Hi Jan,
Patch looks good to me (but I am not an approvee nor a reviewer).
I think always having these functions in the debug info would be helpful
but maybe instead of making them optional we could mark them such that a
tool reading the dwarf info can decide to use them or not.
Remi
On 10/1/25 12:11, Jan Hubicka wrote:
> External email: Use caution opening links or attachments
>
>
> Hi,
> this change was discussed on Cauldron. Auto-profile needs to know linkage
> names of functions, even those that has been inlined, to correctly map the
> profile back to symbol table.
>
> Currently dwarf2out does not output linkage names of non-public functions
> which
> makes them appear by their dwarf name that is not even unique within single
> unit.
>
> Note that this patch does not solve the problem that internal linkage names
> may
> clash across translation unit. LLVM uses -funique-internal-linkage-names that
> adds .uniq_<md5hash> suffixes to all internal symbols. This breaks ASM
> statements and ohter things. They are working on replacing it by using IDs
> essentially ideantical to our profile ID (which is a hash of symbol name and
> for insternal symbols also of translation unit). The profile IDs are not
> stored
> in debug info but go into specal section.
>
> I think we can get around by storing (linkage name,tranlsation unit name)
> pairs
> into the auto-profile for which there is already patch that needs some extra
> work
> I plan to work on next.
>
> I wonder if we want to have -gdebug-for-auto-profile (probably on by default)
> that controls parts of debug info used only for auto-fdo, such as this change.
> THis could also control discriminators. While it would be nice to have
> auto-fdo to work with default debug info, I think this would be useful to keep
> track what we do for autofdo only and how expensive it is.
>
> Bootstrapped/regtested x86_64-linux, OK?
> As a followup i will remove a twisted heuiristics i added to auto-fdo to
> handle
> dwarf names next.
>
> gcc/ChangeLog:
>
> * dwarf2out.cc (add_linkage_name): Store linkage names
> of private function symbols to help auto-fdo.
>
> diff --git a/gcc/dwarf2out.cc b/gcc/dwarf2out.cc
> index 0bd8474bc37..95d9f219cf0 100644
> --- a/gcc/dwarf2out.cc
> +++ b/gcc/dwarf2out.cc
> @@ -22235,7 +22235,10 @@ add_linkage_name (dw_die_ref die, tree decl)
> {
> if (debug_info_level > DINFO_LEVEL_NONE
> && VAR_OR_FUNCTION_DECL_P (decl)
> - && TREE_PUBLIC (decl)
> + && (TREE_PUBLIC (decl)
> + /* Linkage names of internal function symbols
> + are used by auto-fdo. */
> + || TREE_CODE (decl) == FUNCTION_DECL)
> && !(VAR_P (decl) && DECL_REGISTER (decl))
> && die->die_tag != DW_TAG_member)
> add_linkage_name_raw (die, decl);
