Fix shl to produce the correct result when the bitwidth is > 64 and the
shift amount is 0. Previously this code would do a lshr by the bit width
which can lead to incorrect results.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@37010 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Support/APInt.cpp b/lib/Support/APInt.cpp
index 4142c6e..2a35aa0 100644
--- a/lib/Support/APInt.cpp
+++ b/lib/Support/APInt.cpp
@@ -1199,6 +1199,12 @@
if (shiftAmt == BitWidth)
return APInt(BitWidth, 0);
+ // If none of the bits are shifted out, the result is *this. This avoids a
+ // lshr by the words size in the loop below which can produce incorrect
+ // results. It also avoids the expensive computation below for a common case.
+ if (shiftAmt == 0)
+ return *this;
+
// Create some space for the result.
uint64_t * val = new uint64_t[getNumWords()];