[c-family] Issue a warning in C++ on pragma scalar_storage_order

[Eric Botcazou]

Hi,

this plugs the hole reported by Florian on the gcc@ list, namely that no 
warning is issued with -Wall in C++ on pragma scalar_storage_order.

Tested on x86_64-suse-linux, OK for the mainline?  And some branches?


2017-09-15  Eric Botcazou  <ebotca...@adacore.com>

        * c-pragma.c (handle_pragma_scalar_storage_order): Expand on error
        message for non-uniform endianness and issue a warning in C++.


2017-09-15  Eric Botcazou  <ebotca...@adacore.com>

        * g++.dg/sso-1.C: New test.
        * g++.dg/sso-2.C: Likewise.

-- 
Eric Botcazou
Index: c-family/c-pragma.c
===================================================================
--- c-family/c-pragma.c	(revision 252749)
+++ c-family/c-pragma.c	(working copy)
@@ -415,7 +415,19 @@ handle_pragma_scalar_storage_order (cpp_
   tree x;
 
   if (BYTES_BIG_ENDIAN != WORDS_BIG_ENDIAN)
-    error ("scalar_storage_order is not supported");
+    {
+      error ("scalar_storage_order is not supported because endianness "
+	     "is not uniform");
+      return;
+    }
+
+  if (c_dialect_cxx ())
+    {
+      if (warn_unknown_pragmas > in_system_header_at (input_location))
+	warning (OPT_Wunknown_pragmas,
+		 "%<#pragma scalar_storage_order%> is not supported for C++");
+      return;
+    }
 
   token = pragma_lex (&x);
   if (token != CPP_NAME)

/* Test support of scalar_storage_order attribute */

/* { dg-do compile } */

struct __attribute__((scalar_storage_order("little-endian"))) Rec /* { dg-warning "attribute ignored" } */
{
  int i;
};

/* Test support of scalar_storage_order pragma */

/* { dg-do compile } */
/* { dg-options "-Wall" } */

#pragma scalar_storage_order little-endian /* { dg-warning "not supported" } */