Re: [Patch, Fortran] PR 78392: ICE in gfc_trans_auto_array_allocation, at fortran/trans-array.c:5979

[Janus Weil <janus@gcc.gnu.org>]

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Hi all,

> I previously assumed that the test case for this PR would be legal,
> but by now I think that's wrong. The test case should be rejected, and
> we already have checking mechanisms for this (see
> resolve_fl_variable), but apparently they are not working.
>
> My current suspicion is that 'gfc_is_constant_expr' has a bug, because
> it claims the call to the function 'get_i' to be a constant
> expression. This is not true, because get_i() can not be reduced to a
> compile-time constant.

some more reading in the standard confirms this suspicion: In
gfc_is_constant_expr there is a piece of code which claims that
specification functions are constant. That is certainly not true, and
so what I'm doing in the attached fix is to remove that code and add
some references to the standard to make things clearer.

The code that I'm removing has last been touched in this commit by
Jerry six years ago:

https://gcc.gnu.org/viewcvs/gcc?view=revision&revision=166520

However, this did not introduce the bug in the first place (not sure
when that happened).

In any case the new patch in the attachment regtests cleanly and
correctly rejects the original test case as well as one of the cases
mentioned by Dominique. Ok for trunk?

Cheers,
Janus



2016-11-19  Janus Weil  <janus@gcc.gnu.org>

    PR fortran/78392
    * expr.c (gfc_is_constant_expr): Specification functions are not
    compile-time constants. Update documentation (add reference to F08
    standard), add a FIXME.
    (external_spec_function): Add reference to F08 standard.
    * resolve.c (resolve_fl_variable): Ditto.

2016-11-19  Janus Weil  <janus@gcc.gnu.org>

    PR fortran/78392
    * gfortran.dg/constant_shape.f90: New test case.

[-- Attachment #2: pr78392_v3.diff --]
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Index: gcc/fortran/expr.c
===================================================================
--- gcc/fortran/expr.c	(Revision 242620)
+++ gcc/fortran/expr.c	(Arbeitskopie)
@@ -883,8 +883,9 @@ done:
 }
 
 
-/* Function to determine if an expression is constant or not.  This
-   function expects that the expression has already been simplified.  */
+/* Determine if an expression is constant in the sense of F08:7.1.12.
+ * This function expects that the expression has already been simplified.
+ * FIXME: Return a bool, not an int.  */
 
 int
 gfc_is_constant_expr (gfc_expr *e)
@@ -891,7 +892,6 @@ gfc_is_constant_expr (gfc_expr *e)
 {
   gfc_constructor *c;
   gfc_actual_arglist *arg;
-  gfc_symbol *sym;
 
   if (e == NULL)
     return 1;
@@ -920,25 +920,6 @@ gfc_is_constant_expr (gfc_expr *e)
 	      return 0;
 	}
 
-      /* Specification functions are constant.  */
-      /* F95, 7.1.6.2; F2003, 7.1.7  */
-      sym = NULL;
-      if (e->symtree)
-	sym = e->symtree->n.sym;
-      if (e->value.function.esym)
-	sym = e->value.function.esym;
-
-      if (sym
-	  && sym->attr.function
-	  && sym->attr.pure
-	  && !sym->attr.intrinsic
-	  && !sym->attr.recursive
-	  && sym->attr.proc != PROC_INTERNAL
-	  && sym->attr.proc != PROC_ST_FUNCTION
-	  && sym->attr.proc != PROC_UNKNOWN
-	  && gfc_sym_get_dummy_args (sym) == NULL)
-	return 1;
-
       if (e->value.function.isym
 	  && (e->value.function.isym->elemental
 	      || e->value.function.isym->pure
@@ -2741,7 +2722,8 @@ restricted_args (gfc_actual_arglist *a)
 /************* Restricted/specification expressions *************/
 
 
-/* Make sure a non-intrinsic function is a specification function.  */
+/* Make sure a non-intrinsic function is a specification function,
+ * see F08:7.1.11.5.  */
 
 static bool
 external_spec_function (gfc_expr *e)
Index: gcc/fortran/resolve.c
===================================================================
--- gcc/fortran/resolve.c	(Revision 242620)
+++ gcc/fortran/resolve.c	(Arbeitskopie)
@@ -11831,8 +11831,8 @@ resolve_fl_variable (gfc_symbol *sym, int mp_flag)
       && !sym->attr.pointer
       && is_non_constant_shape_array (sym))
     {
-      /* The shape of a main program or module array needs to be
-	 constant.  */
+      /* F08:C541. The shape of an array defined in a main program or module
+       * needs to be constant.  */
       gfc_error ("The module or main program array %qs at %L must "
 		 "have constant shape", sym->name, &sym->declared_at);
       specification_expr = saved_specification_expr;

[-- Attachment #3: constant_shape.f90 --]
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! { dg-do compile }
!
! PR 78392: ICE in gfc_trans_auto_array_allocation, at fortran/trans-array.c:5979
!
! Contributed by Janus Weil <janus@gcc.gnu.org>

module mytypes
   implicit none
 contains
   pure integer function get_i ()
     get_i = 13
   end function
end module

program test
  use mytypes
  implicit none
  integer, dimension(get_i()) :: x  ! { dg-error "must have constant shape" }
  print *, size (x)
end