Re: [Patch, Fortran] PR55758 - Non-C_Bool handling with BIND(C)

[Tobias Burnus <burnus@net-b.de>]

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** ping **

Attached is a small variation, which in addition handles the case that a 
non-BOOL_C LOGICAL, Bind(C) dummy argument (or result variable) is used 
in a procedure call. In that case, the variable is now converted to a 
TYPE_PRECISION == 1 variable. -- The updated patch was build and 
regtested successfully.

As written before, I believe that the patch avoids some pitfalls with C 
interoperability of logical variables:  On one hand, it improves 
cross-compiler portability by rejecting non C_BOOL ones with 
-std=f2003/f2008/f2008ts; on the other hand, it makes wrong-code issues 
due to using non-0/1 integers from C much less likely. In both cases, 
the type-precision==1 handling for non-BIND(C) Fortran LOGICALs or for 
Bind(C) LOGICAL(kind=C_BOOL) remains the same; hence, no optimization 
issue is caused.

OK for the trunk?

Tobias

PS: If there is consensus that this patch is a bad idea, I propose to 
reject non-C_BOOL LOGICALs unconditionally as dummy argument or result 
variable of BIND(C) procedures. Or do you have a better suggestion?


On December 30, 2012, Tobias Burnus wrote:
> Janne Blomqvist wrote:
>> On Fri, Dec 28, 2012 at 12:31 AM, Tobias Burnus <burnus@net-b.de> wrote:
>>> a) The Fortran standard only defines LOGICAL(kind=C_Bool) as being
>>> interoperable with C - no other LOGICAL type. That matches GCC: With 
>>> gcc
>>> (the C compiler) only _Bool is a BOOLEAN_TYPE with TYPE_PRECISION == 1.
>>> Hence, this patch rejects other logical kinds as dummy argument/result
>>> variable in BIND(C) procedures if -std=f2003/f2008/f2008ts is specified
>>> (using -pedantic, one gets a warning).
>> Sorry, I don't understand, what is the -pedantic warning about if it's
>> already rejected? Or do you mean std=gnu -pedantic?
>
> The latter. Actually, I use "gfc_notify_std(GFC_STD_GNU, ..." and just 
> observed the -pedantic result. (I have to admit that I never quite 
> understood - and still don't - what -pedantic exactly does.)
>
>>> b) As GNU extension, other logical kinds are accepted in BIND(C) 
>>> procedures;
>>> however, as the main use of "LOGICAL(kind=4)" (for BIND(C) 
>>> procedures) is to
>>> handle logical expressions which use C's int, one has to deal with all
>>> integer values and not only 0 and 1. Hence, a normal integer type is 
>>> used
>>> internally in that case. That has been done to avoid surprises of 
>>> users and
>>> hard to trace bugs.
>> Does this actually work robustly?
>
> I think it does in the sense that it mitigates the problems related to 
> LOGICAL(kind=4) and BIND(C) procedures. No, if one thinks of it as 
> full cure for the problem. The only way to ensure this is to turn all 
> of gfortran's LOGICALs into integers - and even that won't prevent 
> issues related to interoperability with C's _Bool as that one expects 
> only 0 and 1. Thus, either C<->Fortran or Fortran <-> Fortran 
> logical(kind=C_Bool) could still lead to problems.
>
>> E.g. if you have a logical but really integer under the covers, what 
>> happens if you equivalence it with a "normal" logical variable.
>
> Well, equivalencing of actual arguments / result variables is not 
> allowed (I think, not checked). Besides, if you have equivalenced two 
> variables, if you have set one, you may not access the other, e.g.:
>
> logical :: A
> integer :: B
> equivalence (A,B)
> A = .true.
> B = 1
> if (A) ...
>
> is invalid as "A" is not defined, even if A = .true. and B = 1 have 
> exactly the same storage size and bit patterns and, hence, in practice 
> "A" would be a well defined .true.
>
>> Or pass it as an argument to a procedure expecting a normal logical etc.
>
> If the value is only 1 or 0, there shouldn't be any problems. Only if 
> one uses in turn ".not. dummy" there might be one.
>
> The idea of the patch was only to mitigate the problems - a full cure 
> is not possible (cf. above). I think the most likely problematic code is
>    if (.not. c_function())
> which is fixed by the patch. And the hope is that fold-converting to a 
> type-precision=1, Boolean-type logical fixes most of the remaining 
> issues.
>
> I think the current solution which only affects non-C_BOOL-kind actual 
> arguments and result variables of BIND(C) procedures is a good 
> compromise.
>
> * * *
>
> But if others do not like this approach, one could turn the 
> gfc_notify_std into a gfc_error are completely reject logicals with 
> kinds /= C_Bool for dummy arguments/result variables in BIND(C) 
> procedures. Would you prefer that approach?
>
> (Doing so will break user code (e.g. Open MPI) and make users unhappy 
> but it will be a tad safer as the current patch.)
>
> Tobias
>


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2013-01-06  Tobias Burnus  <burnus@net-b.de>

	PR fortran/55758
	* resolve.c (resolve_symbol): Reject non-C_Bool logicals
	in BIND(C) procedures with -std=f*.
	* trans-types.c (gfc_sym_type): Use a non-BOOLEAN_TYPE
	integer for non-C_Bool logicals in BIND(C) procedures.
	* trans-expr.c (gfc_conv_unary_op): Add fold convert for
	INTRINSIC_NOT.
	(gfc_conv_procedure_call): Convert type-precision != 1
	logicals to type-precision == 1.

2013-01-06  Tobias Burnus  <burnus@net-b.de>

	PR fortran/55758
	* gfortran.dg/bind_c_bool_1.f90: New.
	* gfortran.dg/bind_c_bool_2.f90: New.
	* gfortran.dg/bind_c_bool_2_c.c: New.
	* gfortran.dg/bind_c_bool_3.f90: New.
	* gfortran.dg/do_5.f90: Add dg-warning.

diff --git a/gcc/fortran/resolve.c b/gcc/fortran/resolve.c
index 54ac3c6..0403396 100644
--- a/gcc/fortran/resolve.c
+++ b/gcc/fortran/resolve.c
@@ -13658,6 +13662,32 @@ resolve_symbol (gfc_symbol *sym)
       return;
     }
 
+  if (sym->ts.type == BT_LOGICAL
+      && ((sym->attr.function && sym->attr.is_bind_c && sym->result == sym)
+	  || ((sym->attr.dummy || sym->attr.result) && sym->ns->proc_name
+	      && sym->ns->proc_name->attr.is_bind_c)))
+    {
+      int i;
+      for (i = 0; gfc_logical_kinds[i].kind; i++)
+        if (gfc_logical_kinds[i].kind == sym->ts.kind)
+          break;
+      if (!gfc_logical_kinds[i].c_bool && sym->attr.dummy
+	  && gfc_notify_std (GFC_STD_GNU, "LOGICAL dummy argument '%s' at %L "
+			     "with non-C_Bool kind in BIND(C) procedure '%s'",
+			     sym->name, &sym->declared_at,
+			     sym->ns->proc_name->name) == FAILURE)
+	return;
+      else if (!gfc_logical_kinds[i].c_bool
+	       && gfc_notify_std (GFC_STD_GNU, "LOGICAL result variable '%s' at"
+				  " %L with non-C_Bool kind in BIND(C) "
+				  "procedure '%s'", sym->name,
+				  &sym->declared_at,
+				  sym->attr.function ? sym->name
+						     : sym->ns->proc_name->name)
+		  == FAILURE)
+	return;
+    }
+
   switch (sym->attr.flavor)
     {
     case FL_VARIABLE:
diff --git a/gcc/fortran/trans-expr.c b/gcc/fortran/trans-expr.c
index 01d3595..59a0ab4 100644
--- a/gcc/fortran/trans-expr.c
+++ b/gcc/fortran/trans-expr.c
@@ -1850,7 +1850,8 @@ gfc_conv_unary_op (enum tree_code code, gfc_se * se, gfc_expr * expr)
      We must convert it to a compare to 0 (e.g. EQ_EXPR (op1, 0)).
      All other unary operators have an equivalent GIMPLE unary operator.  */
   if (code == TRUTH_NOT_EXPR)
-    se->expr = fold_build2_loc (input_location, EQ_EXPR, type, operand.expr,
+    se->expr = fold_build2_loc (input_location, EQ_EXPR, type,
+				fold_convert (type, operand.expr),
 				build_int_cst (type, 0));
   else
     se->expr = fold_build1_loc (input_location, code, type, operand.expr);
@@ -4208,6 +4209,14 @@ gfc_conv_procedure_call (gfc_se * se, gfc_symbol * sym,
 		    }
 		  else
 		    gfc_conv_expr (&parmse, e);
+
+		  /* Special case: non-kind=C_BOOL LOGICALs of BIND(C) are
+		     integer types and have to be converted to Booleans.  */
+		  if (e->ts.type == BT_LOGICAL
+		      && TYPE_PRECISION (TREE_TYPE (parmse.expr)) != 1)
+		    parmse.expr
+			= fold_convert (gfc_get_logical_type (e->ts.kind),
+					parmse.expr);
 		}
 	      else if (arg->name && arg->name[0] == '%')
 		/* Argument list functions %VAL, %LOC and %REF are signalled
@@ -4260,6 +4269,28 @@ gfc_conv_procedure_call (gfc_se * se, gfc_symbol * sym,
 		    base_object = build_fold_indirect_ref_loc (input_location,
 							       parmse.expr);
 
+		  /* Special case: non-kind=C_BOOL LOGICALs of BIND(C) are
+		     integer types and have to be converted to Booleans.  */
+		  if (e->ts.type == BT_LOGICAL
+		      && TYPE_PRECISION (TREE_TYPE (TREE_TYPE (parmse.expr)))
+			 != 1)
+		    {
+		      tmp = build_fold_indirect_ref_loc (input_location,
+							 parmse.expr);
+		      parmse.expr
+			= gfc_create_var (gfc_get_logical_type (e->ts.kind),
+					  NULL);
+		      gfc_add_modify_loc (input_location, &se->pre, parmse.expr,
+				fold_convert (gfc_get_logical_type (e->ts.kind),
+					      tmp));
+		      if (e->expr_type == EXPR_VARIABLE
+			  && (!fsym || fsym->attr.intent != INTENT_IN
+			      || fsym->attr.pointer))
+			gfc_add_modify_loc (input_location, &se->post, tmp,
+				fold_convert (TREE_TYPE (tmp), parmse.expr));
+		      parmse.expr = gfc_build_addr_expr (NULL_TREE, parmse.expr);
+		    }
+
 		  /* A class array element needs converting back to be a
 		     class object, if the formal argument is a class object.  */
 		  if (fsym && fsym->ts.type == BT_CLASS
diff --git a/gcc/fortran/trans-types.c b/gcc/fortran/trans-types.c
index 8394bf9..73ed5aa 100644
--- a/gcc/fortran/trans-types.c
+++ b/gcc/fortran/trans-types.c
@@ -2128,6 +2128,25 @@ gfc_sym_type (gfc_symbol * sym)
 	      && sym->ns->proc_name
 	      && sym->ns->proc_name->attr.is_bind_c)))
     type = gfc_character1_type_node;
+  else if (sym->ts.type == BT_LOGICAL
+	   && ((sym->attr.function && sym->attr.is_bind_c)
+	       || ((sym->attr.dummy || sym->attr.result) && sym->ns->proc_name
+		   && sym->ns->proc_name->attr.is_bind_c)))
+    {
+      /* For LOGICAL dummy arguments or result value of a C binding procedure,
+         which do not match _Bool (C_Bool kind), a normal integer variable
+         is used instead of a BOOLEAN_TYPE with a TYPE_PRECISION of 1. The
+	 reason is that on the C side, a normal integer such as "int" is used,
+	 implying that any integer value could be used - not only 0 and 1.  */
+      int i;
+      for (i = 0; gfc_logical_kinds[i].kind; i++)
+        if (gfc_logical_kinds[i].kind == sym->ts.kind)
+          break;
+      if (!gfc_logical_kinds[i].c_bool)
+	type = gfc_get_int_type (sym->ts.kind);
+      else
+	type = gfc_typenode_for_spec (&sym->ts);
+    }
   else
     type = gfc_typenode_for_spec (&sym->ts);
 
diff --git a/gcc/testsuite/gfortran.dg/bind_c_bool_1.f90 b/gcc/testsuite/gfortran.dg/bind_c_bool_1.f90
new file mode 100644
index 0000000..467bdc1
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/bind_c_bool_1.f90
@@ -0,0 +1,25 @@
+! { dg-do compile }
+! { dg-options "-std=f2003" }
+!
+! PR fortran/55758
+!
+
+function sub2() bind(C) ! { dg-error "GNU Extension: LOGICAL result variable 'sub2' at .1. with non-C_Bool kind in BIND.C. procedure 'sub2'" }
+  logical(kind=8) :: sub2
+  logical(kind=4) :: local ! OK
+end function sub2
+
+function sub4() bind(C) result(res) ! { dg-error "GNU Extension: LOGICAL result variable 'res' at .1. with non-C_Bool kind in BIND.C. procedure 'sub4'" }
+  logical(kind=2) :: res
+  logical(kind=4) :: local ! OK
+end function sub4
+
+
+subroutine sub(x) bind(C) ! { dg-error "GNU Extension: LOGICAL dummy argument 'x' at .1. with non-C_Bool kind in BIND.C. procedure 'sub'" }
+  logical(kind=4) :: x
+end subroutine sub
+
+subroutine sub3(y) bind(C)
+  use iso_c_binding, only : c_bool
+  logical(kind=c_bool) :: y ! OK
+end subroutine sub3
diff --git a/gcc/testsuite/gfortran.dg/bind_c_bool_2.f90 b/gcc/testsuite/gfortran.dg/bind_c_bool_2.f90
new file mode 100644
index 0000000..1feb28d
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/bind_c_bool_2.f90
@@ -0,0 +1,32 @@
+! { dg-do run }
+! { dg-options "" }
+! { dg-additional-sources bind_c_bool_2_c.c }
+!
+! PR fortran/55758
+!
+! Ensure that logical(c_int) in a BIND(C) function is properly handled,
+! i.e. ".not.-1" is not "-2" but 0 as a C programmer would expect.
+!
+
+program main
+  use iso_c_binding, only : c_int, c_bool
+  implicit none
+  logical(4) :: result
+
+  interface
+    function C_true() bind(C, name="C_true")
+      import :: c_int
+      logical(c_int) :: C_true ! { dg-warning "C kind type parameter is for type INTEGER but type at .1. is LOGICAL" }
+    end function C_true
+  end interface
+
+  if (c_int == c_bool) stop
+
+  result = C_true()
+  if (result .neqv. .true.) call abort ()
+  if (transfer(result, 0) /= 1) call abort()
+
+  result = .not.C_true()
+  if (transfer(result, 0) /= 0) call abort()
+  if (result .neqv. .false.) call abort ()
+end program main
diff --git a/gcc/testsuite/gfortran.dg/bind_c_bool_2_c.c b/gcc/testsuite/gfortran.dg/bind_c_bool_2_c.c
new file mode 100644
index 0000000..3673bdc
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/bind_c_bool_2_c.c
@@ -0,0 +1,7 @@
+/* To be used by bind_c_bool_2.f90.  PR fortran/55758  */
+
+int
+C_true (void)
+{
+  return -1;
+}
diff --git a/gcc/testsuite/gfortran.dg/bind_c_bool_3.f90 b/gcc/testsuite/gfortran.dg/bind_c_bool_3.f90
new file mode 100644
index 0000000..a73bf6e
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/bind_c_bool_3.f90
@@ -0,0 +1,59 @@
+! { dg-do run }
+! { dg-options "" }
+!
+! PR fortran/55758
+!
+! Ensure that a BIND(C) non-C_BOOL LOGICAL with TYPE_PRECISION != 1 is
+! correctly converted into a Fortran LOGICAL with TYPE_PRECSION == 1 in
+! Procedure calls.
+!
+
+subroutine bar3(x)
+  logical(kind=4) :: x
+  logical(kind=4) :: y
+  y = .not.x
+  !print *, y, transfer(x,0)
+  if (y .or. .not. x) call abort()
+  x = .true.
+end subroutine bar3
+
+module m
+contains
+subroutine foo(x) bind(C)
+  integer :: i
+  logical(kind=4) :: x
+  i = -1
+  x = transfer(i,.true._4)
+  call bar(x)
+
+  x = transfer(i,.true._4)
+  call bar2(x)
+  if (transfer (x, 1) /= 1) call abort()
+
+  x = transfer(i,.true._4)
+  call bar3(x)
+  if (transfer (x, 1) /= 1) call abort()
+end subroutine foo
+
+subroutine bar(x)
+  logical(kind=4), value :: x
+  logical(kind=4) :: y
+  y = .not.x
+  !print *, y, transfer(x,0)
+  if (y .or. .not. x) call abort()
+  x = .true.
+end subroutine bar
+
+subroutine bar2(x)
+  logical(kind=4) :: x
+  logical(kind=4) :: y
+  y = .not.x
+  if (y .or. .not. x) call abort()
+  !print *, y, transfer(x,0)
+end subroutine bar2
+end
+
+use m
+logical(kind=4) :: x
+call foo(x)
+end
diff --git a/gcc/testsuite/gfortran.dg/do_5.f90 b/gcc/testsuite/gfortran.dg/do_5.f90
index 08cd8e6..9272d87 100644
--- a/gcc/testsuite/gfortran.dg/do_5.f90
+++ b/gcc/testsuite/gfortran.dg/do_5.f90
@@ -15,7 +15,7 @@
       L = .FALSE.
       END FUNCTION
 
-      LOGICAL(8) FUNCTION L2() BIND(C)
+      LOGICAL(8) FUNCTION L2() BIND(C) ! { dg-error "GNU Extension: LOGICAL result variable 'l2' at .1. with non-C_Bool kind in BIND.C. procedure 'l2'" }
       L2 = .FALSE._8
       END FUNCTION