[Bug middle-end/48124] [4.4/4.5/4.6/4.7 Regression] likely wrong code bug

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48124

--- Comment #10 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-02-01 
12:48:56 UTC ---
(In reply to comment #9)
> Simpler patch I am going to test.  Let's hope the wreckage adjust_address
> does to the to_rtx MEM (apart from setting its mode) is harmless.
> 
> Index: expr.c
> ===================================================================
> --- expr.c      (revision 183791)
> +++ expr.c      (working copy)
> @@ -4705,6 +4705,21 @@ expand_assignment (tree to, tree from, b
>             to_rtx = adjust_address (to_rtx, mode1, 0);
>           else if (GET_MODE (to_rtx) == VOIDmode)
>             to_rtx = adjust_address (to_rtx, BLKmode, 0);
> +         /* If the alignment of tem is larger than its size and we
> +            are performing a bitfield access limit the mode we use
> +            for the access to make sure we do not access the decl
> +            beyond its end.  See PR48124.  */
> +         else if (GET_MODE (to_rtx) == BLKmode
> +                  && mode1 == VOIDmode
> +                  && DECL_P (tem)
> +                  && TREE_CODE (DECL_SIZE (tem)) == INTEGER_CST
> +                  && TREE_INT_CST_LOW (DECL_SIZE (tem)) % DECL_ALIGN (tem))
> +           {
> +             mode1 = mode_for_size (TREE_INT_CST_LOW (DECL_SIZE (tem))
> +                                    % DECL_ALIGN (tem),
> +                                    MODE_INT, 0);
> +             to_rtx = adjust_address (to_rtx, mode1, 0);
> +           }
>         }
> 
>        if (offset != 0)

Or rather

Index: gcc/expr.c
===================================================================
--- gcc/expr.c  (revision 183791)
+++ gcc/expr.c  (working copy)
@@ -4705,6 +4705,22 @@ expand_assignment (tree to, tree from, b
            to_rtx = adjust_address (to_rtx, mode1, 0);
          else if (GET_MODE (to_rtx) == VOIDmode)
            to_rtx = adjust_address (to_rtx, BLKmode, 0);
+         /* If the alignment of tem is larger than its size and we
+            are performing a bitfield access limit the mode we use
+            for the access to make sure we do not access the decl
+            beyond its end.  See PR48124.  */
+         else if (GET_MODE (to_rtx) == BLKmode
+                  && mode1 == VOIDmode
+                  && DECL_P (tem)
+                  && TREE_CODE (DECL_SIZE (tem)) == INTEGER_CST
+                  && (TREE_INT_CST_LOW (DECL_SIZE (tem))
+                      & (DECL_ALIGN (tem) - 1)) != 0)
+           {
+             unsigned HOST_WIDE_INT mis;
+             mis = TREE_INT_CST_LOW (DECL_SIZE (tem)) & (DECL_ALIGN (tem) -
1);
+             mode1 = mode_for_size (mis & -mis, MODE_INT, 0);
+             to_rtx = adjust_address (to_rtx, mode1, 0);
+           }
        }

       if (offset != 0)