#include "AsyncProducers.h"
#include "ExprUsesVar.h"
#include "Function.h"
#include "IREquality.h"
#include "IRMutator.h"
#include "IROperator.h"

namespace Halide {
namespace Internal {

using std::map;
using std::pair;
using std::set;
using std::string;
using std::vector;

namespace {

/** A mutator which eagerly folds no-op stmts */
class NoOpCollapsingMutator : public IRMutator {
protected:
 using IRMutator::visit;

 Stmt visit(const LetStmt *op) override {
 Stmt body = mutate(op->body);
 if (is_no_op(body)) {
 return body;
 } else {
 return LetStmt::make(op->name, op->value, body);
 }
 }

 Stmt visit(const For *op) override {
 Stmt body = mutate(op->body);
 if (is_no_op(body)) {
 return body;
 } else {
 return For::make(op->name, op->min, op->extent, op->for_type, op->device_api, body);
 }
 }

 Stmt visit(const Block *op) override {
 Stmt first = mutate(op->first);
 Stmt rest = mutate(op->rest);
 if (is_no_op(first)) {
 return rest;
 } else if (is_no_op(rest)) {
 return first;
 } else {
 return Block::make(first, rest);
 }
 }

 Stmt visit(const Fork *op) override {
 Stmt first = mutate(op->first);
 Stmt rest = mutate(op->rest);
 if (is_no_op(first)) {
 return rest;
 } else if (is_no_op(rest)) {
 return first;
 } else {
 return Fork::make(first, rest);
 }
 }

 Stmt visit(const Realize *op) override {
 Stmt body = mutate(op->body);
 if (is_no_op(body)) {
 return body;
 } else {
 return Realize::make(op->name, op->types, op->memory_type,
 op->bounds, op->condition, body);
 }
 }

 Stmt visit(const Allocate *op) override {
 Stmt body = mutate(op->body);
 if (is_no_op(body)) {
 return body;
 } else {
 return Allocate::make(op->name, op->type, op->memory_type,
 op->extents, op->condition, body,
 op->new_expr, op->free_function, op->padding);
 }
 }

 Stmt visit(const IfThenElse *op) override {
 Stmt then_case = mutate(op->then_case);
 Stmt else_case = mutate(op->else_case);
 if (is_no_op(then_case) && is_no_op(else_case)) {
 return then_case;
 } else {
 return IfThenElse::make(op->condition, then_case, else_case);
 }
 }

 Stmt visit(const Atomic *op) override {
 Stmt body = mutate(op->body);
 if (is_no_op(body)) {
 return body;
 } else {
 return Atomic::make(op->producer_name,
 op->mutex_name,
 std::move(body));
 }
 }
};

class GenerateProducerBody : public NoOpCollapsingMutator {
 const string &func;
 vector<Expr> sema;

 using NoOpCollapsingMutator::visit;

 // Preserve produce nodes and add synchronization
 Stmt visit(const ProducerConsumer *op) override {
 if (op->name == func && op->is_producer) {
 // Add post-synchronization
 internal_assert(!sema.empty()) << "Duplicate produce node: " << op->name << "\n";
 Stmt body = op->body;
 while (!sema.empty()) {
 Expr release = Call::make(Int(32), "halide_semaphore_release", {sema.back(), 1}, Call::Extern);
 body = Block::make(body, Evaluate::make(release));
 sema.pop_back();
 }
 return ProducerConsumer::make_produce(op->name, body);
 } else {
 Stmt body = mutate(op->body);
 if (is_no_op(body) || op->is_producer) {
 return body;
 } else {
 return ProducerConsumer::make(op->name, op->is_producer, body);
 }
 }
 }

 // Other stmt leaves get replaced with no-ops
 Stmt visit(const Evaluate *) override {
 return Evaluate::make(0);
 }

 Stmt visit(const Provide *) override {
 return Evaluate::make(0);
 }

 Stmt visit(const Store *op) override {
 if (starts_with(op->name, func + ".folding_semaphore.") && ends_with(op->name, ".head")) {
 // This is a counter associated with the producer side of a storage-folding semaphore. Keep it.
 return op;
 } else {
 return Evaluate::make(0);
 }
 }

 Stmt visit(const AssertStmt *) override {
 return Evaluate::make(0);
 }

 Stmt visit(const Prefetch *) override {
 return Evaluate::make(0);
 }

 Stmt visit(const Acquire *op) override {
 Stmt body = mutate(op->body);
 const Variable *var = op->semaphore.as<Variable>();
 internal_assert(var);
 if (is_no_op(body)) {
 return body;
 } else if (starts_with(var->name, func + ".folding_semaphore.")) {
 // This is a storage-folding semaphore for the func we're producing. Keep it.
 return Acquire::make(op->semaphore, op->count, body);
 } else {
 // This semaphore will end up on both sides of the fork,
 // so we'd better duplicate it.
 vector<string> &clones = cloned_acquires[var->name];
 clones.push_back(var->name + unique_name('_'));
 return Acquire::make(Variable::make(type_of<halide_semaphore_t *>(), clones.back()), op->count, body);
 }
 }

 Stmt visit(const Atomic *op) override {
 return Evaluate::make(0);
 }

 Expr visit(const Call *op) override {
 if (op->name == "halide_semaphore_init") {
 internal_assert(op->args.size() == 2);
 const Variable *var = op->args[0].as<Variable>();
 internal_assert(var);
 inner_semaphores.insert(var->name);
 }
 return op;
 }

 map<string, vector<string>> &cloned_acquires;
 set<string> inner_semaphores;

public:
 GenerateProducerBody(const string &f, const vector<Expr> &s, map<string, vector<string>> &a)
 : func(f), sema(s), cloned_acquires(a) {
 }
};

class GenerateConsumerBody : public NoOpCollapsingMutator {
 const string &func;
 vector<Expr> sema;

 using NoOpCollapsingMutator::visit;

 Stmt visit(const ProducerConsumer *op) override {
 if (op->name == func) {
 if (op->is_producer) {
 // Remove the work entirely
 return Evaluate::make(0);
 } else {
 // Synchronize on the work done by the producer before beginning consumption
 Expr acquire_sema = sema.back();
 sema.pop_back();
 return Acquire::make(acquire_sema, 1, op);
 }
 } else {
 return NoOpCollapsingMutator::visit(op);
 }
 }

 Stmt visit(const Allocate *op) override {
 // Don't want to keep the producer's storage-folding tracker - it's dead code on the consumer side
 if (starts_with(op->name, func + ".folding_semaphore.") && ends_with(op->name, ".head")) {
 return mutate(op->body);
 } else {
 return NoOpCollapsingMutator::visit(op);
 }
 }

 Stmt visit(const Store *op) override {
 if (starts_with(op->name, func + ".folding_semaphore.") && ends_with(op->name, ".head")) {
 return Evaluate::make(0);
 } else {
 return NoOpCollapsingMutator::visit(op);
 }
 }

 Stmt visit(const Acquire *op) override {
 // Don't want to duplicate any semaphore acquires.
 // Ones from folding should go to the producer side.
 const Variable *var = op->semaphore.as<Variable>();
 internal_assert(var);
 if (starts_with(var->name, func + ".folding_semaphore.")) {
 return mutate(op->body);
 } else {
 return NoOpCollapsingMutator::visit(op);
 }
 }

public:
 GenerateConsumerBody(const string &f, const vector<Expr> &s)
 : func(f), sema(s) {
 }
};

class CloneAcquire : public IRMutator {
 using IRMutator::visit;

 const string &old_name;
 Expr new_var;

 Stmt visit(const Evaluate *op) override {
 const Call *call = op->value.as<Call>();
 const Variable *var = ((call && !call->args.empty()) ? call->args[0].as<Variable>() : nullptr);
 if (var && var->name == old_name &&
 (call->name == "halide_semaphore_release" ||
 call->name == "halide_semaphore_init")) {
 vector<Expr> args = call->args;
 args[0] = new_var;
 Stmt new_stmt =
 Evaluate::make(Call::make(call->type, call->name, args, call->call_type));
 return Block::make(op, new_stmt);
 } else {
 return op;
 }
 }

public:
 CloneAcquire(const string &o, const string &new_name)
 : old_name(o) {
 new_var = Variable::make(type_of<halide_semaphore_t *>(), new_name);
 }
};

class CountConsumeNodes : public IRVisitor {
 const string &func;

 using IRVisitor::visit;

 void visit(const ProducerConsumer *op) override {
 if (op->name == func && !op->is_producer) {
 count++;
 }
 IRVisitor::visit(op);
 }

public:
 CountConsumeNodes(const string &f)
 : func(f) {
 }
 int count = 0;
};

class ForkAsyncProducers : public IRMutator {
 using IRMutator::visit;

 const map<string, Function> &env;

 map<string, vector<string>> cloned_acquires;

 Stmt visit(const Realize *op) override {
 auto it = env.find(op->name);
 internal_assert(it != env.end());
 Function f = it->second;
 if (f.schedule().async()) {
 Stmt body = op->body;

 // Make two copies of the body, one which only does the
 // producer, and one which only does the consumer. Inject
 // synchronization to preserve dependencies. Put them in a
 // task-parallel block.

 // Make a semaphore per consume node
 CountConsumeNodes consumes(op->name);
 body.accept(&consumes);

 vector<string> sema_names;
 vector<Expr> sema_vars;
 for (int i = 0; i < consumes.count; i++) {
 sema_names.push_back(op->name + ".semaphore_" + std::to_string(i));
 sema_vars.push_back(Variable::make(type_of<halide_semaphore_t *>(), sema_names.back()));
 }

 Stmt producer = GenerateProducerBody(op->name, sema_vars, cloned_acquires).mutate(body);
 Stmt consumer = GenerateConsumerBody(op->name, sema_vars).mutate(body);

 // Recurse on both sides
 producer = mutate(producer);
 consumer = mutate(consumer);

 // Run them concurrently
 body = Fork::make(producer, consumer);

 for (const string &sema_name : sema_names) {
 // Make a semaphore on the stack
 Expr sema_space = Call::make(type_of<halide_semaphore_t *>(), "halide_make_semaphore",
 {0}, Call::Extern);

 // If there's a nested async producer, we may have
 // recursively cloned this semaphore inside the mutation
 // of the producer and consumer.
 const vector<string> &clones = cloned_acquires[sema_name];
 for (const auto &i : clones) {
 body = CloneAcquire(sema_name, i).mutate(body);
 body = LetStmt::make(i, sema_space, body);
 }

 body = LetStmt::make(sema_name, sema_space, body);
 }

 return Realize::make(op->name, op->types, op->memory_type,
 op->bounds, op->condition, body);
 } else {
 return IRMutator::visit(op);
 }
 }

public:
 ForkAsyncProducers(const map<string, Function> &e)
 : env(e) {
 }
};

// Lowers semaphore initialization from a call to
// "halide_make_semaphore" to an alloca followed by a call into the
// runtime to initialize. If something crashes before releasing a
// semaphore, the task system is responsible for propagating the
// failure to all branches of the fork. This depends on all semaphore
// acquires happening as part of the halide_do_parallel_tasks logic,
// not via explicit code in the closure. The current design for this
// does not propagate failures downward to subtasks of a failed
// fork. It assumes these will be able to reach completion in spite of
// the failure, which remains to be proven. (There is a test for the
// simple failure case, error_async_require_fail. One has not been
// written for the complex nested case yet.)
class InitializeSemaphores : public IRMutator {
 using IRMutator::visit;

 const Type sema_type = type_of<halide_semaphore_t *>();

 Stmt visit(const LetStmt *op) override {
 vector<const LetStmt *> frames;

 // Find first op that is of sema_type
 while (op && op->value.type() != sema_type) {
 frames.push_back(op);
 op = op->body.as<LetStmt>();
 }

 Stmt body;
 if (op) {
 body = mutate(op->body);
 // Peel off any enclosing let expressions from the value
 vector<pair<string, Expr>> lets;
 Expr value = op->value;
 while (const Let *l = value.as<Let>()) {
 lets.emplace_back(l->name, l->value);
 value = l->body;
 }
 const Call *call = value.as<Call>();
 if (call && call->name == "halide_make_semaphore") {
 internal_assert(call->args.size() == 1);

 Expr sema_var = Variable::make(sema_type, op->name);
 Expr sema_init = Call::make(Int(32), "halide_semaphore_init",
 {sema_var, call->args[0]}, Call::Extern);
 Expr sema_allocate = Call::make(sema_type, Call::alloca,
 {(int)sizeof(halide_semaphore_t)}, Call::Intrinsic);
 body = Block::make(Evaluate::make(sema_init), std::move(body));
 body = LetStmt::make(op->name, std::move(sema_allocate), std::move(body));

 // Re-wrap any other lets
 for (auto it = lets.rbegin(); it != lets.rend(); it++) {
 body = LetStmt::make(it->first, it->second, std::move(body));
 }
 }
 } else {
 body = mutate(frames.back()->body);
 }

 for (auto it = frames.rbegin(); it != frames.rend(); it++) {
 Expr value = mutate((*it)->value);
 if (value.same_as((*it)->value) && body.same_as((*it)->body)) {
 body = *it;
 } else {
 body = LetStmt::make((*it)->name, std::move(value), std::move(body));
 }
 }
 return body;
 }

 Expr visit(const Call *op) override {
 internal_assert(op->name != "halide_make_semaphore")
 << "Call to halide_make_semaphore in unexpected place\n";
 return op;
 }
};

// Tighten the scope of consume nodes as much as possible to avoid needless synchronization.
class TightenProducerConsumerNodes : public IRMutator {
 using IRMutator::visit;

 Stmt make_producer_consumer(const string &name, bool is_producer, Stmt body, const Scope<int> &scope) {
 if (const LetStmt *let = body.as<LetStmt>()) {
 Stmt orig = body;
 // 'orig' is only used to keep a reference to the let
 // chain in scope. We're going to be keeping pointers to
 // LetStmts we peeled off 'body' while also mutating
 // 'body', which is probably the only reference counted
 // object that keeps those pointers live.

 // Peel off all lets that don't depend on any vars in scope.
 vector<const LetStmt *> containing_lets;
 while (let && !expr_uses_vars(let->value, scope)) {
 containing_lets.push_back(let);
 body = let->body;
 let = body.as<LetStmt>();
 }

 if (let) {
 // That's as far as we can go
 body = ProducerConsumer::make(name, is_producer, body);
 } else {
 // Recurse onto a non-let-node
 body = make_producer_consumer(name, is_producer, body, scope);
 }

 for (auto it = containing_lets.rbegin(); it != containing_lets.rend(); it++) {
 body = LetStmt::make((*it)->name, (*it)->value, body);
 }

 return body;
 } else if (const Block *block = body.as<Block>()) {
 if (is_producer) {
 // We don't push produce nodes into blocks
 return ProducerConsumer::make(name, is_producer, body);
 }
 vector<Stmt> sub_stmts;
 Stmt rest;
 do {
 Stmt first = block->first;
 sub_stmts.push_back(block->first);
 rest = block->rest;
 block = rest.as<Block>();
 } while (block);
 sub_stmts.push_back(rest);

 for (Stmt &s : sub_stmts) {
 if (stmt_uses_vars(s, scope)) {
 s = make_producer_consumer(name, is_producer, s, scope);
 }
 }

 return Block::make(sub_stmts);
 } else if (const ProducerConsumer *pc = body.as<ProducerConsumer>()) {
 return ProducerConsumer::make(pc->name, pc->is_producer, make_producer_consumer(name, is_producer, pc->body, scope));
 } else if (const Realize *r = body.as<Realize>()) {
 return Realize::make(r->name, r->types, r->memory_type,
 r->bounds, r->condition,
 make_producer_consumer(name, is_producer, r->body, scope));
 } else {
 return ProducerConsumer::make(name, is_producer, body);
 }
 }

 Stmt visit(const ProducerConsumer *op) override {
 Stmt body = mutate(op->body);
 Scope<int> scope;
 scope.push(op->name, 0);
 Function f = env.find(op->name)->second;
 if (f.outputs() == 1) {
 scope.push(op->name + ".buffer", 0);
 } else {
 for (int i = 0; i < f.outputs(); i++) {
 scope.push(op->name + "." + std::to_string(i) + ".buffer", 0);
 }
 }
 return make_producer_consumer(op->name, op->is_producer, body, scope);
 }

 const map<string, Function> &env;

public:
 TightenProducerConsumerNodes(const map<string, Function> &e)
 : env(e) {
 }
};

// Broaden the scope of acquire nodes to pack trailing work into the
// same task and to potentially reduce the nesting depth of tasks.
class ExpandAcquireNodes : public IRMutator {
 using IRMutator::visit;

 Stmt visit(const Block *op) override {
 // Do an entire sequence of blocks in a single visit method to conserve stack space.
 vector<Stmt> stmts;
 Stmt result;
 do {
 stmts.push_back(mutate(op->first));
 result = op->rest;
 } while ((op = result.as<Block>()));

 result = mutate(result);

 vector<pair<Expr, Expr>> semaphores;
 for (auto it = stmts.rbegin(); it != stmts.rend(); it++) {
 Stmt s = *it;
 while (const Acquire *a = s.as<Acquire>()) {
 semaphores.emplace_back(a->semaphore, a->count);
 s = a->body;
 }
 result = Block::make(s, result);
 while (!semaphores.empty()) {
 result = Acquire::make(semaphores.back().first, semaphores.back().second, result);
 semaphores.pop_back();
 }
 }

 return result;
 }

 Stmt visit(const Realize *op) override {
 Stmt body = mutate(op->body);
 if (const Acquire *a = body.as<Acquire>()) {
 // Don't do the allocation until we have the
 // semaphore. Reduces peak memory use.
 return Acquire::make(a->semaphore, a->count,
 mutate(Realize::make(op->name, op->types, op->memory_type,
 op->bounds, op->condition, a->body)));
 } else {
 return Realize::make(op->name, op->types, op->memory_type,
 op->bounds, op->condition, body);
 }
 }

 Stmt visit(const LetStmt *op) override {
 Stmt orig = op;
 Stmt body;
 vector<const LetStmt *> frames;
 do {
 frames.push_back(op);
 body = op->body;
 op = body.as<LetStmt>();
 } while (op);

 Stmt s = mutate(body);

 if (const Acquire *a = s.as<Acquire>()) {
 // Pull the acquire node outside as many lets as possible,
 // wrapping them around the Acquire node's original body.
 body = a->body;
 while (!frames.empty() &&
 !expr_uses_var(a->semaphore, frames.back()->name) &&
 !expr_uses_var(a->count, frames.back()->name)) {
 body = LetStmt::make(frames.back()->name, frames.back()->value, body);
 frames.pop_back();
 }
 s = Acquire::make(a->semaphore, a->count, body);
 } else if (body.same_as(s)) {
 return orig;
 }

 // Rewrap the rest of the lets
 for (auto it = frames.rbegin(); it != frames.rend(); it++) {
 s = LetStmt::make((*it)->name, (*it)->value, s);
 }

 return s;
 }

 Stmt visit(const ProducerConsumer *op) override {
 Stmt body = mutate(op->body);
 if (const Acquire *a = body.as<Acquire>()) {
 return Acquire::make(a->semaphore, a->count,
 mutate(ProducerConsumer::make(op->name, op->is_producer, a->body)));
 } else {
 return ProducerConsumer::make(op->name, op->is_producer, body);
 }
 }
};

class TightenForkNodes : public IRMutator {
 using IRMutator::visit;

 Stmt make_fork(const Stmt &first, const Stmt &rest) {
 const LetStmt *lf = first.as<LetStmt>();
 const LetStmt *lr = rest.as<LetStmt>();
 const Realize *rf = first.as<Realize>();
 const Realize *rr = rest.as<Realize>();
 if (lf && lr &&
 lf->name == lr->name &&
 equal(lf->value, lr->value)) {
 return LetStmt::make(lf->name, lf->value, make_fork(lf->body, lr->body));
 } else if (lf && !stmt_uses_var(rest, lf->name)) {
 return LetStmt::make(lf->name, lf->value, make_fork(lf->body, rest));
 } else if (lr && !stmt_uses_var(first, lr->name)) {
 return LetStmt::make(lr->name, lr->value, make_fork(first, lr->body));
 } else if (rf && !stmt_uses_var(rest, rf->name)) {
 return Realize::make(rf->name, rf->types, rf->memory_type,
 rf->bounds, rf->condition, make_fork(rf->body, rest));
 } else if (rr && !stmt_uses_var(first, rr->name)) {
 return Realize::make(rr->name, rr->types, rr->memory_type,
 rr->bounds, rr->condition, make_fork(first, rr->body));
 } else {
 return Fork::make(first, rest);
 }
 }

 Stmt visit(const Fork *op) override {
 Stmt first, rest;
 {
 ScopedValue<bool> old_in_fork(in_fork, true);
 first = mutate(op->first);
 rest = mutate(op->rest);
 }

 if (is_no_op(first)) {
 return rest;
 } else if (is_no_op(rest)) {
 return first;
 } else {
 return make_fork(first, rest);
 }
 }

 // This is also a good time to nuke any dangling allocations and lets in the fork children.
 Stmt visit(const Realize *op) override {
 Stmt body = mutate(op->body);
 if (in_fork && !stmt_uses_var(body, op->name) && !stmt_uses_var(body, op->name + ".buffer")) {
 return body;
 } else {
 return Realize::make(op->name, op->types, op->memory_type,
 op->bounds, op->condition, body);
 }
 }

 Stmt visit(const LetStmt *op) override {
 Stmt body = mutate(op->body);
 if (in_fork && !stmt_uses_var(body, op->name)) {
 return body;
 } else {
 return LetStmt::make(op->name, op->value, body);
 }
 }

 bool in_fork = false;
};

// TODO: merge semaphores?

} // namespace

Stmt fork_async_producers(Stmt s, const map<string, Function> &env) {
 s = TightenProducerConsumerNodes(env).mutate(s);
 s = ForkAsyncProducers(env).mutate(s);
 s = ExpandAcquireNodes().mutate(s);
 s = TightenForkNodes().mutate(s);
 s = InitializeSemaphores().mutate(s);
 return s;
}

} // namespace Internal
} // namespace Halide