On Mon, 2007-11-05 at 10:20 -0800, Joe Buck wrote: > On Mon, Nov 05, 2007 at 10:15:55AM -0800, Ian Lance Taylor wrote: > > skaller <[EMAIL PROTECTED]> writes: > > > Ah, I see. So turning [strict aliasing] off isn't really all that bad > > > for optimisation. > > > > It depends on the processor. For an in-order processor with a deep > > pipeline (e.g., Itanium, but there are others), the ability to reorder > > loads and stores is very important to permit scheduling flexibility. > > Strict aliasing reportedly makes a difference for x86, but I don't > > think it makes a huge difference. > > It also depends on the input: for scientific codes that process both > integer and real data, strict aliasing could make a large difference > on any processor.
Hmm .. the problem is that C is fairly brain dead, and people regularly use casts: strict aliasing almost seems to break a fundamental feature of the language. [Hmm .. how strict is it? int* and unsigned* have to be aliased, there's even a rule that guarantees that for the common subset of values the representation is the same (that rule would be useless if you couldn't alias an int and an unsigned!) Similarly for const. pointers to pointer and intptr_t is another one used heavily] -- John Skaller <skaller at users dot sf dot net> Felix, successor to C++: http://felix.sf.net
