From: Justin Bogner <mail@justinbogner.com>
Date: Tue, 23 Jun 2015 07:32:55 +0000 (+0000)
Subject: MCExpr: Avoid UB by evaluating this shift as unsigned
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=1e4a7e02f84e3ff320ebb5fdaf04dff29a4e70f3;p=oota-llvm.git

MCExpr: Avoid UB by evaluating this shift as unsigned

We hit undefined behaviour in some MCExpr tests when the LHS of a left
shift is -1. Twos-complement semantics are completely reasonable here,
so we should just do the shift in unsigned.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@240385 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/MC/MCExpr.cpp b/lib/MC/MCExpr.cpp
index b16245ac3f4..a30ceecc952 100644
--- a/lib/MC/MCExpr.cpp
+++ b/lib/MC/MCExpr.cpp
@@ -752,7 +752,7 @@ bool MCExpr::evaluateAsRelocatableImpl(MCValue &Res, const MCAssembler *Asm,
     case MCBinaryExpr::Mul:  Result = LHS * RHS; break;
     case MCBinaryExpr::NE:   Result = LHS != RHS; break;
     case MCBinaryExpr::Or:   Result = LHS | RHS; break;
-    case MCBinaryExpr::Shl:  Result = LHS << RHS; break;
+    case MCBinaryExpr::Shl:  Result = uint64_t(LHS) << uint64_t(RHS); break;
     case MCBinaryExpr::Sub:  Result = LHS - RHS; break;
     case MCBinaryExpr::Xor:  Result = LHS ^ RHS; break;
     }