selftests/bpf: add loop test 5

Add a test with multiple exit conditions.
It's not an infinite loop only when the verifier can properly track
all math on variable 'i' through all possible ways of executing this loop.

barrier()s are needed to disable llvm optimization that combines multiple
branches into fewer branches.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>

tools/testing/selftests/bpf/progs/loop5.c

@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2019 Facebook
+#include <linux/bpf.h>
+#include "bpf_helpers.h"
+#define barrier() __asm__ __volatile__("": : :"memory")
+
+char _license[] SEC("license") = "GPL";
+
+SEC("socket")
+int while_true(volatile struct __sk_buff* skb)
+{
+	int i = 0;
+
+	while (1) {
+		if (skb->len)
+			i += 3;
+		else
+			i += 7;
+		if (i == 9)
+			break;
+		barrier();
+		if (i == 10)
+			break;
+		barrier();
+		if (i == 13)
+			break;
+		barrier();
+		if (i == 14)
+			break;
+	}
+	return i;
+}