[APInt] Fix extractBits to correctly handle Result.isSingleWord() case.

[timshen]

Summary

extractBits assumes that !this->isSingleWord() implies !Result.isSingleWord(), which may not necessarily be true. Handle both cases.

[echristo]

I don't know the code well enough here to just say yes or no, I'd be fine with you doing post commit review here since this is reasonably well tested and nothing else has broken.

[timshen]

Landed. Reopen for post-commit review.

[craig.topper]

llvm/trunk/lib/Support/APInt.cpp

436

Alternatively this could be

getRawData()[word] =....

but I don't care much.

[timshen]

llvm/trunk/lib/Support/APInt.cpp

436

Unfortunately getRawData() returns a const pointer. :P

[RKSimon]

LGTM, thanks. TBH I don't think its worth adding a non-const version of getRawData()

llvm/trunk/lib/Support/APInt.cpp

APInt APInt::extractBits(unsigned numBits, unsigned bitPosition) const {
   if (loBit == 0)
     return APInt(numBits, makeArrayRef(U.pVal + loWord, 1 + hiWord - loWord));
 
   // General case - shift + copy source words directly into place.
   APInt Result(numBits, 0);
   unsigned NumSrcWords = getNumWords();
   unsigned NumDstWords = Result.getNumWords();
 
+  uint64_t *DestPtr = Result.isSingleWord() ? &Result.U.VAL : Result.U.pVal;
   for (unsigned word = 0; word < NumDstWords; ++word) {
     uint64_t w0 = U.pVal[loWord + word];
     uint64_t w1 =
         (loWord + word + 1) < NumSrcWords ? U.pVal[loWord + word + 1] : 0;
-    Result.U.pVal[word] = (w0 >> loBit) | (w1 << (APINT_BITS_PER_WORD - loBit));
+    DestPtr[word] = (w0 >> loBit) | (w1 << (APINT_BITS_PER_WORD - loBit));
   }
 
   return Result.clearUnusedBits();
 }
 
 unsigned APInt::getBitsNeeded(StringRef str, uint8_t radix) {
   assert(!str.empty() && "Invalid string length");
   assert((radix == 10 || radix == 8 || radix == 16 || radix == 2 ||

llvm/trunk/unittests/ADT/APIntTest.cpp

TEST(APIntTest, extractBits) {
   EXPECT_EQ((0xFFu >> 1), i257.extractBits(16, 1));
   EXPECT_EQ(-1, i257.extractBits(32, 64).getSExtValue());
   EXPECT_EQ(-1, i257.extractBits(128, 128).getSExtValue());
   EXPECT_EQ(-1, i257.extractBits(66, 191).getSExtValue());
   EXPECT_EQ(static_cast<int64_t>(0xFFFFFFFFFF80007Full),
             i257.extractBits(128, 1).getSExtValue());
   EXPECT_EQ(static_cast<int64_t>(0xFFFFFFFFFF80007Full),
             i257.extractBits(129, 1).getSExtValue());
+
+  EXPECT_EQ(APInt(48, 0),
+            APInt(144, "281474976710655", 10).extractBits(48, 48));
+  EXPECT_EQ(APInt(48, 0x0000ffffffffffffull),
+            APInt(144, "281474976710655", 10).extractBits(48, 0));
+  EXPECT_EQ(APInt(48, 0x00007fffffffffffull),
+            APInt(144, "281474976710655", 10).extractBits(48, 1));
 }
 
 TEST(APIntTest, getLowBitsSet) {
   APInt i128lo64 = APInt::getLowBitsSet(128, 64);
   EXPECT_EQ(0u, i128lo64.countLeadingOnes());
   EXPECT_EQ(64u, i128lo64.countLeadingZeros());
   EXPECT_EQ(64u, i128lo64.getActiveBits());
   EXPECT_EQ(0u, i128lo64.countTrailingZeros());