First declosure impl

compiler/src/declass/step_1.rs

@@ -10,6 +10,9 @@
 //! `get_field "prototype" ; put_field @meth`; the field-initialiser tail is
 //! dropped. Detection (`find_class_seqs`) records the ranges; replacement
 //! (`ClassSequence::emit_prototype`) reads operands out of each matched range.
+//!
+//! Derived classes (`extends`) are unsupported and panic: prototype form would
+//! have to flatten the parent's prototype in and lower `super`.
 
 use std::range::Range;
 
@@ -160,6 +163,16 @@ fn find_class_seqs(mut ins: &[RegInstr]) -> Vec<ClassSequence> {
 
 fn match_class_seq(ins: &[RegInstr]) -> Result<(&[RegInstr], usize), &[RegInstr]> {
     let ins = match_one(ins, |i| i.op == OpCode::PushConst8)?;
+
+    // A class build is `push_const8 ; define_class`. Derived classes (`extends`)
+    // are unsupported: prototype form would have to flatten the parent's
+    // prototype in and lower `super`, neither of which is implemented.
+    if let Some(i) = ins.first() {
+        if i.op == OpCode::DefineClass && is_derived(i) {
+            panic!("declass: derived classes (extends) are not supported");
+        }
+    }
+
     let ins = match_one(ins, |i| i.op == OpCode::DefineClass)?;
     let (ins, num_methods) = match_many(ins, match_method_seq);
     let ins = match_opt(ins, match_field_init_seq);
@@ -167,6 +180,15 @@ fn match_class_seq(ins: &[RegInstr]) -> Result<(&[RegInstr], usize), &[RegInstr]
     Ok((ins, num_methods))
 }
 
+/// A derived class: `define_class` with the derived flag set.
+fn is_derived(i: &RegInstr) -> bool {
+    matches!(i.imm, ImmOperand::AtomU8 { arg, .. } if arg & 1 == 1)
+}
+
+// TODO: accessors are not handled. A getter/setter is a `define_method` with a
+// non-zero kind in `arg`; this matcher takes it for an ordinary method, so it
+// is wrongly lowered to a `put_field` (a data property) instead of an accessor
+// property. It should instead make the whole class pass through untouched.
 fn match_method_seq(ins: &[RegInstr]) -> Result<&[RegInstr], &[RegInstr]> {
     let ins = match_one(ins, |i| i.op == OpCode::Fclosure8)?;
     let ins = match_one(ins, |i| i.op == OpCode::DefineMethod)?;
@@ -177,7 +199,12 @@ fn match_field_init_seq(ins: &[RegInstr]) -> Result<&[RegInstr], &[RegInstr]> {
     let is_put_loc = |op| {
         matches!(
             op,
-            OpCode::PutLoc | OpCode::PutLoc0 | OpCode::PutLoc1 | OpCode::PutLoc2 | OpCode::PutLoc3
+            OpCode::PutLoc
+                | OpCode::PutLoc8
+                | OpCode::PutLoc0
+                | OpCode::PutLoc1
+                | OpCode::PutLoc2
+                | OpCode::PutLoc3
         )
     };
 

compiler/src/declosure.rs

@@ -0,0 +1,317 @@
+//! declosure: closures become plain objects.
+//!
+//! A closure becomes an object holding its function plus its captured
+//! variables (docs/declosure_algo.txt). Field 0 is the function; fields 1..
+//! are the captures, in capture order. The object doubles as the environment,
+//! so there is no second env value to track. Field names are plain integers,
+//! so a field operand reads `Atom(int(k))`.
+//!
+//! Three steps, one property each:
+//!
+//!   1. `take_env_param`             -- every function takes the env as its
+//!      LAST parameter and reads its captures out of it: `get_var_ref` /
+//!      `put_var_ref` become field access on the env.
+//!   2. `build_closure_objects`      -- every `fclosure` builds the object: the
+//!      function in field 0, then one field per capture, loaded from the
+//!      parent frame.
+//!   3. `route_calls_through_object` -- every plain call reads field 0 and
+//!      passes the object itself as the trailing env argument.
+//!
+//! Every function takes an env whether it captures anything or not, so step 3
+//! can append the object at a uniform call site.
+//!
+//! Two facts about the register form this leans on:
+//!
+//!   * A function is a plain constant -- an index into the cpool. `fclosure`
+//!     becomes `push_const`, so it loads like any other const, and storing it
+//!     in a field is no different from storing a number.
+//!   * The callee of a call is its LAST argument (the deepest stack slot,
+//!     popped last), so step 3 reads `args.last()`.
+//!
+//! Known gaps, in rough order of how likely they are to bite:
+//!
+//!   * A captured variable the parent later writes. The write produces a new
+//!     value instead of storing through the alias, so the closure never sees
+//!     it. A capture aliases the value a slot held at capture time.
+//!   * Non-local capture sources. Step 2 can materialise a capture that comes
+//!     from a parent local or arg. A capture that itself comes from the
+//!     parent's captures, a module binding, or a global is left as an
+//!     `undefined` placeholder -- it needs the parent to forward its own env.
+//!   * Foreign callees. Step 3 rewrites every plain call into a field-0 read.
+//!     That is only valid for functions we produced; a host builtin such as
+//!     `Math.sqrt` has no such field.
+//!   * Entry points. Step 1 gives every function an env parameter, but the
+//!     module root and any host-invoked function have no caller of ours to
+//!     supply one.
+//!   * `call_method` and `call_constructor` carry a receiver, so they belong
+//!     to the class passes; step 3 leaves them untouched. Same for `apply`.
+
+use crate::{
+    flatten::CaptureFrom,
+    parse::{AtomRef, ImmOperand, JsValue, opcodes::OpCode},
+    regify::{RegFn, RegInstr},
+};
+
+pub fn declosure(reg_fns: Vec<RegFn>) -> Vec<RegFn> {
+    // Where each function's captures come from, per fn id. Snapshotted first,
+    // because step 1 clears the capture lists that step 2 reads.
+    let capture_sources: Vec<Vec<CaptureFrom>> = reg_fns
+        .iter()
+        .map(|f| f.captures.iter().map(|c| c.from).collect())
+        .collect();
+
+    reg_fns
+        .into_iter()
+        .map(|f| declosure_one(f, &capture_sources))
+        .collect()
+}
+
+fn declosure_one(reg_fn: RegFn, capture_sources: &[Vec<CaptureFrom>]) -> RegFn {
+    let reg_fn = take_env_param(reg_fn);
+    let reg_fn = build_closure_objects(reg_fn, capture_sources);
+    route_calls_through_object(reg_fn)
+}
+
+// ── 1. every function takes an env ─────────────────────────────────────────
+
+/// Append `env` as the last parameter -- existing arguments keep their numbers
+/// -- and turn every capture access into a field access on it.
+fn take_env_param(mut reg_fn: RegFn) -> RegFn {
+    let env_arg = reg_fn.arg_count;
+    reg_fn.arg_count += 1;
+
+    let code = std::mem::take(&mut reg_fn.code);
+    let touches_captures = code.iter().any(|i| capture_access(i).is_some());
+
+    let mut out = Vec::with_capacity(code.len() + 1);
+    let env = reg_fn.fresh_val();
+
+    // Load the env once at entry -- only if a capture is actually accessed.
+    if touches_captures {
+        out.push(get_arg(env, env_arg));
+    }
+
+    for instr in code {
+        match capture_access(&instr) {
+            // A read keeps its destination, so downstream uses do not change.
+            Some(CaptureAccess::Read(k)) => {
+                out.push(get_field(int_field(k + 1), instr.dsts[0], env))
+            }
+            Some(CaptureAccess::Write(k)) => {
+                out.push(put_field(int_field(k + 1), instr.args[0], env))
+            }
+            None => out.push(instr),
+        }
+    }
+
+    reg_fn.code = out;
+    reg_fn.captures.clear();
+    reg_fn
+}
+
+/// Which capture an instruction reads or writes, if any.
+enum CaptureAccess {
+    Read(u32),
+    Write(u32),
+}
+
+fn capture_access(i: &RegInstr) -> Option<CaptureAccess> {
+    // The numbered forms fold the slot into the opcode; the rest carry it.
+    let slot = || match i.imm {
+        ImmOperand::VarRef(k) => k as u32,
+        _ => unreachable!("a var_ref opcode without a var_ref operand"),
+    };
+    Some(match i.op {
+        OpCode::GetVarRef | OpCode::GetVarRefCheck => CaptureAccess::Read(slot()),
+        OpCode::GetVarRef0 => CaptureAccess::Read(0),
+        OpCode::GetVarRef1 => CaptureAccess::Read(1),
+        OpCode::GetVarRef2 => CaptureAccess::Read(2),
+        OpCode::GetVarRef3 => CaptureAccess::Read(3),
+        OpCode::PutVarRef | OpCode::PutVarRefCheck | OpCode::PutVarRefCheckInit => {
+            CaptureAccess::Write(slot())
+        }
+        OpCode::PutVarRef0 => CaptureAccess::Write(0),
+        OpCode::PutVarRef1 => CaptureAccess::Write(1),
+        OpCode::PutVarRef2 => CaptureAccess::Write(2),
+        OpCode::PutVarRef3 => CaptureAccess::Write(3),
+        _ => return None,
+    })
+}
+
+// ── 2. every fclosure builds the object ────────────────────────────────────
+
+/// Replace each `fclosure` with the object that stands for it: the function in
+/// field 0, then one field per capture, each loaded from the parent frame.
+fn build_closure_objects(mut reg_fn: RegFn, capture_sources: &[Vec<CaptureFrom>]) -> RegFn {
+    let code = std::mem::take(&mut reg_fn.code);
+    let mut out = Vec::with_capacity(code.len());
+
+    for instr in code {
+        let Some(child) = closure_child(&instr, &reg_fn.cpool) else {
+            out.push(instr);
+            continue;
+        };
+        // The value the rest of the code already uses for this closure.
+        let closure = instr.dsts[0];
+        let captures: &[CaptureFrom] = capture_sources
+            .get(child)
+            .map(Vec::as_slice)
+            .unwrap_or(&[]);
+
+        // The function is a plain constant, so it loads with `push_const`.
+        let load = match instr.op {
+            OpCode::Fclosure8 => OpCode::PushConst8,
+            _ => OpCode::PushConst,
+        };
+        let func = reg_fn.fresh_val();
+        out.push(RegInstr::new(load, instr.imm, vec![func], vec![]));
+
+        let mut obj = reg_fn.fresh_val();
+        out.push(object(obj));
+
+        // Each define_field returns the object, so the stores chain. The LAST
+        // store must land in `closure`.
+        let dst = if captures.is_empty() {
+            closure
+        } else {
+            reg_fn.fresh_val()
+        };
+        out.push(define_field(int_field(0), dst, func, obj));
+        obj = dst;
+
+        for (k, source) in captures.iter().enumerate() {
+            let value = reg_fn.fresh_val();
+            out.push(load_capture(*source, value));
+
+            let dst = if k + 1 == captures.len() {
+                closure
+            } else {
+                reg_fn.fresh_val()
+            };
+            out.push(define_field(int_field(k as u32 + 1), dst, value, obj));
+            obj = dst;
+        }
+    }
+
+    reg_fn.code = out;
+    reg_fn
+}
+
+/// The nested function an `fclosure` instantiates, as a fn id.
+fn closure_child(i: &RegInstr, cpool: &[JsValue]) -> Option<usize> {
+    if !matches!(i.op, OpCode::Fclosure | OpCode::Fclosure8) {
+        return None;
+    }
+    let ImmOperand::Const(index) = i.imm else {
+        return None;
+    };
+    match cpool.get(index as usize) {
+        Some(JsValue::FnById(id)) => Some(*id),
+        _ => None,
+    }
+}
+
+/// Load one captured value out of the parent frame into `into`. Only parent
+/// locals and args are supported; any other source is a preserved gap and
+/// loads `undefined`.
+fn load_capture(source: CaptureFrom, into: usize) -> RegInstr {
+    match source {
+        CaptureFrom::ParentLocal(slot) => get_loc(into, slot),
+        CaptureFrom::ParentArg(slot) => get_arg(into, slot),
+        _ => RegInstr::new(OpCode::Undefined, ImmOperand::None, vec![into], vec![]),
+    }
+}
+
+// ── 3. every call goes through the object ──────────────────────────────────
+
+/// A call names a closure object now, not a function. Read the function out of
+/// field 0, and pass the object itself as the trailing env argument.
+fn route_calls_through_object(mut reg_fn: RegFn) -> RegFn {
+    let code = std::mem::take(&mut reg_fn.code);
+    let mut out = Vec::with_capacity(code.len());
+
+    for instr in code {
+        let Some((op, argc)) = plain_call(&instr) else {
+            out.push(instr);
+            continue;
+        };
+
+        // The callee is the deepest stack slot, so it is popped last.
+        let closure = *instr.args.last().unwrap();
+        let func = reg_fn.fresh_val();
+        out.push(get_field(int_field(0), func, closure));
+
+        // Args become [ env, <original args>, func ]: the env is pushed last so
+        // it pops first, and the callee stays last.
+        let mut args = Vec::with_capacity(instr.args.len() + 1);
+        args.push(closure);
+        args.extend_from_slice(&instr.args[..instr.args.len() - 1]);
+        args.push(func);
+
+        out.push(RegInstr::new(
+            op,
+            ImmOperand::Npop(argc + 1),
+            instr.dsts,
+            args,
+        ));
+    }
+
+    reg_fn.code = out;
+    reg_fn
+}
+
+/// The opcode to emit and the argument count, for a plain call. `None` if this
+/// is not one: the receiver-carrying calls (`call_method`, `call_constructor`,
+/// `apply`) are deliberately excluded.
+///
+/// A tail call stays a tail call -- it pushes nothing and returns, so turning
+/// it into an ordinary `call` would leave a value behind and drop the return.
+fn plain_call(i: &RegInstr) -> Option<(OpCode, u16)> {
+    if i.args.is_empty() {
+        return None;
+    }
+    let npop = || match i.imm {
+        ImmOperand::Npop(n) => n,
+        _ => unreachable!("a call opcode without an npop operand"),
+    };
+    Some(match i.op {
+        OpCode::Call0 => (OpCode::Call, 0),
+        OpCode::Call1 => (OpCode::Call, 1),
+        OpCode::Call2 => (OpCode::Call, 2),
+        OpCode::Call3 => (OpCode::Call, 3),
+        OpCode::Call => (OpCode::Call, npop()),
+        OpCode::TailCall => (OpCode::TailCall, npop()),
+        _ => return None,
+    })
+}
+
+// ── emitted instructions ───────────────────────────────────────────────────
+
+fn get_arg(dst: usize, arg: usize) -> RegInstr {
+    RegInstr::new(OpCode::GetArg, ImmOperand::Arg(arg as u16), vec![dst], vec![])
+}
+
+fn get_loc(dst: usize, loc: usize) -> RegInstr {
+    RegInstr::new(OpCode::GetLoc, ImmOperand::Loc(loc as u16), vec![dst], vec![])
+}
+
+fn object(dst: usize) -> RegInstr {
+    RegInstr::new(OpCode::Object, ImmOperand::None, vec![dst], vec![])
+}
+
+fn get_field(field: ImmOperand, dst: usize, obj: usize) -> RegInstr {
+    RegInstr::new(OpCode::GetField, field, vec![dst], vec![obj])
+}
+
+fn put_field(field: ImmOperand, value: usize, obj: usize) -> RegInstr {
+    RegInstr::new(OpCode::PutField, field, vec![], vec![value, obj])
+}
+
+fn define_field(field: ImmOperand, dst: usize, value: usize, obj: usize) -> RegInstr {
+    RegInstr::new(OpCode::DefineField, field, vec![dst], vec![value, obj])
+}
+
+/// A plain integer field name, as an operand.
+fn int_field(n: u32) -> ImmOperand {
+    ImmOperand::Atom(AtomRef::TaggedInt(n))
+}

compiler/src/flatten.rs

@@ -4,7 +4,7 @@ use crate::parse::{
     Atom, AtomRef, ClosureKind, Function, Instr, JsString, JsValue, QuickJSBinary, atom_names,
 };
 
-#[derive(Debug)]
+#[derive(Debug, Clone, Copy)]
 pub enum CaptureFrom {
     /// `parent.var_defs[i]`
     ParentArg(usize),

compiler/src/main.rs

@@ -1,4 +1,5 @@
 mod declass;
+mod declosure;
 mod flatten;
 mod parse;
 mod regify;
@@ -6,6 +7,7 @@ mod regify;
 use std::process::Command;
 
 use declass::declass;
+use declosure::declosure;
 use flatten::flatten;
 use parse::QuickJSBinary;
 use regify::regify;
@@ -41,6 +43,10 @@ fn main() {
     let declassed = declass(reg_fns, &atoms);
     println!("{declassed:#?}");
 
+    println!("=== after declosure ===");
+    let declosured = declosure(declassed);
+    println!("{declosured:#?}");
+
     println!("{atoms:#?}");
 
     /*println!("=== after deprototype ===");

compiler/src/regify.rs

@@ -1,10 +1,8 @@
-#![allow(non_snake_case)]
-
 use std::fmt::Debug;
 
 use crate::{
     flatten::{Capture, FlatFn},
-    parse::{AtomRef, ImmOperand, Instr, JsValue, opcodes::OpCode},
+    parse::{AtomRef, ImmOperand, JsValue, opcodes::OpCode},
 };
 
 pub struct RegInstr {
@@ -51,7 +49,7 @@ impl RegFn {
     fn from_flat(flat_fn: FlatFn) -> Self {
         let mut stack = vec![];
         let mut output = Vec::with_capacity(flat_fn.code.len());
-        let mut next_val = flat_fn.var_count;
+        let mut next_val = flat_fn.var_count; // Reserve values for locals
 
         let mut fresh_val = || {
             let v = next_val;

docs/declass_algo.txt

@@ -175,16 +175,29 @@ Swap, CallMethod, PutLoc1, Drop) still occur elsewhere for ordinary reasons.
 Only the specific class-pattern instances listed above are removed.
 
 
+====================================================================
+UNSUPPORTED (the pass panics)
+====================================================================
+
+    DefineClass AtomU8 { arg: 1 }        derived class (extends)
+
+    Prototype form would have to flatten the parent's prototype into the
+    child's and lower `super`. Neither is implemented, so declass panics
+    rather than emit a class that has silently lost its parent.
+
+
 ====================================================================
 NOT TOUCHED (passed through unchanged)
 ====================================================================
 
-    DefineClass AtomU8 { arg: 1 }        derived class
-    DefineMethod AtomU8 { arg: 1 }       getter
-    DefineMethod AtomU8 { arg: 2 }       setter
     DefineMethodComputed ...             computed method name
     DefineClassComputed ...              computed class name
 
+    Known gap: a getter or setter (DefineMethod with a non-zero kind) is
+    NOT yet passed through. It is wrongly lowered as an ordinary method,
+    to a put_field, giving a data property instead of an accessor. It
+    should instead make the whole class pass through untouched.
+
 
 ====================================================================
 LEFT BEHIND (removed by a later pass)

docs/declosure_algo.txt

@@ -120,8 +120,12 @@ last argument, so it is args.last().
 
 DETECT, abstractly:
 
-    plain call   call | call0..3         (callee = last arg; not call_method,
-                                          call_constructor, or apply)
+    plain call   call | call0..3 | tail_call   (callee = last arg; not
+                                               call_method, call_constructor,
+                                               or apply)
+
+    A tail call stays a tail call. It pushes nothing and returns, so turning it
+    into an ordinary call would leave a value behind and drop the return.
 
 outer, which in the example is: