Microbenchmark of stack- and register-based calling convention

reg.s

// Copyright 2020 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

#include "textflag.h"

TEXT ·stack(SB),NOSPLIT,$16-4
	MOVD	n+0(FP), CX
loop:
	MOVQ	CX, 0(SP)
	CALL	stackSub1<>(SB)
	MOVQ	8(SP), CX
	TESTQ	CX, CX
	JHI	loop
	RET

TEXT stackSub1<>(SB),NOSPLIT,$0-16
	MOVQ	x+0(FP), AX
	DECQ	AX
	MOVQ	AX, ret+8(FP)
	RET

TEXT ·reg(SB),NOSPLIT,$0-4
	MOVD	n+0(FP), AX
loop:
	CALL	regSub1<>(SB)
	TESTQ	AX, AX
	JHI	loop
	RET

TEXT regSub1<>(SB),NOSPLIT,$0-0
	DECQ	AX
	RET

reg_test.go

// Copyright 2020 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package stackreg

import "testing"

func BenchmarkStack(b *testing.B) {
	stack(uint32(b.N))
}

func stack(n uint32)

func BenchmarkReg(b *testing.B) {
	reg(uint32(b.N))
}

func reg(n uint32)