vm, runtime: add slots! macro and port filter primop to typed slots

Cargo.lock

@@ -546,6 +546,7 @@ dependencies = [
  "fix-bytecode",
  "fix-error",
  "fix-lang",
+ "fix-macros",
  "fix-runtime",
  "gc-arena",
  "hashbrown 0.16.1",

fix-bytecode/src/lib.rs

@@ -199,6 +199,7 @@ pub enum Continuation {
     PFetchUrl,
 
     PFilterForceList,
+    PFilterSetupStack,
     PFilterCallPred,
     PFilterCheck,
 

fix-runtime/src/lib.rs

@@ -4,6 +4,7 @@ mod host;
 mod machine;
 mod path_util;
 mod resolve;
+mod slot;
 mod state;
 mod string_context;
 mod value;
@@ -14,6 +15,7 @@ pub use host::*;
 pub use machine::*;
 pub use path_util::*;
 pub use resolve::*;
+pub use slot::*;
 pub use state::*;
 pub use string_context::*;
 pub use value::*;

fix-runtime/src/slot.rs

@@ -0,0 +1,87 @@
+use std::marker::PhantomData;
+use std::ops::ControlFlow;
+
+use fix_bytecode::BytecodeReader;
+use gc_arena::Mutation;
+
+use crate::{Break, Forced, Machine, NixType, Step, StrictValue, Value, ValueVariant};
+
+pub trait SlotContent<'gc> {
+    type Ty: Into<Value<'gc>> + TryFrom<Value<'gc>> + 'gc;
+}
+
+impl<'gc> SlotContent<'gc> for Value<'gc> {
+    type Ty = Value<'gc>;
+}
+
+impl<'gc> SlotContent<'gc> for StrictValue<'gc> {
+    type Ty = StrictValue<'gc>;
+}
+
+impl<'gc, T> SlotContent<'gc> for T
+where
+    T: ValueVariant<'gc>,
+{
+    type Ty = T::Ty;
+}
+
+pub struct Slot<T> {
+    depth: u8,
+    _marker: PhantomData<T>,
+}
+
+impl<T> Slot<T> {
+    #[inline(always)]
+    pub const fn new(depth: u8) -> Self {
+        Self {
+            depth,
+            _marker: PhantomData,
+        }
+    }
+}
+
+impl<'gc, T> Slot<T>
+where
+    T: SlotContent<'gc>,
+    <T::Ty as TryFrom<Value<'gc>>>::Error: std::fmt::Debug,
+{
+    #[inline(always)]
+    pub fn read<M: Machine<'gc>>(&self, m: &M) -> T::Ty {
+        T::Ty::try_from(m.peek(self.depth as usize)).expect("slot held a value of the wrong type")
+    }
+
+    #[inline(always)]
+    pub fn read_checked<M: Machine<'gc>>(&self, m: &M) -> Result<T::Ty, NixType> {
+        let val = m.peek(self.depth as usize);
+        T::Ty::try_from(val).map_err(|_err| val.ty())
+    }
+
+    #[inline(always)]
+    pub fn write<M: Machine<'gc>>(&self, m: &mut M, val: T::Ty) {
+        m.replace(self.depth as usize, T::Ty::into(val));
+    }
+}
+
+impl<'gc> Slot<Value<'gc>> {
+    #[inline(always)]
+    pub fn force<T: Forced<'gc>, M: Machine<'gc>>(
+        &self,
+        m: &mut M,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> ControlFlow<Break, Slot<T>> {
+        T::force_and_check(m, reader, mc, self.depth as usize, reader.inst_start_pc())?;
+        ControlFlow::Continue(Slot::new(self.depth))
+    }
+
+    #[inline(always)]
+    pub fn force_to_pc<M: Machine<'gc>>(
+        &self,
+        m: &mut M,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+        pc: usize,
+    ) -> Step {
+        m.force_slot_to_pc(self.depth as usize, reader, mc, pc)
+    }
+}

fix-vm/Cargo.toml

@@ -12,6 +12,7 @@ sysinfo = { version = "0.38", default-features = false, features = ["system"] }
 fix-bytecode = { path = "../fix-bytecode" }
 fix-error = { path = "../fix-error" }
 fix-lang = { path = "../fix-lang" }
+fix-macros = { path = "../fix-macros" }
 fix-runtime = { path = "../fix-runtime" }
 
 [features]

fix-vm/src/primops/list.rs

@@ -1,91 +1,130 @@
 use fix_bytecode::Continuation;
-use fix_runtime::{BytecodeReader, List, Machine, MachineExt, NixType, Step, StrictValue, Value};
+use fix_runtime::{
+    BytecodeReader, List, Machine, MachineExt, NixType, Slot, Step, StrictValue, Value,
+};
 use gc_arena::Mutation;
 
-pub fn filter_force_list<'gc, M: Machine<'gc>>(
-    m: &mut M,
-    reader: &mut BytecodeReader<'_>,
-    mc: &Mutation<'gc>,
-) -> Step {
-    m.force_slot(0, reader, mc)?;
-    let list = match m.peek_forced(0).expect::<List>() {
-        Ok(list) => list,
-        Err(got) => return m.finish_type_err(NixType::List, got),
-    };
-    if list.inner.borrow().is_empty() {
-        let val = m.pop();
-        let _pred = m.pop();
-        return m.return_from_primop(val, reader);
-    }
-    // prepare stack layout: [ pred list idx acc ]
-    m.push(Value::new(0));
-    m.push(Value::new(List::new_gc(mc)));
-    reader.set_pc(Continuation::PFilterCallPred.ip() as usize);
-    Step::Continue(())
-}
+use crate::slots;
 
-#[expect(
-    clippy::indexing_slicing,
-    clippy::cast_sign_loss,
-    reason = "idx is a non-negative loop counter in 0..list.len(), so it indexes the list in bounds"
-)]
-pub fn filter_call_pred<'gc, M: Machine<'gc>>(
-    m: &mut M,
-    reader: &mut BytecodeReader<'_>,
-    mc: &Mutation<'gc>,
-) -> Step {
-    m.force_slot(3, reader, mc)?;
-    let pred = m.peek_forced(3);
-    let idx = m
-        .peek(1)
-        .downcast::<i32>()
-        .expect("stack slot must be an integer");
-    let elem = m
-        .peek_forced(2)
-        .downcast::<List>()
-        .expect("stack slot must be a list")
-        .inner
-        .borrow()[idx as usize];
-    m.push(pred.relax());
-    m.call(reader, mc, elem, Continuation::PFilterCheck.ip() as usize)
-}
+pub mod filter {
+    use super::*;
 
-#[expect(
-    clippy::indexing_slicing,
-    clippy::cast_sign_loss,
-    reason = "idx is a non-negative loop counter in 0..list.len(), so it indexes the list in bounds"
-)]
-pub fn filter_check<'gc, M: Machine<'gc>>(
-    m: &mut M,
-    reader: &mut BytecodeReader<'_>,
-    mc: &Mutation<'gc>,
-) -> Step {
-    let ret = m.force_and_retry::<bool>(reader, mc)?;
-    let idx = m
-        .peek(1)
-        .downcast::<i32>()
-        .expect("stack slot must be an integer");
-    let list = m
-        .peek_forced(2)
-        .downcast::<List>()
-        .expect("stack slot must be a list");
-    let list = list.inner.borrow();
-    let acc = m
-        .peek_forced(0)
-        .downcast::<List>()
-        .expect("stack slot must be a list");
-    if ret {
-        let mut acc = acc.unlock(mc).borrow_mut();
-        acc.push(list[idx as usize]);
+    #[expect(
+        clippy::unreachable,
+        reason = "dispatch_cont routes only the PFilter* continuations to this function, so the fallback arm is unreachable"
+    )]
+    pub fn dispatch<'gc, M: Machine<'gc>>(
+        m: &mut M,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+        cont: Continuation,
+    ) -> Step {
+        use Continuation::*;
+
+        match cont {
+            PFilterForceList => force_list(m, reader, mc),
+            PFilterSetupStack => setup_stack(m, reader, mc),
+            PFilterCallPred => call_pred(m, reader, mc),
+            PFilterCheck => check(m, reader, mc),
+            _ => unreachable!(),
+        }
     }
-    if idx as usize == list.len() - 1 {
-        let acc = m.pop();
-        m.drop_n(3);
-        return m.return_from_primop(acc, reader);
+
+    fn force_list<'gc, M: Machine<'gc>>(
+        m: &mut M,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> Step {
+        slots! {
+            list: Value;
+            _pred: Value;
+        };
+        list.force_to_pc(m, reader, mc, Continuation::PFilterSetupStack.ip() as usize)?;
+        setup_stack(m, reader, mc)
+    }
+
+    fn setup_stack<'gc, M: Machine<'gc>>(
+        m: &mut M,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> Step {
+        slots! {
+            list: List;
+            _pred: Value;
+        };
+        let list = match list.read_checked(m) {
+            Ok(list) => list,
+            Err(got) => return m.finish_type_err(NixType::List, got),
+        };
+        if list.inner.borrow().is_empty() {
+            let val = m.pop();
+            let _pred = m.pop();
+            return m.return_from_primop(val, reader);
+        }
+        // prepare stack layout: [ pred list idx acc ]
+        m.push(Value::new(0));
+        m.push(Value::new(List::new_gc(mc)));
+        reader.set_pc(Continuation::PFilterCallPred.ip() as usize);
+        Step::Continue(())
+    }
+
+    #[expect(
+        clippy::indexing_slicing,
+        clippy::cast_sign_loss,
+        reason = "idx is a non-negative loop counter in 0..list.len(), so it indexes the list in bounds"
+    )]
+    fn call_pred<'gc, M: Machine<'gc>>(
+        m: &mut M,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> Step {
+        slots! {
+            _acc: List;
+            idx: i32;
+            list: List;
+            pred: Value;
+        };
+
+        let pred: Slot<StrictValue> = pred.force(m, reader, mc)?;
+        let elem = list.read(m).inner.borrow()[idx.read(m) as usize];
+        m.push(pred.read(m).relax());
+        m.call(reader, mc, elem, Continuation::PFilterCheck.ip() as usize)
+    }
+
+    #[expect(
+        clippy::indexing_slicing,
+        clippy::cast_sign_loss,
+        reason = "idx is a non-negative loop counter in 0..list.len(), so it indexes the list in bounds"
+    )]
+    pub fn check<'gc, M: Machine<'gc>>(
+        m: &mut M,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> Step {
+        slots! {
+            acc: List;
+            idx: i32;
+            list: List;
+            _pred: StrictValue;
+        };
+
+        let ret = m.force_and_retry::<bool>(reader, mc)?;
+        let list = list.read(m).as_ref().inner.borrow();
+        let acc = acc.read(m);
+        let old_idx = idx.read(m);
+        if ret {
+            let mut acc = acc.unlock(mc).borrow_mut();
+            acc.push(list[old_idx as usize]);
+        }
+        if old_idx as usize == list.len() - 1 {
+            let acc = m.pop();
+            m.drop_n(3);
+            return m.return_from_primop(acc, reader);
+        }
+        idx.write(m, old_idx + 1);
+        reader.set_pc(Continuation::PFilterCallPred.ip() as usize);
+        Step::Continue(())
     }
-    m.replace(1, Value::new(idx + 1));
-    reader.set_pc(Continuation::PFilterCallPred.ip() as usize);
-    Step::Continue(())
 }
 
 // foldl' op nul list

fix-vm/src/primops/mod.rs

@@ -18,6 +18,27 @@ pub use io::*;
 pub use list::*;
 pub use path::*;
 
+#[macro_export]
+macro_rules! slots {
+    { $($ident:ident : $ty:ty);* $(;)? } => {
+        slots! { @acc [ 0 ] $($ident : $ty;)* }
+    };
+    /* { $($ident:ident : $ty:ty);* $(;)? } => {
+        slots! { @reverse [ $($ident : $ty;)* ] [] }
+    };
+    { @reverse [ $ident:ident : $ty:ty; $($remain:tt)* ] [ $($acc:tt)* ] } => {
+        slots! { @reverse [ $($remain)* ] [ $ident : $ty; $($acc)* ] }
+    };
+    { @reverse [] [ $($rev_id:ident : $rev_ty:ty;)* ] } => {
+        slots! { @acc [ 0 ] $($rev_id : $rev_ty;)* }
+    }; */
+    { @acc [ $($acc:tt)* ] $ident:ident : $ty:ty; $($remain:tt)* } => {
+        let $ident : Slot<$ty> = Slot::new($($acc)*);
+        slots! { @acc [ $($acc)* + 1 ] $($remain)* }
+    };
+    { @acc [ $($acc:tt)* ] } => {};
+}
+
 pub fn dispatch_cont<'gc, M: Machine<'gc>>(
     m: &mut M,
     ctx: &mut impl VmRuntimeCtx,
@@ -45,9 +66,9 @@ pub fn dispatch_cont<'gc, M: Machine<'gc>>(
         PDeepSeqLoop => deep_seq_loop(m, reader, mc),
         PSeq => seq(m, reader, mc),
 
-        PFilterForceList => filter_force_list(m, reader, mc),
-        PFilterCallPred => filter_call_pred(m, reader, mc),
-        PFilterCheck => filter_check(m, reader, mc),
+        PFilterForceList | PFilterSetupStack | PFilterCallPred | PFilterCheck => {
+            filter::dispatch(m, reader, mc, cont)
+        }
 
         PFoldlStrict => foldl_strict_entry(m, reader, mc),
         PFoldlStrictEmpty => foldl_strict_empty(m, reader, mc),