On Sat, Apr 13, 2019 at 8:48 PM Thomas Koenig <tkoe...@netcologne.de> wrote: > > Hello world, > > the attached patch fixes a 8/9 regression where _def_init, an internal > Fortran variable containing only zeros, was placed into the .rodata > section. This led to a large increase in executable size. > > There should be no impact on other languages because the change to > varasm.c is guarded by lang_GNU_Fortran (). > > Regarding the test case: I did find one other test which checks > for .bss, so I suppose this is safe. > > Regression-tested with a full test (--enable-languages=all and > make -j64 -k check) on POWER9. > > I would like to apply it to both affected branches. > > OK for the general and the Fortran part?
This won't work with LTO. Note we have the issue in the middle-end as well
since we promote variables we see are not written to to TREE_READONLY.
This can be seen with (the somewhat artificial...):
int a[1024*1024] = { 0 };
int __attribute__((noinline)) foo() { return *(volatile int *)a; }
int main()
{
return foo ();
}
where without -flto a gets placed into .bss while with -flto it
gets into .rodata. So I believe we should add a DECL flag
specifying whether for section placement we can "ignore"
TREE_READONLY. We'd initialize that with the original
state of TREE_READONLY so that the R/O promotion doesn't
change section placement. Also the Fortran FE can then
simply set this flag on variables that may live in .bss.
There are 14 unused bits in tree_decl_with_vis so a
patch for the middle-end part could look like the attached
(w/o solving the LTO issue yet).
Of course adding sth like a .robss section would be nice.
Richard.
> Regards
>
> Thomas
>
> 2019-04-13 Thomas Koenig <tkoe...@gcc.gnu.org>
>
> PR fortran/84487
> * trans-decl.c (gfc_get_symbol_decl): Mark _def_init as
> artificial.
>
> 2019-04-13 Thomas Koenig <tkoe...@gcc.gnu.org>
>
> PR fortran/84487
> * varasm.c (bss_initializer_p): If we are compiling Fortran, the
> decl is artifical and it has a size larger than 255, it can be
> put into BSS.
>
> 2019-04-13 Thomas Koenig <tkoe...@gcc.gnu.org>
>
> PR fortran/84487
> * gfortran.dg/def_init_1.f90: New test.
>
>
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