Question: What is the difference between the schism-stageN.wasm about schism HOT 4 CLOSED

This comes out of the self-hosted nature of Schism.

Stage0 is also called the snapshot. We keep it checked into the repo, but it doesn't have to be (and probably shouldn't be). It's a working version of the compiler in binary form (Wasm, in this case), that is used to jump start the rest of the compilation process. Note that you can also use bootstrap-from-guile.sh to regenerate this.

Stage1 is Schism compiled by the stage0 compiler. I'll say more about this in a second.

Stage2 is Schism compiled by the stage1 compiler. From time to time, we "update the snapshot," which basically means we rename schism-stage2.wasm to schism-stage0.wasm, so the stage 2 compiler becomes the new snapshot.

There's also a stage3 compiler, which is Schism compiled by the stage2 compiler. This should be exactly the same as the stage2 compiler, so we don't generally build the stage3 compiler. From time to time we do though to make sure stage 2 and 3 actually are identical.

The distinction comes up when adding optimizations or features to the compiler.

If you add a new optimization, you would write it into Schism, at compiler.ss. You then compile this into the stage1 compiler using the stage0 compiler. The stage1 compiler now knows how to do your optimization, but it has not itself been optimized. Stage2 would then both be able to perform the optimization, and has also had the optimization applied. If you look at compiler performance in this case, it's pretty common for stage1 to be slower than stage0, because it has to do additional work to perform the optimization, But then, stage2 is often faster than both stage0 and stage1 because it has been optimized by the new optimization.

When adding a new feature, such as when I was adding support for lambdas, you have to implement the feature without using it in the compiler. Once you've implemented it, stage1 can compile code with the new feature. So, if you have test cases that use the feature, these will start to pass. However, you can't use the new feature in the compiler until you take a new snapshot, so that stage0 will support the feature as well.

I hope this helps!

from schism.

Thanks a lot, it helps a lot.

from schism.

Feel free to close the issue or copy / paste your explanation in the doc folder ;)

from schism.

I added a cleaned up version of my explanation above to the docs/ folder, so I'll go ahead and close this issue.

from schism.