[MSVC Compat] Support for '__unaligned' attribute in function declaration

[olga.a.chupina]

Summary

This patch supports using '__unaligned' attribute in function declaration:

struct UnalignedS {

void foo(double) __unaligned { ; }

};

void bar(void (UnalignedS::*pf)(double)__unaligned);

Olga Chupina,
Software Engineer,
Intel Compiler Team

[olga.a.chupina]

Reid, cloud you please review the patch.

[aaron.ballman]

lib/Parse/ParseDecl.cpp

4811

MSDN suggests that __unaligned is only valid on a pointer declaration. Is there something this is expected to support, or does MSVC just happen to silently accept the keyword in this position?

[rnk]

Unless there is a compelling example of Microsoft or a popular third-party header relying on this behavior, I don't think we should implement it.

lib/Parse/ParseDecl.cpp

4813

This will allow __unaligned in a variety of other locations where we shouldn't accept it.

[olga.a.chupina]

lib/Parse/ParseDecl.cpp

4811

It rather silently accepts the keyword in this position.

4813

Could you please help me with narrowing it down to the case I'm interested in?

[aaron.ballman]

In D17709#374561, @rnk wrote:

Unless there is a compelling example of Microsoft or a popular third-party header relying on this behavior, I don't think we should implement it.

Agreed.

lib/Parse/ParseDecl.cpp

4811

I'm not keen on inferring undocumented behaviors from MSVC keywords; we should only accept if there's some reason to do so (we don't want to hijack MSVC's keyword and give it different behavior than MSVC).

lib/Parse/ParseDecl.cpp

while (1) {
     case tok::kw___ptr64:
     case tok::kw___ptr32:
     case tok::kw___cdecl:
     case tok::kw___stdcall:
     case tok::kw___fastcall:
     case tok::kw___thiscall:
     case tok::kw___vectorcall:
     case tok::kw___unaligned:
-      if (AttrReqs & AR_DeclspecAttributesParsed) {
+      // Allow __unaligned in function definition after a parameter list
+      if ((AttrReqs & AR_DeclspecAttributesParsed) ||
+          (Tok.getKind() == tok::kw___unaligned)) {
         ParseMicrosoftTypeAttributes(DS.getAttributes());
         continue;
       }
       goto DoneWithTypeQuals;
     case tok::kw___pascal:
       if (AttrReqs & AR_VendorAttributesParsed) {
         ParseBorlandTypeAttributes(DS.getAttributes());
         continue;

lib/Parse/ParseTentative.cpp

Parser::TPResult Parser::TryParseFunctionDeclarator() {
   if (TPR == TPResult::False || TPR == TPResult::Error)
     return TPR;
 
   // Parse through the parens.
   if (!SkipUntil(tok::r_paren, StopAtSemi))
     return TPResult::Error;
 
   // cv-qualifier-seq
-  while (Tok.isOneOf(tok::kw_const, tok::kw_volatile, tok::kw_restrict))
+  while (Tok.isOneOf(tok::kw_const, tok::kw_volatile, tok::kw_restrict,
+                     tok::kw___unaligned))
     ConsumeToken();
 
   // ref-qualifier[opt]
   if (Tok.isOneOf(tok::amp, tok::ampamp))
     ConsumeToken();
   
   // exception-specification
   if (Tok.is(tok::kw_throw)) {

test/SemaCXX/MicrosoftExtensions.cpp

 struct M {
     int __stdcall addP();
     float __stdcall subtractP();
 };
 
 // __unaligned handling
 typedef char __unaligned *aligned_type;
 typedef struct UnalignedTag { int f; } __unaligned *aligned_type2;
+struct UnalignedS {
+  void foo(double) __unaligned { ; }
+};
+void bar(void (UnalignedS::*pf)(double)__unaligned);
 
 
 template<typename T> void h1(T (__stdcall M::* const )()) { }
 
 void m1() {
   h1<int>(&M::addP);
   h1(&M::subtractP);
 }