-O3 -freduce-all-givs creates invalid code

[Thomas Richter <thor@math.TU-Berlin.DE>]

>Submitter-Id:  net
>Originator:    Thomas Richter
>Organization:
>Confidential:  no
>Synopsis:      -O3 -freduce-all-givs creates invalid code
>Severity:      serious
>Priority:      medium
>Category:      c++
>Class:         wrong-code
>Release:       3.2.3 (Debian testing/unstable)
>Environment:
System: Linux skywise 2.4.20 #7 Thu May 15 19:53:29 CEST 2003 i686 unknown
Architecture: i686


host: i386-pc-linux-gnu
build: i386-pc-linux-gnu
target: i386-pc-linux-gnu
configured with: ../src/configure -v 
--enable-languages=c,c++,java,f77,objc,ada --prefix=/usr 
--mandir=/usr/share/man --inf
odir=/usr/share/info --with-gxx-include-dir=/usr/include/c++/3.2 
--enable-shared --with-system-zlib --enable-nls --without-
included-gettext --enable-__cxa_atexit --enable-clocale=gnu 
--enable-java-gc=boehm --enable-objc-gc i386-linux
>Description:
        The compiler generates wrong code and hence a segfault if the 
following code gets compiled
        with the options -O3 -freduce-all-givs:

/* snip: Save the following lines as buggy.hpp */
class GTIA {
public:
  struct PMObject {
    char Graphics;
    PMObject(void)
    { }
    void Render(void *target);
  }     Player[4],Missile[4];
  char GractlShadow;
  void TriggerGTIAScanline(char *playfield,int pmdisplace,int 
width,bool fiddling);
};
/* snip: save the following lnes as buggy.cpp */

#include "buggy.hpp"

int main(int,char **)
{
  class GTIA gtia;
  gtia.GractlShadow = 127;
  gtia.TriggerGTIAScanline(0,0,0,false);

  return 0;
}

void GTIA::PMObject::Render(void *)
{
  return;
}

void GTIA::TriggerGTIAScanline(char *,int,int,bool)
{
  struct PMObject *player,*missile;
  int i;

  if (GractlShadow & 0x01) {
    int mask,dmask,shift;
    for (i = 0,mask = 0x01,dmask = 0x03,shift = 6,missile = Missile;i < 
4;i++) {
      missile->Graphics = 0;
      missile++;
      mask    <<= 1;
      dmask   <<= 2;
      shift    -= 2;
    }
  for(i=0,player=Player;i<4;i++) {
    player->Render(0);
    player++;
  }
  for(i=0,missile=Missile;i<4;i++) {
    missile->Render(0);
    missile++;
  }
}
/* snip */
>How-To-Repeat:
With the above header and .cpp file, run the compiler as follows:

$ g++-3.2 -O3 -freduce-all-givs buggy.cpp

Then run the resulting binary:

$ a.out

Result is a segfault. The problem does not occur if "-freduce-all-givs" 
is dropped,
or the 2.95.xx release of the compiler is used.
>Fix:
        Avoid "-freduce-all-givs"