[Bug target/115324] [12/13 Regression] PCH of rs6000 builtins broken

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115324

--- Comment #7 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-12 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:bda8c28e6fcdbe0b486b54616877eec32c86d322

commit r12-10531-gbda8c28e6fcdbe0b486b54616877eec32c86d322
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Mon Jun 3 23:11:06 2024 +0200

    rs6000: Fix up PCH in --enable-host-pie builds [PR115324]

    PCH doesn't work properly in --enable-host-pie configurations on
    powerpc*-linux*.
    The problem is that the rs6000_builtin_info and rs6000_instance_info
    arrays mix pointers to .rodata/.data (bifname and attr_string point
    to string literals in .rodata section, and the next member is either NULL
    or &rs6000_instance_info[XXX]) and GC member (tree fntype).
    Now, for normal GC this works just fine, we emit
      {
        &rs6000_instance_info[0].fntype,
        1 * (RS6000_INST_MAX),
        sizeof (rs6000_instance_info[0]),
        &gt_ggc_mx_tree_node,
        &gt_pch_nx_tree_node
      },
      {
        &rs6000_builtin_info[0].fntype,
        1 * (RS6000_BIF_MAX),
        sizeof (rs6000_builtin_info[0]),
        &gt_ggc_mx_tree_node,
        &gt_pch_nx_tree_node
      },
    GC roots which are strided and thus cover only the fntype members of all
    the elements of the two arrays.
    For PCH though it actually results in saving those huge arrays (one is
    130832 bytes, another 81568 bytes) into the .gch files and loading them
back
    in full.  While the bifname and attr_string and next pointers are marked as
    GTY((skip)), they are actually saved to point to the .rodata and .data
    sections of the process which writes the PCH, but because cc1/cc1plus etc.
    are position independent executables with --enable-host-pie, when it is
    loaded from the PCH file, it can point in a completely different addresses
    where nothing is mapped at all or some random different thing appears at.
    While gengtype supports the callback option, that one is meant for
    relocatable function pointers and doesn't work in the case of GTY arrays
    inside of .data section anyway.

    So, either we'd need to add some further GTY extensions, or the following
    patch instead reworks it such that the fntype members which were the only
    reason for PCH in those arrays are moved to separate arrays.

    Size-wise in .data sections it is (in bytes):

                                 vanilla    patched
    rs6000_builtin_info          130832     110704
    rs6000_instance_info          81568      40784
    rs6000_overload_info           7392       7392
    rs6000_builtin_info_fntype        0      10064
    rs6000_instance_info_fntype       0      20392
    sum                          219792     189336

    where previously we saved/restored for PCH those 130832+81568 bytes, now we
    save/restore just 10064+20392 bytes, so this change is beneficial for the
    data section size.

    Unfortunately, it grows the size of the rs6000_init_generated_builtins
    function, vanilla had 218328 bytes, patched has 228668.

    When I applied
     void
     rs6000_init_generated_builtins ()
     {
    +  bifdata *rs6000_builtin_info_p;
    +  tree *rs6000_builtin_info_fntype_p;
    +  ovlddata *rs6000_instance_info_p;
    +  tree *rs6000_instance_info_fntype_p;
    +  ovldrecord *rs6000_overload_info_p;
    +  __asm ("" : "=r" (rs6000_builtin_info_p) : "0" (rs6000_builtin_info));
    +  __asm ("" : "=r" (rs6000_builtin_info_fntype_p) : "0"
(rs6000_builtin_info_fntype));
    +  __asm ("" : "=r" (rs6000_instance_info_p) : "0" (rs6000_instance_info));
    +  __asm ("" : "=r" (rs6000_instance_info_fntype_p) : "0"
(rs6000_instance_info_fntype));
    +  __asm ("" : "=r" (rs6000_overload_info_p) : "0" (rs6000_overload_info));
    +  #define rs6000_builtin_info rs6000_builtin_info_p
    +  #define rs6000_builtin_info_fntype rs6000_builtin_info_fntype_p
    +  #define rs6000_instance_info rs6000_instance_info_p
    +  #define rs6000_instance_info_fntype rs6000_instance_info_fntype_p
    +  #define rs6000_overload_info rs6000_overload_info_p
    +
    hack by hand, the size of the function is 209700 though, so if really
    wanted, we could add __attribute__((__noipa__)) to the function when
    building with recent enough GCC and pass pointers to the first elements
    of the 5 arrays to the function as arguments.  If you want such a change,
    could that be done incrementally?

    2024-06-03  Jakub Jelinek  <jakub@redhat.com>

            PR target/115324
            * config/rs6000/rs6000-gen-builtins.cc (write_decls): Remove
            GTY markup from struct bifdata and struct ovlddata and remove their
            fntype members.  Change next member in struct ovlddata and
            first_instance member of struct ovldrecord to have int type rather
            than struct ovlddata *.  Remove GTY markup from rs6000_builtin_info
            and rs6000_instance_info arrays, declare new
            rs6000_builtin_info_fntype and rs6000_instance_info_fntype arrays,
            which have GTY markup.
            (write_bif_static_init): Adjust for the above changes.
            (write_ovld_static_init): Likewise.
            (write_init_bif_table): Likewise.
            (write_init_ovld_table): Likewise.
            * config/rs6000/rs6000-builtin.cc (rs6000_init_builtins): Likewise.
            * config/rs6000/rs6000-c.cc (find_instance): Likewise.  Make
static.
            (altivec_resolve_overloaded_builtin): Adjust for the above changes.

    (cherry picked from commit 4cf2de9b5268224816a3d53fdd2c3d799ebfd9c8)