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[Bug c++/10928] New: -O3 -freduce-all-givs creates invalid code
- From: "thor at math dot tu-berlin dot de" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 22 May 2003 11:17:25 -0000
- Subject: [Bug c++/10928] New: -O3 -freduce-all-givs creates invalid code
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=10928
Summary: -O3 -freduce-all-givs creates invalid code
Product: gcc
Version: 3.2.2
Status: UNCONFIRMED
Severity: critical
Priority: P2
Component: c++
AssignedTo: unassigned@gcc.gnu.org
ReportedBy: thor@math.tu-berlin.de
CC: gcc-bugs@gcc.gnu.org
GCC build triplet: i386-pc-linux-gnu
GCC host triplet: i386-pc-linux-gnu
GCC target triplet: i386-pc-linux-gnu
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 lines 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 */
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.
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