[Flang] Intrinsic LEN and C_SIZEOF returns incorrect result when the argument is a CFI_CDESC_T descriptor of character type.

[DanielCChen]

Consider the following code:

#include <stdio.h>
#include <string.h>
#include <assert.h>
#include "ISO_Fortran_binding.h"
void sub(CFI_cdesc_t* a);
int main()
{
    int rc;
    char *p = "12345";
    CFI_cdesc_t* a;
    CFI_CDESC_T(1) at1;
    a = (CFI_cdesc_t *) &at1;

    rc = CFI_establish(a, p, CFI_attribute_pointer, CFI_type_signed_char, 5, 0, 0);
    assert(rc == CFI_SUCCESS);
    sub(a);
}

Fortran subroutine sub is as:

      subroutine sub(c_arg2) bind(c)
        use, intrinsic :: iso_c_binding
        character(*) :: c_arg2!(*)
        print*, "LEN(c_arg2)=", LEN(c_arg2)
        print*, "c_sizeof(c_arg2)=", c_sizeof(c_arg2)
      end

The expected result is

 LEN(c_arg2)= 5
 c_sizeof(c_arg2)= 5

But Flang currently outputs

 LEN(c_arg2)= 1
 c_sizeof(c_arg2)= 1

[jeanPerier]

@DanielCChen, is there a reason the code is using CFI_type_signed_char and not CFI_type_char?

The problem is that CFI_type_signed_char is not recognized as being a character type in CFI_establish, that ends-up overriding the elem_len argument (5) with1.

llvm-project/flang/runtime/ISO_Fortran_binding.cpp

Line 116 in 525bd66

!IsCharacterType(type)) {

llvm-project/flang/runtime/ISO_Fortran_util.h

Line 21 in 525bd66

static inline constexpr RT_API_ATTRS bool IsCharacterType(CFI_type_t ty) {

I think flang is doing a correct interpretation given that CFI_type_signed_char is considered to be an integer type in in table 18.2/18.4. CFI_type_char should be used instead. The CFI_establish requirements in F2023 18.5.5.5 requires elem_len to be ignored if type is nor CFI_type_struct, nor CFI_type_other, nor a Fortran character type code.

[DanielCChen]

@jeanPerier Thanks for the comment. You are right. c_sighed_char is indeed listed as Fortran integer type.

[llvmbot]

@llvm/issue-subscribers-flang-runtime

Author: Daniel Chen (DanielCChen)

Consider the following code: ``` #include <stdio.h> #include <string.h> #include <assert.h> #include "ISO_Fortran_binding.h" void sub(CFI_cdesc_t* a); int main() { int rc; char *p = "12345"; CFI_cdesc_t* a; CFI_CDESC_T(1) at1; a = (CFI_cdesc_t *) &at1;

rc = CFI_establish(a, p, CFI_attribute_pointer, CFI_type_signed_char, 5, 0, 0);
assert(rc == CFI_SUCCESS);
sub(a);

}

Fortran subroutine `sub` is as:

  subroutine sub(c_arg2) bind(c)
    use, intrinsic :: iso_c_binding
    character(*) :: c_arg2!(*)
    print*, "LEN(c_arg2)=", LEN(c_arg2)
    print*, "c_sizeof(c_arg2)=", c_sizeof(c_arg2)
  end

The expected result is

LEN(c_arg2)= 5
c_sizeof(c_arg2)= 5

But Flang currently outputs

LEN(c_arg2)= 1
c_sizeof(c_arg2)= 1

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