Re: [PATCH] c++, v3: Improve handling of foreigner namespace attributes

[Jason Merrill <jason@redhat.com>]

On 10/6/22 14:29, Jakub Jelinek wrote:
> On Thu, Oct 06, 2022 at 01:30:18PM -0400, Jason Merrill wrote:
>> Yes, except I was thinking the new function would take the attribute
>> TREE_LIST as its parameter so that all the callers don't have to also call
>> get_attribute_namespace.
> 
> Ok, here it is in patch form.
> 
> 2022-10-06  Jakub Jelinek  <jakub@redhat.com>
> 
> gcc/
> 	* attribs.h (is_attribute_namespace_p): New inline function.
> 	(lookup_attribute): Document meaning of ATTR_NS equal to "".
> 	* attribs.cc (remove_attribute): Use is_attribute_namespace_p.
> 	(private_lookup_attribute): For ATTR_NS "" match either standard
> 	attribute or "gnu" namespace one.
> gcc/c-family/
> 	* c-common.cc (attribute_fallthrough_p): Lookup fallthrough attribute
> 	only in gnu namespace or as standard attribute, treat fallthrough
> 	attributes in other namespaces like any other unknown attribute.
> gcc/cp/
> 	* parser.cc (cp_parser_check_std_attribute): Only do checks if
> 	attribute is a standard attribute or in gnu namespace and only
> 	lookup other attributes in those namespaces.
> 	* cp-gimplify.cc (lookup_hotness_attribute): Adjust function comment.
> 	Only return true for standard attribute or gnu namespace attribute.
> 	(remove_hotness_attribute): Only remove hotness attributes when
> 	they are standard or in gnu namespace, implement it in a single
> 	loop rather than former 4 now 8 remove_attribute calls.
> gcc/testsuite/
> 	* g++.dg/cpp1z/fallthrough2.C: New test.
> 	* g++.dg/cpp2a/attr-likely7.C: New test.
> 
> --- gcc/attribs.h.jj	2022-10-05 16:15:29.834889059 +0200
> +++ gcc/attribs.h	2022-10-06 20:22:37.946494304 +0200
> @@ -188,6 +188,22 @@ is_attribute_p (const char *attr_name, c
>   		      IDENTIFIER_POINTER (ident), IDENTIFIER_LENGTH (ident));
>   }
>   
> +/* Given an attribute name ATTR and a string ATTR_NS, return true

The word "name" here is wrong now.  OK with that fixed, thanks.

> +   if the identifier node is a valid attribute namespace for the string.
> +   ATTR_NS "" stands for standard attribute (NULL IDENT) or "gnu"
> +   namespace.  */
> +
> +static inline bool
> +is_attribute_namespace_p (const char *attr_ns, const_tree attr)
> +{
> +  tree ident = get_attribute_namespace (attr);
> +  if (attr_ns == NULL)
> +    return ident == NULL_TREE;
> +  if (attr_ns[0])
> +    return ident && is_attribute_p (attr_ns, ident);
> +  return ident == NULL_TREE || is_attribute_p ("gnu", ident);
> +}
> +
>   /* Given an attribute name ATTR_NAME and a list of attributes LIST,
>      return a pointer to the attribute's list element if the attribute
>      is part of the list, or NULL_TREE if not found.  If the attribute
> @@ -217,7 +233,8 @@ lookup_attribute (const char *attr_name,
>       }
>   }
>   
> -/* Similar to lookup_attribute, but also match the attribute namespace.  */
> +/* Similar to lookup_attribute, but also match the attribute namespace.
> +   ATTR_NS "" stands for either standard attribute or "gnu" namespace.  */
>   
>   static inline tree
>   lookup_attribute (const char *attr_ns, const char *attr_name, tree list)
> --- gcc/attribs.cc.jj	2022-10-04 23:13:10.289090796 +0200
> +++ gcc/attribs.cc	2022-10-06 20:23:35.693713861 +0200
> @@ -1645,7 +1645,8 @@ remove_attribute (const char *attr_name,
>     return list;
>   }
>   
> -/* Similarly but also match namespace on the removed attributes.  */
> +/* Similarly but also match namespace on the removed attributes.
> +   ATTR_NS "" stands for NULL or "gnu" namespace.  */
>   
>   tree
>   remove_attribute (const char *attr_ns, const char *attr_name, tree list)
> @@ -1659,15 +1660,11 @@ remove_attribute (const char *attr_ns, c
>         tree l = *p;
>   
>         tree attr = get_attribute_name (l);
> -      if (is_attribute_p (attr_name, attr))
> +      if (is_attribute_p (attr_name, attr)
> +	  && is_attribute_namespace_p (attr_ns, l))
>   	{
> -	  tree ns = get_attribute_namespace (l);
> -	  if ((ns == NULL_TREE && attr_ns == NULL)
> -	      || (ns && attr_ns && is_attribute_p (attr_ns, ns)))
> -	    {
> -	      *p = TREE_CHAIN (l);
> -	      continue;
> -	    }
> +	  *p = TREE_CHAIN (l);
> +	  continue;
>   	}
>         p = &TREE_CHAIN (l);
>       }
> @@ -2088,14 +2085,20 @@ private_lookup_attribute (const char *at
>   	  tree ns = get_attribute_namespace (list);
>   	  if (ns == NULL_TREE)
>   	    {
> -	      if (attr_ns == NULL)
> +	      if (attr_ns_len == 0)
>   		break;
>   	    }
>   	  else if (attr_ns)
>   	    {
>   	      ident_len = IDENTIFIER_LENGTH (ns);
> -	      if (cmp_attribs (attr_ns, attr_ns_len, IDENTIFIER_POINTER (ns),
> -			       ident_len))
> +	      if (attr_ns_len == 0)
> +		{
> +		  if (cmp_attribs ("gnu", strlen ("gnu"),
> +				   IDENTIFIER_POINTER (ns), ident_len))
> +		    break;
> +		}
> +	      else if (cmp_attribs (attr_ns, attr_ns_len,
> +				    IDENTIFIER_POINTER (ns), ident_len))
>   		break;
>   	    }
>   	}
> --- gcc/c-family/c-common.cc.jj	2022-10-06 17:43:47.880502941 +0200
> +++ gcc/c-family/c-common.cc	2022-10-06 20:24:17.220152623 +0200
> @@ -6008,12 +6008,12 @@ attribute_fallthrough_p (tree attr)
>   {
>     if (attr == error_mark_node)
>      return false;
> -  tree t = lookup_attribute ("fallthrough", attr);
> +  tree t = lookup_attribute ("", "fallthrough", attr);
>     if (t == NULL_TREE)
>       return false;
>     /* It is no longer true that "this attribute shall appear at most once in
>        each attribute-list", but we still give a warning.  */
> -  if (lookup_attribute ("fallthrough", TREE_CHAIN (t)))
> +  if (lookup_attribute ("", "fallthrough", TREE_CHAIN (t)))
>       warning (OPT_Wattributes, "attribute %<fallthrough%> specified multiple "
>   	     "times");
>     /* No attribute-argument-clause shall be present.  */
> @@ -6024,7 +6024,8 @@ attribute_fallthrough_p (tree attr)
>     for (t = attr; t != NULL_TREE; t = TREE_CHAIN (t))
>       {
>         tree name = get_attribute_name (t);
> -      if (!is_attribute_p ("fallthrough", name))
> +      if (!is_attribute_p ("fallthrough", name)
> +	  || !is_attribute_namespace_p ("", t))
>   	{
>   	  if (!c_dialect_cxx () && get_attribute_namespace (t) == NULL_TREE)
>   	    /* The specifications of standard attributes in C mean
> --- gcc/cp/parser.cc.jj	2022-10-06 17:43:42.418576616 +0200
> +++ gcc/cp/parser.cc	2022-10-06 20:25:01.004560878 +0200
> @@ -29265,7 +29265,8 @@ cp_parser_check_std_attribute (location_
>     if (attributes)
>       for (const auto &a : alist)
>         if (is_attribute_p (a, get_attribute_name (attribute))
> -	  && lookup_attribute (a, attributes))
> +	  && is_attribute_namespace_p ("", attribute)
> +	  && lookup_attribute ("", a, attributes))
>   	{
>   	  if (!from_macro_expansion_at (loc))
>   	    warning_at (loc, OPT_Wattributes, "attribute %qs specified "
> --- gcc/cp/cp-gimplify.cc.jj	2022-10-06 17:43:42.413576684 +0200
> +++ gcc/cp/cp-gimplify.cc	2022-10-06 20:24:43.145802239 +0200
> @@ -3027,7 +3027,7 @@ cp_fold (tree x)
>     return x;
>   }
>   
> -/* Look up either "hot" or "cold" in attribute list LIST.  */
> +/* Look up "hot", "cold", "likely" or "unlikely" in attribute list LIST.  */
>   
>   tree
>   lookup_hotness_attribute (tree list)
> @@ -3035,24 +3035,36 @@ lookup_hotness_attribute (tree list)
>     for (; list; list = TREE_CHAIN (list))
>       {
>         tree name = get_attribute_name (list);
> -      if (is_attribute_p ("hot", name)
> -	  || is_attribute_p ("cold", name)
> -	  || is_attribute_p ("likely", name)
> -	  || is_attribute_p ("unlikely", name))
> +      if ((is_attribute_p ("hot", name)
> +	   || is_attribute_p ("cold", name)
> +	   || is_attribute_p ("likely", name)
> +	   || is_attribute_p ("unlikely", name))
> +	  && is_attribute_namespace_p ("", list))
>   	break;
>       }
>     return list;
>   }
>   
> -/* Remove both "hot" and "cold" attributes from LIST.  */
> +/* Remove "hot", "cold", "likely" and "unlikely" attributes from LIST.  */
>   
>   static tree
>   remove_hotness_attribute (tree list)
>   {
> -  list = remove_attribute ("hot", list);
> -  list = remove_attribute ("cold", list);
> -  list = remove_attribute ("likely", list);
> -  list = remove_attribute ("unlikely", list);
> +  for (tree *p = &list; *p; )
> +    {
> +      tree l = *p;
> +      tree name = get_attribute_name (l);
> +      if ((is_attribute_p ("hot", name)
> +	   || is_attribute_p ("cold", name)
> +	   || is_attribute_p ("likely", name)
> +	   || is_attribute_p ("unlikely", name))
> +	  && is_attribute_namespace_p ("", l))
> +	{
> +	  *p = TREE_CHAIN (l);
> +	  continue;
> +	}
> +      p = &TREE_CHAIN (l);
> +    }
>     return list;
>   }
>   
> --- gcc/testsuite/g++.dg/cpp1z/fallthrough2.C.jj	2022-10-06 17:45:55.452782142 +0200
> +++ gcc/testsuite/g++.dg/cpp1z/fallthrough2.C	2022-10-06 17:45:55.452782142 +0200
> @@ -0,0 +1,24 @@
> +// { dg-do compile { target c++17 } }
> +// { dg-options "-Wextra -Wall -Wpedantic" }
> +
> +int
> +foo (int i)
> +{
> +  switch (i)
> +    {
> +    case 2:
> +      ++i;
> +      [[fallthrough, whatever::fallthrough]];		// { dg-bogus "attribute 'fallthrough' specified multiple times" }
> +    case 3:						// { dg-warning "'fallthrough' attribute ignored" "" { target *-*-* } .-1 }
> +      ++i;
> +      [[fallthrough, whatever2::fallthrough(1, 2, 3)]];	// { dg-bogus "attribute 'fallthrough' specified multiple times" }
> +    case 4:						// { dg-warning "'fallthrough' attribute ignored" "" { target *-*-* } .-1 }
> +      [[whatever3::fallthrough("abcd")]];		// { dg-warning "attributes at the beginning of statement are ignored" }
> +    case 5:
> +      [[whatever4::fallthrough]];			// { dg-bogus "attribute 'fallthrough' not preceding a case label or default label" }
> +      ++i;						// { dg-warning "attributes at the beginning of statement are ignored" "" { target *-*-* } .-1 }
> +    default:
> +      break;
> +    }
> +  return i;
> +}
> --- gcc/testsuite/g++.dg/cpp2a/attr-likely7.C.jj	2022-10-06 17:45:55.452782142 +0200
> +++ gcc/testsuite/g++.dg/cpp2a/attr-likely7.C	2022-10-06 17:45:55.452782142 +0200
> @@ -0,0 +1,38 @@
> +// { dg-do compile { target c++20 } }
> +// { dg-additional-options -fdump-tree-gimple }
> +// { dg-final { scan-tree-dump-times "hot label" 5 "gimple" } }
> +// { dg-final { scan-tree-dump-times "cold label" 3 "gimple" } }
> +
> +bool b;
> +
> +template <class T> int f()
> +{
> +  if (b)
> +    [[likely, whatever::unlikely ("abcd")]] return 0;		// { dg-bogus "ignoring attribute 'unlikely' after earlier 'likely'" }
> +  else								// { dg-warning "attributes at the beginning of statement are ignored" "" { target *-*-* } .-1 }
> +    [[unlikely, whatever2::hot]] flabel: return 1;		// { dg-warning "'whatever2::hot' scoped attribute directive ignored" }
> +  switch (b)
> +    {
> +      [[likely, whatever3::cold (1, 2, 3)]] case true: break;	// { dg-warning "'whatever3::cold' scoped attribute directive ignored" }
> +    };
> +  return 1;
> +}
> +
> +int main()
> +{
> +  if (b)
> +    [[whatever4::unlikely (1), likely]] return 0;		// { dg-bogus "ignoring attribute 'likely' after earlier 'unlikely'" }
> +  else if (b)							// { dg-warning "attributes at the beginning of statement are ignored" "" { target *-*-* } .-1 }
> +    [[whatever5::hot, unlikely]] elabel:			// { dg-warning "'whatever5::hot' scoped attribute directive ignored" }
> +      return 1;
> +  else
> +    [[whatever6::cold, likely]] b = false;			// { dg-bogus "ignoring attribute 'likely' after earlier 'cold'" }
> +								// { dg-warning "attributes at the beginning of statement are ignored" "" { target *-*-* } .-1 }
> +  f<int>();
> +
> +  switch (b)
> +    {
> +      [[whatever7::unlikely (1), likely]] case true: break;	// { dg-warning "'whatever7::unlikely' scoped attribute directive ignored" }
> +      [[whatever8::unlikely, unlikely]] case false: break;	// { dg-bogus "attribute 'unlikely' specified multiple times" }
> +    };								// { dg-warning "'whatever8::unlikely' scoped attribute directive ignored" "" { target *-*-* } .-1 }
> +}
> 
> 
> 	Jakub
>