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* [gcc r12-3429] Avoid full DOM walk in LIM fill_always_executed_in
@ 2021-09-09 9:17 Richard Biener
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From: Richard Biener @ 2021-09-09 9:17 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:6e27bc2b885207d51500b2c42f949ca5073dbe72
commit r12-3429-g6e27bc2b885207d51500b2c42f949ca5073dbe72
Author: Richard Biener <rguenther@suse.de>
Date: Thu Sep 9 10:52:12 2021 +0200
Avoid full DOM walk in LIM fill_always_executed_in
This avoids a full DOM walk via get_loop_body_in_dom_order in the
loop body walk of fill_always_executed_in which is often terminating
the walk of a loop body early by integrating the DOM walk of
get_loop_body_in_dom_order with the actual processing done by
fill_always_executed_in. This trades the fully populated loop
body array with a worklist allocation of the same size and thus
should be a strict improvement over the recursive approach of
get_loop_body_in_dom_order.
2021-09-09 Richard Biener <rguenther@suse.de>
* tree-ssa-loop-im.c (fill_always_executed_in_1): Integrate
DOM walk from get_loop_body_in_dom_order using a worklist
approach.
Diff:
---
gcc/tree-ssa-loop-im.c | 39 +++++++++++++++++++++++++++++++--------
1 file changed, 31 insertions(+), 8 deletions(-)
diff --git a/gcc/tree-ssa-loop-im.c b/gcc/tree-ssa-loop-im.c
index 01f3fc2f7f0..5d6845478e7 100644
--- a/gcc/tree-ssa-loop-im.c
+++ b/gcc/tree-ssa-loop-im.c
@@ -3030,19 +3030,19 @@ do_store_motion (void)
static void
fill_always_executed_in_1 (class loop *loop, sbitmap contains_call)
{
- basic_block bb = NULL, *bbs, last = NULL;
- unsigned i;
+ basic_block bb = NULL, last = NULL;
edge e;
class loop *inn_loop = loop;
if (ALWAYS_EXECUTED_IN (loop->header) == NULL)
{
- bbs = get_loop_body_in_dom_order (loop);
-
- for (i = 0; i < loop->num_nodes; i++)
+ auto_vec<basic_block, 64> worklist;
+ worklist.reserve_exact (loop->num_nodes);
+ worklist.quick_push (loop->header);
+ do
{
edge_iterator ei;
- bb = bbs[i];
+ bb = worklist.pop ();
if (!flow_bb_inside_loop_p (inn_loop, bb))
{
@@ -3083,7 +3083,32 @@ fill_always_executed_in_1 (class loop *loop, sbitmap contains_call)
since it might not be finite. */
inn_loop = bb->loop_father;
}
+
+ /* Walk the body of LOOP sorted by dominance relation. Additionally,
+ if a basic block S dominates the latch, then only blocks dominated
+ by S are after it.
+ This is get_loop_body_in_dom_order using a worklist algorithm and
+ stopping once we are no longer interested in visiting further
+ blocks. */
+ unsigned old_len = worklist.length ();
+ unsigned postpone = 0;
+ for (basic_block son = first_dom_son (CDI_DOMINATORS, bb);
+ son;
+ son = next_dom_son (CDI_DOMINATORS, son))
+ {
+ if (!flow_bb_inside_loop_p (loop, son))
+ continue;
+ if (dominated_by_p (CDI_DOMINATORS, loop->latch, son))
+ postpone = worklist.length ();
+ worklist.quick_push (son);
+ }
+ if (postpone)
+ /* Postponing the block that dominates the latch means
+ processing it last and thus putting it earliest in the
+ worklist. */
+ std::swap (worklist[old_len], worklist[postpone]);
}
+ while (!worklist.is_empty ());
while (1)
{
@@ -3095,8 +3120,6 @@ fill_always_executed_in_1 (class loop *loop, sbitmap contains_call)
break;
last = get_immediate_dominator (CDI_DOMINATORS, last);
}
-
- free (bbs);
}
for (loop = loop->inner; loop; loop = loop->next)
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