Bug 116366

Summary: gcc optimizer produces incorrect code
Product: [Retired] Red Hat Linux Reporter: Need Real Name <jboorn>
Component: gccAssignee: Jakub Jelinek <jakub>
Status: CLOSED NOTABUG QA Contact: David Lawrence <dkl>
Severity: medium Docs Contact:
Priority: medium    
Version: 9   
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Target Release: ---   
Hardware: i686   
OS: Linux   
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Fixed In Version: Doc Type: Bug Fix
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Clone Of: Environment:
Last Closed: 2004-02-20 16:38:17 UTC Type: ---
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description Need Real Name 2004-02-20 16:32:01 UTC 
Description of problem:
gcc optimizer option -O2 produces incorrect code

Version-Release number of selected component (if applicable):
gcc-3.2.2-5 [gcc version 3.2.2 20030222 (Red Hat Linux 3.2.2-5)]

How reproducible:
Every time.

Steps to Reproduce:
1.compile and run test program with -O2 option

cat <<EOF > t.c
#include <stdio.h>
#include <string.h>
#include <ctype.h>

int main(int argc, char** argv)
{
    char *str;
    char *s;

    str = strdup("abc");
    s = str;
    printf("str is [%s], s is %c\n", str, *s);
    *s++ = toupper(*s);
    printf("str is [%s], s is %c\n", str, *s);
    free(str);
    return 0;
}
EOF
gcc -o t t.c
./t
gcc -O2 -o t t.c
./t
  
Actual results:
str is [abc], s is a
str is [Bbc], s is b

Expected results:
str is [abc], s is a
str is [Abc], s is b


Additional info:
Comment 1 Jakub Jelinek 2004-02-20 16:38:17 UTC 
That's not a bug, your code is broken.
There is no sequence point between s++ on the left side of = operator
and s use on the right side, so the actual result of the operation
is undefined.
See ISO C99 (or earlier standards) for details on sequence points.
Comment 2 Jakub Jelinek 2004-02-20 16:50:31 UTC 
*** Bug 116372 has been marked as a duplicate of this bug. ***