Do more aggressive lambda lifting

[OlivierNicole]

With @vouillon we realized that the Lambda_lifting_simple pass that is performed by double translation makes some programs significantly faster. We measured roughly a 1.45 speedup on a large (proprietary) Bonsai benchmark. Presumably V8 is much faster with more toplevel functions and less nested closures.

Making this a draft PR for now because:

• It should probably be behind a flag: it makes the generated Javascript further from the source code structure;
• It theoretically results in a quadratic code size.

We probably need to do some measurements before merging. (And maybe with other engines.)

[OlivierNicole]

This seems to result in a modest speedup on average, including on partial_render_table. Is this the version of the benchmark that has a memory leak?

[vouillon]

This seems to result in a modest speedup on average, including on partial_render_table. Is this the version of the benchmark that has a memory leak?

No, I'm using a workaround.

[OlivierNicole]

Should I guard this by an --enable lambda-lift-all option?

[vouillon]

Yes, you should add a flag.

[OlivierNicole]

I re-ran the CI a few times to double-check whether this new pass increases the compilation time. The compilation time seems to oscillate around ±2 %, so I would say it’s in the noise.