c-opts.c (c_common_post_options): Warn about useless -Wabi.

	* c-opts.c (c_common_post_options): Warn about useless -Wabi.

	(c_common_handle_option) [OPT_Wabi_]: Remove flag_abi_compat_version
	handling.

From-SVN: r261571

gcc/c-family/ChangeLog

 2018-06-13  Jason Merrill  <jason@redhat.com>
 
+	* c-opts.c (c_common_post_options): Warn about useless -Wabi.
+	(c_common_handle_option) [OPT_Wabi_]: Remove flag_abi_compat_version
+	handling.
+
 	PR c++/86094 - wrong code with defaulted move ctor.
 	* c-opts.c (c_common_post_options): Bump the current ABI version to
 	13.  Set warn_abi_version and flag_abi_compat_version to the current

gcc/c-family/c-opts.c

@@ -417,8 +417,6 @@ c_common_handle_option (size_t scode, const char *arg, int value,
 	  value = 2;
 	}
       warn_abi_version = value;
-      if (flag_abi_compat_version == -1)
-	flag_abi_compat_version = value;
       break;
 
     case OPT_fcanonical_system_headers:
@@ -942,7 +940,17 @@ c_common_post_options (const char **pfilename)
     {
       warn_abi_version = latest_abi_version;
       if (flag_abi_version == latest_abi_version)
+	{
+	  if (warning (OPT_Wabi, "-Wabi won't warn about anything"))
+	    {
+	      inform (input_location, "-Wabi warns about differences "
+		      "from the most up-to-date ABI, which is also used "
+		      "by default");
+	      inform (input_location, "use e.g. -Wabi=11 to warn about "
+		      "changes from GCC 7");
+	    }
 	  flag_abi_compat_version = abi_compat_default;
+	}
       else
 	flag_abi_compat_version = latest_abi_version;
     }

gcc/testsuite/g++.dg/abi/pr83489.C

 // PR c++/83489
-// { dg-options "-Wabi" }
+// { dg-options "-Wabi=11" }
 
 struct A
 {

gcc/testsuite/obj-c++.dg/bitfield-1.mm

@@ -5,7 +5,7 @@
    superclasses should be removed).  */
 /* Contributed by Ziemowit Laski <zlaski@apple.com>.  */
 /* { dg-do run } */
-/* { dg-options "-Wpadded -Wabi" } */
+/* { dg-options "-Wpadded -Wabi=8" } */
 
 /* Leave blank lines here to keep warnings on the same lines.  */
 

gcc/testsuite/obj-c++.dg/layout-1.mm

 /* Ensure that we do not get bizarre warnings referring to
    __attribute__((packed)) or some such.  */
 /* { dg-do compile } */
-/* { dg-options "-Wpadded -Wpacked -Wabi" } */
+/* { dg-options "-Wpadded -Wpacked -Wabi=8" } */
 
 #include "../objc-obj-c++-shared/TestsuiteObject.h"