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* [Bug c++/101817] New: g++ apply optimization irrespective of -O0 flag is set
@ 2021-08-08 7:29 mohan.rajanna at ict dot nl
2021-08-08 7:37 ` [Bug c++/101817] " pinskia at gcc dot gnu.org
` (4 more replies)
0 siblings, 5 replies; 6+ messages in thread
From: mohan.rajanna at ict dot nl @ 2021-08-08 7:29 UTC (permalink / raw)
To: gcc-bugs
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
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c++/101817] g++ apply optimization irrespective of -O0 flag is set
2021-08-08 7:29 [Bug c++/101817] New: g++ apply optimization irrespective of -O0 flag is set mohan.rajanna at ict dot nl
@ 2021-08-08 7:37 ` pinskia at gcc dot gnu.org
2021-08-08 7:43 ` mohan.rajanna at ict dot nl
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-08-08 7:37 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101817
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Use -fno-builtins
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c++/101817] g++ apply optimization irrespective of -O0 flag is set
2021-08-08 7:29 [Bug c++/101817] New: g++ apply optimization irrespective of -O0 flag is set mohan.rajanna at ict dot nl
2021-08-08 7:37 ` [Bug c++/101817] " pinskia at gcc dot gnu.org
@ 2021-08-08 7:43 ` mohan.rajanna at ict dot nl
2021-08-13 19:38 ` pinskia at gcc dot gnu.org
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: mohan.rajanna at ict dot nl @ 2021-08-08 7:43 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101817
--- Comment #2 from Mohan <mohan.rajanna at ict dot nl> ---
With -fno-builtins argument, it works good !!
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c++/101817] g++ apply optimization irrespective of -O0 flag is set
2021-08-08 7:29 [Bug c++/101817] New: g++ apply optimization irrespective of -O0 flag is set mohan.rajanna at ict dot nl
2021-08-08 7:37 ` [Bug c++/101817] " pinskia at gcc dot gnu.org
2021-08-08 7:43 ` mohan.rajanna at ict dot nl
@ 2021-08-13 19:38 ` pinskia at gcc dot gnu.org
2021-08-16 6:22 ` mohan.rajanna at ict dot nl
2021-08-16 10:01 ` redi at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-08-13 19:38 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101817
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution|--- |INVALID
--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Invalid, we do some simplifications at -O0 including inlining of some builtins
which includes strncmp. As I mentioned use -fno-builtins if you don't want
builtins to be reconigized.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c++/101817] g++ apply optimization irrespective of -O0 flag is set
2021-08-08 7:29 [Bug c++/101817] New: g++ apply optimization irrespective of -O0 flag is set mohan.rajanna at ict dot nl
` (2 preceding siblings ...)
2021-08-13 19:38 ` pinskia at gcc dot gnu.org
@ 2021-08-16 6:22 ` mohan.rajanna at ict dot nl
2021-08-16 10:01 ` redi at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: mohan.rajanna at ict dot nl @ 2021-08-16 6:22 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101817
Mohan <mohan.rajanna at ict dot nl> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|INVALID |WORKSFORME
--- Comment #4 from Mohan <mohan.rajanna at ict dot nl> ---
Thank you for the information.
It works good now. Please reject this bug.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c++/101817] g++ apply optimization irrespective of -O0 flag is set
2021-08-08 7:29 [Bug c++/101817] New: g++ apply optimization irrespective of -O0 flag is set mohan.rajanna at ict dot nl
` (3 preceding siblings ...)
2021-08-16 6:22 ` mohan.rajanna at ict dot nl
@ 2021-08-16 10:01 ` redi at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: redi at gcc dot gnu.org @ 2021-08-16 10:01 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101817
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|WORKSFORME |INVALID
--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Mohan from comment #4)
> It works good now. Please reject this bug.
We already did, by setting the resolution to INVALID.
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2021-08-16 10:01 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
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2021-08-08 7:29 [Bug c++/101817] New: g++ apply optimization irrespective of -O0 flag is set mohan.rajanna at ict dot nl
2021-08-08 7:37 ` [Bug c++/101817] " pinskia at gcc dot gnu.org
2021-08-08 7:43 ` mohan.rajanna at ict dot nl
2021-08-13 19:38 ` pinskia at gcc dot gnu.org
2021-08-16 6:22 ` mohan.rajanna at ict dot nl
2021-08-16 10:01 ` redi at gcc dot gnu.org
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