[APInt] byteSwap - handle any whole byte bitwidth greater than 16-bits

[RKSimon]

Summary

As noted on D74621, the bswap intrinsic has a self imposed limitation that the type's bitwidth must be divisible by 16, but there's no reason that APInt::byteSwap must have the same limitation, given that it can already handle any byte width.

[lebedev.ri]

SGTM, i'm not sure why bswap intrinsic has that limitation.

[RKSimon]

rG366ae9c90fe6

[arsenm]

In D74667#1877745, @lebedev.ri wrote:

SGTM, i'm not sure why bswap intrinsic has that limitation.

I don't think it really does. Nothing is enforcing it, there's just a note in the LangRef

[RKSimon]

In D74667#1877767, @arsenm wrote:

In D74667#1877745, @lebedev.ri wrote:

SGTM, i'm not sure why bswap intrinsic has that limitation.

I don't think it really does. Nothing is enforcing it, there's just a note in the LangRef

The legalizers probably assume it though.

llvm/lib/Support/APInt.cpp

bool APInt::isSubsetOfSlowCase(const APInt &RHS) const {
   for (unsigned i = 0, e = getNumWords(); i != e; ++i)
     if ((U.pVal[i] & ~RHS.U.pVal[i]) != 0)
       return false;
 
   return true;
 }
 
 APInt APInt::byteSwap() const {
-  assert(BitWidth >= 16 && BitWidth % 16 == 0 && "Cannot byteswap!");
+  assert(BitWidth >= 16 && BitWidth % 8 == 0 && "Cannot byteswap!");
   if (BitWidth == 16)
     return APInt(BitWidth, ByteSwap_16(uint16_t(U.VAL)));
   if (BitWidth == 32)
     return APInt(BitWidth, ByteSwap_32(unsigned(U.VAL)));
   if (BitWidth <= 64) {
     uint64_t Tmp1 = ByteSwap_64(U.VAL);
     Tmp1 >>= (64 - BitWidth);
     return APInt(BitWidth, Tmp1);

llvm/unittests/ADT/APIntTest.cpp

 #pragma clang diagnostic pop
 #pragma clang diagnostic pop
 #endif
 #endif // _MSC_VER
 
 TEST(APIntTest, byteSwap) {
   EXPECT_EQ(0x00000000, APInt(16, 0x0000).byteSwap());
   EXPECT_EQ(0x0000010f, APInt(16, 0x0f01).byteSwap());
+  EXPECT_EQ(0x00ff8000, APInt(24, 0x0080ff).byteSwap());
   EXPECT_EQ(0x117700ff, APInt(32, 0xff007711).byteSwap());
+  EXPECT_EQ(0x228811aaffULL, APInt(40, 0xffaa118822ULL).byteSwap());
   EXPECT_EQ(0x050403020100ULL, APInt(48, 0x000102030405ULL).byteSwap());
+  EXPECT_EQ(0xff050403020100ULL, APInt(56, 0x000102030405ffULL).byteSwap());
   EXPECT_EQ(0xff050403020100aaULL, APInt(64, 0xaa000102030405ffULL).byteSwap());
 
-  for (unsigned N : {16, 32, 48, 64, 80, 96, 112, 128, 256, 1024, 1040}) {
+  for (unsigned N : {16, 24, 32, 48, 56, 64, 72, 80, 96, 112, 128, 248, 256,
+                     1024, 1032, 1040}) {
     for (unsigned I = 0; I < N; I += 8) {
       APInt X = APInt::getBitsSet(N, I, I + 8);
       APInt Y = APInt::getBitsSet(N, N - I - 8, N - I);
       EXPECT_EQ(Y, X.byteSwap());
       EXPECT_EQ(X, Y.byteSwap());
     }
   }
 }