Project Stage 2: Testing

 To test my custom pass I first extracted the spo600-test-clone files into my gcc-test-001 directory and simply compiled and ran the program with -fdump-tree-ctyler.

I ran it on the vol1.c file, the contents of vol1.c are as following:

[dpark39@aarch64-002 test-clone]$ cat vol1.c

// vol1.c - fixed-point volume scaling algorithm

// Chris Tyler 2017.11.29-2021.11.16 - Licensed under GPLv3.

// For the Seneca College SPO600 Course

#include <stdlib.h>

#include <stdio.h>

#include <stdint.h>

#include <stdbool.h>

#include "vol.h"

int16_t scale_sample(int16_t sample, int volume) {

        return ((((int32_t) sample) * ((int32_t) (32767 * volume / 100) <<1) ) >> 16);

}

int main() {

        int             x;

        int             ttl=0;

// ---- Create in[] and out[] arrays

        int16_t*        in;

        int16_t*        out;

        in=(int16_t*) calloc(SAMPLES, sizeof(int16_t));

        out=(int16_t*) calloc(SAMPLES, sizeof(int16_t));

// ---- Create dummy samples in in[]

        vol_createsample(in, SAMPLES);

// ---- This is the part we're interested in!

// ---- Scale the samples from in[], placing results in out[]

        for (x = 0; x < SAMPLES; x++) {

                out[x]=scale_sample(in[x], VOLUME);

        }

// ---- This part sums the samples.

// ---- Q: Why is this needed?

        for (x = 0; x < SAMPLES; x++) {

                ttl=(ttl+out[x])%1000;

        }

// ---- Print the sum of the samples.

// ---- Q: Why is this needed?

        printf("Result: %d\n", ttl);

        return 0;

}

After running my pass on it I got a very long dump file below. 

[dpark39@aarch64-002 gcc-test-001]$ cat test-vol1.c.263t.ctyler

;; Function scale_sample (scale_sample, funcdef_no=22, decl_uid=5488, cgraph_uid=23, symbol_order=22)

_1 = (int) sample_7(D);

_2 = volume_8(D) * 32767;

_3 = _2 / 100;

_4 = _3 << 1;

_5 = _1 * _4;

_6 = _5 >> 16;

_9 = (int16_t) _6;

return _9;

PRUNE: scale_sample

int16_t scale_sample (int16_t sample, int volume)

{

  int _1;

  int _2;

  int _3;

  int _4;

  int _5;

  int _6;

  int16_t _9;

  <bb 2> [local count: 1073741824]:

  _1 = (int) sample_7(D);

  _2 = volume_8(D) * 32767;

  _3 = _2 / 100;

  _4 = _3 << 1;

  _5 = _1 * _4;

  _6 = _5 >> 16;

  _9 = (int16_t) _6;

  return _9;

}

;; Function main (main, funcdef_no=23, decl_uid=5490, cgraph_uid=24, symbol_order=23) (executed once)

in_18 = calloc (50000000, 2);

out_20 = calloc (50000000, 2);

vol_createsample (in_18, 50000000);

vect__4.11_53 = MEM <vector(8) short int> [(int16_t *)in_18 + ivtmp.29_30 * 1];

vect_patt_14.12_54 = WIDEN_MULT_LO_EXPR <vect__4.11_53, { 32766, 32766, 32766, 32766, 32766, 32766, 32766, 32766 }>;

vect_patt_14.12_55 = WIDEN_MULT_HI_EXPR <vect__4.11_53, { 32766, 32766, 32766, 32766, 32766, 32766, 32766, 32766 }>;

vect__29.13_56 = vect_patt_14.12_54 >> 16;

vect__29.13_57 = vect_patt_14.12_55 >> 16;

vect__30.14_58 = VEC_PACK_TRUNC_EXPR <vect__29.13_56, vect__29.13_57>;

MEM <vector(8) short int> [(int16_t *)out_20 + ivtmp.29_30 * 1] = vect__30.14_58;

ivtmp.29_29 = ivtmp.29_30 + 16;

if (ivtmp.29_29 != 100000000)

ivtmp.24_15 = (unsigned long) out_20;

_27 = ivtmp.24_15 + 100000000;

_14 = (void *) ivtmp.24_26;

_9 = MEM[(int16_t *)_14];

_10 = (int) _9;

_11 = _10 + ttl_37;

ttl_23 = _11 % 1000;

ivtmp.24_31 = ivtmp.24_26 + 2;

if (_27 != ivtmp.24_31)

printf ("Result: %d\n", ttl_23);

return 0;

PRUNE: main

int main ()

{

  sizetype ivtmp.29;

  unsigned long ivtmp.24;

  vector(8) short int vect__30.14;

  vector(4) int vect__29.13;

  vector(4) int vect_patt_14.12;

  vector(8) short int vect__4.11;

  int16_t * out;

  int16_t * in;

  int ttl;

  short int _9;

  int _10;

  int _11;

  void * _14;

  unsigned long _27;

  <bb 2> [local count: 10737416]:

  in_18 = calloc (50000000, 2);

  out_20 = calloc (50000000, 2);

  vol_createsample (in_18, 50000000);

  <bb 3> [local count: 1063004408]:

  # ivtmp.29_30 = PHI <ivtmp.29_29(7), 0(2)>

  vect__4.11_53 = MEM <vector(8) short int> [(int16_t *)in_18 + ivtmp.29_30 * 1];

  vect_patt_14.12_54 = WIDEN_MULT_LO_EXPR <vect__4.11_53, { 32766, 32766, 32766, 32766, 32766, 32766, 32766, 32766 }>;

  vect_patt_14.12_55 = WIDEN_MULT_HI_EXPR <vect__4.11_53, { 32766, 32766, 32766, 32766, 32766, 32766, 32766, 32766 }>;

  vect__29.13_56 = vect_patt_14.12_54 >> 16;

  vect__29.13_57 = vect_patt_14.12_55 >> 16;

  vect__30.14_58 = VEC_PACK_TRUNC_EXPR <vect__29.13_56, vect__29.13_57>;

  MEM <vector(8) short int> [(int16_t *)out_20 + ivtmp.29_30 * 1] = vect__30.14_58;

  ivtmp.29_29 = ivtmp.29_30 + 16;

  if (ivtmp.29_29 != 100000000)

    goto <bb 7>; [98.99%]

  else

    goto <bb 4>; [1.01%]

  <bb 7> [local count: 1052266995]:

  goto <bb 3>; [100.00%]

  <bb 4> [local count: 10737413]:

  ivtmp.24_15 = (unsigned long) out_20;

  _27 = ivtmp.24_15 + 100000000;

  <bb 5> [local count: 1063004408]:

  # ttl_37 = PHI <ttl_23(8), 0(4)>

  # ivtmp.24_26 = PHI <ivtmp.24_31(8), ivtmp.24_15(4)>

  _14 = (void *) ivtmp.24_26;

  _9 = MEM[(int16_t *)_14];

  _10 = (int) _9;

  _11 = _10 + ttl_37;

  ttl_23 = _11 % 1000;

  ivtmp.24_31 = ivtmp.24_26 + 2;

  if (_27 != ivtmp.24_31)

    goto <bb 8>; [98.99%]

  else

    goto <bb 6>; [1.01%]

  <bb 8> [local count: 1052266995]:

  goto <bb 5>; [100.00%]

  <bb 6> [local count: 10737416]:

  printf ("Result: %d\n", ttl_23);

  return 0;

}

The two functions that were processed by my GCC pass was scale_sample and the main function. The result shows that my program has decided to prune both of them.

The functions scale_sample and main were found to be identical by my code and it was decided they should be pruned. Although the pruning process did not actually take place this is a good step towards creating a pass that can accurately prune functions in a program. 

The steps my pass took were: It analyzed the gimple representation and got the structure of both scale_sample and main, next it compared clones and found them to be basically the same, thus printing diagnostics and deciding those functions to be pruned.