<table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Issue</th>
<td>
<a href=https://github.com/llvm/llvm-project/issues/75740>75740</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>
Unexpected results in some optimization levels.
</td>
</tr>
<tr>
<th>Labels</th>
<td>
new issue
</td>
</tr>
<tr>
<th>Assignees</th>
<td>
</td>
</tr>
<tr>
<th>Reporter</th>
<td>
bfsyrgz
</td>
</tr>
</table>
<pre>
For the following two c files, I performed the equivalent transformation of loop from file1.c to file2.c. I ran these two files respectively using different optimization levels including -O0, -O1, -O2, -O3, -Os, -Ofast. The exact output results(i.e. checksum values) are:
```
-O0 -O1 -O2 -O3 -Os -Ofast
file1.c 119775CA 119775CA 119775CA 119775CA 119775CA E8961535
file2.c 2D8D485E 2D8D485E 2D8D485E 2D8D485E 2D8D485E E8961535
```
using command line:
```
clang <filename.c> <optimization level> -lm -I $CSMITH_HOME/include && ./a.out
```
Besides, I ran the command line ```clang <filename.c> <optimization level> -fsanitize=<option> -I /usr/include/csmith/ && ./a.out```, **options** include **address**, **undefined** and **memory**, and the terminal showed that my programs have no undefined behavior. Meanwhile, both test cases appear not to be relying on uninitialized memory, at least according to valgrind.
Please help me to explain why these two files produced different output results when using the same optimization level(i.e. -O0, -O1, O2, -O3, -Os), thank you.
version: clang+llvm 14.0.0
os: ubuntu 22.04
And the content of ```csmith.h``` is as follows.
```
/* -*- mode: C -*-
*
* Copyright (c) 2007-2011, 2013, 2014 The University of Utah
* All rights reserved.
*
* This file is part of `csmith', a random generator of C programs.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* * Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
*
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
#ifndef RANDOM_RUNTIME_H
#define RANDOM_RUNTIME_H
#ifdef CSMITH_MINIMAL
#include "csmith_minimal.h"
#else
/*****************************************************************************/
#include <string.h>
#include <float.h>
#include <math.h>
#define __STDC_LIMIT_MACROS
#include "random_inc.h"
static uint32_t crc32_tab[256];
static uint32_t crc32_context = 0xFFFFFFFFUL;
static void
crc32_gentab (void)
{
uint32_t crc;
const uint32_t poly = 0xEDB88320UL;
int i, j;
for (i = 0; i < 256; i++) {
crc = i;
for (j = 8; j > 0; j--) {
if (crc & 1) {
crc = (crc >> 1) ^ poly;
} else {
crc >>= 1;
}
}
crc32_tab[i] = crc;
}
}
static void
crc32_byte (uint8_t b) {
crc32_context =
((crc32_context >> 8) & 0x00FFFFFF) ^
crc32_tab[(crc32_context ^ b) & 0xFF];
}
#if defined(__SPLAT__) || defined(NO_LONGLONG)
static void
crc32_8bytes (uint32_t val)
{
crc32_byte ((val>>0) & 0xff);
crc32_byte ((val>>8) & 0xff);
crc32_byte ((val>>16) & 0xff);
crc32_byte ((val>>24) & 0xff);
}
static void
transparent_crc (uint32_t val, char* vname, int flag)
{
crc32_8bytes(val);
if (flag) {
printf("...checksum after hashing %s : %X\n", vname, crc32_context ^ 0xFFFFFFFFU);
}
}
#else
static void
crc32_8bytes (uint64_t val)
{
crc32_byte ((val>>0) & 0xff);
crc32_byte ((val>>8) & 0xff);
crc32_byte ((val>>16) & 0xff);
crc32_byte ((val>>24) & 0xff);
crc32_byte ((val>>32) & 0xff);
crc32_byte ((val>>40) & 0xff);
crc32_byte ((val>>48) & 0xff);
crc32_byte ((val>>56) & 0xff);
}
static void
transparent_crc (uint64_t val, char* vname, int flag)
{
crc32_8bytes(val);
if (flag) {
printf("...checksum after hashing %s : %lX\n", vname, crc32_context ^ 0xFFFFFFFFUL);
}
}
#endif
static void
transparent_crc_bytes (char *ptr, int nbytes, char* vname, int flag)
{
int i;
for (i=0; i<nbytes; i++) {
crc32_byte(ptr[i]);
}
if (flag) {
printf("...checksum after hashing %s : %lX\n", vname, crc32_context ^ 0xFFFFFFFFUL);
}
}
/*****************************************************************************/
#endif
#endif /* RANDOM_RUNTIME_H */
/*
* Local Variables:
* c-basic-offset: 4
* tab-width: 4
* End:
*/
/* End of file. */
```
**file1.c**
```
#include <math.h>
#include <stdlib.h>
#include "csmith.h"
struct S0 {
int f0;
volatile short f1;
long f2;
int f3;
int f4;
};
static unsigned char g_8 = 0xF3L;
static short g_12 = 0xDEE2L;
static int g_26 = 0x37F4A7D2L;
static int *volatile g_27[1][3][1] = {{{&g_26}, {&g_26}, {&g_26}}};
static volatile struct S0 g_39 = {2UL, 0x8215L, 1L, 0x5BD66052L, 0xBC40293EL};
static volatile struct S0 *volatile g_41 = &g_39;
static int *g_48 = (void *)0;
static int **volatile g_119 = &g_48;
static int *func_1(void);
static int *func_1(void) {
int l_24 = 0xAB56411DL;
int l_31 = 2L;
int l_37 = 4294967295UL;
for (g_8 = 0; (g_8 <= 1); g_8 += 1) {
int *l_28 = &g_26;
(*l_28) = (((safe_div_func_int8_t_s_s((l_24 |= (safe_sub_func_uint32_t_u_u((2UL >= (18446744073709551615UL ^ g_8)), 1UL))), 0xFFL)), (void *)0) != (void *)0);
for (l_31 = 1; (l_31 >= 0); l_31 -= 1) {
// unswitching
for (l_37 = 0; (l_37 <= 1); l_37 += 1) {
if (sqrt((*g_27[0][0][0]))) {
return &g_26;
} else {
(*g_41) = g_39;
}
g_26 = -1;
}
g_12 = -1;
}
}
return (*g_119);
}
int main(void) {
int print_hash_value = 0;
platform_main_begin();
crc32_gentab();
func_1();
transparent_crc(g_8, "g_8", print_hash_value);
transparent_crc(g_12, "g_12", print_hash_value);
transparent_crc(g_26, "g_26", print_hash_value);
transparent_crc(g_39.f0, "g_39.f0", print_hash_value);
transparent_crc(g_39.f1, "g_39.f1", print_hash_value);
transparent_crc(g_39.f2, "g_39.f2", print_hash_value);
transparent_crc(g_39.f3, "g_39.f3", print_hash_value);
transparent_crc(g_39.f4, "g_39.f4", print_hash_value);
platform_main_end(crc32_context ^ 0xFFFFFFFFUL, print_hash_value);
return 0;
}
```
**file2.c**
```
#include <math.h>
#include <stdlib.h>
#include "csmith.h"
struct S0 {
int f0;
volatile short f1;
long f2;
int f3;
int f4;
};
static unsigned char g_8 = 0xF3L;
static short g_12 = 0xDEE2L;
static int g_26 = 0x37F4A7D2L;
static int *volatile g_27[1][3][1] = {{{&g_26}, {&g_26}, {&g_26}}};
static volatile struct S0 g_39 = {2UL, 0x8215L, 1L, 0x5BD66052L, 0xBC40293EL};
static volatile struct S0 *volatile g_41 = &g_39;
static int *g_48 = (void *)0;
static int **volatile g_119 = &g_48;
static int *func_1(void);
static int *func_1() {
int l_24 = 0xAB56411DL;
int l_31 = 2L;
int l_37 = 4294967295UL;
for (g_8 = 0; (g_8 <= 1); g_8 += 1) {
int *l_28 = &g_26;
(*l_28) = (((safe_div_func_int8_t_s_s((l_24 |= (safe_sub_func_uint32_t_u_u((2UL >= (18446744073709551615UL ^ g_8)), 1UL))), 0xFFL)), (void *)0) != (void *)0);
for (l_31 = 1; (l_31 >= 0); l_31 -= 1) {
// unswitching
if (sqrt((*g_27[0][0][0]))) {
for (l_37 = 0; (l_37 <= 1); l_37 += 1) {
{ return &g_26; }
}
g_26 = -1;
} else {
for (l_37 = 0; (l_37 <= 1); l_37 += 1) {
{ (*g_41) = g_39; }
g_26 = -1;
}
}
g_12 = -1;
}
}
return (*g_119);
}
int main(void) {
int print_hash_value = 0;
platform_main_begin();
crc32_gentab();
func_1();
transparent_crc(g_8, "g_8", print_hash_value);
transparent_crc(g_12, "g_12", print_hash_value);
transparent_crc(g_26, "g_26", print_hash_value);
transparent_crc(g_39.f0, "g_39.f0", print_hash_value);
transparent_crc(g_39.f1, "g_39.f1", print_hash_value);
transparent_crc(g_39.f2, "g_39.f2", print_hash_value);
transparent_crc(g_39.f3, "g_39.f3", print_hash_value);
transparent_crc(g_39.f4, "g_39.f4", print_hash_value);
platform_main_end(crc32_context ^ 0xFFFFFFFFUL, print_hash_value);
return 0;
}
```
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJzsW1lzo8iy_jX4JcMKKLQ--AEBahMhC1-EuqefCASFVHNYdKCQ2_Prb2SxCJDU0-05N2LumXYwTS2ZWVlfLpWFPX5RsENK6ZM0WUoT48Ev-THLn_ZR8Z4f_njYZ-H70yrLgR8pRFkcZ28sPQB_yyCAiMW0kIgOFpxoHmV5QkNBSP9dsrMf05QDz_20wCmfsyyFLII4y04Q5Vki-JVRADwTTTIKRmBB7qcopKBiFbEG5LQ40YCzM43foSxQhZBFEc1xiezEWcL-qBaI6ZnGBbA0iMsQ6R5tGVV8tJXqRaqXWr2K6hX5BR-Bi6p_8wMOWclPJcdly5gXEpmzER1BcKTBv4oygbMfl7jzBfg5lVRNkg1J1qSpXD-iC92fR1se9JVBn6BSg7Fi0Ec16061RoOg-FGUxWw20bVLYzD-g31zvpgqE3XSWYM0axBjboznE7OhHfTvTg8n2jUuexnAV1k5yJLET0OIWXoX6CD20wNIqo6apn5CR4Gkmjhw7Rk48Rgn8GiBRMb69sVyn71n-8WUyKryGQoSmUpkCiOJrPxRVvKbiy5pwcLG-2uX7WkLLcNP6xcVfso4-4NKqlFTZamYQa1XZZFftJXIKigSxo8SWV1r3upMdACJaBLRKmlF1YHLnrHrh2FOi3oOeapWmYY0YikNaybcYtVMaJLl7xd6nEEgOM0TlvoxFMfsTSQFn0PyDqc8O-R-UsDRP1NIM2hFw54e_TPL8hG8UD99O7KYosR9xo_AacEh8AtagH86UT-HNOOYNvYUchq_o6dkKZQpQ9z8mP1BQ2h008HnEFMMHT8IslxkBZ5hEB9yloaj2r7i31ckpHCk8QkSimT02yn2WQpvx_ertHTKs7AMaNhNRr3MAW9HmtYJC3Ep_ITeyFdNgunnqutUtcAWP_rpv-A9K3uKn2leCC_RQPibRJZxfE5AGY_kUe2zWYHT5b5MeQmEjORxV4JW2y7IUi52EnVcWLjY6NgOACvAL-oToRjdDBGJrNBbHiWiPUKShRjAoFf9OkWi27Qt0LPTe84ORw4SmQeYXokszx6JrAg8iKyo9XsscvUuZWLb_B2V3XH_2BGmxTEIYeL0oPmZNpYerOoeWSHsiXs6-Xmz8yasZsKFMMbDLIEDTWnu8yxHKr116NuiHRqygudsXwpbY3SUBQWWQpGVeUDFyJ6lfv4OeEaKdPLG-BGyXLzb7CPEJVnIIhYIxxFK5RQP3oRxTkNU5czCJtj653WQpSETcS-YEsrbZDpQGW4oXuBea42DLKSQlAW6OMe4wIX8fXbGqcZ8acZZgOHbEwzAEeqYFQLirk61610UDlkRxD5LaH4b2dtqsrSLZqNmHaW3NB3o1-r9IU2hQmMgM8yCMqEp9xsXkAjWUxk_0hwSn9Oc-XFxsZ4wPy7R3dodz322trC1V-4XzTHB2sKrY3-2DNOA5Vdwn03Q7devjvXp2YVne22Yzha0jQG6vXEda7lzbWcLEiHaFqytREg3eDYGaJuvYP726pjbLdgOWC-va8s04IvmONrGtcytOPs2-npnWJtP2FnuXNjYLqytF8s1DXBtHHWfzY7kazFgr-DFdPRnbeNqS2ttuV_F-ivL3eDaK9sBDV41x7X03Vpz4HXnvNrbrlDcvmFt9bVmvZjGCKwNbGwwP5sbF7bP2no9QMP-sjEd3FQPimVX5NrSlmuzWnzzFQzLMXW32nG3rVuGuXG1Nfa2r6ZuVU3zN_Plda05X0Ued7o5zt5szf_ZmRvX0tZgaC_aJxOtMP8BJF8dW9855gtuy151hG53y61ruTvXhE-2bQh7bU3ns6WbW0ldwtreCph3WxPlGJqrVYqhyJXlCiLbgeVuayHmXXttXNNxdq-uZW8wIz_bX8zPpgO6ttuahjCUvREQuc-m7XzFZRA7YUdc5Muz6T6bDlibPgquo1Ugbl3H0t0-k-2AaztuDxfYmJ_W1idzo5s4b6PULxbuaNFzBWuLxFal1BftK9g7hEu4wG5rVs1O4Ah7fTY3YK1AMz5buK2KvCP21d5urdo57RVsd_pzbbxuaJJV90CViMoirG_A0TaG_eI5u41rvZjecztfFT_35i9SUEhdrL5YG-tFW18m2wqOVCeWl7CUJX48OrYxLRGVxgXti101Zdt__XNllQYyVccUmx5GR0k1b01Hcebzu7OJL2qidnJgVc_buobuiRj2XjTdsbe3rFYVFh5Lg67FxL8FnhoBlCzlKvE4BHmAb38vTZZkMpUmhqQuv0cqarlvHCTVAPnbqv7ZrVu2HvM5Y2F9GavYD3hu7TEKcaoNNGnWci-6C3akLoIsLfhFnVMWv9damMZyPleJ3NNiwVIODEPx9-5o24iyHNVglQxMV9jUAVHAjkSW4llAVznUIw8ED-uLbQT-LibnKAObZiX798fHG6JQy0iUpiiTTEG5TdRZtSFWTZRd0U9MgcZAH3xmBmCYfk-kKR4DlJvsvZF-t-s6TJoYQr2BzS4sF97vucf-naMHz9HKc4_DfojHtRP2NCTzCp8ejUBqLiSRKcjfZLly2ga7e5u6FjUxa42EnNWqGy6DHYokC-0td-5529e15npetSNdmumd2Y3tre3NJ_yvjYl7GM0RpKJBScTC2Y9vhlIfVAw6P67wkC_biCLkVX-Ea_4hLmX6ITYyvsv2Z84kPhGefLw-e1VoDbDSITj6OR7D59RPRH2O6SKK_cN3gKyQr3Xsb6MK45r_4rFQedUpZymPxP7IaDRqv_r5Eac5HP3iiHW_RCYF4I1WIpPfpImeYu4m-kXFa2_sZOCBQjcir3tk_5hzTcf_QOf6HptKPsQ2_hgi449BMrkPyQcD5-IHf_vAiX8-ctZ_HjptAKUhi34KQq8NKAQOa_oTzxvY0hqXn0IVAKCqbdTOSFPOSKpRFTOSqtfi71QzcPEgicxRq-oc76IhvqV3jv171vp7muufex-58tNmDOpPqMP74c3LpsCv8wEjC_wYPvs58_cx-lV3Mnjc-wULHrMoKsS3QBh3Zrm_f3xjIT8OJ8w07H83vKUDUkEWiU-qoz5V-_W4z4VP_ZusGqI--Y_cvQa3ujBm-1tXs6vb8o07V14GHLZyN2BEfMuXQDtnsc9ZTKE4ZjmHSOnEYJylB4hIZ0Rwq8OBcS_R37yQlan45WwoEg4cvHlzkVPXw4tfpcjBU0hNY5gmuaLChQ8emdY06mw11mbGbTqJaO02Dx6ZSZOlgglnslSrl9JcIxCo6iFTlI77ITr8yUD1DBa-ANua4eCpi2YZshOf1-Rvc6JMRFOpByZLYzqVJ6TuLvWxTBaquf6xNfp7HSv15W2Ka9_B5uCN580drzpQ0HUX8h3y_gqKsrgsMZ7f4YnKNPCUzu37ppPcIR66b-yRcW12bTmZjhXFWA9cMvbUaufkxsxMzIzJYryYzshisuvS1OdZ66F4irV9vbqwCv0rJybLZgiuDkqJaLFH5hd4yLR_wOF5JUgEe2WA6in8iHohO3sCi-pS6hVeUc1WAMz0mkUQF-W-Im4uHF7plRU52a2hvmxLZK7Mx-PpbDyWZ-pMXkwmylSZIMHExB2J38yJX84p1YHX9vEkXF-6Q18RlZ9yy4sGx3oNcGshpUa4HjAr1CuIxdjjbYShOlJWmFreGA_wiO_OXtaZ9SxZD_RMWY3ds6WwpyhAin_nvLGRVmcSuUoh3VcD27UYgJzyMk-v_eH6k8mFp1lvrDSO0ovmlqypQ5qBNj8-KgPiAWmbbAeEHbJOs91CpZWiLL5T62MgJD5L74ezKN48LNI88dcorbVqolPs8yjLEw_FeHt6EML6btX9yHc12eaT3vCgXq5ivPJsIlqiNBwq15d8S4ZCWiHY_KAUMm2lYPODUtTFKJJbQXXvL8hSerKUvySL9GR9HCnkVnuy1L8ka9yTNf4hWX0XpWl48xNe_y7xZzLrKJNvBNawmmyqTvKr6vxVdf6jq87_XO35q-78VXd-qO78q5Xif7ZuxcJteV10dsq5n6sa79So_xdK3616r1X-ntJXxe6v2vdX7fur9v3_Xvs-hE9quFAX_gN9UmYymRN1RmYPxyd1IsvTmTKOfLKQJzKZ-SRY7MlsEc1nUzkIH9gTkYmqEGWmjNUJmY2i8WRK9xGNFvP9IpgtpLFME5_Fozg-J6MsPzywoijp02wyG8sPsb-ncSH-JxNCUvoGYhKhmhgP-RPyPO7LQyGN5ZgVvLhI4YzH9GmX0m8nGnAatn9aLf6K9uafUxejhzKPn46cn8R3b3HyHBg_lvtRkCUSWaH0-vV4yrPfacAlshI6FRJZCZ3_NwAA__9mRsSp">