Re: Add fnspec attributes to cxa_* functions

[Jason Merrill <jason@redhat.com>]

On 6/23/22 09:59, Jan Hubicka via Gcc-patches wrote:

Note that your email subject line is missing "[PATCH]" and a component 
tag like "c++:".

> this patch adds fnspecs for cxa_* functions in except.cc.  Main goal is to make
> modref to see proper side-effects of functions which may throw. So in general
> we get
>   - cxa_allocate_exception
>      which gets the same annotations as malloc (since it is kind of same thing)
>   - cxa_free_exception
>      which gets the same annotations as free
>   - cxa_throw which is marked as const except for first parameter which is believed
>      that it makes it escape (which is necessary) and modify (which is not necessary
>      but it would matter inly if we would like to do constant propagation across
>      EH edges.

Makes sense.

> gcc/cp/ChangeLog:
> 
> 2022-06-23  Jan Hubicka  <hubicka@ucw.cz>
> 
> 	* except.cc (declare_library_fn_1): Add fnspec parameter.
> 	(declare_library_fn): Add fnspec parameter.
> 	(do_allocate_exception): Declare fnspecs.
> 	(do_free_exception): Declare fnspecs.
> 	(build_throw): Declare fnspecs.
> 
> gcc/testsuite/ChangeLog:
> 
> 2022-06-23  Jan Hubicka  <hubicka@ucw.cz>
> 
> 	* g++.dg/opt/eh6.C: New test.
> 	* g++.dg/tree-ssa/kill.C: New test.
> 
> diff --git a/gcc/cp/except.cc b/gcc/cp/except.cc
> index da0a65c613d..bb9a5aee6da 100644
> --- a/gcc/cp/except.cc
> +++ b/gcc/cp/except.cc
> @@ -133,13 +133,14 @@ build_exc_ptr (void)
>   }
>   
>   /* Declare an exception ABI entry point called NAME.
> -   ECF are the library flags, RTYPE the return type and ARGS[NARGS]
> +   ECF are the library flags, FNSPEC is the attr "fn spec" string (or NULL),

It might be helpful to refer to attr_fnspec or attr-fnspec.h, since 
that's where I found the documentation for that string?  OK either way.

> +   RTYPE the return type and ARGS[NARGS]
>      the parameter types.  We return the DECL -- which might be one
>      found via the symbol table pushing, if the user already declared
>      it.  If we pushed a new decl, the user will see it.  */
>   
>   static tree
> -declare_library_fn_1 (const char *name, int ecf,
> +declare_library_fn_1 (const char *name, int ecf, const char *fnspec,
>   		      tree rtype, int nargs, tree args[])
>   {
>     tree ident = get_identifier (name);
> @@ -150,6 +151,14 @@ declare_library_fn_1 (const char *name, int ecf,
>     for (unsigned ix = nargs; ix--;)
>       arg_list = tree_cons (NULL_TREE, args[ix], arg_list);
>     tree fntype = build_function_type (rtype, arg_list);
> +  if (fnspec)
> +    {
> +      tree attr_args = build_tree_list (NULL_TREE,
> +					build_string (strlen (fnspec), fnspec));
> +      tree attrs = tree_cons (get_identifier ("fn spec"),
> +			      attr_args, TYPE_ATTRIBUTES (fntype));
> +      fntype = build_type_attribute_variant (fntype, attrs);
> +    }
>     tree res = push_library_fn (ident, fntype, except, ecf);
>   
>     return res;
> @@ -157,7 +166,8 @@ declare_library_fn_1 (const char *name, int ecf,
>   
>   /* Find or declare a function NAME, returning RTYPE, taking a single
>      parameter PTYPE, with an empty exception specification. ECF are the
> -   library fn flags.  If TM_ECF is non-zero, also find or create a
> +   library fn flags.  FNSPEC is the attr "fn spec" string (or NULL).
> +   If TM_ECF is non-zero, also find or create a
>      transaction variant and record it as a replacement, when flag_tm is
>      in effect.
>   
> @@ -167,9 +177,10 @@ declare_library_fn_1 (const char *name, int ecf,
>   
>   static tree
>   declare_library_fn (const char *name, tree rtype, tree ptype,
> -		    int ecf, int tm_ecf)
> +		    int ecf, int tm_ecf, const char *fnspec = NULL)
>   {
> -  tree res = declare_library_fn_1 (name, ecf, rtype, ptype ? 1 : 0, &ptype);
> +  tree res = declare_library_fn_1 (name, ecf, fnspec,
> +				   rtype, ptype ? 1 : 0, &ptype);
>     if (res == error_mark_node)
>       return res;
>   
> @@ -177,7 +188,7 @@ declare_library_fn (const char *name, tree rtype, tree ptype,
>       {
>         char *tm_name = concat ("_ITM_", name + 2, NULL_TREE);
>   
> -      tree tm_fn = declare_library_fn_1 (tm_name, ecf | tm_ecf, rtype,
> +      tree tm_fn = declare_library_fn_1 (tm_name, ecf | tm_ecf, fnspec, rtype,
>   					 ptype ? 1 : 0, &ptype);
>         free (tm_name);
>         if (tm_fn != error_mark_node)
> @@ -547,7 +558,8 @@ do_allocate_exception (tree type)
>       allocate_exception_fn
>         = declare_library_fn ("__cxa_allocate_exception",
>   			    ptr_type_node, size_type_node,
> -			    ECF_NOTHROW | ECF_MALLOC | ECF_COLD, ECF_TM_PURE);
> +			    ECF_NOTHROW | ECF_MALLOC | ECF_COLD, ECF_TM_PURE,
> +			    "mc");
>   
>     return cp_build_function_call_nary (allocate_exception_fn,
>   				      tf_warning_or_error,
> @@ -565,7 +577,8 @@ do_free_exception (tree ptr)
>       free_exception_fn
>         = declare_library_fn ("__cxa_free_exception",
>   			    void_type_node, ptr_type_node,
> -			    ECF_NOTHROW | ECF_LEAF, ECF_TM_PURE);
> +			    ECF_NOTHROW | ECF_LEAF, ECF_TM_PURE,
> +			    ".co ");
>   
>     return cp_build_function_call_nary (free_exception_fn,
>   				      tf_warning_or_error, ptr, NULL_TREE);
> @@ -653,11 +666,13 @@ build_throw (location_t loc, tree exp)
>   
>   	  throw_fn = declare_library_fn_1 ("__cxa_throw",
>   					   ECF_NORETURN | ECF_COLD,
> +					   ".c. X X ",
>   					   void_type_node, 3, args);
>   	  if (flag_tm && throw_fn != error_mark_node)
>   	    {
>   	      tree itm_fn = declare_library_fn_1 ("_ITM_cxa_throw",
>   						  ECF_NORETURN | ECF_COLD,
> +						  ".c. X X ",
>   						  void_type_node, 3, args);
>   	      if (itm_fn != error_mark_node)
>   		{
> @@ -804,6 +819,7 @@ build_throw (location_t loc, tree exp)
>   	{
>   	  rethrow_fn = declare_library_fn_1 ("__cxa_rethrow",
>   					     ECF_NORETURN | ECF_COLD,
> +					     ".c",
>   					     void_type_node, 0, NULL);
>   	  if (flag_tm && rethrow_fn != error_mark_node)
>   	    apply_tm_attr (rethrow_fn, get_identifier ("transaction_pure"));
> diff --git a/gcc/testsuite/g++.dg/opt/eh6.C b/gcc/testsuite/g++.dg/opt/eh6.C
> new file mode 100644
> index 00000000000..fa891fb2559
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/opt/eh6.C
> @@ -0,0 +1,34 @@
> +// PR middle-end/106057
> +// { dg-do run }
> +// { dg-options "-O2" }
> +struct a {int a; int b;} a;
> +int b;
> +
> +__attribute__((noinline))
> +struct a maybethrow(int b)
> +{
> +        if (!b)
> +                throw(0);
> +        return {0,0};
> +}
> +
> +void
> +test(int b)
> +{
> +        a={1,1};
> +        a=maybethrow(b);
> +        a={0,0};
> +}
> +int
> +main()
> +{
> +        try {
> +                test(b);
> +        }
> +        catch(int) {
> +                if (!a.a)
> +                        __builtin_abort ();
> +        }
> +        return 0;
> +}
> +
> diff --git a/gcc/testsuite/g++.dg/tree-ssa/kill.C b/gcc/testsuite/g++.dg/tree-ssa/kill.C
> new file mode 100644
> index 00000000000..bee58cd91fe
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/tree-ssa/kill.C
> @@ -0,0 +1,20 @@
> +/* { dg-do run } */
> +/* { dg-options "-O2 -fdump-tree-modref1" } */
> +__attribute__ ((noinline))
> +void test(int a)
> +{
> +	if (a)
> +		throw (1);
> +}
> +int mem;
> +void link_error ();
> +int
> +main()
> +{
> +	mem = 0;
> +	test (0);
> +	if (mem)
> +		link_error ();
> +	return 0;
> +}
> +// { dg-final { scan-tree-dump-not "modref done with result: tracked." "modref1" } }
>