Synthesis time is linear in the size of Index

[rowanG077]

The following:

foo
  :: forall
    (deadlinePicoSeconds :: Nat)
    (dom :: Domain)
   . (HiddenClockResetEnable dom)
  => (KnownNat (DomainPeriod dom))
  => (1 <= DomainPeriod dom)
  => (KnownNat deadlinePicoSeconds)
  => 1 <= DivRU deadlinePicoSeconds (DomainPeriod dom)
  => Signal dom Bool
  -> Signal dom Bool
foo activity =
  let initCnt = (0 :: Index (DivRU deadlinePicoSeconds (DomainPeriod dom)))
      cntr = register initCnt $ mux activity (pure 0) (satSucc SatWrap <$> cntr)
  in register False $ cntr .==. (pure maxBound)

topEntity = exposeClockResetEnable (foo @5_000_000_000_000 @System)

Takes a whopping 25 seconds to synthesize on my machine using GHC 9.6.6 and clash 1.8.2. As part of a larger circuit it never finished synthesizing.

[rowanG077]

Normalization is not to blame, it's stuck at the Clash: Compiling ... stage. It's a regression as this exact same component had no trouble in clash 1.6.4 with GHC 9.0.2.

deadlinePicoSeconds influences how long it takes. It looks to be linear, a doubling of deadlinePicoSeconds doubles the time to synthesize.

[christiaanb]

Does compiling the file with regular GHC to an .o object file also take longer when you use GHC 9.6.6 vs 9.0.2?

[rowanG077]

Doesn't seem to be different. How large deadlinePicoSeconds is also doesn't factor into it. With both it's around 0.150 seconds.

Just to be clear. It takes so long after clash normalization has taken place. I see now that my original comment was ambiguous. This is the output:

GHC: Setting up GHC took: 0.040s
GHC: Compiling and loading modules took: 0.078s
Clash: Parsing and compiling primitives took 0.133s
GHC+Clash: Loading modules cumulatively took 0.497s
Clash: Compiling TopEntity.topEntity
Clash: Normalization took 0.012s
Clash: Netlist generation took 0.000s
-- Here it takes a ages
Clash: Compiling TopEntity.topEntity took 23.663s
Clash: Total compilation took 24.161s

[rowanG077]

It's actually just literally how large the n is for an Index...

topEntity :: Index 1_000_000_000
topEntity = 0

Takes 5 seconds on my machine.

topEntity :: Index 5_000_000_000
topEntity = 0

Takes approx 27 seconds. Amazing.

[christiaanb]

Probably a duplicate of #2813, in which case it will be fixed by #2816

[rowanG077]

Yes this seems to be the case. I will close this.