[Haskell-cafe] GHC optimizer consuming memory

[mike frai]

Hi,

While using Michael Snoyman's persistent package, I discovered that a
certain bit of code generated from it made the GHC optimizer consume a
ridiculous amount of memory (ie. only when using the "-O" flag). I
know very little about the GHC compiler and Michael Snoyman
recommended I post my findings here to see what others thought.

I've done what I can to extract the code generated from the persistent
package and simplify/strip it down to the bare minimum of what's
needed to cause this issue. You can find it in the attachment
FromTest.hs. From my testing, removing five fields from Rec and the
equivalent from the fromValue function - the memory consumption drops
dramatically and I am able to compile.

For your convenience, I've also attached FromTest.out, which is the
output I get when compiling FromTest.hs using "ghc -O -v3". This is
just the output up to the point it starts consuming a lot of memory.
I've never seen anything after this point because my system slows down
to a crawl (due to swapping) and I end up killing the process.

Please let me know what you guys think or if you need any more
information about this. Thanks,
- Mike
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