Programming language benchmark

[Don]

bearophile wrote:
> Don:
> 
> Sorry for my slow answer, I was quite busy for days.
> 
> 
>> I've never heard that claim before. Do you have evidence for that?
> 
> I compare/convert code to D every day, so I am aware that D code compiled with DMD is often slower than C/C++ code compiled with GCC. Since some years I even keep a collection of snippets of slow code.
> 
> But I am also aware that the low performance has many different causes, like some missing inlining, missing loop unrolling, etc, so spotting a clear and small case of integer arithmetic code that causes a slow down, to give you evidence, is not easy. So I am sorry for my overly broad claim. 

It is true in general that DMD's inliner is not very good. I _suspect_ 
that it is the primary cause of most instances of poor integer 
performance. It's actually part of the front-end, not the back-end. So 
many of those performance problems won't apply to DMC.

It's also true that the DMD/DMC instruction scheduler doesn't schedule 
for modern processors. But last I checked, GCC wasn't really much better 
in practice (you have to be almost perfect to get a benefit from 
instruction scheduling these days, the hardware does a very good job on 
unscheduled code).

Otherwise, I don't think there's any major optimisation it misses. But 
it's quite likely that it misses several very specific minor optimizations.

>> If it is true, there's a strong possibility that it's a small, fixable issue (for example, DMD used to have terrible performance for ulong multiplication).<
> 
> You are right, the case I'm going to show is a precise problem that's fixable. 

[snip]
> -----------------------
> 
> For a more real case see:
> http://d.puremagic.com/issues/show_bug.cgi?id=5607


Thanks, that's helpful. It's a major speed difference (factor of 20, 
maybe) so it wouldn't have to occur very often to be noticeable.