Missed opportunity for let-no-esape

readArray/writeArray call GHC.Arr.index, which seems inexplicably slow for 2d arrays. inexplicably, because simply copying the default implementation of index from GHC.Arr into the local module can speed things up considerably.

originally raised in this thread: http://www.haskell.org/pipermail/haskell-cafe/2007-March/023394.html

shortened example or matrix/vector-multiplication attached. comment out the first line of myindex to use the local copy. this results in a speedup from 20s to 13s (time ./Index 100000) on my system, not to mention the difference in space usage (a factor of 1000 in allocation, according to +RTS -sstderr..).

Trac metadata

Trac field	Value
Version	6.6
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system	Unknown
Architecture	Unknown