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From: "xicojovor at dropjar dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c/100432] New: gcc arm compilation binary output is bigger with
 -Os than -O2
Date: Wed, 05 May 2021 12:18:32 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D100432

            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 (>=3D 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 t=
he
whole 3 instructions (sub sp, str, add sp) are totally not needed (the vari=
able
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)=