Perform packing/unpacking of arguments and results in HDL

Running three experiments with the old and the new code shows that
avoiding packing/unpacking in Haskell yields a ~50% performance
increase.

Figures are taken by observing `clash-vexriscv-sim:unittests`'s debug
times.

| Old 1 | Old 2 | Old 3 | Old min | New 1 | New 2 | New 3 | New min | New faster |
|-------|-------|-------|---------|-------|-------|-------|---------|------------|
| 0.25  | 0.31  | 0.3   | 0.25    | 0.28  | 0.24  | 0.26  | 0.24    | 4.2%       |
| 0.65  | 0.69  | 0.74  | 0.65    | 0.51  | 0.48  | 0.5   | 0.48    | 35.4%      |
| 0.44  | 0.48  | 0.53  | 0.44    | 0.36  | 0.31  | 0.34  | 0.31    | 41.9%      |
| 1.84  | 1.72  | 1.7   | 1.7     | 1.12  | 1.08  | 1.12  | 1.08    | 57.4%      |
| 1.57  | 1.58  | 1.58  | 1.57    | 1.03  | 1.06  | 1.01  | 1.01    | 55.4%      |
| 0.43  | 0.4   | 0.4   | 0.4     | 0.33  | 0.33  | 0.32  | 0.32    | 25.0%      |
| 4.62  | 4.18  | 4.5   | 4.18    | 2.69  | 2.73  | 2.73  | 2.69    | 55.4%      |
| 0.17  | 0.18  | 0.24  | 0.17    | 0.18  | 0.24  | 0.23  | 0.18    | -5.6%      |
| 2.26  | 2.57  | 2.43  | 2.26    | 1.35  | 1.45  | 1.42  | 1.35    | 67.4%      |

clash-vexriscv-sim/src/Utils/Cpu.hs

@@ -61,8 +61,8 @@ cpu bootIMem bootDMem = (output, writes, iS2M, dS2M)
             { timerInterrupt = low,
               externalInterrupt = low,
               softwareInterrupt = low,
-              iBusWbS2M = makeDefined iBus,
-              dBusWbS2M = makeDefined dBus
+              iBusWbS2M = iBus,
+              dBusWbS2M = dBus
             }
       )
         <$> iS2M

clash-vexriscv/clash-vexriscv.cabal

@@ -102,24 +102,36 @@ library
   default-language: Haskell2010
   exposed-modules:
     VexRiscv
+    VexRiscv.BlackBox
     VexRiscv.ClockTicks
     VexRiscv.FFI
     VexRiscv.TH
     VexRiscv.VecToTuple
 
+  -- See https://github.com/clash-lang/clash-compiler/pull/2511
+  if impl(ghc >= 9.4)
+    CPP-Options: -DCLASH_OPAQUE=OPAQUE
+  else
+    CPP-Options: -DCLASH_OPAQUE=NOINLINE
+
   build-depends:
     base,
     bytestring >= 0.10 && < 0.13,
+    clash-lib,
     clash-prelude,
     clash-protocols,
     containers,
     directory >= 1.3 && < 1.4,
     filepath,
     Glob,
+    infinite-list,
+    mtl,
+    pretty-show,
     process >= 1.6 && < 1.8,
     string-interpolate,
     tagged,
     template-haskell,
+    text,
   extra-libraries: VexRiscvFFI, stdc++
   include-dirs: src/