Benchmarking

BenchmarkLoopOne.s

func BenchmarkLoopOne(b *testing.B) {
; omitted
        for i := 0; i < b.N; i++ {
  0x10ef016             eb03                    JMP 0x10ef01b
  0x10ef018             48ffc0                  INCQ AX
  0x10ef01b             488b542458              MOVQ 0x58(SP), DX
  0x10ef020             488b9af0000000          MOVQ 0xf0(DX), BX
  0x10ef027             4839d8                  CMPQ BX, AX
  0x10ef02a             7d3c                    JGE 0x10ef068
  
  ; like the generated POPCNT code
                if isSupported {
  0x10ef02c             0fb61dcd9f0d00          MOVZX 0xd9fcd(IP), BX
  0x10ef033             84db                    TESTL BL, BL
  0x10ef035             7405                    JE 0x10ef03c
                        cnt += i
  0x10ef037             4801c1                  ADDQ AX, CX
                if isSupported {
  0x10ef03a             ebdc                    JMP 0x10ef018
  
  ; call a function if isSupported is false
  
  0x10ef03c             4889442420              MOVQ AX, 0x20(SP)
  0x10ef041             48894c2428              MOVQ CX, 0x28(SP)
                        cnt += someOtherFunc(i)
  0x10ef046             48890424                MOVQ AX, 0(SP)
  0x10ef04a             e891ffffff              CALL command-line-arguments.someOtherFunc(SB)
  0x10ef04f             488b442408              MOVQ 0x8(SP), AX
  0x10ef054             488b4c2428              MOVQ 0x28(SP), CX
  0x10ef059             4801c1                  ADDQ AX, CX
  0x10ef05c             488b442420              MOVQ 0x20(SP), AX
  0x10ef061             488b542458              MOVQ 0x58(SP), DX
                if isSupported {
  0x10ef066             ebb0                    JMP 0x10ef018

benchmarks.txt

BenchmarkLoopOne-8     	2000000000	         0.59 ns/op
BenchmarkLoopTwo-8     	2000000000	         0.39 ns/op
BenchmarkLoopThree-8   	1000000000	         1.99 ns/op

main_test.go

package main

import (
	"testing"
)

var (
	isSupported = true
)

//go:noinline
func someOtherFunc(v int) int {
	return v
}

func BenchmarkLoopOne(b *testing.B) {
	var cnt int
	for i := 0; i < b.N; i++ {
		if isSupported {
			cnt += i
		} else {
			cnt += someOtherFunc(i)
		}
	}
	b.Log(cnt)
}

func BenchmarkLoopTwo(b *testing.B) {
	var cnt int
	for i := 0; i < b.N; i++ {
		cnt += i
	}
	b.Log(cnt)
}

func BenchmarkLoopThree(b *testing.B) {
	var cnt int
	for i := 0; i < b.N; i++ {
		cnt += someOtherFunc(i)
	}
	b.Log(cnt)
}