(from successors to predecessors).
This ordering can be used for forward dataflow problems among others.
+ Optionally if START_POINTS is specified, start from exit block and all
+ basic blocks in START_POINTS. This is used by CD-DCE.
+
This function assumes that all blocks in the CFG are reachable
from the ENTRY (but not necessarily from EXIT).
and do another inverted traversal from that block. */
int
-inverted_post_order_compute (int *post_order)
+inverted_post_order_compute (int *post_order,
+ sbitmap *start_points)
{
basic_block bb;
edge_iterator *stack;
/* None of the nodes in the CFG have been visited yet. */
bitmap_clear (visited);
+ if (start_points)
+ {
+ FOR_ALL_BB_FN (bb, cfun)
+ if (bitmap_bit_p (*start_points, bb->index)
+ && EDGE_COUNT (bb->preds) > 0)
+ {
+ stack[sp++] = ei_start (bb->preds);
+ bitmap_set_bit (visited, bb->index);
+ }
+ if (EDGE_COUNT (EXIT_BLOCK_PTR_FOR_FN (cfun)->preds))
+ {
+ stack[sp++] = ei_start (EXIT_BLOCK_PTR_FOR_FN (cfun)->preds);
+ bitmap_set_bit (visited, EXIT_BLOCK_PTR_FOR_FN (cfun)->index);
+ }
+ }
+ else
/* Put all blocks that have no successor into the initial work list. */
FOR_ALL_BB_FN (bb, cfun)
if (EDGE_COUNT (bb->succs) == 0)
to be recomputed. */
static bool cfg_altered;
+/* When non-NULL holds map from basic block index into the postorder. */
+static int *bb_postorder;
+
/* If STMT is not already marked necessary, mark it, and add it to the
worklist if ADD_TO_WORKLIST is true. */
gimple_set_plf (stmt, STMT_NECESSARY, true);
if (add_to_worklist)
worklist.safe_push (stmt);
- if (bb_contains_live_stmts && !is_gimple_debug (stmt))
+ if (add_to_worklist && bb_contains_live_stmts && !is_gimple_debug (stmt))
bitmap_set_bit (bb_contains_live_stmts, gimple_bb (stmt)->index);
}
return something_changed;
}
-/* Forward edge E to respective POST_DOM_BB and update PHIs. */
-
-static edge
-forward_edge_to_pdom (edge e, basic_block post_dom_bb)
-{
- gphi_iterator gsi;
- edge e2 = NULL;
- edge_iterator ei;
-
- if (dump_file && (dump_flags & TDF_DETAILS))
- fprintf (dump_file, "Redirecting edge %i->%i to %i\n", e->src->index,
- e->dest->index, post_dom_bb->index);
-
- e2 = redirect_edge_and_branch (e, post_dom_bb);
- cfg_altered = true;
-
- /* If edge was already around, no updating is necessary. */
- if (e2 != e)
- return e2;
-
- if (!gimple_seq_empty_p (phi_nodes (post_dom_bb)))
- {
- /* We are sure that for every live PHI we are seeing control dependent BB.
- This means that we can pick any edge to duplicate PHI args from. */
- FOR_EACH_EDGE (e2, ei, post_dom_bb->preds)
- if (e2 != e)
- break;
- for (gsi = gsi_start_phis (post_dom_bb); !gsi_end_p (gsi);)
- {
- gphi *phi = gsi.phi ();
- tree op;
- source_location locus;
-
- /* PHIs for virtuals have no control dependency relation on them.
- We are lost here and must force renaming of the symbol. */
- if (virtual_operand_p (gimple_phi_result (phi)))
- {
- mark_virtual_phi_result_for_renaming (phi);
- remove_phi_node (&gsi, true);
- continue;
- }
-
- /* Dead PHI do not imply control dependency. */
- if (!gimple_plf (phi, STMT_NECESSARY))
- {
- gsi_next (&gsi);
- continue;
- }
-
- op = gimple_phi_arg_def (phi, e2->dest_idx);
- locus = gimple_phi_arg_location (phi, e2->dest_idx);
- add_phi_arg (phi, op, e, locus);
- /* The resulting PHI if not dead can only be degenerate. */
- gcc_assert (degenerate_phi_p (phi));
- gsi_next (&gsi);
- }
- }
- return e;
-}
/* Remove dead statement pointed to by iterator I. Receives the basic block BB
containing I so that we don't have to look it up. */
stats.removed++;
/* If we have determined that a conditional branch statement contributes
- nothing to the program, then we not only remove it, but we also change
- the flow graph so that the current block will simply fall-thru to its
- immediate post-dominator. The blocks we are circumventing will be
- removed by cleanup_tree_cfg if this change in the flow graph makes them
- unreachable. */
+ nothing to the program, then we not only remove it, but we need to update
+ the CFG. We can chose any of edges out of BB as long as we are sure to not
+ close infinite loops. This is done by always choosing the edge closer to
+ exit in inverted_post_order_compute order. */
if (is_ctrl_stmt (stmt))
{
- basic_block post_dom_bb;
- edge e, e2;
edge_iterator ei;
-
- post_dom_bb = get_immediate_dominator (CDI_POST_DOMINATORS, bb);
-
- e = find_edge (bb, post_dom_bb);
-
- /* If edge is already there, try to use it. This avoids need to update
- PHI nodes. Also watch for cases where post dominator does not exists
- or is exit block. These can happen for infinite loops as we create
- fake edges in the dominator tree. */
- if (e)
- ;
- else if (! post_dom_bb || post_dom_bb == EXIT_BLOCK_PTR_FOR_FN (cfun))
- e = EDGE_SUCC (bb, 0);
- else
- e = forward_edge_to_pdom (EDGE_SUCC (bb, 0), post_dom_bb);
+ edge e = NULL, e2;
+
+ /* See if there is only one non-abnormal edge. */
+ if (single_succ_p (bb))
+ e = single_succ_edge (bb);
+ /* Otherwise chose one that is closer to bb with live statement in it.
+ To be able to chose one, we compute inverted post order starting from
+ all BBs with live statements. */
+ if (!e)
+ {
+ if (!bb_postorder)
+ {
+ int *postorder = XNEWVEC (int, n_basic_blocks_for_fn (cfun));
+ int postorder_num
+ = inverted_post_order_compute (postorder,
+ &bb_contains_live_stmts);
+ bb_postorder = XNEWVEC (int, last_basic_block_for_fn (cfun));
+ for (int i = 0; i < postorder_num; ++i)
+ bb_postorder[postorder[i]] = i;
+ free (postorder);
+ }
+ FOR_EACH_EDGE (e2, ei, bb->succs)
+ if (!e || e2->dest == EXIT_BLOCK_PTR_FOR_FN (cfun)
+ || bb_postorder [e->dest->index]
+ < bb_postorder [e2->dest->index])
+ e = e2;
+ }
gcc_assert (e);
e->probability = REG_BR_PROB_BASE;
e->count = bb->count;
/* The edge is no longer associated with a conditional, so it does
- not have TRUE/FALSE flags. */
- e->flags &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE);
+ not have TRUE/FALSE flags.
+ We are also safe to drop EH/ABNORMAL flags and turn them into
+ normal control flow, because we know that all the destinations (including
+ those odd edges) are equivalent for program execution. */
+ e->flags &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE | EDGE_EH | EDGE_ABNORMAL);
/* The lone outgoing edge from BB will be a fallthru edge. */
e->flags |= EDGE_FALLTHRU;
something_changed |= remove_dead_phis (bb);
}
+ if (bb_postorder)
+ free (bb_postorder);
+ bb_postorder = NULL;
+
return something_changed;
}
projects / gcc.git / commitdiff