a0, a0
+; CHECK-NEXT:    vsetvli zero, a1, e8, mf4, tu, mu
+; CHECK-NEXT:    vslideup.vx v0, v25, a0
+; CHECK-NEXT:    ret
+  %vc = fcmp oeq <vscale x 16 x double> %va, zeroinitializer
+  ret <vscale x 16 x i1> %vc
+}
+
 attributes #0 = { "no-nans-fp-math"="true" }
diff --git a/llvm/test/CodeGen/RISCV/rvv/setcc-fp-rv64.ll b/llvm/test/CodeGen/RISCV/rvv/setcc-fp-rv64.ll
--- a/llvm/test/CodeGen/RISCV/rvv/setcc-fp-rv64.ll
+++ b/llvm/test/CodeGen/RISCV/rvv/setcc-fp-rv64.ll
@@ -1,5 +1,5 @@
 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
-; RUN: llc -mtriple=riscv64 -mattr=+d,+experimental-zfh,+experimental-v -target-abi=lp64d \
+; RUN: llc -mtriple=riscv64 -mattr=+m,+d,+experimental-zfh,+experimental-v -target-abi=lp64d \
 ; RUN:     -verify-machineinstrs < %s | FileCheck %s
 
 ; FIXME: The scalar/vector operations ('fv' tests) should swap operands and
@@ -2507,4 +2507,23 @@
   ret <vscale x 8 x i1> %vc
 }
 
+; This fcmp/setcc is split and so we find a scalable-vector mask CONCAT_VECTOR
+; node. Ensure we correctly (custom) lower this.
+define <vscale x 16 x i1> @fcmp_oeq_vf_nx16f64(<vscale x 16 x double> %va) {
+; CHECK-LABEL: fcmp_oeq_vf_nx16f64:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    fmv.d.x ft0, zero
+; CHECK-NEXT:    vsetvli a0, zero, e64, m8, ta, mu
+; CHECK-NEXT:    vmfeq.vf v25, v16, ft0
+; CHECK-NEXT:    vmfeq.vf v0, v8, ft0
+; CHECK-NEXT:    csrr a0, vlenb
+; CHECK-NEXT:    srli a0, a0, 3
+; CHECK-NEXT:    add a1, a0, a0
+; CHECK-NEXT:    vsetvli zero, a1, e8, mf4, tu, mu
+; CHECK-NEXT:    vslideup.vx v0, v25, a0
+; CHECK-NEXT:    ret
+  %vc = fcmp oeq <vscale x 16 x double> %va, zeroinitializer
+  ret <vscale x 16 x i1> %vc
+}
+
 attributes #0 = { "no-nans-fp-math"="true" }
diff --git a/llvm/test/CodeGen/RISCV/rvv/setcc-integer-rv32.ll b/llvm/test/CodeGen/RISCV/rvv/setcc-integer-rv32.ll
--- a/llvm/test/CodeGen/RISCV/rvv/setcc-integer-rv32.ll
+++ b/llvm/test/CodeGen/RISCV/rvv/setcc-integer-rv32.ll
@@ -1,5 +1,5 @@
 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
-; RUN: llc -mtriple=riscv32 -mattr=+experimental-v -verify-machineinstrs < %s | FileCheck %s
+; RUN: llc -mtriple=riscv32 -mattr=+m,+experimental-v -verify-machineinstrs < %s | FileCheck %s
 
 define <vscale x 8 x i1> @icmp_eq_vv_nxv8i8(<vscale x 8 x i8> %va, <vscale x 8 x i8> %vb) {
 ; CHECK-LABEL: icmp_eq_vv_nxv8i8:
@@ -3087,3 +3087,20 @@
   ret <vscale x 8 x i1> %vc
 }
 
+; This icmp/setcc is split and so we find a scalable-vector mask CONCAT_VECTOR
+; node. Ensure we correctly (custom) lower this.
+define <vscale x 16 x i1> @icmp_eq_vi_nx16i64(<vscale x 16 x i64> %va) {
+; CHECK-LABEL: icmp_eq_vi_nx16i64:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    csrr a0, vlenb
+; CHECK-NEXT:    srli a0, a0, 3
+; CHECK-NEXT:    add a1, a0, a0
+; CHECK-NEXT:    vsetvli a2, zero, e64, m8, ta, mu
+; CHECK-NEXT:    vmseq.vi v25, v16, 0
+; CHECK-NEXT:    vmseq.vi v0, v8, 0
+; CHECK-NEXT:    vsetvli zero, a1, e8, mf4, tu, mu
+; CHECK-NEXT:    vslideup.vx v0, v25, a0
+; CHECK-NEXT:    ret
+  %vc = icmp eq <vscale x 16 x i64> %va, zeroinitializer
+  ret <vscale x 16 x i1> %vc
+}
diff --git a/llvm/test/CodeGen/RISCV/rvv/setcc-integer-rv64.ll b/llvm/test/CodeGen/RISCV/rvv/setcc-integer-rv64.ll
--- a/llvm/test/CodeGen/RISCV/rvv/setcc-integer-rv64.ll
+++ b/llvm/test/CodeGen/RISCV/rvv/setcc-integer-rv64.ll
@@ -1,5 +1,5 @@
 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
-; RUN: llc -mtriple=riscv64 -mattr=+experimental-v -verify-machineinstrs < %s | FileCheck %s
+; RUN: llc -mtriple=riscv64 -mattr=+m,+experimental-v -verify-machineinstrs < %s | FileCheck %s
 
 define <vscale x 8 x i1> @icmp_eq_vv_nxv8i8(<vscale x 8 x i8> %va, <vscale x 8 x i8> %vb) {
 ; CHECK-LABEL: icmp_eq_vv_nxv8i8:
@@ -2941,3 +2941,20 @@
   ret <vscale x 8 x i1> %vc
 }
 
+; This icmp/setcc is split and so we find a scalable-vector mask CONCAT_VECTOR
+; node. Ensure we correctly (custom) lower this.
+define <vscale x 16 x i1> @icmp_eq_vi_nx16i64(<vscale x 16 x i64> %va) {
+; CHECK-LABEL: icmp_eq_vi_nx16i64:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    csrr a0, vlenb
+; CHECK-NEXT:    srli a0, a0, 3
+; CHECK-NEXT:    add a1, a0, a0
+; CHECK-NEXT:    vsetvli a2, zero, e64, m8, ta, mu
+; CHECK-NEXT:    vmseq.vi v25, v16, 0
+; CHECK-NEXT:    vmseq.vi v0, v8, 0
+; CHECK-NEXT:    vsetvli zero, a1, e8, mf4, tu, mu
+; CHECK-NEXT:    vslideup.vx v0, v25, a0
+; CHECK-NEXT:    ret
+  %vc = icmp eq <vscale x 16 x i64> %va, zeroinitializer
+  ret <vscale x 16 x i1> %vc
+}