clos_conv.cpp

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#include "thorin/plug/clos/phase/clos_conv.h"
 
#include "thorin/check.h"
 
#include "thorin/analyses/scope.h"
 
#include "thorin/plug/mem/autogen.h"
#include "thorin/plug/mem/mem.h"
 
using namespace std::literals;
 
namespace thorin::plug::clos {
 
namespace {
 
bool is_toplevel(const Def* fd) {
    return fd->dep_const() || fd->isa_mut<Global>() || fd->isa<Axiom>() || !fd->is_term();
}
 
bool is_memop_res(const Def* fd) {
    auto proj = fd->isa<Extract>();
    if (!proj) return false;
    auto types = proj->tuple()->type()->ops();
    return std::any_of(types.begin(), types.end(), [](auto d) { return match<mem::M>(d); });
}
 
} // namespace
 
/*
 * Free variable analysis
 */
 
void FreeDefAna::split_fd(Node* node, const Def* fd, bool& init_node, NodeQueue& worklist) {
    assert(!match<mem::M>(fd) && "mem tokens must not be free");
    if (is_toplevel(fd)) return;
    if (auto [var, lam] = ca_isa_var<Lam>(fd); var && lam) {
        if (var != lam->ret_var()) node->add_fvs(fd);
    } else if (auto q = match(attr::freeBB, fd)) {
        node->add_fvs(q);
    } else if (auto pred = fd->isa_mut()) {
        if (pred != node->mut) {
            auto [pnode, inserted] = build_node(pred, worklist);
            node->preds.push_back(pnode);
            pnode->succs.push_back(node);
            init_node |= inserted;
        }
    } else if (fd->dep() == Dep::Var && !fd->isa<Tuple>()) {
        // Note: Var's can still have Def::Top, if their type is a mut!
        // So the first case is *not* redundant
        node->add_fvs(fd);
    } else if (is_memop_res(fd)) {
        // Results of memops must not be floated down
        node->add_fvs(fd);
    } else {
        for (auto op : fd->ops()) split_fd(node, op, init_node, worklist);
    }
}
 
std::pair<FreeDefAna::Node*, bool> FreeDefAna::build_node(Def* mut, NodeQueue& worklist) {
    auto& w            = world();
    auto [p, inserted] = lam2nodes_.emplace(mut, nullptr);
    if (!inserted) return {p->second.get(), false};
    w.DLOG("FVA: create node: {}", mut);
    p->second      = std::make_unique<Node>(Node{mut, {}, {}, {}, 0});
    auto node      = p->second.get();
    auto scope     = Scope(mut);
    bool init_node = false;
    for (auto v : scope.free_defs()) split_fd(node, v, init_node, worklist);
    if (!init_node) {
        worklist.push(node);
        w.DLOG("FVA: init {}", mut);
    }
    return {node, true};
}
 
void FreeDefAna::run(NodeQueue& worklist) {
    while (!worklist.empty()) {
        auto node = worklist.front();
        worklist.pop();
        if (is_done(node)) continue;
        auto changed = is_bot(node);
        mark(node);
        for (auto p : node->preds) {
            auto& pfvs = p->fvs;
            for (auto&& pfv : pfvs) changed |= node->add_fvs(pfv).second;
        }
        if (changed)
            for (auto s : node->succs) worklist.push(s);
    }
}
 
DefSet& FreeDefAna::run(Lam* lam) {
    auto worklist  = NodeQueue();
    auto [node, _] = build_node(lam, worklist);
    if (!is_done(node)) {
        cur_pass_id++;
        run(worklist);
    }
 
    return node->fvs;
}
 
/*
 * Closure Conversion
 */
 
void ClosConv::start() {
    auto externals = Vector(world().externals().begin(), world().externals().end());
    auto subst     = Def2Def();
    for (auto [_, ext_def] : externals) rewrite(ext_def, subst);
    while (!worklist_.empty()) {
        auto def = worklist_.front();
        subst    = Def2Def();
        worklist_.pop();
        if (auto i = closures_.find(def); i != closures_.end()) {
            rewrite_body(i->second.fn, subst);
        } else {
            world().DLOG("RUN: rewrite def {}", def);
            rewrite(def, subst);
        }
    }
}
 
void ClosConv::rewrite_body(Lam* new_lam, Def2Def& subst) {
    auto& w = world();
    auto it = closures_.find(new_lam);
    assert(it != closures_.end() && "closure should have a stub if rewrite_body is called!");
    auto [old_fn, num_fvs, env, new_fn] = it->second;
 
    if (!old_fn->is_set()) return;
 
    w.DLOG("rw body: {} [old={}, env={}]\nt", new_fn, old_fn, env);
    auto env_param = new_fn->var(Clos_Env_Param)->set("closure_env");
    if (num_fvs == 1) {
        subst.emplace(env, env_param);
    } else {
        for (size_t i = 0; i < num_fvs; i++) {
            auto fv  = env->op(i);
            auto sym = w.sym("fv_"s + (fv->sym() ? fv->sym().str() : std::to_string(i)));
            subst.emplace(fv, env_param->proj(i)->set(sym));
        }
    }
 
    auto params = w.tuple(DefVec(old_fn->num_doms(), [&](auto i) { return new_lam->var(skip_env(i)); }));
    subst.emplace(old_fn->var(), params);
 
    auto filter = rewrite(new_fn->filter(), subst);
    auto body   = rewrite(new_fn->body(), subst);
    new_fn->reset({filter, body});
}
 
const Def* ClosConv::rewrite(const Def* def, Def2Def& subst) {
    switch (def->node()) {
        case Node::Type:
        case Node::Univ:
        case Node::Nat:
        case Node::Bot: // TODO This is used by the AD stuff????
        case Node::Top: return def;
        default: break;
    }
 
    auto& w  = world();
    auto map = [&](const Def* new_def) {
        subst[def] = new_def;
        assert(subst[def] == new_def);
        return new_def;
    };
 
    if (auto i = subst.find(def); i != subst.end()) {
        return i->second;
    } else if (auto pi = Pi::isa_cn(def)) {
        return map(type_clos(pi, subst));
    } else if (auto lam = def->isa_mut<Lam>(); lam && Lam::isa_cn(lam)) {
        auto [_, __, fv_env, new_lam] = make_stub(lam, subst);
        auto clos_ty                  = rewrite(lam->type(), subst);
        auto env                      = rewrite(fv_env, subst);
        auto closure                  = clos_pack(env, new_lam, clos_ty);
        world().DLOG("RW: pack {} ~> {} : {}", lam, closure, clos_ty);
        return map(closure);
    } else if (auto a = match<attr>(def)) {
        switch (a.id()) {
            case attr::ret:
                if (auto ret_lam = a->arg()->isa_mut<Lam>()) {
                    // assert(ret_lam && ret_lam->is_basicblock());
                    //  Note: This should be cont_lam's only occurance after η-expansion, so its okay to
                    //  put into the local subst only
                    auto new_doms
                        = DefVec(ret_lam->num_doms(), [&](auto i) { return rewrite(ret_lam->dom(i), subst); });
                    auto new_lam   = ret_lam->stub(w.cn(new_doms));
                    subst[ret_lam] = new_lam;
                    if (ret_lam->is_set()) {
                        new_lam->set_filter(rewrite(ret_lam->filter(), subst));
                        new_lam->set_body(rewrite(ret_lam->body(), subst));
                    }
                    return new_lam;
                }
                break;
            case attr::fstclassBB:
            case attr::freeBB: {
                // Note: Same thing about η-conversion applies here
                auto bb_lam = a->arg()->isa_mut<Lam>();
                assert(bb_lam && Lam::isa_basicblock(bb_lam));
                auto [_, __, ___, new_lam] = make_stub({}, bb_lam, subst);
                subst[bb_lam]              = clos_pack(w.tuple(), new_lam, rewrite(bb_lam->type(), subst));
                rewrite_body(new_lam, subst);
                return map(subst[bb_lam]);
            }
            default: break;
        }
    } else if (auto [var, lam] = ca_isa_var<Lam>(def); var && lam && lam->ret_var() == var) {
        // HACK to rewrite a retvar that is defined in an enclosing lambda
        // If we put external bb's into the env, this should never happen
        auto new_lam = make_stub(lam, subst).fn;
        auto new_idx = skip_env(Lit::as(var->index()));
        return map(new_lam->var(new_idx));
    }
 
    auto new_type = rewrite(def->type(), subst);
 
    if (auto mut = def->isa_mut()) {
        if (auto global = def->isa_mut<Global>()) {
            if (auto i = glob_muts_.find(global); i != glob_muts_.end()) return i->second;
            auto subst             = Def2Def();
            return glob_muts_[mut] = rewrite_mut(global, new_type, subst);
        }
        assert(!isa_clos_type(mut));
        w.DLOG("RW: mut {}", mut);
        auto new_mut = rewrite_mut(mut, new_type, subst);
        // Try to reduce the amount of muts that are created
        if (!mut->isa_mut<Global>() && Check::alpha(mut, new_mut)) return map(mut);
        if (auto imm = new_mut->immutabilize()) return map(imm);
        return map(new_mut);
    } else {
        auto new_ops = DefVec(def->num_ops(), [&](auto i) { return rewrite(def->op(i), subst); });
        if (auto app = def->isa<App>(); app && new_ops[0]->type()->isa<Sigma>())
            return map(clos_apply(new_ops[0], new_ops[1]));
        else if (def->isa<Axiom>())
            return def;
        else
            return map(def->rebuild(new_type, new_ops));
    }
 
    fe::unreachable();
}
 
Def* ClosConv::rewrite_mut(Def* mut, const Def* new_type, Def2Def& subst) {
    auto new_mut = mut->stub(new_type);
    subst.emplace(mut, new_mut);
    for (size_t i = 0; i < mut->num_ops(); i++)
        if (mut->op(i)) new_mut->set(i, rewrite(mut->op(i), subst));
    return new_mut;
}
 
const Pi* ClosConv::rewrite_type_cn(const Pi* pi, Def2Def& subst) {
    assert(Pi::isa_basicblock(pi));
    auto new_ops = DefVec(pi->num_doms(), [&](auto i) { return rewrite(pi->dom(i), subst); });
    return world().cn(new_ops);
}
 
const Def* ClosConv::type_clos(const Pi* pi, Def2Def& subst, const Def* env_type) {
    if (auto i = glob_muts_.find(pi); i != glob_muts_.end() && !env_type) return i->second;
    auto& w       = world();
    auto new_doms = DefVec(pi->num_doms(), [&](auto i) {
        return (i == pi->num_doms() - 1 && Pi::isa_returning(pi)) ? rewrite_type_cn(pi->ret_pi(), subst)
                                                                  : rewrite(pi->dom(i), subst);
    });
    auto ct       = ctype(w, new_doms, env_type);
    if (!env_type) {
        glob_muts_.emplace(pi, ct);
        w.DLOG("C-TYPE: pct {} ~~> {}", pi, ct);
    } else {
        w.DLOG("C-TYPE: ct {}, env = {} ~~> {}", pi, env_type, ct);
    }
    return ct;
}
 
ClosConv::Stub ClosConv::make_stub(const DefSet& fvs, Lam* old_lam, Def2Def& subst) {
    auto& w          = world();
    auto env         = w.tuple(DefVec(fvs.begin(), fvs.end()));
    auto num_fvs     = fvs.size();
    auto env_type    = rewrite(env->type(), subst);
    auto new_fn_type = type_clos(old_lam->type(), subst, env_type)->as<Pi>();
    auto new_lam     = old_lam->stub(new_fn_type);
    // TODO
    // new_lam->set_debug_name((old_lam->is_external() || !old_lam->is_set()) ? "cc_" + old_lam->name() :
    // old_lam->name());
    if (!isa_workable(old_lam)) {
        auto new_ext_type = w.cn(clos_remove_env(new_fn_type->dom()));
        auto new_ext_lam  = old_lam->stub(new_ext_type);
        w.DLOG("wrap ext lam: {} -> stub: {}, ext: {}", old_lam, new_lam, new_ext_lam);
        if (old_lam->is_set()) {
            old_lam->transfer_external(new_ext_lam);
            new_ext_lam->app(false, new_lam, clos_insert_env(env, new_ext_lam->var()));
            new_lam->set(old_lam->filter(), old_lam->body());
        } else {
            new_ext_lam->unset();
            new_lam->app(false, new_ext_lam, clos_remove_env(new_lam->var()));
        }
    } else {
        new_lam->set(old_lam->filter(), old_lam->body());
    }
    w.DLOG("STUB {} ~~> ({}, {})", old_lam, env, new_lam);
    auto closure = Stub{old_lam, num_fvs, env, new_lam};
    closures_.emplace(old_lam, closure);
    closures_.emplace(closure.fn, closure);
    return closure;
}
 
ClosConv::Stub ClosConv::make_stub(Lam* old_lam, Def2Def& subst) {
    if (auto i = closures_.find(old_lam); i != closures_.end()) return i->second;
    auto fvs     = fva_.run(old_lam);
    auto closure = make_stub(fvs, old_lam, subst);
    worklist_.emplace(closure.fn);
    return closure;
}
 
} // namespace thorin::plug::clos