Describe how Open MPI was installed

Oct 13, 2025 by wbrum.org 5 views

Background information

What version of Open MPI are you using?

5.0.7

Describe how Open MPI was installed

Tarball/source

Please describe the system on which you are running

I'm trying to build Open MPI with MPI_f08 bindings on a Linux system, using clang and flang build from recent llvm-project Git repository:

$ flang --version
flang version 21.0.0git (https://github.com/llvm/llvm-project.git 5d50af3f0368847ab9ce1d86cb6e46ffaf317b59)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /opt/llvm/llvm-project/install/bin

By default, quad precision is disabled when building flang except when explicitly enabled. I did not enable that when building flang.

Details of the problem

I configure Open MPI with few options: ./configure --with-pic --prefix=/opt/llvm/openmpi/openmpi-5.0.5/install, I am on this system not interested in any fancy interconnects or anything special.

Relevant output of the configure-script is:

checking size of Fortran REAL... 4
checking for C type corresponding to REAL... float
checking alignment of Fortran REAL... 4
checking for corresponding KIND value of REAL... C_FLOAT
checking KIND value of Fortran C_FLOAT... 4
checking if Fortran compiler supports REAL*2... yes
checking size of Fortran REAL*2... 2
checking for C type corresponding to REAL*2... opal_short_float_t
checking alignment of Fortran REAL*2... 2
checking for corresponding KIND value of REAL*2... C_SHORT_FLOAT
checking KIND value of Fortran C_SHORT_FLOAT... no ISO_C_BINDING -- fallback
checking Fortran value of selected_int_kind(4)... 2
2
checking if Fortran compiler supports REAL*4... yes
checking size of Fortran REAL*4... 4
checking for C type corresponding to REAL*4... float
checking alignment of Fortran REAL*4... 4
checking for corresponding KIND value of REAL*4... C_FLOAT
checking KIND value of Fortran C_FLOAT... (cached) 4
checking if Fortran compiler supports REAL*8... yes
checking size of Fortran REAL*8... 8
checking for C type corresponding to REAL*8... double
checking alignment of Fortran REAL*8... 8
checking for corresponding KIND value of REAL*8... C_DOUBLE
checking KIND value of Fortran C_DOUBLE... 8
checking if Fortran compiler supports REAL*16... no
checking for C type matching bit representation of REAL*16... skipped (no REAL*16)
configure: WARNING: MPI_REAL16 and MPI_COMPLEX32 support have been disabled
checking if Fortran compiler supports DOUBLE PRECISION... yes
checking size of Fortran DOUBLE PRECISION... 8
checking for C type corresponding to DOUBLE PRECISION... double
checking alignment of Fortran DOUBLE PRECISION... 8
checking for corresponding KIND value of DOUBLE PRECISION... C_DOUBLE
checking KIND value of Fortran C_DOUBLE... (cached) 8
checking if Fortran compiler supports COMPLEX... yes
checking size of Fortran COMPLEX... 8
checking for C type corresponding to COMPLEX... float _Complex
checking alignment of Fortran COMPLEX... 4
checking for corresponding KIND value of COMPLEX... C_FLOAT_COMPLEX
checking KIND value of Fortran C_FLOAT_COMPLEX... 4
checking if Fortran compiler supports COMPLEX*4... yes
checking size of Fortran COMPLEX*4... 4
checking for C type corresponding to COMPLEX*4... opal_short_float_complex_t
checking alignment of Fortran COMPLEX*4... 2
checking for corresponding KIND value of COMPLEX*4... C_SHORT_FLOAT_COMPLEX
checking KIND value of Fortran C_SHORT_FLOAT_COMPLEX... no ISO_C_BINDING -- fallback
checking Fortran value of selected_int_kind(4)... (cached) 2
2
checking if Fortran compiler supports COMPLEX*8... yes
checking size of Fortran COMPLEX*8... 8
checking for C type corresponding to COMPLEX*8... float _Complex
checking alignment of Fortran COMPLEX*8... 4
checking for corresponding KIND value of COMPLEX*8... C_FLOAT_COMPLEX
checking KIND value of Fortran C_FLOAT_COMPLEX... (cached) 4
checking if Fortran compiler supports COMPLEX*16... yes
checking size of Fortran COMPLEX*16... 16
checking for C type corresponding to COMPLEX*16... double _Complex
checking alignment of Fortran COMPLEX*16... 8
checking for corresponding KIND value of COMPLEX*16... C_DOUBLE_COMPLEX
checking KIND value of Fortran C_DOUBLE_COMPLEX... 8
checking if Fortran compiler supports COMPLEX*32... yes
checking size of Fortran COMPLEX*32... 32
checking for C type corresponding to COMPLEX*32... long double _Complex
checking alignment of Fortran COMPLEX*32... 16
checking for corresponding KIND value of COMPLEX*32... C_LONG_DOUBLE_COMPLEX
checking KIND value of Fortran C_LONG_DOUBLE_COMPLEX... 10
checking if Fortran compiler supports DOUBLE COMPLEX... yes
checking size of Fortran DOUBLE COMPLEX... 16
checking for C type corresponding to DOUBLE COMPLEX... double _Complex
checking alignment of Fortran DOUBLE COMPLEX... 8
checking for corresponding KIND value of DOUBLE COMPLEX... C_DOUBLE_COMPLEX
checking KIND value of Fortran C_DOUBLE_COMPLEX... (cached) 8

So Open MPI configure correctly detect that quad precision/real128 support is not present in the compiler.

When compiling Open MPI I get the following error:

  FC       psizeof_f.lo
error: Semantic errors in psizeof_f.f90
./psizeof_f.f90:161:7: error: COMPLEX(KIND=-1) is not a supported type
        COMPLEX(REAL128)::x
        ^^^^^^^^^^^^^^^^^^^
./psizeof_f.f90:171:7: error: COMPLEX(KIND=-1) is not a supported type
        COMPLEX(REAL128), DIMENSION(*)::x
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
./psizeof_f.f90:181:7: error: COMPLEX(KIND=-1) is not a supported type
        COMPLEX(REAL128), DIMENSION(1,*)::x
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
./psizeof_f.f90:191:7: error: COMPLEX(KIND=-1) is not a supported type
        COMPLEX(REAL128), DIMENSION(1,1,*)::x
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
./psizeof_f.f90:201:7: error: COMPLEX(KIND=-1) is not a supported type
        COMPLEX(REAL128), DIMENSION(1,1,1,*)::x
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
./psizeof_f.f90:211:7: error: COMPLEX(KIND=-1) is not a supported type
        COMPLEX(REAL128), DIMENSION(1,1,1,1,*)::x
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
./psizeof_f.f90:221:7: error: COMPLEX(KIND=-1) is not a supported type
        COMPLEX(REAL128), DIMENSION(1,1,1,1,1,*)::x
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
./psizeof_f.f90:231:7: error: COMPLEX(KIND=-1) is not a supported type
        COMPLEX(REAL128), DIMENSION(1,1,1,1,1,1,*)::x
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
./psizeof_f.f90:241:7: error: COMPLEX(KIND=-1) is not a supported type
        COMPLEX(REAL128), DIMENSION(1,1,1,1,1,1,1,*)::x
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
./psizeof_f.f90:251:7: error: COMPLEX(KIND=-1) is not a supported type
        COMPLEX(REAL128), DIMENSION(1,1,1,1,1,1,1,1,*)::x
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
./psizeof_f.f90:261:7: error: COMPLEX(KIND=-1) is not a supported type
        COMPLEX(REAL128), DIMENSION(1,1,1,1,1,1,1,1,1,*)::x
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
./psizeof_f.f90:271:7: error: COMPLEX(KIND=-1) is not a supported type
        COMPLEX(REAL128), DIMENSION(1,1,1,1,1,1,1,1,1,1,*)::x
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
./psizeof_f.f90:281:7: error: COMPLEX(KIND=-1) is not a supported<br/>
# OpenMPI 5.0.7 does not compile with most recent flang

## Q&A

### Q: What is the issue with OpenMPI 5.0.7 and flang?

A: The issue is that OpenMPI 5.0.7 is trying to use `COMPLEX(REAL128)` which is not supported by the flang compiler.

### Q: Why is OpenMPI trying to use `COMPLEX(REAL128)`?

A: OpenMPI is trying to use `COMPLEX(REAL128)` because it is configured to support quad precision/real128 support, but the flang compiler does not support it.

### Q: How can I fix this issue?

A: There are two possible solutions:

1. Recompile the flang compiler with quad precision support.
2. Disable quad precision support in OpenMPI.

### Q: How do I recompile the flang compiler with quad precision support?

A: To recompile the flang compiler with quad precision support, you need to enable the `REAL128` option when building the compiler. This can be done by adding the `--enable-real128` option to the `cmake` command.

### Q: How do I disable quad precision support in OpenMPI?

A: To disable quad precision support in OpenMPI, you need to configure OpenMPI with the `--disable-real128` option.

### Q: What are the implications of disabling quad precision support in OpenMPI?

A: Disabling quad precision support in OpenMPI will prevent it from using `COMPLEX(REAL128)` and will instead use `COMPLEX` which is supported by the flang compiler.

### Q: What are the implications of recompiling the flang compiler with quad precision support?

A: Recompiling the flang compiler with quad precision support will allow OpenMPI to use `COMPLEX(REAL128)` and will provide better support for quad precision arithmetic.

### Q: How do I know if I need to recompile the flang compiler or disable quad precision support in OpenMPI?

A: If you are using a recent version of flang that does not support quad precision, you will need to recompile the compiler with quad precision support. If you are using an older version of flang that supports quad precision, you can disable quad precision support in OpenMPI.

### Q: What are the benefits of using OpenMPI with quad precision support?

A: Using OpenMPI with quad precision support provides better support for high-precision arithmetic and can improve the accuracy of simulations and calculations.

### Q: What are the benefits of using OpenMPI without quad precision support?

A: Using OpenMPI without quad precision support can improve performance and reduce memory usage, but may not provide the same level of accuracy as using quad precision support.

### Q: Can I use both OpenMPI with quad precision support and without quad precision support?

A: Yes, you can use both OpenMPI with quad precision support and without quad precision support, but you will need to configure OpenMPI separately for each case.

### Q: How do I configure OpenMPI for both quad precision support and without quad precision support?

A: To configure OpenMPI for both quad precision support and without quad precision support, you need to use the `--enable-real128` and `--disable-real128` options separately when configuring OpenMPI.

### Q: What are the implications of using both OpenMPI with quad precision support and without quad precision support?

A: Using both OpenMPI with quad precision support and without quad precision support can lead to confusion and errors, and is not recommended. It is better to choose one configuration and stick with it.