Golang基准测试中的alloc / op零是什么？

Here I have a benchmark test:

// bench_test.go

package main

import (
    "testing"
)

func BenchmarkHello(b *testing.B) {
    for i := 0; i < b.N; i++ {
        a := 1
        a++
    }
}

The test result are strange. The metric allocs/op shows zero. I know variable a is a int type and doesn't take too much memory, but it's not zero.

> go test -bench=. -benchmem
goos: darwin
goarch: amd64
pkg: a
BenchmarkHello-4    2000000000           0.26 ns/op        0 B/op          0 allocs/op
PASS
ok      a   0.553s

Questions

This post points that allocs/op means how many distinct memory allocations occurred per op (single iteration).

• But what does memory allocation mean? does that mean set a value for a variable? Is it kind ofmalloc in C` ?

• Why is this metric allocs/ops zero?

Possible Answer

From Dave Cheney, one of the Go contributors:

The benchmark tool only reports heap allocations. Stack allocations via escape analysis are less costly, possibly free, so are not reported.

Reference

Why is this simple benchmark showing zero allocations?

Why is this metric allocs/ops zero?

package main

import (
  "testing"
)

func BenchmarkHello(b *testing.B) {
  for i := 0; i < b.N; i++ {
      a := 1
      a++
  }
}

The allocs/ops average only counts heap allocations, not stack allocations.

The allocs/ops average is rounded down to the nearest integer value.

The Go gc compiler is an optimizing compiler. Since

{
    a := 1
    a++
}

doesn't accomplish anything, it is elided.