[lto] Also fix up nothrow attributes for callees

[Diego Novillo <dnovillo at google dot com>]

When a cgraph node N is being partitioned in a different file
than one of its callees M, the file that holds N does not have
fixup information for M (since M is never written to that file).
This causes the call to M to be inside an EH region when it
doesn't really throw, causing the EH verification error:

lto1: error: statement marked for throw, but doesn't

The solution is for output_wpa_fixup to also process all the
callees of a cgraph node N.  Since the callees are the ones that
will be inside EH regions in N's body, we have to have
information about them as well as N.

Bootstrapped and tested on x86_64.  The original test case is
quite large and it still hasn't finished reducing.  I will commit
it once I get a minimal test case.


Diego.



       * lto-wpa-fixup.c (output_wpa_fixup): Also check the
       callees of a node to see if they are nothrow functions.
       (gate_wpa_fixup): Return true if flag_ltrans is set.

Index: lto-wpa-fixup.c
===================================================================
--- lto-wpa-fixup.c	(revision 142219)
+++ lto-wpa-fixup.c	(working copy)
@@ -45,8 +45,7 @@ Boston, MA 02110-1301, USA.  */
    In WPA mode, LTO cannot access function bodies.  Some modifications in
    IR require additional updates in function bodies,  which are not possible
    in WPA mode.  So we write out information about these modifications for
-   LTRANS to fix up the function bodies accordingly.
- */
+   LTRANS to fix up the function bodies accordingly.  */
 
 /* The vectors records function DECLs having multiple copies with different
    exception throwing attributes.  We do not mark a DECL if all copies of it
@@ -80,7 +79,7 @@ static bitmap lto_nothrow_fndecls;
    
    When main.cc is compiled, gcc only sees the constructor declaration, so
    the constructor and hence the call to it are marked as exception throwing.
-   When a.cc is compiled, body of the constructor is available and is
+   When a.cc is compiled, the body of the constructor is available and is
    obviously not exception throwing. Thus DECL of a::a in a.o has the NOTHROW
    attribute.  When LTO runs, two DECLs of a::a with different exception
    attributes are merged.  We want the merged DECL to be not exception
@@ -155,13 +154,35 @@ output_wpa_fixup (cgraph_node_set set)
   if (lto_nothrow_fndecls)
     for (csi = csi_start (set); !csi_end_p (csi); csi_next (&csi))
       {
-	fndecl = csi_node (csi)->decl;
-	if (!bitmap_bit_p (seen_decls, (DECL_UID (fndecl))))
+	struct cgraph_edge *e;
+	struct cgraph_node *n;
+	
+	n = csi_node (csi);
+	fndecl = n->decl;
+
+	/* Check if the N's function is in the set of nothrow functions.  */
+	if (!bitmap_bit_p (seen_decls, DECL_UID (fndecl)))
 	  {
 	    bitmap_set_bit (seen_decls, (DECL_UID (fndecl)));
 	    if (bitmap_bit_p (lto_nothrow_fndecls, DECL_UID (fndecl)))
 	      VEC_safe_push (tree, heap, decls, fndecl);
 	  }
+
+	/* Now check the callees and also add them if they are nothrow.  This
+	   is needed because node N may end up in a different partition than
+	   its callees.  In which case, when the file holding N is compiled,
+	   the calls it makes to nothrow functions will not be fixed up,
+	   causing verification issues.  */
+	for (e = n->callees; e; e = e->next_callee)
+	  {
+	    fndecl = e->callee->decl;
+	    if (!bitmap_bit_p (seen_decls, DECL_UID (fndecl)))
+	      {
+		bitmap_set_bit (seen_decls, (DECL_UID (fndecl)));
+		if (bitmap_bit_p (lto_nothrow_fndecls, DECL_UID (fndecl)))
+		  VEC_safe_push (tree, heap, decls, fndecl);
+	      }
+	  }
       }
 
   /* Write out number of DECLs, followed by the DECLs.  */
@@ -232,7 +253,7 @@ input_wpa_fixup (void)
 static bool
 gate_wpa_fixup (void)
 {
-  return flag_wpa && gate_lto_out ();
+  return (flag_wpa || flag_ltrans) && gate_lto_out ();
 }
 
 struct ipa_opt_pass pass_ipa_lto_wpa_fixup =