When combining "-Wunreachable-code" with any optimizing above zero, "warning:
will never be executed" under certain circumstances.
I've managed to create a small program that does show this bug, unless "nobug"
is defined when compiling.
$ gcc -v
Reading specs from /usr/lib/gcc/i386-redhat-linux/3.4.2/specs
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --enable-shared --enable-threads=posix
--disable-checking --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-java-awt=gtk --host=i386-redhat-linux
Thread model: posix
gcc version 3.4.2 20041017 (Red Hat 3.4.2-6.fc3)
$ make
cc -O3 -Wunreachable-code -save-temps test.c -o test
test.c: In function `x':
test.c:5: warning: will never be executed
$ cat test.i
# 1 "test.c"
# 1 "<built-in>"
# 1 "<command line>"
# 1 "test.c"
int x(int i,int *j) {
*j = i;
if (*j > 31) {
printf("statement is executed\n");
} else {
return 1;
}
return 0;
}
int main(int argc,char *argv[]) {
int i,j,k;
if (argc != 2) {
printf("Usage: test <integer>\n");
return 1;
} else {
i=atoi(argv[1]);
}
k=x(i,&j);
printf("j is now: %i\n",j);
}
$ ./test 123
statement is executed
j is now: 123
$ ./test 1
j is now: 1
rm test
mv test.i test.i.old
$ cc -O3 -Wunreachable-code -save-temps test.c -o test -Dnobug
$ diff test.i test.i.old
12c12
< printf("statement is not executed\n");
---
>
In case it isn't clear: my test.c program contains:
} else {
#ifdef nobug
printf("statement is not executed\n");
#endif
return 1;
}
--
Summary: -O3 -Wunreachable-code failing
Product: gcc
Version: 3.4.2
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: alex at ergens dot op dot het dot net
CC: gcc-bugs at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19354
