When compiled with optimization -O2 and higher, the SVN trunk version of
GCC miscompiles CLN's autoconf/intparam.c file. I cannot reproduce this
with GCC-4.1.0 (no intermediate versions tested). The consequence of
this is that the build fails very early due to #error's in the generated
intparam.h file.
I have reduced the difference to compiling the program below on
GNU/Linux x86:
$ gcc-4.3 -W -Wall -o foo foo.i
$ ./foo
/* Integers of type int have 32 bits. */
#define int_bitsize 32
$ gcc-4.3 -O2 -W -Wall -o foo foo.i
$ ./foo
#error "Integers of type int have no binary representation!!"
Now, I was about to report a compiler bug ... except that I think the
compiler is right here: integer overflow produces undefined behavior,
so I think intparam.c should be fixed instead.
With unsigned 'x', things are computed correctly. I guess you could
just always use the respective unsigned variant for computing the
bitsize of a type. (Using 'volatile int' helps with this GCC version,
but I don't think that is guaranteed by the standard.)
Next, please note that intparam.c uses exit but does not provide for a
prototype. I recommend returning from main instead.
Furthermore, please note that the CLN headers cause many "might break
strict aliasing" warnings, and a few "will break strict aliasing"
warnings. The latter are (at least) here:
src/complex/ring/cl_C_ring.cc:131
src/rational/ring/cl_RA_ring.cc:129
src/real/ring/cl_R_ring.cc:133
Hope that helps.
Cheers,
Ralf
/* foo.i */
extern int printf (__const char *__restrict __format, ...);
static int int_bitsize;
int main(void)
{
int x = 1;
int bits = 0;
while(1) {
if (x==0)
break;
x = x+x;
bits++;
if (bits==1000) {
bits = -1;
break;
}
}
int_bitsize = bits;
if (int_bitsize >= 0) {
printf("/* Integers of t%spe %s have %ld bits. */\n","y","int",(long)int_bitsize);
if (!("int"[0] == 'u')) {
printf("#define ");
printf("int");
printf("_bitsize %ld\n",(long)int_bitsize);
}
printf("\n");
} else {
printf("#error \"Integers of t%spe %s have no binary representation!!\"\n","y","int");
}
return 0;
}