RFC: C++ PATCH to remove -fabi-version=1 support

[Jason Merrill <jason at redhat dot com>]

I'm updating -Wabi to allow for warnings about changes between a 
previous ABI version and the currently selected one, and rather than 
adjust all the warnings for -fabi-version=1 I'd like to tear it out.  It 
has now been 10 years since GCC 3.4.

Any thoughts?

commit a1a98ba5d18a57832ea1f3df1cc1f5f9eeb621a1
Author: Jason Merrill <jason@redhat.com>
Date:   Mon Jun 9 16:41:07 2014 -0400

    gcc/c-family/
    	* c.opt (fabi-compat-version): New.
    	* c-opts.c (c_common_handle_option): Disallow -fabi-compat-version=1.
    	(c_common_post_options): Set flag_abi_compat_version.
    	* c-common.h (abi_version_crosses): New.
    gcc/cp/
    	* call.c (convert_arg_to_ellipsis): Use abi_version_crosses.
    	* mangle.c (write_type, write_expression): Likewise.
    	(write_template_arg): Likewise.
    	(finish_mangling_internal): Adjust -Wabi warning.
    	(mangle_decl): Make alias based on flag_abi_compat_version.

diff --git a/gcc/c-family/c-common.h b/gcc/c-family/c-common.h
index 83d5dee..6bf4051 100644
--- a/gcc/c-family/c-common.h
+++ b/gcc/c-family/c-common.h
@@ -619,6 +619,13 @@ extern const char *constant_string_class_name;
 /* C++ language option variables.  */
 
 
+/* Return TRUE if one of {flag_abi_version,flag_abi_compat_version} is
+   less than N and the other is at least N, for use by -Wabi.  */
+#define abi_version_crosses(N)			\
+  (abi_version_at_least(N)			\
+   != (flag_abi_compat_version == 0		\
+       || flag_abi_compat_version >= (N)))
+
 /* Nonzero means generate separate instantiation control files and
    juggle them at link time.  */
 
diff --git a/gcc/c-family/c-opts.c b/gcc/c-family/c-opts.c
index 4307507..8ff66a6 100644
--- a/gcc/c-family/c-opts.c
+++ b/gcc/c-family/c-opts.c
@@ -465,6 +465,15 @@ c_common_handle_option (size_t scode, const char *arg, int value,
 	}
       break;
 
+    case OPT_fabi_compat_version_:
+      if (value == 1)
+	{
+	  /* -fabi-version=1 support was removed after GCC 4.9.  */
+	  warning (0, "%qs is no longer supported", option->opt_text);
+	  flag_abi_compat_version = 2;
+	}
+      break;
+
     case OPT_fcanonical_system_headers:
       cpp_opts->canonical_system_headers = value;
       break;
@@ -919,6 +928,10 @@ c_common_post_options (const char **pfilename)
   if (flag_declone_ctor_dtor == -1)
     flag_declone_ctor_dtor = optimize_size;
 
+  /* Check compatibility with ABI version 2 (3.4-4.9) by default.  */
+  if (flag_abi_compat_version == -1)
+    flag_abi_compat_version = (flag_abi_version == 0 ? 2 : 0);
+
   if (cxx_dialect >= cxx11)
     {
       /* If we're allowing C++0x constructs, don't warn about C++98
diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
index 76e67d7..de5d555 100644
--- a/gcc/c-family/c.opt
+++ b/gcc/c-family/c.opt
@@ -845,6 +845,10 @@ d
 C ObjC C++ ObjC++ Joined
 ; Documented in common.opt.  FIXME - what about -dI, -dD, -dN and -dD?
 
+fabi-compat-version=
+C++ ObjC++ Joined RejectNegative UInteger Var(flag_abi_compat_version) Init(-1)
+The version of the C++ ABI used for -Wabi warnings and link compatibility aliases
+
 faccess-control
 C++ ObjC++ Var(flag_access_control) Init(1)
 Enforce class member access control semantics
diff --git a/gcc/cp/call.c b/gcc/cp/call.c
index ac14ce2..158984e 100644
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -6508,12 +6508,14 @@ convert_arg_to_ellipsis (tree arg, tsubst_flags_t complain)
     arg = null_pointer_node;
   else if (INTEGRAL_OR_ENUMERATION_TYPE_P (arg_type))
     {
-      if (SCOPED_ENUM_P (arg_type) && !abi_version_at_least (6))
+      if (SCOPED_ENUM_P (arg_type))
 	{
-	  if (complain & tf_warning)
-	    warning_at (loc, OPT_Wabi, "scoped enum %qT will not promote to an "
-			"integral type in a future version of GCC", arg_type);
-	  arg = cp_convert (ENUM_UNDERLYING_TYPE (arg_type), arg, complain);
+	  if (abi_version_crosses (6)
+	      && (complain & tf_warning))
+	    warning_at (loc, OPT_Wabi, "scoped enum %qT stopped promoting to "
+			"an integral type in -fabi-version=6", arg_type);
+	  if (!abi_version_at_least (6))
+	    arg = cp_convert (ENUM_UNDERLYING_TYPE (arg_type), arg, complain);
 	}
       arg = cp_perform_integral_promotions (arg, complain);
     }
diff --git a/gcc/cp/mangle.c b/gcc/cp/mangle.c
index 86319c6..8ed06f2 100644
--- a/gcc/cp/mangle.c
+++ b/gcc/cp/mangle.c
@@ -2012,10 +2012,9 @@ write_type (tree type)
 		  write_char ('_');
 		}
 	      else
-		{
-		  G.need_abi_warning = 1;
-		  write_string ("U8__vector");
-		}
+		write_string ("U8__vector");
+	      if (abi_version_crosses (4))
+		G.need_abi_warning = 1;
 	      write_type (TREE_TYPE (type));
 	      break;
 
@@ -2030,7 +2029,7 @@ write_type (tree type)
 			  && !DECLTYPE_FOR_LAMBDA_PROXY (type));
 
 	      /* In ABI <5, we stripped decltype of a plain decl.  */
-	      if (!abi_version_at_least (5)
+	      if (abi_version_crosses (5)
 		  && DECLTYPE_TYPE_ID_EXPR_OR_MEMBER_ACCESS_P (type))
 		{
 		  tree expr = DECLTYPE_TYPE_EXPR (type);
@@ -2053,8 +2052,11 @@ write_type (tree type)
 		  if (etype && !type_uses_auto (etype))
 		    {
 		      G.need_abi_warning = 1;
-		      write_type (etype);
-		      return;
+		      if (!abi_version_at_least (5))
+			{
+			  write_type (etype);
+			  return;
+			}
 		    }
 		}
 
@@ -2621,7 +2623,7 @@ write_expression (tree expr)
 	      write_char ('L');
 	      write_unsigned_number (delta - 1);
 	    }
-	  else
+	  if (abi_version_crosses (5))
 	    G.need_abi_warning = true;
 	}
       write_char ('p');
@@ -2853,12 +2855,13 @@ write_expression (tree expr)
       name = operator_name_info[(int) code].mangled_name;
 
       /* We used to mangle const_cast and static_cast like a C cast.  */
-      if (!abi_version_at_least (6)
+      if (abi_version_crosses (6)
 	  && (code == CONST_CAST_EXPR
 	      || code == STATIC_CAST_EXPR))
 	{
-	  name = operator_name_info[CAST_EXPR].mangled_name;
 	  G.need_abi_warning = 1;
+	  if (!abi_version_at_least (6))
+	    name = operator_name_info[CAST_EXPR].mangled_name;
 	}
 
       if (name == NULL)
@@ -2929,7 +2932,7 @@ write_expression (tree expr)
 	case PREDECREMENT_EXPR:
 	  if (abi_version_at_least (6))
 	    write_char ('_');
-	  else
+	  if (abi_version_crosses (6))
 	    G.need_abi_warning = 1;
 	  /* Fall through.  */
 
@@ -3064,7 +3067,7 @@ write_template_arg (tree node)
     {
       if (abi_version_at_least (6))
 	node = BASELINK_FUNCTIONS (node);
-      else
+      if (abi_version_crosses (6))
 	/* We wrongly wrapped a class-scope function in X/E.  */
 	G.need_abi_warning = 1;
     }
@@ -3077,10 +3080,9 @@ write_template_arg (tree node)
       if (abi_version_at_least (6))
 	write_char ('J');
       else
-	{
-	  write_char ('I');
-	  G.need_abi_warning = 1;
-	}
+	write_char ('I');
+      if (abi_version_crosses (6))
+	G.need_abi_warning = 1;
       for (i = 0; i < length; ++i)
         write_template_arg (TREE_VEC_ELT (args, i));
       write_char ('E');
@@ -3100,12 +3102,11 @@ write_template_arg (tree node)
       /* Until ABI version 3, the underscore before the mangled name
 	 was incorrectly omitted.  */
       if (!abi_version_at_least (3))
-	{
-	  G.need_abi_warning = 1;
-	  write_char ('Z');
-	}
+	write_char ('Z');
       else
 	write_string ("_Z");
+      if (abi_version_crosses (3))
+	G.need_abi_warning = 1;
       write_encoding (node);
       write_char ('E');
     }
@@ -3289,9 +3290,16 @@ static void
 finish_mangling_internal (const bool warn)
 {
   if (warn_abi && warn && G.need_abi_warning)
-    warning (OPT_Wabi, "the mangled name of %qD will change in a future "
-	     "version of GCC",
-	     G.entity);
+    {
+      int v1, v2;
+      if (abi_version_at_least (flag_abi_compat_version))
+	v1 = flag_abi_compat_version, v2 = flag_abi_version;
+      else
+	v1 = flag_abi_version, v2 = flag_abi_compat_version;
+      warning (OPT_Wabi, "the mangled name of %qD changes between "
+	       "-fabi-version=%d and -fabi-version=%d",
+	       G.entity, v1, v2);
+    }
 
   /* Clear all the substitutions.  */
   vec_safe_truncate (G.substitutions, 0);
@@ -3439,12 +3447,17 @@ mangle_decl (const tree decl)
 
 #ifdef ASM_OUTPUT_DEF
       save_ver = flag_abi_version;
-      flag_abi_version = 0;
+      flag_abi_version = flag_abi_compat_version;
       id2 = mangle_decl_string (decl);
       id2 = targetm.mangle_decl_assembler_name (decl, id2);
       flag_abi_version = save_ver;
 
+      if (flag_abi_compat_version != 0
+	  && IDENTIFIER_GLOBAL_VALUE (id2))
+	return;
+
       alias = make_alias_for (decl, id2);
+      SET_IDENTIFIER_GLOBAL_VALUE (id2, alias);
       DECL_IGNORED_P (alias) = 1;
       TREE_PUBLIC (alias) = TREE_PUBLIC (decl);
       DECL_VISIBILITY (alias) = DECL_VISIBILITY (decl);
diff --git a/gcc/testsuite/g++.dg/cpp0x/enum13.C b/gcc/testsuite/g++.dg/cpp0x/enum13.C
index 5e4a532..e399bb5 100644
--- a/gcc/testsuite/g++.dg/cpp0x/enum13.C
+++ b/gcc/testsuite/g++.dg/cpp0x/enum13.C
@@ -15,7 +15,5 @@ void foo(int x, ...) {
 }
 
 int main() {
-   foo(0, A::X);		// { dg-warning "will not promote" }
+   foo(0, A::X);		// { dg-warning "promot" }
 }
-
-// { dg-prune-output "note" }