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Callgraph after normalization contains recursive components #2839

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DigitalBrains1 opened this issue Nov 3, 2024 · 2 comments · Fixed by #2844
Closed

Callgraph after normalization contains recursive components #2839

DigitalBrains1 opened this issue Nov 3, 2024 · 2 comments · Fixed by #2844

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@DigitalBrains1
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DigitalBrains1 commented Nov 3, 2024 •
edited
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Probably related to my reproducers in #2570.

Using GHC 9.8.2, the following code:

module Rec where

import Clash.Explicit.Prelude
import Clash.Explicit.Testbench

topEntity ::
  Signal System (Unsigned 8)
topEntity = register clk noReset enableGen 100 0
 where
  cntr = register clk noReset enableGen (0 :: Unsigned 8) 0
  done = (== 100) <$> cntr
  clk = tbClockGen $ not <$> done

gives

Clash.Normalize(187): Expr belonging to bndr: topEntity_clk (:: Clock "System") remains recursive after normalization:
letrec
  v1 :: Unsigned 8
  = register# @"System" @(Unsigned 8) (removedArg @(KnownDomain "System")) (removedArg @(NFDataX (Unsigned 8))) topEntity_clk[GlobalId]
      (unsafeToReset @"System" (removedArg @(KnownDomain "System")) False)
      (Enable @"System" True)
      (fromInteger# @8 8 0)
      (fromInteger# @8 8 0)
      (fromInteger# @8 8 0)
  result :: Clock "System"
  = tbClockGen @"System" (removedArg @(KnownDomain "System")) (not (eq# @8 v1[LocalId] (fromInteger# @8 8 100)))
in result[LocalId]
Full output 
Clash: Compiling Rec.topEntity
Clash.Normalize(187): Expr belonging to bndr: topEntity_clk (:: Clock "System") remains recursive after normalization:
letrec
  v1 :: Unsigned 8
  = register# @"System" @(Unsigned 8) (removedArg @(KnownDomain "System")) (removedArg @(NFDataX (Unsigned 8))) topEntity_clk[GlobalId]
      (unsafeToReset @"System" (removedArg @(KnownDomain "System")) False)
      (Enable @"System" True)
      (fromInteger# @8 8 0)
      (fromInteger# @8 8 0)
      (fromInteger# @8 8 0)
  result :: Clock "System"
  = tbClockGen @"System" (removedArg @(KnownDomain "System")) (not (eq# @8 v1[LocalId] (fromInteger# @8 8 100)))
in result[LocalId]

<no location info>: error:
    Clash error call:
    Clash.Normalize(230): Callgraph after normalization contains following recursive components: Rec.topEntity_clk[8214565720323804629] :: Clash.Signal.Internal.Clock[8214565720323789999]
                                                "System"letrec
                                                          v1[4755801206503243778] :: Clash.Sized.Internal.Unsigned.Unsigned[8214565720323790099]
                                                                                       8
                                                          = Clash.Signal.Internal.register#
                                                              @"System"
                                                              @(Clash.Sized.Internal.Unsigned.Unsigned[8214565720323790099]
                                                                  8)
                                                              (Clash.Normalize.Primitives.removedArg
                                                                 @(Clash.Signal.Internal.KnownDomain[8214565720323790028]
                                                                     "System"))
                                                              (Clash.Normalize.Primitives.removedArg
                                                                 @(Clash.XException.NFDataX[8214565720323790111]
                                                                     (Clash.Sized.Internal.Unsigned.Unsigned[8214565720323790099]
                                                                        8)))
                                                              Rec.topEntity_clk[8214565720323804629][GlobalId]
                                                              (Clash.Signal.Internal.unsafeToReset
                                                                 @"System"
                                                                 (Clash.Normalize.Primitives.removedArg
                                                                    @(Clash.Signal.Internal.KnownDomain[8214565720323790028]
                                                                        "System"))
                                                                 <prefixName>"noReset2"
                                                                 GHC.Types.False[3891110078048108556])
                                                              <prefixName>"enableGen"
                                                              (Clash.Signal.Internal.Enable[8214565720323790215]
                                                                 @"System"
                                                                 <prefixName>"clockGen1"
                                                                 GHC.Types.True[3891110078048108586])
                                                              (Clash.Sized.Internal.Unsigned.fromInteger#
                                                                 @8
                                                                 8
                                                                 0)
                                                              (Clash.Sized.Internal.Unsigned.fromInteger#
                                                                 @8
                                                                 8
                                                                 0)
                                                              (Clash.Sized.Internal.Unsigned.fromInteger#
                                                                 @8
                                                                 8
                                                                 0)
                                                          result[4869] :: Clash.Signal.Internal.Clock[8214565720323789999]
                                                                            "System"
                                                          = Clash.Signal.Internal.tbClockGen
                                                              @"System"
                                                              (Clash.Normalize.Primitives.removedArg
                                                                 @(Clash.Signal.Internal.KnownDomain[8214565720323790028]
                                                                     "System"))
                                                              (<prefixName>"not"
                                                                 GHC.Classes.not
                                                                 (Clash.Sized.Internal.Unsigned.eq#
                                                                    @8
                                                                    v1[4755801206503243778][LocalId]
                                                                    (Clash.Sized.Internal.Unsigned.fromInteger#
                                                                       @8
                                                                       8
                                                                       100)))
    in result[4869][LocalId]
    CallStack (from HasCallStack):
      error, called at src/Clash/Normalize.hs:230:10 in clash-lib-1.9.0-inplace:Clash.Normalize
@christiaanb
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After GHC desugaring we get:

topEntity
  = let { $dKnownNat_a4TQ = (NS 8##) `cast` <Co:7> :: ... } in
    let { $dNum_a4T6 = $fNumUnsigned $dKnownNat_a4TQ } in
    letrec {
      clk_a4QC
        = $ (tbClockGen $fKnownDomain"System")
            (<$>
               $fFunctorSignal
               not
               (<$>
                  $fFunctorSignal
                  (let { v_B1 = == $fEqUnsigned } in
                   let { v_B3 = fromInteger $dNum_a4T6 (IS 100#) } in
                   \ v_B2 -> v_B1 v_B2 v_B3)
                  (register
                     $fKnownDomain"System"
                     $fNFDataXUnsigned
                     clk_a4QC
                     (noReset $fKnownDomain"System")
                     enableGen
                     (fromInteger $dNum_a4T6 (IS 0#))
                     (fromInteger ($fNumSignal $dNum_a4T6) (IS 0#))))); } in
    register
      $fKnownDomain"System"
      $fNFDataXUnsigned
      clk_a4QC
      (noReset $fKnownDomain"System")
      enableGen
      (fromInteger $dNum_a4Y0 (IS 100#))
      (fromInteger ($fNumSignal $dNum_a4Y0) (IS 0#))

but then after GHC optimisation we get:

Rec {
topEntity_clk
  = tbClockGen
      $fKnownDomain"System"
      (mapSignal#
         not
         (mapSignal#
            (let {
               v_B3
                 = fromInteger# (topEntity2 `cast` <Co:7> :: ...) (IS 100#) } in
             \ v1_B2 -> eq# v1_B2 v_B3)
            (let {
               initial_X1
                 = fromInteger# (topEntity2 `cast` <Co:7> :: ...) (IS 0#) } in
             register#
               $fKnownDomain"System"
               $fNFDataXUnsigned
               topEntity_clk
               (unsafeToReset $fKnownDomain"System" noReset2)
               enableGen
               initial_X1
               initial_X1
               (signal#
                  (fromInteger# (topEntity2 `cast` <Co:7> :: ...) (IS 0#))))))
end Rec }

topEntity_initial
  = fromInteger# (topEntity1 `cast` <Co:7> :: ...) (IS 100#)

topEntity
  = register#
      $fKnownDomain"System"
      $fNFDataXUnsigned
      topEntity_clk
      (unsafeToReset $fKnownDomain"System" noReset2)
      enableGen
      topEntity_initial
      topEntity_initial
      (signal# (fromInteger# (topEntity1 `cast` <Co:7> :: ...) (IS 0#)))

The best that Clash can currently do is:

Rec.topEntity_clk[8214565720323804625] after normalization:

letrec
  v1[4755801206503243778] :: Clash.Sized.Internal.Unsigned.Unsigned[8214565720323790099]
                               8
  = Clash.Signal.Internal.register# @"System"
      @(Clash.Sized.Internal.Unsigned.Unsigned[8214565720323790099]
          8)
      (Clash.Normalize.Primitives.removedArg
         @(Clash.Signal.Internal.KnownDomain[8214565720323790028]
             "System"))
      (Clash.Normalize.Primitives.removedArg
         @(Clash.XException.NFDataX[8214565720323790111]
             (Clash.Sized.Internal.Unsigned.Unsigned[8214565720323790099]
                8)))
      Rec.topEntity_clk[8214565720323804625][GlobalId]
      c$v1_app_arg[4865][LocalId]
      <prefixName>"enableGen"
      (Clash.Signal.Internal.Enable[8214565720323790215]
         @"System"
         <prefixName>"clockGen1"
         GHC.Types.True[3891110078048108586])
      (Clash.Sized.Internal.Unsigned.fromInteger# @8 8
         0)
      (Clash.Sized.Internal.Unsigned.fromInteger# @8 8
         0)
      (Clash.Sized.Internal.Unsigned.fromInteger# @8 8
         0)
  c$v1_app_arg[4865] :: Clash.Signal.Internal.Reset[8214565720323790036]
                          "System"
  = Clash.Signal.Internal.unsafeToReset @"System"
      (Clash.Normalize.Primitives.removedArg
         @(Clash.Signal.Internal.KnownDomain[8214565720323790028]
             "System"))
      <prefixName>"noReset2"
      GHC.Types.False[3891110078048108556]
  result[4868] :: Clash.Signal.Internal.Clock[8214565720323789999]
                    "System"
  = Clash.Signal.Internal.tbClockGen @"System"
      (Clash.Normalize.Primitives.removedArg
         @(Clash.Signal.Internal.KnownDomain[8214565720323790028]
             "System"))
      (<prefixName>"not"
         GHC.Classes.not
         (Clash.Sized.Internal.Unsigned.eq# @8
            v1[4755801206503243778][LocalId]
            (Clash.Sized.Internal.Unsigned.fromInteger# @8 8
               100)))
in result[4868][LocalId]

Where the recToLetrec transformation

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

Lines 266 to 270 in 10f26ff

-- | Turn a normalized recursive function, where the recursive calls only pass
-- along the unchanged original arguments, into let-recursive function. This
-- means that all recursive calls are replaced by the same variable reference as
-- found in the body of the top-level let-expression.
recToLetRec :: HasCallStack => NormRewrite
will only replace the recursive calls when they occur in the function position (and only if they are let-bound). I guess the way to go is to further special-case the ANF transformation to also let-bind global self-recursive calls. This is probably fine as the ANF transformation already has a couple of special cases anyhow.

@christiaanb
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Actually, it seems ANF already does the right thing:

ANF {39}
Changes when applying rewrite to:
Clash.Signal.Internal.tbClockGen @"System"
  (Clash.Normalize.Primitives.removedArg
     @(Clash.Signal.Internal.KnownDomain[8214565720323790028]
         "System"))
  (<prefixName>"not"
     GHC.Classes.not
     (letrec
        v1[4755801206503243778] :: Clash.Sized.Internal.Unsigned.Unsigned[8214565720323790099]
                                     8
        = Clash.Signal.Internal.register# @"System"
            @(Clash.Sized.Internal.Unsigned.Unsigned[8214565720323790099]
                8)
            (Clash.Normalize.Primitives.removedArg
               @(Clash.Signal.Internal.KnownDomain[8214565720323790028]
                   "System"))
            (Clash.Normalize.Primitives.removedArg
               @(Clash.XException.NFDataX[8214565720323790111]
                   (Clash.Sized.Internal.Unsigned.Unsigned[8214565720323790099]
                      8)))
            Rec.topEntity_clk[8214565720323804625][GlobalId]
            (Clash.Signal.Internal.unsafeToReset @"System"
               (Clash.Normalize.Primitives.removedArg
                  @(Clash.Signal.Internal.KnownDomain[8214565720323790028]
                      "System"))
               <prefixName>"noReset2"
               GHC.Types.False[3891110078048108556])
            <prefixName>"enableGen"
            (Clash.Signal.Internal.Enable[8214565720323790215]
               @"System"
               <prefixName>"clockGen1"
               GHC.Types.True[3891110078048108586])
            (Clash.Sized.Internal.Unsigned.fromInteger# @8
               (GHC.Num.Natural.NS 8##)
               (GHC.Num.Integer.IS 0#))
            (Clash.Sized.Internal.Unsigned.fromInteger# @8
               (GHC.Num.Natural.NS 8##)
               (GHC.Num.Integer.IS 0#))
            (Clash.Sized.Internal.Unsigned.fromInteger# @8
               (GHC.Num.Natural.NS 8##)
               (GHC.Num.Integer.IS 0#))
     in Clash.Sized.Internal.Unsigned.eq# @8
          v1[4755801206503243778][LocalId]
          (Clash.Sized.Internal.Unsigned.fromInteger# @8
             (GHC.Num.Natural.NS 8##)
             (GHC.Num.Integer.IS 100#))))
Result:
letrec
  c$app_arg[4867] :: GHC.Types.Bool[3674937295934324744]
  = <prefixName>"not"
      GHC.Classes.not
      result[4866][LocalId]
  v1[4755801206503243778] :: Clash.Sized.Internal.Unsigned.Unsigned[8214565720323790099]
                               8
  = Clash.Signal.Internal.register# @"System"
      @(Clash.Sized.Internal.Unsigned.Unsigned[8214565720323790099]
          8)
      (Clash.Normalize.Primitives.removedArg
         @(Clash.Signal.Internal.KnownDomain[8214565720323790028]
             "System"))
      (Clash.Normalize.Primitives.removedArg
         @(Clash.XException.NFDataX[8214565720323790111]
             (Clash.Sized.Internal.Unsigned.Unsigned[8214565720323790099]
                8)))
      c$v1_app_arg[4864][LocalId]
      c$v1_app_arg[4865][LocalId]
      <prefixName>"enableGen"
      (Clash.Signal.Internal.Enable[8214565720323790215]
         @"System"
         <prefixName>"clockGen1"
         GHC.Types.True[3891110078048108586])
      (Clash.Sized.Internal.Unsigned.fromInteger# @8
         (GHC.Num.Natural.NS 8##)
         (GHC.Num.Integer.IS 0#))
      (Clash.Sized.Internal.Unsigned.fromInteger# @8
         (GHC.Num.Natural.NS 8##)
         (GHC.Num.Integer.IS 0#))
      (Clash.Sized.Internal.Unsigned.fromInteger# @8
         (GHC.Num.Natural.NS 8##)
         (GHC.Num.Integer.IS 0#))
  result[4866] :: GHC.Types.Bool[3674937295934324744]
  = Clash.Sized.Internal.Unsigned.eq# @8
      v1[4755801206503243778][LocalId]
      (Clash.Sized.Internal.Unsigned.fromInteger# @8
         (GHC.Num.Natural.NS 8##)
         (GHC.Num.Integer.IS 100#))
  c$v1_app_arg[4865] :: Clash.Signal.Internal.Reset[8214565720323790036]
                          "System"
  = Clash.Signal.Internal.unsafeToReset @"System"
      (Clash.Normalize.Primitives.removedArg
         @(Clash.Signal.Internal.KnownDomain[8214565720323790028]
             "System"))
      <prefixName>"noReset2"
      GHC.Types.False[3891110078048108556]
  c$v1_app_arg[4864] :: Clash.Signal.Internal.Clock[8214565720323789999]
                          "System"
  = Rec.topEntity_clk[8214565720323804625][GlobalId]
in Clash.Signal.Internal.tbClockGen @"System"
     (Clash.Normalize.Primitives.removedArg
        @(Clash.Signal.Internal.KnownDomain[8214565720323790028]
            "System"))
     c$app_arg[4867][LocalId]

It's the subsequent bindConstantVar transformation that "messes it up":

bindConstantVar {40}
Changes when applying rewrite to:
letrec
  c$app_arg[4867] :: GHC.Types.Bool[3674937295934324744]
  = <prefixName>"not"
      GHC.Classes.not
      result[4866][LocalId]
  v1[4755801206503243778] :: Clash.Sized.Internal.Unsigned.Unsigned[8214565720323790099]
                               8
  = Clash.Signal.Internal.register# @"System"
      @(Clash.Sized.Internal.Unsigned.Unsigned[8214565720323790099]
          8)
      (Clash.Normalize.Primitives.removedArg
         @(Clash.Signal.Internal.KnownDomain[8214565720323790028]
             "System"))
      (Clash.Normalize.Primitives.removedArg
         @(Clash.XException.NFDataX[8214565720323790111]
             (Clash.Sized.Internal.Unsigned.Unsigned[8214565720323790099]
                8)))
      c$v1_app_arg[4864][LocalId]
      c$v1_app_arg[4865][LocalId]
      <prefixName>"enableGen"
      (Clash.Signal.Internal.Enable[8214565720323790215]
         @"System"
         <prefixName>"clockGen1"
         GHC.Types.True[3891110078048108586])
      (Clash.Sized.Internal.Unsigned.fromInteger# @8
         (GHC.Num.Natural.NS 8##)
         (GHC.Num.Integer.IS 0#))
      (Clash.Sized.Internal.Unsigned.fromInteger# @8
         (GHC.Num.Natural.NS 8##)
         (GHC.Num.Integer.IS 0#))
      (Clash.Sized.Internal.Unsigned.fromInteger# @8
         (GHC.Num.Natural.NS 8##)
         (GHC.Num.Integer.IS 0#))
  result[4866] :: GHC.Types.Bool[3674937295934324744]
  = Clash.Sized.Internal.Unsigned.eq# @8
      v1[4755801206503243778][LocalId]
      (Clash.Sized.Internal.Unsigned.fromInteger# @8
         (GHC.Num.Natural.NS 8##)
         (GHC.Num.Integer.IS 100#))
  c$v1_app_arg[4865] :: Clash.Signal.Internal.Reset[8214565720323790036]
                          "System"
  = Clash.Signal.Internal.unsafeToReset @"System"
      (Clash.Normalize.Primitives.removedArg
         @(Clash.Signal.Internal.KnownDomain[8214565720323790028]
             "System"))
      <prefixName>"noReset2"
      GHC.Types.False[3891110078048108556]
  c$v1_app_arg[4864] :: Clash.Signal.Internal.Clock[8214565720323789999]
                          "System"
  = Rec.topEntity_clk[8214565720323804625][GlobalId]
in Clash.Signal.Internal.tbClockGen @"System"
     (Clash.Normalize.Primitives.removedArg
        @(Clash.Signal.Internal.KnownDomain[8214565720323790028]
            "System"))
     c$app_arg[4867][LocalId]
Result:
letrec
  c$app_arg[4867] :: GHC.Types.Bool[3674937295934324744]
  = <prefixName>"not"
      GHC.Classes.not
      result[4866][LocalId]
  v1[4755801206503243778] :: Clash.Sized.Internal.Unsigned.Unsigned[8214565720323790099]
                               8
  = Clash.Signal.Internal.register# @"System"
      @(Clash.Sized.Internal.Unsigned.Unsigned[8214565720323790099]
          8)
      (Clash.Normalize.Primitives.removedArg
         @(Clash.Signal.Internal.KnownDomain[8214565720323790028]
             "System"))
      (Clash.Normalize.Primitives.removedArg
         @(Clash.XException.NFDataX[8214565720323790111]
             (Clash.Sized.Internal.Unsigned.Unsigned[8214565720323790099]
                8)))
      Rec.topEntity_clk[8214565720323804625][GlobalId]
      c$v1_app_arg[4865][LocalId]
      <prefixName>"enableGen"
      (Clash.Signal.Internal.Enable[8214565720323790215]
         @"System"
         <prefixName>"clockGen1"
         GHC.Types.True[3891110078048108586])
      (Clash.Sized.Internal.Unsigned.fromInteger# @8
         (GHC.Num.Natural.NS 8##)
         (GHC.Num.Integer.IS 0#))
      (Clash.Sized.Internal.Unsigned.fromInteger# @8
         (GHC.Num.Natural.NS 8##)
         (GHC.Num.Integer.IS 0#))
      (Clash.Sized.Internal.Unsigned.fromInteger# @8
         (GHC.Num.Natural.NS 8##)
         (GHC.Num.Integer.IS 0#))
  result[4866] :: GHC.Types.Bool[3674937295934324744]
  = Clash.Sized.Internal.Unsigned.eq# @8
      v1[4755801206503243778][LocalId]
      (Clash.Sized.Internal.Unsigned.fromInteger# @8
         (GHC.Num.Natural.NS 8##)
         (GHC.Num.Integer.IS 100#))
  c$v1_app_arg[4865] :: Clash.Signal.Internal.Reset[8214565720323790036]
                          "System"
  = Clash.Signal.Internal.unsafeToReset @"System"
      (Clash.Normalize.Primitives.removedArg
         @(Clash.Signal.Internal.KnownDomain[8214565720323790028]
             "System"))
      <prefixName>"noReset2"
      GHC.Types.False[3891110078048108556]
in Clash.Signal.Internal.tbClockGen @"System"
     (Clash.Normalize.Primitives.removedArg
        @(Clash.Signal.Internal.KnownDomain[8214565720323790028]
            "System"))
     c$app_arg[4867][LocalId]

christiaanb added a commit that referenced this issue Nov 18, 2024
@christiaanb
Do not inline let-bound recursive calls
fd263bd 
This prevents `recToLetRec` from turning a globally recursive
function into a local let-bound recursive function which can
be synthesized to hardware.

Fixes #2839
@christiaanb christiaanb mentioned this issue Nov 18, 2024
Merged
2 tasks
christiaanb added a commit that referenced this issue Nov 18, 2024
@christiaanb
Do not inline let-bound recursive calls
f08d0ad 
This prevents `recToLetRec` from turning a globally recursive
function into a local let-bound recursive function which can
be synthesized to hardware.

Fixes #2839
mergify bot pushed a commit that referenced this issue Nov 26, 2024
@christiaanb @mergify
Do not inline let-bound recursive calls
76f4d27 
This prevents `recToLetRec` from turning a globally recursive
function into a local let-bound recursive function which can
be synthesized to hardware.

Fixes #2839

(cherry picked from commit 0072241)

# Conflicts:
#	tests/Main.hs
@mergify mergify bot mentioned this issue Nov 26, 2024
Merged
2 tasks
christiaanb added a commit that referenced this issue Nov 26, 2024
@christiaanb
Do not inline let-bound recursive calls
68b6dc7 
This prevents `recToLetRec` from turning a globally recursive
function into a local let-bound recursive function which can
be synthesized to hardware.

Fixes #2839

(cherry picked from commit 0072241)
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Do not inline let-bound recursive calls clash-lang/clash-compiler
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@christiaanb @DigitalBrains1