[Bug c/100432] New: gcc arm compilation binary output is bigger with -Os than -O2

[Bug c/100432] New: gcc arm compilation binary output is bigger with -Os than -O2

[xicojovor at dropjar dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100432

            Bug ID: 100432
           Summary: gcc arm compilation binary output is bigger with -Os
                    than -O2
           Product: gcc
           Version: 11.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: xicojovor at dropjar dot com
  Target Milestone: ---

example: https://godbolt.org/z/rYxTPdTcd

while compiling for ARM, gcc versions after 4 (>= 5) generate a redundant stack
frame as can be seen in the attached example, while gcc version 4 generates
correct code that is also minimal in size as requested (-Os).

The code generation in newer gcc versions is strange even without thinking
about the -Os flag, since the generated stack frame is not even used, and the
whole 3 instructions (sub sp, str, add sp) are totally not needed (the variable
on the stack is not used).
also reported in https://bugs.launchpad.net/gcc-arm-embedded/+bug/1927055 (not
sure where this should be reported)

[Bug target/100432] gcc arm compilation binary output is bigger with -Os than -O2

[rearnsha at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100432

Richard Earnshaw <rearnsha at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |WAITING
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2021-05-05

--- Comment #1 from Richard Earnshaw <rearnsha at gcc dot gnu.org> ---
godbolt urls expire in time.  Please attach your testcase here.

[Bug target/100432] gcc arm compilation binary output is bigger with -Os than -O2

[xicojovor at dropjar dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100432

--- Comment #2 from xicojovor at dropjar dot com ---
The minimal example is:


int main(void)
{
    return 0;
}

void* get_self_address(void)
{
    return (void*)get_self_address;
}


compiled with -marm -Os -fPIC

working good (maybe not the best) with gcc 4.5.4, and not ok with gcc version
5.4, 6.3.0, 10.2, 10.3.

[Bug target/100432] gcc arm compilation binary output is bigger with -Os than -O2

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100432

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|1                           |0
             Status|WAITING                     |UNCONFIRMED