[gcc r13-2835] fortran: Move clobbers after evaluation of all arguments [PR106817]

[Mikael Morin]

https://gcc.gnu.org/g:29919bf3b6449bafd02e795abbb1966e3990c1fc

commit r13-2835-g29919bf3b6449bafd02e795abbb1966e3990c1fc
Author: Mikael Morin <mikael@gcc.gnu.org>
Date:   Sat Sep 3 11:58:47 2022 +0200

    fortran: Move clobbers after evaluation of all arguments [PR106817]
    
    For actual arguments whose dummy is INTENT(OUT), we used to generate
    clobbers on them at the same time we generated the argument reference
    for the function call.  This was wrong if for an argument coming
    later, the value expression was depending on the value of the just-
    clobbered argument, and we passed an undefined value in that case.
    
    With this change, clobbers are collected separatedly and appended
    to the procedure call preliminary code after all the arguments have been
    evaluated.
    
            PR fortran/106817
    
    gcc/fortran/ChangeLog:
    
            * trans-expr.cc (gfc_conv_procedure_call): Collect all clobbers
            to their own separate block.  Append the block of clobbers to
            the procedure preliminary block after the argument evaluation
            codes for all the arguments.
    
    gcc/testsuite/ChangeLog:
    
            * gfortran.dg/intent_optimize_4.f90: New test.

Diff:
---
 gcc/fortran/trans-expr.cc                       |  6 ++--
 gcc/testsuite/gfortran.dg/intent_optimize_4.f90 | 43 +++++++++++++++++++++++++
 2 files changed, 47 insertions(+), 2 deletions(-)

diff --git a/gcc/fortran/trans-expr.cc b/gcc/fortran/trans-expr.cc
index 8fb63359ba5..f93923b5bdb 100644
--- a/gcc/fortran/trans-expr.cc
+++ b/gcc/fortran/trans-expr.cc
@@ -6018,7 +6018,6 @@ gfc_conv_procedure_call (gfc_se * se, gfc_symbol * sym,
   gfc_charlen cl;
   gfc_expr *e;
   gfc_symbol *fsym;
-  stmtblock_t post;
   enum {MISSING = 0, ELEMENTAL, SCALAR, SCALAR_POINTER, ARRAY};
   gfc_component *comp = NULL;
   int arglen;
@@ -6062,7 +6061,9 @@ gfc_conv_procedure_call (gfc_se * se, gfc_symbol * sym,
   else
     info = NULL;
 
+  stmtblock_t post, clobbers;
   gfc_init_block (&post);
+  gfc_init_block (&clobbers);
   gfc_init_interface_mapping (&mapping);
   if (!comp)
     {
@@ -6531,7 +6532,7 @@ gfc_conv_procedure_call (gfc_se * se, gfc_symbol * sym,
 			  var = build_fold_indirect_ref_loc (input_location,
 							     parmse.expr);
 			  tree clobber = build_clobber (TREE_TYPE (var));
-			  gfc_add_modify (&se->pre, var, clobber);
+			  gfc_add_modify (&clobbers, var, clobber);
 			}
 		    }
 		  /* Catch base objects that are not variables.  */
@@ -7399,6 +7400,7 @@ gfc_conv_procedure_call (gfc_se * se, gfc_symbol * sym,
 
       vec_safe_push (arglist, parmse.expr);
     }
+  gfc_add_block_to_block (&se->pre, &clobbers);
   gfc_finish_interface_mapping (&mapping, &se->pre, &se->post);
 
   if (comp)
diff --git a/gcc/testsuite/gfortran.dg/intent_optimize_4.f90 b/gcc/testsuite/gfortran.dg/intent_optimize_4.f90
new file mode 100644
index 00000000000..effbaa12a2d
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/intent_optimize_4.f90
@@ -0,0 +1,43 @@
+! { dg-do run }
+! { dg-additional-options "-fdump-tree-original" }
+! { dg-final { scan-tree-dump-times "CLOBBER" 2 "original" } }
+!
+! PR fortran/106817
+! Check that for an actual argument whose dummy is INTENT(OUT),
+! the clobber that is emitted in the caller before a procedure call
+! happens after any expression depending on the argument value has been
+! evaluated.
+! 
+
+module m
+  implicit none
+contains
+  subroutine copy1(out, in)
+    integer, intent(in) :: in
+    integer, intent(out) :: out
+    out = in
+  end subroutine copy1
+  subroutine copy2(in, out)
+    integer, intent(in) :: in
+    integer, intent(out) :: out
+    out = in
+  end subroutine copy2
+end module m
+
+program p
+  use m
+  implicit none
+  integer :: a, b
+
+  ! Clobbering of a should happen after a+1 has been evaluated.
+  a = 3
+  call copy1(a, a+1)
+  if (a /= 4) stop 1
+
+  ! Clobbering order does not depend on the order of arguments.
+  ! It should also come last with reversed arguments.
+  b = 12
+  call copy2(b+1, b)
+  if (b /= 13) stop 2
+
+end program p