On Jan 4, 2007, at 13:34, Segher Boessenkool wrote:
The "signed wrap is undefined" thing doesn't fit in this category though: -- It is an important optimisation for loops with a signed induction variable;
It certainly isn't that important. Even SpecINT compiled with -O3 and top-of-tree GCC *improves* 1% by adding -fwrapv. If the compiler itself can rely on wrap-around semantics and doesn't have to worry about introducing overflows between optimization passes, it can reorder simple chains of additions. This is more important for many real-world applications than being able to perform some complex loop-interchange. Compiler developers always make the mistake of overrating their optimizations. If GCC does really poorly on a few important loops that matter, that issue is easily addressed. If GCC generates unreliable code for millions of boring lines of important real-world C, the compiler is worthless. -Geert - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/