[Bug fortran/99816] fortran do loop line table issue

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99816

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-debug
   Last reconfirmed|                            |2021-03-29
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
The IL from the frontend is (with line numbers):

__attribute__((fn spec (". w w ")))
void sub (real(kind=4)[0:D.3943] * restrict a, integer(kind=4) & restrict n)
[t.f90:1:16] {
  integer(kind=8) ubound.0;
  integer(kind=8) size.1;
  integer(kind=4) i;
  integer(kind=8) D.3943;
  bitsizetype D.3944;
  sizetype D.3945;

  [t.f90:1:18] ubound.0 = [t.f90:1:18] (integer(kind=8)) [t.f90:1:18] *n;
  [t.f90:1:18] size.1 = [t.f90:1:18] NON_LVALUE_EXPR <ubound.0>;
  [t.f90:1:18] size.1 = [t.f90:1:18] MAX_EXPR <size.1, 0>;
  [t.f90:1:18] D.3943 = [t.f90:1:16] size.1 + -1;
  [t.f90:1:18] D.3944 = (bitsizetype) (sizetype) NON_LVALUE_EXPR <size.1> * 32;
  [t.f90:1:18] D.3945 = (sizetype) NON_LVALUE_EXPR <size.1> * 4;
  [t.f90:3:22] {
    integer(kind=4) D.3938;

    [t.f90:3:22] D.3938 = [t.f90:3:22] *n;
    [t.f90:3:17] i = 1;
    [t.f90:3:17] while (1)
      {
        [t.f90:5:34] {
          logical(kind=4) D.3941;

          [t.f90:3:17] D.3941 = [t.f90:3:17] i > D.3938;
          [t.f90:3:17] if (D.3941) [t.f90:3:17] goto L.2;
          [t.f90:4:15] [t.f90:4:15] ([t.f90:4:15] *a)[[t.f90:4:15]
(integer(kind=8)) i + -1] = (real(kind=4)) i;
          [t.f90:4:15] __label_000100:;
          [t.f90:5:34] L.1:;
          [t.f90:3:17] i = [t.f90:3:17] i + 1;
        }
      }
    [t.f90:5:34] L.2:;
  }
  [t.f90:6:13] return;
}

where we have two labels / empty stmts with line number 5, one inside and
one outside of the loop.  Note the actual "continue" is the end of the
while loop.

gimplification turns this into

  [t.f90:3:22] {
    integer(kind=4) D.3938;

    [t.f90:3:22] D.3938 = [t.f90:3:22] *n;
    [t.f90:3:17] i = 1;
    <D.3974>:
    [t.f90:5:34] {
      logical(kind=4) D.3941;

      [t.f90:3:17] D.3941 = i > D.3938;
      [t.f90:3:17] if (D.3941 != 0) goto L.2; else goto <D.3975>;
      <D.3975>:
      [t.f90:4:15] _5 = (integer(kind=8)) i;
      [t.f90:4:15] _6 = _5 + -1;
      [t.f90:4:15] _7 = (real(kind=4)) i;
      [t.f90:4:15] [t.f90:4:15] [t.f90:4:15] (*a)[_6] = _7;
      [t.f90:4:15] __label_000100:
      [t.f90:5:34] L.1:
      [t.f90:3:17] i = i + 1;
    }
    [t.f90:3:17] goto <D.3974>;
    [t.f90:5:34] L.2:
  }

note how the while (1) backwards jump gets line number 3.  How the Fortran
frontend uses LOOP_EXPR but does control flow by itself makes it difficult
to deal with this.