perf: add lean_instantiate_level_mvars (#4910)

The new code is not active yet because of bootstrapping issues.
It requires an `update_stage0`.

src/Lean/MetavarContext.lean

@@ -336,6 +336,8 @@ structure MetavarContext where
   For more information about delayed abstraction, see the docstring for `DelayedMetavarAssignment`. -/
   dAssignment    : PersistentHashMap MVarId DelayedMetavarAssignment := {}
 
+instance : Inhabited MetavarContext := ⟨{}⟩
+
 /-- A monad with a stateful metavariable context, defining `getMCtx` and `modifyMCtx`. -/
 class MonadMCtx (m : Type → Type) where
   getMCtx    : m MetavarContext
@@ -358,15 +360,27 @@ abbrev setMCtx [MonadMCtx m] (mctx : MetavarContext) : m Unit :=
 abbrev getLevelMVarAssignment? [Monad m] [MonadMCtx m] (mvarId : LMVarId) : m (Option Level) :=
   return (← getMCtx).lAssignment.find? mvarId
 
+@[export lean_get_lmvar_assignment]
+def getLevelMVarAssignmentExp (m : MetavarContext) (mvarId : LMVarId) : Option Level :=
+  m.lAssignment.find? mvarId
+
 def MetavarContext.getExprAssignmentCore? (m : MetavarContext) (mvarId : MVarId) : Option Expr :=
   m.eAssignment.find? mvarId
 
+@[export lean_get_mvar_assignment]
+def MetavarContext.getExprAssignmentExp (m : MetavarContext) (mvarId : MVarId) : Option Expr :=
+  m.eAssignment.find? mvarId
+
 def getExprMVarAssignment? [Monad m] [MonadMCtx m] (mvarId : MVarId) : m (Option Expr) :=
   return (← getMCtx).getExprAssignmentCore? mvarId
 
 def MetavarContext.getDelayedMVarAssignmentCore? (mctx : MetavarContext) (mvarId : MVarId) : Option DelayedMetavarAssignment :=
   mctx.dAssignment.find? mvarId
 
+@[export lean_get_delayed_mvar_assignment]
+def MetavarContext.getDelayedMVarAssignmentExp (mctx : MetavarContext) (mvarId : MVarId) : Option DelayedMetavarAssignment :=
+  mctx.dAssignment.find? mvarId
+
 def getDelayedMVarAssignment? [Monad m] [MonadMCtx m] (mvarId : MVarId) : m (Option DelayedMetavarAssignment) :=
   return (← getMCtx).getDelayedMVarAssignmentCore? mvarId
 
@@ -478,6 +492,10 @@ def hasAssignableMVar [Monad m] [MonadMCtx m] : Expr → m Bool
 def assignLevelMVar [MonadMCtx m] (mvarId : LMVarId) (val : Level) : m Unit :=
   modifyMCtx fun m => { m with lAssignment := m.lAssignment.insert mvarId val }
 
+@[export lean_assign_lmvar]
+def assignLevelMVarExp (m : MetavarContext) (mvarId : LMVarId) (val : Level) : MetavarContext :=
+  { m with lAssignment := m.lAssignment.insert mvarId val }
+
 /--
 Add `mvarId := x` to the metavariable assignment.
 This method does not check whether `mvarId` is already assigned, nor it checks whether
@@ -487,6 +505,10 @@ This is a low-level API, and it is safer to use `isDefEq (mkMVar mvarId) x`.
 def _root_.Lean.MVarId.assign [MonadMCtx m] (mvarId : MVarId) (val : Expr) : m Unit :=
   modifyMCtx fun m => { m with eAssignment := m.eAssignment.insert mvarId val }
 
+@[export lean_assign_mvar]
+def assignExp (m : MetavarContext) (mvarId : MVarId) (val : Expr) : MetavarContext :=
+  { m with eAssignment := m.eAssignment.insert mvarId val }
+
 /--
 Add a delayed assignment for the given metavariable. You must make sure that
 the metavariable is not already assigned or delayed-assigned.
@@ -516,6 +538,9 @@ To avoid this term eta-expanded term, we apply beta-reduction when instantiating
 This operation is performed at `instantiateExprMVars`, `elimMVarDeps`, and `levelMVarToParam`.
 -/
 
+@[extern "lean_instantiate_level_mvars"]
+opaque instantiateLevelMVarsImp (mctx : MetavarContext) (l : Level) : MetavarContext × Level
+
 partial def instantiateLevelMVars [Monad m] [MonadMCtx m] : Level → m Level
   | lvl@(Level.succ lvl₁)      => return Level.updateSucc! lvl (← instantiateLevelMVars lvl₁)
   | lvl@(Level.max lvl₁ lvl₂)  => return Level.updateMax! lvl (← instantiateLevelMVars lvl₁) (← instantiateLevelMVars lvl₂)
@@ -531,6 +556,9 @@ partial def instantiateLevelMVars [Monad m] [MonadMCtx m] : Level → m Level
     | none        => pure lvl
   | lvl => pure lvl
 
+@[extern "lean_instantiate_expr_mvars"]
+opaque instantiateExprMVarsImp (mctx : MetavarContext) (e : Expr) : MetavarContext × Expr
+
 /-- instantiateExprMVars main function -/
 partial def instantiateExprMVars [Monad m] [MonadMCtx m] [STWorld ω m] [MonadLiftT (ST ω) m] (e : Expr) : MonadCacheT ExprStructEq Expr m Expr :=
   if !e.hasMVar then
@@ -792,8 +820,6 @@ def localDeclDependsOnPred [Monad m] [MonadMCtx m] (localDecl : LocalDecl) (pf :
 
 namespace MetavarContext
 
-instance : Inhabited MetavarContext := ⟨{}⟩
-
 @[export lean_mk_metavar_ctx]
 def mkMetavarContext : Unit → MetavarContext := fun _ => {}
 

src/kernel/CMakeLists.txt

@@ -2,4 +2,4 @@ add_library(kernel OBJECT level.cpp expr.cpp expr_eq_fn.cpp
 for_each_fn.cpp replace_fn.cpp abstract.cpp instantiate.cpp
 local_ctx.cpp declaration.cpp environment.cpp type_checker.cpp
 init_module.cpp expr_cache.cpp equiv_manager.cpp quot.cpp
-inductive.cpp trace.cpp)
+inductive.cpp trace.cpp instantiate_mvars.cpp)

src/kernel/instantiate_mvars.cpp

@@ -0,0 +1,95 @@
+/*
+Copyright (c) 2024 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+
+Authors: Leonardo de Moura
+*/
+#include <unordered_map>
+#include "runtime/option_ref.h"
+#include "kernel/instantiate.h"
+#include "kernel/abstract.h"
+
+/*
+This module is not used by the kernel. It just provides an efficient implementation of
+`instantiateExprMVars`
+*/
+
+namespace lean {
+
+extern "C" object * lean_get_lmvar_assignment(obj_arg mctx, obj_arg mid);
+extern "C" object * lean_assign_lmvar(obj_arg mctx, obj_arg mid, obj_arg val);
+
+typedef object_ref metavar_ctx;
+void assign_lmvar(metavar_ctx & mctx, name const & mid, level const & l) {
+    object * r = lean_assign_lmvar(mctx.steal(), mid.to_obj_arg(), l.to_obj_arg());
+    mctx.set_box(r);
+}
+
+option_ref<level> get_lmvar_assignment(metavar_ctx & mctx, name const & mid) {
+    return option_ref<level>(lean_get_lmvar_assignment(mctx.to_obj_arg(), mid.to_obj_arg()));
+}
+
+class instantiate_lmvar_fn {
+    metavar_ctx & m_mctx;
+    std::unordered_map<lean_object *, lean_object *> m_cache;
+
+    inline level cache(level const & l, level && r, bool shared) {
+        if (shared) {
+            m_cache.insert(mk_pair(l.raw(), r.raw()));
+        }
+        return r;
+    }
+public:
+    instantiate_lmvar_fn(metavar_ctx & mctx):m_mctx(mctx) {}
+    level visit(level const & l) {
+        if (!has_mvar(l))
+            return l;
+        bool shared = false;
+        if (is_shared(l)) {
+            auto it = m_cache.find(l.raw());
+            if (it != m_cache.end()) {
+                return level(it->second, true);
+            }
+            shared = true;
+        }
+        switch (l.kind()) {
+        case level_kind::Succ:
+            return cache(l, update_succ(l, visit(succ_of(l))), shared);
+        case level_kind::Max: case level_kind::IMax:
+            return cache(l, update_max(l, visit(level_lhs(l)), visit(level_rhs(l))), shared);
+        case level_kind::Zero: case level_kind::Param:
+            lean_unreachable();
+        case level_kind::MVar: {
+            option_ref<level> r = get_lmvar_assignment(m_mctx, mvar_id(l));
+            if (!r) {
+                return l;
+            } else {
+                level a(r.get_val());
+                if (!has_mvar(a)) {
+                    return a;
+                } else {
+                    level a_new = visit(a);
+                    if (!is_eqp(a, a_new)) {
+                        assign_lmvar(m_mctx, mvar_id(l), a_new);
+                    }
+                    return a_new;
+                }
+            }
+        }}
+    }
+    level operator()(level const & l) { return visit(l); }
+};
+
+extern "C" LEAN_EXPORT object * lean_instantiate_level_mvars(object * m, object * l) {
+    metavar_ctx mctx(m);
+    level l_new = instantiate_lmvar_fn(mctx)(level(l));
+    object * r = alloc_cnstr(0, 2, 0);
+    cnstr_set(r, 0, mctx.steal());
+    cnstr_set(r, 1, l_new.steal());
+    return r;
+}
+
+extern "C" LEAN_EXPORT object * lean_instantiate_expr_mvars(object *, object *) {
+    lean_internal_panic("not implemented yet");
+}
+}

src/kernel/level.h

@@ -82,6 +82,8 @@ inline bool operator!=(level const & l1, level const & l2) { return !operator==(
 struct level_hash { unsigned operator()(level const & n) const { return n.hash(); } };
 struct level_eq { bool operator()(level const & n1, level const & n2) const { return n1 == n2; } };
 
+inline bool is_shared(level const & l) { return !is_exclusive(l.raw()); }
+
 inline optional<level> none_level() { return optional<level>(); }
 inline optional<level> some_level(level const & e) { return optional<level>(e); }
 inline optional<level> some_level(level && e) { return optional<level>(std::forward<level>(e)); }

src/runtime/object_ref.h

@@ -35,6 +35,10 @@ public:
         s.m_obj = box(0);
         return *this;
     }
+    void set_box(object * o) {
+        lean_assert(is_scalar(m_obj));
+        m_obj = o;
+    }
     object * raw() const { return m_obj; }
     object * steal() { object * r = m_obj; m_obj = box(0); return r; }
     object * to_obj_arg() const { inc(m_obj); return m_obj; }

src/runtime/option_ref.h

@@ -28,6 +28,8 @@ public:
     explicit operator bool() const { return !is_scalar(raw()); }
     optional<T> get() const { return *this ? some(static_cast<T const &>(cnstr_get_ref(*this, 0))) : optional<T>(); }
 
+    T get_val() const { lean_assert(*this); return static_cast<T const &>(cnstr_get_ref(*this, 0)); }
+
     /** \brief Structural equality. */
     friend bool operator==(option_ref const & o1, option_ref const & o2) {
         return o1.get() == o2.get();