On Wednesday, 23 May 2018 at 20:08:53 UTC, Jonathan Marler wrote:
I've recently been looking into how QEMU works and it uses
something called TCG (Tiny Code Generator). QEMU works by
taking code from another platform/cpu and translates it to TCG,
which then gets "jitted" to the instructions for the host.
From what I understand, TCG is fairly small. I think it aims
to be simple rather than highly optimized, unlike LLVM which
allows more complexity for the sake of performance.
TCG:
https://git.qemu.org/?p=qemu.git;a=blob_plain;f=tcg/README;hb=HEAD
Thank you for pointing me to this - I wasn't aware of it. I
already use something similar - a little more complex product
that supports floating points too - NanoJIT. However to my
knowledge most of these products do register allocation locally
within a basic block - and spill registers when jumping across
blocks. This basically results in unacceptable performance in any
code that has branching or loops. I could enhance NanoJIT but its
written in a way that makes changes difficult (i.e. too many low
level optimizations in the code).
It seems there is a lack of something in between LLVM and these
implementations - either you get all powerful optimizations or
you get very little ... my intention is to create something that
is small but also has at least some form of global (actually per
function) register allocator.
I thought of hacking DMD as it favours speed of compilation and
simplicity - but what I am not sure about is how easy / difficult
it would be to modify DMD (mostly remove stuff).
Regards
Dibyendu
