[gcc r12-3865] libiberty: prevent null dereferencing on dlang_type

[Jeff Law]

https://gcc.gnu.org/g:b3585c0836e729bed56b9afd4292177673a25ca0

commit r12-3865-gb3585c0836e729bed56b9afd4292177673a25ca0
Author: Luís Ferreira <contact@lsferreira.net>
Date:   Thu Sep 23 11:54:00 2021 -0400

    libiberty: prevent null dereferencing on dlang_type
    
    libiberty/
            * d-demangle.c (dlang_Type): Validate MANGLED is nonnull.
    
            * testsuite/d-demangle-expected: New test.

Diff:
---
 libiberty/d-demangle.c                  | 2 +-
 libiberty/testsuite/d-demangle-expected | 5 ++++-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/libiberty/d-demangle.c b/libiberty/d-demangle.c
index 7ded3e2a256..3adf7b562d1 100644
--- a/libiberty/d-demangle.c
+++ b/libiberty/d-demangle.c
@@ -875,7 +875,7 @@ dlang_type (string *decl, const char *mangled, struct dlang_info *info)
       szmods = string_length (&mods);
 
       /* Back referenced function type.  */
-      if (*mangled == 'Q')
+      if (mangled && *mangled == 'Q')
 	mangled = dlang_type_backref (decl, mangled, info, 1);
       else
 	mangled = dlang_function_type (decl, mangled, info);
diff --git a/libiberty/testsuite/d-demangle-expected b/libiberty/testsuite/d-demangle-expected
index c35185c3e1e..799f4724b72 100644
--- a/libiberty/testsuite/d-demangle-expected
+++ b/libiberty/testsuite/d-demangle-expected
@@ -991,11 +991,14 @@ _D88
 _D5__T1aZv
 _D5__T1aZv
 #
---format=dlang
 _D00
 _D00
 #
 --format=dlang
+_D01_D
+_D01_D
+#
+--format=dlang
 _D9223372036854775817
 _D9223372036854775817
 #