diff options
Diffstat (limited to 'lib/AST/ExprConstant.cpp')
| -rw-r--r-- | lib/AST/ExprConstant.cpp | 29 |
1 files changed, 23 insertions, 6 deletions
diff --git a/lib/AST/ExprConstant.cpp b/lib/AST/ExprConstant.cpp index 731bddd6b8..3209bb343b 100644 --- a/lib/AST/ExprConstant.cpp +++ b/lib/AST/ExprConstant.cpp @@ -4347,6 +4347,9 @@ bool IntExprEvaluator::VisitBinaryOperator(const BinaryOperator *E) { // - Pointer subtractions must be on elements of the same array. // - Pointer comparisons must be between members with the same access. + const CharUnits &LHSOffset = LHSValue.getLValueOffset(); + const CharUnits &RHSOffset = RHSValue.getLValueOffset(); + if (E->getOpcode() == BO_Sub) { QualType Type = E->getLHS()->getType(); QualType ElementType = Type->getAs<PointerType>()->getPointeeType(); @@ -4355,14 +4358,28 @@ bool IntExprEvaluator::VisitBinaryOperator(const BinaryOperator *E) { if (!HandleSizeof(Info, ElementType, ElementSize)) return false; - CharUnits Diff = LHSValue.getLValueOffset() - - RHSValue.getLValueOffset(); - return Success(Diff / ElementSize, E); + // FIXME: LLVM and GCC both compute LHSOffset - RHSOffset at runtime, + // and produce incorrect results when it overflows. Such behavior + // appears to be non-conforming, but is common, so perhaps we should + // assume the standard intended for such cases to be undefined behavior + // and check for them. + + // Compute (LHSOffset - RHSOffset) / Size carefully, checking for + // overflow in the final conversion to ptrdiff_t. + APSInt LHS( + llvm::APInt(65, (int64_t)LHSOffset.getQuantity(), true), false); + APSInt RHS( + llvm::APInt(65, (int64_t)RHSOffset.getQuantity(), true), false); + APSInt ElemSize( + llvm::APInt(65, (int64_t)ElementSize.getQuantity(), true), false); + APSInt TrueResult = (LHS - RHS) / ElemSize; + APSInt Result = TrueResult.trunc(Info.Ctx.getIntWidth(E->getType())); + + if (Result.extend(65) != TrueResult) + HandleOverflow(Info, E, TrueResult, E->getType()); + return Success(Result, E); } - const CharUnits &LHSOffset = LHSValue.getLValueOffset(); - const CharUnits &RHSOffset = RHSValue.getLValueOffset(); - // C++11 [expr.rel]p3: // Pointers to void (after pointer conversions) can be compared, with a // result defined as follows: If both pointers represent the same |