On 09/23/2011 11:16 AM, Ian Lance Taylor wrote:
David Brown<david@xxxxxxxxxxxxxxx> writes:It's the same for if (x == 1) { a=b; c=d; e=f; foo(); } else if (x == 2) { a=b; c=d; e=f; foo(); } GCC don't factor out the common partYou are right - which is odd, since there is no reason why it could not (unlike the original case where there is no "else"). Surely this would count as a significant missed optimisation, especially for big switch() code.I don't think it is a significant missed optimization, as people rarely write code like that. They normally write if (x == 1 || x == 2) { a=b; c=d; e=f; foo(); } The proposed optimization only applies when somebody has laboriously written out the exact same sequence of code twice. I'm not opposed to such an optimization if it works reliably and is not too expensive. I just don't think it will make much difference on ordinary code. Ian
People don't write that kind of code (we hope), but machine generated code can have all kinds of weirdness. Still not a big deal, but it might be more common than you think.
--jeff
