From e129122f0f6909bbc59075678ea72d744612e69e Mon Sep 17 00:00:00 2001
From: Nick Gasson <nick@nickg.me.uk>
Date: Wed, 26 Oct 2022 20:25:42 +0100
Subject: [PATCH] Avoid error with null-range aggregate. Issue #552

---
 src/bounds.c              |  3 +++
 test/bounds/nullrange.vhd | 12 ++++++++++++
 test/test_bounds.c        | 13 +++++++++++++
 3 files changed, 28 insertions(+)
 create mode 100644 test/bounds/nullrange.vhd

diff --git a/src/bounds.c b/src/bounds.c
index 9e9bd8bf..7617af7e 100644
--- a/src/bounds.c
+++ b/src/bounds.c
@@ -185,6 +185,9 @@ static bool bounds_check_index(tree_t index, tree_t ref, type_t type,
                                range_kind_t kind, const char *what,
                                int64_t low, int64_t high)
 {
+   if (low > high)
+      return true;   // Null range allows any index
+
    int64_t folded;
    unsigned folded_u;
    if (folded_int(index, &folded)) {
diff --git a/test/bounds/nullrange.vhd b/test/bounds/nullrange.vhd
new file mode 100644
index 00000000..8fd5647d
--- /dev/null
+++ b/test/bounds/nullrange.vhd
@@ -0,0 +1,12 @@
+entity test is
+end entity test;
+architecture beh of test is
+    signal sig : bit_vector(-1 downto 0);
+    signal sig2 : bit_vector(0 to -1);
+begin
+    process(sig,sig2)
+    begin
+        sig <= (sig'range => '0');            -- OK
+        sig2 <= (sig2'range => '0');          -- OK
+    end process;
+end architecture beh;
diff --git a/test/test_bounds.c b/test/test_bounds.c
index 28aec9ae..5696796f 100644
--- a/test/test_bounds.c
+++ b/test/test_bounds.c
@@ -568,6 +568,18 @@ START_TEST(test_driver1)
 }
 END_TEST
 
+START_TEST(test_nullrange)
+{
+   input_from_file(TESTDIR "/bounds/nullrange.vhd");
+
+   tree_t a = parse_check_and_simplify(T_ENTITY, T_ARCH);
+   fail_unless(error_count() == 0);
+
+   bounds_check(a);
+   fail_if_errors();
+}
+END_TEST
+
 Suite *get_bounds_tests(void)
 {
    Suite *s = suite_create("bounds");
@@ -596,6 +608,7 @@ Suite *get_bounds_tests(void)
    tcase_add_test(tc_core, test_issue477b);
    tcase_add_test(tc_core, test_case3);
    tcase_add_test(tc_core, test_driver1);
+   tcase_add_test(tc_core, test_nullrange);
    suite_add_tcase(s, tc_core);
 
    return s;
-- 
2.39.2