v2.0.0-beta.4 - 2026/07/01

Added

• Added support for the Wasm deterministic profile. #1947
  • Enable Wasm deterministic profile by enabling the new deterministic crate feature.
• Added support to enable or disable memory64 support. #1934
  • Disabling memory64 slightly reduces the artifact binary size
    and may improve execution performance, especially on embedded targets.
• Added the portable-dispatch crate feature to the Wasmi C-API. #1950
  • The wasmi_c_api_impl (and wasmi_c_api) crates now forward a portable-dispatch
    feature to the underlying wasmi crate, so C-API users can opt into the portable
    (loop-based) operator dispatch that does not rely on tail calls.
  • This automatically enables the portable-dispatch feature for CMAKE_BUILD_TYPE=Debug.
• Added more optimizations and improvements for the Wasmi IR and codegen:
  • Added fcopysign lowerings to fabs and fnabs. #1917
  • Emit better optimized copy operators in more places. #1924
  • Added highly specialized and optimized u64_copy_sNsM operators. #1935
  • Improved multi-value return codegen. #1944
  • Unify Wasmi IR return operators. #1948
• Expanded the configurable crate features of the Wasmi C-API. #1951
  • The wasmi_c_api_impl and wasmi_c_api crates now forward most features exposed by wasmi.
  • Fixed a bug that the std feature was not forwarded to wasmi.

Fixed

• Fixed a stackoverflow issue when compiling Wasmi without portable-dispatch. [#1942]
  • Previously Wasmi was required to be compiled with at least opt-level = 3 and codegen-units = 1
    to avoid the stackoverflow issue.
  • With this update a mere opt-level = 2 is enough to make LLVM generate the tail-call dispatch
    for all but memory.grow and table.grow operators.
  • Users who want tail calls even for those 2 remaining operators can compile Wasmi with a nightly
    toolchain and use the unstable crate feature to make Wasmi use Rust's unstable become keyword.
• Fixed a bug that caused Wasmi's compile-time to explode when using indirect-dispatch. #1939
  • Users were able to circumvent this LLVM codegen bug by using llvm-args=--switch-to-lookup=true.
    However, with this fix, that is no longer needed and Wasmi compile-times are back to normal again.
  • This bug also negatively affected the execution performance of Wasmi which is fixed as well.
• Fixed an incorrect macOS linker flag in the C-API CMake build. #1952
  • Shared-library builds added a Linux-only $ORIGIN rpath on macOS, which dyld does not expand.
    It is now omitted on macOS (matching Wasmtime). Consumers of the shared libwasmi.dylib on
    macOS should add their own rpath (e.g. -Wl,-rpath,@loader_path) to locate it at runtime.
• Fixed Wasmi C-API no_std support. #1915
• Fixed a bug in the lowering of isub with immediate rhs to iadd. #1914

Internal

• Strengthened the CI guard for tail-call operator dispatch. [#1942]
  • The tail-call CI job now runs the entire wasmi_wast suite (not just the call tests) on the
    non-portable-dispatch path at codegen-units > 1, plus a new wasmi_torture test that loops
    every Wasm operator category under a small RUST_MIN_STACK so any handler that stops tail-calling
    overflows the native stack and fails CI.
• The wasmi_wast test runner verifies NaN canonicalization when built with the deterministic feature. #1947
  • This requires nan:arithmetic results to match the canonical NaN.
• Simplify SIMD specific load operator IR and translation. #1922
• Remove copy_span operators from Wasmi IR. #1929
  • Now all copies are always copying single values.
  • Benchmarks showed that this is actually executing faster.
• Add cfg-guard badges to docs rendered at docs.rs. #1913
• Update the nightly Rust toolchain used for the Wasmi CI. #1936