[gcc r13-2837] fortran: Support clobbering of reference variables [PR41453]

[Mikael Morin <mikael@gcc.gnu.org>]

https://gcc.gnu.org/g:51c9480f9f0a80ef112ba2aed040b0b2ad0fc2a2

commit r13-2837-g51c9480f9f0a80ef112ba2aed040b0b2ad0fc2a2
Author: Mikael Morin <mikael@gcc.gnu.org>
Date:   Mon Aug 29 13:27:02 2022 +0200

    fortran: Support clobbering of reference variables [PR41453]
    
    This adds support for clobbering of variables passed by reference,
    when the reference is forwarded to a subroutine as actual argument
    whose associated dummy has the INTENT(OUT) attribute.
    This was explicitly disabled by a condition added with
    r9-3032-gee7fb0588c6361b4d77337ab0f7527be64fcdde2 and removing that
    condition seems to work, as demonstrated by the new testcase.
    
            PR fortran/41453
            PR fortran/87395
    
    gcc/fortran/ChangeLog:
    
            * trans-expr.cc (gfc_conv_procedure_call): Remove condition
            disabling clobber generation for dummy variables.  Remove
            obsolete comment.
    
    gcc/testsuite/ChangeLog:
    
            * gfortran.dg/intent_optimize_6.f90: New test.

Diff:
---
 gcc/fortran/trans-expr.cc                       |  4 ---
 gcc/testsuite/gfortran.dg/intent_optimize_6.f90 | 34 +++++++++++++++++++++++++
 2 files changed, 34 insertions(+), 4 deletions(-)

diff --git a/gcc/fortran/trans-expr.cc b/gcc/fortran/trans-expr.cc
index 214726220f7..11b7c05929c 100644
--- a/gcc/fortran/trans-expr.cc
+++ b/gcc/fortran/trans-expr.cc
@@ -6527,8 +6527,6 @@ gfc_conv_procedure_call (gfc_se * se, gfc_symbol * sym,
 			  && !e->symtree->n.sym->attr.dimension
 			  && !e->symtree->n.sym->attr.pointer
 			  && !e->symtree->n.sym->attr.allocatable
-			  /* See PR 41453.  */
-			  && !e->symtree->n.sym->attr.dummy
 			  /* FIXME - PR 87395 and PR 41453  */
 			  && e->symtree->n.sym->attr.save == SAVE_NONE
 			  && !e->symtree->n.sym->attr.associate_var
@@ -6538,8 +6536,6 @@ gfc_conv_procedure_call (gfc_se * se, gfc_symbol * sym,
 			  && !sym->attr.elemental)
 			{
 			  tree var;
-			  /* FIXME: This fails if var is passed by reference, see PR
-			     41453.  */
 			  var = build_fold_indirect_ref_loc (input_location,
 							     parmse.expr);
 			  tree clobber = build_clobber (TREE_TYPE (var));
diff --git a/gcc/testsuite/gfortran.dg/intent_optimize_6.f90 b/gcc/testsuite/gfortran.dg/intent_optimize_6.f90
new file mode 100644
index 00000000000..72fec3db583
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/intent_optimize_6.f90
@@ -0,0 +1,34 @@
+! { dg-do run }
+! { dg-additional-options "-fno-inline -fno-ipa-modref -fdump-tree-optimized -fdump-tree-original" }
+!
+! PR fortran/41453
+! Check that the INTENT(OUT) attribute causes one clobber to be emitted in
+! the caller before each call to FOO in the *.original dump, and the
+! initialization constant to be optimized away in the *.optimized dump,
+! in the case of an argument passed by reference to the caller.
+
+module x
+implicit none
+contains
+  subroutine foo(a)
+    integer(kind=4), intent(out) :: a
+    a = 42
+  end subroutine foo
+  subroutine bar(b)
+    integer(kind=4) :: b
+    b = 123456789
+    call foo(b)
+  end subroutine bar
+end module x
+
+program main
+  use x
+  implicit none
+  integer(kind=4) :: c
+  call bar(c)
+  if (c /= 42) stop 1
+end program main
+
+! { dg-final { scan-tree-dump-times "CLOBBER" 1 "original" } }
+! { dg-final { scan-tree-dump "\\*\\\(integer\\\(kind=4\\\) \\*\\\) b = {CLOBBER};" "original" } }
+! { dg-final { scan-tree-dump-not "123456789" "optimized" { target __OPTIMIZE__ } } }