Re: dmd codegen improvements

[via Digitalmars-d]

On Wednesday, 19 August 2015 at 08:22:58 UTC, Dmitry Olshansky 
wrote:
Also DMD's backend strives to stay fast _and_ generate fine 
machine code. Getting within 10% of GCC/LLVM and being fast is 
IMHO both possible and should be done.

But if iOS/OS-X and others are essentially requiring an LLVM-like 
IR as the object code format then it makes most sense to have 
LLVM as the default backend. If WebAsm et al is focusing on 
mimicing LLVM, then D's backend have to do the same. And that is 
not unlikely giving PNACL being LLVM based. Intel is also 
supportive of LLVM…

Replicating a scalar SSA like LLVM does not make a lot of sense. 
What would make a lot of sense would be to start work on an 
experimental SIMD SSA implemented in D that could leverage 
benefits for next gen x86 SIMD and make Phobos target it. That 
could attract new people to D and make D beat LLVM. You could 
even combine LLVM and your own SIMD backend (run both, then 
profile and pick the best code in production on a 
function-by-function base)

Or a high level compile-time oriented IR for D that can boost 
templates semantics and compilation speed.

And there is plenty of research papers on optimization floating 
around and implemented in GCC/LLVM/MSVC so most of R&D cost is 
payed by other backends/researchers.

I think you underestimate the amount of experimental work that 
has gone into those backends, work that ends up being trashed. 
It's not like you have to implement what LLVM has now. You have 
to implement what LLVM has and a lot of the stuff they have 
thrown out.