feat(codegen): relocate per-binder consume_count into MIR; delete codegen's second uniqueness run (mir.3a)

First of two iterations delivering spec 0060's mir.3 row (plan
docs/plans/0117-mir.3a-consume-count-relocation.md). The per-binder
consume_count — the only thing codegen read from its second
infer_module_with_cross run — now lives on a new binder-keyed
MirDef.consume: BTreeMap<String,u32>, filled once by lower_to_mir on the
post-mono body. Codegen builds its existing (def,binder)->consume_count
lookup from those maps and the three scope-close drop sites (own-param,
let-binder, match-arm) read it; the codegen uniqueness run, its
UniquenessTable field, and the import are deleted.

mir.3 is split into two iterations (recorded in spec 0060): the named
deletion depends ONLY on consume_count. All three drop sites read
consume_count from self.uniqueness, while the modes they also gate on
(param_modes for the own-param dec, scrutinee_is_owned for the match
dec) come from the type, not the uniqueness pass (UniquenessInfo carries
no mode). So mir.3a relocates consume_count and ships the deletion;
mir.3b (next) fills MArg.mode/MTerm::Let.mode and switches emit_call's
anon-temp gate onto MArg.mode. The split halves the change at the
codebase's highest-risk surface (RC/drop correctness, the raw-buf leak
saga) and makes each half independently verifiable against the live=0
leak pins.

Design: consume_count lands on MirDef (binder-keyed), NOT on MArg. The
drop sites key by (def, binder_name) — a per-binder aggregate — while the
spec-sketched MArg.consume_count is per-arg-position and never reaches
them; the per-def map matches the UniquenessTable's own keying and all
three binder kinds (param/let/pattern) uniformly. MArg.consume_count
stays a mir.1 default. Source = run check's infer_module_with_cross
inside lower_to_mir post-mono (the synth_pure single-engine-re-walked
pattern); retaining a check-time result is blocked (check's uniqueness
is pre-mono and runs on-demand-from-codegen, never in check_workspace,
so it would miss the mono specialisations). cross_module_types
(= codegen's module_def_ail_types) is rebuilt in elaborate_workspace
from the post-mono workspace.

Safety property held: this is a PURE RELOCATION of an identical
computation — infer_module_with_cross ran on the post-mono module in
codegen and now runs on the same post-mono module in lower_to_mir, so
drop placement is byte-identical. cross_module_types matches
module_def_ail_types exactly (both insert f.name->f.ty over post-mono
Def::Fn), confirmed by the leak pins staying green.

Verification (orchestrator, post-implement inspect): diff matches the
plan; codegen grep-clean for infer_module_with_cross + UniquenessTable
(now ailang-check-internal); cargo build --workspace clean (no errors,
no unused warnings — module_def_ail_types survives for emit_call's
anon-temp param_modes gate); cargo test --workspace 701 passed / 0
failed / 3 ignored (+1 = the new producer pin
mirdef_consume_is_populated_for_let_binder; no #[ignore] added). The
live=0 drop-correctness witnesses all green:
alloc_rc_loop_valued_rawbuf_binder_drops_at_scope_close (#43/#47),
alloc_rc_heap_loop_binder_replaced_by_recur_does_not_leak,
alloc_rc_print_int_does_not_leak_show_result_str. #49 stays #[ignore]
(mir.4); #51/#53 build guards green.

crates/ailang-check/src/lib.rs

@@ -1343,9 +1343,28 @@ pub fn elaborate_workspace(
         .map_err(|e| vec![internal_diag(format!("monomorphise_workspace: {e}"))])?;
     // 3. lower each post-mono module to MIR.
     let env = build_check_env(&mono);
+    // Workspace-flat `module -> def -> Type` table — the shape
+    // `uniqueness::infer_module_with_cross` consumes to resolve a
+    // cross-module callee's `param_modes` (so a Borrow-mode arg is
+    // walked as a borrow, not a consume). Identical in content to
+    // codegen's `module_def_ail_types`; built here from the post-mono
+    // workspace so the uniqueness pass runs in the producer (mir.3a).
+    let mut cross_module_types: std::collections::BTreeMap<
+        String,
+        std::collections::BTreeMap<String, ailang_core::ast::Type>,
+    > = std::collections::BTreeMap::new();
+    for (mname, m) in &mono.modules {
+        let mut def_tys = std::collections::BTreeMap::new();
+        for def in &m.defs {
+            if let ailang_core::ast::Def::Fn(f) = def {
+                def_tys.insert(f.name.clone(), f.ty.clone());
+            }
+        }
+        cross_module_types.insert(mname.clone(), def_tys);
+    }
     let mut modules = std::collections::BTreeMap::new();
     for (name, m) in &mono.modules {
-        let mir = lower_to_mir::lower_module(m, &env)
+        let mir = lower_to_mir::lower_module(m, &env, &cross_module_types)
             .map_err(|e| vec![internal_diag(format!("lower_to_mir in `{name}`: {e}"))])?;
         modules.insert(name.clone(), mir);
     }

crates/ailang-check/src/lower_to_mir.rs

@@ -408,7 +408,11 @@ fn lower_term(ctx: &mut Ctx, t: &Term) -> Result<MTerm> {
 /// env (built by `build_check_env`); this fn sets `env.imports` for
 /// the module and seeds per-fn `locals` from the declared params,
 /// mirroring mono.rs:771-816.
-pub fn lower_module(module: &Module, env: &Env) -> Result<MirModule> {
+pub fn lower_module(
+    module: &Module,
+    env: &Env,
+    cross_module_types: &std::collections::BTreeMap<String, std::collections::BTreeMap<String, Type>>,
+) -> Result<MirModule> {
     let mut env = env.clone();
     env.current_module = module.name.clone();
     // Seed `env.globals` from the current module's fns so `synth`'s
@@ -458,6 +462,14 @@ pub fn lower_module(module: &Module, env: &Env) -> Result<MirModule> {
     for m in all_modules {
         env.imports.entry(m.clone()).or_insert(m);
     }
+    // mir.3a: run the single uniqueness engine ONCE on this post-mono
+    // module. The resulting per-(def, binder) consume_count is attached
+    // to each `MirDef.consume` below; codegen reads it instead of
+    // re-running `infer_module_with_cross`. Same pass, same post-mono
+    // input as codegen used — a pure relocation, so drop placement is
+    // unchanged.
+    let uniqueness =
+        crate::uniqueness::infer_module_with_cross(module, cross_module_types);
     let mut defs = Vec::new();
     let mut consts = Vec::new();
     for def in &module.defs {
@@ -521,6 +533,11 @@ pub fn lower_module(module: &Module, env: &Env) -> Result<MirModule> {
             sig: f.ty.clone(),
             params: f.params.clone(),
             body,
+            consume: uniqueness
+                .iter()
+                .filter(|((d, _), _)| d == &f.name)
+                .map(|((_, b), info)| (b.clone(), info.consume_count))
+                .collect(),
         });
     }
     Ok(MirModule { name: module.name.clone(), ast: module.clone(), defs, consts })

crates/ailang-check/tests/lower_to_mir_ty.rs

@@ -149,6 +149,23 @@ fn callee_classification_builtin_and_static() {
     }
 }
 
+#[test]
+fn mirdef_consume_is_populated_for_let_binder() {
+    // mir.3a: lower_to_mir runs the uniqueness pass and attaches the
+    // per-binder consume_count to MirDef.consume. `main`'s `(let c …)`
+    // binder must appear in the map (the exact count is validated
+    // end-to-end by the RC-stats leak pins; this pin guards that the
+    // producer fills the field at all, so codegen has it to read).
+    let ws = elaborate_fixture("new_counter_user_adt");
+    let m = ws.modules.get("new_counter_user_adt").expect("module");
+    let main = m.defs.iter().find(|d| d.name == "main").expect("main");
+    assert!(
+        main.consume.contains_key("c"),
+        "MirDef.consume must carry the `c` let-binder, got {:?}",
+        main.consume,
+    );
+}
+
 /// Recursively search for a `MTerm::Str { rep: Static }` reachable
 /// from a loop binder init (the seed).
 fn find_static_str_seed(t: &MTerm) -> bool {

crates/ailang-codegen/src/lib.rs

@@ -39,8 +39,6 @@ use ailang_core::Workspace;
 use ailang_mir::{Callee, MArg, MTerm, MirDef, MirWorkspace};
 use std::collections::{BTreeMap, BTreeSet};
 
-use ailang_check::uniqueness::{infer_module_with_cross, UniquenessTable};
-
 mod drop;
 mod escape;
 mod intercepts;
@@ -839,13 +837,15 @@ struct Emitter<'a> {
     /// Decided at the top-level entry point (`lower_workspace_inner`)
     /// and propagated to every site that emits a `call ptr @<alloc>(...)`.
     alloc: AllocStrategy,
-    /// per-binder uniqueness side-table for the current
-    /// module, keyed by `(def_name, binder_name)`. Built once per
-    /// emitter and consulted by `Term::Let` lowering to decide whether
-    /// to emit `call void @ailang_rc_dec(ptr %v)` at scope close. The
-    /// table is module-scoped because the inference is whole-fn local;
-    /// no cross-module entries appear.
-    uniqueness: UniquenessTable,
+    /// per-binder consume_count for the current module, keyed by
+    /// `(def_name, binder_name)`. Consulted by `Term::Let` lowering
+    /// (and the own-param / match-arm drop sites) to decide whether to
+    /// emit `call void @ailang_rc_dec(ptr %v)` at scope close. The table
+    /// is module-scoped because the inference is whole-fn local; no
+    /// cross-module entries appear. Built from `MirDef.consume` (mir.3a)
+    /// — codegen no longer re-runs the uniqueness pass; `lower_to_mir`
+    /// owns the single run.
+    consume: std::collections::BTreeMap<(String, String), u32>,
     /// per-closure-pair drop-function symbol. Keyed by the
     /// closure-pair SSA value (e.g. `%v17`) the most-recent
     /// `lower_lambda` call returned. Consulted by the `Term::Let`
@@ -1016,17 +1016,18 @@ impl<'a> Emitter<'a> {
             }
         }
 
-        // build the per-module uniqueness side-table once
-        // per emitter. The inference is pure (no I/O, no global state),
-        // so doing it here is cheap and keeps codegen's input self-
-        // contained. Pass the workspace-flat cross-module signature
-        // table so a qualified cross-module borrow callee (e.g. the
-        // monomorphised intrinsic `raw_buf.RawBuf_get__Int` reached
-        // from a `main` in another module) resolves to its registered
-        // `param_modes` instead of defaulting every arg to Consume —
-        // which otherwise inflates the borrow binder's consume_count
-        // and gates off its scope-close drop.
-        let uniqueness = infer_module_with_cross(module, module_def_ail_types);
+        // mir.3a: read the per-binder consume_count off MIR (filled by
+        // lower_to_mir from the single uniqueness pass) instead of
+        // re-running the uniqueness pass here.
+        let consume: std::collections::BTreeMap<(String, String), u32> = mir_bodies
+            .iter()
+            .flat_map(|d| {
+                let dname = d.name.clone();
+                d.consume
+                    .iter()
+                    .map(move |(b, c)| ((dname.clone(), b.clone()), *c))
+            })
+            .collect();
 
         Self {
             module,
@@ -1054,7 +1055,7 @@ impl<'a> Emitter<'a> {
             deferred_thunks: Vec::new(),
             non_escape: NonEscapeSet::new(),
             alloc,
-            uniqueness,
+            consume,
             closure_drops: BTreeMap::new(),
             moved_slots: BTreeMap::new(),
             current_param_modes: BTreeMap::new(),
@@ -1508,9 +1509,9 @@ impl<'a> Emitter<'a> {
                         continue;
                     }
                     let consume_count = self
-                        .uniqueness
+                        .consume
                         .get(&(self.current_def.clone(), pname.clone()))
-                        .map(|info| info.consume_count)
+                        .copied()
                         .unwrap_or(u32::MAX);
                     if consume_count != 0 {
                         continue;
@@ -1875,9 +1876,9 @@ impl<'a> Emitter<'a> {
                 // so the refcount story is unchanged.
                 if trackable && val_ty == "ptr" && !self.block_terminated {
                     let consume_count = self
-                        .uniqueness
+                        .consume
                         .get(&(self.current_def.clone(), name.clone()))
-                        .map(|info| info.consume_count)
+                        .copied()
                         .unwrap_or(u32::MAX); // Defensive: skip if missing.
                     let body_returns_binder = match &r {
                         Ok((body_ssa, _)) => body_ssa == &val_ssa,

crates/ailang-codegen/src/match_lower.rs

@@ -794,9 +794,9 @@ impl<'a> Emitter<'a> {
                         continue;
                     }
                     let consume_count = self
-                        .uniqueness
+                        .consume
                         .get(&(self.current_def.clone(), bname.clone()))
-                        .map(|info| info.consume_count)
+                        .copied()
                         .unwrap_or(u32::MAX);
                     if consume_count != 0 {
                         continue;

crates/ailang-mir/src/lib.rs

@@ -55,6 +55,14 @@ pub struct MirDef {
     pub sig: Type,
     pub params: Vec<String>,
     pub body: MTerm,
+    /// Per-binder consume count for this def's body, keyed by binder
+    /// name (let-binders, params, pattern-binders). `0` means the
+    /// binder is exclusively borrowed/unused in its scope and codegen
+    /// must emit the scope-close `dec` under `--alloc=rc`. Filled by
+    /// `lower_to_mir` from `ailang_check::uniqueness::infer_module_with_cross`
+    /// (mir.3a) — the single uniqueness engine, run once on the
+    /// post-mono body. Codegen reads it instead of re-running the pass.
+    pub consume: BTreeMap<String, u32>,
 }
 
 /// One MIR node — structural counterpart of `ast::Term`, plus the