[Bug c++/18120] New: -O2 -funroll-loops causes bad loop behavior on fedora

[anndirkvg at gmail dot com]

The main loop in this code should loop from 'a' to 'z'.  On gcc3.3.3 on fedora
with -O2 and -funroll-loops, it loops the correct number of times but the 
key value alternates between 97 and 98.  
Compile line:
 g++ -o gccBug -O2 -funroll-loops main.cpp

Contents of main.cpp:
#include <stdio.h>
 
#define CP_ALPHA_STATE(x)       (1<<((x)-'a'))
 
class GptoKeyState {
public:
    GptoKeyState() {
        for (int i=0; i< 256; ++i) {
            _keyDown[i] = 0;
        }
    }
    ///
    int IsDown(unsigned char key) const {
        return _keyDown[key];
    }
 
    void SetDownKey(unsigned char key, int down) {
         _keyDown[(unsigned int)key] = down;
    }
 
    ///
    void SetDown(unsigned char key, int down) {
         _keyDown[(unsigned int)key] = down;
    }
private:
    int _keyDown[256];
};
 
 
 
 
int
main(int, char**)
{
    GptoKeyState _keyState;
    char key;
    int status2 = 8;
 
    for (key = 'a'; key<= 'z'; ++key) {
        int keyDown;
 
        printf("Testing %d\n", (int) key);
 
        // the & can return a value greater than 1, we want a boolean
        if (status2 & CP_ALPHA_STATE(key))
            keyDown = 1;
        else
            keyDown = 0;
 
 
        if (_keyState.IsDown((unsigned char)key) != keyDown) {
            _keyState.SetDown((unsigned char)key, keyDown);
        }
    }
}


Results of g++ -v:

Reading specs from /usr/lib/gcc-lib/x86_64-redhat-linux/3.3.3/specs
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --enable-shared --enable-threads=posix
--disable-checking --disable-libunwind-exceptions --with-system-zlib
--enable-__cxa_atexit --host=x86_64-redhat-linux
Thread model: posix
gcc version 3.3.3 20040412 (Red Hat Linux 3.3.3-7)



Output from generating ii file:
Reading specs from /usr/lib/gcc-lib/x86_64-redhat-linux/3.3.3/specs
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --enable-shared --enable-threads=posix
--disable-checking --disable-libunwind-exceptions --with-system-zlib
--enable-__cxa_atexit --host=x86_64-redhat-linux
Thread model: posix
gcc version 3.3.3 20040412 (Red Hat Linux 3.3.3-7)
 /usr/lib/gcc-lib/x86_64-redhat-linux/3.3.3/cc1plus -E -D__GNUG__=3 -quiet -v
-D__GNUC__=3 -D__GNUC_MINOR__=3 -D__GNUC_PATCHLEVEL__=3 -D_GNU_SOURCE main.cpp
-funroll-loops -O2 main.ii
ignoring nonexistent directory "/usr/x86_64-redhat-linux/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/include/c++/3.3.3
 /usr/include/c++/3.3.3/x86_64-redhat-linux
 /usr/include/c++/3.3.3/backward
 /usr/local/include
 /usr/lib/gcc-lib/x86_64-redhat-linux/3.3.3/include
 /usr/include
End of search list.
 /usr/lib/gcc-lib/x86_64-redhat-linux/3.3.3/cc1plus -fpreprocessed main.ii
-quiet -dumpbase main.cpp -auxbase main -O2 -version -funroll-loops -o main.s
GNU C++ version 3.3.3 20040412 (Red Hat Linux 3.3.3-7) (x86_64-redhat-linux)
        compiled by GNU C version 3.3.3 20040412 (Red Hat Linux 3.3.3-7).
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
 as -V -Qy -o main.o main.s
GNU assembler version 2.15.90.0.3 (x86_64-redhat-linux) using BFD version
2.15.90.0.3 20040415
 /usr/lib/gcc-lib/x86_64-redhat-linux/3.3.3/collect2 --eh-frame-hdr -m
elf_x86_64 -dynamic-linker /lib64/ld-linux-x86-64.so.2 -o gccBug
/usr/lib/gcc-lib/x86_64-redhat-linux/3.3.3/../../../../lib64/crt1.o
/usr/lib/gcc-lib/x86_64-redhat-linux/3.3.3/../../../../lib64/crti.o
/usr/lib/gcc-lib/x86_64-redhat-linux/3.3.3/crtbegin.o
-L/usr/lib/gcc-lib/x86_64-redhat-linux/3.3.3
-L/usr/lib/gcc-lib/x86_64-redhat-linux/3.3.3/../../../../lib64
-L/usr/lib/gcc-lib/x86_64-redhat-linux/3.3.3/../../.. -L/lib/../lib64
-L/usr/lib/../lib64 main.o -lstdc++ -lm -lgcc_s -lgcc -lc -lgcc_s -lgcc
/usr/lib/gcc-lib/x86_64-redhat-linux/3.3.3/crtend.o
/usr/lib/gcc-lib/x86_64-redhat-linux/3.3.3/../../../../lib64/crtn.o


I'll try and attach main.ii after submitting the bug.

Sorry if this isn't quite the right format, this is my first g++ bug.

-Dirk  (reporting from Pixar Animation Studios software development group)

-- 
           Summary: -O2 -funroll-loops causes bad loop behavior on fedora
           Product: gcc
           Version: 3.3.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: anndirkvg at gmail dot com
                CC: anndirkvg at gmail dot com,gcc-bugs at gcc dot gnu dot
                    org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18120