PATCH: PR middle-end/47383: ivopts miscompiles Pmode != ptr_mode

[Richard Guenther]

On Wed, Feb 9, 2011 at 12:08 AM, H.J. Lu <hongjiu.lu@intel.com> wrote:
> Hi,
>
> tree-ssa-loop-ivopts.c has
>
> ---
> /* Returns variant of TYPE that can be used as base for different uses.
>   We return unsigned type with the same precision, which avoids problems
>   with overflows.  */
>
> static tree
> generic_type_for (tree type)
> {
>  if (POINTER_TYPE_P (type))
>    return unsigned_type_for (type);
>
>  if (TYPE_UNSIGNED (type))
>    return type;
>
>  return unsigned_type_for (type);
> }
> ---
>
> It converts negative step to unsigned type with the same precision.
> It doesn't work when Pmode != ptr_mode.  This patch disables it.
> OK for trunk in stage 1?

This does not look correct.  It rather sounds you are expanding
TARGET_MEM_REFs the wrong way - the address computed by
it is supposed to be calculated in ptr_mode and only the final
result extended to Pmode.

Richard.

> Thanks.
>
>
> H.J.
> ---
> commit 9e7f4aa92d09f7ae75086c52f0c5fa66257da4ca
> Author: H.J. Lu <hjl.tools@gmail.com>
> Date:   Tue Feb 8 14:58:19 2011 -0800
>
>    Disable bivs when step is negative for Pmode != ptr_mode.
>
> diff --git a/gcc/ChangeLog.x32 b/gcc/ChangeLog.x32
> index 41bfe18..e7c20bf 100644
> --- a/gcc/ChangeLog.x32
> +++ b/gcc/ChangeLog.x32
> @@ -1,3 +1,9 @@
> +2011-02-08  H.J. Lu  <hongjiu.lu@intel.com>
> +
> +       PR middle-end/47383
> +       * tree-ssa-loop-ivopts.c (find_bivs): Disabled when step is
> +       negative for Pmode != ptr_mode.
> +
>  2011-01-29  H.J. Lu  <hongjiu.lu@intel.com>
>
>        PR target/47537
> diff --git a/gcc/testsuite/ChangeLog.x32 b/gcc/testsuite/ChangeLog.x32
> index 8759881..f87c9f9 100644
> --- a/gcc/testsuite/ChangeLog.x32
> +++ b/gcc/testsuite/ChangeLog.x32
> @@ -1,3 +1,8 @@
> +2011-02-08  H.J. Lu  <hongjiu.lu@intel.com>
> +
> +       PR middle-end/47383
> +       * gcc.dg/torture/pr47383.c: New.
> +
>  2011-01-27  H.J. Lu  <hongjiu.lu@intel.com>
>
>        PR rtl-optimization/47502
> diff --git a/gcc/testsuite/gcc.dg/torture/pr47383.c b/gcc/testsuite/gcc.dg/torture/pr47383.c
> new file mode 100644
> index 0000000..ae8d670
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/torture/pr47383.c
> @@ -0,0 +1,30 @@
> +/* { dg-do run } */
> +
> +static int heap[2*(256 +1+29)+1];
> +static int heap_len;
> +static int heap_max;
> +void
> +__attribute__ ((noinline))
> +foo (int elems)
> +{
> +  int n, m;
> +  int max_code = -1;
> +  int node = elems;
> +  heap_len = 0, heap_max = (2*(256 +1+29)+1);
> +  for (n = 0; n < elems; n++)
> +    heap[++heap_len] = max_code = n;
> +  do {
> +    n = heap[1];
> +    heap[1] = heap[heap_len--];
> +    m = heap[1];
> +    heap[--heap_max] = n;
> +    heap[--heap_max] = m;
> +  } while (heap_len >= 2);
> +}
> +
> +int
> +main ()
> +{
> +  foo (286);
> +  return 0;
> +}
> diff --git a/gcc/tree-ssa-loop-ivopts.c b/gcc/tree-ssa-loop-ivopts.c
> index 479b46f..8427bb5 100644
> --- a/gcc/tree-ssa-loop-ivopts.c
> +++ b/gcc/tree-ssa-loop-ivopts.c
> @@ -1026,6 +1026,15 @@ find_bivs (struct ivopts_data *data)
>       base = fold_convert (type, base);
>       if (step)
>        {
> +         /* FIXME: add_candidate_1 calls generic_type_for to cast STEP
> +            to unsigned type with the same precision when BASE isn't
> +            NULL.  It leads to many problems when STEP is negative and
> +            Pmode != ptr_mode.  Disable it for now.  */
> +         if (base
> +             && Pmode != ptr_mode
> +             && !tree_expr_nonnegative_p (step))
> +           continue;
> +
>          if (POINTER_TYPE_P (type))
>            step = fold_convert (sizetype, step);
>          else
>