From 81ee020f649a5f18f7e2c969fa4ed81c34e19f1f 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. llvm-svn: 37010 --- llvm/lib/Support/APInt.cpp | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/llvm/lib/Support/APInt.cpp b/llvm/lib/Support/APInt.cpp index 4142c6ec8bc4..2a35aa057ef3 100644 --- a/llvm/lib/Support/APInt.cpp +++ b/llvm/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()];