On Thu, Nov 12, 2009 at 08:26:13AM -0500, Stuart Barkley wrote: > <theory> > If the fortran code is doing virtual subscripts (e.g. array2(i*2 + j)) > it would likely generate about the same code as the compiler would > generate for 2 dimensions. In theory, the compiler can generate > better subscript computation but I suspect in most reasonable (or > simple testing) cases the actual code size difference is a wash. > </theory>
Putting my "I used to work near a compiler group" hat on, I suspect a good compiler guy would tell you that they've worked hard to make sure both methods generate the same code for address computation. Strength reduction and the like are elementary optimizations these days. However, there is an issue that the compiler may have a better idea of the dimensions of the 2-dimensional array at compile time, leading to better optimization. That has nothing to do with the address computations, but everything to do with loop fusion, splitting, unrolling, pipelining, SIMDizing, cache effects, etc. -- greg _______________________________________________ Beowulf mailing list, Beowulf@beowulf.org sponsored by Penguin Computing To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
