Re: [PATCH] PR60092 - lower posix_memalign to make align-info accessible

[Andreas Krebbel <krebbel at linux dot vnet dot ibm dot com>]

On 07/02/14 10:33, Richard Biener wrote:
> + static void
> + lower_builtin_posix_memalign (gimple_stmt_iterator *gsi)
> + {
> +   gimple stmt = gsi_stmt (*gsi);
> +   tree pptr = gimple_call_arg (stmt, 0);
> +   tree align = gimple_call_arg (stmt, 1);
> +   tree ptr = create_tmp_reg (ptr_type_node, NULL);
> +   if (TREE_CODE (pptr) == ADDR_EXPR)
> +     {
> +       tree tem = create_tmp_var (ptr_type_node, NULL);
> +       TREE_ADDRESSABLE (tem) = 1;
> +       gimple_call_set_arg (stmt, 0, build_fold_addr_expr (tem));
> +       stmt = gimple_build_assign (ptr, tem);
> +     }
> +   else
> +     stmt = gimple_build_assign (ptr,
> + 				fold_build2 (MEM_REF, ptr_type_node, pptr,
> + 					     build_int_cst (ptr_type_node, 0)));
> +   gsi_insert_after (gsi, stmt, GSI_NEW_STMT);
> +   stmt = gimple_build_call (builtin_decl_implicit (BUILT_IN_ASSUME_ALIGNED),
> + 			    2, ptr, align);
> +   gimple_call_set_lhs (stmt, ptr);
> +   gsi_insert_after (gsi, stmt, GSI_NEW_STMT);
> +   stmt = gimple_build_assign (fold_build2 (MEM_REF, ptr_type_node, pptr,
> + 					   build_int_cst (ptr_type_node, 0)),
> + 			      ptr);
> +   gsi_insert_after (gsi, stmt, GSI_NEW_STMT);
> + }

Hi,

creating a new var for the output parameter throws away the value already in there.  But this value
must not change when posix_memalign e.g. returns with ENOMEM.  It breaks the glibc posix_memalign
testcase on s390 (somewhat reduced here):

typedef unsigned long size_t;
extern int posix_memalign(void **memptr, size_t alignment, size_t size);
extern void abort(void);
int
main (void)
{
  void *p;
  int ret;

  p = 0;
  ret = posix_memalign (&p, sizeof (void *), -1);
  if (p != 0)
    abort ();
  return 0;
}

.c.170r.expand

main ()
{
  void * D.1395;
  void * D.1394;
  int ret;
  void * p;
  int D.1393;
  void * p.0;
  void * _2;
  void * _3;
  void * p.0_4;
  int _5;

;;   basic block 2, loop depth 0
;;    pred:       ENTRY
  p = 0B;
  ret_1 = posix_memalign (&D.1395, 4, 4294967295);
  _2 = D.1395;
  _3 = __builtin_assume_aligned (_2, 4);
  MEM[(void *)&p] = _3;
  p.0_4 = p;
  if (p.0_4 != 0B)
    goto <bb 3>;
  else
    goto <bb 4>;
;;    succ:       3
;;                4

;;   basic block 3, loop depth 0
;;    pred:       2
  abort ();
;;    succ:

;;   basic block 4, loop depth 0
;;    pred:       2
  _5 = 0;
  p ={v} {CLOBBER};
;;    succ:       5

;;   basic block 5, loop depth 0
;;    pred:       4
<L3>:
  return _5;
;;    succ:       EXIT

}