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branch prediction test
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#include <stdio.h> | |
#include <stdlib.h> | |
#include <immintrin.h> | |
// gcc -std=c99 -D IS_RAND=0 branch-test.c ; for i in -1 -2 1 3 2 4 8 16; do echo '### ' $i; perf stat -r5 -o _stats_pred_base --append ./a.out $i; echo; done | |
// gcc -O3 -std=c99 -D IS_RAND=0 branch-test.c ; for i in -1 -2 1 3 2 4 8 16; do echo '### ' $i; perf stat -r5 -o _stats_pred_o3 --append ./a.out $i; echo; done | |
// gcc -std=c99 -D IS_RAND=1 branch-test.c ; for i in 8 16 32 64 128 256; do echo '### ' $i; perf stat -r5 -o _stats_rand_base --append ./a.out $i; echo; done | |
// gcc -O3 -std=c99 -D IS_RAND=1 branch-test.c ; for i in 8 16 32 64 128 256; do echo '### ' $i; perf stat -r5 -o _stats_rand_o3 --append ./a.out $i; echo; done | |
unsigned long x = 47; | |
unsigned long xorShiftRandom() { | |
x ^= (x << 21); | |
x ^= (x >> 35); | |
x ^= (x << 4); | |
return x; | |
} | |
int main (int argc, char *argv[]) { | |
int param = atol(argv[1]); | |
if (param == -1) param = 0x80000000; | |
if (param == -2) param = 0xffffffff; | |
if (param == 0) | |
return 1; | |
#if IS_RAND == 0 | |
// predictable pattern | |
int sum = 0; | |
for (int i = 0; i < 100000000; i++) { | |
if ((i & param) == 0) sum += 1; | |
} | |
printf("condition (i & %d) == 0\n", param); | |
#else | |
// random pattern | |
unsigned long *vals = malloc(sizeof(unsigned long) * param); | |
for (int i = 0; i < param; i++) { | |
vals[i] = xorShiftRandom(); | |
} | |
int sum = 0; | |
for (int i = 0; i < 100000000; i++) { | |
unsigned long r = vals[i & (param - 1)]; | |
if ((r & 1) == 0) sum++; | |
} | |
printf("random pattern length %d\n", param); | |
#endif | |
printf("sum = %d\n", sum); | |
} |
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gcc -std=c99 -D IS_RAND=0 branch-test.c ; for i in -1 -2 1 3 2 4 8 16; do echo '### ' $i; perf stat -r5 -o _stats_pred_base --append ./a.out $i; echo; done | |
gcc -O3 -std=c99 -D IS_RAND=0 branch-test.c ; for i in -1 -2 1 3 2 4 8 16; do echo '### ' $i; perf stat -r5 -o _stats_pred_o3 --append ./a.out $i; echo; done | |
gcc -std=c99 -D IS_RAND=1 branch-test.c ; for i in 8 16 32 64 128 256; do echo '### ' $i; perf stat -r5 -o _stats_rand_base --append ./a.out $i; echo; done | |
gcc -O3 -std=c99 -D IS_RAND=1 branch-test.c ; for i in 8 16 32 64 128 256; do echo '### ' $i; perf stat -r5 -o _stats_rand_o3 --append ./a.out $i; echo; done |
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