diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -2940,6 +2940,21 @@
       return Result;
     }
 
+    // BSWAP - most likely due to us previous matching a partial bswap.
+    if (match(V, m_BSwap(m_Value(X)))) {
+      const auto &Res =
+          collectBitParts(X, MatchBSwaps, MatchBitReversals, BPS, Depth + 1);
+      if (!Res)
+        return Result;
+
+      Result = BitPart(Res->Provider, BitWidth);
+      for (unsigned ByteIdx = 0; ByteIdx < BitWidth; ByteIdx += 8)
+        for (unsigned BitIdx = 0; BitIdx < 8; ++BitIdx)
+          Result->Provenance[(BitWidth - 8 - ByteIdx) + BitIdx] =
+              Res->Provenance[ByteIdx + BitIdx];
+      return Result;
+    }
+
     // Funnel 'double' shifts take 3 operands, 2 inputs and the shift
     // amount (modulo).
     // fshl(X,Y,Z): (X << (Z % BW)) | (Y >> (BW - (Z % BW)))
@@ -3032,10 +3047,15 @@
   // Now, is the bit permutation correct for a bswap or a bitreverse? We can
   // only byteswap values with an even number of bytes.
   unsigned DemandedBW = DemandedTy->getBitWidth();
+  APInt DemandedMask = APInt::getAllOnesValue(DemandedBW);
   bool OKForBSwap = MatchBSwaps && (DemandedBW % 16) == 0;
   bool OKForBitReverse = MatchBitReversals;
   for (unsigned BitIdx = 0;
        (BitIdx < DemandedBW) && (OKForBSwap || OKForBitReverse); ++BitIdx) {
+    if (BitProvenance[BitIdx] == BitPart::Unset) {
+      DemandedMask.clearBit(BitIdx);
+      continue;
+    }
     OKForBSwap &= bitTransformIsCorrectForBSwap(BitProvenance[BitIdx], BitIdx,
                                                 DemandedBW);
     OKForBitReverse &= bitTransformIsCorrectForBitReverse(BitProvenance[BitIdx],
@@ -3061,12 +3081,18 @@
     Provider = Trunc;
   }
 
-  auto *CI = CallInst::Create(F, Provider, "rev", I);
-  InsertedInsts.push_back(CI);
+  Instruction *Result = CallInst::Create(F, Provider, "rev", I);
+  InsertedInsts.push_back(Result);
+
+  if (!DemandedMask.isAllOnesValue()) {
+    auto *Mask = ConstantInt::get(DemandedTy, DemandedMask);
+    Result = BinaryOperator::Create(Instruction::And, Result, Mask, "mask", I);
+    InsertedInsts.push_back(Result);
+  }
 
   // We may need to zeroextend back to the result type.
-  if (ITy != CI->getType()) {
-    auto *ExtInst = CastInst::Create(Instruction::ZExt, CI, ITy, "zext", I);
+  if (ITy != Result->getType()) {
+    auto *ExtInst = CastInst::Create(Instruction::ZExt, Result, ITy, "zext", I);
     InsertedInsts.push_back(ExtInst);
   }
 
diff --git a/llvm/test/Transforms/InstCombine/bswap.ll b/llvm/test/Transforms/InstCombine/bswap.ll
--- a/llvm/test/Transforms/InstCombine/bswap.ll
+++ b/llvm/test/Transforms/InstCombine/bswap.ll
@@ -347,10 +347,9 @@
 
 define i64 @bswap_and_mask_0(i64 %0) {
 ; CHECK-LABEL: @bswap_and_mask_0(
-; CHECK-NEXT:    [[TMP2:%.*]] = lshr i64 [[TMP0:%.*]], 56
-; CHECK-NEXT:    [[TMP3:%.*]] = shl i64 [[TMP0]], 56
-; CHECK-NEXT:    [[TMP4:%.*]] = or i64 [[TMP2]], [[TMP3]]
-; CHECK-NEXT:    ret i64 [[TMP4]]
+; CHECK-NEXT:    [[TMP2:%.*]] = and i64 [[TMP0:%.*]], -72057594037927681
+; CHECK-NEXT:    [[TMP3:%.*]] = call i64 @llvm.bswap.i64(i64 [[TMP2]])
+; CHECK-NEXT:    ret i64 [[TMP3]]
 ;
   %2 = lshr i64 %0, 56
   %3 = shl i64 %0, 56
@@ -375,13 +374,12 @@
 
 define i64 @bswap_and_mask_2(i64 %0) {
 ; CHECK-LABEL: @bswap_and_mask_2(
-; CHECK-NEXT:    [[TMP2:%.*]] = lshr i64 [[TMP0:%.*]], 56
-; CHECK-NEXT:    [[TMP3:%.*]] = shl i64 [[TMP0]], 56
-; CHECK-NEXT:    [[TMP4:%.*]] = or i64 [[TMP2]], [[TMP3]]
-; CHECK-NEXT:    [[TMP5:%.*]] = shl i64 [[TMP0]], 40
-; CHECK-NEXT:    [[TMP6:%.*]] = and i64 [[TMP5]], 71776119061217280
-; CHECK-NEXT:    [[TMP7:%.*]] = or i64 [[TMP4]], [[TMP6]]
-; CHECK-NEXT:    ret i64 [[TMP7]]
+; CHECK-NEXT:    [[TMP2:%.*]] = and i64 [[TMP0:%.*]], -72057594037927681
+; CHECK-NEXT:    [[TMP3:%.*]] = call i64 @llvm.bswap.i64(i64 [[TMP2]])
+; CHECK-NEXT:    [[TMP4:%.*]] = shl i64 [[TMP0]], 40
+; CHECK-NEXT:    [[TMP5:%.*]] = and i64 [[TMP4]], 71776119061217280
+; CHECK-NEXT:    [[TMP6:%.*]] = or i64 [[TMP3]], [[TMP5]]
+; CHECK-NEXT:    ret i64 [[TMP6]]
 ;
   %2 = lshr i64 %0, 56
   %3 = shl i64 %0, 56
@@ -504,28 +502,8 @@
 
 define i64 @PR47191_problem1(i64 %0) {
 ; CHECK-LABEL: @PR47191_problem1(
-; CHECK-NEXT:    [[TMP2:%.*]] = lshr i64 [[TMP0:%.*]], 56
-; CHECK-NEXT:    [[TMP3:%.*]] = lshr i64 [[TMP0]], 40
-; CHECK-NEXT:    [[TMP4:%.*]] = and i64 [[TMP3]], 65280
-; CHECK-NEXT:    [[TMP5:%.*]] = lshr i64 [[TMP0]], 24
-; CHECK-NEXT:    [[TMP6:%.*]] = and i64 [[TMP5]], 16711680
-; CHECK-NEXT:    [[TMP7:%.*]] = lshr i64 [[TMP0]], 8
-; CHECK-NEXT:    [[TMP8:%.*]] = and i64 [[TMP7]], 4278190080
-; CHECK-NEXT:    [[TMP9:%.*]] = shl i64 [[TMP0]], 56
-; CHECK-NEXT:    [[TMP10:%.*]] = shl i64 [[TMP0]], 40
-; CHECK-NEXT:    [[TMP11:%.*]] = and i64 [[TMP10]], 71776119061217280
-; CHECK-NEXT:    [[TMP12:%.*]] = shl i64 [[TMP0]], 24
-; CHECK-NEXT:    [[TMP13:%.*]] = and i64 [[TMP12]], 280375465082880
-; CHECK-NEXT:    [[TMP14:%.*]] = or i64 [[TMP9]], [[TMP2]]
-; CHECK-NEXT:    [[TMP15:%.*]] = or i64 [[TMP14]], [[TMP4]]
-; CHECK-NEXT:    [[TMP16:%.*]] = or i64 [[TMP15]], [[TMP6]]
-; CHECK-NEXT:    [[TMP17:%.*]] = or i64 [[TMP16]], [[TMP8]]
-; CHECK-NEXT:    [[TMP18:%.*]] = or i64 [[TMP17]], [[TMP11]]
-; CHECK-NEXT:    [[TMP19:%.*]] = or i64 [[TMP18]], [[TMP13]]
-; CHECK-NEXT:    [[TMP20:%.*]] = shl i64 [[TMP0]], 8
-; CHECK-NEXT:    [[TMP21:%.*]] = and i64 [[TMP20]], 1095216660480
-; CHECK-NEXT:    [[TMP22:%.*]] = add i64 [[TMP19]], [[TMP21]]
-; CHECK-NEXT:    ret i64 [[TMP22]]
+; CHECK-NEXT:    [[TMP2:%.*]] = call i64 @llvm.bswap.i64(i64 [[TMP0:%.*]])
+; CHECK-NEXT:    ret i64 [[TMP2]]
 ;
   %2 = lshr i64 %0, 56
   %3 = lshr i64 %0, 40
@@ -553,28 +531,8 @@
 
 define i64 @PR47191_problem2(i64 %0) {
 ; CHECK-LABEL: @PR47191_problem2(
-; CHECK-NEXT:    [[TMP2:%.*]] = lshr i64 [[TMP0:%.*]], 56
-; CHECK-NEXT:    [[TMP3:%.*]] = lshr i64 [[TMP0]], 40
-; CHECK-NEXT:    [[TMP4:%.*]] = and i64 [[TMP3]], 65280
-; CHECK-NEXT:    [[TMP5:%.*]] = lshr i64 [[TMP0]], 24
-; CHECK-NEXT:    [[TMP6:%.*]] = and i64 [[TMP5]], 16711680
-; CHECK-NEXT:    [[TMP7:%.*]] = lshr i64 [[TMP0]], 8
-; CHECK-NEXT:    [[TMP8:%.*]] = and i64 [[TMP7]], 4278190080
-; CHECK-NEXT:    [[TMP9:%.*]] = shl i64 [[TMP0]], 56
-; CHECK-NEXT:    [[TMP10:%.*]] = shl i64 [[TMP0]], 40
-; CHECK-NEXT:    [[TMP11:%.*]] = and i64 [[TMP10]], 71776119061217280
-; CHECK-NEXT:    [[TMP12:%.*]] = or i64 [[TMP9]], [[TMP2]]
-; CHECK-NEXT:    [[TMP13:%.*]] = or i64 [[TMP12]], [[TMP4]]
-; CHECK-NEXT:    [[TMP14:%.*]] = or i64 [[TMP13]], [[TMP6]]
-; CHECK-NEXT:    [[TMP15:%.*]] = or i64 [[TMP14]], [[TMP8]]
-; CHECK-NEXT:    [[TMP16:%.*]] = or i64 [[TMP15]], [[TMP11]]
-; CHECK-NEXT:    [[TMP17:%.*]] = shl i64 [[TMP0]], 24
-; CHECK-NEXT:    [[TMP18:%.*]] = and i64 [[TMP17]], 280375465082880
-; CHECK-NEXT:    [[TMP19:%.*]] = shl i64 [[TMP0]], 8
-; CHECK-NEXT:    [[TMP20:%.*]] = and i64 [[TMP19]], 1095216660480
-; CHECK-NEXT:    [[TMP21:%.*]] = or i64 [[TMP20]], [[TMP18]]
-; CHECK-NEXT:    [[TMP22:%.*]] = xor i64 [[TMP21]], [[TMP16]]
-; CHECK-NEXT:    ret i64 [[TMP22]]
+; CHECK-NEXT:    [[TMP2:%.*]] = call i64 @llvm.bswap.i64(i64 [[TMP0:%.*]])
+; CHECK-NEXT:    ret i64 [[TMP2]]
 ;
   %2 = lshr i64 %0, 56
   %3 = lshr i64 %0, 40
@@ -602,28 +560,8 @@
 
 define i64 @PR47191_problem3(i64 %0) {
 ; CHECK-LABEL: @PR47191_problem3(
-; CHECK-NEXT:    [[TMP2:%.*]] = lshr i64 [[TMP0:%.*]], 56
-; CHECK-NEXT:    [[TMP3:%.*]] = lshr i64 [[TMP0]], 40
-; CHECK-NEXT:    [[TMP4:%.*]] = and i64 [[TMP3]], 65280
-; CHECK-NEXT:    [[TMP5:%.*]] = lshr i64 [[TMP0]], 24
-; CHECK-NEXT:    [[TMP6:%.*]] = and i64 [[TMP5]], 16711680
-; CHECK-NEXT:    [[TMP7:%.*]] = lshr i64 [[TMP0]], 8
-; CHECK-NEXT:    [[TMP8:%.*]] = and i64 [[TMP7]], 4278190080
-; CHECK-NEXT:    [[TMP9:%.*]] = shl i64 [[TMP0]], 56
-; CHECK-NEXT:    [[TMP10:%.*]] = shl i64 [[TMP0]], 40
-; CHECK-NEXT:    [[TMP11:%.*]] = and i64 [[TMP10]], 71776119061217280
-; CHECK-NEXT:    [[TMP12:%.*]] = or i64 [[TMP9]], [[TMP2]]
-; CHECK-NEXT:    [[TMP13:%.*]] = or i64 [[TMP12]], [[TMP4]]
-; CHECK-NEXT:    [[TMP14:%.*]] = or i64 [[TMP13]], [[TMP6]]
-; CHECK-NEXT:    [[TMP15:%.*]] = or i64 [[TMP14]], [[TMP8]]
-; CHECK-NEXT:    [[TMP16:%.*]] = or i64 [[TMP15]], [[TMP11]]
-; CHECK-NEXT:    [[TMP17:%.*]] = shl i64 [[TMP0]], 24
-; CHECK-NEXT:    [[TMP18:%.*]] = and i64 [[TMP17]], 280375465082880
-; CHECK-NEXT:    [[TMP19:%.*]] = shl i64 [[TMP0]], 8
-; CHECK-NEXT:    [[TMP20:%.*]] = and i64 [[TMP19]], 1095216660480
-; CHECK-NEXT:    [[TMP21:%.*]] = or i64 [[TMP20]], [[TMP18]]
-; CHECK-NEXT:    [[TMP22:%.*]] = xor i64 [[TMP21]], [[TMP16]]
-; CHECK-NEXT:    ret i64 [[TMP22]]
+; CHECK-NEXT:    [[TMP2:%.*]] = call i64 @llvm.bswap.i64(i64 [[TMP0:%.*]])
+; CHECK-NEXT:    ret i64 [[TMP2]]
 ;
   %2 = lshr i64 %0, 56
   %3 = lshr i64 %0, 40
@@ -651,28 +589,8 @@
 
 define i64 @PR47191_problem4(i64 %0) {
 ; CHECK-LABEL: @PR47191_problem4(
-; CHECK-NEXT:    [[TMP2:%.*]] = lshr i64 [[TMP0:%.*]], 56
-; CHECK-NEXT:    [[TMP3:%.*]] = shl i64 [[TMP0]], 56
-; CHECK-NEXT:    [[TMP4:%.*]] = or i64 [[TMP2]], [[TMP3]]
-; CHECK-NEXT:    [[TMP5:%.*]] = lshr i64 [[TMP0]], 40
-; CHECK-NEXT:    [[TMP6:%.*]] = and i64 [[TMP5]], 65280
-; CHECK-NEXT:    [[TMP7:%.*]] = or i64 [[TMP4]], [[TMP6]]
-; CHECK-NEXT:    [[TMP8:%.*]] = shl i64 [[TMP0]], 40
-; CHECK-NEXT:    [[TMP9:%.*]] = and i64 [[TMP8]], 71776119061217280
-; CHECK-NEXT:    [[TMP10:%.*]] = or i64 [[TMP7]], [[TMP9]]
-; CHECK-NEXT:    [[TMP11:%.*]] = lshr i64 [[TMP0]], 24
-; CHECK-NEXT:    [[TMP12:%.*]] = and i64 [[TMP11]], 16711680
-; CHECK-NEXT:    [[TMP13:%.*]] = or i64 [[TMP10]], [[TMP12]]
-; CHECK-NEXT:    [[TMP14:%.*]] = shl i64 [[TMP0]], 24
-; CHECK-NEXT:    [[TMP15:%.*]] = and i64 [[TMP14]], 280375465082880
-; CHECK-NEXT:    [[TMP16:%.*]] = or i64 [[TMP13]], [[TMP15]]
-; CHECK-NEXT:    [[TMP17:%.*]] = lshr i64 [[TMP0]], 8
-; CHECK-NEXT:    [[TMP18:%.*]] = and i64 [[TMP17]], 4278190080
-; CHECK-NEXT:    [[TMP19:%.*]] = or i64 [[TMP16]], [[TMP18]]
-; CHECK-NEXT:    [[TMP20:%.*]] = shl i64 [[TMP0]], 8
-; CHECK-NEXT:    [[TMP21:%.*]] = and i64 [[TMP20]], 1095216660480
-; CHECK-NEXT:    [[TMP22:%.*]] = add i64 [[TMP19]], [[TMP21]]
-; CHECK-NEXT:    ret i64 [[TMP22]]
+; CHECK-NEXT:    [[TMP2:%.*]] = call i64 @llvm.bswap.i64(i64 [[TMP0:%.*]])
+; CHECK-NEXT:    ret i64 [[TMP2]]
 ;
   %2 = lshr i64 %0, 56
   %3 = shl i64 %0, 56