This should fix the endless PRE antic iterations for good. OK, it's
somewhat of a hack but unless I fix another two or three parts of the
antic algorithm to not prune values that may later re-appear I see
no other way to guarantee this. And this isn't the time to fiddle
with PRE further...
Bootstrapped on x86_64-unknown-linux-gnu, testing in progress.
The assert I added previously is now defunct for CFG cycles which
makes it useless, I'll rip it out as a followup.
Richard.
2018-03-13 Richard Biener <rguent...@suse.de>
PR tree-optimization/84830
* tree-ssa-pre.c (compute_antic_aux): Intersect the new ANTIC_IN
with the old one to avoid oscillations.
* gcc.dg/torture/pr84830.c: New testcase.
Index: gcc/tree-ssa-pre.c
===================================================================
--- gcc/tree-ssa-pre.c (revision 258480)
+++ gcc/tree-ssa-pre.c (working copy)
@@ -2154,6 +2154,35 @@ compute_antic_aux (basic_block block, bo
/* clean (ANTIC_IN (block)) is defered to after the iteration converged
because it can cause non-convergence, see for example PR81181. */
+ /* Intersect ANTIC_IN with the old ANTIC_IN. This is required until
+ we properly represent the maximum expression set, thus not prune
+ values without expressions during the iteration. */
+ if (was_visited
+ && bitmap_and_into (&ANTIC_IN (block)->values, &old->values))
+ {
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ fprintf (dump_file, "warning: intersecting with old ANTIC_IN "
+ "shrinks the set\n");
+ /* Prune expressions not in the value set. */
+ bitmap_iterator bi;
+ unsigned int i;
+ unsigned int to_clear = -1U;
+ FOR_EACH_EXPR_ID_IN_SET (ANTIC_IN (block), i, bi)
+ {
+ if (to_clear != -1U)
+ {
+ bitmap_clear_bit (&ANTIC_IN (block)->expressions, to_clear);
+ to_clear = -1U;
+ }
+ pre_expr expr = expression_for_id (i);
+ unsigned int value_id = get_expr_value_id (expr);
+ if (!bitmap_bit_p (&ANTIC_IN (block)->values, value_id))
+ to_clear = i;
+ }
+ if (to_clear != -1U)
+ bitmap_clear_bit (&ANTIC_IN (block)->expressions, to_clear);
+ }
+
if (!bitmap_set_equal (old, ANTIC_IN (block)))
{
changed = true;
Index: gcc/testsuite/gcc.dg/torture/pr84830.c
===================================================================
--- gcc/testsuite/gcc.dg/torture/pr84830.c (nonexistent)
+++ gcc/testsuite/gcc.dg/torture/pr84830.c (working copy)
@@ -0,0 +1,46 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-fno-tree-ch -fno-tree-vrp" } */
+
+int x0;
+
+void
+br (int yp, int oo)
+{
+ int *qi = &yp;
+
+ if (oo == 0)
+ {
+g8:
+ if (x0 != 0)
+ x0 = yp;
+ else if (oo != 0)
+ x0 = yp;
+
+ if (x0 == 0)
+ {
+ *qi = 0;
+ x0 = *qi;
+ }
+
+ if (x0 != 0)
+ {
+ ++oo;
+ goto g8;
+ }
+
+ if (yp == oo)
+ yp += !!oo;
+ }
+ else
+ {
+ x0 = 1;
+ while (x0 < 2)
+ {
+ qi = &oo;
+ ++oo;
+ x0 = 1;
+ }
+ }
+
+ goto g8;
+}
