Hi,
This simple program:
#include <stdio.h>
#include <limits.h>
int main(void) {
volatile int i = INT_MAX + 1u;
puts("so far so good");
i = i * -1u;
puts("never reached with 4.1");
return 0;
}
when compiled with -ftrapv (using GCC 4.1.1) aborts during the
i = i * -1u;
Compiling with -ftrapv with older GCC versions (3.3.6, 3.4.6 and 4.0.3)
gets both lines printed. If I understand correctly, both the addition
and the multiplication are done unsigned and so shouldn't cause the
program to abort, and the conversion to int by storing it in i isn't
supposed to cause the program to abort either (and doesn't the first
time), so am I missing something obvious, or might this be a bug?
Something I noticed while writing this mail: probably also interesting
is that if I don't declare i as volatile, and return !i to prevent it
from being optimised away, GCC 4.1.1 ICEs if compiled with -O[23s],
aborts (as with volatile) with -O0, but behaves correctly with -O1. I
can't imagine an ICE not being a bug, but is it the same problem as the
first one, or does it just happen to show up with similar code?
