tree-optimization/102798 - avoid copying PTA info to old SSA names

The vectorizer duplicates pointer-info to created pointer bases
but it has to avoid changing points-to info on existing SSA names
because there's now flow-sensitive info in there (pt->pt_null as
set from VRP).

2021-10-18  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/102798
	* tree-vect-data-refs.c (vect_create_addr_base_for_vector_ref):
	Only copy points-to info to newly generated SSA names.

	* gcc.dg/pr102798.c: New testcase.

2 files changed, 47 insertions, 2 deletions

diff --git a/gcc/testsuite/gcc.dg/pr102798.c b/gcc/testsuite/gcc.dg/pr102798.c
new file mode 100644
index 0000000..3a50546
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr102798.c
@@ -0,0 +1,41 @@
+/* { dg-do run } */
+/* { dg-options "-O3 -fno-tree-pta" } */
+
+typedef __SIZE_TYPE__ size_t;
+
+__attribute__((__noipa__))
+void BUF_reverse (unsigned char *out, const unsigned char *in, size_t size)
+{
+  size_t i;
+  if (in)
+    {
+      out += size - 1;
+      for (i = 0; i < size; i++)
+        *out++ = *in++;
+    }
+  else
+    {
+      unsigned char *q;
+      char c;
+      q = out + size - 1;
+      for (i = 0; i < size ; i++)
+            {
+              *out++ = 1;
+            }
+    }
+}
+
+int
+main (void)
+{
+  unsigned char buf[40];
+  unsigned char buf1[40];
+  for (unsigned i = 0; i < sizeof (buf); i++)
+    buf[i] = i;
+  BUF_reverse (buf, 0, sizeof (buf));
+  for (unsigned i = 0; i < sizeof (buf); i++)
+    if (buf[i] != 1)
+      __builtin_abort ();
+
+  return 0;
+}
diff --git a/gcc/tree-vect-data-refs.c b/gcc/tree-vect-data-refs.c
index 1e13148..a19045f 100644
--- a/gcc/tree-vect-data-refs.c
+++ b/gcc/tree-vect-data-refs.c
@@ -4785,8 +4785,12 @@ vect_create_addr_base_for_vector_ref (vec_info *vinfo, stmt_vec_info stmt_info,
 
   if (DR_PTR_INFO (dr)
       && TREE_CODE (addr_base) == SSA_NAME
-      && !SSA_NAME_PTR_INFO (addr_base))
-    vect_duplicate_ssa_name_ptr_info (addr_base, dr_info);
+      /* We should only duplicate pointer info to newly created SSA names.  */
+      && SSA_NAME_VAR (addr_base) == dest)
+    {
+      gcc_assert (!SSA_NAME_PTR_INFO (addr_base));
+      vect_duplicate_ssa_name_ptr_info (addr_base, dr_info);
+    }
 
   if (dump_enabled_p ())
     dump_printf_loc (MSG_NOTE, vect_location, "created %T\n", addr_base);