@@ -1,3 +1,11 @@
+2013-08-28 Jeff Law <law@redhat.com>
+
+ * tree-ssa-threadedge.c (thread_around_empty_block): Remove
+ checks for the number of predecessors and successors allowed.
+ * tree-ssa-threadupdate.c (mark_threaded_blocks): Ignore requests
+ which require copying a joiner block if there is a request which
+ is a subpath that requires no joiner block copying.
+
2013-08-28 Jakub Jelinek <jakub@redhat.com>
PR middle-end/58257
@@ -761,14 +761,6 @@ thread_around_empty_block (edge taken_edge,
gimple stmt;
tree cond;
- /* This block must have a single predecessor (E->dest). */
- if (!single_pred_p (bb))
- return NULL;
-
- /* This block must have more than one successor. */
- if (single_succ_p (bb))
- return NULL;
-
/* This block can have no PHI nodes. This is overly conservative. */
if (!gsi_end_p (gsi_start_phis (bb)))
return NULL;
@@ -1146,17 +1146,56 @@ mark_threaded_blocks (bitmap threaded_blocks)
edge e;
edge_iterator ei;
+ /* It is possible to have jump threads in which one is a subpath
+ of the other. ie, (A, B), (B, C), (C, D) where B is a joiner
+ block and (B, C), (C, D) where no joiner block exists.
+
+ When this occurs ignore the jump thread request with the joiner
+ block. It's totally subsumed by the simpler jump thread request.
+
+ This results in less block copying, simpler CFGs. More improtantly,
+ when we duplicate the joiner block, B, in this case we will create
+ a new threading opportunity that we wouldn't be able to optimize
+ until the next jump threading iteration.
+
+ So first convert the jump thread requests which do not require a
+ joiner block. */
for (i = 0; i < threaded_edges.length (); i += 3)
{
edge e = threaded_edges[i];
- edge *x = XNEWVEC (edge, 2);
- e->aux = x;
- THREAD_TARGET (e) = threaded_edges[i + 1];
- THREAD_TARGET2 (e) = threaded_edges[i + 2];
- bitmap_set_bit (tmp, e->dest->index);
+ if (threaded_edges[i + 2] == NULL)
+ {
+ edge *x = XNEWVEC (edge, 2);
+
+ e->aux = x;
+ THREAD_TARGET (e) = threaded_edges[i + 1];
+ THREAD_TARGET2 (e) = NULL;
+ bitmap_set_bit (tmp, e->dest->index);
+ }
}
+
+ /* Now iterate again, converting cases where we threaded through
+ a joiner block, but ignoring those where we have already
+ threaded through the joiner block. */
+ for (i = 0; i < threaded_edges.length (); i += 3)
+ {
+ edge e = threaded_edges[i];
+
+ if (threaded_edges[i + 2] != NULL
+ && threaded_edges[i + 1]->aux == NULL)
+ {
+ edge *x = XNEWVEC (edge, 2);
+
+ e->aux = x;
+ THREAD_TARGET (e) = threaded_edges[i + 1];
+ THREAD_TARGET2 (e) = threaded_edges[i + 2];
+ bitmap_set_bit (tmp, e->dest->index);
+ }
+ }
+
+
/* If optimizing for size, only thread through block if we don't have
to duplicate it or it's an otherwise empty redirection block. */
if (optimize_function_for_size_p (cfun))
When the code was written to thread jumps through joiner blocks, out of an abundance of caution I severely restricted the form allowed for the successors of the joiner block. In particular we required the successor of the joiner block to have just one predecessor and more than one successor. This patch removes those restrictions. By allowing the successor of the joiner to have > 2 pred, we immediately expose more jump threading opportunities. By allowing the successor to have a single successor, we can thread through forwarder blocks after the joiner (which is important for the FSA optimization). This patch also filters out jump threading requests which are not useful because they're subsumed by a simpler jump threading request. Consider (A, B) (B, C) (C, D). In this case B is a joiner block and will need to be copied. The outgoing edge B->C will be threaded to C->D. If we have a jump threading request (B, C) (C, D), we get the same effect without copying B and thus its preferred. In fact, if we copy B it's likely B' will have a threadable jump, but we can't optimize it until the next iteration, which is obviously bad. Bootstrapped and regression tested on x86_64-unknown-linux-gnu. Installed onto the trunk. commit 06df8aadeebff5f4cad3082efe3c12e87d3347e5 Author: Jeff Law <law@redhat.com> Date: Wed Aug 28 09:04:09 2013 -0600 * tree-ssa-threadedge.c (thread_around_empty_block): Remove checks for the number of predecessors and successors allowed. * tree-ssa-threadupdate.c (mark_threaded_blocks): Ignore requests which require copying a joiner block if there is a request which is a subpath that requires no joiner block copying.