zeek/src/script_opt/UseDefs.cc

// See the file "COPYING" in the main distribution directory for copyright.

#include "zeek/script_opt/UseDefs.h"

#include "zeek/Desc.h"
#include "zeek/Reporter.h"
#include "zeek/Stmt.h"
#include "zeek/script_opt/Reduce.h"
#include "zeek/script_opt/ScriptOpt.h"

namespace zeek::detail
	{

void UseDefSet::Dump() const
	{
	for ( const auto& u : IterateOver() )
		printf(" %s", u->Name());
	}

UseDefs::UseDefs(StmtPtr _body, std::shared_ptr<Reducer> _rc)
	{
	body = std::move(_body);
	rc = std::move(_rc);
	}

void UseDefs::Analyze()
	{
	// Start afresh.
	use_defs_map.clear();
	UDs_are_copies.clear();
	stmts.clear();
	successor.clear();
	successor2.clear();

	(void)PropagateUDs(body, nullptr, nullptr, false);
	}

StmtPtr UseDefs::RemoveUnused()
	{
	int iter = 0;
	while ( RemoveUnused(++iter) )
		{
		body = rc->Reduce(body);
		Analyze();

		if ( reporter->Errors() > 0 )
			break;
		}

	return body;
	}

void UseDefs::Dump()
	{
	for ( int i = stmts.size(); --i >= 0; )
		{
		const auto& s = stmts[i];
		auto uds = FindUsage(s);
		auto are_copies = (UDs_are_copies.find(s) != UDs_are_copies.end());

		printf("UDs (%s) for %s:\n", are_copies ? "copy" : "orig", obj_desc(s).c_str());

		if ( uds )
			uds->Dump();
		else
			printf(" <none>");

		printf("\n\n");
		}
	}

bool UseDefs::RemoveUnused(int iter)
	{
	rc->ResetAlteredStmts();

	bool did_omission = false;

	for ( const auto& s : stmts )
		{
		if ( s->Tag() == STMT_INIT )
			{
			auto init = s->AsInitStmt();
			const auto& inits = init->Inits();
			std::vector<IDPtr> used_ids;

			for ( auto id : inits )
				if ( is_atomic_type(id->GetType()) || ! CheckIfUnused(s, id.get(), false) )
					used_ids.emplace_back(id);

			if ( used_ids.empty() )
				{ // There aren't any ID's to keep.
				rc->AddStmtToOmit(s);
				continue;
				}

			if ( used_ids.size() < inits.size() )
				{
				// Need to replace the current Init statement
				// with one that only includes the actually
				// used identifiers.

				auto new_init = make_intrusive<InitStmt>(used_ids);
				rc->AddStmtToReplace(s, std::move(new_init));
				}

			continue;
			}

		// The only other statements we might revise or remove
		// are assignments.

		if ( s->Tag() != STMT_EXPR )
			continue;

		auto s_e = s->AsExprStmt();
		auto e = s_e->StmtExpr();

		if ( e->Tag() != EXPR_ASSIGN )
			continue;

		auto a = e->AsAssignExpr();
		auto r = a->GetOp1();

		// Because we're dealing with reduced statements, the
		// assignment expression should be to a simple variable.
		if ( r->Tag() != EXPR_REF )
			reporter->InternalError("lhs ref inconsistency in UseDefs::RemoveUnused");

		auto n = r->AsRefExprPtr()->GetOp1();
		if ( n->Tag() != EXPR_NAME )
			reporter->InternalError("lhs name inconsistency in UseDefs::RemoveUnused");

		auto id = n->AsNameExpr()->Id();

		auto rhs = a->GetOp2();
		auto rt = rhs->Tag();

		if ( rt == EXPR_CALL && ! rhs->IsPure() )
			// Need to do the call for the side effects.
			// Could prune out the assignment and just
			// keep the call, but not clear that that's
			// worth the complexity.
			continue;

		if ( rt == EXPR_EVENT || rt == EXPR_SCHEDULE )
			// These always have side effects.
			continue;

		// Check for degenerate assignment "x = x".
		bool degen = rt == EXPR_NAME && id == rhs->AsNameExpr()->Id();

		if ( CheckIfUnused(s, id, iter == 1) || degen )
			{
			rc->AddStmtToOmit(s);
			did_omission = true;
			}
		}

	return did_omission;
	}

bool UseDefs::CheckIfUnused(const Stmt* s, const ID* id, bool report)
	{
	if ( id->IsGlobal() )
		return false;

	auto uds = FindSuccUsage(s);
	if ( ! uds || ! uds->HasID(id) )
		{
		if ( report && analysis_options.usage_issues > 0 && ! rc->IsTemporary(id) &&
		     ! rc->IsConstantVar(id) && ! rc->IsNewLocal(id) && ! id->GetAttr(ATTR_IS_USED) )
			reporter->Warning("%s assignment unused: %s", id->Name(), obj_desc(s).c_str());

		return true;
		}

	return false;
	}

UDs UseDefs::PropagateUDs(const Stmt* s, UDs succ_UDs, const Stmt* succ_stmt, bool second_pass)
	{
	if ( ! second_pass )
		stmts.push_back(s);

	switch ( s->Tag() )
		{
		case STMT_LIST:
			{
			auto sl = s->AsStmtList();
			const auto& stmts = sl->Stmts();

			for ( int i = stmts.length(); --i >= 0; )
				{
				auto s_i = stmts[i];

				const Stmt* succ;

				if ( i == stmts.length() - 1 )
					{ // Very last statement.
					succ = succ_stmt;
					if ( successor2.find(s) != successor2.end() )
						successor2[s_i] = successor2[s];
					}
				else
					succ = stmts[i + 1];

				succ_UDs = PropagateUDs(s_i, succ_UDs, succ, second_pass);
				}

			return UseUDs(s, succ_UDs);
			}

		case STMT_CATCH_RETURN:
			{
			auto cr = s->AsCatchReturnStmt();
			auto block = cr->Block();

			auto uds = PropagateUDs(block.get(), succ_UDs, succ_stmt, second_pass);

			return UseUDs(s, uds);
			}

		case STMT_NULL:
		case STMT_NEXT:
		case STMT_BREAK:
		case STMT_FALLTHROUGH:
			// When we back up to one of these, its successor isn't
			// actually succ_stmt (other than for STMT_NULL).  However,
			// in the contexts in which these can occur, it doesn't
			// actually do any harm to use the successor anyway.
			return UseUDs(s, succ_UDs);

		case STMT_PRINT:
			return CreateExprUDs(s, s->AsPrintStmt()->ExprList(), succ_UDs);

		case STMT_EVENT:
		case STMT_CHECK_ANY_LEN:
		case STMT_ADD:
		case STMT_DELETE:
		case STMT_RETURN:
			{
			auto e = static_cast<const ExprStmt*>(s)->StmtExpr();

			if ( e )
				return CreateExprUDs(s, e, succ_UDs);
			else
				return UseUDs(s, succ_UDs);
			}

		case STMT_EXPR:
			{
			auto e = s->AsExprStmt()->StmtExpr();

			if ( e->Tag() != EXPR_ASSIGN )
				return CreateExprUDs(s, e, succ_UDs);

			// Change in use-defs as here we have a definition.
			auto a = e->AsAssignExpr();
			auto lhs_ref = a->GetOp1();

			if ( lhs_ref->Tag() != EXPR_REF )
				// Since we're working on reduced form ...
				reporter->InternalError("lhs inconsistency in UseDefs::ExprUDs");

			auto lhs_var = lhs_ref->GetOp1();
			auto lhs_id = lhs_var->AsNameExpr()->Id();
			auto lhs_UDs = RemoveID(lhs_id, succ_UDs);
			auto rhs_UDs = ExprUDs(a->GetOp2().get());
			auto uds = UD_Union(lhs_UDs, rhs_UDs);

			if ( ! second_pass )
				successor[s] = succ_stmt;

			return CreateUDs(s, uds);
			}

		case STMT_IF:
			{
			auto i = s->AsIfStmt();
			auto cond = i->StmtExpr();

			auto cond_UDs = ExprUDs(cond);
			auto true_UDs = PropagateUDs(i->TrueBranch(), succ_UDs, succ_stmt, second_pass);
			auto false_UDs = PropagateUDs(i->FalseBranch(), succ_UDs, succ_stmt, second_pass);

			auto uds = CreateUDs(s, UD_Union(cond_UDs, true_UDs, false_UDs));

			return uds;
			}

		case STMT_INIT:
			if ( ! second_pass )
				successor[s] = succ_stmt;

			return UseUDs(s, succ_UDs);

		case STMT_WHEN:
			// ### Once we support compiling functions with "when"
			// statements in them, we'll need to revisit this.
			// For now, we don't worry about it (because the current
			// "when" body semantics of deep-copy frames has different
			// implications than potentially switching those shallow-copy
			// frames).
			return UseUDs(s, succ_UDs);

		case STMT_SWITCH:
			{
			auto sw_UDs = std::make_shared<UseDefSet>();

			auto sw = s->AsSwitchStmt();
			auto cases = sw->Cases();

			for ( const auto& c : *cases )
				{
				auto body = c->Body();
				auto uds = PropagateUDs(body, succ_UDs, succ_stmt, second_pass);

				auto exprs = c->ExprCases();
				if ( exprs )
					{
					auto e_UDs = ExprUDs(exprs);
					uds = UD_Union(uds, e_UDs);
					}

				auto type_ids = c->TypeCases();
				if ( type_ids )
					for ( const auto& id : *type_ids )
						uds = RemoveID(id, uds);

				FoldInUDs(sw_UDs, uds);
				}

			auto e_UDs = ExprUDs(sw->StmtExpr());

			if ( sw->HasDefault() )
				FoldInUDs(sw_UDs, e_UDs);
			else
				// keep successor definitions in the mix
				FoldInUDs(sw_UDs, succ_UDs, e_UDs);

			return CreateUDs(s, sw_UDs);
			}

		case STMT_FOR:
			{
			auto f = s->AsForStmt();
			auto body = f->LoopBody();

			// The loop body has two potential successors, itself
			// and the successor of the entire "for" statement.
			successor2[body] = succ_stmt;
			auto body_UDs = PropagateUDs(body, succ_UDs, body, second_pass);

			auto e = f->LoopExpr();
			auto f_UDs = ExprUDs(e);
			FoldInUDs(f_UDs, body_UDs);

			// Confluence: loop the top UDs back around to the bottom.
			auto bottom_UDs = UD_Union(f_UDs, succ_UDs);
			(void)PropagateUDs(body, bottom_UDs, body, true);

			auto ids = f->LoopVars();
			for ( const auto& id : *ids )
				RemoveUDFrom(f_UDs, id);

			auto val_var = f->ValueVar();
			if ( val_var )
				RemoveUDFrom(f_UDs, val_var.get());

			// The loop might not execute at all.
			FoldInUDs(f_UDs, succ_UDs);

			return CreateUDs(s, f_UDs);
			}

		case STMT_WHILE:
			{
			auto w = s->AsWhileStmt();
			auto body = w->Body();
			auto cond_stmt = w->CondPredStmt();

			// See note above for STMT_FOR regarding propagating
			// around the loop.
			auto succ = cond_stmt ? cond_stmt : body;
			successor2[body.get()] = succ_stmt;
			auto body_UDs = PropagateUDs(body.get(), succ_UDs, succ.get(), second_pass);

			const auto& cond = w->Condition();
			auto w_UDs = UD_Union(ExprUDs(cond.get()), body_UDs);
			FoldInUDs(w_UDs, body_UDs);

			if ( cond_stmt )
				{
				// Create a successor for the cond_stmt
				// that has the correct UDs associated with it.
				const auto& c_as_s = w->ConditionAsStmt();
				auto c_as_s_UDs = std::make_shared<UseDefSet>(w_UDs);
				CreateUDs(c_as_s.get(), c_as_s_UDs);

				w_UDs = PropagateUDs(cond_stmt, w_UDs, c_as_s, second_pass);
				}

			// Confluence: loop the top UDs back around to the bottom.
			auto bottom_UDs = UD_Union(w_UDs, succ_UDs);
			(void)PropagateUDs(body, bottom_UDs, succ, true);

			// The loop might not execute at all.
			FoldInUDs(w_UDs, succ_UDs);

			return CreateUDs(s, w_UDs);
			}

		default:
			reporter->InternalError("non-reduced statement in use-def analysis");
		}
	}

UDs UseDefs::FindUsage(const Stmt* s) const
	{
	auto s_map = use_defs_map.find(s);

	if ( s_map == use_defs_map.end() )
		reporter->InternalError("missing use-defs");

	return s_map->second;
	}

UDs UseDefs::FindSuccUsage(const Stmt* s) const
	{
	auto succ = successor.find(s);
	auto no_succ = (succ == successor.end() || ! succ->second);
	auto uds = no_succ ? nullptr : FindUsage(succ->second);

	auto succ2 = successor2.find(s);
	auto no_succ2 = (succ2 == successor2.end() || ! succ2->second);
	auto uds2 = no_succ2 ? nullptr : FindUsage(succ2->second);

	if ( uds && uds2 )
		return UD_Union(uds, uds2);
	else if ( uds )
		return uds;
	else
		return uds2;
	}

UDs UseDefs::ExprUDs(const Expr* e)
	{
	auto uds = std::make_shared<UseDefSet>();

	switch ( e->Tag() )
		{
		case EXPR_NAME:
			AddInExprUDs(uds, e);
			break;

		case EXPR_FIELD_LHS_ASSIGN:
			{
			AddInExprUDs(uds, e->GetOp1().get());
			auto rhs_UDs = ExprUDs(e->GetOp2().get());
			uds = UD_Union(uds, rhs_UDs);
			break;
			}

		case EXPR_INCR:
		case EXPR_DECR:
			AddInExprUDs(uds, e->GetOp1()->AsRefExprPtr()->GetOp1().get());
			break;

		case EXPR_ADD_TO:
		case EXPR_REMOVE_FROM:
			{
			AddInExprUDs(uds, e->GetOp1().get());
			auto rhs_UDs = ExprUDs(e->GetOp2().get());
			uds = UD_Union(uds, rhs_UDs);
			break;
			}

		case EXPR_RECORD_CONSTRUCTOR:
			{
			auto r = static_cast<const RecordConstructorExpr*>(e);
			AddInExprUDs(uds, r->Op().get());
			break;
			}

		case EXPR_CONST:
			break;

		case EXPR_LAMBDA:
			{
			auto l = static_cast<const LambdaExpr*>(e);
			auto ids = l->OuterIDs();

			for ( const auto& id : ids )
				AddID(uds, id);
			break;
			}

		case EXPR_CALL:
			{
			auto c = e->AsCallExpr();
			AddInExprUDs(uds, c->Func());
			AddInExprUDs(uds, c->Args());
			break;
			}

		case EXPR_LIST:
			{
			auto l = e->AsListExpr();
			for ( const auto& l_e : l->Exprs() )
				AddInExprUDs(uds, l_e);

			break;
			}

		default:
			auto op1 = e->GetOp1();
			auto op2 = e->GetOp2();
			auto op3 = e->GetOp3();

			if ( ! op1 )
				reporter->InternalError("expression inconsistency in UseDefs::ExprUDs");

			AddInExprUDs(uds, op1.get());
			if ( op2 )
				AddInExprUDs(uds, op2.get());
			if ( op3 )
				AddInExprUDs(uds, op3.get());

			break;
		}

	return uds;
	}

void UseDefs::AddInExprUDs(UDs uds, const Expr* e)
	{
	switch ( e->Tag() )
		{
		case EXPR_REF:
			AddInExprUDs(uds, e->GetOp1().get());
			break;

		case EXPR_NAME:
			AddID(uds, e->AsNameExpr()->Id());
			break;

		case EXPR_LIST:
			{
			auto l = e->AsListExpr();
			for ( const auto& l_e : l->Exprs() )
				AddInExprUDs(uds, l_e);
			}
			break;

		case EXPR_EVENT:
			AddInExprUDs(uds, e->GetOp1().get());
			break;

		case EXPR_INCR:
		case EXPR_DECR:
			AddInExprUDs(uds, e->GetOp1()->AsRefExprPtr()->GetOp1().get());
			break;

		case EXPR_ASSIGN: // can occur inside a table constructor
		case EXPR_ADD_TO:
		case EXPR_REMOVE_FROM:
			AddInExprUDs(uds, e->GetOp1().get());
			AddInExprUDs(uds, e->GetOp2().get());
			break;

		case EXPR_FIELD_ASSIGN:
			AddInExprUDs(uds, static_cast<const FieldAssignExpr*>(e)->Op());
			break;

		case EXPR_FIELD:
			// This happens for append-to-field.
			AddInExprUDs(uds, e->AsFieldExpr()->Op());
			break;

		case EXPR_CONST:
			// Nothing to do.
			break;

		default:
			reporter->InternalError("bad tag in UseDefs::AddInExprUDs");
			break;
		}
	}

void UseDefs::AddID(UDs uds, const ID* id) const
	{
	uds->Add(id);
	}

UDs UseDefs::RemoveID(const ID* id, const UDs& uds)
	{
	if ( ! uds )
		return nullptr;

	UDs new_uds = std::make_shared<UseDefSet>();

	new_uds->Replicate(uds);
	new_uds->Remove(id);

	return new_uds;
	}

void UseDefs::RemoveUDFrom(UDs uds, const ID* id)
	{
	if ( uds )
		uds->Remove(id);
	}

void UseDefs::FoldInUDs(UDs& main_UDs, const UDs& u1, const UDs& u2)
	{
	auto old_main = main_UDs;
	main_UDs = std::make_shared<UseDefSet>();

	if ( old_main )
		main_UDs->Replicate(old_main);

	if ( u1 )
		for ( auto ud : u1->IterateOver() )
			main_UDs->Add(ud);

	if ( u2 )
		for ( auto ud : u2->IterateOver() )
			main_UDs->Add(ud);
	}

void UseDefs::UpdateUDs(const Stmt* s, const UDs& uds)
	{
	auto curr_uds = FindUsage(s);

	if ( ! curr_uds || UDs_are_copies.find(s) != UDs_are_copies.end() )
		{
		// Copy-on-write.
		auto new_uds = std::make_shared<UseDefSet>();

		if ( curr_uds )
			new_uds->Replicate(curr_uds);

		CreateUDs(s, new_uds);

		curr_uds = new_uds;
		}

	if ( uds )
		{
		for ( auto u : uds->IterateOver() )
			curr_uds->Add(u);
		}
	}

UDs UseDefs::UD_Union(const UDs& u1, const UDs& u2, const UDs& u3) const
	{
	auto new_uds = std::make_shared<UseDefSet>();

	if ( u1 )
		new_uds->Replicate(u1);

	if ( u2 )
		for ( auto& u : u2->IterateOver() )
			AddID(new_uds, u);

	if ( u3 )
		for ( auto& u : u3->IterateOver() )
			AddID(new_uds, u);

	return new_uds;
	}

UDs UseDefs::UseUDs(const Stmt* s, UDs uds)
	{
	use_defs_map[s] = uds;
	UDs_are_copies.insert(s);
	return uds;
	}

UDs UseDefs::CreateExprUDs(const Stmt* s, const Expr* e, const UDs& uds)
	{
	auto e_UDs = ExprUDs(e);
	auto new_UDs = UD_Union(uds, e_UDs);

	return CreateUDs(s, new_UDs);
	}

UDs UseDefs::CreateUDs(const Stmt* s, UDs uds)
	{
	use_defs_map[s] = uds;
	UDs_are_copies.erase(s);
	return uds;
	}

	} // zeek::detail