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The Bag of Holding



Release 14 imminent...

Posted by , 14 April 2013 - - - - - - · 554 views
Epoch
So I've been looking over my past notes and decided that I'm pretty happy with the state of affairs over in Epoch land. The garbage collector is running, tuned for reasonable performance, and successfully keeps the native-code realtime raytracer clamped at a decently small degree of RAM usage.

The only thing that really bugs me is that the GC has imposed a serious performance hit on the raytracer - to the tune of halving its old performance. I still need to do a full release build of the runtime to make sure I can't improve on that any, but I suspect the GC root spilling in LLVM is taking a toll on optimization passes. I might need to work on improving the front-end of the compiler to generate more optimal code in the first place so that I don't have to spill so many registers onto the stack all the time.

It'll take some analysis and study of the emitted machine code, but I'm optimistic about being able to reclaim at least some of the performance.

If nothing else, this is a good motivation for introducing a "manually reclaimed" semantic to object allocations in Epoch, so programs that don't want to incur GC overhead can bypass it entirely.



[As I wrote this, I kept alt-tabbing over to Visual Studio and mucking around. I managed to suppress garbage collection invocation for a large percentage of functions, which got me back to 21FPS - compared to 24FPS previously. I'm happy.]


Victory is mine!

Posted by , 14 April 2013 - - - - - - · 611 views
Epoch
It was an epic fight, but I finally managed to subdue the last few LLVM garbage collection bugs and get a full test suite pass.

I'm kind of tired (it's 5:30AM and I've been running all night) so I'll try to reword that a little more clearly:


Epoch is, as of right now, passing all compilation and runtime tests (all 62 of them) with full, aggressive, and accurate garbage collection, running as 100% native code.


This support includes correct handling of circular references, correct handling of algebraic sum types (aka discriminated unions), correct reclamation of resources besides pointer types (strings and buffers, in Epoch parlance), and even works across multiple-dispatch calls.

I have a feeling there's some edge cases missing from the test suite, but for now, I'm damn happy with the results of the last several days of work. I figured on GC being a nightmare (and don't get me wrong - it was) but overall the experience has been completely worth it.

I still want to ponder submitting an LLVM patch to make all this less hackish, but I also sort of don't really care because my changes are really minimal and doing them "right" would involve a lot of heavy lifting. Maybe I'll tackle it some other time.


For now, I'm going to just sit here and bask in the glow of all 62 tests passing, and maybe drool on myself a little bit as I fall asleep.





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