void test(int *&p) {
p+= 1; // modifies p in register
(char*&)p+= 8; // modifies p in memory
// finally the value from register wins
}
This prints 4 (BAD):
g++ -O2 -march=athlon bug.cc -o bug; ./bug; echo $?
This prints 12 (CORRECT):
g++ -O1 -march=athlon bug.cc -o bug; ./bug; echo $?
This prints 12, but works by chance (assembly code is incorrect):
g++ -O2 bug.cc -o bug; ./bug; echo $?
# gcc -v
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 20041006 (Red Hat 3.4.2-5)
--
Summary: Pointer reference optimized into register is not used
when referenced through type cast.
Product: gcc
Version: 3.4.2
Status: UNCONFIRMED
Severity: critical
Priority: P2
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: zybi at talex dot pl
CC: gcc-bugs at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17998
