AIX Encode function section and rs6000 MI Thunk

AIX XCOFF symbols can be labels or qualnames (names with an appended
    mapping class).  CSECTs must be declared with a mapping class.
    Within an assembler file, the symbol names with and without the mapping
    class are unique.  An object file symbol table only presents the symbol
    name without the mapping class, but the section of the symbol depends on
    the mapping class.

    The AIX XCOFF assembly language does not support first class aliases.
    GCC implements symbol aliases by emitting additional labels for the function
    or object.  When GCC encodes sections for a DECL, it must distinguish
    between the primary definition and the aliases, which don't have a
    mapping class encoding.

            .globl foo[DS]
            .globl .foo
            .globl foo1
            .globl .foo1
            .csect foo[DS]
    foo:
    foo1:
            .long .foo, TOC[tc0] 0
            .csect .foo[PR]
    .foo:
    .foo1:

The CSECT foo[DS] and label foo are distinct.  foo1 is another label (alias)
for foo, and .foo1 is another label (alias) for .foo.  foo is the function
descriptor and .foo is the code.

    This patch adds the [DS] mapping class to the encoding of FUNCTION_DECL
    but ensures that mapping class is not added to function aliases.

    rs6000_output_mi_thunk is updated to emit the function name that matches
    the behavior of GCC final.c for normal functions: get_fnname_from_decl based
    on the RTL name, not the DECL name.

Bootstrapped on powerpc-ibm-aix7.2.3.0 and powerpc64le-linux.

            * config/rs6000/rs6000-call.c (rs6000_output_mi_thunk): Use
            get_fnname_from_decl for name of thunk.
            * config/rs6000/rs6000.c (rs6000_declare_alias): Use assemble_name
            and ASM_OUTPUT_LABEL.
            (rs6000_xcoff_declare_function_name): Use assemble_name and
            ASM_OUTPUT_LABEL.
            (rs6000_xcoff_declare_object_name): Use ASM_OUTPUT_LABEL.
            (rs6000_xcoff_encode_section_info): Don't add mapping class
            for aliases.  Always add [DS] mapping class to primary
            FUNCTION_DECL.
            (rs6000_asm_weaken_decl): Don't explicitly add [DS].

 @@ -21574,21 +21573,24 @@ rs6000_xcoff_declare_function_name (FILE
*file, const char *name, tree decl)
       RS6000_OUTPUT_BASENAME (file, buffer);
       putc ('\n', file);
     }
+
   fputs ("\t.csect ", file);
-  RS6000_OUTPUT_BASENAME (file, buffer);
-  fputs (TARGET_32BIT ? "[DS]\n" : "[DS],3\n", file);
-  RS6000_OUTPUT_BASENAME (file, buffer);
-  fputs (":\n", file);
+  assemble_name (file, buffer);
+  fputs (TARGET_32BIT ? "\n" : ",3\n", file);
+
+  ASM_OUTPUT_LABEL (file, buffer);
+
   symtab_node::get (decl)->call_for_symbol_and_aliases (rs6000_declare_alias,
                                                        &data, true);
   fputs (TARGET_32BIT ? "\t.long ." : "\t.llong .", file);
   RS6000_OUTPUT_BASENAME (file, buffer);
   fputs (", TOC[tc0], 0\n", file);
+
   in_section = NULL;
   switch_to_section (function_section (decl));
   putc ('.', file);
-  RS6000_OUTPUT_BASENAME (file, buffer);
-  fputs (":\n", file);
+  ASM_OUTPUT_LABEL (file, buffer);
+
   data.function_descriptor = true;
   symtab_node::get (decl)->call_for_symbol_and_aliases (rs6000_declare_alias,
                                                        &data, true);
@@ -21683,8 +21685,7 @@ void
 rs6000_xcoff_declare_object_name (FILE *file, const char *name, tree decl)
 {
   struct declare_alias_data data = {file, false};
-  RS6000_OUTPUT_BASENAME (file, name);
-  fputs (":\n", file);
+  ASM_OUTPUT_LABEL (file, name);
   symtab_node::get_create (decl)->call_for_symbol_and_aliases
(rs6000_declare_alias,
                                                               &data, true);
 }
@@ -21740,20 +21741,19 @@ rs6000_xcoff_encode_section_info (tree decl,
rtx rtl, int first)

   symname = XSTR (symbol, 0);

-  /* Append CSECT mapping class, unless the symbol already is qualified.  */
+  /* Append CSECT mapping class, unless the symbol already is qualified.
+     Aliases are implemented as labels, so the symbol name should not add
+     a mapping class.  */
   if (decl
       && DECL_P (decl)
       && VAR_OR_FUNCTION_DECL_P (decl)
-      && lookup_attribute ("alias", DECL_ATTRIBUTES (decl)) == NULL_TREE
+      && symtab_node::get (decl)->alias == 0
       && symname[strlen (symname) - 1] != ']')
     {
       const char *smclass = NULL;

       if (TREE_CODE (decl) == FUNCTION_DECL)
-       {
-         if (DECL_EXTERNAL (decl))
-           smclass = "[DS]";
-       }
+       smclass = "[DS]";
       else if (DECL_THREAD_LOCAL_P (decl))
        {
          if (bss_initializer_p (decl))
@@ -21796,8 +21796,6 @@ rs6000_asm_weaken_decl (FILE *stream, tree decl,
   if (decl && TREE_CODE (decl) == FUNCTION_DECL
       && DEFAULT_ABI == ABI_AIX && DOT_SYMBOLS)
     {
-      if (TARGET_XCOFF && name[strlen (name) - 1] != ']')
-       fputs ("[DS]", stream);
 #if TARGET_XCOFF && HAVE_GAS_HIDDEN
       if (TARGET_XCOFF)
        fputs (rs6000_xcoff_visibility (decl), stream);
@@ -21810,6 +21808,7 @@ rs6000_asm_weaken_decl (FILE *stream, tree decl,
     fputs (rs6000_xcoff_visibility (decl), stream);
 #endif
   fputc ('\n', stream);
+
   if (val)
     {
 #ifdef ASM_OUTPUT_DEF