On Wednesday, 15 January 2014 at 02:22:22 UTC, David Nadlinger
wrote:
On Wednesday, 15 January 2014 at 01:42:07 UTC, Manu wrote:
Right, thanks for that.
I'm quite surprised by how bad that turned out actually, and
with LDC,
which is usually the best at optimising that sort of thing.
Need to do some intensive experimentation... but this is a bit
concerning.
GCC might do some loop merging, I haven't checked. It's just
that this pattern doesn't tend to appear too much in
traditional C/C++ code (after all, who splits up their loops
into two parts just for fun?), so it could be that the LLVM
people just never really bothered to write a pass to merge
single loops that have been split (as opposed to classical loop
fusion, where the loop ranges are the same, but the operations
performed/target data different).
Maybe it would be possible to implement something like this
fairly easily using the existing LLVM loop analyses though.
David
Actually this is a useful optimization technique when you need to
skip a lot of objects that way. See
http://www.onversity.com/load/d-loop.pdf
