ludic/selfhost/backend/emit_escape.ludic

# emit_escape.ludic — 25.3: which allocations never outlive the frame that made them. Every value a
# function handles is in a class (flow-insensitive: a local, a parameter, a function's result, an
# allocating construct), joined by two kinds of edge:
#   flow   a -> b  a's value can become b's (a let, an assignment, an argument into its parameter,
#                  a returned value into the function's result, that result into the call's value)
#   store  v -> t  v is written into t's contents (a field, an element, a push)
# HEAP: the class may alias memory that outlives a frame (a parameter, a state, a global, a value
# an unknown call hands back); it flows forward. ESC: the class's values may be kept - stored into
# something HEAP, into a global, handed to an unknown callee; it flows backward, along a flow edge
# from the escaping class and along a store edge from an escaping or HEAP target. A load is its
# base's class (field-insensitive), so what a record holds escapes with it.
# An allocating construct that ends up neither ESC nor in a function that spans frames (one that
# reaches Mem.frame) is LOCAL: uns = ES_SCRATCH marks its node, and it allocates from the current
# scratch (the frame's arena, emit_fence_ir). A text built by + copies its pieces, so they stay apart.

const ES_SCRATCH: int = 77                          # Node.uns on an allocating expression: scratch
const ES_ESC: int = 1
const ES_HEAP: int = 2
const ES_FREED: int = 4                             # given back with free(): not a leak at birth

var g_es_flag: []int = new []int
var g_es_why: []Node = new []Node                   # per class: the statement that made it escape
var g_es_own: []pointer = new []pointer             # per class: the state that holds it (25.5c's census)
var g_es_gname: []pointer = new []pointer           # a class per state global, so each state is its own
var g_es_gcls: []int = new []int
var g_es_ok: []pointer = new []pointer              # file:line of a kept site -> the state that holds it
var g_es_ov: []Node = new []Node
var g_es_swhy: []Node = new []Node                  # per store edge: its statement
var g_es_stmt: Node = null                          # the statement being walked
var g_es_aok: int = 0                               # inside a statement under @alloc_ok
var g_es_site_aok: []bool = new []bool              # the site is (not reported by the region rule)
var g_es_site_grow: []bool = new []bool             # the site is a push's growth (25.5's capacities, not the rule)
var g_es_done: bool = false
var g_es_fnrefs: []pointer = new []pointer          # functions taken as values (fn f): called from anywhere
var g_es_consumed: []Node = new []Node              # text used up where it is made (a + or == operand): freed at once
var g_es_ft: []int = new []int                      # flow edges
var g_es_ff: []int = new []int
var g_es_st: []int = new []int                      # store edges: value, target
var g_es_sv: []int = new []int
var g_es_site: []Node = new []Node                  # allocating constructs and their classes
var g_es_site_cls: []int = new []int
var g_es_site_fn: []int = new []int                 # the function each site is in
var g_es_fk: []pointer = new []pointer              # function records by name (ck_tab)
var g_es_fv: []Node = new []Node
var g_es_fparam: []int = new []int                  # per function: its first parameter's class
var g_es_fret: []int = new []int                    # its result's class
var g_es_fnode: []Node = new []Node
var g_es_fspans: []bool = new []bool                # it reaches Mem.frame: its sites stay on the heap
var g_es_calls_f: []int = new []int                 # direct calls, caller -> callee (function indexes)
var g_es_calls_t: []int = new []int
var g_es_ln: []pointer = new []pointer              # the current function's locals and their classes
var g_es_lc: []int = new []int
var g_es_lt: []pointer = new []pointer              # ... and their types, where known
var g_es_cur: int = -1
var g_es_heap: int = -1                             # the one class for globals, states and the unknown

function es_new(flags: int) -> int { push(g_es_flag, flags);  push(g_es_why, null);  push(g_es_own, null);  return len(g_es_flag) - 1 }
function es_flow(a: int, b: int) -> void { if a >= 0 and b >= 0 { push(g_es_ff, a);  push(g_es_ft, b) } }
function es_store(v: int, t: int) -> void {
  if v < 0 { return }
  if t < 0 { es_escape(v);  return }
  push(g_es_sv, v)
  push(g_es_st, t)
  push(g_es_swhy, g_es_stmt)
}
function es_escape(v: int) -> void {
  if v < 0 { return }
  g_es_flag[v] = g_es_flag[v] | ES_ESC
  if g_es_why[v] == null { g_es_why[v] = g_es_stmt }
}

function es_local(name: pointer) -> int {
  var i = len(g_es_ln) - 1
  while i >= 0 { if (g_es_ln[i] == name) { return g_es_lc[i] };  i -= 1 }
  return -1
}
function es_bind_local(name: pointer) -> int {
  let c = es_local(name)
  if c >= 0 { return c }
  let n = es_new(0)
  push(g_es_ln, name)
  push(g_es_lc, n)
  push(g_es_lt, null)
  return n
}

# a value of one of these types holds no reference: it takes part in no flow and no store, so a
# number copied out of a frame's list into a state's does not make the list kept
function es_prim(t: pointer) -> bool {
  if t == null { return false }
  return (t == "int") or (t == "float") or (t == "long") or (t == "double") or (t == "fixed") or (t == "bool") or (t == "byte")
}
function es_elem_of(t: pointer) -> pointer {
  if t == null { return null }
  if (t == "words") { return "int" }
  if (t == "floats") { return "float" }
  if (t == "doubles") { return "double" }
  if (t == "fixeds") { return "fixed" }
  if len(t) > 2 and t[0] == '[' and t[1] == ']' { return t[2..len(t)] }
  return null
}
function es_local_ty(name: pointer) -> pointer {
  var i = len(g_es_ln) - 1
  while i >= 0 { if (g_es_ln[i] == name) { return g_es_lt[i] };  i -= 1 }
  return null
}
# the static type of an expression, as far as the analysis can tell without emitting it
function es_type(e: Node) -> pointer {
  if e == null { return null }
  let k = e.kind
  if k == E_INT { return "int" }
  if k == E_FLOAT { return "float" }
  if k == E_BOOL { return "bool" }
  if k == E_STR or k == E_SLICE { return "string" }
  if k == E_ID {
    if es_local(e.s) >= 0 { return es_local_ty(e.s) }
    let g = find_global(e.s)
    if g != null { return g.ty }
    return null
  }
  if k == E_MEMBER {
    let bt = es_type(e.a)
    if bt != null {
      let c = find_comp(bt)
      if c != null { return field_type(c, e.s) }
    }
    return null
  }
  if k == E_INDEX { return es_elem_of(es_type(e.a)) }
  if k == E_NEW { return e.s }
  if k == E_BIN {
    let o = e.s
    if (o == "==") or (o == "!=") or (o == "<") or (o == ">") or (o == "<=") or (o == ">=") or (o == "and") or (o == "or") { return "bool" }
    if (o == "+") and fr_is_textish(e) { return "string" }
    let at = es_type(e.a)
    if es_prim(at) { return at }
    return null
  }
  if k == E_CALL and e.a != null and e.a.kind == E_ID {
    let nm = e.a.s
    if (nm == "len") { return "int" }
    if (nm == "string") { return "string" }
    if (nm == "int") or (nm == "float") or (nm == "long") or (nm == "double") or (nm == "fixed") { return nm }
    if (nm == "words") or (nm == "floats") or (nm == "doubles") or (nm == "fixeds") { return nm }
    let fi = es_fn(nm)
    if fi >= 0 { return g_es_fnode[fi].ty }
  }
  return null
}
# LOCAL: never kept (ESC); and for a push's growth, whose buffer is its list's, the list may not be
# one that outlives the frame (HEAP) either. A fresh value that flows into a local also holding kept
# memory is still the frame's - storing it anywhere kept would have made it ESC
function es_local_class(c: int, grow: bool) -> bool {
  if (g_es_flag[c] & ES_ESC) != 0 { return false }
  if grow and (g_es_flag[c] & ES_HEAP) != 0 { return false }
  return true
}

# a value's class, or -1 when its type holds no reference
function es_ref(e: Node) -> int {
  let v = es_val(e)
  if es_prim(es_type(e)) { return -1 }
  return v
}
function es_fn(name: pointer) -> int {
  let n = ck_tab_get(g_es_fk, g_es_fv, name)
  if n == null { return -1 }
  return n.ival
}
function es_site(n: Node) -> int {
  let c = es_new(0)
  push(g_es_site, n)
  push(g_es_site_cls, c)
  push(g_es_site_fn, g_es_cur)
  push(g_es_site_aok, g_es_aok > 0)
  push(g_es_site_grow, false)
  return c
}

function es_is_mem_frame(n: Node) -> bool {
  return n.kind == E_CALL and n.a != null and n.a.kind == E_MEMBER and n.a.a != null and n.a.a.kind == E_ID and (n.a.a.s == "Mem") and (n.a.s == "frame")
}

# the class of an expression's value (-1: not a reference worth following), walking its parts
function es_val(e: Node) -> int {
  if e == null { return -1 }
  let k = e.kind
  if k == E_FNREF {                                # a function handed on as a value: whoever calls it keeps what it returns
    if e.s != null { push(g_es_fnrefs, e.s) }
    return -1
  }
  if k == E_STR or k == E_INT or k == E_BOOL or k == E_FLOAT or k == E_NULL { return -1 }
  if k == E_ID {
    let c = es_local(e.s)
    if c >= 0 { return c }
    let g = find_global(e.s)
    if g != null and is_state_ty(g.ty) {
      var i = 0
      while i < len(g_es_gname) { if (g_es_gname[i] == e.s) { return g_es_gcls[i] };  i += 1 }
      let sc = es_new(ES_ESC | ES_HEAP)
      g_es_own[sc] = g.ty
      push(g_es_gname, e.s)
      push(g_es_gcls, sc)
      return sc
    }
    return g_es_heap
  }
  if k == E_MEMBER { return es_val(e.a) }
  if k == E_INDEX {
    es_val(e.b)
    return es_val(e.a)
  }
  if k == E_SLICE {
    es_val(e.a);  es_val(e.b);  es_val(e.c)
    return es_site(e)
  }
  if k == E_BIN {
    es_val(e.a)
    es_val(e.b)
    if (e.s == "+") or (e.s == "==") or (e.s == "!=") {
      if e.a != null and (e.a.kind == E_BIN or e.a.kind == E_CALL or e.a.kind == E_SLICE) { push(g_es_consumed, e.a) }
      if e.b != null and (e.b.kind == E_BIN or e.b.kind == E_CALL or e.b.kind == E_SLICE) { push(g_es_consumed, e.b) }
    }
    if (e.s == "+") and fr_is_textish(e) { return es_site(e) }
    return -1
  }
  if k == E_UN { es_val(e.a);  return -1 }
  if k == E_NEW and e.b != null {                  # a dispatch fills the queue's kept record: kept
    if e.a != null and e.a.kids != null {
      var i = 0
      while i < len(e.a.kids) { es_escape(es_val(e.a.kids[i].a));  i += 1 }
    }
    return g_es_heap
  }
  if k == E_NEW {
    let s = es_site(e)
    if e.a != null and e.a.kids != null {
      var i = 0
      while i < len(e.a.kids) { es_store(es_ref(e.a.kids[i].a), s);  i += 1 }
    }
    # a field's default is made with the record and held by it (`facts: Queue<F> = queue_new(...)`)
    let lay = find_comp(e.s)
    if lay != null and lay.kids != null {
      var j = 0
      while j < len(lay.kids) {
        let fd = lay.kids[j]
        if fd.a != null and not es_overridden(e, fd.s) { es_store(es_ref(fd.a), s) }
        j += 1
      }
    }
    return s
  }
  if k == E_LIST {
    let s = es_site(e)
    var i = 0
    while i < len(e.kids) { es_store(es_ref(e.kids[i]), s);  i += 1 }
    return s
  }
  if k == E_CALL { return es_call(e) }
  # anything else: walk it, and what it hands back may be anything
  es_walk(e.a);  es_walk(e.b);  es_walk(e.c)
  if e.kids != null {
    var j = 0
    while j < len(e.kids) { es_walk(e.kids[j]);  j += 1 }
  }
  return g_es_heap
}

function es_overridden(e: Node, field: pointer) -> bool {
  if e.a == null or e.a.kids == null { return false }
  var i = 0
  while i < len(e.a.kids) { if (e.a.kids[i].s == field) { return true };  i += 1 }
  return false
}

# the function records a call to `nm` reaches: nm itself, or every instance of a generic nm
function es_fns_for(nm: pointer) -> []int {
  let out = new []int
  let f = es_fn(nm)
  if f >= 0 {
    push(out, f)
    return out
  }
  let pre = `{nm}$`
  var i = 0
  while i < len(g_es_fnode) {
    let d = g_es_fnode[i]
    if d.s != null and str_starts(d.s, pre) { push(out, i) }
    i += 1
  }
  return out
}

function es_keeps_nothing(nm: pointer) -> bool {
  if (nm == "quit") or (nm == "exit") or (nm == "panic") or (nm == "assert") or (nm == "expect") or (nm == "expect_eq") or (nm == "expect_near") { return true }
  if (nm == "min") or (nm == "max") or (nm == "abs") or (nm == "clamp") or (nm == "sqrt") or (nm == "floor") or (nm == "ceil") or (nm == "round") { return true }
  if (nm == "int") or (nm == "float") or (nm == "long") or (nm == "double") or (nm == "fixed") or (nm == "as_int") or (nm == "as_fixed") { return true }
  if (nm == "float_bits") or (nm == "float_from_bits") or (nm == "sin") or (nm == "cos") or (nm == "atan2") or (nm == "file_write") or (nm == "file_close") { return true }
  return false
}

function es_args_escape(e: Node) -> void {
  var i = 0
  while i < len(e.kids) { es_escape(es_val(e.kids[i]));  i += 1 }
}
function es_args_walk(e: Node) -> void {
  var i = 0
  while i < len(e.kids) { es_val(e.kids[i]);  i += 1 }
}

function es_call(e: Node) -> int {
  let c = e.a
  if c != null and c.kind == E_ID and c.s != null {
    let nm = c.s
    if es_local(nm) >= 0 {                          # a function value in a local: anything
      es_args_escape(e)
      return g_es_heap
    }
    if (nm == "string") {
      es_args_walk(e)
      return es_site(e)
    }
    if (nm == "keep") or (nm == "intern") {         # a heap copy on purpose: a site for the census's owner, never scratch
      es_args_walk(e)
      let kc = es_site(e)
      g_es_flag[kc] = g_es_flag[kc] | ES_ESC
      g_es_site_aok[len(g_es_site_aok) - 1] = true   # deliberate: not a keep to report, nor a birth
      return kc
    }
    if (nm == "push") and len(e.kids) >= 2 {
      let t = es_val(e.kids[0])
      es_store(es_ref(e.kids[1]), t)
      # the grown buffer is the list's own
      push(g_es_site, e);  push(g_es_site_cls, t);  push(g_es_site_fn, g_es_cur);  push(g_es_site_aok, g_es_aok > 0);  push(g_es_site_grow, true)
      return -1
    }
    if (nm == "words") or (nm == "floats") or (nm == "doubles") or (nm == "buffer") or (nm == "bytes") or (nm == "fixeds") or (nm == "pointers") {
      es_args_walk(e)
      return es_site(e)
    }
    if (nm == "free") and len(e.kids) == 1 {        # given back: what flows into it is not kept by nothing
      let v = es_val(e.kids[0])
      if v >= 0 { g_es_flag[v] = g_es_flag[v] | ES_FREED }
      return -1
    }
    if (nm == "print") {                            # print frees a fresh text it is handed
      es_args_walk(e)
      var i = 0
      while i < len(e.kids) { push(g_es_consumed, e.kids[i]);  i += 1 }
      return -1
    }
    if (nm == "len") { es_args_walk(e);  return -1 }
    if (nm == "view") and len(e.kids) >= 1 {        # a view shares its list's storage
      let base = es_val(e.kids[0])
      var vi = 1
      while vi < len(e.kids) { es_val(e.kids[vi]);  vi += 1 }
      return base
    }
    # a generic's call names the generic; its instances (ui_kept$UiNode) are what is analysed, and
    # the call reaches every one of them
    let fs = es_fns_for(nm)
    if len(fs) > 0 {
      let r = es_new(0)
      var fi = 0
      while fi < len(fs) {
        let f = fs[fi]
        push(g_es_calls_f, g_es_cur)
        push(g_es_calls_t, f)
        es_flow(g_es_fret[f], r)
        fi += 1
      }
      var i = 0
      while i < len(e.kids) {
        let v = es_ref(e.kids[i])
        var fj = 0
        while fj < len(fs) {
          let d = g_es_fnode[fs[fj]]
          if i < len(d.kids) and d.kids[i].kind == N_PARAM {
            if not es_prim(d.kids[i].ty) { es_flow(v, g_es_fparam[fs[fj]] + i) }
          } else { es_escape(v) }
          fj += 1
        }
        i += 1
      }
      return r
    }
    # an intrinsic known to keep nothing it is handed; anything else unknown keeps it all - the
    # arena is only as safe as this default
    if es_keeps_nothing(nm) {
      es_args_walk(e)
      return g_es_heap
    }
    es_args_escape(e)
    return g_es_heap
  }
  if es_is_mem_frame(e) {
    if g_es_cur >= 0 { g_es_fspans[g_es_cur] = true }
    return -1
  }
  if c != null and c.kind == E_MEMBER and c.a != null and c.a.kind == E_ID and ns_alias_find(c.a.s, c.s) >= 0 {
    let al = ns_alias_find(c.a.s, c.s)
    let f = es_fn(g_al_target[al])
    if f >= 0 {
      push(g_es_calls_f, g_es_cur)
      push(g_es_calls_t, f)
      var i = 0
      let d = g_es_fnode[f]
      while i < len(e.kids) {
        let v = es_ref(e.kids[i])
        if i < len(d.kids) and d.kids[i].kind == N_PARAM {
          if not es_prim(d.kids[i].ty) { es_flow(v, g_es_fparam[f] + i) }
        } else { es_escape(v) }
        i += 1
      }
      let r = es_new(0)
      es_flow(g_es_fret[f], r)
      return r
    }
  }
  if c != null and c.kind == E_MEMBER and c.a != null and c.a.kind == E_ID and es_local(c.a.s) < 0 and ck_global(c.a.s) == null {
    # Ns.method, the emitter's own: what it is handed after the first may be kept in the first
    # (List.insert, Dict.put, ...); a namespace that only reads (Text, Math) costs a false escape
    if len(e.kids) > 0 {
      let t = es_val(e.kids[0])
      var i = 1
      while i < len(e.kids) { es_store(es_val(e.kids[i]), t);  i += 1 }
    }
    return g_es_heap
  }
  # a function value in a field: anything
  es_val(c)
  es_args_escape(e)
  return g_es_heap
}

function es_walk(n: Node) -> void {
  if n == null { return }
  if n.uns == FR_AOK_STMT and n.kind != E_ID {
    g_es_aok += 1
    es_walk_in(n)
    g_es_aok -= 1
    return
  }
  es_walk_in(n)
}

function es_walk_in(n: Node) -> void {
  let k = n.kind
  if k == S_LET or k == S_ASSIGN or k == S_RETURN or k == S_EXPR or k == S_EMIT { g_es_stmt = n }
  if k == S_LET {
    var t = n.ty
    if t == null { t = es_type(n.a) }
    let fresh = es_local(n.s) < 0
    let c = es_bind_local(n.s)
    if fresh { g_es_lt[len(g_es_lt) - 1] = t }
    if es_prim(t) { es_val(n.a);  return }
    es_flow(es_val(n.a), c)
    return
  }
  if k == S_ASSIGN {
    let v = es_ref(n.b)
    let t = n.a
    if t != null and t.kind == E_ID {
      let c = es_local(t.s)
      if c >= 0 { es_flow(v, c) } else { es_escape(v) }
      return
    }
    es_store(v, es_val(t))
    return
  }
  if k == S_RETURN {
    if n.a != null and g_es_cur >= 0 { es_flow(es_ref(n.a), g_es_fret[g_es_cur]) }
    return
  }
  if k == S_FOR {
    if es_local(n.s) < 0 {
      es_bind_local(n.s)
      g_es_lt[len(g_es_lt) - 1] = "int"
    }
    es_val(n.a);  es_val(n.b)
    es_walk(n.c)
    return
  }
  if k == S_EXPR { es_val(n.a);  return }
  if k == S_EMIT {                                  # an event's fields reach its listeners: kept
    if n.a != null and n.a.kids != null {
      var i = 0
      while i < len(n.a.kids) { es_escape(es_val(n.a.kids[i].a));  i += 1 }
    }
    return
  }
  if k == E_REC {                                   # named values handed on (a dispatch, a spawn, ...): kept
    if n.kids != null {
      var i = 0
      while i < len(n.kids) { es_escape(es_val(n.kids[i].a));  i += 1 }
    }
    return
  }
  if k == E_CALL or k == E_NEW or k == E_BIN or k == E_LIST or k == E_SLICE or k == E_ID or k == E_MEMBER or k == E_INDEX {
    es_val(n)
    return
  }
  es_walk(n.a)
  es_walk(n.b)
  es_walk(n.c)
  if n.kids != null {
    var i = 0
    while i < len(n.kids) { es_walk(n.kids[i]);  i += 1 }
  }
}

# HEAP forward along flows; ESC backward along flows, and from an ESC or HEAP target along stores
function es_solve() -> void {
  var changed = true
  while changed {
    changed = false
    var i = 0
    while i < len(g_es_ff) {
      let a = g_es_ff[i]
      let b = g_es_ft[i]
      if (g_es_flag[a] & ES_HEAP) != 0 and (g_es_flag[b] & ES_HEAP) == 0 { g_es_flag[b] = g_es_flag[b] | ES_HEAP;  changed = true }
      if (g_es_flag[b] & ES_FREED) != 0 and (g_es_flag[a] & ES_FREED) == 0 { g_es_flag[a] = g_es_flag[a] | ES_FREED;  changed = true }
      if (g_es_flag[b] & ES_ESC) != 0 and (g_es_flag[a] & ES_ESC) == 0 {
        g_es_flag[a] = g_es_flag[a] | ES_ESC
        g_es_why[a] = g_es_why[b]
        changed = true
      }
      i += 1
    }
    # kept memory outlives the frame: an ESC class is HEAP too, so every alias of it (let x = y,
    # a load, a call's result) is, and what is stored through the alias is kept
    i = 0
    while i < len(g_es_flag) {
      if (g_es_flag[i] & ES_ESC) != 0 and (g_es_flag[i] & ES_HEAP) == 0 { g_es_flag[i] = g_es_flag[i] | ES_HEAP;  changed = true }
      i += 1
    }
    i = 0
    while i < len(g_es_sv) {
      let v = g_es_sv[i]
      let t = g_es_st[i]
      if (g_es_flag[t] & (ES_ESC | ES_HEAP)) != 0 and (g_es_flag[v] & ES_ESC) == 0 {
        g_es_flag[v] = g_es_flag[v] | ES_ESC
        g_es_why[v] = g_es_swhy[i]
        changed = true
      }
      i += 1
    }
  }
  # 25.5c: which state holds what - a container's owner flows forward, a stored value takes its
  # target's, and what flowed into a value takes the value's; the first found stays
  changed = true
  while changed {
    changed = false
    var o = 0
    while o < len(g_es_ff) {
      let a = g_es_ff[o]
      let b = g_es_ft[o]
      if g_es_own[a] != null and g_es_own[b] == null { g_es_own[b] = g_es_own[a];  changed = true }
      if g_es_own[b] != null and g_es_own[a] == null and (g_es_flag[a] & ES_ESC) != 0 { g_es_own[a] = g_es_own[b];  changed = true }
      o += 1
    }
    o = 0
    while o < len(g_es_sv) {
      let v = g_es_sv[o]
      let t = g_es_st[o]
      if g_es_own[t] != null and g_es_own[v] == null { g_es_own[v] = g_es_own[t];  changed = true }
      o += 1
    }
  }
  # a function that reaches Mem.frame spans frames: so does every caller
  changed = true
  while changed {
    changed = false
    var j = 0
    while j < len(g_es_calls_f) {
      let f = g_es_calls_f[j]
      let t = g_es_calls_t[j]
      if f >= 0 and g_es_fspans[t] and not g_es_fspans[f] { g_es_fspans[f] = true;  changed = true }
      j += 1
    }
  }
}

# mark every LOCAL allocating construct; the count of them, and of those that escape
var g_es_local_n: int = 0
var g_es_esc_n: int = 0
function escape_analyse() -> void {
  if g_es_done { return }
  g_es_done = true
  ck_tab_init(g_es_ok, g_es_ov)
  g_es_heap = es_new(ES_ESC | ES_HEAP)
  ck_tab_init(g_es_fk, g_es_fv)
  var i = 0
  while i < len(prog) {
    let d = prog[i]
    # an entry has no name, and must be walked all the same: what it keeps, it keeps for good
    var dn = d.s
    if d.kind == N_MAIN and dn == null { dn = "$entry" }
    if (d.kind == N_FN or d.kind == N_SYS or d.kind == N_MAIN) and dn != null and ck_tab_get(g_es_fk, g_es_fv, dn) == null {
      let h = new Node
      h.ival = len(g_es_fnode)
      ck_tab_put(g_es_fk, g_es_fv, dn, h)
      push(g_es_fnode, d)
      push(g_es_fspans, d.kind == N_MAIN)
      push(g_es_fparam, len(g_es_flag))
      var p = 0
      while p < len(d.kids) {
        let pc = es_new(ES_HEAP)
        if d.kids[p].kind == N_PARAM and is_state_ty(d.kids[p].ty) { g_es_own[pc] = d.kids[p].ty }
        p += 1
      }
      push(g_es_fret, es_new(0))
    }
    i += 1
  }
  var f = 0
  while f < len(g_es_fnode) {
    let d = g_es_fnode[f]
    g_es_cur = f
    g_es_ln = new []pointer
    g_es_lc = new []int
    g_es_lt = new []pointer
    var p = 0
    while p < len(d.kids) {
      if d.kids[p].kind == N_PARAM { push(g_es_ln, d.kids[p].s);  push(g_es_lc, g_es_fparam[f] + p);  push(g_es_lt, d.kids[p].ty) }
      p += 1
    }
    es_walk(d.a)
    f += 1
  }
  g_es_cur = -1
  # a global's initializer - a state's instance, a module's table - is made to be kept
  var gi = 0
  while gi < len(prog) {
    let gd = prog[gi]
    if gd.kind == N_VAR and gd.a != null {
      g_es_ln = new []pointer
      g_es_lc = new []int
      g_es_lt = new []pointer
      es_escape(es_ref(gd.a))
    }
    gi += 1
  }
  # an @On body keeps nothing it makes unless it stores it; it has no function record of its own
  var li = 0
  while li < len(g_onlisten) {
    g_es_ln = new []pointer
    g_es_lc = new []int
    g_es_lt = new []pointer
    es_walk(g_onlisten[li].a)
    li += 1
  }
  # a function taken as a value is called where the analysis cannot see (a UiClass's make, a step
  # list, a System's tick): its result is kept by whoever calls it, whatever it returns
  var fr = 0
  while fr < len(g_es_fnrefs) {
    let fs = es_fns_for(g_es_fnrefs[fr])
    var fq = 0
    while fq < len(fs) { es_escape(g_es_fret[fs[fq]]);  fq += 1 }
    fr += 1
  }
  es_solve()
  # a node analysed more than once (a field's default, walked at every `new` of its record) is
  # scratch only if every walk found it LOCAL: mark the LOCAL ones, then take the mark off any node
  # one walk found kept
  var s = 0
  while s < len(g_es_site) {
    let n = g_es_site[s]
    let c = g_es_site_cls[s]
    let fi = g_es_site_fn[s]
    let spans = fi < 0 or g_es_fspans[fi]
    # LOCAL only when it can neither be kept (ESC) nor share storage with what is (HEAP): a push's
    # growth into a parameter's list is the list's own buffer, and the list may be a state's
    if c >= 0 and es_local_class(c, g_es_site_grow[s]) and not spans {
      n.uns = ES_SCRATCH
      g_es_local_n += 1
    } else {
      g_es_esc_n += 1
      if c >= 0 and g_es_own[c] != null and n.file != null {
        let h = new Node
        h.s = g_es_own[c]
        ck_tab_put(g_es_ok, g_es_ov, `{n.file}:{itoa(n.line)}`, h)
      }
    }
    s += 1
  }
  var u = 0
  while u < len(g_es_site) {
    let n2 = g_es_site[u]
    let c2 = g_es_site_cls[u]
    let fi2 = g_es_site_fn[u]
    let spans2 = fi2 < 0 or g_es_fspans[fi2]
    if n2.uns == ES_SCRATCH and (c2 < 0 or not es_local_class(c2, g_es_site_grow[u]) or spans2) { n2.uns = 0 }
    u += 1
  }
}

var g_es_report: bool = false
# --escape-report: the analysis on its own (the arena that uses it is not wired yet), each site that
# escapes or stays LOCAL as a line on stderr, then the totals
function escape_report() -> void {
  escape_analyse()
  var s = 0
  while s < len(g_es_site) {
    let n = g_es_site[s]
    var what = "kept"
    if n.uns == ES_SCRATCH { what = "local" }
    var fname = "?"
    let fi = g_es_site_fn[s]
    if fi >= 0 { fname = g_es_fnode[fi].s }
    var file = n.file
    if file == null { file = "?" }
    let line = `escape: {what} {file}:{itoa(n.line)} {fname}\n`
    file_write(file_stderr(), line, len(line))
    s += 1
  }
  var fl = 0
  while fl < len(g_es_fnrefs) {
    let fm = `escape: fn value {g_es_fnrefs[fl]} ({itoa(len(es_fns_for(g_es_fnrefs[fl])))} functions)\n`
    file_write(file_stderr(), fm, len(fm))
    fl += 1
  }
  let tot = `escape: {itoa(g_es_local_n)} local, {itoa(g_es_esc_n)} kept\n`
  file_write(file_stderr(), tot, len(tot))
}

# keep(x): x copied onto the heap - a string's bytes, a slice's header and elements, a record's
# fields (shallow) - so a frame's value can become a state's on purpose (25.3's region rule)
function emit_keep(a: Val) -> Val {
  if (a.ty == "string") {
    let n = emit_bind(`call i64 @strlen(ptr {a.code})`)
    let n1 = emit_bind(`add i64 {n}, 1`)
    let p = emit_bind(`call ptr @lp_malloc(i64 {n1})`)
    emit(`  call ptr @memcpy(ptr {p}, ptr {a.code}, i64 {n1})\n`)
    return val(p, "string")
  }
  if is_slice_ty(a.ty) {
    let esz = emit_sizeof(llty(slice_elem(a.ty)))
    let hsz = emit_sizeof("%LSlice")
    let h = emit_bind(`call ptr @lp_malloc(i64 {hsz})`)
    let od = emit_bind(`load ptr, ptr {slice_field(a.code, 0)}`)
    let ln = emit_bind(`load i32, ptr {slice_field(a.code, 1)}`)
    let ln64 = emit_bind(`zext i32 {ln} to i64`)
    let bytes = emit_bind(`mul i64 {ln64}, {esz}`)
    let b1 = emit_bind(`add i64 {bytes}, 1`)
    let d = emit_bind(`call ptr @lp_malloc(i64 {b1})`)
    emit(`  call ptr @memcpy(ptr {d}, ptr {od}, i64 {bytes})\n`)
    emit(`  store ptr {d}, ptr {slice_field(h, 0)}\n`)
    emit(`  store i32 {ln}, ptr {slice_field(h, 1)}\n`)
    emit(`  store i32 {ln}, ptr {slice_field(h, 2)}\n`)
    return val(h, a.ty)
  }
  if layout_node(a.ty) != null {
    let sz = emit_sizeof(layout_ty(a.ty))
    let p = emit_bind(`call ptr @lp_malloc(i64 {sz})`)
    emit(`  call ptr @memcpy(ptr {p}, ptr {a.code}, i64 {sz})\n`)
    return val(p, a.ty)
  }
  return a
}

# the state that holds what a site makes, when the analysis ran and found one
function es_owner_at(file: pointer, line: int) -> pointer {
  if not g_es_done or file == null { return null }
  let h = ck_tab_get(g_es_ok, g_es_ov, `{file}:{itoa(line)}`)
  if h == null { return null }
  return h.s
}