r183883 - Implement core issue 903: only integer literals with value 0 and prvalues of

[Jordan Rose]

*sigh* I can't say this is the wrong thing to do—in fact, it's the kind of restriction I usually like—but for the record this breaks OS X's (ancient) libstdc++ implementation of <tr1/unordered_map> when compiling under -std=c++11. I don't think that's such an important configuration, though.

*goes off to unstick internal buildbot*
Jordan


On Jun 12, 2013, at 19:46 , Richard Smith <richard-llvm at metafoo.co.uk> wrote:

> Author: rsmith
> Date: Wed Jun 12 21:46:14 2013
> New Revision: 183883
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=183883&view=rev
> Log:
> Implement core issue 903: only integer literals with value 0 and prvalues of
> type std::nullptr_t are null pointer constants from C++11 onwards.
> 
> Modified:
>    cfe/trunk/lib/AST/Expr.cpp
>    cfe/trunk/test/SemaCXX/constant-expression-cxx11.cpp
>    cfe/trunk/test/SemaCXX/lambda-expressions.cpp
> 
> Modified: cfe/trunk/lib/AST/Expr.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/Expr.cpp?rev=183883&r1=183882&r2=183883&view=diff
> ==============================================================================
> --- cfe/trunk/lib/AST/Expr.cpp (original)
> +++ cfe/trunk/lib/AST/Expr.cpp Wed Jun 12 21:46:14 2013
> @@ -3024,7 +3024,7 @@ bool Expr::hasNonTrivialCall(ASTContext
> Expr::NullPointerConstantKind
> Expr::isNullPointerConstant(ASTContext &Ctx,
>                             NullPointerConstantValueDependence NPC) const {
> -  if (isValueDependent()) {
> +  if (isValueDependent() && !Ctx.getLangOpts().CPlusPlus11) {
>     switch (NPC) {
>     case NPC_NeverValueDependent:
>       llvm_unreachable("Unexpected value dependent expression!");
> @@ -3085,7 +3085,8 @@ Expr::isNullPointerConstant(ASTContext &
>     return NPCK_CXX11_nullptr;
> 
>   if (const RecordType *UT = getType()->getAsUnionType())
> -    if (UT && UT->getDecl()->hasAttr<TransparentUnionAttr>())
> +    if (!Ctx.getLangOpts().CPlusPlus11 &&
> +        UT && UT->getDecl()->hasAttr<TransparentUnionAttr>())
>       if (const CompoundLiteralExpr *CLE = dyn_cast<CompoundLiteralExpr>(this)){
>         const Expr *InitExpr = CLE->getInitializer();
>         if (const InitListExpr *ILE = dyn_cast<InitListExpr>(InitExpr))
> @@ -3096,14 +3097,14 @@ Expr::isNullPointerConstant(ASTContext &
>       (Ctx.getLangOpts().CPlusPlus && getType()->isEnumeralType()))
>     return NPCK_NotNull;
> 
> -  // If we have an integer constant expression, we need to *evaluate* it and
> -  // test for the value 0. Don't use the C++11 constant expression semantics
> -  // for this, for now; once the dust settles on core issue 903, we might only
> -  // allow a literal 0 here in C++11 mode.
>   if (Ctx.getLangOpts().CPlusPlus11) {
> -    if (!isCXX98IntegralConstantExpr(Ctx))
> -      return NPCK_NotNull;
> +    // C++11 [conv.ptr]p1: A null pointer constant is an integer literal with
> +    // value zero or a prvalue of type std::nullptr_t.
> +    const IntegerLiteral *Lit = dyn_cast<IntegerLiteral>(this);
> +    return (Lit && !Lit->getValue()) ? NPCK_ZeroLiteral : NPCK_NotNull;
>   } else {
> +    // If we have an integer constant expression, we need to *evaluate* it and
> +    // test for the value 0.
>     if (!isIntegerConstantExpr(Ctx))
>       return NPCK_NotNull;
>   }
> 
> Modified: cfe/trunk/test/SemaCXX/constant-expression-cxx11.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/constant-expression-cxx11.cpp?rev=183883&r1=183882&r2=183883&view=diff
> ==============================================================================
> --- cfe/trunk/test/SemaCXX/constant-expression-cxx11.cpp (original)
> +++ cfe/trunk/test/SemaCXX/constant-expression-cxx11.cpp Wed Jun 12 21:46:14 2013
> @@ -769,15 +769,22 @@ static_assert(&ok2 == pok2, "");
> static_assert((Base2*)(Derived*)(Base*)pb1 == pok2, "");
> static_assert((Derived*)(Base*)pb1 == (Derived*)pok2, "");
> 
> -constexpr Base *nullB = 42 - 6 * 7; // expected-warning {{expression which evaluates to zero treated as a null pointer constant of type 'Class::Base *const'}}
> +// Core issue 903: we do not perform constant evaluation when checking for a
> +// null pointer in C++11. Just check for an integer literal with value 0.
> +constexpr Base *nullB = 42 - 6 * 7; // expected-error {{cannot initialize a variable of type 'Class::Base *const' with an rvalue of type 'int'}}
> +constexpr Base *nullB1 = 0;
> static_assert((Bottom*)nullB == 0, "");
> static_assert((Derived*)nullB == 0, "");
> static_assert((void*)(Bottom*)nullB == (void*)(Derived*)nullB, "");
> -Base * nullB2 = '\0'; // expected-warning {{expression which evaluates to zero treated as a null pointer constant of type 'Class::Base *'}}
> -Base * nullB3 = (0);
> -// We suppress the warning in unevaluated contexts to workaround some gtest
> -// behavior. Once this becomes an error this isn't a problem anymore.
> -static_assert(nullB == (1 - 1), "");
> +Base *nullB2 = '\0'; // expected-error {{cannot initialize a variable of type 'Class::Base *' with an rvalue of type 'char'}}
> +Base *nullB3 = (0);
> +Base *nullB4 = false; // expected-error {{cannot initialize a variable of type 'Class::Base *' with an rvalue of type 'bool'}}
> +Base *nullB5 = ((0ULL));
> +Base *nullB6 = 0.; // expected-error {{cannot initialize a variable of type 'Class::Base *' with an rvalue of type 'double'}}
> +enum Null { kNull };
> +Base *nullB7 = kNull; // expected-error {{cannot initialize a variable of type 'Class::Base *' with an rvalue of type 'Class::Null'}}
> +static_assert(nullB1 == (1 - 1), ""); // expected-error {{comparison between pointer and integer}}
> +
> 
> 
> namespace ConversionOperators {
> 
> Modified: cfe/trunk/test/SemaCXX/lambda-expressions.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/lambda-expressions.cpp?rev=183883&r1=183882&r2=183883&view=diff
> ==============================================================================
> --- cfe/trunk/test/SemaCXX/lambda-expressions.cpp (original)
> +++ cfe/trunk/test/SemaCXX/lambda-expressions.cpp Wed Jun 12 21:46:14 2013
> @@ -109,27 +109,30 @@ namespace PR12031 {
>   }
> }
> 
> -namespace NullPtr {
> +namespace Array {
>   int &f(int *p);
>   char &f(...);
>   void g() {
> -    int n = 0;
> +    int n = -1;
>     [=] {
> -      char &k = f(n); // not a null pointer constant
> +      int arr[n]; // VLA
>     } ();
> 
> -    const int m = 0;
> -    [=] {
> -      int &k = f(m); // expected-warning{{expression which evaluates to zero treated as a null pointer constant of type 'int *'}}
> +    const int m = -1;
> +    [] {
> +      int arr[m]; // expected-error{{negative size}}
> +    } ();
> +
> +    [&] {
> +      int arr[m]; // expected-error{{negative size}}
>     } ();
> 
> -    [=] () -> bool {
> -      int &k = f(m); // expected-warning{{expression which evaluates to zero treated as a null pointer constant of type 'int *'}}
> -      return &m == 0;
> +    [=] {
> +      int arr[m]; // expected-error{{negative size}}
>     } ();
> 
>     [m] {
> -      int &k = f(m); // expected-warning{{expression which evaluates to zero treated as a null pointer constant of type 'int *'}}
> +      int arr[m]; // expected-error{{negative size}}
>     } ();
>   }
> }
> 
> 
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