From 92c728350011c7d7df29d42166ad3436f1285249 Mon Sep 17 00:00:00 2001 From: Reid Spencer Date: Sat, 12 May 2007 18:01:57 +0000 Subject: [PATCH] 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 --- lib/Support/APInt.cpp | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/lib/Support/APInt.cpp b/lib/Support/APInt.cpp index 4142c6ec8bc..2a35aa057ef 100644 --- a/lib/Support/APInt.cpp +++ b/lib/Support/APInt.cpp @@ -1199,6 +1199,12 @@ APInt APInt::shl(uint32_t shiftAmt) const { 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()];