Benchmark IMULQ against SHL on x86-64

test-imul-shl.c

#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
/*
Compile with:
gcc -g -O0 -Wall -Werror
*/

static int64_t mul_imul(int64_t n) {
	asm __volatile__ (
	"movq %1, %%rax\n\t"
	"imulq $8, %%rax\n\t"
	"movq %%rax, %0\n\t"
	"\n"
	:"=r"(n)
	:"r"(n)
	:"%rax"
	);
    return n;
}

static int64_t mul_shl(int64_t n) {
	asm __volatile__ (
	"movq %1, %%rax\n\t"
	"shl $3, %%rax\n\t"
	"movq %%rax, %0\n\t"
	"\n"
	:"=r"(n)
	:"r"(n)
	:"%rax"
	);
    return n;
}

void test(int64_t n) {
	printf("Testing %ld\n", n);

	int64_t expected = n * 8;
	int64_t result_imul = mul_imul(n);
	int64_t result_shl = mul_shl(n);

	if (result_imul != expected) {
		printf("error: imul: expected: %ld got: %ld\n", expected, result_imul);
		exit(1);
	}
	if (result_shl != expected) {
		printf("error: shl: expected: %ld got: %ld\n", expected, result_shl);
		exit(1);
	}
}

int main(void) {
	int64_t i = 0;

	for (i = -260; i < 17000; i++) {
		test(i);
	}

	return 0;
}