Re: [PATCH v5] i386: Allow -mlarge-data-threshold with -mcmodel=large

[Fangrui Song <maskray@google.com>]

On Mon, Oct 16, 2023 at 12:10 PM Uros Bizjak <ubizjak@gmail.com> wrote:
>
> On Mon, Oct 16, 2023 at 8:24 PM Fangrui Song <maskray@google.com> wrote:
> >
> > On 2023-10-16, Uros Bizjak wrote:
> > >On Tue, Aug 1, 2023 at 9:51 PM Fangrui Song <maskray@google.com> wrote:
> > >>
> > >> When using -mcmodel=medium, large data objects larger than the
> > >> -mlarge-data-threshold threshold are placed into large data sections
> > >> (.lrodata, .ldata, .lbss and some variants).  GNU ld and ld.lld 17 place
> > >> .l* sections into separate output sections.  If small and medium code
> > >> model object files are mixed, the .l* sections won't exert relocation
> > >> overflow pressure on sections in object files built with -mcmodel=small.
> > >>
> > >> However, when using -mcmodel=large, -mlarge-data-threshold doesn't
> > >> apply.  This means that the .rodata/.data/.bss sections may exert
> > >> relocation overflow pressure on sections in -mcmodel=small object files.
> > >>
> > >> This patch allows -mcmodel=large to generate .l* sections and drops an
> > >> unneeded documentation restriction that the value must be the same.
> > >>
> > >> Link: https://groups.google.com/g/x86-64-abi/c/jnQdJeabxiU
> > >> ("Large data sections for the large code model")
> > >>
> > >> Signed-off-by: Fangrui Song <maskray@google.com>
> > >>
> > >> ---
> > >> Changes from v1 (https://gcc.gnu.org/pipermail/gcc-patches/2023-April/616947.html):
> > >> * Clarify commit message. Add link to https://groups.google.com/g/x86-64-abi/c/jnQdJeabxiU
> > >>
> > >> Changes from v2
> > >> * Drop an uneeded limitation in the documentation.
> > >>
> > >> Changes from v3
> > >> * Change scan-assembler directives to use \. to match literal .
> > >> ---
> > >>  gcc/config/i386/i386.cc                    | 15 +++++++++------
> > >>  gcc/config/i386/i386.opt                   |  2 +-
> > >>  gcc/doc/invoke.texi                        |  6 +++---
> > >>  gcc/testsuite/gcc.target/i386/large-data.c | 13 +++++++++++++
> > >>  4 files changed, 26 insertions(+), 10 deletions(-)
> > >>  create mode 100644 gcc/testsuite/gcc.target/i386/large-data.c
> > >>
> > >> diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc
> > >> index eabc70011ea..37e810cc741 100644
> > >> --- a/gcc/config/i386/i386.cc
> > >> +++ b/gcc/config/i386/i386.cc
> > >> @@ -647,7 +647,8 @@ ix86_can_inline_p (tree caller, tree callee)
> > >>  static bool
> > >>  ix86_in_large_data_p (tree exp)
> > >>  {
> > >> -  if (ix86_cmodel != CM_MEDIUM && ix86_cmodel != CM_MEDIUM_PIC)
> > >> +  if (ix86_cmodel != CM_MEDIUM && ix86_cmodel != CM_MEDIUM_PIC &&
> > >> +      ix86_cmodel != CM_LARGE && ix86_cmodel != CM_LARGE_PIC)
> > >
> > >Please split multi-line expression before the operator, not after it,
> > >as instructed in GNU Coding Standards [1] ...
> > >
> > >[1] https://www.gnu.org/prep/standards/html_node/Formatting.html
> > >
> > >>      return false;
> > >>
> > >>    if (exp == NULL_TREE)
> > >> @@ -858,8 +859,9 @@ x86_elf_aligned_decl_common (FILE *file, tree decl,
> > >>                         const char *name, unsigned HOST_WIDE_INT size,
> > >>                         unsigned align)
> > >>  {
> > >> -  if ((ix86_cmodel == CM_MEDIUM || ix86_cmodel == CM_MEDIUM_PIC)
> > >> -      && size > (unsigned int)ix86_section_threshold)
> > >> +  if ((ix86_cmodel == CM_MEDIUM || ix86_cmodel == CM_MEDIUM_PIC ||
> > >> +      ix86_cmodel == CM_LARGE || ix86_cmodel == CM_LARGE_PIC) &&
> > >> +     size > (unsigned int)ix86_section_threshold)
> > >
> > >... also here ...
> > >
> > >>      {
> > >>        switch_to_section (get_named_section (decl, ".lbss", 0));
> > >>        fputs (LARGECOMM_SECTION_ASM_OP, file);
> > >> @@ -879,9 +881,10 @@ void
> > >>  x86_output_aligned_bss (FILE *file, tree decl, const char *name,
> > >>                         unsigned HOST_WIDE_INT size, unsigned align)
> > >>  {
> > >> -  if ((ix86_cmodel == CM_MEDIUM || ix86_cmodel == CM_MEDIUM_PIC)
> > >> -      && size > (unsigned int)ix86_section_threshold)
> > >> -    switch_to_section (get_named_section (decl, ".lbss", 0));
> > >> +  if ((ix86_cmodel == CM_MEDIUM || ix86_cmodel == CM_MEDIUM_PIC ||
> > >> +       ix86_cmodel == CM_LARGE || ix86_cmodel == CM_LARGE_PIC) &&
> > >> +      size > (unsigned int)ix86_section_threshold)
> > >
> > >... and here.
> > >
> > >OK with these formatting changes.
> > >
> > >Thanks,
> > >Uros.
> >
> > Thank you for the review!
> > Posted PATCH v5 https://gcc.gnu.org/pipermail/gcc-patches/2023-October/633153.html
> > with the formatting.
> >
> > I don't have write access to the gcc repository:)
>
> Please provide the ChangeLog entry (see [1,2]) and I'll commit the
> patch for you.
>
> [1] https://gcc.gnu.org/contribute.html
> [2] https://gcc.gnu.org/codingconventions.html#ChangeLogs
>
> Thanks,
> Uros.

It's so kind of you! Attached the ChangeLog:

gcc/
    * config/i386/i386.cc (ix86_can_inline_p):
    Handle CM_LARGE and CM_LARGE_PIC.
    (x86_elf_aligned_decl_common): Ditto.
    (x86_output_aligned_bss): Ditto.
    * config/i386/i386.opt: Update doc for -mlarge-data-threshold=.
    * doc/invoke.texi: Update doc for -mlarge-data-threshold=.

gcc/testsuite/:
    * gcc.target/i386/large-data.c: New test.


-- 
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