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:
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.
*** Bug 116372 has been marked as a duplicate of this bug. ***