test: add order of evaluation test case that gccgo got wrong

Updates #23188

Change-Id: Idc5567546d1c4c592f997a4cebbbf483b85331e0
Reviewed-on: https://go-review.googlesource.com/123115
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

diff --git a/test/fixedbugs/issue23188.go b/test/fixedbugs/issue23188.go
new file mode 100644 (file)
index 0000000..c224340
--- /dev/null
+++ b/test/fixedbugs/issue23188.go
@@ -0,0 +1,32 @@
+// run
+
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Test order of evaluation of index operations.
+
+package main
+
+func main() {
+       arr := []int{1, 2}
+
+       // The spec says that in an assignment statement the operands
+       // of all index expressions and pointer indirections on the
+       // left, and the expressions on the right, are evaluated in
+       // the usual order. The usual order means function calls and
+       // channel operations are done first. Then the assignments are
+       // carried out one at a time. The operands of an index
+       // expression include both the array and the index. So this
+       // evaluates as
+       //   tmp1 := arr
+       //   tmp2 := len(arr) - 1
+       //   tmp3 := len(arr)
+       //   arr = arr[:tmp3-1]
+       //   tmp1[tmp2] = 3
+       arr, arr[len(arr)-1] = arr[:len(arr)-1], 3
+
+       if len(arr) != 1 || arr[0] != 1 || arr[:2][1] != 3 {
+               panic(arr)
+       }
+}