How to check fused vector function?

[Magalame]

Hi!

I'm having trouble with fused function, notably here:

mulSub :: Vector Double -> Vector Double -> Double
mulSub v1 v2 =  U.sum $ U.zipWith (*) v1 v2

v :: Vector Double
v = U.fromList [1,2,3]

mul :: Double 
mul = mulSub v v

inspect $ ('mul `hasNoType` ''Vector)

mul fails the test, although mulSub is fused. What would be a way around this issue?

[nomeata]

I would guess that because you use v twice, GHC doesn't inline it and fusion doesn't happen.

[Magalame]

It seems like this:

v :: Vector Double
v = U.fromList [1,2,3]

u :: Vector Double
u = U.fromList [1,2,3]

mulSub :: Vector Double -> Vector Double -> Double
mulSub v1 v2 =  U.sum $ U.zipWith (*) v1 v2

mul :: Double 
mul = mulSub v u

inspect $ ('mul `hasNoType` ''Vector) 

still fails. Am I missing something?

[nomeata]

Use the Core :-) It should show you what’s happening. Likely GHC has combined v and u because they are the same. Or it is reluctant to inline to-level things.

Have you tried the following?

mulUpTo :: Double -> Double -> Double
mulUpTo x1 x2 = U.sum (U.zipWith (*) (U.fromList [0 .. x1]) (U.fromList [0 .. x2])
inspect $ ('mulUpto `hasNoType` ''Vector) 

These tests work better (and are more realistic!) if you don't use constant top-level values, but rather write functions. But in the end it depends on what you actually want to test for.

Also see haskell/vector#229

[Magalame]

Unfortunately Core is a bit hard on the eye :/

A more practical example of what I'm actually trying to test is: I have a Matrix which contains the row data as a U.Vector, the number of row, and the number of column. And for example I want to write matrix multiplication such that multiply a (multiply a b) actually allocates only one matrix, the one containing the end result

[Magalame]

So far I've been using weigh to measure allocation, and it turned out to be successful in most cases, but there seem to be some cases where it's not : fpco/weigh#37