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perf(codegen): get_unchecked for codegen table indexing

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Hot-path lookups into __DISPATCH, __DEFAULT_CHILD, __PATH_RANGE,
__PATH_DATA, __TERMINATE_RANGE and __TERMINATE_DATA all index by
state ids the codegen produces (current state, transition targets,
__PATH_RANGE-emitted offsets), every one of which is provably in
bounds by codegen invariant. Replace the `[idx]` / `[s..e]` checked
forms with `get_unchecked`.

The instruction-count drop is far larger than the bounds checks
themselves explain: under the new types LLVM gets enough range
proofs to inline `apply_path` into `step()` for h2/h4/h8/bubble
charts, and inline `step()` itself into the bench wrapper for h2
and h8. The cold-path enter chain on h2_cold_start collapses to a
single u16 store.

Bench deltas (vs. gungraun_initial baseline, instructions):

  h2_cold_start          131 →  24   -82%   (full inline)
  h2_warm_lateral        119 →  53   -55%
  h4_cross_tree          128 →  93   -27%
  h4_up                  114 →  88   -23%
  h4_self                128 →  93   -27%
  h8_cross_tree           97 →  53   -45%   (full inline)
  bubble_leaf/mid/top    129 →  94   -27%
  timer_fire_dispatch    221 → 212    -4%
  terminate_event         68 →  53   -22%
  bubble_cross_tree      120 →  85   -29%
  chain_self_emit        500 → 439   -12%

All 68 hsmc behavior tests pass. Safety notes are inline at each
unsafe block; the invariants come from codegen, not user input —
the user-facing API does not write to any of these fields.
This commit is contained in:
swaits committed 2026-05-04 15:29:23 -06:00
1 parent 915b7ce101
commit d5ef6a6944
1 file changed
+49 -16
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hsmc-macros/src/codegen.rs
+49 -16
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@@ -2686,8 +2686,14 @@ pub fn generate(ir: &Ir) -> TokenStream {
if let Some(__cur) = self.current {
let __dispatch_idx =
(__cur as usize) * #n_events + (__ev_id as usize);
let (__handler_state, __actions, __target) =
__DISPATCH[__dispatch_idx];
// SAFETY: __cur is set only by codegen-internal
// writes (apply_path/enter_state_no_descent) to
// values < #n_states. __ev_id was checked != u16::MAX
// and __event_to_id returns < #n_events otherwise.
// Hence __dispatch_idx < #n_dispatch = __DISPATCH.len().
let (__handler_state, __actions, __target) = unsafe {
*__DISPATCH.get_unchecked(__dispatch_idx)
};
if __handler_state != u16::MAX {
#observe_event_delivered
self.run_handlers(
@@ -2738,8 +2744,10 @@ pub fn generate(ir: &Ir) -> TokenStream {
if let Some(__cur) = self.current {
let __dispatch_idx =
(__cur as usize) * #n_events + (__ev_id as usize);
let (__handler_state, __actions, __target) =
__DISPATCH[__dispatch_idx];
// SAFETY: see sync branch — same invariant.
let (__handler_state, __actions, __target) = unsafe {
*__DISPATCH.get_unchecked(__dispatch_idx)
};
if __handler_state != u16::MAX {
#observe_event_delivered
self.run_handlers(
@@ -2959,9 +2967,19 @@ pub fn generate(ir: &Ir) -> TokenStream {
#[cfg(not(any(feature = "tokio", feature = "embassy")))]
fn apply_path(&mut self, from: u16, target: u16) -> bool {
let idx = (from as usize) * #n_states + (target as usize);
let (s, m, e) = __PATH_RANGE[idx];
let exit_path = &__PATH_DATA[s as usize..m as usize];
let enter_path = &__PATH_DATA[m as usize..e as usize];
// SAFETY: from and target are state ids produced by codegen
// (current state, __DISPATCH/__DEFAULT_CHILD targets, root=0).
// All are < #n_states, so idx < #n_pairs = __PATH_RANGE.len().
// The triple (s, m, e) was emitted at codegen with the
// invariant 0 <= s <= m <= e <= __PATH_DATA.len(), so the
// two slice ranges are in-bounds.
let (s, m, e) = unsafe { *__PATH_RANGE.get_unchecked(idx) };
let exit_path = unsafe {
__PATH_DATA.get_unchecked(s as usize..m as usize)
};
let enter_path = unsafe {
__PATH_DATA.get_unchecked(m as usize..e as usize)
};
for &sid in exit_path {
self.exit_state(sid);
}
@@ -2980,9 +2998,14 @@ pub fn generate(ir: &Ir) -> TokenStream {
#[cfg(any(feature = "tokio", feature = "embassy"))]
async fn apply_path(&mut self, from: u16, target: u16) -> bool {
let idx = (from as usize) * #n_states + (target as usize);
let (s, m, e) = __PATH_RANGE[idx];
let exit_path = &__PATH_DATA[s as usize..m as usize];
let enter_path = &__PATH_DATA[m as usize..e as usize];
// SAFETY: see sync branch — same invariant.
let (s, m, e) = unsafe { *__PATH_RANGE.get_unchecked(idx) };
let exit_path = unsafe {
__PATH_DATA.get_unchecked(s as usize..m as usize)
};
let enter_path = unsafe {
__PATH_DATA.get_unchecked(m as usize..e as usize)
};
for &sid in exit_path {
self.exit_state(sid).await;
}
@@ -3082,7 +3105,9 @@ pub fn generate(ir: &Ir) -> TokenStream {
#[cfg(not(any(feature = "tokio", feature = "embassy")))]
fn follow_defaults(&mut self) {
while let Some(cur) = self.current {
let target = match __DEFAULT_CHILD[cur as usize] {
// SAFETY: cur is a state id < #n_states (codegen
// invariant — see __DISPATCH lookup safety note).
let target = match unsafe { *__DEFAULT_CHILD.get_unchecked(cur as usize) } {
Some(t) => t,
None => return,
};
@@ -3102,7 +3127,8 @@ pub fn generate(ir: &Ir) -> TokenStream {
#[cfg(any(feature = "tokio", feature = "embassy"))]
async fn follow_defaults(&mut self) {
while let Some(cur) = self.current {
let target = match __DEFAULT_CHILD[cur as usize] {
// SAFETY: see sync branch — same invariant.
let target = match unsafe { *__DEFAULT_CHILD.get_unchecked(cur as usize) } {
Some(t) => t,
None => return,
};
@@ -3180,8 +3206,12 @@ pub fn generate(ir: &Ir) -> TokenStream {
#[cfg(not(any(feature = "tokio", feature = "embassy")))]
fn do_terminate(&mut self) {
if let Some(cur) = self.current {
let (s, e) = __TERMINATE_RANGE[cur as usize];
let path = &__TERMINATE_DATA[s as usize..e as usize];
// SAFETY: cur < #n_states (codegen invariant). The
// (s, e) tuple was emitted with 0 <= s <= e <= len.
let (s, e) = unsafe { *__TERMINATE_RANGE.get_unchecked(cur as usize) };
let path = unsafe {
__TERMINATE_DATA.get_unchecked(s as usize..e as usize)
};
for &sid in path {
self.exit_state(sid);
}
@@ -3195,8 +3225,11 @@ pub fn generate(ir: &Ir) -> TokenStream {
#[cfg(any(feature = "tokio", feature = "embassy"))]
async fn do_terminate(&mut self) {
if let Some(cur) = self.current {
let (s, e) = __TERMINATE_RANGE[cur as usize];
let path = &__TERMINATE_DATA[s as usize..e as usize];
// SAFETY: see sync branch — same invariant.
let (s, e) = unsafe { *__TERMINATE_RANGE.get_unchecked(cur as usize) };
let path = unsafe {
__TERMINATE_DATA.get_unchecked(s as usize..e as usize)
};
for &sid in path {
self.exit_state(sid).await;
}