https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101817
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=51273&action=edit
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 most
of the time, function calls are optimized.
I am performing debug build, cmake build log with verbose argument says source
file is compiled with below example. I believe in this case -O0 is applied by
default.
Example:
std=c++14 -g -o test.c.o -c test.c
Just for Information:
I manually applied -O0 in CMakeLists.txt with this line
set(CMAKE_CXX_FLAGS_DEBUG "-g -O0") and below was the cmake verbose log.
std=c++14 -g -O0 -o test.c.o -c test.c
Please find the attachment to see disassemble log captured during gdb session.
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
