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
@@ -3010,26 +3010,35 @@
   IntegerType *ITy = dyn_cast<IntegerType>(I->getType());
   if (!ITy || ITy->getBitWidth() > 128)
     return false;   // Can't do vectors or integers > 128 bits.
-  unsigned BW = ITy->getBitWidth();
 
-  unsigned DemandedBW = BW;
   IntegerType *DemandedTy = ITy;
-  if (I->hasOneUse()) {
-    if (TruncInst *Trunc = dyn_cast<TruncInst>(I->user_back())) {
+  if (I->hasOneUse())
+    if (auto *Trunc = dyn_cast<TruncInst>(I->user_back()))
       DemandedTy = cast<IntegerType>(Trunc->getType());
-      DemandedBW = DemandedTy->getBitWidth();
-    }
-  }
 
   // Try to find all the pieces corresponding to the bswap.
   std::map<Value *, Optional<BitPart>> BPS;
   auto Res = collectBitParts(I, MatchBSwaps, MatchBitReversals, BPS, 0);
   if (!Res)
     return false;
-  auto &BitProvenance = Res->Provenance;
+  ArrayRef<int8_t> BitProvenance = Res->Provenance;
+
+  // If the upper half is zero, then attempt to perform as a truncated op.
+  if (isPowerOf2_32(BitProvenance.size())) {
+    // Keep halving the demanded width while the upper half is zero.
+    while (BitProvenance.size() > 2) {
+      unsigned HalfBW = BitProvenance.size() / 2;
+      ArrayRef<int8_t> UpperBits = BitProvenance.slice(HalfBW);
+      if (!llvm::all_of(UpperBits, [](int8_t x) { return x < 0; }))
+        break;
+      BitProvenance = BitProvenance.slice(0, HalfBW);
+    }
+    DemandedTy = IntegerType::get(I->getContext(), BitProvenance.size());
+  }
 
   // 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();
   bool OKForBSwap = DemandedBW % 16 == 0, OKForBitReverse = true;
   for (unsigned i = 0; i < DemandedBW; ++i) {
     OKForBSwap &=
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
@@ -187,8 +187,8 @@
 
 define i16 @test8(i16 %a) {
 ; CHECK-LABEL: @test8(
-; CHECK-NEXT:    [[REV:%.*]] = call i16 @llvm.bswap.i16(i16 [[A:%.*]])
-; CHECK-NEXT:    ret i16 [[REV]]
+; CHECK-NEXT:    [[OR:%.*]] = call i16 @llvm.bswap.i16(i16 [[A:%.*]])
+; CHECK-NEXT:    ret i16 [[OR]]
 ;
   %conv = zext i16 %a to i32
   %shr = lshr i16 %a, 8
@@ -201,8 +201,8 @@
 
 define i16 @test9(i16 %a) {
 ; CHECK-LABEL: @test9(
-; CHECK-NEXT:    [[REV:%.*]] = call i16 @llvm.bswap.i16(i16 [[A:%.*]])
-; CHECK-NEXT:    ret i16 [[REV]]
+; CHECK-NEXT:    [[OR:%.*]] = call i16 @llvm.bswap.i16(i16 [[A:%.*]])
+; CHECK-NEXT:    ret i16 [[OR]]
 ;
   %conv = zext i16 %a to i32
   %shr = lshr i32 %conv, 8
@@ -229,18 +229,10 @@
 
 define i64 @PR39793_bswap_u64_as_u32(i64 %0) {
 ; CHECK-LABEL: @PR39793_bswap_u64_as_u32(
-; CHECK-NEXT:    [[TMP2:%.*]] = lshr i64 [[TMP0:%.*]], 24
-; CHECK-NEXT:    [[TMP3:%.*]] = and i64 [[TMP2]], 255
-; CHECK-NEXT:    [[TMP4:%.*]] = lshr i64 [[TMP0]], 8
-; CHECK-NEXT:    [[TMP5:%.*]] = and i64 [[TMP4]], 65280
-; CHECK-NEXT:    [[TMP6:%.*]] = or i64 [[TMP3]], [[TMP5]]
-; CHECK-NEXT:    [[TMP7:%.*]] = shl i64 [[TMP0]], 8
-; CHECK-NEXT:    [[TMP8:%.*]] = and i64 [[TMP7]], 16711680
-; CHECK-NEXT:    [[TMP9:%.*]] = or i64 [[TMP6]], [[TMP8]]
-; CHECK-NEXT:    [[TMP10:%.*]] = shl i64 [[TMP0]], 24
-; CHECK-NEXT:    [[TMP11:%.*]] = and i64 [[TMP10]], 4278190080
-; CHECK-NEXT:    [[TMP12:%.*]] = or i64 [[TMP9]], [[TMP11]]
-; CHECK-NEXT:    ret i64 [[TMP12]]
+; CHECK-NEXT:    [[TRUNC:%.*]] = trunc i64 [[TMP0:%.*]] to i32
+; CHECK-NEXT:    [[REV:%.*]] = call i32 @llvm.bswap.i32(i32 [[TRUNC]])
+; CHECK-NEXT:    [[TMP2:%.*]] = zext i32 [[REV]] to i64
+; CHECK-NEXT:    ret i64 [[TMP2]]
 ;
   %2 = lshr i64 %0, 24
   %3 = and i64 %2, 255
@@ -258,13 +250,10 @@
 
 define i16 @PR39793_bswap_u64_as_u32_trunc(i64 %0) {
 ; CHECK-LABEL: @PR39793_bswap_u64_as_u32_trunc(
-; CHECK-NEXT:    [[TMP2:%.*]] = lshr i64 [[TMP0:%.*]], 24
-; CHECK-NEXT:    [[TMP3:%.*]] = and i64 [[TMP2]], 255
-; CHECK-NEXT:    [[TMP4:%.*]] = lshr i64 [[TMP0]], 8
-; CHECK-NEXT:    [[TMP5:%.*]] = and i64 [[TMP4]], 65280
-; CHECK-NEXT:    [[TMP6:%.*]] = or i64 [[TMP3]], [[TMP5]]
-; CHECK-NEXT:    [[TMP7:%.*]] = trunc i64 [[TMP6]] to i16
-; CHECK-NEXT:    ret i16 [[TMP7]]
+; CHECK-NEXT:    [[TRUNC:%.*]] = trunc i64 [[TMP0:%.*]] to i32
+; CHECK-NEXT:    [[REV:%.*]] = call i32 @llvm.bswap.i32(i32 [[TRUNC]])
+; CHECK-NEXT:    [[TMP2:%.*]] = trunc i32 [[REV]] to i16
+; CHECK-NEXT:    ret i16 [[TMP2]]
 ;
   %2 = lshr i64 %0, 24
   %3 = and i64 %2, 255
@@ -283,12 +272,10 @@
 
 define i64 @PR39793_bswap_u64_as_u16(i64 %0) {
 ; CHECK-LABEL: @PR39793_bswap_u64_as_u16(
-; CHECK-NEXT:    [[TMP2:%.*]] = lshr i64 [[TMP0:%.*]], 8
-; CHECK-NEXT:    [[TMP3:%.*]] = and i64 [[TMP2]], 255
-; CHECK-NEXT:    [[TMP4:%.*]] = shl i64 [[TMP0]], 8
-; CHECK-NEXT:    [[TMP5:%.*]] = and i64 [[TMP4]], 65280
-; CHECK-NEXT:    [[TMP6:%.*]] = or i64 [[TMP3]], [[TMP5]]
-; CHECK-NEXT:    ret i64 [[TMP6]]
+; CHECK-NEXT:    [[TRUNC:%.*]] = trunc i64 [[TMP0:%.*]] to i16
+; CHECK-NEXT:    [[REV:%.*]] = call i16 @llvm.bswap.i16(i16 [[TRUNC]])
+; CHECK-NEXT:    [[TMP2:%.*]] = zext i16 [[REV]] to i64
+; CHECK-NEXT:    ret i64 [[TMP2]]
 ;
   %2 = lshr i64 %0, 8
   %3 = and i64 %2, 255
@@ -300,9 +287,9 @@
 
 define i8 @PR39793_bswap_u64_as_u16_trunc(i64 %0) {
 ; CHECK-LABEL: @PR39793_bswap_u64_as_u16_trunc(
-; CHECK-NEXT:    [[TMP2:%.*]] = lshr i64 [[TMP0:%.*]], 8
-; CHECK-NEXT:    [[TMP3:%.*]] = trunc i64 [[TMP2]] to i8
-; CHECK-NEXT:    ret i8 [[TMP3]]
+; CHECK-NEXT:    [[REV1:%.*]] = lshr i64 [[TMP0:%.*]], 8
+; CHECK-NEXT:    [[TMP2:%.*]] = trunc i64 [[REV1]] to i8
+; CHECK-NEXT:    ret i8 [[TMP2]]
 ;
   %2 = lshr i64 %0, 8
   %3 = and i64 %2, 255
@@ -315,12 +302,10 @@
 
 define i32 @PR39793_bswap_u32_as_u16(i32 %0) {
 ; CHECK-LABEL: @PR39793_bswap_u32_as_u16(
-; CHECK-NEXT:    [[TMP2:%.*]] = lshr i32 [[TMP0:%.*]], 8
-; CHECK-NEXT:    [[TMP3:%.*]] = and i32 [[TMP2]], 255
-; CHECK-NEXT:    [[TMP4:%.*]] = shl i32 [[TMP0]], 8
-; CHECK-NEXT:    [[TMP5:%.*]] = and i32 [[TMP4]], 65280
-; CHECK-NEXT:    [[TMP6:%.*]] = or i32 [[TMP3]], [[TMP5]]
-; CHECK-NEXT:    ret i32 [[TMP6]]
+; CHECK-NEXT:    [[TRUNC:%.*]] = trunc i32 [[TMP0:%.*]] to i16
+; CHECK-NEXT:    [[REV:%.*]] = call i16 @llvm.bswap.i16(i16 [[TRUNC]])
+; CHECK-NEXT:    [[TMP2:%.*]] = zext i16 [[REV]] to i32
+; CHECK-NEXT:    ret i32 [[TMP2]]
 ;
   %2 = lshr i32 %0, 8
   %3 = and i32 %2, 255
@@ -332,9 +317,9 @@
 
 define i8 @PR39793_bswap_u32_as_u16_trunc(i32 %0) {
 ; CHECK-LABEL: @PR39793_bswap_u32_as_u16_trunc(
-; CHECK-NEXT:    [[TMP2:%.*]] = lshr i32 [[TMP0:%.*]], 8
-; CHECK-NEXT:    [[TMP3:%.*]] = trunc i32 [[TMP2]] to i8
-; CHECK-NEXT:    ret i8 [[TMP3]]
+; CHECK-NEXT:    [[REV1:%.*]] = lshr i32 [[TMP0:%.*]], 8
+; CHECK-NEXT:    [[TMP2:%.*]] = trunc i32 [[REV1]] to i8
+; CHECK-NEXT:    ret i8 [[TMP2]]
 ;
   %2 = lshr i32 %0, 8
   %3 = and i32 %2, 255