tree-optimization/95049 - fix not terminating RPO VN iteration

This rejects lattice changes from one constant to another.

2020-05-11  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/95049
	* tree-ssa-sccvn.c (set_ssa_val_to): Reject lattice transition
	between different constants.

	* gcc.dg/torture/pr95049.c: New testcase.

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index cf6eafd..9ddd085 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2020-05-11  Richard Biener  <rguenther@suse.de>
+
+       PR tree-optimization/95049
+       * tree-ssa-sccvn.c (set_ssa_val_to): Reject lattice transition
+       between different constants.
+
 2020-05-11  Richard Sandiford  <richard.sandiford@arm.com>
 
        * tree-pretty-print.c (dump_generic_node): Handle BOOLEAN_TYPEs.

diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 65feee5..92e1d40 100644 (file)
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2020-05-11  Richard Biener  <rguenther@suse.de>
+
+       PR tree-optimization/95049
+       * gcc.dg/torture/pr95049.c: New testcase.
+
 2020-05-11  Kelvin Nilsen  <kelvin@gcc.gnu.org>
            Bill Schmidt  <wschmidt@linux.ibm.com>
 

diff --git a/gcc/testsuite/gcc.dg/torture/pr95049.c b/gcc/testsuite/gcc.dg/torture/pr95049.c
new file mode 100644 (file)
index 0000000..164bfdb
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr95049.c
@@ -0,0 +1,7 @@
+/* { dg-do compile } */
+
+void a()
+{
+  for (int b; b; b = !b)
+    ;
+}

diff --git a/gcc/tree-ssa-sccvn.c b/gcc/tree-ssa-sccvn.c
index 39e9900..4b3f31c 100644 (file)
--- a/gcc/tree-ssa-sccvn.c
+++ b/gcc/tree-ssa-sccvn.c
@@ -4472,6 +4472,8 @@ set_ssa_val_to (tree from, tree to)
   vn_ssa_aux_t from_info = VN_INFO (from);
   tree currval = from_info->valnum; // SSA_VAL (from)
   poly_int64 toff, coff;
+  bool curr_undefined = false;
+  bool curr_invariant = false;
 
   /* The only thing we allow as value numbers are ssa_names
      and invariants.  So assert that here.  We don't allow VN_TOP
@@ -4514,9 +4516,9 @@ set_ssa_val_to (tree from, tree to)
            }
          return false;
        }
-      bool curr_invariant = is_gimple_min_invariant (currval);
-      bool curr_undefined = (TREE_CODE (currval) == SSA_NAME
-                            && ssa_undefined_value_p (currval, false));
+      curr_invariant = is_gimple_min_invariant (currval);
+      curr_undefined = (TREE_CODE (currval) == SSA_NAME
+                       && ssa_undefined_value_p (currval, false));
       if (currval != VN_TOP
          && !curr_invariant
          && !curr_undefined
@@ -4571,9 +4573,8 @@ set_and_exit:
       && !operand_equal_p (currval, to, 0)
       /* Different undefined SSA names are not actually different.  See
          PR82320 for a testcase were we'd otherwise not terminate iteration.  */
-      && !(TREE_CODE (currval) == SSA_NAME
+      && !(curr_undefined
           && TREE_CODE (to) == SSA_NAME
-          && ssa_undefined_value_p (currval, false)
           && ssa_undefined_value_p (to, false))
       /* ???  For addresses involving volatile objects or types operand_equal_p
          does not reliably detect ADDR_EXPRs as equal.  We know we are only
@@ -4585,6 +4586,22 @@ set_and_exit:
               == get_addr_base_and_unit_offset (TREE_OPERAND (to, 0), &toff))
           && known_eq (coff, toff)))
     {
+      if (to != from
+         && currval != VN_TOP
+         && !curr_undefined
+         /* We do not want to allow lattice transitions from one value
+            to another since that may lead to not terminating iteration
+            (see PR95049).  Since there's no convenient way to check
+            for the allowed transition of VAL -> PHI (loop entry value,
+            same on two PHIs, to same PHI result) we restrict the check
+            to invariants.  */
+         && curr_invariant
+         && is_gimple_min_invariant (to))
+       {
+         if (dump_file && (dump_flags & TDF_DETAILS))
+           fprintf (dump_file, " forced VARYING");
+         to = from;
+       }
       if (dump_file && (dump_flags & TDF_DETAILS))
        fprintf (dump_file, " (changed)\n");
       from_info->valnum = to;