testsuite: add regression test for PR analyzer/94596

This use-after-free false positive affected GCC 10, but seems to be
fixed in trunk for GCC 11; adding a reduced version as a regression
test.

gcc/testsuite/ChangeLog:
	PR analyzer/94596
	* gcc.dg/analyzer/pr94596.c: New test.

gcc/testsuite/gcc.dg/analyzer/pr94596.c

@@ -0,0 +1,97 @@
+/* Minimized/hacked up from openvswitch lib/conntrack.c, which had this license
+   header:  */
+/*
+ * Copyright (c) 2015-2019 Nicira, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+typedef __SIZE_TYPE__ size_t;
+#define NULL ((void *)0)
+#define false 0
+
+#define OBJECT_OFFSETOF(OBJECT, MEMBER)\
+    __builtin_offsetof(typeof(*(OBJECT)), MEMBER)
+
+#define OBJECT_CONTAINING(POINTER, OBJECT, MEMBER)                      \
+    ((typeof(OBJECT)) (void *)                                      \
+     ((char *) (POINTER) - OBJECT_OFFSETOF(OBJECT, MEMBER)))
+
+#define ASSIGN_CONTAINER(OBJECT, POINTER, MEMBER)			\
+    ((OBJECT) = OBJECT_CONTAINING(POINTER, OBJECT, MEMBER), (void) 0)
+
+#define INIT_CONTAINER(OBJECT, POINTER, MEMBER)				\
+    ((OBJECT) = NULL, ASSIGN_CONTAINER(OBJECT, POINTER, MEMBER))
+
+#define HMAP_FOR_EACH_POP(NODE, MEMBER, HMAP)				\
+    for (size_t bucket__ = 0;                                               \
+         INIT_CONTAINER(NODE, hmap_pop_helper__(HMAP, &bucket__), MEMBER),  \
+         (NODE != OBJECT_CONTAINING(NULL, NODE, MEMBER))                    \
+         || ((NODE = NULL), false);)
+
+struct hmap {
+    struct hmap_node **buckets;
+    struct hmap_node *one;
+    size_t mask;
+    size_t n;
+};
+
+struct hmap_node {
+    size_t hash;
+    struct hmap_node *next;
+};
+
+static inline void hmap_remove(struct hmap *, struct hmap_node *);
+
+struct hmap_node *
+hmap_pop_helper__(struct hmap *hmap, size_t *bucket) {
+
+    for (; *bucket <= hmap->mask; (*bucket)++) {
+        struct hmap_node *node = hmap->buckets[*bucket];
+
+        if (node) {
+            hmap_remove(hmap, node);
+            return node;
+        }
+    }
+
+    return NULL;
+}
+
+static inline void
+hmap_remove(struct hmap *hmap, struct hmap_node *node)
+{
+    struct hmap_node **bucket = &hmap->buckets[node->hash & hmap->mask];
+    while (*bucket != node) {
+        bucket = &(*bucket)->next;
+    }
+    *bucket = node->next;
+    hmap->n--;
+}
+
+struct conntrack {
+    struct hmap zone_limits;
+};
+
+struct zone_limit {
+    struct hmap_node node;
+};
+
+void
+conntrack_destroy(struct conntrack *ct)
+{
+    struct zone_limit *zl;
+    HMAP_FOR_EACH_POP (zl, node, &ct->zone_limits) {
+      __builtin_free(zl);
+    }
+}