crypto/rand: Read should not escape the input buffer

[dsnet]

Go version

go1.22

Output of go env in your module/workspace:

n/a

What did you do?

Ran this benchmark:

func Benchmark(b *testing.B) {
	b.ReportAllocs()
	for range b.N {
		sink = cryptoRandRead()
	}
}

//go:noinline
func cryptoRandRead() (out [8]byte) {
	rand.Read(out[:])
	return out
}

What did you see happen?

Benchmark-24    	 1877874	       616.4 ns/op	       8 B/op	       1 allocs/op

What did you expect to see?

Benchmark-24    	 1877874	       616.4 ns/op	       0 B/op	       0 allocs/op

The Read function is a static function. With some work to the underlying implementation (and avoid going through an io.Reader), we should be able to make it not escape the input.

Thus, you could do something like:

var arr [32]byte
rand.Read(arr[:])

and know that it doesn't allocate.

[thepudds]

See also #66779 and https://go.dev/cl/578516.

[gabyhelp]

Related Issues

• crypto/rand: Read argument escapes to heap #66779
• crypto/rand: Read performance improvements #33256
• crypto/rand: make Read not escape the byte slice #66801
• crypto/rand: Reader is internally buffered inconsistently on different platforms #16593
• crypto/rand: rand.Reader.Read is buffered on some systems #45217

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[rsc]

Duplicate of #66779.