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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.
// Liveness calculations were wrong for a result parameter pushed onto
// the heap in a function that used defer. Program would crash with
// runtime: bad pointer in frame main.A at 0xc4201e6838: 0x1
package main
import "errors"
var sink interface{}
//go:noinline
func f(err *error) {
if err != nil {
sink = err
}
}
//go:noinline
func A(n, m int64) (res int64, err error) {
defer f(&err) // output parameter's address escapes to a defer.
if n < 0 {
err = errors.New("No negative")
return
}
if n <= 1 {
res = n
return
}
res = B(m) // This call to B drizzles a little junk on the stack.
res, err = A(n-1, m)
res++
return
}
// B does a little bit of recursion dribbling not-zero onto the stack.
//go:noinline
func B(n int64) (res int64) {
if n <= 1 { // Prefer to leave a 1 on the stack.
return n
}
return 1 + B(n-1)
}
func main() {
x, e := A(0, 0)
for j := 0; j < 4; j++ { // j controls amount of B's stack dribble
for i := 0; i < 1000; i++ { // try more and more recursion until stack growth occurs in newobject in prologue
x, e = A(int64(i), int64(j))
}
}
_, _ = x, e
}
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