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 *-O2* optimization level, while the results of both were the same
when using other levels of optimization such as *-O0*, *-O1*, *-O3*, *-Os*,
*-Ofast*.
Please help me to explain why this is, thank you.
command line: *gcc file.c -O2 -lm -I $CSMITH_HOME/include && ./a.out*
version: gcc 12.2.0
os: ubuntu 22.04
#include "csmith.h"
static int32_t g_a321[3];
static int64_t g_b321[3];
union U0 {
const int32_t f0;
};
union U1 {
const uint16_t f0;
const uint64_t f1;
int32_t f2;
const signed f3 : 29;
};
union U2 {
int64_t f0;
int16_t f1;
};
static uint32_t g_39 = 0x78C76445L;
static union U0 g_87 = {0xA9ACF304L};
static union U0 *g_89[1][3][2] = {{{&g_87, &g_87}, {&g_87, &g_87}, {&g_87, &g_87}}};
static union U0 **volatile g_88[3][1] = {{&g_89[0][2][1]}, {&g_89[0][2][1]}, {&g_89[0][2][1]}};
static int32_t g_165 = 2L;
static union U2 g_261[3] = {{0xDF9C6E8BCC63CCAELL}, {0xDF9C6E8BCC63CCAELL}, {0xDF9C6E8BCC63CCAELL}};
static union U1 g_412 = {3UL};
static void func_1(void);
static void func_1() {
uint8_t l_19 = 1UL;
for (l_19 = 0; (l_19 <= 2); l_19 += 1) {
int i, j;
for (i = 0; i < 1; i++) {
for (j = 0; j < 3; j++) {
}
}
int ii_7;
// fusion in add execTimes
for (g_39 = 0, ii_7 = 0; (g_39 <= 1); g_39 += 1, ii_7++) {
g_a321[ii_7] = (*g_89[0][2][0]).f0 * l_19 + g_165;
}
int jj_7;
for (jj_7 = 0; jj_7 < 3; jj_7++) {
g_b321[jj_7] = g_261[1].f0 * g_a321[jj_7] + g_412.f2;
}
}
}
int main(void) {
int i;
int print_hash_value = 0;
platform_main_begin();
crc32_gentab();
func_1();
transparent_crc(g_39, "g_39", print_hash_value);
transparent_crc(g_87.f0, "g_87.f0", print_hash_value);
transparent_crc(g_165, "g_165", print_hash_value);
for (i = 0; i < 3; i++) {
transparent_crc(g_261[i].f0, "g_261[i].f0", print_hash_value);
}
transparent_crc(g_412.f0, "g_412.f0", print_hash_value);
for (i = 0; i < 3; i++) {
transparent_crc(g_a321[i], "g_a321[i]", print_hash_value);
}
for (i = 0; i < 3; i++) {
transparent_crc(g_b321[i], "g_b321[i]", print_hash_value);
}
platform_main_end(crc32_context ^ 0xFFFFFFFFUL, print_hash_value);
return 0;
}
#include "csmith.h"
static int32_t g_a321[3];
static int64_t g_b321[3];
union U0 {
const int32_t f0;
};
union U1 {
const uint16_t f0;
const uint64_t f1;
int32_t f2;
const signed f3 : 29;
};
union U2 {
int64_t f0;
int16_t f1;
};
static uint32_t g_39 = 0x78C76445L;
static union U0 g_87 = {0xA9ACF304L};
static union U0 *g_89[1][3][2] = {{{&g_87, &g_87}, {&g_87, &g_87}, {&g_87, &g_87}}};
static union U0 **volatile g_88[3][1] = {{&g_89[0][2][1]}, {&g_89[0][2][1]}, {&g_89[0][2][1]}};
static int32_t g_165 = 2L;
static union U2 g_261[3] = {{0xDF9C6E8BCC63CCAELL}, {0xDF9C6E8BCC63CCAELL}, {0xDF9C6E8BCC63CCAELL}};
static union U1 g_412 = {3UL};
static void func_1(void);
static void func_1() {
uint8_t l_19 = 1UL;
for (l_19 = 0; (l_19 <= 2); l_19 += 1) {
int i, j;
for (i = 0; i < 1; i++) {
for (j = 0; j < 3; j++) {
}
}
int ii_7;
int jj_7;
int ij_7;
// fusion in add execTimes
for (g_39 = 0, ii_7 = 0, jj_7 = 0, ij_7 = 0; ij_7 < 5; ij_7++) {
if (ij_7 <= 2 && (g_39 <= 1)) {
g_a321[ii_7] = (*g_89[0][2][0]).f0 * l_19 + g_165;
g_39 += 1;
ii_7++;
} else {
jj_7 = ij_7 - 2;
g_b321[jj_7] = g_261[1].f0 * g_a321[jj_7] + g_412.f2;
}
}
}
}
int main(void) {
int i;
int print_hash_value = 0;
platform_main_begin();
crc32_gentab();
func_1();
transparent_crc(g_39, "g_39", print_hash_value);
transparent_crc(g_87.f0, "g_87.f0", print_hash_value);
transparent_crc(g_165, "g_165", print_hash_value);
for (i = 0; i < 3; i++) {
transparent_crc(g_261[i].f0, "g_261[i].f0", print_hash_value);
}
transparent_crc(g_412.f0, "g_412.f0", print_hash_value);
for (i = 0; i < 3; i++) {
transparent_crc(g_a321[i], "g_a321[i]", print_hash_value);
}
for (i = 0; i < 3; i++) {
transparent_crc(g_b321[i], "g_b321[i]", print_hash_value);
}
platform_main_end(crc32_context ^ 0xFFFFFFFFUL, print_hash_value);
return 0;
}
