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// 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))
}
}
}
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