issue71932.go

     1  // run
     2  
     3  // Copyright 2025 The Go Authors. All rights reserved.
     4  // Use of this source code is governed by a BSD-style
     5  // license that can be found in the LICENSE file.
     6  
     7  package main
     8  
     9  import "runtime"
    10  
    11  const C = 16
    12  
    13  type T [C * C]byte
    14  
    15  func main() {
    16  	var ts []*T
    17  
    18  	for i := 0; i < 100; i++ {
    19  		t := new(T)
    20  		// Save every even object.
    21  		if i%2 == 0 {
    22  			ts = append(ts, t)
    23  		}
    24  	}
    25  	// Make sure the odd objects are collected.
    26  	runtime.GC()
    27  
    28  	for _, t := range ts {
    29  		f(t, C, C)
    30  	}
    31  }
    32  
    33  //go:noinline
    34  func f(t *T, i, j uint) {
    35  	if i == 0 || i > C || j == 0 || j > C {
    36  		return // gets rid of bounds check below (via prove pass)
    37  	}
    38  	p := &t[i*j-1]
    39  	*p = 0
    40  	runtime.GC()
    41  	*p = 0
    42  
    43  	// This goes badly if compiled to
    44  	//   q := &t[i*j]
    45  	//   *(q-1) = 0
    46  	//   runtime.GC()
    47  	//   *(q-1) = 0
    48  	// as at the GC call, q is an invalid pointer
    49  	// (it points past the end of t's allocation).
    50  }
    51
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