issue: unexpected results in optimizations

[Jingwen Wu <elowen.jjw@gmail.com>]

[-- Attachment #1.1: Type: text/plain, Size: 774 bytes --]

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

[-- Attachment #2: initial.c --]
[-- Type: text/x-c-code, Size: 1866 bytes --]


#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;
}

[-- Attachment #3: transformed.c --]
[-- Type: text/x-c-code, Size: 1966 bytes --]


#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;
}