The following C++, when compiled with g++-4.0.0, produces incorrect code when
compiled with -O1 -funroll-loops on both sparc-sun-solaris2.8 and i686-pc-linux-
gnu. This is a bare-bones simplification of real code from an application
using
the Boost.Spirit library. If compiled without -funroll-loops, then the
behaviour is as expected (no exception thrown; see below).
$ /opt/gcc-4.0.0-cross/sparc-sun-solaris2.8/bin/sparc-sun-solaris2.8-g++ -v
Using built-in specs.
Target: sparc-sun-solaris2.8
Configured with: ../../gcc-4.0.0/configure --with-dwarf2 --enable-languages=c,
c++ --enable-threads=no --disable-shared --prefix=/opt/gcc-4.0.0-cross/sparc-
sun-solaris2.8 --with-gnu-as --with-gnu-ld --disable-multilib --enable-concept-
checks --enable-clocale=generic --enable-libstdcxx-allocator=mt --build=i686-pc-
linux-gnu --host=i686-pc-linux-gnu --target=sparc-sun-solaris2.8 --with-
sysroot=/opt/sysroot/sparc-sun-solaris2.8/
Thread model: single
gcc version 4.0.0
$ /opt/gcc-4.0.0-cross/i686-pc-linux-gnu/bin/i686-pc-linux-gnu-g++ -v
Using built-in specs.
Target: i686-pc-linux-gnu
Configured with: ../../gcc-4.0.0/configure --with-dwarf2 --enable-languages=c,
c++ --enable-threads=no --disable-shared --prefix=/opt/gcc-4.0.0-cross/i686-pc-
linux-gnu --with-gnu-as --with-gnu-ld --disable-multilib
--enable-concept-checks
--enable-clocale=generic --enable-libstdcxx-allocator=mt --build=i686-pc-linux-
gnu --host=i686-pc-linux-gnu --target=i686-pc-linux-gnu
Thread model: single
gcc version 4.0.0
The (poor, but simple) C++ program is as follows:
// sparc-sun-solaris2.8-g++ -Wall -O1 -funroll-loops -o opt-sparc
test_optimizer.cc
//
// or
//
// i686-pc-linux-gnu-g++ -Wall -O1 -funroll-loops -o opt-x86 test_optimizer.cc
#include <bitset>
#include <stdexcept>
class basic
{
public:
void set(char from, char to)
{
for (int i = from; i <= to; ++i) {
bset.set(static_cast<unsigned char>(i));
}
}
private:
std::bitset<256> bset;
};
// Nevermind that this is not robust code; it's the simplest failure case.
void func(basic * const ptr,
const char *definition)
{
char ch = *definition;
++definition;
while (ch) {
char next = *definition;
++definition;
if (next == '-') {
next = *definition;
++definition;
ptr->set(ch, next);
}
ch = next;
}
}
int
main(const int argc,
const char * const * const argv)
{
basic ptr;
func(&ptr, "A-B");
}
This program should just set a couple of bits in the bitset and exit without
any
output. However, if compiled as described above, it triggers bitset's throw of
std::out_of_range:
$ ./opt-sparc
terminate called after throwing an instance of 'std::out_of_range'
what(): bitset::set
Abort
$ ./opt-x86
terminate called after throwing an instance of 'std::out_of_range'
what(): bitset::set
Aborted
The loop in func() has been "simplified" to remove all untaken branch pathways
while still triggering the bug.
This appears to be a regression since gcc-3.4.3 (for both targets) has no
trouble with this code. Version info from those compilers is shown below.
$ /opt/gcc-3.4.3-cross/sparc-sun-solaris2.8/bin/sparc-sun-solaris2.8-g++ -v
Reading specs from /opt/gcc-3.4.3-cross/sparc-sun-solaris2.8/lib/gcc/sparc-sun-
solaris2.8/3.4.3/specs
Configured with: ../../gcc-3.4.3/configure --with-dwarf2 --enable-languages=c,
c++ --enable-threads=no --disable-shared --prefix=/opt/gcc-3.4.3-cross/sparc-
sun-solaris2.8 --with-gnu-as --with-gnu-ld --disable-multilib --enable-concept-
checks --enable-clocale=generic --enable-libstdcxx-allocator=mt --build=i686-pc-
linux-gnu --host=i686-pc-linux-gnu --target=sparc-sun-solaris2.8 --with-
sysroot=/opt/sysroot/sparc-sun-solaris2.8/
Thread model: single
gcc version 3.4.3
$ /opt/gcc-3.4.3-cross/i686-pc-linux-gnu/bin/i686-pc-linux-gnu-g++ -v
Reading specs from /opt/gcc-3.4.3-cross/i686-pc-linux-gnu/lib/gcc/i686-pc-linux-
gnu/3.4.3/specs
Configured with: ../../gcc-3.4.3/configure --with-dwarf2 --enable-languages=c,
c++ --enable-threads=no --disable-shared --prefix=/opt/gcc-3.4.3-cross/i686-pc-
linux-gnu --with-gnu-as --with-gnu-ld --disable-multilib
--enable-concept-checks
--enable-clocale=generic --enable-libstdcxx-allocator=mt --build=i686-pc-linux-
gnu --host=i686-pc-linux-gnu --target=i686-pc-linux-gnu
Thread model: single
gcc version 3.4.3
--
Summary: Incorrect code with -funroll-loops for multiple targets
with same code
Product: gcc
Version: 4.0.0
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: tree-optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: spencer at infointeractive dot com
CC: gcc-bugs at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21254
