Re: g++ doesn't unroll a loop it should unroll

[Benoit Jacob <jacob at math dot jussieu dot fr>]

On Wed, 13 Dec 2006, Ian Lance Taylor wrote:
> When I try it, gcc does unroll the loops.  It completely unrolls the
> inner loop, but only partially unrolls the outer loop.  The reason it
> doesn't completely unroll the outer loop is simply that gcc doesn't
> attempt to completely unroll loops which contain inner loops.

OK, I don't have the skill to check the binary code. All I know is that 
with UNROLL defined it runs more than 5x faster, so there is room for 
improvement :)

> This could probably be fixed: we could probably completely unroll a
> loop if all its inner loop were completely unrolled.  I encourage you
> to file a bug report.  See http://gcc.gnu.org/bugs.html.

OK: I didn't dare decide on my own that it's a bug, but if you say so... I 
file a bug report now.

Benoit