Hello, I'm sorry to bother you. And I have some gcc compiler optimization
questions to ask you.
First of all, I used csmith tools to generate c files randomly. Meanwhile,
the final running result was the checksum for global variables in a c file.
For the two c files in the attachment, I performed the equivalent
transformation of loop from *initial.**c* to *transformed.c*. And the two
files produced different results (i.e. different checksum values) when
using *-O3 and -Ofast* optimization level, while the results of both were
the same when using other levels of optimization such as *-O0*, *-O1*,
*-O2, **-Os*.
Please help me to explain why this is, thank you.
command line: *gcc file.c -O3 -lm -I $CSMITH_HOME/include && ./a.out*
*gcc file.c -Ofast -lm -I $CSMITH_HOME/include &&
./a.out*
version: gcc 12.2.0
os: ubuntu 22.04
#include "csmith.h"
static int32_t g_a75[4];
static int32_t g_b75[4];
struct S0 {
uint32_t f0;
const uint16_t f1;
volatile int32_t f2;
uint16_t f3;
int64_t f4;
};
struct S1 {
int32_t f0;
const uint32_t f1;
uint32_t f2;
};
struct S2 {
const int64_t f0;
int32_t f1;
volatile int64_t f2;
int8_t f3;
volatile struct S0 f4;
};
static int8_t g_11 = (-6L);
static int32_t g_13 = 0xC869B7D6L;
static int32_t *g_12[2][3][1] = {{{&g_13}, {&g_13}, {&g_13}}, {{&g_13}, {&g_13}, {&g_13}}};
static volatile uint8_t g_27 = 2UL;
static struct S1 g_237 = {0xD8430CE5L, 0x74A446EAL, 0UL};
static struct S1 g_239 = {9L, 0UL, 18446744073709551615UL};
static int64_t func_1(void);
static int64_t func_1(void) {
int32_t **l_488 = &g_12[1][1][0];
int i, j, k;
for (i = 0; i < 1; i++) {
int ii_1;
// fusion in max execTimes
for (j = 0, ii_1 = 0; j < 2; j++, ii_1++) {
for (k = 0; k < 1; k++) {
g_a75[ii_1] = g_237.f0 * g_11 - g_27;
}
}
int jj_1;
for (jj_1 = 0; jj_1 < 4; jj_1++) {
g_b75[jj_1] = g_239.f0 * g_a75[jj_1] - g_13;
}
}
return (**l_488);
}
int main(void) {
int i, j, k;
int print_hash_value = 0;
platform_main_begin();
crc32_gentab();
func_1();
transparent_crc(g_11, "g_11", print_hash_value);
transparent_crc(g_13, "g_13", print_hash_value);
transparent_crc(g_27, "g_27", print_hash_value);
transparent_crc(g_237.f0, "g_237.f0", print_hash_value);
transparent_crc(g_237.f1, "g_237.f1", print_hash_value);
transparent_crc(g_237.f2, "g_237.f2", print_hash_value);
transparent_crc(g_239.f0, "g_239.f0", print_hash_value);
transparent_crc(g_239.f1, "g_239.f1", print_hash_value);
transparent_crc(g_239.f2, "g_239.f2", print_hash_value);
for (i = 0; i < 4; i++) {
transparent_crc(g_a75[i], "g_a75[i]", print_hash_value);
}
for (i = 0; i < 4; i++) {
transparent_crc(g_b75[i], "g_b75[i]", print_hash_value);
}
platform_main_end(crc32_context ^ 0xFFFFFFFFUL, print_hash_value);
return 0;
}
#include "csmith.h"
static int32_t g_a75[4];
static int32_t g_b75[4];
struct S0 {
uint32_t f0;
const uint16_t f1;
volatile int32_t f2;
uint16_t f3;
int64_t f4;
};
struct S1 {
int32_t f0;
const uint32_t f1;
uint32_t f2;
};
struct S2 {
const int64_t f0;
int32_t f1;
volatile int64_t f2;
int8_t f3;
volatile struct S0 f4;
};
static int8_t g_11 = (-6L);
static int32_t g_13 = 0xC869B7D6L;
static int32_t *g_12[2][3][1] = {{{&g_13}, {&g_13}, {&g_13}}, {{&g_13}, {&g_13}, {&g_13}}};
static volatile uint8_t g_27 = 2UL;
static struct S1 g_237 = {0xD8430CE5L, 0x74A446EAL, 0UL};
static struct S1 g_239 = {9L, 0UL, 18446744073709551615UL};
static int64_t func_1(void);
static int64_t func_1(void) {
int32_t **l_488 = &g_12[1][1][0];
int i, j, k;
for (i = 0; i < 1; i++) {
int ii_1;
int jj_1;
int ij_1;
// fusion in max execTimes
for (j = 0, ii_1 = 0, jj_1 = 0, ij_1 = 0; ij_1 <= 4; ij_1++) {
if (ij_1 <= 2 && j < 2) {
for (k = 0; k < 1; k++) {
g_a75[ii_1] = g_237.f0 * g_11 - g_27;
}
j++;
ii_1++;
}
if (ij_1 <= 4 && jj_1 < 4) {
g_b75[jj_1] = g_239.f0 * g_a75[jj_1] - g_13;
jj_1++;
}
}
}
return (**l_488);
}
int main(void) {
int i, j, k;
int print_hash_value = 0;
platform_main_begin();
crc32_gentab();
func_1();
transparent_crc(g_11, "g_11", print_hash_value);
transparent_crc(g_13, "g_13", print_hash_value);
transparent_crc(g_27, "g_27", print_hash_value);
transparent_crc(g_237.f0, "g_237.f0", print_hash_value);
transparent_crc(g_237.f1, "g_237.f1", print_hash_value);
transparent_crc(g_237.f2, "g_237.f2", print_hash_value);
transparent_crc(g_239.f0, "g_239.f0", print_hash_value);
transparent_crc(g_239.f1, "g_239.f1", print_hash_value);
transparent_crc(g_239.f2, "g_239.f2", print_hash_value);
for (i = 0; i < 4; i++) {
transparent_crc(g_a75[i], "g_a75[i]", print_hash_value);
}
for (i = 0; i < 4; i++) {
transparent_crc(g_b75[i], "g_b75[i]", print_hash_value);
}
platform_main_end(crc32_context ^ 0xFFFFFFFFUL, print_hash_value);
return 0;
}
