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Optimize DJ spanning tree back-edge check

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Instead of walking the DJ spanning tree upwards, record entry and
exit times during the DFS and use these to determine whether CJ
edges are sp-back edges.
This commit is contained in:
Nikita Popov
2017-03-16 17:02:11 +01:00
parent 6633e8492e
commit f1f68b60f5
1 changed files with 19 additions and 21 deletions
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ext/opcache/Optimizer/zend_cfg.c
+19 -21
View File
@@ -765,9 +765,9 @@ static void swap_blocks(block_info *a, block_info *b) {
int zend_cfg_identify_loops(const zend_op_array *op_array, zend_cfg *cfg, uint32_t *flags) /* {{{ */
{
int i, j, k, n;
int depth;
int depth, time;
zend_basic_block *blocks = cfg->blocks;
int *dj_spanning_tree;
int *entry_times, *exit_times;
zend_worklist work;
int flag = ZEND_FUNC_NO_LOOPS;
block_info *sorted_blocks;
@@ -776,19 +776,24 @@ int zend_cfg_identify_loops(const zend_op_array *op_array, zend_cfg *cfg, uint32
ALLOCA_FLAG(sorted_blocks_use_heap)
ZEND_WORKLIST_ALLOCA(&work, cfg->blocks_count, list_use_heap);
dj_spanning_tree = do_alloca(sizeof(int) * cfg->blocks_count, tree_use_heap);
for (i = 0; i < cfg->blocks_count; i++) {
dj_spanning_tree[i] = -1;
}
/* We don't materialize the DJ spanning tree explicitly, as we are only interested in ancestor
* querties. These are implemented by checking entry/exit times of the DFS search. */
entry_times = do_alloca(2 * sizeof(int) * cfg->blocks_count, tree_use_heap);
exit_times = entry_times + cfg->blocks_count;
memset(entry_times, -1, 2 * sizeof(int) * cfg->blocks_count);
zend_worklist_push(&work, 0);
time = 0;
while (zend_worklist_len(&work)) {
next:
i = zend_worklist_peek(&work);
if (entry_times[i] == -1) {
entry_times[i] = time++;
}
/* Visit blocks immediately dominated by i. */
for (j = blocks[i].children; j >= 0; j = blocks[j].next_child) {
if (zend_worklist_push(&work, j)) {
dj_spanning_tree[j] = i;
goto next;
}
}
@@ -800,10 +805,10 @@ int zend_cfg_identify_loops(const zend_op_array *op_array, zend_cfg *cfg, uint32
} else if (blocks[succ].idom == i) {
continue;
} else if (zend_worklist_push(&work, succ)) {
dj_spanning_tree[succ] = i;
goto next;
}
}
exit_times[i] = time++;
zend_worklist_pop(&work);
}
@@ -840,18 +845,11 @@ int zend_cfg_identify_loops(const zend_op_array *op_array, zend_cfg *cfg, uint32
zend_worklist_push(&work, pred);
} else {
/* Otherwise it's a cross-join edge. See if it's a branch
to an ancestor on the dominator spanning tree. */
int dj_parent = pred;
while (dj_parent >= 0) {
if (dj_parent == i) {
/* An sp-back edge: mark as irreducible. */
blocks[i].flags |= ZEND_BB_IRREDUCIBLE_LOOP;
flag |= ZEND_FUNC_IRREDUCIBLE;
flag &= ~ZEND_FUNC_NO_LOOPS;
break;
} else {
dj_parent = dj_spanning_tree[dj_parent];
}
to an ancestor on the DJ spanning tree. */
if (entry_times[pred] > entry_times[i] && exit_times[pred] < exit_times[i]) {
blocks[i].flags |= ZEND_BB_IRREDUCIBLE_LOOP;
flag |= ZEND_FUNC_IRREDUCIBLE;
flag &= ~ZEND_FUNC_NO_LOOPS;
}
}
}
@@ -867,7 +865,7 @@ int zend_cfg_identify_loops(const zend_op_array *op_array, zend_cfg *cfg, uint32
}
free_alloca(sorted_blocks, sorted_blocks_use_heap);
free_alloca(dj_spanning_tree, tree_use_heap);
free_alloca(entry_times, tree_use_heap);
ZEND_WORKLIST_FREE_ALLOCA(&work, list_use_heap);
*flags |= flag;