[Patch, fortran] PRs 96100 and 96101 - Problems with string lengths of array constructors

[Paul Richard Thomas via Gcc-patches]

Hi All,

The fix for PR9601 is rather trivial and is the last chunk of the patch.
Finding the fix for PR96100 took a silly amount of time but it now looks
rather obvious. Trying to evaluate the string length by calling
gfc_conv_expr_descriptor, when this function is already failing to find it
is kind of doomed to failure :-) Therefore, gfc_conv_expr is used with
tse.descriptor_only set. This has the effect of ignoring trailing array
references and making use of gfc_conv_component_ref's being able to extract
the hidden string length for deferred length components. Finally, the
string length of the first element in the array constructor is set if this
is a deferred length component.

Regtests OK on FC31/x86_64 - OK for master?

Paul

This patch fixes PR96100 and PR96101 by making some minor changes to
the evaluation of string lengths for gfc_conv_expr_descriptor.

2020-08-13  Paul Thomas  <pa...@gcc.gnu.org>

gcc/fortran
PR fortran/96100
PR fortran/96101
* trans-array.c (get_array_charlen): Tidy up the evaluation of
the string length for array constructors. Avoid trailing array
references. Ensure string lengths of deferred length components
are set. For parentheses operator apply string  length to both
the primary expression and the enclosed expression.

gcc/testsuite/
PR fortran/96100
PR fortran/96101
* gfortran.dg/char_length_23.f90: New test.

diff --git a/gcc/fortran/trans-array.c b/gcc/fortran/trans-array.c
index 8f93b43bafb..ad3286487e8 100644
--- a/gcc/fortran/trans-array.c
+++ b/gcc/fortran/trans-array.c
@@ -7018,7 +7018,12 @@ get_array_charlen (gfc_expr *expr, gfc_se *se)
       e = gfc_constructor_first (expr->value.constructor)->expr;
 
       gfc_init_se (&tse, NULL);
+
+      /* Avoid evaluating trailing array references since all we need is
+	 the string length.  */
       if (e->rank)
+	tse.descriptor_only = 1;
+      if (e->rank && e->expr_type != EXPR_VARIABLE)
 	gfc_conv_expr_descriptor (&tse, e);
       else
 	gfc_conv_expr (&tse, e);
@@ -7036,14 +7041,26 @@ get_array_charlen (gfc_expr *expr, gfc_se *se)
       gfc_add_modify (&se->pre, expr->ts.u.cl->backend_decl,
 		      tse.string_length);
 
+      /* Make sure that deferred length components point to the hidden
+	 string_length component.  */
+      if (TREE_CODE (tse.expr) == COMPONENT_REF
+	  && TREE_CODE (tse.string_length) == COMPONENT_REF
+	  && TREE_OPERAND (tse.expr, 0) == TREE_OPERAND (tse.string_length, 0))
+	e->ts.u.cl->backend_decl = expr->ts.u.cl->backend_decl;
+
       return;
 
     case EXPR_OP:
       get_array_charlen (expr->value.op.op1, se);
 
-      /* For parentheses the expression ts.u.cl is identical.  */
+      /* For parentheses the expression ts.u.cl should be identical.  */
       if (expr->value.op.op == INTRINSIC_PARENTHESES)
-	return;
+	{
+	  if (expr->value.op.op1->ts.u.cl != expr->ts.u.cl)
+	    expr->ts.u.cl->backend_decl
+			= expr->value.op.op1->ts.u.cl->backend_decl;
+	  return;
+	}
 
       expr->ts.u.cl->backend_decl =
 		gfc_create_var (gfc_charlen_type_node, "sln");

! { dg-do compile }
!
! Test the fix for PRs 96100 and 96101.
!
! Contributed by Gerhardt Steinmetz  <gs...@t-online.de>
!
program p
   type t
      character(:), allocatable :: c(:)
   end type
   type(t) :: x
   character(:), allocatable :: w

! PR96100
   allocate(x%c(2), source = 'def')
   associate (y => [x%c(1:1)])       ! ICE
     print *,y
   end associate

! PR96101
   w = 'abc'
   associate (y => ([w(:)]))
      print *, y                     ! ICE
   end associate

end