[patch, fortran] Clobber some intent(out) variables on call

[Thomas Koenig]

Hello world,

the attached patch lets the middle-end know that variables
associated with intent(out) arguments become undefined, by
issuing an assignment to a special value (a "clobber")
before entering the procedure.

Originally, I had also planned to do so on entry to the
procedure, see https://gcc.gnu.org/ml/fortran/2018-09/msg00148.html .
This turned out to cause regressions; some details are outlined
in the PR.

Regression-tested. OK for trunk?

Regards

Thomas

2018-09-22 Thomas Koenig <***@gcc.gnu.org>

PR fortran/41453
* trans.h (gfc_conv_expr_reference): Add optional argument
add_clobber to prototype.
(gfc_conv_procedure_call): Set add_clobber argument to
gfc_conv_procedure_reference to true for scalar, INTENT(OUT),
non-pointer, non-allocatable, non-dummy variables whose type
is neither BT_CHARACTER, BT_DERIVED or BT_CLASS, but only if
the procedure is not elemental.
* trans-expr.c (gfc_conv_procedure_reference): Add clobber
statement before call if add_clobber is set.

2018-09-22 Thomas Koenig <***@gcc.gnu.org>

PR fortran/41453
* gfortran.dg/intent_optimize_2.f90: New test.

[Jerry DeLisle]

Minor typo, see below.

Post by Thomas Koenig
Hello world,
the attached patch lets the middle-end know that variables
associated with intent(out) arguments become undefined, by
issuing an assignment to a special value (a "clobber")
before entering the procedure.
Originally, I had also planned to do so on entry to the
procedure, see https://gcc.gnu.org/ml/fortran/2018-09/msg00148.html .
This turned out to cause regressions; some details are outlined
in the PR.
Regression-tested. OK for trunk?

! { dg-do compile }
! { dg-options "-O -fno-inline -fdump-tree-optimized -fdump-tree-original" }
! PR fortran/41453
! Check that there is one clobber in the *.original tree, plus that
! the constant 123456789 has been removed tue to the INTENT(OUT).

s/tue/due/

and

program main
use x
implicit none
integer :: a
a = 12345689 <---- missing 7 digit?
call foo(a)
print *,a
end program main

Otherwise OK.

Jerry

[Thomas Koenig]

Hi Jerry,

Post by Jerry DeLisle
s/tue/due/
a = 12345689  <---- missing 7 digit?

Yep, you're right. Corrected, committed as r264506.

Regards

Thomas