A bad SYB traversal eats up a lot of memory

[mpickering]

Observe this heap profile which was taken whilst loading the Cabal library into h-i-e.

You can see that when opening the LicenseId.hs module, something very bad happens. I'm not sure which IntervalMap gets so large but it's probably because a SYB traversal traverses into some generated definitions which it should avoid.

http://mpickering.github.io/cabal.hp.html

[mpickering]

I fixed it here. Any volunteers to backport to master?

mpickering@13daf07

When the .hie stuff gets merged then this will be unnecessary but for now it makes a huge difference on some modules.

[fendor]

I volunteer

[mpickering]

This patch doesn't completely solve the issue but it does get part of the way. I am still seeing big memory spikes (300mb of list cons) which must come from generating some of the other maps.

[mpickering]

Merged.