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
@@ -162,7 +162,8 @@
   }
 
   if (Subtarget.hasStdExtZbp()) {
-    setOperationAction(ISD::BITREVERSE, XLenVT, Legal);
+    setOperationAction(ISD::BITREVERSE, XLenVT, Custom);
+    setOperationAction(ISD::BSWAP, XLenVT, Custom);
 
     if (Subtarget.is64Bit()) {
       setOperationAction(ISD::BITREVERSE, MVT::i32, Custom);
@@ -495,6 +496,20 @@
   }
   case ISD::INTRINSIC_WO_CHAIN:
     return LowerINTRINSIC_WO_CHAIN(Op, DAG);
+  case ISD::BSWAP:
+  case ISD::BITREVERSE: {
+    // Convert BSWAP/BITREVERSE to GREVI to enable GREVI combinining.
+    assert(Subtarget.hasStdExtZbp() && "Unexpected custom legalisation");
+    MVT VT = Op.getSimpleValueType();
+    SDLoc DL(Op);
+    // Start with the maximum immediate value which is the bitwidth - 1.
+    unsigned Imm = VT.getSizeInBits() - 1;
+    // If this is BSWAP rather than BITREVERSE, clear the lower 3 bits.
+    if (Op.getOpcode() == ISD::BSWAP)
+      Imm &= ~0x7U;
+    return DAG.getNode(RISCVISD::GREVI, DL, VT, Op.getOperand(0),
+                       DAG.getTargetConstant(Imm, DL, Subtarget.getXLenVT()));
+  }
   }
 }
 
@@ -1288,6 +1303,29 @@
   return SDValue();
 }
 
+static SDValue combineGREVI(SDNode *N, SelectionDAG &DAG,
+                            const RISCVSubtarget &Subtarget) {
+  // Combine (GREVI (GREVI x, C2), C1) -> (GREVI x, C1^C2) when C1^C2 is
+  // non-zero, and to x when it is. Any repeated GREVI stage undoes itself.
+  uint64_t ShAmt1 = N->getConstantOperandVal(1);
+  SDValue GREVSrc = N->getOperand(0);
+
+  if (GREVSrc->getOpcode() != N->getOpcode())
+    return SDValue();
+
+  uint64_t ShAmt2 = GREVSrc.getConstantOperandVal(1);
+  GREVSrc = GREVSrc->getOperand(0);
+
+  uint64_t CombinedShAmt = ShAmt1 ^ ShAmt2;
+  if (CombinedShAmt == 0)
+    return GREVSrc;
+
+  SDLoc DL(N);
+  return DAG.getNode(
+      N->getOpcode(), DL, N->getValueType(0), GREVSrc,
+      DAG.getTargetConstant(CombinedShAmt, DL, Subtarget.getXLenVT()));
+}
+
 SDValue RISCVTargetLowering::PerformDAGCombine(SDNode *N,
                                                DAGCombinerInfo &DCI) const {
   SelectionDAG &DAG = DCI.DAG;
@@ -1383,6 +1421,11 @@
         DCI.AddToWorklist(N);
       return SDValue(N, 0);
     }
+
+    if (N->getOpcode() == RISCVISD::GREVIW)
+      if (SDValue V = combineGREVI(N, DCI.DAG, Subtarget))
+        return V;
+
     break;
   }
   case RISCVISD::FMV_X_ANYEXTW_RV64: {
@@ -1415,23 +1458,8 @@
     return DAG.getNode(ISD::AND, DL, MVT::i64, NewFMV,
                        DAG.getConstant(~SignBit, DL, MVT::i64));
   }
-  case RISCVISD::GREVI: {
-    // Combine (GREVI (GREVI x, C2), C1) -> (GREVI x, C1^C2) when C1^C2 is
-    // non-zero, and to x when it is. Any repeated GREVI stage undoes itself.
-    SDLoc DL(N);
-    auto GREVSrc = N->getOperand(0);
-    uint64_t ShAmt1 = N->getConstantOperandVal(1);
-    if (GREVSrc->getOpcode() != RISCVISD::GREVI)
-      break;
-    uint64_t ShAmt2 = GREVSrc.getConstantOperandVal(1);
-    GREVSrc = GREVSrc->getOperand(0);
-    uint64_t CombinedShAmt = ShAmt1 ^ ShAmt2;
-    if (CombinedShAmt == 0)
-      return GREVSrc;
-    return DAG.getNode(
-        RISCVISD::GREVI, DL, N->getValueType(0), GREVSrc,
-        DAG.getTargetConstant(CombinedShAmt, DL, Subtarget.getXLenVT()));
-  }
+  case RISCVISD::GREVI:
+    return combineGREVI(N, DCI.DAG, Subtarget);
   case ISD::OR:
     if (auto GREV = combineORToGREV(SDValue(N, 0), DCI.DAG, Subtarget))
       return GREV;
diff --git a/llvm/lib/Target/RISCV/RISCVInstrInfoB.td b/llvm/lib/Target/RISCV/RISCVInstrInfoB.td
--- a/llvm/lib/Target/RISCV/RISCVInstrInfoB.td
+++ b/llvm/lib/Target/RISCV/RISCVInstrInfoB.td
@@ -730,17 +730,10 @@
 } // Predicates = [HasStdExtZbp]
 
 let Predicates = [HasStdExtZbp, IsRV32] in {
-def : Pat<(rotr (bswap GPR:$rs1), (i32 16)), (GREVI GPR:$rs1, 8)>;
-def : Pat<(rotl (bswap GPR:$rs1), (i32 16)), (GREVI GPR:$rs1, 8)>;
-def : Pat<(bswap GPR:$rs1), (GREVI GPR:$rs1, (i32 24))>;
-def : Pat<(bitreverse GPR:$rs1), (GREVI GPR:$rs1, (i32 31))>;
+def : Pat<(rotr (riscv_grevi GPR:$rs1, (i32 24)), (i32 16)), (GREVI GPR:$rs1, 8)>;
+def : Pat<(rotl (riscv_grevi GPR:$rs1, (i32 24)), (i32 16)), (GREVI GPR:$rs1, 8)>;
 } // Predicates = [HasStdExtZbp, IsRV32]
 
-let Predicates = [HasStdExtZbp, IsRV64] in {
-def : Pat<(bswap GPR:$rs1), (GREVI GPR:$rs1, (i64 56))>;
-def : Pat<(bitreverse GPR:$rs1), (GREVI GPR:$rs1, (i64 63))>;
-} // Predicates = [HasStdExtZbp, IsRV64]
-
 let Predicates = [HasStdExtZbt] in {
 def : Pat<(or (and (not GPR:$rs2), GPR:$rs3), (and GPR:$rs2, GPR:$rs1)),
           (CMIX GPR:$rs1, GPR:$rs2, GPR:$rs3)>;
diff --git a/llvm/test/CodeGen/RISCV/rv32Zbp.ll b/llvm/test/CodeGen/RISCV/rv32Zbp.ll
--- a/llvm/test/CodeGen/RISCV/rv32Zbp.ll
+++ b/llvm/test/CodeGen/RISCV/rv32Zbp.ll
@@ -1849,6 +1849,175 @@
   ret i32 %2
 }
 
+define i32 @bitreverse_bswap_i32(i32 %a) {
+; RV32I-LABEL: bitreverse_bswap_i32:
+; RV32I:       # %bb.0:
+; RV32I-NEXT:    srli a1, a0, 8
+; RV32I-NEXT:    lui a2, 16
+; RV32I-NEXT:    addi a2, a2, -256
+; RV32I-NEXT:    and a1, a1, a2
+; RV32I-NEXT:    srli a3, a0, 24
+; RV32I-NEXT:    or a1, a1, a3
+; RV32I-NEXT:    slli a3, a0, 8
+; RV32I-NEXT:    lui a4, 4080
+; RV32I-NEXT:    and a3, a3, a4
+; RV32I-NEXT:    slli a0, a0, 24
+; RV32I-NEXT:    or a0, a0, a3
+; RV32I-NEXT:    or a0, a0, a1
+; RV32I-NEXT:    lui a1, 61681
+; RV32I-NEXT:    addi a1, a1, -241
+; RV32I-NEXT:    and a1, a0, a1
+; RV32I-NEXT:    slli a1, a1, 4
+; RV32I-NEXT:    lui a3, 986895
+; RV32I-NEXT:    addi a3, a3, 240
+; RV32I-NEXT:    and a0, a0, a3
+; RV32I-NEXT:    srli a0, a0, 4
+; RV32I-NEXT:    or a0, a0, a1
+; RV32I-NEXT:    lui a1, 209715
+; RV32I-NEXT:    addi a1, a1, 819
+; RV32I-NEXT:    and a1, a0, a1
+; RV32I-NEXT:    slli a1, a1, 2
+; RV32I-NEXT:    lui a3, 838861
+; RV32I-NEXT:    addi a3, a3, -820
+; RV32I-NEXT:    and a0, a0, a3
+; RV32I-NEXT:    srli a0, a0, 2
+; RV32I-NEXT:    or a0, a0, a1
+; RV32I-NEXT:    lui a1, 349525
+; RV32I-NEXT:    addi a1, a1, 1365
+; RV32I-NEXT:    and a1, a0, a1
+; RV32I-NEXT:    slli a1, a1, 1
+; RV32I-NEXT:    lui a3, 699051
+; RV32I-NEXT:    addi a3, a3, -1366
+; RV32I-NEXT:    and a0, a0, a3
+; RV32I-NEXT:    srli a0, a0, 1
+; RV32I-NEXT:    or a0, a0, a1
+; RV32I-NEXT:    srli a1, a0, 8
+; RV32I-NEXT:    and a1, a1, a2
+; RV32I-NEXT:    srli a2, a0, 24
+; RV32I-NEXT:    or a1, a1, a2
+; RV32I-NEXT:    slli a2, a0, 8
+; RV32I-NEXT:    and a2, a2, a4
+; RV32I-NEXT:    slli a0, a0, 24
+; RV32I-NEXT:    or a0, a0, a2
+; RV32I-NEXT:    or a0, a0, a1
+; RV32I-NEXT:    ret
+;
+; RV32IB-LABEL: bitreverse_bswap_i32:
+; RV32IB:       # %bb.0:
+; RV32IB-NEXT:    rev.b a0, a0
+; RV32IB-NEXT:    ret
+;
+; RV32IBP-LABEL: bitreverse_bswap_i32:
+; RV32IBP:       # %bb.0:
+; RV32IBP-NEXT:    rev.b a0, a0
+; RV32IBP-NEXT:    ret
+  %1 = call i32 @llvm.bitreverse.i32(i32 %a)
+  %2 = call i32 @llvm.bswap.i32(i32 %1)
+  ret i32 %2
+}
+
+define i64 @bitreverse_bswap_i64(i64 %a) {
+; RV32I-LABEL: bitreverse_bswap_i64:
+; RV32I:       # %bb.0:
+; RV32I-NEXT:    srli a3, a1, 8
+; RV32I-NEXT:    lui a2, 16
+; RV32I-NEXT:    addi t1, a2, -256
+; RV32I-NEXT:    and a3, a3, t1
+; RV32I-NEXT:    srli a4, a1, 24
+; RV32I-NEXT:    or a4, a3, a4
+; RV32I-NEXT:    slli a5, a1, 8
+; RV32I-NEXT:    lui a6, 4080
+; RV32I-NEXT:    and a5, a5, a6
+; RV32I-NEXT:    slli a1, a1, 24
+; RV32I-NEXT:    or a1, a1, a5
+; RV32I-NEXT:    or a1, a1, a4
+; RV32I-NEXT:    lui a4, 61681
+; RV32I-NEXT:    addi a7, a4, -241
+; RV32I-NEXT:    and a5, a1, a7
+; RV32I-NEXT:    slli a5, a5, 4
+; RV32I-NEXT:    lui a3, 986895
+; RV32I-NEXT:    addi t0, a3, 240
+; RV32I-NEXT:    and a1, a1, t0
+; RV32I-NEXT:    srli a1, a1, 4
+; RV32I-NEXT:    or a1, a1, a5
+; RV32I-NEXT:    lui a5, 209715
+; RV32I-NEXT:    addi t2, a5, 819
+; RV32I-NEXT:    and a4, a1, t2
+; RV32I-NEXT:    slli a4, a4, 2
+; RV32I-NEXT:    lui a3, 838861
+; RV32I-NEXT:    addi t3, a3, -820
+; RV32I-NEXT:    and a1, a1, t3
+; RV32I-NEXT:    srli a1, a1, 2
+; RV32I-NEXT:    or a1, a1, a4
+; RV32I-NEXT:    lui a4, 349525
+; RV32I-NEXT:    addi a4, a4, 1365
+; RV32I-NEXT:    and a2, a1, a4
+; RV32I-NEXT:    slli a2, a2, 1
+; RV32I-NEXT:    lui a5, 699051
+; RV32I-NEXT:    addi a5, a5, -1366
+; RV32I-NEXT:    and a1, a1, a5
+; RV32I-NEXT:    srli a1, a1, 1
+; RV32I-NEXT:    or a1, a1, a2
+; RV32I-NEXT:    srli a2, a0, 8
+; RV32I-NEXT:    and a2, a2, t1
+; RV32I-NEXT:    srli a3, a0, 24
+; RV32I-NEXT:    or a2, a2, a3
+; RV32I-NEXT:    slli a3, a0, 8
+; RV32I-NEXT:    and a3, a3, a6
+; RV32I-NEXT:    slli a0, a0, 24
+; RV32I-NEXT:    or a0, a0, a3
+; RV32I-NEXT:    or a0, a0, a2
+; RV32I-NEXT:    and a2, a0, a7
+; RV32I-NEXT:    slli a2, a2, 4
+; RV32I-NEXT:    and a0, a0, t0
+; RV32I-NEXT:    srli a0, a0, 4
+; RV32I-NEXT:    or a0, a0, a2
+; RV32I-NEXT:    and a2, a0, t2
+; RV32I-NEXT:    slli a2, a2, 2
+; RV32I-NEXT:    and a0, a0, t3
+; RV32I-NEXT:    srli a0, a0, 2
+; RV32I-NEXT:    or a0, a0, a2
+; RV32I-NEXT:    and a2, a0, a4
+; RV32I-NEXT:    slli a2, a2, 1
+; RV32I-NEXT:    and a0, a0, a5
+; RV32I-NEXT:    srli a0, a0, 1
+; RV32I-NEXT:    or a0, a0, a2
+; RV32I-NEXT:    srli a2, a0, 8
+; RV32I-NEXT:    and a2, a2, t1
+; RV32I-NEXT:    srli a3, a0, 24
+; RV32I-NEXT:    or a2, a2, a3
+; RV32I-NEXT:    slli a3, a0, 8
+; RV32I-NEXT:    and a3, a3, a6
+; RV32I-NEXT:    slli a0, a0, 24
+; RV32I-NEXT:    or a0, a0, a3
+; RV32I-NEXT:    or a0, a0, a2
+; RV32I-NEXT:    srli a2, a1, 8
+; RV32I-NEXT:    and a2, a2, t1
+; RV32I-NEXT:    srli a3, a1, 24
+; RV32I-NEXT:    or a2, a2, a3
+; RV32I-NEXT:    slli a3, a1, 8
+; RV32I-NEXT:    and a3, a3, a6
+; RV32I-NEXT:    slli a1, a1, 24
+; RV32I-NEXT:    or a1, a1, a3
+; RV32I-NEXT:    or a1, a1, a2
+; RV32I-NEXT:    ret
+;
+; RV32IB-LABEL: bitreverse_bswap_i64:
+; RV32IB:       # %bb.0:
+; RV32IB-NEXT:    rev.b a0, a0
+; RV32IB-NEXT:    rev.b a1, a1
+; RV32IB-NEXT:    ret
+;
+; RV32IBP-LABEL: bitreverse_bswap_i64:
+; RV32IBP:       # %bb.0:
+; RV32IBP-NEXT:    rev.b a0, a0
+; RV32IBP-NEXT:    rev.b a1, a1
+; RV32IBP-NEXT:    ret
+  %1 = call i64 @llvm.bitreverse.i64(i64 %a)
+  %2 = call i64 @llvm.bswap.i64(i64 %1)
+  ret i64 %2
+}
+
 define i32 @shfl1_i32(i32 %a, i32 %b) nounwind {
 ; RV32I-LABEL: shfl1_i32:
 ; RV32I:       # %bb.0:
diff --git a/llvm/test/CodeGen/RISCV/rv64Zbp.ll b/llvm/test/CodeGen/RISCV/rv64Zbp.ll
--- a/llvm/test/CodeGen/RISCV/rv64Zbp.ll
+++ b/llvm/test/CodeGen/RISCV/rv64Zbp.ll
@@ -2377,6 +2377,262 @@
   ret i32 %2
 }
 
+define i32 @bitreverse_bswap_i32(i32 %a) {
+; RV64I-LABEL: bitreverse_bswap_i32:
+; RV64I:       # %bb.0:
+; RV64I-NEXT:    srli a1, a0, 24
+; RV64I-NEXT:    lui a2, 4080
+; RV64I-NEXT:    and a1, a1, a2
+; RV64I-NEXT:    srli a2, a0, 8
+; RV64I-NEXT:    addi a3, zero, 255
+; RV64I-NEXT:    slli a4, a3, 24
+; RV64I-NEXT:    and a2, a2, a4
+; RV64I-NEXT:    or a1, a2, a1
+; RV64I-NEXT:    srli a2, a0, 40
+; RV64I-NEXT:    lui a4, 16
+; RV64I-NEXT:    addiw a4, a4, -256
+; RV64I-NEXT:    and a2, a2, a4
+; RV64I-NEXT:    srli a4, a0, 56
+; RV64I-NEXT:    or a2, a2, a4
+; RV64I-NEXT:    or a4, a1, a2
+; RV64I-NEXT:    slli a1, a0, 8
+; RV64I-NEXT:    slli a2, a3, 32
+; RV64I-NEXT:    and a2, a1, a2
+; RV64I-NEXT:    slli a5, a0, 24
+; RV64I-NEXT:    slli a6, a3, 40
+; RV64I-NEXT:    and a5, a5, a6
+; RV64I-NEXT:    or a5, a5, a2
+; RV64I-NEXT:    slli a1, a0, 40
+; RV64I-NEXT:    slli a2, a3, 48
+; RV64I-NEXT:    and a1, a1, a2
+; RV64I-NEXT:    slli a0, a0, 56
+; RV64I-NEXT:    or a0, a0, a1
+; RV64I-NEXT:    or a0, a0, a5
+; RV64I-NEXT:    or a0, a0, a4
+; RV64I-NEXT:    lui a1, 3855
+; RV64I-NEXT:    addiw a1, a1, 241
+; RV64I-NEXT:    slli a1, a1, 12
+; RV64I-NEXT:    addi a1, a1, -241
+; RV64I-NEXT:    slli a1, a1, 12
+; RV64I-NEXT:    addi a1, a1, 241
+; RV64I-NEXT:    slli a1, a1, 12
+; RV64I-NEXT:    addi a1, a1, -241
+; RV64I-NEXT:    and a1, a0, a1
+; RV64I-NEXT:    slli a1, a1, 4
+; RV64I-NEXT:    lui a3, 1044721
+; RV64I-NEXT:    addiw a3, a3, -241
+; RV64I-NEXT:    slli a3, a3, 12
+; RV64I-NEXT:    addi a3, a3, 241
+; RV64I-NEXT:    slli a3, a3, 12
+; RV64I-NEXT:    addi a3, a3, -241
+; RV64I-NEXT:    slli a3, a3, 12
+; RV64I-NEXT:    addi a3, a3, 240
+; RV64I-NEXT:    and a0, a0, a3
+; RV64I-NEXT:    srli a0, a0, 4
+; RV64I-NEXT:    or a0, a0, a1
+; RV64I-NEXT:    lui a1, 13107
+; RV64I-NEXT:    addiw a1, a1, 819
+; RV64I-NEXT:    slli a1, a1, 12
+; RV64I-NEXT:    addi a1, a1, 819
+; RV64I-NEXT:    slli a1, a1, 12
+; RV64I-NEXT:    addi a1, a1, 819
+; RV64I-NEXT:    slli a1, a1, 12
+; RV64I-NEXT:    addi a1, a1, 819
+; RV64I-NEXT:    and a1, a0, a1
+; RV64I-NEXT:    slli a1, a1, 2
+; RV64I-NEXT:    lui a3, 1035469
+; RV64I-NEXT:    addiw a3, a3, -819
+; RV64I-NEXT:    slli a3, a3, 12
+; RV64I-NEXT:    addi a3, a3, -819
+; RV64I-NEXT:    slli a3, a3, 12
+; RV64I-NEXT:    addi a3, a3, -819
+; RV64I-NEXT:    slli a3, a3, 12
+; RV64I-NEXT:    addi a3, a3, -820
+; RV64I-NEXT:    and a0, a0, a3
+; RV64I-NEXT:    srli a0, a0, 2
+; RV64I-NEXT:    or a0, a0, a1
+; RV64I-NEXT:    lui a1, 21845
+; RV64I-NEXT:    addiw a1, a1, 1365
+; RV64I-NEXT:    slli a1, a1, 12
+; RV64I-NEXT:    addi a1, a1, 1365
+; RV64I-NEXT:    slli a1, a1, 12
+; RV64I-NEXT:    addi a1, a1, 1365
+; RV64I-NEXT:    slli a1, a1, 12
+; RV64I-NEXT:    addi a1, a1, 1365
+; RV64I-NEXT:    and a1, a0, a1
+; RV64I-NEXT:    slli a1, a1, 1
+; RV64I-NEXT:    lui a3, 1026731
+; RV64I-NEXT:    addiw a3, a3, -1365
+; RV64I-NEXT:    slli a3, a3, 12
+; RV64I-NEXT:    addi a3, a3, -1365
+; RV64I-NEXT:    slli a3, a3, 12
+; RV64I-NEXT:    addi a3, a3, -1365
+; RV64I-NEXT:    slli a3, a3, 12
+; RV64I-NEXT:    addi a3, a3, -1366
+; RV64I-NEXT:    and a0, a0, a3
+; RV64I-NEXT:    srli a0, a0, 1
+; RV64I-NEXT:    or a0, a0, a1
+; RV64I-NEXT:    slli a1, a0, 24
+; RV64I-NEXT:    addi a3, zero, -1
+; RV64I-NEXT:    slli a3, a3, 56
+; RV64I-NEXT:    and a1, a1, a3
+; RV64I-NEXT:    srli a3, a0, 8
+; RV64I-NEXT:    and a3, a3, a6
+; RV64I-NEXT:    srli a4, a0, 24
+; RV64I-NEXT:    or a3, a3, a4
+; RV64I-NEXT:    slli a0, a0, 8
+; RV64I-NEXT:    and a0, a0, a2
+; RV64I-NEXT:    or a0, a1, a0
+; RV64I-NEXT:    or a0, a0, a3
+; RV64I-NEXT:    srli a0, a0, 32
+; RV64I-NEXT:    ret
+;
+; RV64IB-LABEL: bitreverse_bswap_i32:
+; RV64IB:       # %bb.0:
+; RV64IB-NEXT:    greviw a0, a0, 7
+; RV64IB-NEXT:    ret
+;
+; RV64IBP-LABEL: bitreverse_bswap_i32:
+; RV64IBP:       # %bb.0:
+; RV64IBP-NEXT:    greviw a0, a0, 7
+; RV64IBP-NEXT:    ret
+  %1 = call i32 @llvm.bitreverse.i32(i32 %a)
+  %2 = call i32 @llvm.bswap.i32(i32 %1)
+  ret i32 %2
+}
+
+define i64 @bitreverse_bswap_i64(i64 %a) {
+; RV64I-LABEL: bitreverse_bswap_i64:
+; RV64I:       # %bb.0:
+; RV64I-NEXT:    srli a1, a0, 24
+; RV64I-NEXT:    lui a6, 4080
+; RV64I-NEXT:    and a1, a1, a6
+; RV64I-NEXT:    srli a3, a0, 8
+; RV64I-NEXT:    addi a5, zero, 255
+; RV64I-NEXT:    slli a7, a5, 24
+; RV64I-NEXT:    and a3, a3, a7
+; RV64I-NEXT:    or a3, a3, a1
+; RV64I-NEXT:    srli a4, a0, 40
+; RV64I-NEXT:    lui a1, 16
+; RV64I-NEXT:    addiw a1, a1, -256
+; RV64I-NEXT:    and a4, a4, a1
+; RV64I-NEXT:    srli a2, a0, 56
+; RV64I-NEXT:    or a2, a4, a2
+; RV64I-NEXT:    or a2, a3, a2
+; RV64I-NEXT:    slli a4, a0, 8
+; RV64I-NEXT:    slli t0, a5, 32
+; RV64I-NEXT:    and a3, a4, t0
+; RV64I-NEXT:    slli a4, a0, 24
+; RV64I-NEXT:    slli t1, a5, 40
+; RV64I-NEXT:    and a4, a4, t1
+; RV64I-NEXT:    or a3, a4, a3
+; RV64I-NEXT:    slli a4, a0, 40
+; RV64I-NEXT:    slli a5, a5, 48
+; RV64I-NEXT:    and a4, a4, a5
+; RV64I-NEXT:    slli a0, a0, 56
+; RV64I-NEXT:    or a0, a0, a4
+; RV64I-NEXT:    or a0, a0, a3
+; RV64I-NEXT:    or a0, a0, a2
+; RV64I-NEXT:    lui a2, 3855
+; RV64I-NEXT:    addiw a2, a2, 241
+; RV64I-NEXT:    slli a2, a2, 12
+; RV64I-NEXT:    addi a2, a2, -241
+; RV64I-NEXT:    slli a2, a2, 12
+; RV64I-NEXT:    addi a2, a2, 241
+; RV64I-NEXT:    slli a2, a2, 12
+; RV64I-NEXT:    addi a2, a2, -241
+; RV64I-NEXT:    and a2, a0, a2
+; RV64I-NEXT:    slli a2, a2, 4
+; RV64I-NEXT:    lui a3, 1044721
+; RV64I-NEXT:    addiw a3, a3, -241
+; RV64I-NEXT:    slli a3, a3, 12
+; RV64I-NEXT:    addi a3, a3, 241
+; RV64I-NEXT:    slli a3, a3, 12
+; RV64I-NEXT:    addi a3, a3, -241
+; RV64I-NEXT:    slli a3, a3, 12
+; RV64I-NEXT:    addi a3, a3, 240
+; RV64I-NEXT:    and a0, a0, a3
+; RV64I-NEXT:    srli a0, a0, 4
+; RV64I-NEXT:    or a0, a0, a2
+; RV64I-NEXT:    lui a2, 13107
+; RV64I-NEXT:    addiw a2, a2, 819
+; RV64I-NEXT:    slli a2, a2, 12
+; RV64I-NEXT:    addi a2, a2, 819
+; RV64I-NEXT:    slli a2, a2, 12
+; RV64I-NEXT:    addi a2, a2, 819
+; RV64I-NEXT:    slli a2, a2, 12
+; RV64I-NEXT:    addi a2, a2, 819
+; RV64I-NEXT:    and a2, a0, a2
+; RV64I-NEXT:    slli a2, a2, 2
+; RV64I-NEXT:    lui a3, 1035469
+; RV64I-NEXT:    addiw a3, a3, -819
+; RV64I-NEXT:    slli a3, a3, 12
+; RV64I-NEXT:    addi a3, a3, -819
+; RV64I-NEXT:    slli a3, a3, 12
+; RV64I-NEXT:    addi a3, a3, -819
+; RV64I-NEXT:    slli a3, a3, 12
+; RV64I-NEXT:    addi a3, a3, -820
+; RV64I-NEXT:    and a0, a0, a3
+; RV64I-NEXT:    srli a0, a0, 2
+; RV64I-NEXT:    or a0, a0, a2
+; RV64I-NEXT:    lui a2, 21845
+; RV64I-NEXT:    addiw a2, a2, 1365
+; RV64I-NEXT:    slli a2, a2, 12
+; RV64I-NEXT:    addi a2, a2, 1365
+; RV64I-NEXT:    slli a2, a2, 12
+; RV64I-NEXT:    addi a2, a2, 1365
+; RV64I-NEXT:    slli a2, a2, 12
+; RV64I-NEXT:    addi a2, a2, 1365
+; RV64I-NEXT:    and a2, a0, a2
+; RV64I-NEXT:    slli a2, a2, 1
+; RV64I-NEXT:    lui a3, 1026731
+; RV64I-NEXT:    addiw a3, a3, -1365
+; RV64I-NEXT:    slli a3, a3, 12
+; RV64I-NEXT:    addi a3, a3, -1365
+; RV64I-NEXT:    slli a3, a3, 12
+; RV64I-NEXT:    addi a3, a3, -1365
+; RV64I-NEXT:    slli a3, a3, 12
+; RV64I-NEXT:    addi a3, a3, -1366
+; RV64I-NEXT:    and a0, a0, a3
+; RV64I-NEXT:    srli a0, a0, 1
+; RV64I-NEXT:    or a0, a0, a2
+; RV64I-NEXT:    srli a2, a0, 40
+; RV64I-NEXT:    and a1, a2, a1
+; RV64I-NEXT:    srli a2, a0, 56
+; RV64I-NEXT:    or a1, a1, a2
+; RV64I-NEXT:    srli a2, a0, 24
+; RV64I-NEXT:    and a2, a2, a6
+; RV64I-NEXT:    srli a3, a0, 8
+; RV64I-NEXT:    and a3, a3, a7
+; RV64I-NEXT:    or a2, a3, a2
+; RV64I-NEXT:    or a1, a2, a1
+; RV64I-NEXT:    slli a2, a0, 8
+; RV64I-NEXT:    and a2, a2, t0
+; RV64I-NEXT:    slli a3, a0, 24
+; RV64I-NEXT:    and a3, a3, t1
+; RV64I-NEXT:    or a2, a3, a2
+; RV64I-NEXT:    slli a3, a0, 40
+; RV64I-NEXT:    and a3, a3, a5
+; RV64I-NEXT:    slli a0, a0, 56
+; RV64I-NEXT:    or a0, a0, a3
+; RV64I-NEXT:    or a0, a0, a2
+; RV64I-NEXT:    or a0, a0, a1
+; RV64I-NEXT:    ret
+;
+; RV64IB-LABEL: bitreverse_bswap_i64:
+; RV64IB:       # %bb.0:
+; RV64IB-NEXT:    rev.b a0, a0
+; RV64IB-NEXT:    ret
+;
+; RV64IBP-LABEL: bitreverse_bswap_i64:
+; RV64IBP:       # %bb.0:
+; RV64IBP-NEXT:    rev.b a0, a0
+; RV64IBP-NEXT:    ret
+  %1 = call i64 @llvm.bitreverse.i64(i64 %a)
+  %2 = call i64 @llvm.bswap.i64(i64 %1)
+  ret i64 %2
+}
+
 ; There's no [un]shfliw instruction as slliu.w occupies the encoding slot that
 ; would be occupied by shfliw.