[Bug middle-end/39954] [4.5 Regression] Revision 146817 caused unaligned access in gcc.dg/torture/pr26565.c

["rguenth at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #29 from rguenth at gcc dot gnu dot org  2010-01-18 11:43 -------
(In reply to comment #28)
> Btw, get_pointer_alignment should get passed an access type to put it into
> context.  For alignment of say INDIRECT_REFs it would be the pointed-to type
> but for function arguments in general it needs to be 'char' if you don't know
> anything about the kind of the accesses the function does.  That would be
> the default/fallback align get_pointer_alignment has to assume.

Which, if you look at all current callers, boils down to effectively

Index: gcc/builtins.c
===================================================================
--- gcc/builtins.c      (revision 156006)
+++ gcc/builtins.c      (working copy)
@@ -369,8 +369,7 @@ get_pointer_alignment (tree exp, unsigne
   if (!POINTER_TYPE_P (TREE_TYPE (exp)))
     return 0;

-  align = TYPE_ALIGN (TREE_TYPE (TREE_TYPE (exp)));
-  align = MIN (align, max_align);
+  align = BITS_PER_UNIT;

   while (1)
     {
@@ -380,9 +379,6 @@ get_pointer_alignment (tree exp, unsigne
          exp = TREE_OPERAND (exp, 0);
          if (! POINTER_TYPE_P (TREE_TYPE (exp)))
            return align;
-
-         inner = TYPE_ALIGN (TREE_TYPE (TREE_TYPE (exp)));
-         align = MIN (inner, max_align);
          break;

        case POINTER_PLUS_EXPR:


which of course will regress generated code quite a bit (even though it's
correct).  We might be able to recover some bits by walking SSA defs
here but we'll still lose when reaching function arguments.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39954