Missed loop unwind

[David Nadlinger]

On 26 Mar 2014, at 0:25, bearophile wrote:
> A little cheap unrolling could be present in -O.

I don't think anything is likely to happen here on the LDC side, as it 
seems to be a question of tuning the LLVM optimizer.

I checked the generated IR and there aren't any obvious issues that 
would preclude optimization, and the passes selected by "opt" for the 
highest optimization level do not unroll the loop either.

David