[PATCH] Fix assertion on C++ attributes in fillAttributedTypeLoc (this fixes http://llvm.org/PR17424)

[Aaron Ballman]

On Mon, Apr 27, 2015 at 6:23 AM, Alexey Frolov <alexfrolov1878 at yandex.ru> wrote:
> Hi rsmith, aaron.ballman,
>
> fillAttributedTypeLoc() function is only called with AttributeLists of either //DeclarationChunk// (which is used for each type in a declarator being parsed) or //DeclSpec// (which captures information about declaration specifiers).
> As C++11 attributes actually appertain to declarators, they are moved straight to the declarator’s attr list in distributeFunctionTypeAttrFromDeclSpec() function.
> 'Put them wherever you like' semantics is not supported for C++11 attributes (but is allowed for GNU attributes, for example).
> So when we meet an attribute while parsing the declaration, we cannot be sure if it appertains to either //DeclarationChunk// or //DeclSpec//.
>
> This investigation correlates with the history of changes of SemaType.cpp:
> • Asserts in fillAttributedTypeLoc() were added on 3 Mar 2011 in r126986 (http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20110228/039638.html);
> • Distributing C++11 attrs to the declarator was added on 14 Jan 2013 in r172504 (http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20130114/071830.html).
>
> Considering all written above I changed asserts in fillAttributedTypeLoc() to nullptr checks.

It seems like this means we have an attributed type location that has
no corresponding attribute, which is weird. We then just leave the
type location in this weird state by early returning. I'm not certain
whether that's a good idea or not. It feels like we should not have
the attributed type location in the first place, but I could be wrong.
Richard may have further thoughts.

~Aaron

>
> This fixes PR17424 and related assertion on
> ```
>   [[gnu::fastcall]] void __stdcall foo();
> ```
>
> REPOSITORY
>   rL LLVM
>
> http://reviews.llvm.org/D9288
>
> Files:
>   lib/Sema/SemaType.cpp
>   test/SemaCXX/cxx11-gnu-attrs.cpp
>
> Index: test/SemaCXX/cxx11-gnu-attrs.cpp
> ===================================================================
> --- test/SemaCXX/cxx11-gnu-attrs.cpp
> +++ test/SemaCXX/cxx11-gnu-attrs.cpp
> @@ -8,6 +8,17 @@
>  // expected-error at -1 {{'unused' attribute cannot be applied to types}}
>  int *[[gnu::unused]] attr_on_ptr;
>  // expected-warning at -1 {{attribute 'unused' ignored, because it cannot be applied to a type}}
> +[[gnu::fastcall]] void pr17424_1();
> +// expected-warning at -1 {{calling convention 'fastcall' ignored for this target}}
> +[[gnu::fastcall]] [[gnu::stdcall]] void pr17424_2();
> +// expected-warning at -1 {{calling convention 'fastcall' ignored for this target}}
> +// expected-warning at -2 {{calling convention 'stdcall' ignored for this target}}
> +[[gnu::fastcall]] __stdcall void pr17424_3();
> +// expected-warning at -1 {{calling convention 'fastcall' ignored for this target}}
> +// expected-warning at -2 {{calling convention '__stdcall' ignored for this target}}
> +[[gnu::fastcall]] void pr17424_4() [[gnu::stdcall]];
> +// expected-warning at -1 {{calling convention 'fastcall' ignored for this target}}
> +// expected-warning at -2 {{attribute 'stdcall' ignored, because it cannot be applied to a type}}
>
>  // Valid cases.
>
> Index: lib/Sema/SemaType.cpp
> ===================================================================
> --- lib/Sema/SemaType.cpp
> +++ lib/Sema/SemaType.cpp
> @@ -3492,13 +3492,15 @@
>
>  static void fillAttributedTypeLoc(AttributedTypeLoc TL,
>                                    const AttributeList *attrs) {
> -  AttributedType::Kind kind = TL.getAttrKind();
> +  if (!attrs)
> +    return;
>
> -  assert(attrs && "no type attributes in the expected location!");
> +  AttributedType::Kind kind = TL.getAttrKind();
>    AttributeList::Kind parsedKind = getAttrListKind(kind);
>    while (attrs->getKind() != parsedKind) {
>      attrs = attrs->getNext();
> -    assert(attrs && "no matching attribute in expected location!");
> +    if (!attrs)
> +      return;
>    }
>
>    TL.setAttrNameLoc(attrs->getLoc());
>
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