| // run |
| |
| // Copyright 2026 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. |
| |
| // The prove pass must not use a fact that only becomes valid after a |
| // later value executes to simplify an earlier value. Here make([]byte, n) |
| // teaches prove that n >= 0, but that is only true after the make runs. |
| // A buggy prove lets that fact travel back in time and rewrites the |
| // earlier signed shift n>>1 into an unsigned shift, corrupting the result |
| // for negative n. |
| |
| package main |
| |
| var sink []byte |
| |
| //go:noinline |
| func trigger(n int) (res int) { |
| defer func() { recover() }() |
| if n < 100 { |
| res = n >> 1 // signed arithmetic shift right |
| sink = make([]byte, n) // only asserts n >= 0 after this point |
| } |
| return |
| } |
| |
| func main() { |
| if got := trigger(-2); got != -1 { |
| println("n>>1 =", got, "want -1") |
| panic("prove miscompiled a signed shift") |
| } |
| } |
