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-rw-r--r--test/fixedbugs/issue8606b.go63
1 files changed, 63 insertions, 0 deletions
diff --git a/test/fixedbugs/issue8606b.go b/test/fixedbugs/issue8606b.go
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+++ b/test/fixedbugs/issue8606b.go
@@ -0,0 +1,63 @@
+// run
+
+// Copyright 2020 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.
+
+// This is an optimization check. We want to make sure that we compare
+// string lengths, and other scalar fields, before checking string
+// contents. There's no way to verify this in the language, and
+// codegen tests in test/codegen can't really detect ordering
+// optimizations like this. Instead, we generate invalid strings with
+// bad backing store pointers but nonzero length, so we can check that
+// the backing store never gets compared.
+//
+// We use two different bad strings so that pointer comparisons of
+// backing store pointers fail.
+
+package main
+
+import (
+ "fmt"
+ "reflect"
+ "unsafe"
+)
+
+func bad1() string {
+ s := "foo"
+ (*reflect.StringHeader)(unsafe.Pointer(&s)).Data = 1 // write bad value to data ptr
+ return s
+}
+func bad2() string {
+ s := "foo"
+ (*reflect.StringHeader)(unsafe.Pointer(&s)).Data = 2 // write bad value to data ptr
+ return s
+}
+
+type SI struct {
+ s string
+ i int
+}
+
+type SS struct {
+ s string
+ t string
+}
+
+func main() {
+ for _, test := range []struct {
+ a, b interface{}
+ }{
+ {SI{s: bad1(), i: 1}, SI{s: bad2(), i: 2}},
+ {SS{s: bad1(), t: "a"}, SS{s: bad2(), t: "aa"}},
+ {SS{s: "a", t: bad1()}, SS{s: "b", t: bad2()}},
+ // This one would panic because the length of both strings match, and we check
+ // the body of the bad strings before the body of the good strings.
+ //{SS{s: bad1(), t: "a"}, SS{s: bad2(), t: "b"}},
+ } {
+ if test.a == test.b {
+ panic(fmt.Sprintf("values %#v and %#v should not be equal", test.a, test.b))
+ }
+ }
+
+}