Re: [PATCH] Fix up emitting VAR_DECLs in ubsan

[Marek Polacek]

On Wed, Nov 27, 2013 at 12:31:18AM +0100, Jakub Jelinek wrote:
> Please use here:
>   int z = 2;
>   if (z & 1)
> or similar instead, to make sure it is only early
> GIMPLE optimization passes that optimize it away, if already the
> front end knows it isn't needed, perhaps in the future it could
> just avoid instrumenting it.

Ok.  I've put in const int z = 2;, without const the original problem
disappeared.  Thanks for quick review.

2013-11-27  Marek Polacek  <pola...@redhat.com>

        * ubsan.c (ubsan_type_descriptor): If varpool_get_node returns NULL
        for a decl, recreate that decl.  Save into the hash table VAR_DECLs
        rather than ADDR_EXPRs.
testsuite/
        * c-c++-common/ubsan/undefined-1.c: New test.

--- gcc/ubsan.c.mp3     2013-11-26 18:07:46.225509763 +0100
+++ gcc/ubsan.c 2013-11-27 00:34:37.617849999 +0100
@@ -269,8 +269,12 @@ ubsan_type_descriptor (tree type, bool w
   type = TYPE_MAIN_VARIANT (type);
 
   tree decl = decl_for_type_lookup (type);
-  if (decl != NULL_TREE)
-    return decl;
+  /* It is possible that some of the earlier created DECLs were found
+     unused, in that case they weren't emitted and varpool_get_node
+     returns NULL node on them.  But now we really need them.  Thus,
+     renew them here.  */
+  if (decl != NULL_TREE && varpool_get_node (decl))
+    return build_fold_addr_expr (decl);
 
   tree dtype = ubsan_type_descriptor_type ();
   tree type2 = type;
@@ -369,11 +373,10 @@ ubsan_type_descriptor (tree type, bool w
   DECL_INITIAL (decl) = ctor;
   rest_of_decl_compilation (decl, 1, 0);
 
-  /* Save the address of the VAR_DECL into the hash table.  */
-  decl = build_fold_addr_expr (decl);
+  /* Save the VAR_DECL into the hash table.  */
   decl_for_type_insert (type, decl);
 
-  return decl;
+  return build_fold_addr_expr (decl);
 }
 
 /* Create a structure for the ubsan library.  NAME is a name of the new
--- gcc/testsuite/c-c++-common/ubsan/undefined-1.c.mp3  2013-11-26 
23:56:42.151624262 +0100
+++ gcc/testsuite/c-c++-common/ubsan/undefined-1.c      2013-11-27 
00:34:21.436784807 +0100
@@ -0,0 +1,26 @@
+/* { dg-do run } */
+/* { dg-options "-fsanitize=undefined" } */
+/* { dg-skip-if "" { *-*-* } { "-flto" } { "" } } */
+
+int
+foo (int x, int y)
+{
+  const int z = 2;
+  if (z & 1)
+    return x << y;
+  return 0;
+}
+
+int
+bar (int x, int y)
+{
+  return x + y;
+}
+
+int
+main (void)
+{
+  foo (3, 2);
+  bar (12, 42);
+  return 0;
+}

        Marek