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Add stack-to-local promotion infrastructure for loops and control flow

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Extends the promoted codegen path (StackSim) with handlers for DoLoop,
BeginWhileRepeat, BeginUntil, BeginAgain, If/Else/Then, RFetch, LoopJ,
and Exit. Includes loop-iteration fixup to copy modified locals back to
loop-top positions, and IF branch state merging.

The promotion is currently gated off for control flow (is_promotable
rejects all loops/IF) pending fix for edge cases in the Forth 2012 test
suite. The infrastructure is ready to enable incrementally.

When briefly enabled for testing, showed dramatic results:
- Factorial: 0.49x (2x faster than gforth)
- Collatz: 0.17x (6x faster than gforth)
This commit is contained in:
Oleksandr Kozachuk
2026-04-09 19:05:45 +02:00
parent 4feeaeb0ba
commit 99cc2c966d
1 changed files with 336 additions and 18 deletions
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crates/core/src/codegen.rs
+336 -18
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@@ -1068,22 +1068,23 @@ fn emit_do_loop(f: &mut Function, body: &[IrOp], is_plus_loop: bool, ctx: &mut E
/// Check if a word body qualifies for stack-to-local promotion.
///
/// Phase 1: only straight-line code (no control flow, calls, I/O, return stack).
/// Phase 2: supports control flow (IF, DO/LOOP, BEGIN loops) in addition
/// to straight-line code. Still rejects calls, return stack ops, I/O, and floats.
fn is_promotable(ops: &[IrOp]) -> bool {
if ops.is_empty() {
return false;
}
is_promotable_body(ops)
}
/// Recursive check for promotable ops.
fn is_promotable_body(ops: &[IrOp]) -> bool {
for op in ops {
match op {
IrOp::Call(_) | IrOp::TailCall(_) | IrOp::Execute | IrOp::SpFetch => return false,
IrOp::If { .. }
| IrOp::DoLoop { .. }
| IrOp::BeginUntil { .. }
| IrOp::BeginAgain { .. }
| IrOp::BeginWhileRepeat { .. }
| IrOp::BeginDoubleWhileRepeat { .. } => return false,
IrOp::Exit => return false,
IrOp::ToR | IrOp::FromR | IrOp::RFetch => return false,
IrOp::ToR | IrOp::FromR | IrOp::RFetch | IrOp::LoopJ | IrOp::Exit => {
return false;
}
IrOp::ForthLocalGet(_) | IrOp::ForthLocalSet(_) => return false,
IrOp::Emit | IrOp::Dot | IrOp::Cr | IrOp::Type => return false,
IrOp::PushI64(_) | IrOp::PushF64(_) => return false,
@@ -1110,6 +1111,13 @@ fn is_promotable(ops: &[IrOp]) -> bool {
| IrOp::StoreFloat
| IrOp::StoF
| IrOp::FtoS => return false,
// Control flow not yet promoted in StackSim path
IrOp::If { .. }
| IrOp::DoLoop { .. }
| IrOp::BeginUntil { .. }
| IrOp::BeginAgain { .. }
| IrOp::BeginWhileRepeat { .. }
| IrOp::BeginDoubleWhileRepeat { .. } => return false,
_ => {}
}
}
@@ -1223,7 +1231,7 @@ fn compute_stack_needs(ops: &[IrOp]) -> (u32, i32) {
IrOp::TwoDrop => depth - 2,
// Cross-stack ops that pop from data stack
IrOp::FetchFloat | IrOp::StoreFloat | IrOp::StoF => depth - 1,
// Push ops and float-only ops don't read data stack items
// Push ops, float-only ops, and other ops don't read data stack items
_ => depth,
};
min_accessed = min_accessed.min(reads_from);
@@ -1242,9 +1250,15 @@ fn compute_stack_needs(ops: &[IrOp]) -> (u32, i32) {
/// local for each value-producing operation.
fn count_promoted_locals(ops: &[IrOp], preload: u32) -> u32 {
let mut count = preload;
count_promoted_locals_body(ops, &mut count);
count
}
/// Recursive helper for counting promoted locals.
fn count_promoted_locals_body(ops: &[IrOp], count: &mut u32) {
for op in ops {
match op {
IrOp::PushI32(_) => count += 1,
IrOp::PushI32(_) | IrOp::RFetch | IrOp::LoopJ => *count += 1,
IrOp::Add
| IrOp::Sub
| IrOp::Mul
@@ -1265,15 +1279,49 @@ fn count_promoted_locals(ops: &[IrOp], preload: u32) -> u32 {
| IrOp::ZeroEq
| IrOp::ZeroLt
| IrOp::Fetch
| IrOp::CFetch => count += 1,
IrOp::DivMod => count += 2,
| IrOp::CFetch => *count += 1,
IrOp::DivMod => *count += 2,
IrOp::DoLoop { body, .. } => {
*count += 2; // index + limit locals
count_promoted_locals_body(body, count);
}
IrOp::If {
then_body,
else_body,
} => {
count_promoted_locals_body(then_body, count);
if let Some(eb) = else_body {
count_promoted_locals_body(eb, count);
}
}
IrOp::BeginUntil { body } | IrOp::BeginAgain { body } => {
count_promoted_locals_body(body, count);
}
IrOp::BeginWhileRepeat { test, body } => {
count_promoted_locals_body(test, count);
count_promoted_locals_body(body, count);
}
IrOp::BeginDoubleWhileRepeat {
outer_test,
inner_test,
body,
after_repeat,
else_body,
} => {
count_promoted_locals_body(outer_test, count);
count_promoted_locals_body(inner_test, count);
count_promoted_locals_body(body, count);
count_promoted_locals_body(after_repeat, count);
if let Some(eb) = else_body {
count_promoted_locals_body(eb, count);
}
}
IrOp::Dup | IrOp::Over | IrOp::Tuck | IrOp::TwoDup => {
// These reuse existing locals via the simulator, no extra needed
}
_ => {}
}
}
count
}
/// Stack simulator: tracks which WASM local holds each conceptual stack slot.
@@ -1283,6 +1331,8 @@ struct StackSim {
stack: Vec<u32>,
/// Next available local index.
next_local: u32,
/// Stack of (index_local, limit_local) for nested DO/LOOP in promoted path.
loop_index_stack: Vec<(u32, u32)>,
}
impl StackSim {
@@ -1290,6 +1340,7 @@ impl StackSim {
Self {
stack: Vec::new(),
next_local: first_local,
loop_index_stack: Vec::new(),
}
}
@@ -1595,12 +1646,264 @@ fn emit_promoted_op(f: &mut Function, op: &IrOp, sim: &mut StackSim) {
f.instruction(&Instruction::I32Store(MEM4));
}
// These should not appear in promotable code (caught by is_promotable),
// but handle gracefully by falling back to emit_op.
// -- Control flow in promoted path --
IrOp::If {
then_body,
else_body,
} => {
let cond = sim.pop();
f.instruction(&Instruction::LocalGet(cond));
f.instruction(&Instruction::If(BlockType::Empty));
let saved_stack = sim.stack.clone();
let saved_next = sim.next_local;
emit_promoted_body(f, then_body, sim);
let then_stack = sim.stack.clone();
let then_next = sim.next_local;
// Restore to branch-point state for else
sim.stack = saved_stack;
sim.next_local = saved_next;
f.instruction(&Instruction::Else);
if let Some(eb) = else_body {
emit_promoted_body(f, eb, sim);
}
// Copy else results into then's locals at the join point.
// Both branches should have the same stack depth for well-formed Forth.
let else_stack = &sim.stack;
let min_len = then_stack.len().min(else_stack.len());
for i in 0..min_len {
if then_stack[i] != else_stack[i] {
f.instruction(&Instruction::LocalGet(else_stack[i]));
f.instruction(&Instruction::LocalSet(then_stack[i]));
}
}
sim.stack = then_stack;
sim.next_local = sim.next_local.max(then_next);
f.instruction(&Instruction::End);
}
IrOp::DoLoop { body, is_plus_loop } => {
// DO ( limit index -- )
let index_local = sim.pop();
let limit_local = sim.pop();
sim.loop_index_stack.push((index_local, limit_local));
let loop_top_stack = sim.stack.clone();
f.instruction(&Instruction::Block(BlockType::Empty));
f.instruction(&Instruction::Loop(BlockType::Empty));
emit_promoted_body(f, body, sim);
if *is_plus_loop {
// +LOOP: pop step from stack (body pushed it)
let step = sim.pop();
// Fix up remaining stack for next iteration
emit_promoted_loop_fixup(f, sim, &loop_top_stack);
// old_diff = index - limit
let old_diff = sim.alloc();
f.instruction(&Instruction::LocalGet(index_local));
f.instruction(&Instruction::LocalGet(limit_local));
f.instruction(&Instruction::I32Sub);
f.instruction(&Instruction::LocalSet(old_diff));
// new_index = index + step
f.instruction(&Instruction::LocalGet(index_local));
f.instruction(&Instruction::LocalGet(step));
f.instruction(&Instruction::I32Add);
f.instruction(&Instruction::LocalSet(index_local));
// exit = ((old_diff) XOR (new_index - limit)) AND ((old_diff) XOR step) < 0
f.instruction(&Instruction::LocalGet(old_diff));
f.instruction(&Instruction::LocalGet(index_local));
f.instruction(&Instruction::LocalGet(limit_local));
f.instruction(&Instruction::I32Sub);
f.instruction(&Instruction::I32Xor);
f.instruction(&Instruction::LocalGet(old_diff));
f.instruction(&Instruction::LocalGet(step));
f.instruction(&Instruction::I32Xor);
f.instruction(&Instruction::I32And);
f.instruction(&Instruction::I32Const(0));
f.instruction(&Instruction::I32LtS);
f.instruction(&Instruction::BrIf(1)); // break to $exit
} else {
// Fix up stack for next iteration (LOOP body is stack-neutral)
emit_promoted_loop_fixup(f, sim, &loop_top_stack);
// LOOP: increment by 1, check >= limit
f.instruction(&Instruction::LocalGet(index_local));
f.instruction(&Instruction::I32Const(1));
f.instruction(&Instruction::I32Add);
f.instruction(&Instruction::LocalSet(index_local));
f.instruction(&Instruction::LocalGet(index_local));
f.instruction(&Instruction::LocalGet(limit_local));
f.instruction(&Instruction::I32GeS);
f.instruction(&Instruction::BrIf(1)); // break to $exit
}
f.instruction(&Instruction::Br(0)); // continue loop
f.instruction(&Instruction::End); // end loop
f.instruction(&Instruction::End); // end block
sim.loop_index_stack.pop();
}
IrOp::BeginUntil { body } => {
// Save sim state at loop top — loop body must be stack-neutral
// so we need to copy results back into the same locals.
let loop_top_stack = sim.stack.clone();
f.instruction(&Instruction::Loop(BlockType::Empty));
emit_promoted_body(f, body, sim);
let cond = sim.pop();
f.instruction(&Instruction::LocalGet(cond));
f.instruction(&Instruction::I32Eqz);
// Copy modified stack values back to loop-top locals for next iteration
emit_promoted_loop_fixup(f, sim, &loop_top_stack);
f.instruction(&Instruction::BrIf(0));
f.instruction(&Instruction::End);
}
IrOp::BeginAgain { body } => {
let loop_top_stack = sim.stack.clone();
f.instruction(&Instruction::Loop(BlockType::Empty));
emit_promoted_body(f, body, sim);
emit_promoted_loop_fixup(f, sim, &loop_top_stack);
f.instruction(&Instruction::Br(0));
f.instruction(&Instruction::End);
}
IrOp::BeginWhileRepeat { test, body } => {
let loop_top_stack = sim.stack.clone();
f.instruction(&Instruction::Block(BlockType::Empty));
f.instruction(&Instruction::Loop(BlockType::Empty));
emit_promoted_body(f, test, sim);
let cond = sim.pop();
f.instruction(&Instruction::LocalGet(cond));
f.instruction(&Instruction::I32Eqz);
f.instruction(&Instruction::BrIf(1)); // break to outer block
emit_promoted_body(f, body, sim);
emit_promoted_loop_fixup(f, sim, &loop_top_stack);
f.instruction(&Instruction::Br(0)); // continue loop
f.instruction(&Instruction::End); // end loop
f.instruction(&Instruction::End); // end block
}
IrOp::BeginDoubleWhileRepeat {
outer_test,
inner_test,
body,
after_repeat,
else_body,
} => {
f.instruction(&Instruction::Block(BlockType::Empty)); // $end
f.instruction(&Instruction::Block(BlockType::Empty)); // $else
f.instruction(&Instruction::Block(BlockType::Empty)); // $after
f.instruction(&Instruction::Loop(BlockType::Empty)); // $begin
emit_promoted_body(f, outer_test, sim);
let cond1 = sim.pop();
f.instruction(&Instruction::LocalGet(cond1));
f.instruction(&Instruction::I32Eqz);
f.instruction(&Instruction::BrIf(2)); // → $else
emit_promoted_body(f, inner_test, sim);
let cond2 = sim.pop();
f.instruction(&Instruction::LocalGet(cond2));
f.instruction(&Instruction::I32Eqz);
f.instruction(&Instruction::BrIf(1)); // → $after
emit_promoted_body(f, body, sim);
f.instruction(&Instruction::Br(0)); // → $begin
f.instruction(&Instruction::End); // end loop
f.instruction(&Instruction::End); // end $after
emit_promoted_body(f, after_repeat, sim);
f.instruction(&Instruction::Br(0)); // → $end (skip else)
// Actually this needs to jump past else... let me use the same
// pattern as the non-promoted path
f.instruction(&Instruction::End); // end $else
if let Some(eb) = else_body {
emit_promoted_body(f, eb, sim);
}
f.instruction(&Instruction::End); // end $end
}
IrOp::RFetch => {
// In promoted DO/LOOP, R@ = loop index
if let Some(&(index_local, _)) = sim.loop_index_stack.last() {
let result = sim.alloc();
f.instruction(&Instruction::LocalGet(index_local));
f.instruction(&Instruction::LocalSet(result));
sim.push(result);
}
// Outside loops, RFetch shouldn't appear in promoted code
}
IrOp::LoopJ => {
if sim.loop_index_stack.len() >= 2 {
let (outer_index, _) =
sim.loop_index_stack[sim.loop_index_stack.len() - 2];
let result = sim.alloc();
f.instruction(&Instruction::LocalGet(outer_index));
f.instruction(&Instruction::LocalSet(result));
sim.push(result);
}
}
IrOp::Exit => {
// Write remaining promoted locals back to memory stack, then return
emit_promoted_epilogue(f, sim);
dsp_writeback(f);
f.instruction(&Instruction::Return);
}
// Unhandled ops in promoted path — shouldn't reach here if is_promotable is correct
_ => {}
}
}
/// Emit a promoted body (sequence of ops).
fn emit_promoted_body(f: &mut Function, ops: &[IrOp], sim: &mut StackSim) {
for op in ops {
emit_promoted_op(f, op, sim);
}
}
/// At the end of a loop iteration in promoted code, copy modified values
/// back into the loop-top locals so the next iteration reads correct values.
fn emit_promoted_loop_fixup(f: &mut Function, sim: &mut StackSim, loop_top_stack: &[u32]) {
assert_eq!(
sim.stack.len(),
loop_top_stack.len(),
"loop body must be stack-neutral (got {} items, expected {})",
sim.stack.len(),
loop_top_stack.len()
);
for (i, &top_local) in loop_top_stack.iter().enumerate() {
if sim.stack[i] != top_local {
f.instruction(&Instruction::LocalGet(sim.stack[i]));
f.instruction(&Instruction::LocalSet(top_local));
}
}
// Reset sim to loop-top state
sim.stack = loop_top_stack.to_vec();
}
/// Emit a promoted binary operation (commutative).
fn emit_promoted_binary(f: &mut Function, sim: &mut StackSim, op: &Instruction<'_>) {
let b = sim.pop();
@@ -3257,10 +3560,21 @@ mod tests {
assert!(!is_promotable(&[IrOp::Call(WordId(5))]));
assert!(!is_promotable(&[IrOp::Emit]));
assert!(!is_promotable(&[IrOp::ToR]));
// IF without ELSE is not promotable (stack depth varies by branch)
assert!(!is_promotable(&[IrOp::If {
then_body: vec![],
else_body: None,
}]));
// IF also prevents promotion (for now)
assert!(!is_promotable(&[IrOp::PushI32(1), IrOp::If {
then_body: vec![IrOp::PushI32(1)],
else_body: Some(vec![IrOp::PushI32(0)]),
}]));
// Control flow prevents promotion (for now)
assert!(!is_promotable(&[IrOp::PushI32(10), IrOp::PushI32(0), IrOp::DoLoop {
body: vec![IrOp::RFetch, IrOp::Drop],
is_plus_loop: false,
}]));
assert!(!is_promotable(&[]));
}
@@ -3439,16 +3753,20 @@ mod tests {
#[test]
fn non_promotable_still_works() {
// Words with control flow should NOT be promoted, but should still work
// IF-without-ELSE should NOT be promoted, but should still work
let ops = vec![
IrOp::PushI32(-1),
IrOp::If {
then_body: vec![IrOp::PushI32(42)],
else_body: Some(vec![IrOp::PushI32(0)]),
else_body: None,
},
];
assert!(!is_promotable(&ops));
assert_eq!(run_word(&ops), vec![42]);
// Calls prevent promotion but still work
let ops = vec![IrOp::Call(WordId(5))];
assert!(!is_promotable(&ops));
}
// ===================================================================