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

[Alexey Frolov]

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.

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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