Compiler performance bug: large "do" expression

From Neil Mitchell:

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

Trac metadata

Trac field	Value
Version	6.4.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system	Unknown
Architecture	Unknown

changed weight to 5

added Tbug Trac import labels

changed milestone to %6.6.1

closed

Excellent point. Fixed in the HEAD.

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedFixed

mentioned in commit c186ff3a

Trac metadata

Trac field	Value
Architecture	Unknown → Unknown/Multiple

Trac metadata

Trac field	Value
Operating system	Unknown → Unknown/Multiple

mentioned in issue #3424 (closed)

added Pnormal label