On Fri, Nov 30, 2012 at 11:00:28PM +0100, Eric Botcazou wrote:
> OK, let's tweak the patch as follows:
> 1) when current_loops is not NULL, we compute may_be_loop_header and whether
> the loop has more than 1 latch edge exactly,
> 2) when current_loops is NULL, we use your above method to do the same,
> 3) once this is done, we return from the function before entering the loop
> if
> this is a (potential) header with more than 1 (potential) latch edge. The
> comment can say that threading through a loop header with more than 1 latch
> edge is delicate and cite tree-threadupdate.c:thread_through_loop_header.
Like this? Regtested/bootstrapped on x86_64-linux, ok for trunk?
2012-12-01 Marek Polacek <pola...@redhat.com>
PR middle-end/54838
* cprop.c (bypass_block): Determine number of latches. Return
when there is more than one latch edge.
* gcc.dg/pr54838.c: New test.
--- gcc/cprop.c.mp 2012-11-29 15:49:53.120524295 +0100
+++ gcc/cprop.c 2012-12-01 16:14:59.387335461 +0100
@@ -1510,13 +1510,28 @@ bypass_block (basic_block bb, rtx setcc,
if (note)
find_used_regs (&XEXP (note, 0), NULL);
- may_be_loop_header = false;
- FOR_EACH_EDGE (e, ei, bb->preds)
- if (e->flags & EDGE_DFS_BACK)
- {
- may_be_loop_header = true;
- break;
- }
+ /* Determine whether there are more latch edges. Threading through
+ a loop header with more than one latch is delicate, see e.g.
+ tree-ssa-threadupdate.c:thread_through_loop_header. */
+ if (current_loops)
+ {
+ may_be_loop_header = bb == bb->loop_father->header;
+ if (may_be_loop_header
+ && bb->loop_father->latch == NULL)
+ return 0;
+ }
+ else
+ {
+ unsigned n_back_edges = 0;
+ FOR_EACH_EDGE (e, ei, bb->preds)
+ if (e->flags & EDGE_DFS_BACK)
+ n_back_edges++;
+
+ may_be_loop_header = n_back_edges > 0;
+
+ if (n_back_edges > 1)
+ return 0;
+ }
change = 0;
for (ei = ei_start (bb->preds); (e = ei_safe_edge (ei)); )
--- gcc/testsuite/gcc.dg/pr54838.c.mp 2012-11-26 14:48:43.783980854 +0100
+++ gcc/testsuite/gcc.dg/pr54838.c 2012-11-26 14:49:51.051158719 +0100
@@ -0,0 +1,24 @@
+/* PR middle-end/54838 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fno-forward-propagate -ftracer" } */
+
+void bar (void);
+
+void
+foo (void *b, int *c)
+{
+again:
+ switch (*c)
+ {
+ case 1:
+ if (!b)
+ {
+ bar ();
+ return;
+ }
+ goto again;
+ case 3:
+ if (!b)
+ goto again;
+ }
+}
Marek
