Re: Warning policy?

["Kaveh R. Ghazi" <ghazi at caip dot rutgers dot edu>]

 > From: Joe Buck <jbuck@Synopsys.COM>
 > 
 > >  > Andreas Schwab writes: 
 > >  > > Well, the brute force method would be to just emit a `goto L' before
 > >  > > each label L.
 > >  > 
 > >  > That would only create more warnings, as some of these gotos would be
 > >  > unreachable code, which produces a warning.
 > > 
 > > 	Good point, but I'm not seeing this in actual practice from gcc. 
 > > I wrote a small patch to attempt what Andreas suggested and gcc does not
 > > complain about unreachable code.  Various stage1-cc's might complain,
 > > e.g. SunOS4 cc does in fact, but we could arrange to only output the
 > > goto when __GNUC__ is defined. 
 > 
 > Ah, but if gcc's ability to detect dead code improves, the warnings come
 > back.

	My impression was that gcc's response to dead code was to
eliminate it, not warn about it.  At least that's what the comments/docs
suggest...



 > Now, if there were an attribute that can be attached to a label that says
 > "this label may be unused, if so, don't warn about it" that would be
 > the simplest way to fix things.

	
	I'd call it a better solution, not a simpler one. :-)

Anyway, I went ahead and implemented it.  How's this?

	Okay to install?

		--Kaveh


Fri Jan  1 19:11:54 1999  Kaveh R. Ghazi  <ghazi@caip.rutgers.edu>

	* c-common.c (decl_attributes): Allow applying attribute `unused'
	on a LABEL_DECL.

	* c-parse.in (label): Parse attributes after a label, and call
 	`decl_attributes' to handle them.

	* gansidecl.h (ATTRIBUTE_UNUSED_LABEL): Define.

	* genrecog.c (OUTPUT_LABEL, write_tree_1, write_tree): When
	generating labels, mark them with ATTRIBUTE_UNUSED_LABEL.

	* invoke.texi: Note that labels can be marked `unused'.


diff -rup orig/egcs-CVS19981231/gcc/c-common.c egcs-CVS19981231/gcc/c-common.c
--- orig/egcs-CVS19981231/gcc/c-common.c	Thu Dec 31 12:05:12 1998
+++ egcs-CVS19981231/gcc/c-common.c	Thu Dec 31 23:05:54 1998
@@ -521,7 +521,8 @@ decl_attributes (node, attributes, prefi
 	    TREE_USED (type) = 1;
 	  else if (TREE_CODE (decl) == PARM_DECL
 		   || TREE_CODE (decl) == VAR_DECL
-		   || TREE_CODE (decl) == FUNCTION_DECL)
+		   || TREE_CODE (decl) == FUNCTION_DECL
+		   || TREE_CODE (decl) == LABEL_DECL)
 	    TREE_USED (decl) = 1;
 	  else
 	    warning ("`%s' attribute ignored", IDENTIFIER_POINTER (name));
diff -rup orig/egcs-CVS19981231/gcc/c-parse.in egcs-CVS19981231/gcc/c-parse.in
--- orig/egcs-CVS19981231/gcc/c-parse.in	Thu Dec 31 12:05:15 1998
+++ egcs-CVS19981231/gcc/c-parse.in	Thu Dec 31 23:05:54 1998
@@ -2214,12 +2214,15 @@ label:	  CASE expr_no_commas ':'
 		      error_with_decl (duplicate, "this is the first default label");
 		    }
 		  position_after_white_space (); }
-	| identifier ':'
+	| identifier ':' maybe_attribute
 		{ tree label = define_label (input_filename, lineno, $1);
 		  stmt_count++;
 		  emit_nop ();
 		  if (label)
-		    expand_label (label);
+		    {
+		      expand_label (label);
+		      decl_attributes (label, $3, NULL_TREE);
+		    }
 		  position_after_white_space (); }
 	;
 
diff -rup orig/egcs-CVS19981231/gcc/gansidecl.h egcs-CVS19981231/gcc/gansidecl.h
--- orig/egcs-CVS19981231/gcc/gansidecl.h	Thu Dec 31 12:05:11 1998
+++ egcs-CVS19981231/gcc/gansidecl.h	Thu Dec 31 23:05:55 1998
@@ -38,6 +38,14 @@ Boston, MA 02111-1307, USA.  */
 # define __attribute__(x)
 #endif
 
+#ifndef ATTRIBUTE_UNUSED_LABEL
+# if __GNUC__ < 2 || (__GNUC__ == 2 && __GNUC_MINOR__ < 92)
+#  define ATTRIBUTE_UNUSED_LABEL
+# else
+#  define ATTRIBUTE_UNUSED_LABEL ATTRIBUTE_UNUSED
+# endif /* GNUC < 2.92 */
+#endif /* ATTRIBUTE_UNUSED_LABEL */
+
 #ifndef ATTRIBUTE_UNUSED
 #define ATTRIBUTE_UNUSED __attribute__ ((__unused__))
 #endif /* ATTRIBUTE_UNUSED */
diff -rup orig/egcs-CVS19981231/gcc/genrecog.c egcs-CVS19981231/gcc/genrecog.c
--- orig/egcs-CVS19981231/gcc/genrecog.c	Thu Dec 31 12:06:07 1998
+++ egcs-CVS19981231/gcc/genrecog.c	Thu Dec 31 23:05:55 1998
@@ -51,6 +51,9 @@ Boston, MA 02111-1307, USA.  */
 #include "rtl.h"
 #include "obstack.h"
 
+#define OUTPUT_LABEL(INDENT_STRING, LABEL_NUMBER) \
+  printf("%sL%d: ATTRIBUTE_UNUSED_LABEL\n", (INDENT_STRING), (LABEL_NUMBER))
+
 static struct obstack obstack;
 struct obstack *rtl_obstack = &obstack;
 
@@ -1103,7 +1106,7 @@ write_tree_1 (tree, prevpos, afterward, 
   printf ("\n");
   if (tree && tree->subroutine_number == 0)
     {
-      printf ("  L%d:\n", tree->number);
+      OUTPUT_LABEL ("  ", tree->number);
       tree->label_needed = 0;
     }
 
@@ -1239,7 +1242,7 @@ write_tree_1 (tree, prevpos, afterward, 
 
       if (p->label_needed && (p->retest_mode || p->retest_code))
 	{
-	  printf ("%sL%d:\n", indents[indent - 2], p->number);
+	  OUTPUT_LABEL (indents[indent - 2], p->number);
 	  p->label_needed = 0;
 	}
 
@@ -1330,7 +1333,7 @@ write_tree_1 (tree, prevpos, afterward, 
       /* Now that most mode and code tests have been done, we can write out
 	 a label for an inner node, if we haven't already.  */
       if (p->label_needed)
-	printf ("%sL%d:\n", indents[indent - 2], p->number);
+	OUTPUT_LABEL (indents[indent - 2], p->number);
 
       inner_indent = indent;
 
@@ -1563,7 +1566,7 @@ write_tree (tree, prevpos, afterward, in
 
   if (! initial && tree->subroutine_number > 0)
     {
-      printf (" L%d:\n", tree->number);
+      OUTPUT_LABEL (" ", tree->number);
 
       if (afterward)
 	{
diff -rup orig/egcs-CVS19981231/gcc/invoke.texi egcs-CVS19981231/gcc/invoke.texi
--- orig/egcs-CVS19981231/gcc/invoke.texi	Thu Dec 31 12:06:17 1998
+++ egcs-CVS19981231/gcc/invoke.texi	Thu Dec 31 23:05:55 1998
@@ -1340,7 +1340,7 @@ In order to get a warning about an unuse
 specify both @samp{-W} and @samp{-Wunused}.
 
 To suppress this warning for an expression, simply cast it to void.  For
-unused variables and parameters, use the @samp{unused} attribute
+unused variables, parameters and labels, use the @samp{unused} attribute
 (@pxref{Variable Attributes}).
 
 @item -Wuninitialized