Re: [patch] preserve DECL_ORIGINAL_TYPE invariant in remap_decl

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Wed, Jun 22, 2016 at 2:12 AM, Eric Botcazou <ebotcazou@adacore.com> wrote:
> Hi,
>
> the invariant is that DECL_ORIGINAL_TYPE (t) != TREE_TYPE (t) as pointer value
> if t is a TYPE_DECL.  It's enforced by the DWARF back-end:
>
>       if (DECL_ORIGINAL_TYPE (decl))
>         {
>           type = DECL_ORIGINAL_TYPE (decl);
>
>           if (type == error_mark_node)
>             return;
>
>           gcc_assert (type != TREE_TYPE (decl));
>
> [...]
>
>       /* Prevent broken recursion; we can't hand off to the same type.  */
>       gcc_assert (DECL_ORIGINAL_TYPE (TYPE_NAME (type)) != type);
>
> Unfortunately it can be easily broken in remap_decl:
>
>       /* Remap types, if necessary.  */
>       TREE_TYPE (t) = remap_type (TREE_TYPE (t), id);
>       if (TREE_CODE (t) == TYPE_DECL)
>         DECL_ORIGINAL_TYPE (t) = remap_type (DECL_ORIGINAL_TYPE (t), id);
>
> If TREE_TYPE (t) is for example a pointer to a variably-modified type, then
> the types are remapped by means of build_pointer_type_for_mode, which means
> that they are also canonicalized, so TREE_TYPE (t) == DECL_ORIGINAL_TYPE (t)
> after the remapping.  This happens in Ada, but also in C for:
>
> extern void bar (void *) __attribute__((noreturn));
>
> static int foo (int i, unsigned int n)
> {
>   if (i == 0)
>     {
>       struct S { int a[n]; };
>       typedef struct S *ptr;
>       ptr p = __builtin_malloc (sizeof (struct S));
>       bar (p);
>     }
>
>   return i > 0 ? 1 : -1;
> }
>
> int f1 (int i, unsigned int n)
> {
>   return foo (i, n);
> }
>
> int f2 (int i, unsigned int n)
> {
>   return foo (i, n);
> }
>
> when foo is split into 2 parts at -O2.
>
> This generally goes unnoticed because the inliner sets DECL_ABSTRACT_ORIGIN on
> the remapped TYPE_DECL, so gen_typedef_die skips it:
>
>   type_die = new_die (DW_TAG_typedef, context_die, decl);
>   origin = decl_ultimate_origin (decl);
>   if (origin != NULL)
>     add_abstract_origin_attribute (type_die, origin);
>   else
>     {
>       tree type;
>
>       add_name_and_src_coords_attributes (type_die, decl);
>       if (DECL_ORIGINAL_TYPE (decl))
>         {
>           type = DECL_ORIGINAL_TYPE (decl);
>
>           if (type == error_mark_node)
>             return;
>
>           gcc_assert (type != TREE_TYPE (decl));
>           equate_type_number_to_die (TREE_TYPE (decl), type_die);
>         }
>
> But, in LTO mode, DECL_ABSTRACT_ORIGIN is not streamed so it's another story
> and this for example breaks the LTO build of the Ada compiler at -O2 -g.
>
> Hence the attached ad-hoc attempt at preserving the invariant in remap_decl,
> which appears to work and is sufficient to fix the aforementioned bootstrap.
>
> Tested on x86_64-suse-linux, OK for the mainline?
>
>
> 2016-06-22  Eric Botcazou  <ebotcazou@adacore.com>
>
>         * tree-inline.c (remap_decl): Preserve DECL_ORIGINAL_TYPE invariant.
>

This caused:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71645


-- 
H.J.