Flang Options - Flang Options

Use the following commands to get a list of compiler options.

$flang -help
$flang --help-hidden

The Flang compiler supports all Clang 17.0.1 Compiler Options and the following Flang-specific compiler options.

```
-Kieee
```
Enabled by default from AOCC 2.2.0, it instructs the compiler to conform to the IEEE-754 specifications. The compiler will perform floating-point operations in strict conformance with the IEEE 754 standard. Some optimizations are disabled when this option is specified.
```
-no-flang-libs
```
Do not link against Flang libraries.
```
-mp
```
Enable OpenMP and link with OpenMP library libomp.
```
-nomp
```
Do not link with OpenMP library libomp.
```
-Mbackslash
```
Treat backslash in quoted strings as any other character.
```
-Mnobackslash
```
Treat backslash in quoted strings as a C-style escape character (default).
```
-Mbyteswapio
```
Swap byte-order from big-endian to little-endian or vice-versa for unformatted input/output.
```
-Mfixed
```
Assume fixed-format source.
```
-Mextend
```
Allow source lines up to 132 characters.
```
-Mfreeform
```
Assume free-format source.
```
-Mpreprocess
```
Run preprocessor for Fortran files.
```
-Mstandard
```
Check standard conformance.
```
-Msave
```
Assume all variables have SAVE attribute.
```
-module
```
Path to module file (-I also works).
```
-Mallocatable=95
```
Select Fortran 95 semantics for assignments to allocatable objects (default).
```
-Mallocatable=03
```
Select Fortran 03 semantics for assignments to allocatable objects.
```
-static-flang-libs
```
Link using static Flang libraries.
```
-M[no]daz
```
Treat denormalized numbers as zero.
```
-M[no]flushz
```
Set SSE to flush-to-zero mode.
```
-Mcache_align
```
Align large objects on cache-line boundaries.
```
-M[no]fprelaxed
```
This option is ignored.
```
-fdefault-integer-8
```
Treat INTEGER and LOGICAL as INTEGER*8 and LOGICAL*8.
```
-fdefault-real-8
```
Treat REAL as REAL*8.
```
-i8
```
Treat INTEGER and LOGICAL as INTEGER*8 and LOGICAL*8.
```
-r8
```
Treat REAL as REAL*8.
```
-fno-fortran-main
```
Do not link in Fortran main.
```
-Mrecursive
```
Allocate local variables on the stack thus allowing recursion. Saved, data-initialized, or namelist members are always allocated statically regardless of the setting of this switch.

-fdo-concurrent-to-openmp=<host, none>

Enables/disables parallelization support for Do Concurrent loops by mapping existing Do Concurrent loop to OpenMP constructs. Currently, host and none options are supported. The host option enables parallelization support while the none option disables it.

Usage

 -fopenmp -fdo-concurrent-to-openmp=host

-fopenmp -fdo-concurrent-to-openmp=none

Example

test.f90:

program do_concurrent_reduction
  implicit none
  integer :: i
  real :: arr(1000), sum_val

  arr = [(real(i), i = 1, 1000)]
  sum_val = 0.0

  do concurrent (i = 1:1000) reduce(+:sum_val)
     sum_val = sum_val + arr(i)
  end do

  print *, sum_val
end program do_concurrent_reduction

flang -fopenmp -fdo-concurrent-to-openmp=host test.f90

Flang Options - Flang Options - 57222

AOCC User Guide