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// run
// Copyright 2016 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.
// Previously, cmd/compile would rewrite
//
// check(unsafe.Pointer(testMeth(1).Pointer()), unsafe.Pointer(testMeth(2).Pointer()))
//
// to
//
// var autotmp_1 uintptr = testMeth(1).Pointer()
// var autotmp_2 uintptr = testMeth(2).Pointer()
// check(unsafe.Pointer(autotmp_1), unsafe.Pointer(autotmp_2))
//
// However, that means autotmp_1 is the only reference to the int
// variable containing the value "1", but it's not a pointer type,
// so it was at risk of being garbage collected by the evaluation of
// testMeth(2).Pointer(), even though package unsafe's documentation
// says the original code was allowed.
//
// Now cmd/compile rewrites it to
//
// var autotmp_1 unsafe.Pointer = unsafe.Pointer(testMeth(1).Pointer())
// var autotmp_2 unsafe.Pointer = unsafe.Pointer(testMeth(2).Pointer())
// check(autotmp_1, autotmp_2)
//
// to ensure the pointed-to variables are visible to the GC.
package main
import (
"fmt"
"reflect"
"runtime"
"unsafe"
)
func main() {
// Test all the different ways we can invoke reflect.Value.Pointer.
// Direct method invocation.
check(unsafe.Pointer(testMeth(1).Pointer()), unsafe.Pointer(testMeth(2).Pointer()))
// Invocation via method expression.
check(unsafe.Pointer(reflect.Value.Pointer(testMeth(1))), unsafe.Pointer(reflect.Value.Pointer(testMeth(2))))
// Invocation via interface.
check(unsafe.Pointer(testInter(1).Pointer()), unsafe.Pointer(testInter(2).Pointer()))
// Invocation via method value.
check(unsafe.Pointer(testFunc(1)()), unsafe.Pointer(testFunc(2)()))
}
func check(p, q unsafe.Pointer) {
a, b := *(*int)(p), *(*int)(q)
if a != 1 || b != 2 {
fmt.Printf("got %v, %v; expected 1, 2\n", a, b)
}
}
func testMeth(x int) reflect.Value {
// Force GC to run.
runtime.GC()
return reflect.ValueOf(&x)
}
type Pointerer interface {
Pointer() uintptr
}
func testInter(x int) Pointerer {
return testMeth(x)
}
func testFunc(x int) func() uintptr {
return testMeth(x).Pointer
}
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