I am testing the following.
Richard.
2018-08-28 Richard Biener <rguent...@suse.de>
PR tree-optimization/87126
* tree-ssa-sccvn.c (vn_reference_insert): Remove assert.
* gcc.dg/tree-ssa/pr87126.c: New testcase.
Index: gcc/tree-ssa-sccvn.c
===================================================================
--- gcc/tree-ssa-sccvn.c (revision 263917)
+++ gcc/tree-ssa-sccvn.c (working copy)
@@ -2696,7 +2696,17 @@ vn_reference_insert (tree op, tree resul
but save a lookup if we deal with already inserted refs here. */
if (*slot)
{
- gcc_assert (operand_equal_p ((*slot)->result, vr1->result, 0));
+ /* We cannot assert that we have the same value either because
+ when disentangling an irreducible region we may end up visiting
+ a use before the corresponding def. That's a missed optimization
+ only though. See gcc.dg/tree-ssa/pr87126.c for example. */
+ if (dump_file && (dump_flags & TDF_DETAILS)
+ && !operand_equal_p ((*slot)->result, vr1->result, 0))
+ {
+ fprintf (dump_file, "Keeping old value ");
+ print_generic_expr (dump_file, (*slot)->result);
+ fprintf (dump_file, " because of collision\n");
+ }
free_reference (vr1);
obstack_free (&vn_tables_obstack, vr1);
return;
Index: gcc/testsuite/gcc.dg/tree-ssa/pr87126.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/pr87126.c (nonexistent)
+++ gcc/testsuite/gcc.dg/tree-ssa/pr87126.c (working copy)
@@ -0,0 +1,25 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-fre1" } */
+
+int a, *b;
+
+void f ()
+{
+ int d = 0, e = d;
+ while (a++)
+ ;
+ if (e)
+ goto L2;
+L1:
+ d = e;
+ b = &d;
+L2:
+ if (d)
+ goto L1;
+}
+
+/* The load of d could be eliminated if we'd value-number the
+ irreducible region in RPO of the reducible result. Likewise
+ a redundant store could be removed. */
+/* { dg-final { scan-tree-dump-times "d = 0;" 1 "fre1" { xfail *-*-* } } } */
+/* { dg-final { scan-tree-dump-not " = d;" "fre1" { xfail *-*-* } } } */
