v1.10.1

Highlights:

• Very significant performance improvements, further detailed below. We also created a site https://clash-lang.github.io/clash-benchmarks/ where we track performance improvements. These graphs are for the current master branch, not for released Clash versions.

• We have added support for the checked-literals package. Numeric literals (e.g., 5 or 3.2) can now be checked at compile time. That is, you'll get a compile error if the literal does not fit the target type -- even in polymorphic contexts! You can enable the checker by adding the following to your project's Cabal file:

  library
    [..]
  
    build-depends:
      [..]
      checked-literals
  
    ghc-options: -fplugin=CheckedLiterals
  

  See https://clash-lang.org/blog/2026-04-07-checked-literals/.

Performance:

• clash and clashi now use GHC-style RTS defaults through executable -with-rtsopts flags instead of linking RTS hooks. The existing unused hooks have been removed. Existing users should set -with-rtsopts to -K512M -H -I5 -T if they use their own Clash executable. These flags has been shown to give a ~25% compilation speed up in larger designs. If you used a Clash starter project to initialize your design, you should change:

  executable clash
    [..]

  To:

  executable clash
    [..]
    ghc-options: "-with-rtsopts=-K512M -H -I5 -T"

  in the cabal file. See #3252.

• Improved normalization performance for repeated top-down rewrite loops by avoiding full root restarts after every successful rewrite. This gives a ~17% performance improvements on larger designs #3249.

• Clash now converts GHC Core to its own Clash Core in parallel. For larger projects, this can shave off ~40% of load times. See #3299.

• Clash now prunes the binders it collects from top modules when loading from precompiled core. For larger projects, this can shave off 15% of package loading times. See #3298.

• flattenCallTree now caches intermediate results, reducing Clash normalization by 10% for realistic designs. Fixes #3246.

Added:

• -fclash-debug-manifest-hash. When enabled, Clash emits a __debug_hash object in clash-manifest.json listing the SHA256 of each input that feeds into the top-level hash (tops, prim_map, clash_mod_date, call_graph, opts). As the name implies, this should only be used to debug and should not be relied upon by tooling. See #3280.
• SaturatingNum instances for Erroring, Overflowing, Saturating, Wrapping, and Zeroing.

Changed:

• Replaced the deprecated data-binary-ieee754 dependency with castDoubleToWord64, castFloatToWord32, castWord32ToFloat, and castWord64ToDouble from GHC.Float. See #3174.
• flake.nix now advertises the clash-lang Cachix binary cache via nixConfig.extra-substituters. Running nix develop will prompt you to trust the cache, avoiding having to build Clash from source. See #3213.

Fixed:

• Clash no longer crashes for self-recursive global binders in very specific circumstances. See #3311.
• Clash no longer crashes upon calling sequenceA/traverse# on a zero-sized Vec. See #3290.
• Clash no longer crashes when constant-folding partial primitives in the GHC evaluator. This covers shiftL/shiftR/rotateL/rotateR with negative shift amounts on BitVector/Signed/Unsigned, (^) with negative exponents, chr on out-of-range integers, and quot/rem/div/mod by zero on Int/Word/Int{8,16,32,64}/Word{8,16,32,64}. Such expressions now fold to undefined (rather than crashing the compiler). Fixes #3234.
• Clash no longer crashes with mkVecNil: failed to instantiate Nil DC when unfolding traverse# in very specific circumstances. See #3291.
• Clash no longer errors when two -i import paths refer to the same directory via different syntactic spellings (e.g. -isrc -isrc/.) and a data file lives in that directory. See #3142.
• Clash no longer produces an error when using dataToTag in combination with custom bit representations. See #2724.
• Clash no longer takes exponential time and memory normalizing foldl/scanl/splitAt over a vector when the result keeps the (co-recursively defined) vector spine alive, e.g. snd (foldl const (z, s) (xs :: Vec n a)). The evaluator's zipWith and splitAt reductions now share their arguments instead of duplicating the vector spine on every peel. See #3308.
• Clash now recognizes ~ when solving GADT arms. Fixes #3232.
• Clash will no longer generate duplicate attribute when they're both used for top entity ports and internal signals. See #3218. The VHDL backend now also reports a clearer error when a synthesis attribute is declared with conflicting types in the same design.
• Due to HDL standards, when the result of a top entity is read by another binder Clash is forced to introduce an internal indirection signal. Clash no longer attaches the top entity's Annotate synthesis attributes to that internal signal, preventing duplicate synthesis attributes in the generated HDL. See #3224.
• Errors in Synthesize port annotations (e.g. a PortProduct on a non-product port) are now reported before a design is normalized, instead of afterwards. This avoids waiting for a potentially long normalization only to get a trivial port error. See #3305.
• Run bindConstantVar after post-normalization inlineCleanup/caseCon so constant let-bindings exposed late are inlined before netlist generation #3041.
• The VHDL primitives for integerToNaturalThrow and integerToNaturalClamp no longer contain syntax errors. See #3315.
• The internal function Clash.Util.Interpolate.i in clash-lib no longer inserts an extra blank line after a paragraph that gets reflowed onto multiple lines. See #2753.
• deriveAutoReg no longer fails on GHC versions where KnownNat lives in GHC.Internal.TypeNats rather than GHC.TypeNats. See #3100.
• makeTopEntity now accounts for unary product types. See #3066.