From 3be2b8f475f22c531d6cef1b041c0573b3ea5133 Mon Sep 17 00:00:00 2001
From: Harald Anlauf <anlauf@gmx.de>
Date: Mon, 18 Mar 2024 19:36:59 +0100
Subject: [PATCH] Fortran: error recovery in frontend optimization [PR103715]

gcc/fortran/ChangeLog:

	PR fortran/103715
	* frontend-passes.cc (check_externals_expr): Prevent invalid read
	in case of mismatch of external subroutine with function.

gcc/testsuite/ChangeLog:

	PR fortran/103715
	* gfortran.dg/pr103715.f90: New test.
---
 gcc/fortran/frontend-passes.cc         |  3 +++
 gcc/testsuite/gfortran.dg/pr103715.f90 | 12 ++++++++++++
 2 files changed, 15 insertions(+)
 create mode 100644 gcc/testsuite/gfortran.dg/pr103715.f90

diff --git a/gcc/fortran/frontend-passes.cc b/gcc/fortran/frontend-passes.cc
index 06dfa1a3232..3c06018fdbb 100644
--- a/gcc/fortran/frontend-passes.cc
+++ b/gcc/fortran/frontend-passes.cc
@@ -5807,6 +5807,9 @@ check_externals_expr (gfc_expr **ep, int *walk_subtrees ATTRIBUTE_UNUSED,
   if (e->expr_type != EXPR_FUNCTION)
     return 0;

+  if (e->symtree && e->symtree->n.sym->attr.subroutine)
+    return 0;
+
   sym = e->value.function.esym;
   if (sym == NULL)
     return 0;
diff --git a/gcc/testsuite/gfortran.dg/pr103715.f90 b/gcc/testsuite/gfortran.dg/pr103715.f90
new file mode 100644
index 00000000000..72c5a31fb21
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/pr103715.f90
@@ -0,0 +1,12 @@
+! { dg-do compile }
+! PR fortran/103715 - ICE in gfc_find_gsymbol
+!
+! valgrind did report an invalid read in check_externals_procedure
+
+program p
+  select type (y => g()) ! { dg-error "Selector shall be polymorphic" }
+  end select
+  call g()
+end
+
+! { dg-prune-output "already being used as a FUNCTION" }
--
2.35.3