mirror of
https://github.com/golang/go
synced 2024-11-02 13:42:29 +00:00
c65647d620
Previously statements like
f(unsafe.Pointer(g()), int(h()))
would be reordered into a sequence of statements like
autotmp_g := g()
autotmp_h := h()
f(unsafe.Pointer(autotmp_g), int(autotmp_h))
which can leave g's temporary value on the stack as a uintptr, rather
than an unsafe.Pointer. Instead, recognize uintptr-to-unsafe.Pointer
conversions when reordering function calls to instead produce:
autotmp_g := unsafe.Pointer(g())
autotmp_h := h()
f(autotmp_g, int(autotmp_h))
Fixes #15329.
Change-Id: I2cdbd89d233d0d5c94791513a9fd5fd958d11ed5
Reviewed-on: https://go-review.googlesource.com/22273
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
79 lines
2.1 KiB
Go
79 lines
2.1 KiB
Go
// run
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// Copyright 2016 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Previously, cmd/compile would rewrite
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//
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// check(unsafe.Pointer(testMeth(1).Pointer()), unsafe.Pointer(testMeth(2).Pointer()))
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//
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// to
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//
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// var autotmp_1 uintptr = testMeth(1).Pointer()
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// var autotmp_2 uintptr = testMeth(2).Pointer()
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// check(unsafe.Pointer(autotmp_1), unsafe.Pointer(autotmp_2))
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//
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// However, that means autotmp_1 is the only reference to the int
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// variable containing the value "1", but it's not a pointer type,
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// so it was at risk of being garbage collected by the evaluation of
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// testMeth(2).Pointer(), even though package unsafe's documentation
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// says the original code was allowed.
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//
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// Now cmd/compile rewrites it to
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//
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// var autotmp_1 unsafe.Pointer = unsafe.Pointer(testMeth(1).Pointer())
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// var autotmp_2 unsafe.Pointer = unsafe.Pointer(testMeth(2).Pointer())
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// check(autotmp_1, autotmp_2)
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//
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// to ensure the pointed-to variables are visible to the GC.
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package main
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import (
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"fmt"
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"reflect"
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"runtime"
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"unsafe"
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)
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func main() {
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// Test all the different ways we can invoke reflect.Value.Pointer.
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// Direct method invocation.
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check(unsafe.Pointer(testMeth(1).Pointer()), unsafe.Pointer(testMeth(2).Pointer()))
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// Invocation via method expression.
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check(unsafe.Pointer(reflect.Value.Pointer(testMeth(1))), unsafe.Pointer(reflect.Value.Pointer(testMeth(2))))
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// Invocation via interface.
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check(unsafe.Pointer(testInter(1).Pointer()), unsafe.Pointer(testInter(2).Pointer()))
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// Invocation via method value.
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check(unsafe.Pointer(testFunc(1)()), unsafe.Pointer(testFunc(2)()))
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}
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func check(p, q unsafe.Pointer) {
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a, b := *(*int)(p), *(*int)(q)
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if a != 1 || b != 2 {
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fmt.Printf("got %v, %v; expected 1, 2\n", a, b)
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}
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}
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func testMeth(x int) reflect.Value {
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// Force GC to run.
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runtime.GC()
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return reflect.ValueOf(&x)
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}
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type Pointerer interface {
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Pointer() uintptr
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}
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func testInter(x int) Pointerer {
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return testMeth(x)
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}
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func testFunc(x int) func() uintptr {
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return testMeth(x).Pointer
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}
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