From 7b0c25c84d0b2c138849e427ed8d7cb4da365adf Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Wed, 26 Jul 2023 17:21:33 -0700
Subject: [PATCH] add behavior test for tail calls

closes #9703
---
 test/behavior.zig           |  1 +
 test/behavior/call_tail.zig | 51 +++++++++++++++++++++++++++++++++++++
 2 files changed, 52 insertions(+)
 create mode 100644 test/behavior/call_tail.zig

diff --git a/test/behavior.zig b/test/behavior.zig
index 6ec59fa22df7..249d3191e65d 100644
--- a/test/behavior.zig
+++ b/test/behavior.zig
@@ -149,6 +149,7 @@ test {
     _ = @import("behavior/byval_arg_var.zig");
     _ = @import("behavior/c_char_signedness.zig");
     _ = @import("behavior/call.zig");
+    _ = @import("behavior/call_tail.zig");
     _ = @import("behavior/cast.zig");
     _ = @import("behavior/cast_int.zig");
     _ = @import("behavior/comptime_memory.zig");
diff --git a/test/behavior/call_tail.zig b/test/behavior/call_tail.zig
new file mode 100644
index 000000000000..69bdaf864615
--- /dev/null
+++ b/test/behavior/call_tail.zig
@@ -0,0 +1,51 @@
+const std = @import("std");
+const expect = std.testing.expect;
+
+var base: usize = undefined;
+var result_off: [7]usize = undefined;
+var result_len: [7]usize = undefined;
+var result_index: usize = 0;
+
+noinline fn insertionSort(data: []u64) void {
+    result_off[result_index] = @intFromPtr(data.ptr) - base;
+    result_len[result_index] = data.len;
+    result_index += 1;
+    if (data.len > 1) {
+        var least_i: usize = 0;
+        var i: usize = 1;
+        while (i < data.len) : (i += 1) {
+            if (data[i] < data[least_i])
+                least_i = i;
+        }
+        std.mem.swap(u64, &data[0], &data[least_i]);
+
+        // there used to be a bug where
+        // `data[1..]` is created on the stack
+        // and pointed to by the first argument register
+        // then stack is invalidated by the tailcall and
+        // overwritten by callee
+        // https://github.com/ziglang/zig/issues/9703
+        return @call(.always_tail, insertionSort, .{data[1..]});
+    }
+}
+
+test "arguments pointed to on stack into tailcall" {
+    var data = [_]u64{ 1, 6, 2, 7, 1, 9, 3 };
+    base = @intFromPtr(&data);
+    insertionSort(data[0..]);
+    try expect(result_len[0] == 7);
+    try expect(result_len[1] == 6);
+    try expect(result_len[2] == 5);
+    try expect(result_len[3] == 4);
+    try expect(result_len[4] == 3);
+    try expect(result_len[5] == 2);
+    try expect(result_len[6] == 1);
+
+    try expect(result_off[0] == 0);
+    try expect(result_off[1] == 8);
+    try expect(result_off[2] == 16);
+    try expect(result_off[3] == 24);
+    try expect(result_off[4] == 32);
+    try expect(result_off[5] == 40);
+    try expect(result_off[6] == 48);
+}