tree-optimization/111444 - avoid insertions when skipping defs

The following avoids inserting expressions for IPA CP discovered
equivalences into the VN hashtables when we are optimistically
skipping may-defs in the attempt to prove it's redundant.

	PR tree-optimization/111444
	* tree-ssa-sccvn.cc (vn_reference_lookup_3): Do not use
	vn_reference_lookup_2 when optimistically skipping may-defs.

	* gcc.dg/torture/pr111444.c: New testcase.

diff --git a/gcc/testsuite/gcc.dg/torture/pr111444.c b/gcc/testsuite/gcc.dg/torture/pr111444.c
new file mode 100644 (file)
index 0000000..e613f25
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr111444.c
@@ -0,0 +1,26 @@
+/* { dg-do run } */
+
+int a = 3, d, e;
+int *b = &a;
+char c;
+short f;
+const int **g;
+static long h(int **i, int **j)
+{
+  const int *k[46];
+  const int **l = &k[5];
+  *j = &e;
+  g = l;
+  for (; d; d = d + 1)
+    ;
+  **i = 0;
+  return f;
+}
+int main()
+{
+  int *m = &a;
+  h(&m, &m);
+  c = *b;
+  if (c != 3)
+    __builtin_abort ();
+}

diff --git a/gcc/tree-ssa-sccvn.cc b/gcc/tree-ssa-sccvn.cc
index f0fa718a723db09720848fe3fe84409e33f0515e..9bed9b3cc69ce412f3b2ee027a7f8e63d8829c4e 100644 (file)
--- a/gcc/tree-ssa-sccvn.cc
+++ b/gcc/tree-ssa-sccvn.cc
@@ -2790,25 +2790,29 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *data_,
            }
          else
            {
-             tree *saved_last_vuse_ptr = data->last_vuse_ptr;
-             /* Do not update last_vuse_ptr in vn_reference_lookup_2.  */
-             data->last_vuse_ptr = NULL;
              tree saved_vuse = vr->vuse;
              hashval_t saved_hashcode = vr->hashcode;
-             void *res = vn_reference_lookup_2 (ref, gimple_vuse (def_stmt),
-                                                data);
+             if (vr->vuse)
+               vr->hashcode = vr->hashcode - SSA_NAME_VERSION (vr->vuse);
+             vr->vuse = vuse_ssa_val (gimple_vuse (def_stmt));
+             if (vr->vuse)
+               vr->hashcode = vr->hashcode + SSA_NAME_VERSION (vr->vuse);
+             vn_reference_t vnresult = NULL;
+             /* Do not use vn_reference_lookup_2 since that might perform
+                expression hashtable insertion but this lookup crosses
+                a possible may-alias making such insertion conditionally
+                invalid.  */
+             vn_reference_lookup_1 (vr, &vnresult);
              /* Need to restore vr->vuse and vr->hashcode.  */
              vr->vuse = saved_vuse;
              vr->hashcode = saved_hashcode;
-             data->last_vuse_ptr = saved_last_vuse_ptr;
-             if (res && res != (void *)-1)
+             if (vnresult)
                {
-                 vn_reference_t vnresult = (vn_reference_t) res;
                  if (TREE_CODE (rhs) == SSA_NAME)
                    rhs = SSA_VAL (rhs);
                  if (vnresult->result
                      && operand_equal_p (vnresult->result, rhs, 0))
-                   return res;
+                   return vnresult;
                }
            }
        }