[PATCH,RFC] collect2 LTO for AIX

[David Edelsohn]

The attached patch is an incremental step toward GCC LTO on AIX.  The
recent Libiberty Simple Object improvements for XCOFF provide more
capabilities for operations on XCOFF object files, which are a
prerequisite for GCC LTO functionality.

This patch adds the basic LTO scanning pass to the COFF support in
collect2.  I don't believe that this change should affect other COFF
targets adversely (do they even use collect2?), but I wanted to give
people an opportunity to comment.

(Yes, the formatting is messy, but all of collect2.c is messy.)

Bootstrapped on powerpc-ibm-aix7.2.0.0

Thanks, David

* collect2.c (add_lto_object): Compile for OBJECT_COFF.
(scan_prog_file): Don't skip PASS_LTOINFO. Scan for LTO objects.

Index: collect2.c
===================================================================
--- collect2.c  (revision 253736)
+++ collect2.c  (working copy)
@@ -614,7 +614,7 @@ static const char *const target_machine = TARGET_M
 
    Return 0 if not found, otherwise return its name, allocated with malloc.  */
 
-#ifdef OBJECT_FORMAT_NONE
+#if defined (OBJECT_FORMAT_NONE) || defined (OBJECT_FORMAT_COFF)
 
 /* Add an entry for the object file NAME to object file list LIST.
    New entries are added at the end of the list. The original pointer
@@ -634,7 +634,7 @@ add_lto_object (struct lto_object_list *list, cons
 
   list->last = n;
 }
-#endif /* OBJECT_FORMAT_NONE */
+#endif
 
 
 /* Perform a link-time recompilation and relink if any of the object
@@ -2750,8 +2750,10 @@ scan_prog_file (const char *prog_name, scanpass wh
   LDFILE *ldptr = NULL;
   int sym_index, sym_count;
   int is_shared = 0;
+  int found_lto = 0;
 
-  if (which_pass != PASS_FIRST && which_pass != PASS_OBJ)
+  if (which_pass != PASS_FIRST && which_pass != PASS_OBJ
+      && which_pass != PASS_LTOINFO)
     return;
 
 #ifdef COLLECT_EXPORT_LIST
@@ -2764,6 +2766,7 @@ scan_prog_file (const char *prog_name, scanpass wh
      eliminate scan_libraries() function.  */
   do
     {
+      found_lto = 0;
 #endif
       /* Some platforms (e.g. OSF4) declare ldopen as taking a
         non-const char * filename parameter, even though it will not
@@ -2806,6 +2809,19 @@ scan_prog_file (const char *prog_name, scanpass wh
                        ++name;
 #endif
 
+                      if (which_pass == PASS_LTOINFO)
+                        {
+                         if (found_lto)
+                           continue;
+                         if (strncmp (name, "__gnu_lto_v1", 12) == 0)
+                           {
+                             add_lto_object (&lto_objects, prog_name);
+                             found_lto = 1;
+                             break;
+                           }
+                         continue;
+                       }
+
                      switch (is_ctor_dtor (name))
                        {
 #if TARGET_AIX_VERSION