Bug#429657: gcc-4.1: optimisation bug abs() in nested if
Package: gcc-4.1
Version: 4.1.1-21
Severity: normal
abuse-sdl-0.7.0 has a gun aiming problem due to a mis-optimisation.
attached is a canned example.
(compile with -01 and -02 and compare the differences)
-- System Information:
Debian Release: 4.0
APT prefers stable
APT policy: (990, 'stable'), (500, 'testing')
Architecture: i386 (i686)
Shell: /bin/sh linked to /bin/bash
Kernel: Linux 2.6.18-4-686
Locale: LANG=en_NZ, LC_CTYPE=en_NZ (charmap=ISO-8859-1)
Versions of packages gcc-4.1 depends on:
ii binutils 2.17cvs20070426-8 The GNU assembler, linker and bina
ii cpp-4.1 4.1.1-21 The GNU C preprocessor
ii gcc-4.1-base 4.1.1-21 The GNU Compiler Collection (base
ii libc6 2.5-9+b1 GNU C Library: Shared libraries
ii libgcc1 1:4.1.1-21 GCC support library
ii libssp0 4.1.1-21 GCC stack smashing protection libr
Versions of packages gcc-4.1 recommends:
ii libc6-dev 2.5-9+b1 GNU C Library: Development Librari
pn libmudflap0-dev <none> (no description available)
-- no debconf information
// example of GCC 4.1 optimisation bug
// compile with -01 and -02 and compare the differences
// licence is GPL2 - based on code taken from abuse-sdl
// gcc -o bad example.c -O2 -lm
// gcc -o good example.c -O1 -lm
#include <stdio.h>
#include <math.h>
unsigned short atan_table[1662]={
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 1, 2, 3, 4, 5,
6, 6, 7, 8, 9, 9, 10, 11, 11, 12, 12, 13,
13, 14, 14, 15, 15, 16, 16, 17, 17, 18, 18, 18,
19, 19, 19, 20, 20, 20, 21, 21, 21, 22, 22, 22,
23, 23, 23, 23, 24, 24, 24, 24, 25, 25, 25, 25,
25, 26, 26, 26, 26, 26, 27, 27, 27, 27, 27, 28,
28, 28, 28, 28, 28, 28, 29, 29, 29, 29, 29, 29,
29, 30, 30, 30, 30, 30, 30, 30, 30, 31, 31, 31,
31, 31, 31, 31, 31, 31, 32, 32, 32, 32, 32, 32,
32, 32, 32, 32, 32, 33, 33, 33, 33, 33, 33, 33,
33, 33, 33, 33, 33, 33, 34, 34, 34, 34, 34, 34,
34, 34, 34, 34, 34, 34, 34, 34, 34, 35, 35, 35,
35, 35, 35, 35, 35, 35, 35, 35, 35, 35, 35, 35,
35, 35, 35, 35, 36, 36, 36, 36, 36, 36, 36, 36,
36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36,
36, 36, 36, 37, 37, 37, 37, 37, 37, 37, 37, 37,
37, 37, 37, 37, 37, 37, 37, 37, 37, 37, 37, 37,
37, 37, 37, 37, 37, 37, 37, 37, 37, 38, 38, 38,
38, 38, 38, 38, 38, 38, 38, 38, 38, 38, 38, 38,
38, 38, 38, 38, 38, 38, 38, 38, 38, 38, 38, 38,
38, 38, 38, 38, 38, 38, 38, 38, 38, 38, 38, 38,
39, 39, 39, 39, 39, 39, 39, 39, 39, 39, 39, 39,
39, 39, 39, 39, 39, 39, 39, 39, 39, 39, 39, 39,
39, 39, 39, 39, 39, 39, 39, 39, 39, 39, 39, 39,
39, 39, 39, 39, 39, 39, 39, 39, 39, 39, 39, 39,
39, 39, 39, 39, 39, 39, 39, 39, 40, 40, 40, 40,
40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40,
40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40,
40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40,
40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40,
40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40,
40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40,
40, 40, 40, 40, 40, 40, 40, 41, 41, 41, 41, 41,
41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41,
41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41,
41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41,
41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41,
41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41,
41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41,
41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41,
41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41,
41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41,
41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41,
41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41,
41, 41, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
42, 42, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
43, 43, 43, 44, 44, 44};
#define TBS (1662)
long lisp_atan2(long dy, long dx)
{
if (dy==0)
{
if (dx>0) return 0;
else return 180;
} else if (dx==0)
{
if (dy>0) return 90;
else return 270;
} else
{
if (dx>0)
{
if (dy>0)
{
if (abs(dx)>abs(dy))
{
printf("case1:");
long a=dx*29/dy;
if (a>=TBS) return 0;
else return 45-atan_table[a];
}
else
{
printf("case2:");
long a=dy*29/dx;
if (a>=TBS) return 90;
else return 45+atan_table[a];
}
} else
{
if (abs(dx)>abs(dy))
{
printf("case3:");
long a=dx*29/abs(dy);
if (a>=TBS)
return 0;
else
return 315+atan_table[a];
}
else
{
printf("case4:");
long a=abs(dy)*29/dx;
if (a>=TBS)
return 260;
else
return 315-atan_table[a];
}
}
} else
{
if (dy>0)
{
if (abs(dx)>abs(dy))
{
printf("case5:");
long a=-dx*29/dy;
if (a>=TBS)
return 135+45;
else
return 135+atan_table[a];
}
else
{
printf("case6:");
long a=dy*29/-dx;
if (a>=TBS)
return 135-45;
else
return 135-atan_table[a];
}
} else
{
if (abs(dx)>abs(dy))
{
printf("case7:");
long a=-dx*29/abs(dy);
if (a>=TBS)
return 225-45;
else return 225-atan_table[a];
}
else
{
printf("case8:");
long a=abs(dy)*29/abs(dx);
if (a>=TBS)
return 225+45;
else return 225+atan_table[a];
}
}
}
}
}
int main()
{
double angle;
for( angle=M_PI/32; angle < M_PI * 2 ; angle+=M_PI/16)
{
double s=sin(angle) , c=cos(angle);
long theta = lisp_atan2(s*100,c*100);
printf ( " a=%4.0f theta=%4d %s\n",angle/M_PI * 180,theta,
floor(0.5+angle/M_PI * 180 -theta) ? "ERROR" : "ok");
}
return 0 ;
}
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