Commit ad18665e authored by Richard Smith's avatar Richard Smith
Browse files

PR45087: Fix check for emptiness when determining whether a trivial copy 

operation needs to read from its operand.
parent de2c586a

clang/lib/AST/ExprConstant.cpp

+14 −21
Original line number Diff line number Diff line
@@ -3047,15 +3047,22 @@ static void expandArray(APValue &Array, unsigned Index) { 
/// is trivial. Note that this is never true for a union type with fields

/// (because the copy always "reads" the active member) and always true for

/// a non-class type.

static bool isReadByLvalueToRvalueConversion(const CXXRecordDecl *RD);

static bool isReadByLvalueToRvalueConversion(QualType T) {

  CXXRecordDecl *RD = T->getBaseElementTypeUnsafe()->getAsCXXRecordDecl();

  if (!RD || (RD->isUnion() && !RD->field_empty()))

    return true;

  return !RD || isReadByLvalueToRvalueConversion(RD);

}

static bool isReadByLvalueToRvalueConversion(const CXXRecordDecl *RD) {

  // FIXME: A trivial copy of a union copies the object representation, even if

  // the union is empty.

  if (RD->isUnion())

    return !RD->field_empty();

  if (RD->isEmpty())

    return false;















  for (auto *Field : RD->fields())













    if (isReadByLvalueToRvalueConversion(Field->getType()))













    if (!Field->isUnnamedBitfield() &&













        isReadByLvalueToRvalueConversion(Field->getType()))















      return true;





























  for (auto &BaseSpec : RD->bases())










@@ -5460,22 +5467,6 @@ static bool HandleUnionActiveMemberChange(EvalInfo &Info, const Expr *LHSExpr,













  return true;















}



























/// Determine if a class has any fields that might need to be copied by a













/// trivial copy or move operation.













static bool hasFields(const CXXRecordDecl *RD) {













  if (!RD || RD->isEmpty())













    return false;













  for (auto *FD : RD->fields()) {













    if (FD->isUnnamedBitfield())













      continue;













    return true;













  }













  for (auto &Base : RD->bases())













    if (hasFields(Base.getType()->getAsCXXRecordDecl()))













      return true;













  return false;













}



























namespace {















typedef SmallVector<APValue, 8> ArgVector;















}










@@ -5546,7 +5537,8 @@ static bool HandleFunctionCall(SourceLocation CallLoc,













  const CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(Callee);















  if (MD && MD->isDefaulted() &&















      (MD->getParent()->isUnion() ||













       (MD->isTrivial() && hasFields(MD->getParent())))) {













       (MD->isTrivial() &&













        isReadByLvalueToRvalueConversion(MD->getParent())))) {















    assert(This &&















           (MD->isCopyAssignmentOperator() || MD->isMoveAssignmentOperator()));















    LValue RHS;










@@ -5633,7 +5625,8 @@ static bool HandleConstructorCall(const Expr *E, const LValue &This,













  // actually read them.















  if (Definition->isDefaulted() && Definition->isCopyOrMoveConstructor() &&















      (Definition->getParent()->isUnion() ||













       (Definition->isTrivial() && hasFields(Definition->getParent())))) {













       (Definition->isTrivial() &&













        isReadByLvalueToRvalueConversion(Definition->getParent())))) {















    LValue RHS;















    RHS.setFrom(Info.Ctx, ArgValues[0]);















    return handleLValueToRValueConversion(

































clang/test/SemaCXX/constant-expression-cxx11.cpp



+4
−0






























Original line number
Diff line number
Diff line








@@ -600,6 +600,10 @@ namespace CopyCtor {













  constexpr B c = b;















  static_assert(c.arr[2] == 3, "");















  static_assert(c.arr[7] == 0, "");



























  // OK: the copy ctor for X doesn't read any members.













  struct X { struct Y {} y; } x1;













  constexpr X x2 = x1;















}































constexpr int selfref[2][2][2] = {