Ping.
On Wed, Nov 09, 2016 at 09:46:55PM +0000, Segher Boessenkool wrote:
> This patch changes spread_components to use a simpler algorithm that
> puts prologue components as early as possible, and epilogue components
> as late as possible. This allows better scheduling, and also saves a
> bit of code size. The blocks that run with some specific component
> enabled after this patch is a strict superset of those that had it
> before the patch.
>
> It does this by finding for every component the basic blocks where that
> component is not needed on some path from the entry block (it reuses
> head_components to store this), and similarly the blocks where the
> component is not needed on some path to the exit block (or the exit can
> not be reached from that block) (stored in tail_components). Blocks
> that then are in neither of those two sets get the component active.
>
> Tested on powerpc64-linux {-m32,-m64}. Is this okay for trunk?
>
>
> Segher
>
>
> 2016-11-09 Segher Boessenkool <seg...@kernel.crashing.org>
>
> * shrink-wrap.c (init_separate_shrink_wrap): Do not clear
> head_components and tail_components.
> (spread_components): New algorithm.
> (emit_common_tails_for_components): Clear head_components and
> tail_components.
> (insert_prologue_epilogue_for_components): Write extra output to the
> dump file for sibcalls and abnormal exits.
>
> ---
> gcc/shrink-wrap.c | 181
> +++++++++++++++++++++++++++++++++++++++++++-----------
> 1 file changed, 146 insertions(+), 35 deletions(-)
>
> diff --git a/gcc/shrink-wrap.c b/gcc/shrink-wrap.c
> index 4395d8a..e480d4d 100644
> --- a/gcc/shrink-wrap.c
> +++ b/gcc/shrink-wrap.c
> @@ -1131,8 +1131,6 @@ init_separate_shrink_wrap (sbitmap components)
> SW (bb)->head_components = sbitmap_alloc (SBITMAP_SIZE (components));
> SW (bb)->tail_components = sbitmap_alloc (SBITMAP_SIZE (components));
> bitmap_clear (SW (bb)->has_components);
> - bitmap_clear (SW (bb)->head_components);
> - bitmap_clear (SW (bb)->tail_components);
> }
> }
>
> @@ -1253,48 +1251,151 @@ place_prologue_for_one_component (unsigned int
> which, basic_block head)
> }
> }
>
> -/* Mark HAS_COMPONENTS for every block dominated by at least one block with
> - HAS_COMPONENTS set for the respective components, starting at HEAD. */
> +/* Set HAS_COMPONENTS in every block to the maximum it can be set to without
> + setting it on any path from entry to exit where it was not already set
> + somewhere (or, for blocks that have no path to the exit, consider only
> + paths from the entry to the block itself). */
> static void
> -spread_components (basic_block head)
> +spread_components (sbitmap components)
> {
> - basic_block bb = head;
> - bool first_visit = true;
> - /* This keeps a tally of all components active. */
> - sbitmap components = SW (head)->has_components;
> + basic_block entry_block = ENTRY_BLOCK_PTR_FOR_FN (cfun);
> + basic_block exit_block = EXIT_BLOCK_PTR_FOR_FN (cfun);
>
> - for (;;)
> + /* A stack of all blocks left to consider, and a bitmap of all blocks
> + on that stack. */
> + vec<basic_block> todo;
> + todo.create (n_basic_blocks_for_fn (cfun));
> + bitmap seen = BITMAP_ALLOC (NULL);
> +
> + sbitmap old = sbitmap_alloc (SBITMAP_SIZE (components));
> +
> + /* Find for every block the components that are *not* needed on some path
> + from the entry to that block. Do this with a flood fill from the entry
> + block. Every block can be visited at most as often as the number of
> + components (plus one), and usually much less often. */
> +
> + if (dump_file)
> + fprintf (dump_file, "Spreading down...\n");
> +
> + basic_block bb;
> + FOR_ALL_BB_FN (bb, cfun)
> + bitmap_clear (SW (bb)->head_components);
> +
> + bitmap_copy (SW (entry_block)->head_components, components);
> +
> + edge e;
> + edge_iterator ei;
> +
> + todo.quick_push (single_succ (entry_block));
> + bitmap_set_bit (seen, single_succ (entry_block)->index);
> + while (!todo.is_empty ())
> {
> - if (first_visit)
> - {
> - bitmap_ior (SW (bb)->has_components, SW (bb)->has_components,
> - components);
> + bb = todo.pop ();
>
> - if (first_dom_son (CDI_DOMINATORS, bb))
> - {
> - components = SW (bb)->has_components;
> - bb = first_dom_son (CDI_DOMINATORS, bb);
> - continue;
> - }
> - }
> + bitmap_copy (old, SW (bb)->head_components);
>
> - components = SW (bb)->has_components;
> + FOR_EACH_EDGE (e, ei, bb->preds)
> + bitmap_ior (SW (bb)->head_components, SW (bb)->head_components,
> + SW (e->src)->head_components);
>
> - if (next_dom_son (CDI_DOMINATORS, bb))
> + bitmap_and_compl (SW (bb)->head_components, SW (bb)->head_components,
> + SW (bb)->has_components);
> +
> + if (!bitmap_equal_p (old, SW (bb)->head_components))
> + FOR_EACH_EDGE (e, ei, bb->succs)
> + if (bitmap_set_bit (seen, e->dest->index))
> + todo.quick_push (e->dest);
> +
> + bitmap_clear_bit (seen, bb->index);
> + }
> +
> + /* Find for every block the components that are *not* needed on some
> reverse
> + path from the exit to that block. */
> +
> + if (dump_file)
> + fprintf (dump_file, "Spreading up...\n");
> +
> + /* First, mark all blocks not reachable from the exit block as not needing
> + any component on any path to the exit. Mark everything, and then clear
> + again by a flood fill. */
> +
> + FOR_ALL_BB_FN (bb, cfun)
> + bitmap_copy (SW (bb)->tail_components, components);
> +
> + FOR_EACH_EDGE (e, ei, exit_block->preds)
> + {
> + todo.quick_push (e->src);
> + bitmap_set_bit (seen, e->src->index);
> + }
> +
> + while (!todo.is_empty ())
> + {
> + bb = todo.pop ();
> +
> + if (!bitmap_empty_p (SW (bb)->tail_components))
> + FOR_EACH_EDGE (e, ei, bb->preds)
> + if (bitmap_set_bit (seen, e->src->index))
> + todo.quick_push (e->src);
> +
> + bitmap_clear (SW (bb)->tail_components);
> +
> + bitmap_clear_bit (seen, bb->index);
> + }
> +
> + /* And then, flood fill backwards to find for every block the components
> + not needed on some path to the exit. */
> +
> + bitmap_copy (SW (exit_block)->tail_components, components);
> +
> + FOR_EACH_EDGE (e, ei, exit_block->preds)
> + {
> + todo.quick_push (e->src);
> + bitmap_set_bit (seen, e->src->index);
> + }
> +
> + while (!todo.is_empty ())
> + {
> + bb = todo.pop ();
> +
> + bitmap_copy (old, SW (bb)->tail_components);
> +
> + FOR_EACH_EDGE (e, ei, bb->succs)
> + bitmap_ior (SW (bb)->tail_components, SW (bb)->tail_components,
> + SW (e->dest)->tail_components);
> +
> + bitmap_and_compl (SW (bb)->tail_components, SW (bb)->tail_components,
> + SW (bb)->has_components);
> +
> + if (!bitmap_equal_p (old, SW (bb)->tail_components))
> + FOR_EACH_EDGE (e, ei, bb->preds)
> + if (bitmap_set_bit (seen, e->src->index))
> + todo.quick_push (e->src);
> +
> + bitmap_clear_bit (seen, bb->index);
> + }
> +
> + /* Finally, mark everything not not needed both forwards and backwards. */
> +
> + FOR_EACH_BB_FN (bb, cfun)
> + {
> + bitmap_and (SW (bb)->head_components, SW (bb)->head_components,
> + SW (bb)->tail_components);
> + bitmap_and_compl (SW (bb)->has_components, components,
> + SW (bb)->head_components);
> + }
> +
> + FOR_ALL_BB_FN (bb, cfun)
> + {
> + if (dump_file)
> {
> - bb = next_dom_son (CDI_DOMINATORS, bb);
> - basic_block parent = get_immediate_dominator (CDI_DOMINATORS, bb);
> - components = SW (parent)->has_components;
> - first_visit = true;
> - }
> - else
> - {
> - if (bb == head)
> - return;
> - bb = get_immediate_dominator (CDI_DOMINATORS, bb);
> - first_visit = false;
> + fprintf (dump_file, "bb %d components:", bb->index);
> + dump_components ("has", SW (bb)->has_components);
> + fprintf (dump_file, "\n");
> }
> }
> +
> + sbitmap_free (old);
> + BITMAP_FREE (seen);
> }
>
> /* If we cannot handle placing some component's prologues or epilogues where
> @@ -1384,6 +1485,9 @@ emit_common_heads_for_components (sbitmap components)
> sbitmap tmp = sbitmap_alloc (SBITMAP_SIZE (components));
>
> basic_block bb;
> + FOR_ALL_BB_FN (bb, cfun)
> + bitmap_clear (SW (bb)->head_components);
> +
> FOR_EACH_BB_FN (bb, cfun)
> {
> /* Find which prologue resp. epilogue components are needed for all
> @@ -1470,6 +1574,9 @@ emit_common_tails_for_components (sbitmap components)
> sbitmap tmp = sbitmap_alloc (SBITMAP_SIZE (components));
>
> basic_block bb;
> + FOR_ALL_BB_FN (bb, cfun)
> + bitmap_clear (SW (bb)->tail_components);
> +
> FOR_EACH_BB_FN (bb, cfun)
> {
> /* Find which prologue resp. epilogue components are needed for all
> @@ -1608,6 +1715,10 @@ insert_prologue_epilogue_for_components (sbitmap
> components)
> e->dest->index);
> dump_components ("epi", epi);
> dump_components ("pro", pro);
> + if (e->flags & EDGE_SIBCALL)
> + fprintf (dump_file, " (SIBCALL)");
> + else if (e->flags & EDGE_ABNORMAL)
> + fprintf (dump_file, " (ABNORMAL)");
> fprintf (dump_file, "\n");
> }
>
> @@ -1697,7 +1808,7 @@ try_shrink_wrapping_separate (basic_block first_bb)
> EXECUTE_IF_SET_IN_BITMAP (components, 0, j, sbi)
> place_prologue_for_one_component (j, first_bb);
>
> - spread_components (first_bb);
> + spread_components (components);
>
> disqualify_problematic_components (components);
>
> --
> 1.9.3
