[TableGen] Only normalize the spelling of GNU-style attributes.

[jlebar]

Summary

When Sema looks up an attribute name, it strips off leading and trailing
"" if the attribute is GNU-style. That is, attribute((foo)) and
attribute((foo__)) are equivalent.

This is only true for GNU-style attributes. In particular,
declspec(foo) is not equivalent to declspec(foo), and Sema
respects this difference.

This patch fixes TableGen to match Sema's behavior. The spelling
'GNU<"foo">' should be normalized to 'GNU<"foo">', but
'Declspec<"foo">' should not be changed.

This is necessary to make CUDA compilation work on Windows, because e.g.
the device attribute is spelled declspec(device__).

Attr.td does not contain any Declspec spellings that start or end with
"__", so this change should not affect any other attributes.

[rnk]

lgtm

cfe/trunk/utils/TableGen/ClangAttrEmitter.cpp

 
 // Normalize the name by removing any and all leading and trailing underscores.
 // This is different from NormalizeAttrName in that it also handles names like
 // _pascal and __pascal.
 static StringRef NormalizeNameForSpellingComparison(StringRef Name) {
   return Name.trim("_");
 }
 
-// Normalize attribute spelling only if the spelling has both leading
-// and trailing underscores. For example, __ms_struct__ will be 
-// normalized to "ms_struct"; __cdecl will remain intact.
-static StringRef NormalizeAttrSpelling(StringRef AttrSpelling) {
+// Normalize the spelling of a GNU attribute (i.e. "x" in "__attribute__((x))"),
+// removing "__" if it appears at the beginning and end of the attribute's name.
+static StringRef NormalizeGNUAttrSpelling(StringRef AttrSpelling) {
   if (AttrSpelling.startswith("__") && AttrSpelling.endswith("__")) {
     AttrSpelling = AttrSpelling.substr(2, AttrSpelling.size() - 4);
   }
 
   return AttrSpelling;
 }
 
 typedef std::vector<std::pair<std::string, const Record *>> ParsedAttrMap;
if (SemaHandler || Ignored) {
           Matches = &Microsoft;
         else if (Variety == "Keyword")
           Matches = &Keywords;
         else if (Variety == "Pragma")
           Matches = &Pragma;
 
         assert(Matches && "Unsupported spelling variety found");
 
-        Spelling += NormalizeAttrSpelling(RawSpelling);
+        if (Variety == "GNU")
+          Spelling += NormalizeGNUAttrSpelling(RawSpelling);
+        else
+          Spelling += RawSpelling;
+
         if (SemaHandler)
           Matches->push_back(StringMatcher::StringPair(Spelling,
                               "return AttributeList::AT_" + AttrName + ";"));
         else
           Matches->push_back(StringMatcher::StringPair(Spelling,
                               "return AttributeList::IgnoredAttribute;"));
       }
     }