Clash doesn't respect NOINLINE on polyvariadic functions with "extra" arguments

[martijnbastiaan]

Just going by the title I'm tempted to mark this as easy ;-).

Reproducer

import Data.String.Interpolate (__i)
import Clash.Explicit.Prelude
import Clash.Annotations.Primitive

class X a where
  x :: a

instance X (Signal System Int) where
  x = pure 3

instance X a => X (Signal System Int -> a) where
  x !_i = x

bb :: X a => Int -> a
bb !_ = x
{-# NOINLINE bb #-}
{-# ANN bb hasBlackBox #-}
{-# ANN bb (
  let bbName = show 'bb
  in InlineYamlPrimitive [minBound..] [__i|
    BlackBox:
      name: "#{bbName}"
      kind: Expression
      template: "~ARG[2]"
|]) #-}

bbWrapper :: X a => Int -> a
bbWrapper i = bb i
{-# NOINLINE bbWrapper #-}

topEntity :: Int -> Signal System Int -> Signal System Int
topEntity i0 i1 = bbWrapper i0 i1

Gives:

$ ls vhdl/Main.topEntity/
clash-manifest.json  Main_topEntity_types.vhdl  topEntity.vhdl

bbWrapper did not get its own file. DebugApplied log.

Removing the "extra" argument

import Data.String.Interpolate (__i)
import Clash.Explicit.Prelude
import Clash.Annotations.Primitive

class X a where
  x :: a

instance X (Signal System Int) where
  x = pure 3

instance X a => X (Signal System Int -> a) where
  x !_i = x

bb :: X a => a
bb = x
{-# NOINLINE bb #-}
{-# ANN bb hasBlackBox #-}
{-# ANN bb (
  let bbName = show 'bb
  in InlineYamlPrimitive [minBound..] [__i|
    BlackBox:
      name: "#{bbName}"
      kind: Expression
      template: "~ARG[1]"
|]) #-}

bbWrapper :: X a => a
bbWrapper = bb
{-# NOINLINE bbWrapper #-}

topEntity :: Signal System Int -> Signal System Int
topEntity i1 = bbWrapper i1

Gives:

$ ls vhdl/Main.topEntity/
bb1.vhdl  clash-manifest.json  Main_topEntity_types.vhdl  topEntity.vhdl

bbWrapper did get its own file. DebugApplied log.

Removing the polyvariadic aspect

import Data.String.Interpolate (__i)
import Clash.Explicit.Prelude
import Clash.Annotations.Primitive

bb :: Int -> Signal System Int -> Signal System Int
bb !_ !_ = pure 3
{-# NOINLINE bb #-}
{-# ANN bb hasBlackBox #-}
{-# ANN bb (
  let bbName = show 'bb
  in InlineYamlPrimitive [minBound..] [__i|
    BlackBox:
      name: "#{bbName}"
      kind: Expression
      template: "~ARG[1]"
|]) #-}

bbWrapper :: Int -> Signal System Int -> Signal System Int
bbWrapper i = bb i
{-# NOINLINE bbWrapper #-}

topEntity :: Int -> Signal System Int -> Signal System Int
topEntity i0 i1 = bbWrapper i0 i1

Gives:

$ ls vhdl/Main.topEntity/
bbWrapper.vhdl  clash-manifest.json  Main_topEntity_types.vhdl  topEntity.vhdl

bbWrapper did get its own file. DebugApplied log.

[christiaanb]

Easy when you know where to look:

clash-compiler/clash-lib/src/Clash/Normalize/Transformations/Specialize.hs

Line 443 in 26a4bc2

return (g,maybe inl bindingSpec gTmM, maybe specArg (Left . (`mkApps` gArgs) . bindingTerm) gTmM)

This doesn’t deal well with the case where the argument we specialize on lacks a NOINLINE spec; in two ways:

1. It doesn’t preserve the NOINLINE spec of the function being specialized
2. It doesn’t pick the name of the function being specialized when it has a NOINLINE, while the argument being specialized on does not

[christiaanb]

We've released v1.8.0, which includes a fix for this issue.