Intel oneApi C++ Compiler with Visual Studio 2022

Usage
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1

Hello,

I’m using CMake 3.23.1 with Visual Studio 2022 and the Intel oneApi C++ Compiler 2022. Everything works fine, but I have some trouble with changing some compiler flags for individual projects.

I want to change the optimization from O2 to O3 but I’m not able to get it work. And I also want do enable the optimization output from the Intel compiler.

Overwriting the CMAKE_CXX_FLAGS does not work.

set(CMAKE_CXX_FLAGS_RELEASE "/MD /O3 /DNDEBUG /O3 /Qopt-report:3 " PARENT_SCOPE)

Adding compile option by add_compile_options("/Qopt-report:3") also does not work.

I also tried to set options specific by target, but it also does not work target_compile_options( ${LIBRARY_NAME_RAW} PUBLIC /O3).

What am I doing wrong?

Thanks and best regards,
Dirk

2

The PARENT_SCOPE seems odd to me. Can you reproduce this in a simple example just to make sure nothing else in the project is interfering?

3

Hi Ben,

thanks for the feedback.

Here is a minimum example that shows the behavior.

project(IntelTest)

set(EXECUTABLE_NAME intelTest)

cmake_minimum_required(VERSION 3.22)


set(CMAKE_CONFIGURATION_TYPES "Debug;Release")

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std:c++17 -Qopt-report:3 -O3")


add_executable(${EXECUTABLE_NAME}
    main.cpp
)

The C++ standard is set, but the optimization flag is still /O2

4

It looks like the -O2 flag comes from CMAKE_CXX_FLAGS_RELEASE, so that variable would need to be edited:

string(REPLACE "/O2" "" CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE}")
5

I found something similar and now I think it is an issue with the Intel C++ compiler and Visual Studio.

Visual Studio support Od, O1, O2 and Ox.
The Intel compiler supports Od, O1, O2, Ox and O3[Intel C++].

With

MESSAGE(STATUS "CMAKE_CXX_FLAGS_RELEASE: ${CMAKE_CXX_FLAGS_RELEASE}")
string(REGEX REPLACE "/O[0-4]" "/O3" CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE}")
set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE}" CACHE STRING "" FORCE)
MESSAGE(STATUS "CMAKE_CXX_FLAGS_RELEASE: ${CMAKE_CXX_FLAGS_RELEASE}")

I can change to all possible values for the optimization that are supported by Visual Studio, but I cannot set the value to O3, also the CXX_FLAGS in the CMake window state that O3 is set. In Visual Studio it is still O2

6

If I use Ninja to build the project, the flags for optimization are accepted. So I think there must be a connection to Visual Studio. Changing the values in Visual Studio directly work, but not with CMake.

7

Hmm. I suspect this is just CMake not knowing what fields correlate with Intel compiler flags that well. Please file an issue about this.

8

Thanks for your hints right now.

The issue is created and can be found here:
https://gitlab.kitware.com/cmake/cmake/-/issues/24045