Re: [PATCH] Fix PR44555

[Andrew Pinski <pinskia at gmail dot com>]

Sent from my iPhone

On Jun 16, 2010, at 4:40 AM, Richard Guenther <rguenther@suse.de> wrote:

> This fixes PR44555 where the C frontend thinks that &a->b
> evaluates to non-NULL even when b is at offset zero.

How is that wrong? a->b is a deferencing of a even inside an address  
expression. According to the c (and the c++) standard.




>  The
> patch simply removes that premature optimization from the
> frontend and leaves it to fold where it is properly
> implemented (also with the correct targetm.binds_local_p
> checks, as opposed to the bogus decl_with_nonnull_addr_p
> in c-common.c).
>
> Bootstrap & regtest in progress, ok if that succeeds?
>
> Thanks,
> Richard.
>
> 2010-06-16  Richard Guenther  <rguenther@suse.de>
>
>    PR c/44555
>    * c-common.c (c_common_truthvalue_conversion): Remove
>    premature and wrong optimization concering ADDR_EXPRs.
>
>    * gcc.c-torture/execute/pr44555.c: New testcase.
>
> Index: gcc/c-family/c-common.c
> ===================================================================
> *** gcc/c-family/c-common.c    (revision 160826)
> --- gcc/c-family/c-common.c    (working copy)
> *************** c_common_truthvalue_conversion (location
> *** 3825,3847 ****
>              inner);
>          return truthvalue_true_node;
>        }
> !
> !    /* If we still have a decl, it is possible for its address to
> !       be NULL, so we cannot optimize.  */
> !    if (DECL_P (inner))
> !      {
> !        gcc_assert (DECL_WEAK (inner));
> !        break;
> !      }
> !
> !    if (TREE_SIDE_EFFECTS (inner))
> !      {
> !        expr = build2 (COMPOUND_EXPR, truthvalue_type_node,
> !               inner, truthvalue_true_node);
> !        goto ret;
> !      }
> !    else
> !      return truthvalue_true_node;
>        }
>
>      case COMPLEX_EXPR:
> --- 3825,3831 ----
>              inner);
>          return truthvalue_true_node;
>        }
> !    break;
>        }
>
>      case COMPLEX_EXPR:
> Index: gcc/testsuite/gcc.c-torture/execute/pr44555.c
> ===================================================================
> *** gcc/testsuite/gcc.c-torture/execute/pr44555.c    (revision 0)
> --- gcc/testsuite/gcc.c-torture/execute/pr44555.c    (revision 0)
> ***************
> *** 0 ****
> --- 1,16 ----
> + struct a {
> +     char b[100];
> + };
> + int foo(struct a *a)
> + {
> +   if (&a->b)
> +     return 1;
> +   return 0;
> + }
> + extern void abort (void);
> + int main()
> + {
> +   if (foo((struct a *)0) != 0)
> +     abort ();
> +   return 0;
> + }