Enable OpenMp during vcpkg build

[hrkalona]

Hello I am building mpfr by doing .\vcpkg.exe install mpfr:x64-windows-release

I am not using the original sources that were defined inside portfile.cmake, but rather one updated variant of mine which is packaged into the original tar.xz. (Some files are updated)

Here is the original portfile: https://github.com/microsoft/vcpkg/blob/master/ports/mpfr/portfile.cmake

#vcpkg_download_distfile(ARCHIVE
#    URLS "http://www.mpfr.org/mpfr-${VERSION}/mpfr-${VERSION}.tar.xz" "https://ftp.gnu.org/gnu/mpfr/mpfr-${VERSION}.tar.xz"
#    FILENAME "mpfr-${VERSION}.tar.xz"
#    SHA512 bc68c0d755d5446403644833ecbb07e37360beca45f474297b5d5c40926df1efc3e2067eecffdf253f946288bcca39ca89b0613f545d46a9e767d1d4cf358475
#)

vcpkg_download_distfile(ARCHIVE
    OUT_SOURCE_PATH SOURCE_PATH
    URLS "file:///C:/cygwin64/home/ckalonak/mpfr-4.2.1.tar.xz"
    FILENAME "mpfr-4.2.1.tar.xz"
    SHA512 "2760afad0dbbc098e1d23786dae0d96474355e4dd5d11b9583af0a2d867ab7bede33c697bc68eb29834c24d41e8f7b6a95807fbb17fbea57e2fb2de9a0a8abdd"
)

On this updated code I have some openmp directives so I want to somehow force

vcpkg_configure_make(
    SOURCE_PATH "${SOURCE_PATH}"
    AUTOCONFIG
)

To configure the build in order to use openmp and then build it using:

vcpkg_install_make()
I have tried to find a way to do it for hours, and ChatGPT is hallucinating like hell! Anyone has any ideas of how to make the build use the openmp directives?

[Osyotr]

If you've added openmp directives to the sources you should've modified the buildsystem too.
For autoconfig it's probably something like this: https://stackoverflow.com/questions/9037434/#comment26922785_9037860

[dg0yt]

1. set(CFLAGS "-fopenmp") before configure

Add "CFLAGS=\$CFLAGS -fopenmp" to the OPTIONS of vcpkg_configure_make.

2. add option CONFIGURE_ENVIRONMENT_VARIABLES CFLAGS

Well, CONFIGURE_ENVIRONMENT_VARIABLES might work with MSVC...

[hrkalona]

I changed vcpkg_configure_make to this:
vcpkg_configure_make( SOURCE_PATH "${SOURCE_PATH}" AUTOCONFIG OPTIONS "CFLAGS=\$CFLAGS -fopenmp" )

But I am getting cl : Command line warning D9002 : ignoring unknown option '-fopenmp'

I also tested this:

vcpkg_configure_make( SOURCE_PATH "${SOURCE_PATH}" AUTOCONFIG OPTIONS "CFLAGS=\$CFLAGS /openmp" )

But I am getting this:
cl : Command line warning D9024 : unrecognized source file type 'C:/Users/ckalonak/Documents/vcpkg/downloads/tools/msys2/212eb2bc95cd8a82/openmp', object file assumed

Its the same thing I mentioned before.

[hrkalona]

I have also tried to disregard the configuration on the vcpkg side and add

CFLAGS += /openmp
LDFLAGS += /openmp

Inside the Makefile.am (inside src)
The code builds but the my pragmas are disregarded:

      #pragma omp parallel sections num_threads(2)

       {

           #pragma omp section
           {
               mpfr_add(temp1, re, im, rnd_mode); // temp1 = re + im
               mpfr_sub(temp2, re, im, rnd_mode); // temp2 = re - im
               mpfr_mul(temp2, temp1, temp2, rnd_mode); // temp2 = (re + im) * (re - im)
           }

           #pragma omp section
           {
               mpfr_mul(temp3, re, im, rnd_mode); // temp3 = re * im
               mpfr_mul_2ui(temp3, temp3, 1, rnd_mode); // temp3 = 2 * re * im
           }

       }

This code is still executed on a single thread fashion.
By the way I have built the same code without vcpkg on Linux using -fopenmp and my pragmas work, the performance also reflects that.

[dg0yt]

IIUC -fopenmp isn't understood by MSVC.

/openmp is documented but ... vcpkg_configure_make on Windows needs MSYS sh, and the leading / triggers a heuristical POSIX-to-Windows filepath conversion when calling cl (Windows!) from sh (MSYS!).
Solution: MSVC should also understand -openmp. Or use MSYS2's environment variables to control conversion.

If you need to target different platforms and compilers, you must write cmake code to select and pass the corresponding option.

[hrkalona]

Thank you, OPTIONS "CFLAGS=$CFLAGS -openmp" works!

[hrkalona]

Should I create an issue out of this discussion? I really need to find a way to make this work.

[dg0yt]

No.