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
@@ -5119,6 +5119,9 @@
            "BSWAP types must be a multiple of 16 bits!");
     if (OpOpcode == ISD::UNDEF)
       return getUNDEF(VT);
+    // bswap(bswap(X)) -> X.
+    if (OpOpcode == ISD::BSWAP)
+      return Operand.getOperand(0);
     break;
   case ISD::BITREVERSE:
     assert(VT.isInteger() && VT == Operand.getValueType() &&
diff --git a/llvm/test/CodeGen/RISCV/bswap-bitreverse-ctlz-cttz-ctpop.ll b/llvm/test/CodeGen/RISCV/bswap-bitreverse-ctlz-cttz-ctpop.ll
--- a/llvm/test/CodeGen/RISCV/bswap-bitreverse-ctlz-cttz-ctpop.ll
+++ b/llvm/test/CodeGen/RISCV/bswap-bitreverse-ctlz-cttz-ctpop.ll
@@ -694,13 +694,6 @@
 define i16 @test_bswap_bitreverse_i16(i16 %a) nounwind {
 ; RV32I-LABEL: test_bswap_bitreverse_i16:
 ; RV32I:       # %bb.0:
-; RV32I-NEXT:    slli a1, a0, 8
-; RV32I-NEXT:    slli a2, a0, 16
-; RV32I-NEXT:    srli a2, a2, 24
-; RV32I-NEXT:    or a1, a1, a2
-; RV32I-NEXT:    slli a1, a1, 8
-; RV32I-NEXT:    andi a0, a0, 255
-; RV32I-NEXT:    or a0, a1, a0
 ; RV32I-NEXT:    srli a1, a0, 4
 ; RV32I-NEXT:    lui a2, 1
 ; RV32I-NEXT:    addi a2, a2, -241
@@ -726,13 +719,6 @@
 ;
 ; RV64I-LABEL: test_bswap_bitreverse_i16:
 ; RV64I:       # %bb.0:
-; RV64I-NEXT:    slli a1, a0, 8
-; RV64I-NEXT:    slli a2, a0, 48
-; RV64I-NEXT:    srli a2, a2, 56
-; RV64I-NEXT:    or a1, a1, a2
-; RV64I-NEXT:    slli a1, a1, 8
-; RV64I-NEXT:    andi a0, a0, 255
-; RV64I-NEXT:    or a0, a1, a0
 ; RV64I-NEXT:    srli a1, a0, 4
 ; RV64I-NEXT:    lui a2, 1
 ; RV64I-NEXT:    addiw a2, a2, -241
@@ -758,16 +744,13 @@
 ;
 ; RV32ZBB-LABEL: test_bswap_bitreverse_i16:
 ; RV32ZBB:       # %bb.0:
-; RV32ZBB-NEXT:    rev8 a0, a0
-; RV32ZBB-NEXT:    srli a0, a0, 16
-; RV32ZBB-NEXT:    rev8 a0, a0
-; RV32ZBB-NEXT:    srli a1, a0, 12
-; RV32ZBB-NEXT:    lui a2, 15
-; RV32ZBB-NEXT:    addi a2, a2, 240
+; RV32ZBB-NEXT:    srli a1, a0, 4
+; RV32ZBB-NEXT:    lui a2, 1
+; RV32ZBB-NEXT:    addi a2, a2, -241
 ; RV32ZBB-NEXT:    and a1, a1, a2
-; RV32ZBB-NEXT:    srli a0, a0, 20
-; RV32ZBB-NEXT:    andi a0, a0, -241
-; RV32ZBB-NEXT:    or a0, a0, a1
+; RV32ZBB-NEXT:    and a0, a0, a2
+; RV32ZBB-NEXT:    slli a0, a0, 4
+; RV32ZBB-NEXT:    or a0, a1, a0
 ; RV32ZBB-NEXT:    srli a1, a0, 2
 ; RV32ZBB-NEXT:    lui a2, 3
 ; RV32ZBB-NEXT:    addi a2, a2, 819
@@ -786,16 +769,13 @@
 ;
 ; RV64ZBB-LABEL: test_bswap_bitreverse_i16:
 ; RV64ZBB:       # %bb.0:
-; RV64ZBB-NEXT:    rev8 a0, a0
-; RV64ZBB-NEXT:    srli a0, a0, 48
-; RV64ZBB-NEXT:    rev8 a0, a0
-; RV64ZBB-NEXT:    srli a1, a0, 44
-; RV64ZBB-NEXT:    lui a2, 15
-; RV64ZBB-NEXT:    addiw a2, a2, 240
+; RV64ZBB-NEXT:    srli a1, a0, 4
+; RV64ZBB-NEXT:    lui a2, 1
+; RV64ZBB-NEXT:    addiw a2, a2, -241
 ; RV64ZBB-NEXT:    and a1, a1, a2
-; RV64ZBB-NEXT:    srli a0, a0, 52
-; RV64ZBB-NEXT:    andi a0, a0, -241
-; RV64ZBB-NEXT:    or a0, a0, a1
+; RV64ZBB-NEXT:    and a0, a0, a2
+; RV64ZBB-NEXT:    slli a0, a0, 4
+; RV64ZBB-NEXT:    or a0, a1, a0
 ; RV64ZBB-NEXT:    srli a1, a0, 2
 ; RV64ZBB-NEXT:    lui a2, 3
 ; RV64ZBB-NEXT:    addiw a2, a2, 819
@@ -819,27 +799,6 @@
 define i32 @test_bswap_bitreverse_i32(i32 %a) nounwind {
 ; RV32I-LABEL: test_bswap_bitreverse_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:    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:    srli a1, a0, 4
 ; RV32I-NEXT:    lui a2, 61681
 ; RV32I-NEXT:    addi a2, a2, -241
@@ -865,27 +824,6 @@
 ;
 ; RV64I-LABEL: test_bswap_bitreverse_i32:
 ; RV64I:       # %bb.0:
-; RV64I-NEXT:    srliw a1, a0, 8
-; RV64I-NEXT:    lui a2, 16
-; RV64I-NEXT:    addiw a2, a2, -256
-; RV64I-NEXT:    and a1, a1, a2
-; RV64I-NEXT:    srliw a3, a0, 24
-; RV64I-NEXT:    or a1, a1, a3
-; RV64I-NEXT:    slli a3, a0, 8
-; RV64I-NEXT:    lui a4, 4080
-; RV64I-NEXT:    and a3, a3, a4
-; RV64I-NEXT:    slliw a0, a0, 24
-; RV64I-NEXT:    or a0, a0, a3
-; RV64I-NEXT:    or a0, a0, a1
-; RV64I-NEXT:    srliw a1, a0, 8
-; RV64I-NEXT:    and a1, a1, a2
-; RV64I-NEXT:    srliw a2, a0, 24
-; RV64I-NEXT:    or a1, a1, a2
-; RV64I-NEXT:    slli a2, a0, 8
-; RV64I-NEXT:    and a2, a2, a4
-; RV64I-NEXT:    slliw a0, a0, 24
-; RV64I-NEXT:    or a0, a0, a2
-; RV64I-NEXT:    or a0, a0, a1
 ; RV64I-NEXT:    srli a1, a0, 4
 ; RV64I-NEXT:    lui a2, 61681
 ; RV64I-NEXT:    addiw a2, a2, -241
@@ -936,18 +874,12 @@
 ;
 ; RV64ZBB-LABEL: test_bswap_bitreverse_i32:
 ; RV64ZBB:       # %bb.0:
-; RV64ZBB-NEXT:    rev8 a0, a0
-; RV64ZBB-NEXT:    srli a0, a0, 32
-; RV64ZBB-NEXT:    rev8 a0, a0
-; RV64ZBB-NEXT:    srli a1, a0, 36
+; RV64ZBB-NEXT:    srli a1, a0, 4
 ; RV64ZBB-NEXT:    lui a2, 61681
 ; RV64ZBB-NEXT:    addiw a2, a2, -241
 ; RV64ZBB-NEXT:    and a1, a1, a2
-; RV64ZBB-NEXT:    srli a0, a0, 28
-; RV64ZBB-NEXT:    lui a2, 986895
-; RV64ZBB-NEXT:    addiw a2, a2, 240
 ; RV64ZBB-NEXT:    and a0, a0, a2
-; RV64ZBB-NEXT:    sext.w a0, a0
+; RV64ZBB-NEXT:    slliw a0, a0, 4
 ; RV64ZBB-NEXT:    or a0, a1, a0
 ; RV64ZBB-NEXT:    srli a1, a0, 2
 ; RV64ZBB-NEXT:    lui a2, 209715
@@ -972,155 +904,67 @@
 define i64 @test_bswap_bitreverse_i64(i64 %a) nounwind {
 ; RV32I-LABEL: test_bswap_bitreverse_i64:
 ; RV32I:       # %bb.0:
-; RV32I-NEXT:    srli a2, a1, 8
-; RV32I-NEXT:    lui a3, 16
-; RV32I-NEXT:    addi a3, a3, -256
-; RV32I-NEXT:    and a2, a2, a3
-; RV32I-NEXT:    srli a4, a1, 24
-; RV32I-NEXT:    or a2, a2, a4
-; RV32I-NEXT:    slli a4, a1, 8
-; RV32I-NEXT:    lui a5, 4080
-; RV32I-NEXT:    and a4, a4, a5
-; RV32I-NEXT:    slli a1, a1, 24
-; RV32I-NEXT:    or a1, a1, a4
-; RV32I-NEXT:    or a1, a1, a2
-; RV32I-NEXT:    srli a2, a0, 8
-; RV32I-NEXT:    and a2, a2, a3
-; RV32I-NEXT:    srli a4, a0, 24
-; RV32I-NEXT:    or a2, a2, a4
-; RV32I-NEXT:    slli a4, a0, 8
-; RV32I-NEXT:    and a4, a4, a5
-; RV32I-NEXT:    slli a0, a0, 24
-; RV32I-NEXT:    or a0, a0, a4
-; RV32I-NEXT:    or a0, a0, a2
-; RV32I-NEXT:    srli a2, a0, 8
-; RV32I-NEXT:    and a2, a2, a3
-; RV32I-NEXT:    srli a4, a0, 24
-; RV32I-NEXT:    or a2, a2, a4
-; RV32I-NEXT:    slli a4, a0, 8
-; RV32I-NEXT:    and a4, a4, a5
-; RV32I-NEXT:    slli a0, a0, 24
-; RV32I-NEXT:    or a0, a0, a4
-; RV32I-NEXT:    or a0, a0, a2
 ; RV32I-NEXT:    srli a2, a0, 4
-; RV32I-NEXT:    lui a4, 61681
-; RV32I-NEXT:    addi a4, a4, -241
-; RV32I-NEXT:    and a2, a2, a4
-; RV32I-NEXT:    and a0, a0, a4
+; RV32I-NEXT:    lui a3, 61681
+; RV32I-NEXT:    addi a3, a3, -241
+; RV32I-NEXT:    and a2, a2, a3
+; RV32I-NEXT:    and a0, a0, a3
 ; RV32I-NEXT:    slli a0, a0, 4
 ; RV32I-NEXT:    or a0, a2, a0
 ; RV32I-NEXT:    srli a2, a0, 2
-; RV32I-NEXT:    lui a6, 209715
-; RV32I-NEXT:    addi a6, a6, 819
-; RV32I-NEXT:    and a2, a2, a6
-; RV32I-NEXT:    and a0, a0, a6
+; RV32I-NEXT:    lui a4, 209715
+; RV32I-NEXT:    addi a4, a4, 819
+; RV32I-NEXT:    and a2, a2, a4
+; RV32I-NEXT:    and a0, a0, a4
 ; RV32I-NEXT:    slli a0, a0, 2
 ; RV32I-NEXT:    or a0, a2, a0
 ; RV32I-NEXT:    srli a2, a0, 1
-; RV32I-NEXT:    lui a7, 349525
-; RV32I-NEXT:    addi a7, a7, 1365
-; RV32I-NEXT:    and a2, a2, a7
-; RV32I-NEXT:    and a0, a0, a7
+; RV32I-NEXT:    lui a5, 349525
+; RV32I-NEXT:    addi a5, a5, 1365
+; RV32I-NEXT:    and a2, a2, a5
+; RV32I-NEXT:    and a0, a0, a5
 ; RV32I-NEXT:    slli a0, a0, 1
 ; RV32I-NEXT:    or a0, a2, a0
-; RV32I-NEXT:    srli a2, a1, 8
-; RV32I-NEXT:    and a2, a2, a3
-; RV32I-NEXT:    srli a3, a1, 24
-; RV32I-NEXT:    or a2, a2, a3
-; RV32I-NEXT:    slli a3, a1, 8
-; RV32I-NEXT:    and a3, a3, a5
-; RV32I-NEXT:    slli a1, a1, 24
-; RV32I-NEXT:    or a1, a1, a3
-; RV32I-NEXT:    or a1, a1, a2
 ; RV32I-NEXT:    srli a2, a1, 4
-; RV32I-NEXT:    and a2, a2, a4
-; RV32I-NEXT:    and a1, a1, a4
+; RV32I-NEXT:    and a2, a2, a3
+; RV32I-NEXT:    and a1, a1, a3
 ; RV32I-NEXT:    slli a1, a1, 4
 ; RV32I-NEXT:    or a1, a2, a1
 ; RV32I-NEXT:    srli a2, a1, 2
-; RV32I-NEXT:    and a2, a2, a6
-; RV32I-NEXT:    and a1, a1, a6
+; RV32I-NEXT:    and a2, a2, a4
+; RV32I-NEXT:    and a1, a1, a4
 ; RV32I-NEXT:    slli a1, a1, 2
 ; RV32I-NEXT:    or a1, a2, a1
 ; RV32I-NEXT:    srli a2, a1, 1
-; RV32I-NEXT:    and a2, a2, a7
-; RV32I-NEXT:    and a1, a1, a7
+; RV32I-NEXT:    and a2, a2, a5
+; RV32I-NEXT:    and a1, a1, a5
 ; RV32I-NEXT:    slli a1, a1, 1
 ; RV32I-NEXT:    or a1, a2, a1
 ; RV32I-NEXT:    ret
 ;
 ; RV64I-LABEL: test_bswap_bitreverse_i64:
 ; RV64I:       # %bb.0:
-; RV64I-NEXT:    srli a1, a0, 24
-; RV64I-NEXT:    lui a2, 4080
-; RV64I-NEXT:    and a1, a1, a2
-; RV64I-NEXT:    srli a3, a0, 8
-; RV64I-NEXT:    li a4, 255
-; RV64I-NEXT:    slli a5, a4, 24
-; RV64I-NEXT:    and a3, a3, a5
-; RV64I-NEXT:    or a1, a3, a1
-; RV64I-NEXT:    srli a3, a0, 40
-; RV64I-NEXT:    lui a6, 16
-; RV64I-NEXT:    addiw a6, a6, -256
-; RV64I-NEXT:    and a3, a3, a6
-; RV64I-NEXT:    srli a7, a0, 56
-; RV64I-NEXT:    or a3, a3, a7
-; RV64I-NEXT:    or a1, a1, a3
-; RV64I-NEXT:    slli a3, a0, 24
-; RV64I-NEXT:    slli a7, a4, 40
-; RV64I-NEXT:    and a3, a3, a7
-; RV64I-NEXT:    srliw t0, a0, 24
-; RV64I-NEXT:    slli t0, t0, 32
-; RV64I-NEXT:    or a3, a3, t0
-; RV64I-NEXT:    slli t0, a0, 40
-; RV64I-NEXT:    slli a4, a4, 48
-; RV64I-NEXT:    and t0, t0, a4
-; RV64I-NEXT:    slli a0, a0, 56
-; RV64I-NEXT:    or a0, a0, t0
-; RV64I-NEXT:    or a0, a0, a3
-; RV64I-NEXT:    or a0, a0, a1
-; RV64I-NEXT:    srli a1, a0, 40
-; RV64I-NEXT:    and a1, a1, a6
-; RV64I-NEXT:    srli a3, a0, 56
-; RV64I-NEXT:    or a1, a1, a3
-; RV64I-NEXT:    srli a3, a0, 24
-; RV64I-NEXT:    and a2, a3, a2
-; RV64I-NEXT:    srli a3, a0, 8
-; RV64I-NEXT:    and a3, a3, a5
-; RV64I-NEXT:    or a2, a3, a2
-; RV64I-NEXT:    or a1, a2, a1
-; RV64I-NEXT:    slli a2, a0, 24
-; RV64I-NEXT:    and a2, a2, a7
-; RV64I-NEXT:    srliw a3, a0, 24
-; RV64I-NEXT:    slli a3, a3, 32
-; RV64I-NEXT:    or a2, a2, a3
-; RV64I-NEXT:    slli a3, a0, 40
-; RV64I-NEXT:    and a3, a3, a4
-; RV64I-NEXT:    slli a0, a0, 56
-; RV64I-NEXT:    or a0, a0, a3
-; RV64I-NEXT:    lui a3, %hi(.LCPI9_0)
-; RV64I-NEXT:    ld a3, %lo(.LCPI9_0)(a3)
-; RV64I-NEXT:    or a0, a0, a2
-; RV64I-NEXT:    or a0, a0, a1
-; RV64I-NEXT:    srli a1, a0, 4
-; RV64I-NEXT:    and a1, a1, a3
-; RV64I-NEXT:    and a0, a0, a3
-; RV64I-NEXT:    lui a2, %hi(.LCPI9_1)
-; RV64I-NEXT:    ld a2, %lo(.LCPI9_1)(a2)
+; RV64I-NEXT:    lui a1, %hi(.LCPI9_0)
+; RV64I-NEXT:    ld a1, %lo(.LCPI9_0)(a1)
+; RV64I-NEXT:    srli a2, a0, 4
+; RV64I-NEXT:    and a2, a2, a1
+; RV64I-NEXT:    and a0, a0, a1
+; RV64I-NEXT:    lui a1, %hi(.LCPI9_1)
+; RV64I-NEXT:    ld a1, %lo(.LCPI9_1)(a1)
 ; RV64I-NEXT:    slli a0, a0, 4
-; RV64I-NEXT:    or a0, a1, a0
-; RV64I-NEXT:    srli a1, a0, 2
-; RV64I-NEXT:    and a1, a1, a2
-; RV64I-NEXT:    and a0, a0, a2
-; RV64I-NEXT:    lui a2, %hi(.LCPI9_2)
-; RV64I-NEXT:    ld a2, %lo(.LCPI9_2)(a2)
+; RV64I-NEXT:    or a0, a2, a0
+; RV64I-NEXT:    srli a2, a0, 2
+; RV64I-NEXT:    and a2, a2, a1
+; RV64I-NEXT:    and a0, a0, a1
+; RV64I-NEXT:    lui a1, %hi(.LCPI9_2)
+; RV64I-NEXT:    ld a1, %lo(.LCPI9_2)(a1)
 ; RV64I-NEXT:    slli a0, a0, 2
-; RV64I-NEXT:    or a0, a1, a0
-; RV64I-NEXT:    srli a1, a0, 1
-; RV64I-NEXT:    and a1, a1, a2
-; RV64I-NEXT:    and a0, a0, a2
+; RV64I-NEXT:    or a0, a2, a0
+; RV64I-NEXT:    srli a2, a0, 1
+; RV64I-NEXT:    and a2, a2, a1
+; RV64I-NEXT:    and a0, a0, a1
 ; RV64I-NEXT:    slli a0, a0, 1
-; RV64I-NEXT:    or a0, a1, a0
+; RV64I-NEXT:    or a0, a2, a0
 ; RV64I-NEXT:    ret
 ;
 ; RV32ZBB-LABEL: test_bswap_bitreverse_i64: