On Fri, Jul 11, 2014 at 6:41 PM, Gaius Mulley
<gaius.mul...@southwales.ac.uk> wrote:
>
>
> Hello,
>
> I've been looking through tree-ssa-loop-im.c (while hunting down a bug
> in the modula-2 front end) and found a curiosity in
> gcc/tree-ssa-loop-im.c.
>
> It seems that there is dead code in function determine_max_movement
> as mem_ref_in_stmt can never return NULL.
?
static mem_ref_p
mem_ref_in_stmt (gimple stmt)
{
bool store;
tree *mem = simple_mem_ref_in_stmt (stmt, &store);
hashval_t hash;
mem_ref_p ref;
if (!mem)
return NULL;
and simple_mem_ref_in_stmt _can_ return NULL.
Richard.
>
> static mem_ref_p
> mem_ref_in_stmt (gimple stmt)
> {
> ...
>
> gcc_assert (ref != NULL);
> return ref;
> }
>
> so the patch below could logically be applied as the else statement is
> currently unreachable.
>
>
>
> --- tree-ssa-loop-im.c.orig 2014-07-11 16:54:41.000000000 +0100
> +++ tree-ssa-loop-im.c 2014-07-11 16:55:38.000000000 +0100
> @@ -798,21 +798,11 @@
> {
> mem_ref_p ref = mem_ref_in_stmt (stmt);
>
> - if (ref)
> - {
> - lim_data->max_loop
> - = outermost_indep_loop (lim_data->max_loop, loop, ref);
> - if (!lim_data->max_loop)
> - return false;
> - }
> - else
> - {
> - if ((val = gimple_vuse (stmt)) != NULL_TREE)
> - {
> - if (!add_dependency (val, lim_data, loop, false))
> - return false;
> - }
> - }
> + gcc_assert (ref != NULL);
> + lim_data->max_loop
> + = outermost_indep_loop (lim_data->max_loop, loop, ref);
> + if (!lim_data->max_loop)
> + return false;
> }
>
> lim_data->cost += stmt_cost (stmt);
>
>
> However my question is whether the assert in mem_ref_in_stmt is correct?
> Since the author of determine_max_movement must have thought ref could
> be NULL.
>
> Anyhow, it seems that either the above patch should be applied or the
> 'gcc_assert (ref != NULL);' from mem_ref_p should be removed.
>
> regards,
> Gaius
