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

[alexfrol]

Summary

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.

This fixes PR17424 and related assertion on

[[gnu::fastcall]] void __stdcall foo();

[alexfrol]

This is a kind reminder just in case this got forgotten.

[alexfrol]

Ping!

[alexfrol]

Ping!!

[alexfrol]

Ping!

[alexfrol]

Thank you for the review!
I changed fillAttributedTypeLoc() to search through C++11 attributes in the declarator attribute list if a desired attribute not found in DeclaratorChunk.
I also added a new testcase.

[alexfrol]

Ping!

[rsmith]

LGTM, thanks!

lib/Sema/SemaType.cpp

static AttributeList::Kind getAttrListKind(AttributedType::Kind kind) {
   case AttributedType::attr_uptr:
     return AttributeList::AT_UPtr;
   }
   llvm_unreachable("unexpected attribute kind!");
 }
 
 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());
   if (TL.hasAttrExprOperand()) {
     assert(attrs->isArgExpr(0) && "mismatched attribute operand kind");
     TL.setAttrExprOperand(attrs->getArgAsExpr(0));
   } else if (TL.hasAttrEnumOperand()) {
     assert((attrs->isArgIdent(0) || attrs->isArgExpr(0)) &&

test/SemaCXX/cxx11-gnu-attrs.cpp

 // RUN: %clang_cc1 -triple x86_64-unknown-unknown -std=c++11 -verify %s
 
 // Error cases.
 
 [[gnu::this_attribute_does_not_exist]] int unknown_attr;
 // expected-warning@-1 {{unknown attribute 'this_attribute_does_not_exist' ignored}}
 int [[gnu::unused]] attr_on_type;
 // expected-error@-1 {{'unused' attribute cannot be applied to types}}
 int *[[gnu::unused]] attr_on_ptr;
 // expected-warning@-1 {{attribute 'unused' ignored, because it cannot be applied to a type}}
+[[gnu::fastcall]] void pr17424_1();
+// expected-warning@-1 {{calling convention 'fastcall' ignored for this target}}
+[[gnu::fastcall]] [[gnu::stdcall]] void pr17424_2();
+// expected-warning@-1 {{calling convention 'fastcall' ignored for this target}}
+// expected-warning@-2 {{calling convention 'stdcall' ignored for this target}}
+[[gnu::fastcall]] __stdcall void pr17424_3();
+// expected-warning@-1 {{calling convention 'fastcall' ignored for this target}}
+// expected-warning@-2 {{calling convention '__stdcall' ignored for this target}}
+[[gnu::fastcall]] void pr17424_4() [[gnu::stdcall]];
+// expected-warning@-1 {{calling convention 'fastcall' ignored for this target}}
+// expected-warning@-2 {{attribute 'stdcall' ignored, because it cannot be applied to a type}}
 
 // Valid cases.
 
 void aliasb [[gnu::alias("_Z6alias1v")]] ();
 void alias1() {}
 void aliasa [[gnu::alias("_Z6alias1v")]] ();
 
 extern struct PR22493Ty {