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

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

Reviewers: RKSimon

Subscribers: sanjoy, llvm-commits, hiraditya

Differential Revision: https://reviews.llvm.org/D43363

llvm-svn: 325311

1 files changed, 2 insertions, 1 deletions

diff --git a/llvm/lib/Support/APInt.cpp b/llvm/lib/Support/APInt.cpp
index 1ea6319acfa..48b9613b3ec 100644
--- a/llvm/lib/Support/APInt.cpp
+++ b/llvm/lib/Support/APInt.cpp
@@ -428,11 +428,12 @@ APInt APInt::extractBits(unsigned numBits, unsigned bitPosition) const {
   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();