Test how well compilers optimize division by constants

constant_division.c

// Code to test how well compilers optimize division by constants
// See: http://ridiculousfish.com/blog/posts/labor-of-division-episode-iii.html

// gcc -std=gnu11 -Wall -Wextra -O3 constant_division.c -o constant_division
// objdump -d constant_division | less

#ifndef COUNT
#define COUNT (1000 * 1000)
#endif 

#ifndef SEED
#define SEED 1
#endif 


#include <stdint.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>


#ifdef IACA
// gcc -std=gnu11 -Wall -Wextra -O3 constant_division.c -DIACA -o iaca.o
// /opt/intel/iaca/bin/iaca  -mark 0 -64 -arch HSW -analysis THROUGHPUT iaca.o
#include </opt/intel/iaca/include/iacaMarks.h>
#else
#define IACA_START
#define IACA_END
#endif

#ifdef LIKWID
// cc -std=gnu11 -Wall -Wextra -O3 constant_division.c -o constant_division -DLIKWID -llikwid -lpthread -lm
// likwid -m -C2 -g BRANCH constant_division | grep UNHALTED_CORE
#include <likwid.h>
#else
#define likwid_markerInit()
#define likwid_markerThreadInit()
#define likwid_markerStartRegion(name)
#define likwid_markerStopRegion(name)
#define likwid_markerClose()
#endif // LIKWID

int main(int argc, char **argv) {
    if (argc && ! argv) exit(1); // quiet warnings

    char likwidRegionName[32];
    uint32_t randomInt[COUNT];
    uint32_t compilerSum = 0;

    likwid_markerInit();
    likwid_markerThreadInit();

    srandom(SEED);
    for (int i = 0; i < COUNT; i++) {
        randomInt[i] = random();
    }
    printf("Using %d random 32-bit ints\n", COUNT);

    sprintf(likwidRegionName, "compiler_7");
    likwid_markerStartRegion(likwidRegionName);
    for (int i = 0; i < COUNT; i++) {
        IACA_START;
        compilerSum += randomInt[i]/7;
        IACA_END;
    }
    likwid_markerStopRegion(likwidRegionName);

    sprintf(likwidRegionName, "compiler_37");
    likwid_markerStartRegion(likwidRegionName);
    for (int i = 0; i < COUNT; i++) {
        IACA_START;
        compilerSum += randomInt[i]/37;
        IACA_END;
    }
    likwid_markerStopRegion(likwidRegionName);

    sprintf(likwidRegionName, "compiler_123");
    likwid_markerStartRegion(likwidRegionName);
    for (int i = 0; i < COUNT; i++) {
        IACA_START;
        compilerSum += randomInt[i]/123;
        IACA_END;
    }
    likwid_markerStopRegion(likwidRegionName);
    sprintf(likwidRegionName, "compiler_763");
    likwid_markerStartRegion(likwidRegionName);
    for (int i = 0; i < COUNT; i++) {
        IACA_START;
        compilerSum += randomInt[i]/763;
        IACA_END;
    }
    likwid_markerStopRegion(likwidRegionName);

    sprintf(likwidRegionName, "compiler_1247");
    likwid_markerStartRegion(likwidRegionName);
    for (int i = 0; i < COUNT; i++) {
        IACA_START;
        compilerSum += randomInt[i]/1247;
        IACA_END;
    }
    likwid_markerStopRegion(likwidRegionName);

    sprintf(likwidRegionName, "compiler_9305");
    likwid_markerStartRegion(likwidRegionName);
    for (int i = 0; i < COUNT; i++) {
        IACA_START;
        compilerSum += randomInt[i]/9305;
        IACA_END;
    }
    likwid_markerStopRegion(likwidRegionName);

    sprintf(likwidRegionName, "compiler_13307");
    likwid_markerStartRegion(likwidRegionName);
    for (int i = 0; i < COUNT; i++) {
        IACA_START;
        compilerSum += randomInt[i]/13307;
        IACA_END;
    }
    likwid_markerStopRegion(likwidRegionName);
        
    sprintf(likwidRegionName, "compiler_52513");
    likwid_markerStartRegion(likwidRegionName);
    for (int i = 0; i < COUNT; i++) {
        IACA_START;
        compilerSum += randomInt[i]/52513;
        IACA_END;
    }
    likwid_markerStopRegion(likwidRegionName);


    sprintf(likwidRegionName, "compiler_60978747");
    likwid_markerStartRegion(likwidRegionName);
    for (int i = 0; i < COUNT; i++) {
        IACA_START;
        compilerSum += randomInt[i]/60978747;
        IACA_END;
    }
    likwid_markerStopRegion(likwidRegionName);


    sprintf(likwidRegionName, "compiler_106956295");
    likwid_markerStartRegion(likwidRegionName);
    for (int i = 0; i < COUNT; i++) {
        IACA_START;
        compilerSum += randomInt[i]/106956295;
        IACA_END;
    }
    likwid_markerStopRegion(likwidRegionName);

    likwid_markerClose();

    printf("Sum: %u\n", compilerSum);
    exit(0);
}