From da7c4ba1af98430eb16468d2cf211473a3be175e Mon Sep 17 00:00:00 2001 From: Richard Smith Date: Wed, 8 Feb 2012 06:14:53 +0000 Subject: Implement the agreed resolution to DR1457: a signed left shift of a 1 bit into the sign bit doesn't have undefined behavior, but a signed left shift of a 1 bit out of the sign bit still does. As promised to Howard :) The suppression of the potential constant expression checking in system headers is also removed, since the problem it was working around is gone. llvm-svn: 150059 --- clang/lib/AST/ExprConstant.cpp | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) (limited to 'clang/lib/AST/ExprConstant.cpp') diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp index e33d22a4aa3..410406788dc 100644 --- a/clang/lib/AST/ExprConstant.cpp +++ b/clang/lib/AST/ExprConstant.cpp @@ -4704,12 +4704,11 @@ bool IntExprEvaluator::VisitBinaryOperator(const BinaryOperator *E) { << RHS << E->getType() << LHS.getBitWidth(); } else if (LHS.isSigned()) { // C++11 [expr.shift]p2: A signed left shift must have a non-negative - // operand, and must not overflow. + // operand, and must not overflow the corresponding unsigned type. if (LHS.isNegative()) CCEDiag(E, diag::note_constexpr_lshift_of_negative) << LHS; - else if (LHS.countLeadingZeros() <= SA) - HandleOverflow(Info, E, LHS.extend(LHS.getBitWidth() + SA) << SA, - E->getType()); + else if (LHS.countLeadingZeros() < SA) + CCEDiag(E, diag::note_constexpr_lshift_discards); } return Success(LHS << SA, E); -- cgit v1.2.3