Re: [PATCH] Fix handle_ptr_arith

["Daniel Berlin" <dberlin at dberlin dot org>]

Looks good to me

On Tue, Jun 3, 2008 at 10:44 AM, Richard Guenther <rguenther@suse.de> wrote:
>
> This fixes handle_ptr_arith to fall back to constraints from integer
> if a non-positive offset is added to a pointer.
>
> For the testcase
>
> int foo(int i)
> {
>  int *p = &i + 1;
>  int *q = p - 1;
>  return *q;
> }
>
> we now correctly say p points to { } and q points to { ANYTHING }, while
> previously q pointed to { }.
>
> Bootstrapped and tested on x86_64-unknown-linux-gnu, ok?
>
> Thanks,
> Richard.
>
> 2008-06-03  Richard Guenther  <rguenther@suse.de>
>
>        * tree-ssa-structalias.c (handle_ptr_arith): Correctly handle
>        negative or non-representable offsets.
>
> Index: gcc/tree-ssa-structalias.c
> ===================================================================
> *** gcc/tree-ssa-structalias.c  (revision 136315)
> --- gcc/tree-ssa-structalias.c  (working copy)
> *************** handle_ptr_arith (VEC (ce_s, heap) *lhsc
> *** 3531,3538 ****
>    unsigned int i = 0;
>    unsigned int j = 0;
>    VEC (ce_s, heap) *temp = NULL;
> !   unsigned int rhsoffset = 0;
> !   bool unknown_addend = false;
>
>    if (TREE_CODE (expr) != POINTER_PLUS_EXPR)
>      return false;
> --- 3531,3537 ----
>    unsigned int i = 0;
>    unsigned int j = 0;
>    VEC (ce_s, heap) *temp = NULL;
> !   unsigned HOST_WIDE_INT rhsunitoffset, rhsoffset;
>
>    if (TREE_CODE (expr) != POINTER_PLUS_EXPR)
>      return false;
> *************** handle_ptr_arith (VEC (ce_s, heap) *lhsc
> *** 3541,3553 ****
>    op1 = TREE_OPERAND (expr, 1);
>    gcc_assert (POINTER_TYPE_P (TREE_TYPE (op0)));
>
> !   get_constraint_for (op0, &temp);
>
> !   /* Handle non-constants by making constraints from integer.  */
> !   if (TREE_CODE (op1) == INTEGER_CST)
> !     rhsoffset = TREE_INT_CST_LOW (op1) * BITS_PER_UNIT;
> !   else
> !     unknown_addend = true;
>
>    for (i = 0; VEC_iterate (ce_s, lhsc, i, c); i++)
>      for (j = 0; VEC_iterate (ce_s, temp, j, c2); j++)
> --- 3540,3557 ----
>    op1 = TREE_OPERAND (expr, 1);
>    gcc_assert (POINTER_TYPE_P (TREE_TYPE (op0)));
>
> !   /* If the offset is not a non-negative integer constant that fits
> !      in a HOST_WIDE_INT, we cannot handle it here.  */
> !   if (!host_integerp (op1, 1))
> !     return false;
>
> !   /* Make sure the bit-offset also fits.  */
> !   rhsunitoffset = TREE_INT_CST_LOW (op1);
> !   rhsoffset = rhsunitoffset * BITS_PER_UNIT;
> !   if (rhsunitoffset != rhsoffset / BITS_PER_UNIT)
> !     return false;
> !
> !   get_constraint_for (op0, &temp);
>
>    for (i = 0; VEC_iterate (ce_s, lhsc, i, c); i++)
>      for (j = 0; VEC_iterate (ce_s, temp, j, c2); j++)
> *************** handle_ptr_arith (VEC (ce_s, heap) *lhsc
> *** 3564,3593 ****
>            c2->var = temp->id;
>            c2->offset = 0;
>          }
> -       else if (unknown_addend)
> -         {
> -           /* Can't handle *a + integer where integer is unknown.  */
> -           if (c2->type != SCALAR)
> -             {
> -               struct constraint_expr intc;
> -               intc.var = integer_id;
> -               intc.offset = 0;
> -               intc.type = SCALAR;
> -               process_constraint (new_constraint (*c, intc));
> -             }
> -           else
> -             {
> -               /* We known it lives somewhere within c2->var.  */
> -               varinfo_t tmp = get_varinfo (c2->var);
> -               for (; tmp; tmp = tmp->next)
> -                 {
> -                   struct constraint_expr tmpc = *c2;
> -                   c2->var = tmp->id;
> -                   c2->offset = 0;
> -                   process_constraint (new_constraint (*c, tmpc));
> -                 }
> -             }
> -         }
>        else
>          c2->offset = rhsoffset;
>        process_constraint (new_constraint (*c, *c2));
> --- 3568,3573 ----
>