[Bug c++/111577] New: -Os gives significantly bigger code than -O0

[Bug c++/111577] New: -Os gives significantly bigger code than -O0

[socketpair at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111577

            Bug ID: 111577
           Summary: -Os gives significantly bigger code than -O0
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: socketpair at gmail dot com
  Target Milestone: ---

Yes, I saw #35806, #41175 and others.

See https://godbolt.org/z/Pnh89Y3Yb

```
#include <string>

using namespace std;

int main(int argc, char* argv[]) {
    if (argv[0] == nullptr || argv[1] == nullptr) return 0;

    string zxc(argv[0]);
    string qwe(argv[1]);
    string asd(argv[2]);

    zxc = qwe + asd;

    return zxc.size();
}
```

-Os -std=c++2b -march=skylake -m64 (615 bytes)

compare size with the smae, but with options:

-O0 -std=c++2b -march=skylake -m64 (409 bytes)

-O0 - is much LESS (!) in bytes. I think it's a bug.

[Bug middle-end/111577] -Os gives significantly bigger code than -O0

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111577

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |WORKSFORME

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
[apinski@xeond2 gcc]$ ~/upstream-gcc/bin/g++ -Os  -std=c++2b -march=skylake
-m64 t.cc
[apinski@xeond2 gcc]$ size -A a.out
a.out  :
section                  size      addr
.interp                    28   4195096
.note.gnu.property         32   4195128
.note.ABI-tag              32   4195160
.hash                      76   4195192
.gnu.hash                  52   4195272
.dynsym                   336   4195328
.dynstr                   494   4195664
.gnu.version               28   4196158
.gnu.version_r            144   4196192
.rela.dyn                  48   4196336
.rela.plt                 192   4196384
.init                      27   4198400
.plt                      144   4198432
.text                    1341   4198576
.fini                      13   4199920
.rodata                    99   4202496
.eh_frame_hdr              92   4202596
.eh_frame                 440   4202688
.gcc_except_table          29   4203128
.init_array                 8   4210128
.fini_array                 8   4210136
.dynamic                  528   4210144
.got                       16   4210672
.got.plt                   88   4210688
.data                      16   4210776
.bss                        8   4210792
.comment                  108         0
.gnu.build.attributes    7368   4218992
Total                   11795

[apinski@xeond2 gcc]$ ~/upstream-gcc/bin/g++ -O0  -std=c++2b -march=skylake
-m64 t.cc
[apinski@xeond2 gcc]$ size -A a.out
a.out  :
section                  size      addr
.interp                    28   4195096
.note.gnu.property         32   4195128
.note.ABI-tag              32   4195160
.hash                     368   4195192
.gnu.hash                 356   4195560
.dynsym                  1272   4195920
.dynstr                  3067   4197192
.gnu.version              106   4200260
.gnu.version_r            176   4200368
.rela.dyn                  48   4200544
.rela.plt                 264   4200592
.init                      27   4202496
.plt                      192   4202528
.text                    6162   4202720
.fini                      13   4208884
.rodata                   106   4210688
.eh_frame_hdr             548   4210796
.eh_frame                2276   4211344
.gcc_except_table          85   4213620
.init_array                 8   4218320
.fini_array                 8   4218328
.dynamic                  528   4218336
.got                       16   4218864
.got.plt                  112   4218880
.data                      16   4218992
.bss                        8   4219008
.comment                  108         0
.gnu.build.attributes    7368   4227208
Total                   23330


For me on the trunk with the correct output -Os is smaller. 1341 vs 6162 for
the text size.

[Bug middle-end/111577] -Os gives significantly bigger code than -O0

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111577

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I suspect you forgot to count the other functions which get emitted here. And
you are just counting the size of main but that is wrong really.

Anyways the overall size of the executable's text section is smaller at -Os
which is the point.