[PATCH] fortran: Avoid infinite self-recursion [PR105381]

[Mikael Morin <morin-mikael@orange.fr>]

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Hello,

this is a fix for the regression I recently introduced with the PR102043 
patch.  It is an infinite recursion problem.  I can’t see the memory 
consumption that Harald reported; maybe he doesn’t use the default 
optimization level to build the compiler.

Regression tested on x86_64-pc-linux-gnu.
I plan to push it tonight.

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From 85d57fb88203697d7e52d5f1f148eab35e4f7486 Mon Sep 17 00:00:00 2001
From: Mikael Morin <mikael@gcc.gnu.org>
Date: Tue, 26 Apr 2022 13:05:32 +0200
Subject: [PATCH] fortran: Avoid infinite self-recursion [PR105381]
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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): Don’t recurse
	if the next argument is the same as the current.

gcc/testsuite/ChangeLog:

	* gfortran.dg/character_array_dummy_1.f90: New test.
---
 gcc/fortran/trans-array.cc                    |  3 ++-
 .../gfortran.dg/character_array_dummy_1.f90   | 21 +++++++++++++++++++
 2 files changed, 23 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gfortran.dg/character_array_dummy_1.f90

diff --git a/gcc/fortran/trans-array.cc b/gcc/fortran/trans-array.cc
index e4b6270ccf8..e0070aa080d 100644
--- a/gcc/fortran/trans-array.cc
+++ b/gcc/fortran/trans-array.cc
@@ -3698,7 +3698,8 @@ non_negative_strides_array_p (tree expr)
   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);
+      if (orig_decl != expr)
+	return non_negative_strides_array_p (orig_decl);
 
   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
-- 
2.35.1