feat: add nightly tail-call interpreter dispatch

Signed-off-by: Henry <mail@henrygressmann.de>

Author: explodingcamera

.github/workflows/test.yaml

@@ -54,6 +54,10 @@ jobs:
           - os: ubuntu-latest
             rust: nightly
             name: "Linux x86 (nightly)"
+          - os: ubuntu-latest
+            rust: nightly
+            name: "Linux x86 (nightly tail calls)"
+            args: "--features tinywasm/nightly-tail-calls"
           - os: ubuntu-latest
             rust: stable
             name: "Linux x86 (stable, no default features)"
@@ -62,6 +66,10 @@ jobs:
             rust: nightly
             name: "Linux x86 (nightly, no default features)"
             args: "--no-default-features"
+          - os: ubuntu-latest
+            rust: nightly
+            name: "Linux x86 (nightly tail calls, no default features)"
+            args: "--no-default-features --features tinywasm/nightly-tail-calls"
           - os: macos-14
             rust: stable
             name: "macOS arm64 (Apple M1)"

CHANGELOG.md

@@ -15,6 +15,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Optional parse-time operand deduplication to reduce `.twasm` archive size
 - Optional `send` support for moving stores and store-local handles across threads
 - Optional portable atomic shared pointers and counters for targets without native compare-and-swap
+- Optional `nightly-tail-calls` backend using Rust's unstable explicit tail calls for interpreter dispatch
 
 ### Changed
 

README.md

@@ -50,15 +50,17 @@ See the [examples](./examples) directory and [documentation](https://docs.rs/tin
 
 - **`full`:** Enables `archive`, `parallel-parser`, `parser`, and `validate`. Enabled by default.
 - **`std`:** Enables `std` and parsing from files and streams. Enabled by default.
-- **`log`:** Enables integration with the `log` crate. Enabled by default.
 - **`parser`:** Enables `tinywasm-parser` and top-level parse helpers. Enabled by default.
 - **`validate`:** Enables WebAssembly validation while parsing. Enabled by default and configurable through [`ParserOptions`](https://docs.rs/tinywasm/latest/tinywasm/parser/struct.ParserOptions.html).
+- **`parallel-parser`:** Parallelizes function parsing when `std` is enabled. Enabled by default.
 - **`archive`:** Enables serialization and deserialization of the internal `twasm` format. Enabled by default.
+- **`log`:** Enables integration with the `log` crate. Enabled by default.
+- **`send`:** Makes stores and store-local handles movable across threads.
+- **`portable-atomic`:** Supports targets without native atomic compare-and-swap.
 - **`canonicalize-nans`:** Uses a [canonical NaN](https://en.wikipedia.org/wiki/NaN#Canonical_NaN) for normalized NaN results. Enabled by default.
 - **`debug`:** Derives `Debug` for runtime types. Enabled by default.
-- **`parallel-parser`:** Parallelizes function parsing when `std` is enabled. Enabled by default.
 - **`guest-debug`:** Exposes module-internal by-index inspection APIs (`*_by_index`).
-- **`send`:** Makes stores and store-local handles movable across threads
+- **`nightly-tail-calls`:** Uses Rust's unstable explicit tail calls for interpreter dispatch. Requires nightly Rust (recommended for maximum performance).
 - **`simd-x86`:** Enables x86-specific SIMD intrinsics and uses `unsafe` internally.
 
 With default features disabled, `tinywasm` supports `no_std + alloc` and depends only on `libm`.

crates/cli/src/wast_runner.rs

@@ -50,10 +50,8 @@ impl ModuleRegistry {
     }
 
     fn definition(&self, id: Option<wast::token::Id<'_>>) -> Option<Module> {
-        match id {
-            Some(id) => self.definitions.get(id.name()).cloned(),
-            None => self.last_definition.clone(),
-        }
+        let Some(id) = id else { return self.last_definition.clone() };
+        self.definitions.get(id.name()).cloned()
     }
 
     fn update_last_instance(&mut self, instance: ModuleInstance, name: Option<String>) {
@@ -71,21 +69,13 @@ impl ModuleRegistry {
     }
 
     fn get_idx(&self, module_id: Option<wast::token::Id<'_>>) -> Option<u32> {
-        match module_id {
-            Some(module) => {
-                self.registered.get(module.name()).or_else(|| self.instances.get(module.name())).map(ModuleInstance::id)
-            }
-            None => self.last_instance.as_ref().map(ModuleInstance::id),
-        }
+        let Some(module_id) = module_id else { return self.last_instance.as_ref().map(ModuleInstance::id) };
+        self.registered.get(module_id.name()).or_else(|| self.instances.get(module_id.name())).map(ModuleInstance::id)
     }
 
     fn get(&self, module_id: Option<wast::token::Id<'_>>) -> Option<ModuleInstance> {
-        match module_id {
-            Some(module_id) => {
-                self.registered.get(module_id.name()).or_else(|| self.instances.get(module_id.name())).cloned()
-            }
-            None => self.last_instance.clone(),
-        }
+        let Some(module_id) = module_id else { return self.last_instance.clone() };
+        self.registered.get(module_id.name()).or_else(|| self.instances.get(module_id.name())).cloned()
     }
 }
 

crates/parser/Cargo.toml

@@ -32,3 +32,6 @@ std = ["tinywasm-types/std", "wasmparser/std"]
 
 # validate WebAssembly while parsing
 validate = ["wasmparser/features", "wasmparser/validate"]
+
+[lints.rust]
+unexpected_cfgs = { level = "warn", check-cfg = ["cfg(rust_analyzer)"] }

crates/tinywasm/Cargo.toml

@@ -122,6 +122,9 @@ debug = ["tinywasm-types/debug"]
 # expose module-internal by-index inspection APIs for non-exported entities (for testing and debugging)
 guest-debug = []
 
+# use explicit tail calls for interpreter dispatch (requires nightly Rust)
+nightly-tail-calls = []
+
 # enable x86-specific SIMD intrinsics in Value128 (uses unsafe code)
 # note: for x86 backend selection, compile with x86-64-v3 target features
 # (for example: `RUSTFLAGS="-C target-cpu=x86-64-v3"`)