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https://github.com/Zenithsiz/ftmemsim-valgrind.git
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968bddcd4b
If you do `malloc(100)` followed by `realloc(200)`, DHAT now adds 100 bytes to the read and write counts for the implicit `memcpy`. This gives more reasonable results. I have long been surprised by low writes-per-byte values of around 0.35 for vectors that are grown by doubling. Counting the implicit `memcpy` increases those numbers to well above 0.5, which is what you'd expect. The commit also adds a section to the DHAT docs about `realloc`, because there is some non-obvious behaviour, some of which confused me just a couple of days ago.
29 lines
722 B
C
29 lines
722 B
C
// Some basic allocations and accesses.
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#include <stdint.h>
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#include <stdlib.h>
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#include <string.h>
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int main(void)
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{
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int64_t* m = malloc(1000);
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m[0] = 1; // write 8 bytes
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m[10] = m[1]; // read and write 8 bytes
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char* c = calloc(1, 2000);
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for (int i = 0; i < 1000; i++) {
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c[i + 1000] = c[i]; // read and write 1000 bytes
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}
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char* r = realloc(m, 3000); // read and write 1000 bytes (memcpy)
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for (int i = 0; i < 500; i++) {
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r[i + 2000] = 99; // write 500 bytes
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}
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c = realloc(c, 1000); // read and write 1000 bytes (memcpy)
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free(c);
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// totals: 3008 read, 3516 write
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return 0;
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}
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