Re: DATA_ALIGNMENT vs. DECL_USER_ALIGNMENT

[Ulrich Weigand <weigand@immd1.informatik.uni-erlangen.de>]

Richard Kenner wrote:

> After extensive discussion, I think the proper thing is for the Ada
> front end to set TYPE_USER_ALIGN on all (or nearly all) types, but
> not to set DECL_USER_ALIGN on any decls.  However, when I looked, I see
> that is indeed what it *does* do, so I'm now confused about the problem
> you are seeing.

Well, it looks like DECL_USER_ALIGN is copied from TYPE_USER_ALIGN
in do_type_align (stor-layout.c), called via this call chain:

#0  do_type_align (type=0x100001ff000, decl=0x1000025a680) at ../../gcc-head/gcc/stor-layout.c:369
#1  0x0000000080685996 in layout_decl (decl=0x1000025a680, known_align=0) at ../../gcc-head/gcc/stor-layout.c:429
#2  0x00000000806ae7b8 in build_decl (code=VAR_DECL, name=0x10000258438, type=0x100001ff000) at ../../gcc-head/gcc/tree.c:2428
#3  0x0000000080038a88 in create_var_decl (var_name=0x10000258438, asm_name=0x10000258438, type=0x100001ff000, var_init=0x100001ccb40, const_flag=0,
    public_flag=1, extern_flag=0, static_flag=0, attr_list=0x0) at ../../gcc-head/gcc/ada/utils.c:1290
#4  0x000000008000ae98 in gnat_to_gnu_entity (gnat_entity=1370, gnu_expr=0x100001ccb40, definition=1) at ../../gcc-head/gcc/ada/decl.c:1021
#5  0x0000000080064864 in tree_transform (gnat_node=1376) at ../../gcc-head/gcc/ada/trans.c:773
#6  0x00000000800625b4 in gnat_to_code (gnat_node=1376) at ../../gcc-head/gcc/ada/trans.c:238
#7  0x0000000080075d72 in process_decls (gnat_decls=-99999987, gnat_decls2=0, gnat_end_list=0, pass1p=1, pass2p=1) at ../../gcc-head/gcc/ada/trans.c:4332
#8  0x00000000800712fa in tree_transform (gnat_node=1355) at ../../gcc-head/gcc/ada/trans.c:3229
#9  0x00000000800625b4 in gnat_to_code (gnat_node=1355) at ../../gcc-head/gcc/ada/trans.c:238
#10 0x000000008006256a in gigi (gnat_root=1355, max_gnat_node=1874, number_name=1117, nodes_ptr=0x1000023f010, next_node_ptr=0x100003f7010,
    prev_node_ptr=0x10000428010, elists_ptr=0x80c4f450, elmts_ptr=0x80c4faa0, strings_ptr=0x80cb1c90, string_chars_ptr=0x80cb0900, list_headers_ptr=0x80cd33b0,
    number_units=2, file_info_ptr=0x1ffffffee28 "\021á¦0", standard_integer=42, standard_long_long_float=66, standard_exception_type=1033,
    gigi_operating_mode=0) at ../../gcc-head/gcc/ada/trans.c:221
internal error - unimplemented function unk_lang_create_fundamental_type called.
(looks like my gdb doesn't like Ada ...)

What happens is that build_decl calls make_node (VAR_DECL), which 
returns a node with DECL_ALIGN == 1, and subsequently calls layout_decl,
which calls do_type_align:

static inline void
do_type_align (tree type, tree decl)
{
  if (TYPE_ALIGN (type) > DECL_ALIGN (decl))
    {
      DECL_ALIGN (decl) = TYPE_ALIGN (type);
      DECL_USER_ALIGN (decl) = TYPE_USER_ALIGN (type);
    }
}

and since TYPE_ALIGN is 8 and DECL_ALIGN is 1,
DECL_USER_ALIGN gets set to TYPE_USER_ALIGN (which is set).

Bye,
Ulrich

-- 
  Dr. Ulrich Weigand
  weigand@informatik.uni-erlangen.de