Written: 2021-07-16 17:19 +0000
Enriching ASR nodes at compile time
This post is part of a series based around my weekly GSoC21 project check-ins.
GSoC21 W6: LFortran ASR and Values <– You are here!
- Met with Ondrej on Monday and Wednesday
- Discussed the design choices w.r.t. class hierarchies (and the lack thereof)
Note that the title is rather misleading, this post has nothing to do with the values of the LFortran project (which are by the way, fantastic), but instead is about adding more detail to the ASR nodes.
New Merge Requests
- Implement expr values for Integer Binops (1045)
- First example of using value-enriched nodes for operating during the
Coming from a “throw it in a debugger” mindset, the ASR codebase and design of LFortran can be a bit disconcerting. This is because it is by design implemented mostly in terms of C structs which are cast explicitly throughout the code. Ondrej mentioned that the overhead of having a virtual function table for each instance of
LFortran::ASR was prohibitive.
- Why bother with such speed at the cost of the C++ guarantees?
- Well for one thing, we are building a compiler, and one with an interactive kernel at that, the overhead must be kept low. No one wants to grab a coffee everytime they execute a
Pythonjupyter cell and the goal should be the same for LFortran too.
- Why not just add
- This was a bit of a head scratcher to me, especially my debugger (
lldb) offered no information on the value stored even in
Constant*structures. The real solution, which required more of an understanding of the code (offered freely and kindly by my mentor) involves casting with
Essentially, as far as the code base goes, we have a class based hierarchy, which we manipulate with
Code duplication is a non-squinter though, since only
real have similar implementations, and Ondrej pointed out that over-engineering a design simply because two
if-esle branches are similar is effectively yak shaving.
real was initially implemented as a string, which has now been replaced by Ondrej in 1066, making an extension to it trivial. I expect to focus on getting started on
functions which will have the added benefit of easily adding functionality to the backend (since the
LLVM backend can choose to simply use
value). I intend to refocus my efforts towards getting
minidftatom to work as well.