On Mon, Mar 11, 2013 at 10:52 AM, Richard Biener wrote:
> Given
>
> + well. Return true if all is well, false if something happened
> + that is fatal to the rest of the LIM pass. */
>
> -static void
> +static bool
> gather_mem_refs_stmt (struct loop *loop, gimple stmt)
>
> and
>
> FOR_EACH_BB (bb)
> {
> ...
> + for (bsi = gsi_start_bb (bb);
> + !gsi_end_p (bsi) && all_ok;
> + gsi_next (&bsi))
> + all_ok = gather_mem_refs_stmt (loop, gsi_stmt (bsi));
> +
> + if (! all_ok)
> + bitmap_set_bit (loops_with_too_many_memrefs, loop->num);
> + }
> +
> + /* Propagate the information about loops with too many memory
> + references up the loop hierarchy. */
> + FOR_EACH_LOOP (li, loop, LI_FROM_INNERMOST)
> + {
> + struct loop *outer = loop_outer (loop);
> + if (outer == current_loops->tree_root
> + || ! bitmap_bit_p (loops_with_too_many_memrefs, loop->num))
> + continue;
> + bitmap_set_bit (loops_with_too_many_memrefs, outer->num);
> }
>
> I don't see how this propagation works correctly as you start to mark
> BBs as not-ok starting from a "random" basic-block in the loop tree.
Not at all. The function looks like this:
static void
gather_mem_refs_in_loops (bitmap loops_with_too_many_memrefs)
{
FOR_EACH_BB (bb)
{
for each gimple statement
all_ok = gather_mem_refs_stmt (loop, gsi_stmt (bsi));
if (! all_ok)
bitmap_set_bit (loops_with_too_many_memrefs, loop->num);
}
/* Propagate the information about loops with too many memory
references up the loop hierarchy. */
FOR_EACH_LOOP (li, loop, LI_FROM_INNERMOST)
{
struct loop *outer = loop_outer (loop);
if (outer == current_loops->tree_root
|| ! bitmap_bit_p (loops_with_too_many_memrefs, loop->num))
continue;
bitmap_set_bit (loops_with_too_many_memrefs, outer->num);
}
/* Propagate the information about accessed memory references up
the loop hierarchy. */
FOR_EACH_LOOP (li, loop, LI_FROM_INNERMOST)
/* Propagate stuff */
}
So all basic blocks are visited first.
Note it is also like this without my patch.
> You of course also end up disqualifying very small loops completely
> if they happen to be analyzed after a very big one you disqualify.
> Of course that's partly because memory_accesses contains all
> memory accesses in the function - so I think rather than limiting
> on length of memory_accesses you want to limit on the length of
> memory_accesses.refs_in_loop (well, on memory_accesses.all_refs_in_loop).
Right, I guess the limit should be per-loop, and it's "global" now.
> And you want the initial walk over all BBs to instead walk on BBs
> FOR_EACH_LOOP and LI_FROM_INNERMOST (you can then do the
> propagation to fill all_refs_in_loop there, too).
That is already what happens.
> At this point this should be stage1 material, eventually backported for 4.8.1.
Obviously.
> And yes, aside from the above the rest of the patch looks good to me
> (move loops_with_too_many_memrefs into the memory_accesses struct?)
That's a good idea.
I'll come back with an updated patch for trunk GCC 4.9.
Ciao!
Steven
