Re: GCC optimizes integer overflow: bug or feature?

On Saturday 23 December 2006 10:06, Rask Ingemann Lambertsen wrote: >No, because you'd read past the end of the array: > > #include > > int main (int argc, char *argv[]) > { > char *a; > if ((a == malloc (sizeof (char > { > int r; > > a[0] = 1; > r = f (a); >

Re: GCC optimizes integer overflow: bug or feature?

On Friday 22 December 2006 03:03, Paul Brook wrote: > On Friday 22 December 2006 00:58, Denis Vlasenko wrote: > > On Tuesday 19 December 2006 23:39, Denis Vlasenko wrote: > > > There are a lot of 100.00% safe optimizations which gcc > > > can do. Value range propagation

Re: GCC optimizes integer overflow: bug or feature?

On Tuesday 19 December 2006 23:39, Denis Vlasenko wrote: > There are a lot of 100.00% safe optimizations which gcc > can do. Value range propagation for bitwise operations, for one Or this, absolutely typical C code. i386 arch can compare 16 bits at a time here (luckily, no alighment worr

Re: GCC optimizes integer overflow: bug or feature?

On Tuesday 19 December 2006 22:46, Paul Brook wrote: > > Compiler can optimize it any way it wants, > > as long as result is the same as unoptimized one. > > We have an option for that. It's called -O0. > > Pretty much all optimization will change the behavior of your program. Even x*2 -> x+x? O

Re: GCC optimizes integer overflow: bug or feature?

On Tuesday 19 December 2006 20:05, Andrew Haley wrote: > Denis Vlasenko writes: > > > > I wrote this just a few days ago: > > > > do { > > int32_t v1 = v << 1; > > if (v < 0) v1 ^= mask; > >

Re: GCC optimizes integer overflow: bug or feature?

On Tuesday 19 December 2006 11:37, Paolo Bonzini wrote: > > > By the way, as I've tried to describe here: > > > > variable range tracking can result in reintroduction of > > supposedly-fixed security vulnerabilities. 8-( > > Interes