New option -Wstrict-aliasing=2.

* alias.c (alias_sets_might_conflict_p): New.
	* c-typeck.c (build_c_cast): Call it if warn_strict_aliasing > 1.
	* common.opt (Wstrict-aliasing=): New.
	* flags.h (warn_strict_aliasing): Change type to int.
	* opts.c (warn_strict_aliasing): Change type to int.
	(common_handle_option): Handle OPT_Wstrict_aliasing_.
	* tree.h (alias_sets_might_conflict_p): Declare it.
	* doc/invoke.tex (-Wstrict-aliasing=2): Document it.

From-SVN: r79222

gcc/ChangeLog

@@ -1,3 +1,14 @@
+2004-03-09  James E Wilson  <wilson@specifixinc.com>
+
+	* alias.c (alias_sets_might_conflict_p): New.
+	* c-typeck.c (build_c_cast): Call it if warn_strict_aliasing > 1.
+	* common.opt (Wstrict-aliasing=): New.
+	* flags.h (warn_strict_aliasing): Change type to int.
+	* opts.c (warn_strict_aliasing): Change type to int.
+	(common_handle_option): Handle OPT_Wstrict_aliasing_.
+	* tree.h (alias_sets_might_conflict_p): Declare it.
+	* doc/invoke.tex (-Wstrict-aliasing=2): Document it.
+
 2004-03-10  Roman Zippel  <zippel@linux-m68k.org>
 
 	PR bootstrap/12371

gcc/alias.c

@@ -290,6 +290,19 @@ alias_sets_conflict_p (HOST_WIDE_INT set1, HOST_WIDE_INT set2)
      child of the other.  Therefore, they cannot alias.  */
   return 0;
 }
+
+/* Return 1 if the two specified alias sets might conflict, or if any subtype
+   of these alias sets might conflict.  */
+
+int
+alias_sets_might_conflict_p (HOST_WIDE_INT set1, HOST_WIDE_INT set2)
+{
+  if (set1 == 0 || set2 == 0 || set1 == set2)
+    return 1;
+
+  return 0;
+}
+
 
 /* Return 1 if TYPE is a RECORD_TYPE, UNION_TYPE, or QUAL_UNION_TYPE and has
    has any readonly fields.  If any of the fields have types that

gcc/c-typeck.c

@@ -3027,10 +3027,17 @@ build_c_cast (tree type, tree expr)
 	     if the cast breaks type based aliasing.  */
 	  if (!COMPLETE_TYPE_P (TREE_TYPE (type)))
 	    warning ("type-punning to incomplete type might break strict-aliasing rules");
-	  else if (!alias_sets_conflict_p
-		   (get_alias_set (TREE_TYPE (TREE_OPERAND (expr, 0))),
-		    get_alias_set (TREE_TYPE (type))))
-	    warning ("dereferencing type-punned pointer will break strict-aliasing rules");
+	  else
+	    {
+	      HOST_WIDE_INT set1 = get_alias_set (TREE_TYPE (TREE_OPERAND (expr, 0)));
+	      HOST_WIDE_INT set2 = get_alias_set (TREE_TYPE (type));
+
+	      if (!alias_sets_conflict_p (set1, set2))
+		warning ("dereferencing type-punned pointer will break strict-aliasing rules");
+	      else if (warn_strict_aliasing > 1
+		       && !alias_sets_might_conflict_p (set1, set2))
+		warning ("dereferencing type-punned pointer might break strict-aliasing rules");
+	    }
 	}
 
       /* If pedantic, warn for conversions between function and object

gcc/common.opt

@@ -104,6 +104,10 @@ Wstrict-aliasing
 Common
 Warn about code which might break strict aliasing rules
 
+Wstrict-aliasing=
+Common Joined UInteger
+Warn about code which might break strict aliasing rules
+
 Wswitch
 Common
 Warn about enumerated switches, with no default, missing a case

gcc/doc/invoke.texi

@@ -226,7 +226,7 @@ in the following sections.
 -Wno-multichar  -Wnonnull  -Wpacked  -Wpadded @gol
 -Wparentheses  -Wpointer-arith  -Wredundant-decls @gol
 -Wreturn-type  -Wsequence-point  -Wshadow @gol
--Wsign-compare  -Wstrict-aliasing @gol
+-Wsign-compare  -Wstrict-aliasing -Wstrict-aliasing=2 @gol
 -Wswitch  -Wswitch-default  -Wswitch-enum @gol
 -Wsystem-headers  -Wtrigraphs  -Wundef  -Wuninitialized @gol
 -Wunknown-pragmas  -Wunreachable-code @gol
@@ -2449,6 +2449,13 @@ compiler is using for optimization. The warning does not catch all
 cases, but does attempt to catch the more common pitfalls. It is
 included in @option{-Wall}.
 
+@item -Wstrict-aliasing=2
+@opindex Wstrict-aliasing=2
+This option is only active when @option{-fstrict-aliasing} is active.
+It warns about all code which might break the strict aliasing rules that the
+compiler is using for optimization.  This warning catches all cases, but
+it will also give a warning for some ambiguous cases that are safe.
+
 @item -Wall
 @opindex Wall
 All of the above @samp{-W} options combined.  This enables all the

gcc/flags.h

@@ -184,7 +184,7 @@ extern bool warn_deprecated_decl;
 /* Nonzero means warn about constructs which might not be strict
    aliasing safe.  */
 
-extern bool warn_strict_aliasing;
+extern int warn_strict_aliasing;
 
 /* Nonzero if generating code to do profiling.  */
 

gcc/opts.c

@@ -100,7 +100,7 @@ bool warn_shadow;
 
 /* Nonzero means warn about constructs which might not be
    strict-aliasing safe.  */
-bool warn_strict_aliasing;
+int warn_strict_aliasing;
 
 /* True to warn if a switch on an enum, that does not have a default
    case, fails to have a case for every enum value.  */
@@ -747,6 +747,7 @@ common_handle_option (size_t scode, const char *arg,
       break;
 
     case OPT_Wstrict_aliasing:
+    case OPT_Wstrict_aliasing_:
       warn_strict_aliasing = value;
       break;
 

gcc/tree.h

@@ -2887,6 +2887,7 @@ extern tree strip_float_extensions (tree);
 extern void record_component_aliases (tree);
 extern HOST_WIDE_INT get_alias_set (tree);
 extern int alias_sets_conflict_p (HOST_WIDE_INT, HOST_WIDE_INT);
+extern int alias_sets_might_conflict_p (HOST_WIDE_INT, HOST_WIDE_INT);
 extern int readonly_fields_p (tree);
 extern int objects_must_conflict_p (tree, tree);