[PATCH, CHKP] Keep instrumentation references consistency when merging cgraph nodes

[Ilya Enkovich]

Hi,

Currently cgraph nodes merge may break instrumented_version references.  It 
depends on order nodes are read and merged and therefore problem is not nicely 
reproducible.  I couldn't make a small reproducer.  This patch fixes problem 
and 253.perlbmk benchmark build with '-O3 -flto -fcheck-pointer-bounds -mmpx'.  
Bootstrapped and tested on x86_64-unknown-linux-gnu.  OK for trunk?

Thanks,
Ilya
--
2014-12-02  Ilya Enkovich  <ilya.enkov...@intel.com>

        * lto-cgraph.c (input_cgraph_1): Don't break existing
        instrumentation clone references.
        * lto/lto-symtab.c (lto_cgraph_replace_node): Redirect
        instrumented_version references appropriately.


diff --git a/gcc/lto-cgraph.c b/gcc/lto-cgraph.c
index d424e14..b310b44 100644
--- a/gcc/lto-cgraph.c
+++ b/gcc/lto-cgraph.c
@@ -1562,7 +1562,18 @@ input_cgraph_1 (struct lto_file_decl_data *file_data,
 
              cnode->instrumented_version = cgraph_node::get (cnode->orig_decl);
              if (cnode->instrumented_version)
-               cnode->instrumented_version->instrumented_version = cnode;
+               {
+                 /* We may have multiple nodes for a single function which
+                    will be merged later.  To have a proper merge we need
+                    to keep instrumentation_version reference between nodes
+                    consistent: each instrumented_version reference should
+                    have proper reverse reference.  Thus don't break existing
+                    instrumented_version reference if it already exists.  */
+                 if (cnode->instrumented_version->instrumented_version)
+                   cnode->instrumented_version = NULL;
+                 else
+                   cnode->instrumented_version->instrumented_version = cnode;
+               }
 
              /* Restore decl names reference.  */
              if (IDENTIFIER_TRANSPARENT_ALIAS (DECL_ASSEMBLER_NAME 
(cnode->decl))
diff --git a/gcc/lto/lto-symtab.c b/gcc/lto/lto-symtab.c
index 4c4e48a..f5d82a7 100644
--- a/gcc/lto/lto-symtab.c
+++ b/gcc/lto/lto-symtab.c
@@ -99,6 +99,20 @@ lto_cgraph_replace_node (struct cgraph_node *node,
   /* Redirect incomming references.  */
   prevailing_node->clone_referring (node);
 
+  /* Fix instrumentation references.  */
+  if (node->instrumented_version)
+    {
+      gcc_assert (node->instrumentation_clone
+                 == prevailing_node->instrumentation_clone);
+      node->instrumented_version->instrumented_version = prevailing_node;
+      if (!prevailing_node->instrumented_version)
+       prevailing_node->instrumented_version = node->instrumented_version;
+      /* Need to reset node->instrumented_version to NULL,
+        otherwise node removal code would reset
+        node->instrumented_version->instrumented_version.  */
+      node->instrumented_version = NULL;
+    }
+
   ipa_merge_profiles (prevailing_node, node);
   lto_free_function_in_decl_state_for_node (node);