llvm-project/flang/docs/Directives.md

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# Compiler directives supported by Flang

A list of non-standard directives supported by Flang

* `!dir$ fixed` and `!dir$ free` select Fortran source forms.  Their effect
  persists to the end of the current source file.
* `!dir$ ignore_tkr [[(TKRDMAC)] dummy-arg-name]...` in an interface definition
  disables some semantic checks at call sites for the actual arguments that
  correspond to some named dummy arguments (or all of them, by default).
  The directive allow actual arguments that would otherwise be diagnosed
  as incompatible in type (T), kind (K), rank (R), CUDA device (D), or
  managed (M) status.  The letter (A) is a shorthand for all of these,
  and is the default when no letters appear.  The letter (C) checks for
  contiguity for example allowing an element of an assumed-shape array to be
  passed as a dummy argument. For example, if one wanted to call a "set all
  bytes to zero" utility that could be applied to arrays of any type or rank:
```
  interface
    subroutine clear(arr,bytes)
!dir$ ignore_tkr arr
      integer(1), intent(out) :: arr(bytes)
    end
  end interface
```
* `!dir$ assume_aligned desginator:alignment`, where designator is a variable,
  maybe with array indices, and alignment is what the compiler should assume the
  alignment to be. E.g A:64 or B(1,1,1):128. The alignment should be a power of 2,
  and is limited to 256.
  [This directive is currently recognised by the parser, but not
  handled by the other parts of the compiler].