RFC: PATCH for front end parts of C++ transactional memory TS

[Jason Merrill <jason at redhat dot com>]

This patch implements the front end bits of the transactional memory 
technical specification: apart from parsing, that means treating 
transaction_safe as part of the type and dealing with conversions, 
mangling and such.

Since the transaction_safe attribute now affects type identity, I needed 
to change the C front end to allow declarations of built-ins to change 
whether the function is declared transaction_safe.  Joseph, is that hunk 
(copied at the bottom) OK?

After this patch the compiler sorrys out on atomic_cancel because 
cancel-and-throw hasn't been implemented yet.  RTH, will you be able to 
poke at that any time soon?

The patch also doesn't attempt to do anything about the library.  The 
second patch sets transaction_safe on various built-ins, but without the 
library support this just means references to undefined symbols.  The 
third patch is a beginning of libstdc++ support, which may or may not be 
useful to Jonathan or Torvald in completing that support.

I'm thinking to check in the first patch as is soon, and leave the rest 
for other people to take care of later.

Any thoughts?

> diff --git a/gcc/c/c-decl.c b/gcc/c/c-decl.c
> index a110226..ce8406a 100644
> --- a/gcc/c/c-decl.c
> +++ b/gcc/c/c-decl.c
> @@ -1659,7 +1659,19 @@ match_builtin_function_types (tree newtype, tree oldtype)
>      }
>
>    trytype = build_function_type (newrettype, tryargs);
> -  return build_type_attribute_variant (trytype, TYPE_ATTRIBUTES (oldtype));
> +
> +  /* Allow declaration to change transaction_safe attribute.  */
> +  tree oldattrs = TYPE_ATTRIBUTES (oldtype);
> +  tree oldtsafe = lookup_attribute ("transaction_safe", oldattrs);
> +  tree newattrs = TYPE_ATTRIBUTES (newtype);
> +  tree newtsafe = lookup_attribute ("transaction_safe", newattrs);
> +  if (oldtsafe && !newtsafe)
> +    oldattrs = remove_attribute ("transaction_safe", oldattrs);
> +  else if (newtsafe && !oldtsafe)
> +    oldattrs = tree_cons (get_identifier ("transaction_safe"),
> +                         NULL_TREE, oldattrs);
> +
> +  return build_type_attribute_variant (trytype, oldattrs);
>  }
>
>  /* Subroutine of diagnose_mismatched_decls.  Check for function type

Attachment: tm.patch.gz
Description: application/gzip

Attachment: tm-builtins.patch.gz
Description: application/gzip

Attachment: tm-libstc++.patch.gz
Description: application/gzip