[gcc r12-8280] fortran: Avoid infinite self-recursion [PR105381]

[gcc r12-8280] fortran: Avoid infinite self-recursion [PR105381]

[Mikael Morin]

https://gcc.gnu.org/g:3e0c9fdfd00b5b5cbff1a0bd6ac012a10fe81348

commit r12-8280-g3e0c9fdfd00b5b5cbff1a0bd6ac012a10fe81348
Author: Mikael Morin <mikael@gcc.gnu.org>
Date:   Wed Apr 27 11:36:00 2022 +0200

    fortran: Avoid infinite self-recursion [PR105381]
    
    Dummy array decls are local decls different from the argument decl
    accessible through GFC_DECL_SAVED_DESCRIPTOR.  If the argument decl has
    a DECL_LANG_SPECIFIC set, it is copied over to the local decl at the
    time the latter is created, so that the DECL_LANG_SPECIFIC object is
    shared between local dummy decl and argument decl, and thus the
    GFC_DECL_SAVED_DESCRIPTOR of the argument decl is the argument decl
    itself.
    
    The r12-8230-g7964ab6c364c410c34efe7ca2eba797d36525349 change introduced
    the non_negative_strides_array_p predicate which recurses through
    GFC_DECL_SAVED_DESCRIPTOR to avoid seeing dummy decls as purely local
    decls.  As the GFC_DECL_SAVED_DESCRIPTOR of the argument decl is itself,
    this can cause infinite recursion.
    
    This change adds a check to avoid infinite recursion.
    
            PR fortran/102043
            PR fortran/105381
    
    gcc/fortran/ChangeLog:
    
            * trans-array.cc (non_negative_strides_array_p): Inline variable
            orig_decl and merge nested if conditions.  Add condition to not
            recurse if the next argument is the same as the current.
    
    gcc/testsuite/ChangeLog:
    
            * gfortran.dg/character_array_dummy_1.f90: New test.

Diff:
---
 gcc/fortran/trans-array.cc                          |  7 ++++---
 .../gfortran.dg/character_array_dummy_1.f90         | 21 +++++++++++++++++++++
 2 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/gcc/fortran/trans-array.cc b/gcc/fortran/trans-array.cc
index e4b6270ccf8..05134952db4 100644
--- a/gcc/fortran/trans-array.cc
+++ b/gcc/fortran/trans-array.cc
@@ -3696,9 +3696,10 @@ non_negative_strides_array_p (tree expr)
   /* If the array was originally a dummy with a descriptor, strides can be
      negative.  */
   if (DECL_P (expr)
-      && DECL_LANG_SPECIFIC (expr))
-    if (tree orig_decl = GFC_DECL_SAVED_DESCRIPTOR (expr))
-      return non_negative_strides_array_p (orig_decl);
+      && DECL_LANG_SPECIFIC (expr)
+      && GFC_DECL_SAVED_DESCRIPTOR (expr)
+      && GFC_DECL_SAVED_DESCRIPTOR (expr) != expr)
+    return non_negative_strides_array_p (GFC_DECL_SAVED_DESCRIPTOR (expr));
 
   return true;
 }
diff --git a/gcc/testsuite/gfortran.dg/character_array_dummy_1.f90 b/gcc/testsuite/gfortran.dg/character_array_dummy_1.f90
new file mode 100644
index 00000000000..da5ed636f4f
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/character_array_dummy_1.f90
@@ -0,0 +1,21 @@
+! { dg-do compile }
+!
+! PR fortran/105381
+! Infinite recursion with array references of character dummy arguments.
+!
+! Contributed by Harald Anlauf <anlauf@gmx.de>
+
+MODULE m
+  implicit none
+  integer,  parameter :: ncrit  =  8
+  integer,  parameter :: nterm  =  7
+contains
+
+  subroutine new_thin_rule (rule1)
+    character(*),intent(in) ,optional :: rule1(ncrit)
+    character(len=8) :: rules (ncrit,nterm)
+    rules = ''
+    if (present (rule1)) rules(:,1) = rule1  ! <-- compile time hog
+  end subroutine new_thin_rule
+
+end module m