re PR tree-optimization/87211 (gcc ICE at O2: in set_ssa_val_to, at tree-ssa-sccvn.c:3628)

2018-09-04  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/87211
	* tree-ssa-sccvn.c (visit_phi): When value-numbering to a
	backedge value we're supposed to treat as VARYING also number
	the PHI to VARYING in case it got a different value-number already.

	* gcc.dg/torture/pr87211.c: New testcase.

From-SVN: r264079

gcc/ChangeLog

+2018-09-04  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/87211
+	* tree-ssa-sccvn.c (visit_phi): When value-numbering to a
+	backedge value we're supposed to treat as VARYING also number
+	the PHI to VARYING in case it got a different value-number already.
+
 2018-09-04  Aldy Hernandez  <aldyh@redhat.com>
 
 	* tree-vrp.c (vrp_can_optimize_bit_op): Remove.

gcc/testsuite/ChangeLog

 2018-09-04  Richard Biener  <rguenther@suse.de>
 
+	PR tree-optimization/87211
+	* gcc.dg/torture/pr87211.c: New testcase.
+
+2018-09-04  Richard Biener  <rguenther@suse.de>
+
 	PR tree-optimization/87176
 	* gcc.dg/torture/pr87176.c: New testcase.
 	* gcc.dg/torture/ssa-fre-1.c: Likewise.

gcc/testsuite/gcc.dg/torture/pr87211.c

+/* { dg-do compile } */
+
+int a, b;
+int i(int *);
+int *c(int *d, int *e)
+{
+  for (; b;)
+    d = e;
+  return d;
+}
+void f()
+{
+  for (;;)
+    {
+      int *g[1];
+      int h = 0;
+      for (; h < 3; h++)
+	g[0] = &a;
+      &a == g[0] || i(c((int *)g, g[0]));
+    }
+}

gcc/tree-ssa-sccvn.c

@@ -4180,7 +4180,8 @@ visit_phi (gimple *phi, bool *inserted, bool backedges_varying_p)
       }
 
   /* If the value we want to use is the backedge and that wasn't visited
-     yet drop to VARYING.  This only happens when not iterating.
+     yet or if we should take it as VARYING but it has a non-VARYING
+     value drop to VARYING.  This only happens when not iterating.
      If we value-number a virtual operand never value-number to the
      value from the backedge as that confuses the alias-walking code.
      See gcc.dg/torture/pr87176.c.  If the value is the same on a
@@ -4190,7 +4191,8 @@ visit_phi (gimple *phi, bool *inserted, bool backedges_varying_p)
       && TREE_CODE (backedge_val) == SSA_NAME
       && sameval == backedge_val
       && (SSA_NAME_IS_VIRTUAL_OPERAND (backedge_val)
-	  || !SSA_VISITED (backedge_val)))
+	  || !SSA_VISITED (backedge_val)
+	  || SSA_VAL (backedge_val) != backedge_val))
     /* Note this just drops to VARYING without inserting the PHI into
        the hashes.  */
     result = PHI_RESULT (phi);