performance regression involving minimum
This program (taken from http://stackoverflow.com/questions/32158319/difference-in-performance-for-coin-change-between-haskell-and-c) runs about 50% slower when compiled with ghc-7.10.1 -O compared to ghc-7.8.4 -O.
import Data.Vector.Unboxed as U ((!), constructN, length)
coinchangev :: Int -> [Int] -> Int
coinchangev n cs = v ! n
where v = constructN (n+1) f
f w = case U.length w of
0 -> 0
m -> 1 + minimum [w ! x | x <- map (m-) cs, x >= 0]
main = print $ coinchangev 10000000 [1, 5, 10, 25, 100]However if I change minimum to sum, while the runtime in 7.8.4 is unchanged, the runtime in 7.10.1 drops by a factor of 5! Allocations also decrease by a large factor. So my guess is that something has gone wrong with call arity analysis for minimum (and gone very right for sum).
Trac metadata
| Trac field | Value |
|---|---|
| Version | 7.10.1 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Compiler |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | |
| Architecture |