Optimisation possibilities: current, future and enhancements

[kinke via Digitalmars-d]

On Thursday, 25 August 2016 at 18:09:14 UTC, Cecil Ward wrote:
> On Thursday, 25 August 2016 at 18:07:14 UTC, Cecil Ward wrote:
>> On Thursday, 25 August 2016 at 17:22:27 UTC, kinke wrote:
>>> [...]
>>
>> I think that here the optimisation is only because LDC can 
>> “see” the text of the method. When expansion is not possible, 
>> that would be the real test.
>
> (Assuming LDC behaves like GDC. I'm unfamiliar with LDC, I'm 
> ashamed to admit.)

You're right. The question is whether it pays off to optimize 
heavily for externals. If you build all modules of a binary at 
once via `ldmd2 m1.d m2.d ...` or via `ldc2 -singleobj m1.d m2.d 
...`, LDC emits all the code into a single LLVM module, which can 
then be optimized very aggressively. So call graphs inside the 
binary are taken care of, so if it's a well encapsulated library 
with few (or expensive) calls to externals, it doesn't matter 
much.

druntime and Phobos are treated as externals. But Johan Engelen 
already pointed out that LDC could ship with them as LLVM bitcode 
libraries and then link them in before machine code generation...