re PR lto/78562 (Wrong warning for built-in functions with -flto)

gcc/lto/
	PR lto/78562
	* lto-symtab.c (lto_symtab_merge_decls_2): Don't diagnose type
	mismatch if the two types are built-in.

From-SVN: r243008

gcc/lto/ChangeLog

+2016-11-30  Georg-Johann Lay  <avr@gjlay.de>
+
+	PR lto/78562
+	* lto-symtab.c (lto_symtab_merge_decls_2): Don't diagnose type
+	mismatch if the two types are built-in.
+
 2016-11-26  Prathamesh Kulkarni  <prathamesh.kulkarni@linaro.org>
 
 	* lto-lang.c (lto_init): Remove initialization of ptrdiff_type_node.

gcc/lto/lto-symtab.c

@@ -655,6 +655,14 @@ lto_symtab_merge_decls_2 (symtab_node *first, bool diagnosed_p)
   /* Diagnose all mismatched re-declarations.  */
   FOR_EACH_VEC_ELT (mismatches, i, decl)
     {
+      /* Do not diagnose two built-in declarations, there is no useful
+         location in that case.  It also happens for AVR if two built-ins
+         use the same asm name because their libgcc assembler code is the
+         same, see PR78562.  */
+      if (DECL_IS_BUILTIN (prevailing->decl)
+	  && DECL_IS_BUILTIN (decl))
+	continue;
+
       int level = warn_type_compatibility_p (TREE_TYPE (prevailing->decl),
 					     TREE_TYPE (decl),
 					     DECL_COMDAT (decl));