cmd/compile: extra allocation when returning a non-pointer value > 128KB #76703
Description
Go version
go version go1.26-devel_91267f0a70 Thu Dec 4 17:35:46 2025 -0800 linux/amd64
Output of go env in your module/workspace:
.What did you do?
package main
import "testing"
type Data struct {
v [1 << 17 + 1]byte
}
func NonPointerReturn() Data {
return Data{}
}
var x byte
var n = 12
func useData(d *Data) {
x = d.v[n]
}
func Benchmark_NonPointerReturn_3clause(b *testing.B) {
for i := 0; i < b.N; i++ {
var d = NonPointerReturn()
useData(&d)
}
}
func Benchmark_NonPointerReturn_range(b *testing.B) {
for range b.N {
var d = NonPointerReturn()
useData(&d)
}
}
func Benchmark_NonPointerReturn_1clause(b *testing.B) {
for b.Loop() {
var d = NonPointerReturn()
useData(&d)
}
}
//------
func Benchmark_NonPointerReturnB_3clause(b *testing.B) {
for i := 0; i < b.N; i++ {
var d = new(Data)
*d = NonPointerReturn()
useData(d)
}
}
func Benchmark_NonPointerReturnB_range(b *testing.B) {
for range b.N {
var d = new(Data)
*d = NonPointerReturn()
useData(d)
}
}
func Benchmark_NonPointerReturnB_1clause(b *testing.B) {
for b.Loop() {
var d = new(Data)
*d = NonPointerReturn()
useData(d)
}
}What did you see happen?
Benchmark_NonPointerReturn_3clause-4 26307 51341 ns/op 278528 B/op 2 allocs/op
Benchmark_NonPointerReturn_range-4 23431 50276 ns/op 278528 B/op 2 allocs/op
Benchmark_NonPointerReturn_1clause-4 22632 51538 ns/op 278528 B/op 2 allocs/op
Benchmark_NonPointerReturnB_3clause-4 23570 49242 ns/op 278528 B/op 2 allocs/op
Benchmark_NonPointerReturnB_range-4 24536 49956 ns/op 278528 B/op 2 allocs/op
Benchmark_NonPointerReturnB_1clause-4 23439 48533 ns/op 278528 B/op 2 allocs/op
What did you expect to see?
Benchmark_NonPointerReturn_3clause-4 26307 51341 ns/op 278528 B/op 1 allocs/op
Benchmark_NonPointerReturn_range-4 23431 50276 ns/op 278528 B/op 1 allocs/op
Benchmark_NonPointerReturn_1clause-4 22632 51538 ns/op 278528 B/op 1 allocs/op
Benchmark_NonPointerReturnB_3clause-4 23570 49242 ns/op 278528 B/op 1 allocs/op
Benchmark_NonPointerReturnB_range-4 24536 49956 ns/op 278528 B/op 1 allocs/op
Benchmark_NonPointerReturnB_1clause-4 23439 48533 ns/op 278528 B/op 1 allocs/op