Messages in this thread | | | From | Geert Bosch <> | Subject | Re: kernel + gcc 4.1 = several problems | Date | Thu, 4 Jan 2007 17:02:48 -0500 |
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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.
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