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Source file test/fixedbugs/issue15329.go

Documentation: test/fixedbugs

  // 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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