Templates are slow.

[Johan Engelen via Digitalmars-d]

On Thursday, 8 September 2016 at 19:17:42 UTC, Lewis wrote:
>
> Am I crazy in wondering about caching template instantiations? 
> I understand that an incremental build would kind of accomplish 
> this goal, but that comes with its own set of problems.

Not as good as what you propose, but: LDC 1.1.0 can do _codegen_ 
caching which I guess is some intermediate form of incremental 
building.

My testcase is a unittest piece from Weka.io that instantiates, 
oh, I don't remember exactly, 100.000+ templates. It takes about 
65 seconds to compile. With codegen caching, the re(!)compile 
time on cache-hit is reduced to 39s. Note that the front-end 
still instantiates all those templates, but LDC's codegen at -O0 
is not as fast as DMD's (calculating the hash also takes time and 
could be optimized further).

In summary, for LDC -O3 builds, you can expect a large speed 
boost by just adding `-ir2obj-cache=<cache dir>` to the 
commandline (LDC >= 1.1.0-alpha1).

-Johan