[Bug c/44828] possible integer wrong code bug

[rguenth at gcc dot gnu dot org]

------- Comment #3 from rguenth at gcc dot gnu dot org  2010-07-06 10:35 -------
The bug is that we have in .original

{
  return si1 * si2;
}

while it should have been

{
  return (char)((unsigned char) si1 * (unsigned char) si2);
}

which is premature optimization by convert_to_integer, short-cutting
the correctly implemented fold of (signed char)((int) si1 * (int) si2)
to the above.

Index: gcc/convert.c
===================================================================
--- gcc/convert.c       (revision 161840)
+++ gcc/convert.c       (working copy)
@@ -774,7 +774,8 @@ convert_to_integer (tree type, tree expr
                        || ((!TYPE_OVERFLOW_WRAPS (TREE_TYPE (arg0))
                             || !TYPE_OVERFLOW_WRAPS (TREE_TYPE (arg1)))
                            && (ex_form == PLUS_EXPR
-                               || ex_form == MINUS_EXPR)))
+                               || ex_form == MINUS_EXPR
+                               || ex_form == MULT_EXPR)))
                      typex = unsigned_type_for (typex);
                    else
                      typex = signed_type_for (typex);

fixes this.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |rguenth at gcc dot gnu dot
                   |dot org                     |org
             Status|UNCONFIRMED                 |ASSIGNED
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2010-07-06 10:35:15
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44828