http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46590
--- Comment #31 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-08-23
11:41:50 UTC ---
Btw, I have experimented with
Index: tree-into-ssa.c
===================================================================
--- tree-into-ssa.c (revision 190594)
+++ tree-into-ssa.c (working copy)
@@ -3224,11 +3224,35 @@ update_ssa (unsigned update_flags)
bitmap_head *dfs;
/* If the caller requested PHI nodes to be added, compute
- dominance frontiers. */
+ dominance frontiers for all interesting blocks
+ up to the dominating start_bb. */
dfs = XNEWVEC (bitmap_head, last_basic_block);
FOR_EACH_BB (bb)
bitmap_initialize (&dfs[bb->index], &bitmap_default_obstack);
- compute_dominance_frontiers (dfs);
+ EXECUTE_IF_SET_IN_BITMAP (blocks_to_update, 0, i, bi)
+ {
+ basic_block b = BASIC_BLOCK (i);
+ edge_iterator ei;
+ edge p;
+ if (EDGE_COUNT (b->preds) >= 2)
+ FOR_EACH_EDGE (p, ei, b->preds)
+ {
+ basic_block runner = p->src;
+ basic_block domsb;
+ if (runner == start_bb)
+ continue;
+
+ domsb = get_immediate_dominator (CDI_DOMINATORS, b);
+ while (runner != domsb)
+ {
+ if (!bitmap_set_bit (&dfs[runner->index],
+ b->index))
+ break;
+ runner = get_immediate_dominator (CDI_DOMINATORS,
+ runner);
+ }
+ }
+ }
if (sbitmap_first_set_bit (old_ssa_names) >= 0)
{
which helps reducing the time spent in computing dominance frontiers. But
as we no longer have bitmaps but bitmap_heads in dfs it's hard to verify
we only ever access dfs for entries we computed ... but we should,
looking at how compute_idf works(?).
