perf(core): typed calling convention for words with a known stack effect

Such a word now compiles to a fast entry (i32 x p) -> (i32 x q) carrying
its stack items as WASM values, plus the usual ( -- ) wrapper that keeps
the table slot, so EXECUTE / interpreter / host words / CATCH see the
unchanged memory ABI. Fib(25) 1035 -> 366 us, 4.3x slower than sf64 ->
1.2x; the default guards-on config 1740 -> 361 us. WS-006.

CHANGELOG.md

@@ -5,6 +5,53 @@ All notable changes to WAFER are documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Added
+
+- **A typed calling convention for words with a known stack effect.** Such a
+  word now compiles to two entry points: a fast one whose signature is
+  `(i32 x p) -> (i32 x q)`, carrying its stack items as WASM values, and the
+  usual `( -- )` wrapper that moves those items on and off the memory data
+  stack. The wrapper keeps the function-table slot, so `EXECUTE`, the outer
+  interpreter, host words and `CATCH` see exactly the ABI they saw before;
+  only direct calls inside a module take the fast entry.
+
+  This is what the SwiftForth gap was made of. sf64 keeps TOS in `RBX` and
+  the stack pointer in `RBP`, and both survive a `CALL` untouched, so its
+  `FIB` is 16 instructions and ~7 memory touches per node. WAFER kept the
+  whole stack in linear memory and flushed its cached `$dsp` to an imported
+  global before every call: ~36 memory touches per node. The stack simulator
+  that already promoted loop and `IF` bodies into WASM locals refused any
+  body containing a call or an `EXIT` -- exactly the words where the
+  convention cost the most. It now handles both.
+
+  Fibonacci(25) goes from 1035 to 366 µs, 4.3x slower than `sf64` to 1.2x.
+  Loop-heavy benchmarks are unchanged (they were already promoted, and
+  already beat `sf64`). Words that keep the memory convention: anything
+  using `SP@`, `DEPTH`, `EXECUTE`, `>R`/`R>`, floats or locals; anything
+  calling a word that is itself untyped, which in the JIT path means every
+  call except `RECURSE`; mutually recursive words; and words whose effect is
+  not static -- branches that disagree on depth, `EXIT` at the wrong depth,
+  a non-neutral loop body, or a recursion that grows the stack per level.
+
+  `CONSOLIDATE` extends this across words, since it puts them all in one
+  module: the effects are solved to a fixpoint from the leaves outward, and
+  105 of 187 words in a booted dictionary end up typed.
+
+  Stack guards get cheap as a side effect -- they hang off the memory-stack
+  push/pop choke points, and a typed word barely has any. The default
+  guards-on configuration that the REPL and the web build use went from 1631
+  to 365 µs on the same benchmark.
+
+  `WAFER_TYPED_CALLS=0` falls back to the memory-stack convention.
+
+### Fixed
+
+- The Forth 2012 Core suite now also runs against consolidated code
+  (`compliance_core_after_consolidate`). `CONSOLIDATE` had no correctness
+  test at all before -- only benchmarks.
+
 ## [0.2.6] - 2026-08-07
 
 ### Fixed

README.md

@@ -11,6 +11,7 @@ An optimizing Forth 2012 compiler targeting WebAssembly. WAFER JIT-compiles each
 - **Faster than gforth** on all benchmarks in release mode (2-10x faster)
 - **JIT compilation** — each `:` definition compiles to its own WASM module
 - **Self-recursive direct calls** — RECURSE compiles to native `call` instead of `call_indirect`
+- **Typed calling convention** — a word with a statically known stack effect passes its stack items as WASM values, so a call keeps them in registers instead of round-tripping through memory
 - **Consolidation mode** — recompile all words into a single optimized WASM module
 - **Interactive REPL** with line editing (rustyline)
 - **Browser REPL** — runs entirely in the browser via wasm-pack + js-sys
@@ -79,23 +80,31 @@ git submodule update --init
 
 ## Performance
 
-WAFER beats gforth (the GNU Forth reference implementation) on all benchmarks in release mode:
+WAFER beats gforth (the GNU Forth reference implementation) on all benchmarks in release mode, and is within
+reach of SwiftForth `sf64`, which compiles to native code:
 
 ```
-Benchmark                   WAFER     CONSOL     gforth      WAFER/gf
+Benchmark                   WAFER     CONSOL     gforth       sf64    WAFER/gf   WAFER/sf
-Fibonacci(25)                1629       1535       3422        0.45x
+Fibonacci(25)                 378        359       3238        296       0.11x      1.21x
-Factorial(12)x10K             340        339        638        0.53x
+Factorial(12)x10K             335        320        633        183       0.51x      1.75x
-GCD-bench(500)                 18         15         30        0.50x
+GCD-bench(500)                 14         15         29         31       0.48x      0.45x
-NestedLoops(50)                84         73        720        0.10x
+NestedLoops(50)                72         69        698        207       0.10x      0.33x
-Collatz(2K)                  1212       1202       3914        0.31x
+Collatz(2K)                   994        997       3940        668       0.25x      1.49x
 ```
 
 Times in microseconds. WAFER/gf < 1.0 means WAFER is faster. CONSOL = after `CONSOLIDATE`.
 
+A word whose stack effect is statically known gets a **typed entry point**: its stack items travel in and out
+as WASM values instead of through the memory data stack, so cranelift keeps them in registers across a call
+the way a native Forth keeps TOS in one. The word also keeps a `( -- )` wrapper, which is what the function
+table, `EXECUTE` and the outer interpreter reach, so nothing about the memory ABI changes from the outside.
+Call-heavy code is what this pays for -- Fibonacci went from 4.3x slower than `sf64` to 1.2x. Set
+`WAFER_TYPED_CALLS=0` to fall back to the memory-stack convention.
+
 ## Testing
 
 ```bash
-# All tests (~570 currently passing)
+# All tests (~620 currently passing)
 cargo test --workspace
 
 # Forth 2012 compliance suite

crates/cli/src/main.rs

@@ -263,7 +263,8 @@ fn cmd_run(file: &str) -> anyhow::Result<()> {
 }
 
 /// `WaferConfig` for CLI-created VMs. `WAFER_STACK_GUARDS=0|1` overrides
-/// the per-command default (REPL/file execution on, build off).
+/// the per-command default (REPL/file execution on, build off);
+/// `WAFER_TYPED_CALLS=0` falls back to the memory-stack calling convention.
 fn vm_config(default_guards: bool) -> wafer_core::config::WaferConfig {
     let mut cfg = wafer_core::config::WaferConfig::all();
     cfg.codegen.stack_guards = match std::env::var("WAFER_STACK_GUARDS").ok().as_deref() {
@@ -271,6 +272,7 @@ fn vm_config(default_guards: bool) -> wafer_core::config::WaferConfig {
         Some(_) => true,
         None => default_guards,
     };
+    cfg.codegen.typed_calls = std::env::var("WAFER_TYPED_CALLS").ok().as_deref() != Some("0");
     cfg
 }
 

crates/core/src/config.rs

@@ -12,6 +12,11 @@ pub struct CodegenOpts {
     /// corrupting stack pointers. On by default; benchmarks and
     /// exported production modules turn it off.
     pub stack_guards: bool,
+    /// Compile words with a statically known stack effect to a typed entry
+    /// point that carries stack items in WASM values, so a call keeps them
+    /// in registers instead of round-tripping through the memory stack.
+    /// On by default; `WAFER_TYPED_CALLS=0` turns it off.
+    pub typed_calls: bool,
 }
 
 /// Master configuration for all WAFER optimizations.
@@ -38,6 +43,7 @@ impl WaferConfig {
             codegen: CodegenOpts {
                 stack_to_local_promotion: true,
                 stack_guards: true,
+                typed_calls: true,
             },
         }
     }
@@ -56,6 +62,7 @@ impl WaferConfig {
             codegen: CodegenOpts {
                 stack_to_local_promotion: false,
                 stack_guards: false,
+                typed_calls: false,
             },
         }
     }

crates/core/src/consolidate.rs

@@ -21,7 +21,7 @@ mod tests {
         // Empty word list should produce nothing (but we guard against this at call site)
         let words = vec![];
         let map = HashMap::new();
-        let result = compile_consolidated_module(&words, &map, 16, None);
+        let result = compile_consolidated_module(&words, &map, 16, None, true);
         // Empty is valid -- should produce a valid module with no functions
         assert!(result.is_ok());
     }
@@ -31,7 +31,7 @@ mod tests {
         let words = vec![(WordId(1), vec![IrOp::PushI32(42)])];
         let mut map = HashMap::new();
         map.insert(WordId(1), 1u32); // function index 1 (after emit import)
-        let result = compile_consolidated_module(&words, &map, 16, None);
+        let result = compile_consolidated_module(&words, &map, 16, None, true);
         assert!(result.is_ok());
     }
 
@@ -49,7 +49,7 @@ mod tests {
         map.insert(WordId(1), 1u32);
         map.insert(WordId(2), 2u32);
         map.insert(WordId(3), 3u32);
-        let result = compile_consolidated_module(&words, &map, 16, None);
+        let result = compile_consolidated_module(&words, &map, 16, None, true);
         assert!(result.is_ok());
     }
 
@@ -59,7 +59,7 @@ mod tests {
         let words = vec![(WordId(3), vec![IrOp::Call(WordId(99))])];
         let mut map = HashMap::new();
         map.insert(WordId(3), 1u32);
-        let result = compile_consolidated_module(&words, &map, 256, None);
+        let result = compile_consolidated_module(&words, &map, 256, None, true);
         assert!(result.is_ok());
     }
 
@@ -72,7 +72,7 @@ mod tests {
         let mut map = HashMap::new();
         map.insert(WordId(1), 1u32);
         map.insert(WordId(2), 2u32);
-        let result = compile_consolidated_module(&words, &map, 16, None);
+        let result = compile_consolidated_module(&words, &map, 16, None, true);
         assert!(result.is_ok());
     }
 
@@ -95,7 +95,7 @@ mod tests {
         let mut map = HashMap::new();
         map.insert(WordId(1), 1u32);
         map.insert(WordId(2), 2u32);
-        let result = compile_consolidated_module(&words, &map, 16, None);
+        let result = compile_consolidated_module(&words, &map, 16, None, true);
         assert!(result.is_ok());
     }
 
@@ -120,7 +120,7 @@ mod tests {
         let mut map = HashMap::new();
         map.insert(WordId(1), 1u32);
         map.insert(WordId(2), 2u32);
-        let result = compile_consolidated_module(&words, &map, 16, None);
+        let result = compile_consolidated_module(&words, &map, 16, None, true);
         assert!(result.is_ok());
     }
 
@@ -141,7 +141,7 @@ mod tests {
         let mut map = HashMap::new();
         map.insert(WordId(1), 1u32);
         map.insert(WordId(2), 2u32);
-        let result = compile_consolidated_module(&words, &map, 16, None);
+        let result = compile_consolidated_module(&words, &map, 16, None, true);
         assert!(result.is_ok());
     }
 
@@ -163,7 +163,7 @@ mod tests {
         let mut map = HashMap::new();
         map.insert(WordId(1), 1u32);
         map.insert(WordId(2), 2u32);
-        let result = compile_consolidated_module(&words, &map, 16, None);
+        let result = compile_consolidated_module(&words, &map, 16, None, true);
         assert!(result.is_ok());
     }
 }

crates/core/src/export.rs

@@ -126,6 +126,7 @@ pub fn export_module(
         table_size,
         &export_sections,
         vm.stack_guard_param(),
+        vm.typed_calls(),
     )
     .map_err(|e| anyhow::anyhow!("export codegen error: {e}"))?;
 

crates/core/src/outer.rs

@@ -2644,6 +2644,7 @@ impl<R: Runtime> ForthVM<R> {
             &local_fn_map,
             table_size,
             self.stack_guard_param(),
+            self.config.codegen.typed_calls,
         )
         .map_err(|e| anyhow::anyhow!("consolidation codegen error: {e}"))?;
 
@@ -2674,6 +2675,7 @@ impl<R: Runtime> ForthVM<R> {
             &local_fn_map,
             table_size,
             self.stack_guard_param(),
+            self.config.codegen.typed_calls,
         )
         .map_err(|e| anyhow::anyhow!("batch compile error: {e}"))?;
 
@@ -2966,6 +2968,11 @@ impl<R: Runtime> ForthVM<R> {
             .then_some(self.stack_fault_id)
     }
 
+    /// Whether words with a known stack effect get a typed entry point.
+    pub(crate) fn typed_calls(&self) -> bool {
+        self.config.codegen.typed_calls
+    }
+
     /// Codegen configuration for compiling one word.
     fn codegen_config(&mut self, base_fn_index: u32) -> CodegenConfig {
         CodegenConfig {
@@ -2973,6 +2980,7 @@ impl<R: Runtime> ForthVM<R> {
             table_size: self.table_size(),
             stack_to_local_promotion: self.config.codegen.stack_to_local_promotion,
             stack_guards: self.stack_guard_param(),
+            typed_calls: self.config.codegen.typed_calls,
         }
     }
 
@@ -8180,6 +8188,73 @@ mod tests {
     use super::*;
     use crate::runtime_native::NativeRuntime;
 
+    // -- Typed calling convention -------------------------------------
+
+    #[test]
+    fn test_typed_word_recursion_matches_the_memory_convention() {
+        // FIB is the shape the typed entry exists for: self-recursive with
+        // an early EXIT, so it is compiled as WASM values in and out.
+        let (stack, _) = eval(
+            ": FIB DUP 2 < IF EXIT THEN DUP 1- RECURSE SWAP 2 - RECURSE + ; \
+             0 FIB 1 FIB 2 FIB 10 FIB 25 FIB",
+        );
+        assert_eq!(stack, vec![75025, 55, 1, 1, 0]);
+    }
+
+    #[test]
+    fn test_typed_word_keeps_the_items_below_its_arguments() {
+        // The wrapper may only move the cells the word declared; anything
+        // deeper has to still be there afterwards.
+        let (stack, _) = eval(": SQ DUP * ; 7 8 9 SQ");
+        assert_eq!(stack, vec![81, 8, 7]);
+    }
+
+    #[test]
+    fn test_typed_word_is_reachable_through_execute() {
+        // EXECUTE goes through the table, which holds the `( -- )` wrapper.
+        let (stack, _) = eval(": SQ DUP * ; 6 ' SQ EXECUTE");
+        assert_eq!(stack, vec![36]);
+    }
+
+    #[test]
+    fn test_catch_sees_a_typed_word_underflow() {
+        // A typed word's stack guards live in its wrapper, where the
+        // arguments come off the memory stack. They still THROW -4 rather
+        // than corrupting the stack pointer, and CATCH still reports it.
+        let (stack, _) = eval(": SQ DUP * ; : CHK ['] SQ CATCH ; CHK");
+        assert_eq!(stack, vec![-4]);
+    }
+
+    #[test]
+    fn test_catch_restores_the_stack_around_a_caller_of_typed_code() {
+        // T contains THROW, a host word, so T itself keeps the memory
+        // convention and reaches SQ through its wrapper. CATCH restores the
+        // depth it saved across that boundary -- not the contents, so the 3
+        // that SQ squared stays squared. gforth agrees: `1 2 9 5 4`.
+        let (stack, _) = eval(": SQ DUP * ; : T SQ 5 THROW ; : CHK 1 2 3 ['] T CATCH DEPTH ; CHK");
+        assert_eq!(stack, vec![4, 5, 9, 2, 1]);
+    }
+
+    #[test]
+    fn test_typed_word_underflow_still_throws() {
+        // The stack guards for a typed word live in its wrapper, where the
+        // arguments are taken off the memory stack.
+        let mut vm = ForthVM::<NativeRuntime>::new().unwrap();
+        vm.evaluate(": SQ DUP * ;").unwrap();
+        vm.take_output();
+        let err = vm.evaluate("SQ");
+        assert!(err.is_err(), "empty-stack SQ should throw, got {err:?}");
+    }
+
+    #[test]
+    fn test_deep_typed_recursion_unwinds_cleanly() {
+        // 10k levels of a typed self-call: results come back in WASM values,
+        // so nothing is left on the memory stack afterwards.
+        let (stack, _) =
+            eval(": COUNT-DOWN DUP 0= IF EXIT THEN 1- RECURSE ; 10000 COUNT-DOWN DEPTH");
+        assert_eq!(stack, vec![1, 0]);
+    }
+
     fn eval(input: &str) -> (Vec<i32>, String) {
         let mut vm = ForthVM::<NativeRuntime>::new().unwrap();
         vm.evaluate(input).unwrap();

crates/core/tests/compliance.rs

@@ -344,3 +344,32 @@ fn compliance_tools() {
     let errors = run_suite(&mut vm, "toolstest.fth");
     assert_eq!(errors, 0, "Programming-Tools: {errors} test failures");
 }
+
+/// The Forth 2012 Core suite against consolidated code.
+///
+/// `CONSOLIDATE` recompiles the whole dictionary into one WASM module, which
+/// is where cross-word typed calls live: a word with a known stack effect
+/// gets a fast entry taking and returning its stack items as WASM values,
+/// and its `() -> ()` wrapper keeps the table slot. Nothing else covers that
+/// path for correctness, so run the suite on top of it.
+#[test]
+fn compliance_core_after_consolidate() {
+    let mut vm = ForthVM::<NativeRuntime>::new().expect("Failed to create ForthVM");
+    let tester_path = format!("{SUITE_DIR}/tester.fr");
+    let f1 = load_file(&mut vm, &tester_path);
+    assert_load_fails_within_baseline(&tester_path, f1);
+
+    vm.evaluate("CONSOLIDATE").expect("CONSOLIDATE failed");
+    vm.take_output();
+
+    let core_path = format!("{SUITE_DIR}/core.fr");
+    let f2 = load_file(&mut vm, &core_path);
+    assert_load_fails_within_baseline(&core_path, f2);
+
+    let _ = vm.evaluate("DECIMAL #ERRORS @");
+    let errors = vm.data_stack().first().copied().unwrap_or(-1);
+    assert_eq!(
+        errors, 0,
+        "Core word set after CONSOLIDATE: {errors} failures"
+    );
+}