diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -10961,6 +10961,16 @@
 
 ConstantSDNode *llvm::isConstOrConstSplat(SDValue N, bool AllowUndefs,
                                           bool AllowTruncation) {
+  EVT VT = N.getValueType();
+  APInt DemandedElts = VT.isFixedLengthVector()
+                           ? APInt::getAllOnes(VT.getVectorMinNumElements())
+                           : APInt(1, 1);
+  return isConstOrConstSplat(N, DemandedElts, AllowUndefs, AllowTruncation);
+}
+
+ConstantSDNode *llvm::isConstOrConstSplat(SDValue N, const APInt &DemandedElts,
+                                          bool AllowUndefs,
+                                          bool AllowTruncation) {
   if (ConstantSDNode *CN = dyn_cast<ConstantSDNode>(N))
     return CN;
 
@@ -10976,36 +10986,13 @@
     }
   }
 
-  if (BuildVectorSDNode *BV = dyn_cast<BuildVectorSDNode>(N)) {
-    BitVector UndefElements;
-    ConstantSDNode *CN = BV->getConstantSplatNode(&UndefElements);
-
-    // BuildVectors can truncate their operands. Ignore that case here unless
-    // AllowTruncation is set.
-    if (CN && (UndefElements.none() || AllowUndefs)) {
-      EVT CVT = CN->getValueType(0);
-      EVT NSVT = N.getValueType().getScalarType();
-      assert(CVT.bitsGE(NSVT) && "Illegal build vector element extension");
-      if (AllowTruncation || (CVT == NSVT))
-        return CN;
-    }
-  }
-
-  return nullptr;
-}
-
-ConstantSDNode *llvm::isConstOrConstSplat(SDValue N, const APInt &DemandedElts,
-                                          bool AllowUndefs,
-                                          bool AllowTruncation) {
-  if (ConstantSDNode *CN = dyn_cast<ConstantSDNode>(N))
-    return CN;
-
   if (BuildVectorSDNode *BV = dyn_cast<BuildVectorSDNode>(N)) {
     BitVector UndefElements;
     ConstantSDNode *CN = BV->getConstantSplatNode(DemandedElts, &UndefElements);
 
     // BuildVectors can truncate their operands. Ignore that case here unless
     // AllowTruncation is set.
+    // TODO: Look into whether we should allow UndefElements in non-DemandedElts
     if (CN && (UndefElements.none() || AllowUndefs)) {
       EVT CVT = CN->getValueType(0);
       EVT NSVT = N.getValueType().getScalarType();
@@ -11019,21 +11006,11 @@
 }
 
 ConstantFPSDNode *llvm::isConstOrConstSplatFP(SDValue N, bool AllowUndefs) {
-  if (ConstantFPSDNode *CN = dyn_cast<ConstantFPSDNode>(N))
-    return CN;
-
-  if (BuildVectorSDNode *BV = dyn_cast<BuildVectorSDNode>(N)) {
-    BitVector UndefElements;
-    ConstantFPSDNode *CN = BV->getConstantFPSplatNode(&UndefElements);
-    if (CN && (UndefElements.none() || AllowUndefs))
-      return CN;
-  }
-
-  if (N.getOpcode() == ISD::SPLAT_VECTOR)
-    if (ConstantFPSDNode *CN = dyn_cast<ConstantFPSDNode>(N.getOperand(0)))
-      return CN;
-
-  return nullptr;
+  EVT VT = N.getValueType();
+  APInt DemandedElts = VT.isFixedLengthVector()
+                           ? APInt::getAllOnes(VT.getVectorMinNumElements())
+                           : APInt(1, 1);
+  return isConstOrConstSplatFP(N, DemandedElts, AllowUndefs);
 }
 
 ConstantFPSDNode *llvm::isConstOrConstSplatFP(SDValue N,
@@ -11046,10 +11023,15 @@
     BitVector UndefElements;
     ConstantFPSDNode *CN =
         BV->getConstantFPSplatNode(DemandedElts, &UndefElements);
+    // TODO: Look into whether we should allow UndefElements in non-DemandedElts
     if (CN && (UndefElements.none() || AllowUndefs))
       return CN;
   }
 
+  if (N.getOpcode() == ISD::SPLAT_VECTOR)
+    if (ConstantFPSDNode *CN = dyn_cast<ConstantFPSDNode>(N.getOperand(0)))
+      return CN;
+
   return nullptr;
 }
 
diff --git a/llvm/test/CodeGen/AArch64/sve-knownbits.ll b/llvm/test/CodeGen/AArch64/sve-knownbits.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/CodeGen/AArch64/sve-knownbits.ll
@@ -0,0 +1,27 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=aarch64-linux-gnu -mattr=+sve -verify-machineinstrs < %s | FileCheck %s
+
+define <vscale x 8 x i16> @test_knownzero(<vscale x 8 x i16> %x) {
+; CHECK-LABEL: test_knownzero:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    mov z0.h, #0 // =0x0
+; CHECK-NEXT:    ret
+  %a1 = shl <vscale x 8 x i16> %x, shufflevector (<vscale x 8 x i16> insertelement (<vscale x 8 x i16> poison, i16 8, i32 0), <vscale x 8 x i16> poison, <vscale x 8 x i32> zeroinitializer)
+  %a2 = and <vscale x 8 x i16> %a1, shufflevector (<vscale x 8 x i16> insertelement (<vscale x 8 x i16> poison, i16 8, i32 0), <vscale x 8 x i16> poison, <vscale x 8 x i32> zeroinitializer)
+  ret <vscale x 8 x i16> %a2
+}
+
+define <vscale x 4 x i32> @asrlsr(<vscale x 4 x i64> %va) {
+; CHECK-LABEL: asrlsr:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    lsr z1.d, z1.d, #15
+; CHECK-NEXT:    lsr z0.d, z0.d, #15
+; CHECK-NEXT:    uzp1 z0.s, z0.s, z1.s
+; CHECK-NEXT:    ret
+  %head = insertelement <vscale x 4 x i32> poison, i32 15, i32 0
+  %splat = shufflevector <vscale x 4 x i32> %head, <vscale x 4 x i32> poison, <vscale x 4 x i32> zeroinitializer
+  %vb = zext <vscale x 4 x i32> %splat to <vscale x 4 x i64>
+  %x = ashr <vscale x 4 x i64> %va, %vb
+  %y = trunc <vscale x 4 x i64> %x to <vscale x 4 x i32>
+  ret <vscale x 4 x i32> %y
+}
diff --git a/llvm/test/CodeGen/RISCV/rvv/vnsra-sdnode.ll b/llvm/test/CodeGen/RISCV/rvv/vnsra-sdnode.ll
--- a/llvm/test/CodeGen/RISCV/rvv/vnsra-sdnode.ll
+++ b/llvm/test/CodeGen/RISCV/rvv/vnsra-sdnode.ll
@@ -34,7 +34,7 @@
 ; CHECK-LABEL: vnsra_wi_i32_nxv1i32_sext:
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    vsetvli a0, zero, e32, mf2, ta, ma
-; CHECK-NEXT:    vnsra.wi v8, v8, 15
+; CHECK-NEXT:    vnsrl.wi v8, v8, 15
 ; CHECK-NEXT:    ret
   %head = insertelement <vscale x 1 x i32> poison, i32 15, i32 0
   %splat = shufflevector <vscale x 1 x i32> %head, <vscale x 1 x i32> poison, <vscale x 1 x i32> zeroinitializer
@@ -76,7 +76,7 @@
 ; CHECK-LABEL: vnsra_wi_i32_nxv2i32_sext:
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    vsetvli a0, zero, e32, m1, ta, ma
-; CHECK-NEXT:    vnsra.wi v10, v8, 15
+; CHECK-NEXT:    vnsrl.wi v10, v8, 15
 ; CHECK-NEXT:    vmv.v.v v8, v10
 ; CHECK-NEXT:    ret
   %head = insertelement <vscale x 2 x i32> poison, i32 15, i32 0
@@ -119,7 +119,7 @@
 ; CHECK-LABEL: vnsra_wi_i32_nxv4i32_sext:
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    vsetvli a0, zero, e32, m2, ta, ma
-; CHECK-NEXT:    vnsra.wi v12, v8, 15
+; CHECK-NEXT:    vnsrl.wi v12, v8, 15
 ; CHECK-NEXT:    vmv.v.v v8, v12
 ; CHECK-NEXT:    ret
   %head = insertelement <vscale x 4 x i32> poison, i32 15, i32 0
@@ -162,7 +162,7 @@
 ; CHECK-LABEL: vnsra_wi_i32_nxv8i32_sext:
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    vsetvli a0, zero, e32, m4, ta, ma
-; CHECK-NEXT:    vnsra.wi v16, v8, 15
+; CHECK-NEXT:    vnsrl.wi v16, v8, 15
 ; CHECK-NEXT:    vmv.v.v v8, v16
 ; CHECK-NEXT:    ret
   %head = insertelement <vscale x 8 x i32> poison, i32 15, i32 0
@@ -203,7 +203,7 @@
 ; CHECK-LABEL: vnsra_wi_i32_nxv1i32_zext:
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    vsetvli a0, zero, e32, mf2, ta, ma
-; CHECK-NEXT:    vnsra.wi v8, v8, 15
+; CHECK-NEXT:    vnsrl.wi v8, v8, 15
 ; CHECK-NEXT:    ret
   %head = insertelement <vscale x 1 x i32> poison, i32 15, i32 0
   %splat = shufflevector <vscale x 1 x i32> %head, <vscale x 1 x i32> poison, <vscale x 1 x i32> zeroinitializer
@@ -245,7 +245,7 @@
 ; CHECK-LABEL: vnsra_wi_i32_nxv2i32_zext:
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    vsetvli a0, zero, e32, m1, ta, ma
-; CHECK-NEXT:    vnsra.wi v10, v8, 15
+; CHECK-NEXT:    vnsrl.wi v10, v8, 15
 ; CHECK-NEXT:    vmv.v.v v8, v10
 ; CHECK-NEXT:    ret
   %head = insertelement <vscale x 2 x i32> poison, i32 15, i32 0
@@ -288,7 +288,7 @@
 ; CHECK-LABEL: vnsra_wi_i32_nxv4i32_zext:
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    vsetvli a0, zero, e32, m2, ta, ma
-; CHECK-NEXT:    vnsra.wi v12, v8, 15
+; CHECK-NEXT:    vnsrl.wi v12, v8, 15
 ; CHECK-NEXT:    vmv.v.v v8, v12
 ; CHECK-NEXT:    ret
   %head = insertelement <vscale x 4 x i32> poison, i32 15, i32 0
@@ -331,7 +331,7 @@
 ; CHECK-LABEL: vnsra_wi_i32_nxv8i32_zext:
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    vsetvli a0, zero, e32, m4, ta, ma
-; CHECK-NEXT:    vnsra.wi v16, v8, 15
+; CHECK-NEXT:    vnsrl.wi v16, v8, 15
 ; CHECK-NEXT:    vmv.v.v v8, v16
 ; CHECK-NEXT:    ret
   %head = insertelement <vscale x 8 x i32> poison, i32 15, i32 0