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From: "mohan.rajanna at ict dot nl" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/101817] New: g++ apply optimization irrespective of -O0
 flag is set
Date: Sun, 08 Aug 2021 07:29:41 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101817

            Bug ID: 101817
           Summary: g++ apply optimization irrespective of -O0 flag is set
           Product: gcc
           Version: 9.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mohan.rajanna at ict dot nl
  Target Milestone: ---

Created attachment 51273
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D51273&action=3Dedit
disassemble log captured during gdb session

Hello Team,

I observe g++ applies optimization even when -O0 flag is used for compiling.

I am performing unit testing with CMocka setup. Due to optimization, I am
unable to test stub function call to strncmp().

Please Note: Stub function call to strncmp() will work in some cases but mo=
st
of the time, function calls are optimized.

I am performing debug build, cmake build log with verbose argument says sou=
rce
file is compiled with below example. I believe in this case -O0 is applied =
by
default.
Example:
std=3Dc++14 -g   -o test.c.o -c test.c

Just for Information:
I manually applied -O0 in CMakeLists.txt with this line=20
set(CMAKE_CXX_FLAGS_DEBUG "-g -O0") and below was the cmake verbose log.
std=3Dc++14 -g -O0   -o test.c.o -c test.c

Please find the attachment to see disassemble log captured during gdb sessi=
on.=20

Please find below the versions used for g++, cmake, ubuntu:

g++ --version
g++ (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0

cmake --version
cmake version 3.16.3

Ubuntu 20.04.2 LTS

This is inconsistent behaviour with -O0 flag. Sometimes this flag disables =
the
optimization but not always.

Kind Regards
Mohan=