Re: [patch, Fortran] Fix PR 71902

[Thomas Koenig]

Hello Mikael,

This doesn't look correct, what about substrings following component or
array references?

You're right; corrected in the attached patch.  I have also added a test
case for this.

PS: What about the original fix, wasn't it a dependency
problem/inaccuracy after all?

The main error was using the allocatable attribute on the symbol that
we were dealing with a deferred length.  Changing the test to check for
expr->ts.deferred is the right thing to do.

There are still some some overly pessimistic assumptions in dependency
handling.  However, I am not sure that this causes actual performance
issues.

Regards

        Thomas

2016-08-18  Thomas Koenig  <tkoe...@gcc.gnu.org>

        PR fortran/71902
        * frontend-passes.c (realloc_string_callback):  Check for deferred
        on the expression instead for allocatable on the symbol.  Name 
temporary
        variable "realloc_string".

2016-08-18  Thomas Koenig  <tkoe...@gcc.gnu.org>

        PR fortran/71902
        * gfortran.dg/dependency_47.f90:  New test.
        * gfortran.dg/dependency_48.f90:  New test.

Index: frontend-passes.c
===================================================================
--- frontend-passes.c	(Revision 239488)
+++ frontend-passes.c	(Arbeitskopie)
@@ -164,6 +164,8 @@ realloc_string_callback (gfc_code **c, int *walk_s
   gfc_expr *expr1, *expr2;
   gfc_code *co = *c;
   gfc_expr *n;
+  gfc_ref *ref;
+  bool found_substr;
 
   if (co->op != EXEC_ASSIGN)
     return 0;
@@ -170,7 +172,7 @@ realloc_string_callback (gfc_code **c, int *walk_s
 
   expr1 = co->expr1;
   if (expr1->ts.type != BT_CHARACTER || expr1->rank != 0
-      || !expr1->symtree->n.sym->attr.allocatable)
+      || !expr1->ts.deferred)
     return 0;
 
   expr2 = gfc_discard_nops (co->expr2);
@@ -177,6 +179,18 @@ realloc_string_callback (gfc_code **c, int *walk_s
   if (expr2->expr_type != EXPR_VARIABLE)
     return 0;
 
+  found_substr = false;
+  for (ref = expr2->ref; ref; ref = ref->next)
+    {
+      if (ref->type == REF_SUBSTRING)
+	{
+	  found_substr = true;
+	  break;
+	}
+    }
+  if (!found_substr)
+    return 0;
+
   if (!gfc_check_dependency (expr1, expr2, true))
     return 0;
 
@@ -190,7 +204,7 @@ realloc_string_callback (gfc_code **c, int *walk_s
   current_code = c;
   inserted_block = NULL;
   changed_statement = NULL;
-  n = create_var (expr2, "trim");
+  n = create_var (expr2, "realloc_string");
   co->expr2 = n;
   return 0;
 }
! { dg-do compile }
! { dg-options "-fdump-tree-original" }
! PR fortran/71902 - make sure that component references are followed
! for dependency analysis.
program main
  type foo
     character(len=:), allocatable :: x
  end type foo
  type(foo) :: a
  a%x = 'asdf'
  a%x = a%x(2:3)
  print *,a%x
end program main
! { dg-final { scan-tree-dump-times "__var_1" 4 "original" } }
! { dg-do compile }
! Make sure there is only one instance of a temporary variable here.
! { dg-options "-fdump-tree-original" }

SUBROUTINE prtdata(ilen)
  INTEGER :: ilen
  character(len=ilen), allocatable :: cline(:)
  allocate(cline(2))
  cline(1) = 'a'
  cline(1)(2:3) = cline(1)(1:2)
  cline(2) = cline(1)
  print *,c
END SUBROUTINE prtdata
! { dg-final { scan-tree-dump-not "__var_" "original" } }