reduction of Stmt subclasses - compiles but does not yet link

src/Stmt.cc

@@ -32,6 +32,8 @@ const char* stmt_name(StmtTag t)
 		"for", "next", "break", "return", "add", "delete",
 		"list", "bodylist",
 		"<init>", "fallthrough", "while",
+		"catch-return",
+		"check-any-length",
 		"null",
 	};
 
@@ -94,6 +96,18 @@ const SwitchStmt* Stmt::AsSwitchStmt() const
 	return (const SwitchStmt*) this;
 	}
 
+const ExprStmt* Stmt::AsExprStmt() const
+	{
+	CHECK_TAG(tag, STMT_EXPR, "Stmt::AsExprStmt", stmt_name)
+	return (const ExprStmt*) this;
+	}
+
+const ReturnStmt* Stmt::AsReturnStmt() const
+	{
+	CHECK_TAG(tag, STMT_RETURN, "Stmt::AsReturnStmt", stmt_name)
+	return (const ReturnStmt*) this;
+	}
+
 bool Stmt::SetLocationInfo(const Location* start, const Location* end)
 	{
 	if ( ! Obj::SetLocationInfo(start, end) )
@@ -354,6 +368,11 @@ ExprStmt::ExprStmt(StmtTag t, ExprPtr arg_e) : Stmt(t), e(std::move(arg_e))
 
 ExprStmt::~ExprStmt() = default;
 
+ExprPtr ExprStmt::StmtExprPtr() const
+	{
+	return e;
+	}
+
 ValPtr ExprStmt::Exec(Frame* f, StmtFlowType& flow) const
 	{
 	RegisterAccess();
@@ -961,17 +980,37 @@ TraversalCode SwitchStmt::Traverse(TraversalCallback* cb) const
 	HANDLE_TC_STMT_POST(tc);
 	}
 
-AddStmt::AddStmt(ExprPtr arg_e) : ExprStmt(STMT_ADD, std::move(arg_e))
+
+AddDelStmt::AddDelStmt(StmtTag t, ExprPtr arg_e)
+: ExprStmt(t, std::move(arg_e))
+	{
+	}
+
+bool AddDelStmt::IsPure() const
+	{
+	return false;
+	}
+
+TraversalCode AddDelStmt::Traverse(TraversalCallback* cb) const
+	{
+	TraversalCode tc = cb->PreStmt(this);
+	HANDLE_TC_STMT_PRE(tc);
+
+	// Argument is stored in base class's "e" field.
+	tc = e->Traverse(cb);
+	HANDLE_TC_STMT_PRE(tc);
+
+	tc = cb->PostStmt(this);
+	HANDLE_TC_STMT_POST(tc);
+	}
+
+
+AddStmt::AddStmt(ExprPtr arg_e) : AddDelStmt(STMT_ADD, std::move(arg_e))
 	{
 	if ( ! e->CanAdd() )
 		Error("illegal add statement");
 	}
 
-bool AddStmt::IsPure() const
-	{
-	return false;
-	}
-
 ValPtr AddStmt::Exec(Frame* f, StmtFlowType& flow) const
 	{
 	RegisterAccess();
@@ -981,20 +1020,7 @@ ValPtr AddStmt::Exec(Frame* f, StmtFlowType& flow) const
 	}
 
 
-TraversalCode AddStmt::Traverse(TraversalCallback* cb) const
+DelStmt::DelStmt(ExprPtr arg_e) : AddDelStmt(STMT_DELETE, std::move(arg_e))
-	{
-	TraversalCode tc = cb->PreStmt(this);
-	HANDLE_TC_STMT_PRE(tc);
-
-	// Argument is stored in base class's "e" field.
-	tc = e->Traverse(cb);
-	HANDLE_TC_STMT_PRE(tc);
-
-	tc = cb->PostStmt(this);
-	HANDLE_TC_STMT_POST(tc);
-	}
-
-DelStmt::DelStmt(ExprPtr arg_e) : ExprStmt(STMT_DELETE, std::move(arg_e))
 	{
 	if ( e->IsError() )
 		return;
@@ -1003,11 +1029,6 @@ DelStmt::DelStmt(ExprPtr arg_e) : ExprStmt(STMT_DELETE, std::move(arg_e))
 		Error("illegal delete statement");
 	}
 
-bool DelStmt::IsPure() const
-	{
-	return false;
-	}
-
 ValPtr DelStmt::Exec(Frame* f, StmtFlowType& flow) const
 	{
 	RegisterAccess();
@@ -1016,18 +1037,6 @@ ValPtr DelStmt::Exec(Frame* f, StmtFlowType& flow) const
 	return nullptr;
 	}
 
-TraversalCode DelStmt::Traverse(TraversalCallback* cb) const
-	{
-	TraversalCode tc = cb->PreStmt(this);
-	HANDLE_TC_STMT_PRE(tc);
-
-	// Argument is stored in base class's "e" field.
-	tc = e->Traverse(cb);
-	HANDLE_TC_STMT_PRE(tc);
-
-	tc = cb->PostStmt(this);
-	HANDLE_TC_STMT_POST(tc);
-	}
 
 EventStmt::EventStmt(EventExprPtr arg_e)
 	: ExprStmt(STMT_EVENT, arg_e), event_expr(std::move(arg_e))
@@ -1060,10 +1069,10 @@ TraversalCode EventStmt::Traverse(TraversalCallback* cb) const
 	HANDLE_TC_STMT_POST(tc);
 	}
 
-WhileStmt::WhileStmt(ExprPtr arg_loop_condition,
+WhileStmt::WhileStmt(ExprPtr arg_loop_condition, StmtPtr arg_body)
-                     StmtPtr arg_body)
 	: Stmt(STMT_WHILE),
-	  loop_condition(std::move(arg_loop_condition)), body(std::move(arg_body))
+	  loop_condition(std::move(arg_loop_condition)),
+	  body(std::move(arg_body))
 	{
 	if ( ! loop_condition->IsError() &&
 	     ! IsBool(loop_condition->GetType()->Tag()) )
@@ -1119,6 +1128,9 @@ ValPtr WhileStmt::Exec(Frame* f, StmtFlowType& flow) const
 
 	for ( ; ; )
 		{
+		if ( loop_cond_pred_stmt )
+			loop_cond_pred_stmt->Exec(f, flow);
+
 		auto cond = loop_condition->Eval(f);
 
 		if ( ! cond )
@@ -1568,12 +1580,15 @@ void ReturnStmt::StmtDescribe(ODesc* d) const
 
 StmtList::StmtList() : Stmt(STMT_LIST)
 	{
+	stmts = new StmtPList;
 	}
 
 StmtList::~StmtList()
 	{
-	for ( const auto& stmt : stmts )
+	for ( const auto& stmt : Stmts() )
 		Unref(stmt);
+
+	delete stmts;
 	}
 
 ValPtr StmtList::Exec(Frame* f, StmtFlowType& flow) const
@@ -1581,7 +1596,7 @@ ValPtr StmtList::Exec(Frame* f, StmtFlowType& flow) const
 	RegisterAccess();
 	flow = FLOW_NEXT;
 
-	for ( const auto& stmt : stmts )
+	for ( const auto& stmt : Stmts() )
 		{
 		f->SetNextStmt(stmt);
 
@@ -1604,7 +1619,7 @@ ValPtr StmtList::Exec(Frame* f, StmtFlowType& flow) const
 
 bool StmtList::IsPure() const
 	{
-	for ( const auto& stmt : stmts )
+	for ( const auto& stmt : Stmts() )
 		if ( ! stmt->IsPure() )
 			return false;
 	return true;
@@ -1615,10 +1630,10 @@ void StmtList::StmtDescribe(ODesc* d) const
 	if ( ! d->IsReadable() )
 		{
 		AddTag(d);
-		d->AddCount(stmts.length());
+		d->AddCount(stmts->length());
 		}
 
-	if ( stmts.length() == 0 )
+	if ( stmts->length() == 0 )
 		DescribeDone(d);
 
 	else
@@ -1629,7 +1644,7 @@ void StmtList::StmtDescribe(ODesc* d) const
 			d->NL();
 			}
 
-		for ( const auto& stmt : stmts )
+		for ( const auto& stmt : Stmts() )
 			{
 			stmt->Describe(d);
 			d->NL();
@@ -1645,7 +1660,7 @@ TraversalCode StmtList::Traverse(TraversalCallback* cb) const
 	TraversalCode tc = cb->PreStmt(this);
 	HANDLE_TC_STMT_PRE(tc);
 
-	for ( const auto& stmt : stmts )
+	for ( const auto& stmt : Stmts() )
 		{
 		tc = stmt->Traverse(cb);
 		HANDLE_TC_STMT_PRE(tc);

src/Stmt.h

@@ -26,6 +26,9 @@ public:
 	// Optimization-related:
 	void Inline(Inliner* inl) override;
 
+	bool IsReduced(Reducer* c) const override;
+	StmtPtr DoReduce(Reducer* c) override;
+
 protected:
 	ExprListStmt(StmtTag t, ListExprPtr arg_l);
 
@@ -38,6 +41,12 @@ protected:
 	void StmtDescribe(ODesc* d) const override;
 
 	ListExprPtr l;
+
+	// Optimization-related:
+
+	// Returns a new version of the original derived object
+	// based on the given list of singleton expressions.
+	virtual StmtPtr DoSubclassReduce(ListExprPtr singletons, Reducer* c) = 0;
 };
 
 class PrintStmt final : public ExprListStmt {
@@ -51,6 +60,9 @@ public:
 protected:
 	ValPtr DoExec(std::vector<ValPtr> vals,
 	              StmtFlowType& flow) const override;
+
+	// Optimization-related:
+	StmtPtr DoSubclassReduce(ListExprPtr singletons, Reducer* c) override;
 };
 
 class ExprStmt : public Stmt {
@@ -58,9 +70,15 @@ public:
 	explicit ExprStmt(ExprPtr e);
 	~ExprStmt() override;
 
+	// This constructor is only meant for internal use, but it's
+	// not protected since ExprPtr's mask the actual caller,
+	// not allowing us to use "friend" for protected access.
+	ExprStmt(StmtTag t, ExprPtr e);
+
 	ValPtr Exec(Frame* f, StmtFlowType& flow) const override;
 
 	const Expr* StmtExpr() const	{ return e.get(); }
+	ExprPtr StmtExprPtr() const;
 
 	void StmtDescribe(ODesc* d) const override;
 
@@ -70,9 +88,10 @@ public:
 	StmtPtr Duplicate() override;
 	void Inline(Inliner* inl) override;
 
-protected:
+	bool IsReduced(Reducer* c) const override;
-	ExprStmt(StmtTag t, ExprPtr e);
+	StmtPtr DoReduce(Reducer* c) override;
 
+protected:
 	virtual ValPtr DoExec(Frame* f, Val* v, StmtFlowType& flow) const;
 
 	bool IsPure() const override;
@@ -96,6 +115,11 @@ public:
 	StmtPtr Duplicate() override;
 	void Inline(Inliner* inl) override;
 
+	bool IsReduced(Reducer* c) const override;
+	StmtPtr DoReduce(Reducer* c) override;
+
+	bool NoFlowAfter(bool ignore_break) const override;
+
 protected:
 	ValPtr DoExec(Frame* f, Val* v, StmtFlowType& flow) const override;
 	bool IsPure() const override;
@@ -118,6 +142,8 @@ public:
 	const Stmt* Body() const	{ return s.get(); }
 	Stmt* Body()			{ return s.get(); }
 
+	void UpdateBody(StmtPtr new_body)	{ s = new_body; }
+
 	void Describe(ODesc* d) const override;
 
 	TraversalCode Traverse(TraversalCallback* cb) const;
@@ -148,6 +174,11 @@ public:
 	StmtPtr Duplicate() override;
 	void Inline(Inliner* inl) override;
 
+	bool IsReduced(Reducer* c) const override;
+	StmtPtr DoReduce(Reducer* c) override;
+
+	bool NoFlowAfter(bool ignore_break) const override;
+
 protected:
 	ValPtr DoExec(Frame* f, Val* v, StmtFlowType& flow) const override;
 	bool IsPure() const override;
@@ -178,28 +209,38 @@ protected:
 	std::vector<std::pair<ID*, int>> case_label_type_list;
 };
 
-class AddStmt final : public ExprStmt {
+// Helper class. Added for script optimization, but it makes sense
+// in terms of factoring even without.
+class AddDelStmt : public ExprStmt {
+public:
+	TraversalCode Traverse(TraversalCallback* cb) const override;
+
+	bool IsPure() const override;
+
+	// Optimization-related:
+	StmtPtr DoReduce(Reducer* c) override;
+	bool IsReduced(Reducer* c) const override;
+
+protected:
+	AddDelStmt(StmtTag t, ExprPtr arg_e);
+};
+
+class AddStmt final : public AddDelStmt {
 public:
 	explicit AddStmt(ExprPtr e);
 
-	bool IsPure() const override;
 	ValPtr Exec(Frame* f, StmtFlowType& flow) const override;
 
-	TraversalCode Traverse(TraversalCallback* cb) const override;
-
 	// Optimization-related:
 	StmtPtr Duplicate() override;
 };
 
-class DelStmt final : public ExprStmt {
+class DelStmt final : public AddDelStmt {
 public:
 	explicit DelStmt(ExprPtr e);
 
-	bool IsPure() const override;
 	ValPtr Exec(Frame* f, StmtFlowType& flow) const override;
 
-	TraversalCode Traverse(TraversalCallback* cb) const override;
-
 	// Optimization-related:
 	StmtPtr Duplicate() override;
 };
@@ -215,6 +256,8 @@ public:
 	// Optimization-related:
 	StmtPtr Duplicate() override;
 
+	StmtPtr DoReduce(Reducer* c) override;
+
 protected:
 	EventExprPtr event_expr;
 };
@@ -232,11 +275,20 @@ public:
 	TraversalCode Traverse(TraversalCallback* cb) const override;
 
 	// Optimization-related:
-	const Stmt* CondStmt() const
+	StmtPtr CondPredStmt() const
-		{ return loop_cond_stmt ? loop_cond_stmt.get() : nullptr; }
+		{ return loop_cond_pred_stmt ? loop_cond_pred_stmt : nullptr; }
 	StmtPtr Duplicate() override;
 	void Inline(Inliner* inl) override;
 
+	bool IsReduced(Reducer* c) const override;
+	StmtPtr DoReduce(Reducer* c) override;
+
+	// Note, no need for a NoFlowAfter method because the loop might
+	// execute zero times, so it's always the default of "false".
+
+	const StmtPtr ConditionAsStmt() const
+		{ return stmt_loop_condition; }
+
 protected:
 	ValPtr Exec(Frame* f, StmtFlowType& flow) const override;
 
@@ -246,8 +298,14 @@ protected:
 	// Optimization-related member variables.
 
 	// When in reduced form, the following holds a statement (which
-	// might be a block) for evaluating the loop's conditional.
+	// might be a block) that's a *predecessor* necessary for evaluating
-	StmtPtr loop_cond_stmt = nullptr;
+	// the loop's conditional.
+	StmtPtr loop_cond_pred_stmt = nullptr;
+
+	// When reducing, we create a *statement* associated with
+	// evaluating the reduced conditional, as well as the reduced
+	// expression.  This turns out to be useful in propagating RDs/UDs.
+	StmtPtr stmt_loop_condition = nullptr;
 };
 
 class ForStmt final : public ExprStmt {
@@ -274,6 +332,12 @@ public:
 	StmtPtr Duplicate() override;
 	void Inline(Inliner* inl) override;
 
+	bool IsReduced(Reducer* c) const override;
+	StmtPtr DoReduce(Reducer* c) override;
+
+	// Note, no need for a NoFlowAfter method because the loop might
+	// execute zero times, so it's always the default of "false".
+
 protected:
 	ValPtr DoExec(Frame* f, Val* v, StmtFlowType& flow) const override;
 
@@ -297,6 +361,9 @@ public:
 
 	// Optimization-related:
 	StmtPtr Duplicate() override	{ return SetSucc(new NextStmt()); }
+
+	bool NoFlowAfter(bool ignore_break) const override
+		{ return true; }
 protected:
 };
 
@@ -314,6 +381,9 @@ public:
 	// Optimization-related:
 	StmtPtr Duplicate() override	{ return SetSucc(new BreakStmt()); }
 
+	bool NoFlowAfter(bool ignore_break) const override
+		{ return ! ignore_break; }
+
 protected:
 };
 
@@ -349,6 +419,12 @@ public:
 	// Constructor used for duplication, when we've already done
 	// all of the type-checking.
 	ReturnStmt(ExprPtr e, bool ignored);
+
+	// Optimization-related:
+	StmtPtr DoReduce(Reducer* c) override;
+
+	bool NoFlowAfter(bool ignore_break) const override
+		{ return true; }
 };
 
 class StmtList : public Stmt {
@@ -358,8 +434,8 @@ public:
 
 	ValPtr Exec(Frame* f, StmtFlowType& flow) const override;
 
-	const StmtPList& Stmts() const	{ return stmts; }
+	const StmtPList& Stmts() const	{ return *stmts; }
-	StmtPList& Stmts()		{ return stmts; }
+	StmtPList& Stmts()		{ return *stmts; }
 
 	void StmtDescribe(ODesc* d) const override;
 
@@ -369,6 +445,11 @@ public:
 	StmtPtr Duplicate() override;
 	void Inline(Inliner* inl) override;
 
+	bool IsReduced(Reducer* c) const override;
+	StmtPtr DoReduce(Reducer* c) override;
+
+	bool NoFlowAfter(bool ignore_break) const override;
+
 	// Idioms commonly used in reduction.
 	StmtList(StmtPtr s1, Stmt* s2);
 	StmtList(StmtPtr s1, StmtPtr s2);
@@ -377,7 +458,16 @@ public:
 protected:
 	bool IsPure() const override;
 
-	StmtPList stmts;
+	StmtPList* stmts;
+
+	// Optimization-related:
+	bool ReduceStmt(int& s_i, StmtPList* f_stmts, Reducer* c);
+
+	void ResetStmts(StmtPList* new_stmts)
+		{
+		delete stmts;
+		stmts = new_stmts;
+		}
 };
 
 class InitStmt final : public Stmt {
@@ -396,6 +486,9 @@ public:
 	// Optimization-related:
 	StmtPtr Duplicate() override;
 
+	bool IsReduced(Reducer* c) const override;
+	StmtPtr DoReduce(Reducer* c) override;
+
 protected:
 	std::vector<IDPtr> inits;
 };
@@ -439,6 +532,8 @@ public:
 	StmtPtr Duplicate() override;
 	void Inline(Inliner* inl) override;
 
+	bool IsReduced(Reducer* c) const override;
+
 protected:
 	ExprPtr cond;
 	StmtPtr s1;

src/StmtEnums.h

@@ -18,6 +18,8 @@ enum StmtTag {
 	STMT_INIT,
 	STMT_FALLTHROUGH,
 	STMT_WHILE,
+	STMT_CATCH_RETURN,	// for reduced InlineExpr's
+	STMT_CHECK_ANY_LEN,	// internal reduced statement
 	STMT_NULL
 #define NUM_STMTS (int(STMT_NULL) + 1)
 };

src/script_opt/Stmt.cc

@@ -4,11 +4,50 @@
 
 #include "zeek/Stmt.h"
 #include "zeek/Expr.h"
+#include "zeek/Frame.h"
+#include "zeek/Reporter.h"
+#include "zeek/Desc.h"
+#include "zeek/Traverse.h"
+#include "zeek/script_opt/Reduce.h"
 
 
 namespace zeek::detail {
 
 
+bool Stmt::IsReduced(Reducer* c) const
+	{
+	return true;
+	}
+
+StmtPtr Stmt::Reduce(Reducer* c)
+	{
+	auto this_ptr = ThisPtr();
+
+	auto repl = c->ReplacementStmt(this_ptr);
+	if ( repl )
+		return repl;
+
+	if ( c->ShouldOmitStmt(this_ptr) )
+		{
+		auto null = make_intrusive<NullStmt>();
+		null->SetOriginal(this_ptr);
+		return null;
+		}
+
+	return DoReduce(c);
+	}
+
+StmtPtr Stmt::TransformMe(Stmt* new_me, Reducer* c)
+	{
+	ASSERT(new_me != this);
+
+	// Set the original prior to reduction, to support "original chains"
+	// to ultimately resolve back to the source statement.
+	new_me->SetOriginal(ThisPtr());
+	return new_me->Reduce(c);
+	}
+
+
 void ExprListStmt::Inline(Inliner* inl)
 	{
 	auto& e = l->Exprs();
@@ -16,12 +55,70 @@ void ExprListStmt::Inline(Inliner* inl)
 		e.replace(i, e[i]->Inline(inl).release());
 	}
 
+bool ExprListStmt::IsReduced(Reducer* c) const
+	{
+	const ExprPList& e = l->Exprs();
+	for ( const auto& expr : e )
+		if ( ! expr->IsSingleton(c) )
+			return NonReduced(expr);
+
+	return true;
+	}
+
+StmtPtr ExprListStmt::DoReduce(Reducer* c)
+	{
+	if ( ! c->Optimizing() && IsReduced(c) )
+		return ThisPtr();
+
+	auto new_l = make_intrusive<ListExpr>();
+	auto s = new StmtList;
+
+	ExprPList& e = l->Exprs();
+	for ( auto& expr : e )
+		{
+		if ( c->Optimizing() )
+			new_l->Append(c->OptExpr(expr));
+
+		else if ( expr->IsSingleton(c) )
+			new_l->Append({NewRef{}, expr});
+
+		else
+			{
+			StmtPtr red_e_stmt;
+			auto red_e = expr->ReduceToSingleton(c, red_e_stmt);
+			new_l->Append(red_e);
+
+			if ( red_e_stmt )
+				s->Stmts().push_back(red_e_stmt.release());
+			}
+		}
+
+	if ( c->Optimizing() )
+		{
+		l = new_l;
+		return ThisPtr();
+		}
+
+	else
+		{
+		s->Stmts().push_back(DoSubclassReduce(new_l, c).release());
+		return s->Reduce(c);
+		}
+	}
+
 
 StmtPtr PrintStmt::Duplicate()
 	{
 	return SetSucc(new PrintStmt(l->Duplicate()->AsListExprPtr()));
 	}
 
+StmtPtr PrintStmt::DoSubclassReduce(ListExprPtr singletons, Reducer* c)
+	{
+	auto new_me = make_intrusive<PrintStmt>(singletons);
+	new_me->SetOriginal(ThisPtr());
+	return new_me;
+	}
+
 
 StmtPtr ExprStmt::Duplicate()
 	{
@@ -34,6 +131,61 @@ void ExprStmt::Inline(Inliner* inl)
 		e = e->Inline(inl);
 	}
 
+bool ExprStmt::IsReduced(Reducer* c) const
+	{
+	if ( ! e || e->IsReduced(c) )
+		return true;
+
+	return NonReduced(e.get());
+	}
+
+StmtPtr ExprStmt::DoReduce(Reducer* c)
+	{
+	if ( ! e )
+		// e can be nil for our derived classes (like ReturnStmt).
+		return TransformMe(new NullStmt, c);
+
+	auto t = e->Tag();
+
+	if ( t == EXPR_NOP )
+		return TransformMe(new NullStmt, c);
+
+	if ( c->Optimizing() )
+		{
+		e = c->OptExpr(e);
+		return ThisPtr();
+		}
+
+	if ( e->IsSingleton(c) )
+		// No point evaluating.
+		return TransformMe(new NullStmt, c);
+
+	if ( (t == EXPR_ASSIGN || t == EXPR_CALL ||
+	      t == EXPR_INDEX_ASSIGN || t == EXPR_FIELD_LHS_ASSIGN ||
+	      t == EXPR_APPEND_TO) &&
+	     e->IsReduced(c) )
+		return ThisPtr();
+
+	StmtPtr red_e_stmt;
+
+	if ( t == EXPR_CALL )
+		// A bare call.  If we reduce it regularly, if
+		// it has a non-void type it'll generate an
+		// assignment to a temporary.
+		red_e_stmt = e->ReduceToSingletons(c);
+	else
+		e = e->Reduce(c, red_e_stmt);
+
+	if ( red_e_stmt )
+		{
+		auto s = new StmtList(red_e_stmt, ThisPtr());
+		return TransformMe(s, c);
+		}
+
+	else
+		return ThisPtr();
+	}
+
 
 StmtPtr IfStmt::Duplicate()
 	{
@@ -51,6 +203,119 @@ void IfStmt::Inline(Inliner* inl)
 		s2->Inline(inl);
 	}
 
+bool IfStmt::IsReduced(Reducer* c) const
+	{
+	if ( ! e->IsReducedConditional(c) )
+		return NonReduced(e.get());
+
+	return s1->IsReduced(c) && s2->IsReduced(c);
+	}
+
+StmtPtr IfStmt::DoReduce(Reducer* c)
+	{
+	StmtPtr red_e_stmt;
+
+	if ( e->WillTransformInConditional(c) )
+		e = e->ReduceToConditional(c, red_e_stmt);
+
+	// First, assess some fundamental transformations.
+	if ( e->Tag() == EXPR_NOT )
+		{ // Change "if ( ! x ) s1 else s2" to "if ( x ) s2 else s1".
+		auto s1_orig = s1;
+		s1 = s2;
+		s2 = s1_orig;
+
+		e = e->GetOp1();
+		}
+
+	if ( e->Tag() == EXPR_OR_OR && c->BifurcationOkay() )
+		{
+		c->PushBifurcation();
+
+		// Expand "if ( a || b ) s1 else s2" to
+		// "if ( a ) s1 else { if ( b ) s1 else s2 }"
+		auto a = e->GetOp1();
+		auto b = e->GetOp2();
+
+		auto s1_dup = s1 ? s1->Duplicate() : nullptr;
+		s2 = make_intrusive<IfStmt>(b, s1_dup, s2);
+		e = a;
+
+		auto res = DoReduce(c);
+		c->PopBifurcation();
+		return res;
+		}
+
+	if ( e->Tag() == EXPR_AND_AND && c->BifurcationOkay() )
+		{
+		c->PushBifurcation();
+
+		// Expand "if ( a && b ) s1 else s2" to
+		// "if ( a ) { if ( b ) s1 else s2 } else s2"
+		auto a = e->GetOp1();
+		auto b = e->GetOp2();
+
+		auto s2_dup = s2 ? s2->Duplicate() : nullptr;
+		s1 = make_intrusive<IfStmt>(b, s1, s2_dup);
+		e = a;
+
+		auto res = DoReduce(c);
+		c->PopBifurcation();
+		return res;
+		}
+
+	s1 = s1->Reduce(c);
+	s2 = s2->Reduce(c);
+
+	if ( s1->Tag() == STMT_NULL && s2->Tag() == STMT_NULL )
+		return TransformMe(new NullStmt, c);
+
+	if ( c->Optimizing() )
+		e = c->OptExpr(e);
+	else
+		{
+		StmtPtr cond_red_stmt;
+		e = e->ReduceToConditional(c, cond_red_stmt);
+
+		if ( red_e_stmt && cond_red_stmt )
+			red_e_stmt = make_intrusive<StmtList>(red_e_stmt,
+								cond_red_stmt);
+		else if ( cond_red_stmt )
+			red_e_stmt = cond_red_stmt;
+		}
+
+	if ( e->IsConst() )
+		{
+		auto c_e = e->AsConstExprPtr();
+		auto t = c_e->Value()->AsBool();
+
+		if ( c->Optimizing() )
+			return t ? s1 : s2;
+
+		if ( t )
+			return TransformMe(new StmtList(red_e_stmt, s1), c);
+		else
+			return TransformMe(new StmtList(red_e_stmt, s2), c);
+		}
+
+	if ( red_e_stmt )
+		return TransformMe(new StmtList(red_e_stmt, this), c);
+
+	return ThisPtr();
+	}
+
+bool IfStmt::NoFlowAfter(bool ignore_break) const
+	{
+	if ( s1 && s2 )
+		return s1->NoFlowAfter(ignore_break) &&
+			s2->NoFlowAfter(ignore_break);
+
+	// Assuming the test isn't constant, the non-existent branch
+	// could be picked, so flow definitely continues afterwards.
+	// (Constant branches will be pruned during reduciton.)
+	return false;
+	}
+
 
 IntrusivePtr<Case> Case::Duplicate()
 	{
@@ -86,6 +351,128 @@ void SwitchStmt::Inline(Inliner* inl)
 		c->Body()->Inline(inl);
 	}
 
+bool SwitchStmt::IsReduced(Reducer* r) const
+	{
+	if ( ! e->IsReduced(r) )
+		return NonReduced(e.get());
+
+	for ( const auto& c : *cases )
+		{
+		if ( c->ExprCases() && ! c->ExprCases()->IsReduced(r) )
+			return false;
+
+		if ( c->TypeCases() && ! r->IDsAreReduced(c->TypeCases()) )
+			return false;
+
+		if ( ! c->Body()->IsReduced(r) )
+			return false;
+		}
+
+	return true;
+	}
+
+StmtPtr SwitchStmt::DoReduce(Reducer* rc)
+	{
+	auto s = make_intrusive<StmtList>();
+	StmtPtr red_e_stmt;
+
+	if ( rc->Optimizing() )
+		e = rc->OptExpr(e);
+	else
+		e = e->Reduce(rc, red_e_stmt);
+
+	// Note, the compiler checks for constant switch expressions.
+
+	if ( red_e_stmt )
+		s->Stmts().push_back(red_e_stmt.release());
+
+	for ( const auto& c : *cases )
+		{
+		auto c_e = c->ExprCases();
+		if ( c_e )
+			{
+			StmtPtr c_e_stmt;
+			auto red_cases = c_e->Reduce(rc, c_e_stmt);
+
+			if ( c_e_stmt )
+				s->Stmts().push_back(c_e_stmt.release());
+			}
+
+		auto c_t = c->TypeCases();
+		if ( c_t )
+			rc->UpdateIDs(c_t);
+
+		c->UpdateBody(c->Body()->Reduce(rc));
+		}
+
+	// Upate type cases.
+	for ( auto& i : case_label_type_list )
+		{
+		IDPtr idp = {NewRef{}, i.first};
+		i.first = rc->UpdateID(idp).release();
+		}
+
+	if ( s->Stmts().length() > 0 )
+		{
+		StmtPtr me = ThisPtr();
+		auto pre_and_me = new StmtList(s, me);
+		return TransformMe(pre_and_me, rc);
+		}
+
+	return ThisPtr();
+	}
+
+bool SwitchStmt::NoFlowAfter(bool ignore_break) const
+	{
+	bool control_reaches_end = false;
+	bool default_seen_with_no_flow_after = false;
+
+	for ( const auto& c : *Cases() )
+		{
+		if ( ! c->Body()->NoFlowAfter(true) )
+			return false;
+
+		if ( (! c->ExprCases() ||
+		      c->ExprCases()->Exprs().length() == 0) &&
+		     (! c->TypeCases() ||
+		      c->TypeCases()->length() == 0) )
+			// We saw the default, and the test before this
+			// one established that it has no flow after it.
+			default_seen_with_no_flow_after = true;
+		}
+
+	return default_seen_with_no_flow_after;
+	}
+
+
+bool AddDelStmt::IsReduced(Reducer* c) const
+	{
+	return e->HasReducedOps(c);
+	}
+
+StmtPtr AddDelStmt::DoReduce(Reducer* c)
+	{
+	if ( c->Optimizing() )
+		{
+		e = c->OptExpr(e);
+		return ThisPtr();
+		}
+
+	if ( e->Tag() != EXPR_INDEX && e->Tag() != EXPR_FIELD )
+		Internal("bad \"add\"/\"delete\"");
+
+	auto red_e_stmt = e->ReduceToSingletons(c);
+
+	if ( red_e_stmt )
+		{
+		auto s = new StmtList(red_e_stmt, ThisPtr());
+		return TransformMe(s, c);
+		}
+
+	else
+		return ThisPtr();
+	}
+
 
 StmtPtr AddStmt::Duplicate()
 	{
@@ -104,6 +491,32 @@ StmtPtr EventStmt::Duplicate()
 	return SetSucc(new EventStmt(e->Duplicate()->AsEventExprPtr()));
 	}
 
+StmtPtr EventStmt::DoReduce(Reducer* c)
+	{
+	if ( c->Optimizing() )
+		{
+		e = c->OptExpr(e);
+		event_expr = e->AsEventExprPtr();
+		}
+
+	else if ( ! event_expr->IsSingleton(c) )
+		{
+		StmtPtr red_e_stmt;
+		auto ee_red = event_expr->Reduce(c, red_e_stmt);
+
+		event_expr = ee_red->AsEventExprPtr();
+		e = event_expr;
+
+		if ( red_e_stmt )
+			{
+			auto s = new StmtList(red_e_stmt, ThisPtr());
+			return TransformMe(s, c);
+			}
+		}
+
+	return ThisPtr();
+	}
+
 
 StmtPtr WhileStmt::Duplicate()
 	{
@@ -115,12 +528,55 @@ void WhileStmt::Inline(Inliner* inl)
 	{
 	loop_condition = loop_condition->Inline(inl);
 
-	if ( loop_cond_stmt )
+	if ( loop_cond_pred_stmt )
-		loop_cond_stmt->Inline(inl);
+		loop_cond_pred_stmt->Inline(inl);
 	if ( body )
 		body->Inline(inl);
 	}
 
+bool WhileStmt::IsReduced(Reducer* c) const
+	{
+	// No need to check loop_cond_pred_stmt, as we create it reduced.
+	return loop_condition->IsReducedConditional(c) && body->IsReduced(c);
+	}
+
+StmtPtr WhileStmt::DoReduce(Reducer* c)
+	{
+	if ( c->Optimizing() )
+		loop_condition = c->OptExpr(loop_condition);
+	else
+		{
+		if ( IsReduced(c) )
+			{
+			if ( ! c->IsPruning() )
+				{
+				// See comment below for the particulars
+				// of this constructor.
+				stmt_loop_condition =
+					make_intrusive<ExprStmt>(STMT_EXPR,
+								loop_condition);
+				return ThisPtr();
+				}
+			}
+		else
+			loop_condition = loop_condition->ReduceToConditional(c,
+							loop_cond_pred_stmt);
+		}
+
+	body = body->Reduce(c);
+
+	// We use the more involved ExprStmt constructor here to bypass
+	// its check for whether the expression is being ignored, since
+	// we're not actually creating an ExprStmt for execution.
+	stmt_loop_condition =
+		make_intrusive<ExprStmt>(STMT_EXPR, loop_condition);
+
+	if ( loop_cond_pred_stmt )
+		loop_cond_pred_stmt = loop_cond_pred_stmt->Reduce(c);
+
+	return ThisPtr();
+	}
+
 
 StmtPtr ForStmt::Duplicate()
 	{
@@ -151,6 +607,46 @@ void ForStmt::Inline(Inliner* inl)
 	body->Inline(inl);
 	}
 
+bool ForStmt::IsReduced(Reducer* c) const
+	{
+	if ( ! e->IsReduced(c) )
+		return NonReduced(e.get());
+
+	if ( ! c->IDsAreReduced(loop_vars) )
+		return false;
+
+	if ( value_var && ! c->ID_IsReduced(value_var) )
+		return false;
+
+	return body->IsReduced(c);
+	}
+
+StmtPtr ForStmt::DoReduce(Reducer* c)
+	{
+	StmtPtr red_e_stmt;
+
+	if ( c->Optimizing() )
+		e = c->OptExpr(e);
+	else
+		{
+		e = e->Reduce(c, red_e_stmt);
+		c->UpdateIDs(loop_vars);
+
+		if ( value_var )
+			value_var = c->UpdateID(value_var);
+		}
+
+	body = body->Reduce(c);
+
+	if ( body->Tag() == STMT_NULL )
+		Error("empty \"for\" body leaves loop variables in indeterminant state");
+
+	if ( red_e_stmt )
+		return TransformMe(new StmtList(red_e_stmt, this), c);
+
+	return ThisPtr();
+	}
+
 
 StmtPtr ReturnStmt::Duplicate()
 	{
@@ -162,6 +658,61 @@ ReturnStmt::ReturnStmt(ExprPtr arg_e, bool ignored)
 	{
 	}
 
+StmtPtr ReturnStmt::DoReduce(Reducer* c)
+	{
+	if ( ! e )
+		return ThisPtr();
+
+	if ( c->Optimizing() )
+		{
+		e = c->OptExpr(e);
+		return ThisPtr();
+		}
+
+	if ( ! e->IsSingleton(c) )
+		{
+		StmtPtr red_e_stmt;
+		e = e->Reduce(c, red_e_stmt);
+
+		if ( red_e_stmt )
+			{
+			auto s = new StmtList(red_e_stmt, ThisPtr());
+			return TransformMe(s, c);
+			}
+		}
+
+	return ThisPtr();
+	}
+
+
+StmtList::StmtList(StmtPtr s1, Stmt* s2) : Stmt(STMT_LIST)
+	{
+	stmts = new StmtPList;
+	if ( s1 )
+		stmts->append(s1.release());
+	if ( s2 )
+		stmts->append(s2);
+	}
+
+StmtList::StmtList(StmtPtr s1, StmtPtr s2) : Stmt(STMT_LIST)
+	{
+	stmts = new StmtPList;
+	if ( s1 )
+		stmts->append(s1.release());
+	if ( s2 )
+		stmts->append(s2.release());
+	}
+
+StmtList::StmtList(StmtPtr s1, StmtPtr s2, StmtPtr s3) : Stmt(STMT_LIST)
+	{
+	stmts = new StmtPList;
+	if ( s1 )
+		stmts->append(s1.release());
+	if ( s2 )
+		stmts->append(s2.release());
+	if ( s3 )
+		stmts->append(s3.release());
+	}
 
 StmtPtr StmtList::Duplicate()
 	{
@@ -179,6 +730,181 @@ void StmtList::Inline(Inliner* inl)
 		stmt->Inline(inl);
 	}
 
+bool StmtList::IsReduced(Reducer* c) const
+	{
+	int n = Stmts().length();
+
+	for ( auto i = 0; i < n; ++i )
+		{
+		auto& s_i = Stmts()[i];
+		if ( ! s_i->IsReduced(c) )
+			return false;
+
+		if ( s_i->NoFlowAfter(false) && i < n - 1 )
+			return false;
+		}
+
+	return true;
+	}
+
+StmtPtr StmtList::DoReduce(Reducer* c)
+	{
+	StmtPList* f_stmts = new StmtPList;
+	bool did_change = false;
+
+	int n = Stmts().length();
+
+	for ( auto i = 0; i < n; ++i )
+		{
+		if ( ReduceStmt(i, f_stmts, c) )
+			did_change = true;
+
+		if ( i < n - 1 && Stmts()[i]->NoFlowAfter(false) )
+			{
+			did_change = true;
+			break;
+			}
+
+		if ( reporter->Errors() > 0 )
+			return ThisPtr();
+		}
+
+	if ( f_stmts->length() == 0 )
+		return TransformMe(new NullStmt, c);
+
+	if ( f_stmts->length() == 1 )
+		return (*f_stmts)[0]->Reduce(c);
+
+	if ( did_change )
+		{
+		ResetStmts(f_stmts);
+		return Reduce(c);
+		}
+	else
+		delete f_stmts;
+
+	return ThisPtr();
+	}
+
+bool StmtList::ReduceStmt(int& s_i, StmtPList* f_stmts, Reducer* c)
+	{
+	bool did_change = false;
+	auto stmt = Stmts()[s_i]->ThisPtr();
+
+	auto old_stmt = stmt;
+
+	stmt = stmt->Reduce(c);
+
+	if ( stmt != old_stmt )
+		did_change = true;
+
+	if ( c->Optimizing() && stmt->Tag() == STMT_EXPR )
+		{
+		// There are two potential optimizations that affect
+		// whether we keep assignment statements.  The first is
+		// for potential assignment chains like
+		//
+		//	tmp1 = x;
+		//	tmp2 = tmp1;
+		//
+		// where we can change this pair to simply "tmp2 = x", assuming
+		// no later use of tmp1.
+		//
+		// In addition, if we have "tmp1 = e" and "e" is an expression
+		// already computed into another temporary (say tmp0) that's
+		// safely usable at this point, then we can elide the tmp1
+		// assignment entirely.
+		auto s_e = stmt->AsExprStmt();
+		auto e = s_e->StmtExpr();
+
+		if ( e->Tag() != EXPR_ASSIGN )
+			{
+			f_stmts->append(stmt.release());
+			return false;
+			}
+
+		auto a = e->AsAssignExpr();
+		auto lhs = a->Op1()->AsRefExprPtr()->Op();
+
+		if ( lhs->Tag() != EXPR_NAME )
+			{
+			f_stmts->append(stmt.release());
+			return false;
+			}
+
+		auto var = lhs->AsNameExpr();
+		auto rhs = a->GetOp2();
+
+		if ( s_i < Stmts().length() - 1 )
+			{
+			// See if we can compress an assignment chain.
+			auto& s_i_succ = Stmts()[s_i + 1];
+
+			// Don't reduce s_i_succ.  If it's what we're
+			// looking for, it's already reduced.
+			auto merge = c->MergeStmts(var, rhs, s_i_succ);
+			if ( merge )
+				{
+				f_stmts->append(merge);
+
+				// Skip both this statement and the next,
+				// now that we've substituted the merge.
+				++s_i;
+				return true;
+				}
+			}
+
+		if ( c->IsCSE(a, var, rhs.get()) )
+			{
+			// printf("discarding %s as unnecessary\n", obj_desc(a));
+			// Skip this now unnecessary statement.
+			return true;
+			}
+		}
+
+	if ( stmt->Tag() == STMT_LIST )
+		{ // inline the list
+		auto sl = stmt->AsStmtList();
+
+		for ( auto& sub_stmt : sl->Stmts() )
+			f_stmts->append(sub_stmt->Ref());
+
+		did_change = true;
+		}
+
+	else if ( stmt->Tag() == STMT_NULL )
+		// skip it
+		did_change = true;
+
+	else
+		// No need to Ref() because the StmtPList destructor
+		// doesn't Unref(), only the explict list-walking
+		// in the ~StmtList destructor.
+		f_stmts->append(stmt.release());
+
+	return did_change;
+	}
+
+bool StmtList::NoFlowAfter(bool ignore_break) const
+	{
+	for ( auto& s : Stmts() )
+		{
+		// For "break" statements, if ignore_break is set then
+		// by construction flow *does* go to after this statement
+		// list.  If we just used the second test below, then
+		// while the "break" would indicate there's flow after it,
+		// if there's dead code following that includes a "return",
+		// this would in fact be incorrect.
+		if ( ignore_break && s->Tag() == STMT_BREAK )
+			return false;
+
+		if ( s->NoFlowAfter(ignore_break) )
+			return true;
+		}
+
+	return false;
+	}
+
 
 StmtPtr InitStmt::Duplicate()
 	{
@@ -191,6 +917,17 @@ StmtPtr InitStmt::Duplicate()
 	return SetSucc(new InitStmt(new_inits));
 	}
 
+bool InitStmt::IsReduced(Reducer* c) const
+	{
+	return c->IDsAreReduced(inits);
+	}
+
+StmtPtr InitStmt::DoReduce(Reducer* c)
+	{
+	c->UpdateIDs(inits);
+	return ThisPtr();
+	}
+
 
 StmtPtr WhenStmt::Duplicate()
 	{
@@ -208,5 +945,149 @@ void WhenStmt::Inline(Inliner* inl)
 	// the frames of closures.
 	}
 
+bool WhenStmt::IsReduced(Reducer* c) const
+	{
+	// We consider these always reduced because they're not
+	// candidates for any further optimization.
+	return true;
+	}
+
+
+CatchReturnStmt::CatchReturnStmt(StmtPtr _block, NameExprPtr _ret_var)
+	: Stmt(STMT_CATCH_RETURN)
+	{
+	block = _block;
+	ret_var = _ret_var;
+	}
+
+ValPtr CatchReturnStmt::Exec(Frame* f, StmtFlowType& flow) const
+	{
+	RegisterAccess();
+
+	auto val = block->Exec(f, flow);
+
+	if ( flow == FLOW_RETURN )
+		flow = FLOW_NEXT;
+
+	if ( ret_var )
+		f->SetElement(ret_var->Id()->Offset(), val);
+
+	// Note, do *not* return the value!  That's taken as a signal
+	// that a full return executed.
+	return nullptr;
+	}
+
+bool CatchReturnStmt::IsPure() const
+	{
+	// The ret_var is pure by construction.
+	return block->IsPure();
+	}
+
+StmtPtr CatchReturnStmt::Duplicate()
+	{
+	auto rv_dup = ret_var->Duplicate();
+	auto rv_dup_ptr = rv_dup->AsNameExprPtr();
+	return SetSucc(new CatchReturnStmt(block->Duplicate(), rv_dup_ptr));
+	}
+
+StmtPtr CatchReturnStmt::DoReduce(Reducer* c)
+	{
+	block = block->Reduce(c);
+
+	if ( block->Tag() == STMT_RETURN )
+		{
+		// The whole thing reduced to a bare return.  This can
+		// happen due to constant propagation.
+		auto ret = block->AsReturnStmt();
+		auto ret_e = ret->StmtExprPtr();
+
+		if ( ! ret_e )
+			{
+			if ( ret_var )
+				reporter->InternalError("inlining inconsistency: no return value");
+
+			return make_intrusive<NullStmt>();
+			}
+
+		auto assign = make_intrusive<AssignExpr>(ret_var->Duplicate(),
+							ret_e->Duplicate(),
+							false);
+		assign_stmt = make_intrusive<ExprStmt>(assign);
+		return assign_stmt;
+		}
+
+	return ThisPtr();
+	}
+
+void CatchReturnStmt::StmtDescribe(ODesc* d) const
+	{
+	Stmt::StmtDescribe(d);
+	block->Describe(d);
+	DescribeDone(d);
+	}
+
+TraversalCode CatchReturnStmt::Traverse(TraversalCallback* cb) const
+	{
+	TraversalCode tc = cb->PreStmt(this);
+	HANDLE_TC_STMT_PRE(tc);
+
+	block->Traverse(cb);
+
+	if ( ret_var )
+		ret_var->Traverse(cb);
+
+	tc = cb->PostStmt(this);
+	HANDLE_TC_STMT_POST(tc);
+	}
+
+
+CheckAnyLenStmt::CheckAnyLenStmt(ExprPtr arg_e, int _expected_len)
+	: ExprStmt(STMT_CHECK_ANY_LEN, std::move(arg_e))
+	{
+	expected_len = _expected_len;
+	}
+
+ValPtr CheckAnyLenStmt::Exec(Frame* f, StmtFlowType& flow) const
+	{
+	RegisterAccess();
+	flow = FLOW_NEXT;
+
+	auto& v = e->Eval(f)->AsListVal()->Vals();
+
+	if ( v.size() != expected_len )
+		reporter->ExprRuntimeError(e.get(), "mismatch in list lengths");
+
+	return nullptr;
+	}
+
+StmtPtr CheckAnyLenStmt::Duplicate()
+	{
+	return SetSucc(new CheckAnyLenStmt(e->Duplicate(), expected_len));
+	}
+
+bool CheckAnyLenStmt::IsReduced(Reducer* c) const
+	{
+	return true;
+	}
+
+StmtPtr CheckAnyLenStmt::DoReduce(Reducer* c)
+	{
+	// These are created in reduced form.
+	return ThisPtr();
+	}
+
+void CheckAnyLenStmt::StmtDescribe(ODesc* d) const
+	{
+	Stmt::StmtDescribe(d);
+
+	e->Describe(d);
+	if ( ! d->IsBinary() )
+		d->Add(".length == ");
+
+	d->Add(expected_len);
+
+	DescribeDone(d);
+	}
+
 
 } // namespace zeek::detail