On Friday, 6 December 2013 at 23:59:46 UTC, H. S. Teoh wrote:
On Sat, Dec 07, 2013 at 12:40:35AM +0100, bearophile wrote:
[...]
Regarding Java performance matters, from my experience another
significant source of optimization in the JavaVM that is often
overlooked is that the JavaVM is able to partially unroll even
loops
with a statically-unknown number of cycles. Currently I think
GCC/DMD/LDC2 are not able or willing to do this.
[...]
Really? I've seen gcc/gdc unroll loops with unknown number of
iterations, esp. when you're using -O3. It just unrolls into
something
like:
loop_start:
if (!loopCondition) goto end;
loopBody();
if (!loopCondition) goto end;
loopBody();
if (!loopCondition) goto end;
loopBody();
if (!loopCondition) goto end;
loopBody();
goto loop_start;
end: ...
I'm pretty sure I've seen gcc/gdc do this before.
T
LLVM is also able to generate Duff's device on the fly for loops
where it make sense.
