Poor compile times

[Neil Mitchell]

Hi,

Using GHC 6.4.2 on Windows and 6.4.1 on Linux, I get really poor
compile time performance for large do blocks - for example:

main = do
   return ()
   return ()
   ....
   return ()

The following are the compile times in seconds for a given number of
return () lines, GHC 6.4.1 on Linux, with a very beefy processor (my
department server) and loads of RAM.

100	1.444
200	4.054
300	7.977
400	13.967
500	21.265
600	30.71
700	43.997

For comparison on my desktop machine I get out of heap space with
268Mb of heap, in a few minutes for 700. Compared to Hugs and Yhc,
which both deal with all of these files instantly.

By splitting the 700 line do block into 7 separate do blocks, each 100
lines, I get a compile time of 8.530.

The particular reason I was running into this issue was with an auto
generated file of tests, about 360 lines of reasonably lines in a do
block, which exhausted the memory in GHCi. I have modified my test
generator to split the files into 50 line blocks.

Thanks

Neil