reductions of expressions in ASTs - code compiles but doesn't yet link

src/Expr.cc

@@ -41,6 +41,10 @@ const char* expr_name(BroExprTag t)
 		"coerce", "record_coerce", "table_coerce", "vector_coerce",
 		"sizeof", "cast", "is", "[:]=",
 		"inline()",
+		"[]=", "$=",
+		"vec+=",
+		"to_any_coerce", "from_any_coerce",
+		"any[]",
 		"nop",
 
 	};
@@ -95,12 +99,24 @@ NameExpr* Expr::AsNameExpr()
 	return (NameExpr*) this;
 	}
 
+NameExprPtr Expr::AsNameExprPtr()
+	{
+	CHECK_TAG(tag, EXPR_NAME, "ExprVal::AsNameExpr", expr_name)
+	return {NewRef{}, (NameExpr*) this};
+	}
+
 const ConstExpr* Expr::AsConstExpr() const
 	{
 	CHECK_TAG(tag, EXPR_CONST, "ExprVal::AsConstExpr", expr_name)
 	return (const ConstExpr*) this;
 	}
 
+ConstExprPtr Expr::AsConstExprPtr()
+	{
+	CHECK_TAG(tag, EXPR_CONST, "ExprVal::AsConstExpr", expr_name)
+	return {NewRef{}, (ConstExpr*) this};
+	}
+
 const CallExpr* Expr::AsCallExpr() const
 	{
 	CHECK_TAG(tag, EXPR_CALL, "ExprVal::AsCallExpr", expr_name)
@@ -143,6 +159,12 @@ EventExprPtr Expr::AsEventExprPtr()
 	return {NewRef{}, (EventExpr*) this};
 	}
 
+RefExprPtr Expr::AsRefExprPtr()
+	{
+	CHECK_TAG(tag, EXPR_REF, "ExprVal::AsRefExpr", expr_name)
+	return {NewRef{}, (RefExpr*) this};
+	}
+
 bool Expr::CanAdd() const
 	{
 	return false;
@@ -182,6 +204,132 @@ void Expr::Assign(Frame* /* f */, ValPtr /* v */)
 	Internal("Expr::Assign called");
 	}
 
+void Expr::AssignToIndex(ValPtr v1, ValPtr v2, ValPtr v3) const
+	{
+	bool iterators_invalidated;
+
+	auto error_msg = assign_to_index(v1, v2, v3, iterators_invalidated);
+
+	if ( iterators_invalidated )
+		{
+		ODesc d;
+		Describe(&d);
+		reporter->PushLocation(GetLocationInfo());
+		reporter->Warning("possible loop/iterator invalidation caused by expression: %s", d.Description());
+		reporter->PopLocation();
+		}
+
+	if ( error_msg )
+		RuntimeErrorWithCallStack(error_msg);
+	}
+
+static int get_slice_index(int idx, int len)
+	{
+	if ( abs(idx) > len )
+		idx = idx > 0 ? len : 0; // Clamp maximum positive/negative indices.
+	else if ( idx < 0 )
+		idx += len;  // Map to a positive index.
+
+	return idx;
+	}
+
+const char* assign_to_index(ValPtr v1, ValPtr v2, ValPtr v3,
+				bool& iterators_invalidated)
+	{
+	iterators_invalidated = false;
+
+	if ( ! v1 || ! v2 || ! v3 )
+		return nullptr;
+
+	// Hold an extra reference to 'arg_v' in case the ownership transfer
+	// to the table/vector goes wrong and we still want to obtain
+	// diagnostic info from the original value after the assignment
+	// already unref'd.
+	auto v_extra = v3;
+
+	switch ( v1->GetType()->Tag() ) {
+	case TYPE_VECTOR:
+		{
+		const ListVal* lv = v2->AsListVal();
+		VectorVal* v1_vect = v1->AsVectorVal();
+
+		if ( lv->Length() > 1 )
+			{
+			auto len = v1_vect->Size();
+			bro_int_t first = get_slice_index(lv->Idx(0)->CoerceToInt(), len);
+			bro_int_t last = get_slice_index(lv->Idx(1)->CoerceToInt(), len);
+
+			// Remove the elements from the vector within the slice.
+			for ( auto idx = first; idx < last; idx++ )
+				v1_vect->Remove(first);
+
+			// Insert the new elements starting at the first
+			// position.
+
+			VectorVal* v_vect = v3->AsVectorVal();
+
+			for ( auto idx = 0u; idx < v_vect->Size();
+			      idx++, first++ )
+				v1_vect->Insert(first, v_vect->At(idx));
+			}
+
+		else if ( ! v1_vect->Assign(lv->Idx(0)->CoerceToUnsigned(), std::move(v3)) )
+			{
+			v3 = std::move(v_extra);
+
+			if ( v3 )
+				{
+				ODesc d;
+				v3->Describe(&d);
+				const auto& vt = v3->GetType();
+				auto vtt = vt->Tag();
+				std::string tn = vtt == TYPE_RECORD ?
+					vt->GetName() : type_name(vtt);
+				return util::fmt("vector index assignment failed for invalid type '%s', value: %s",
+					tn.data(), d.Description());
+				}
+			else
+				return "assignment failed with null value";
+			}
+		break;
+		}
+
+	case TYPE_TABLE:
+		{
+		if ( ! v1->AsTableVal()->Assign(std::move(v2), std::move(v3), true, &iterators_invalidated) )
+			{
+			v3 = std::move(v_extra);
+
+			if ( v3 )
+				{
+				ODesc d;
+				v3->Describe(&d);
+				const auto& vt = v3->GetType();
+				auto vtt = vt->Tag();
+				std::string tn = vtt == TYPE_RECORD ?
+					vt->GetName() : type_name(vtt);
+				return util::fmt("table index assignment failed for invalid type '%s', value: %s",
+					tn.data(), d.Description());
+				}
+			else
+				return "assignment failed with null value";
+			}
+
+		break;
+		}
+
+	case TYPE_STRING:
+		return "assignment via string index accessor not allowed";
+		break;
+
+	default:
+		return "bad index expression type in assignment";
+		break;
+	}
+
+	return nullptr;
+	}
+
 TypePtr Expr::InitType() const
 	{
 	return type;
@@ -312,6 +460,12 @@ NameExpr::NameExpr(IDPtr arg_id, bool const_init)
 		h->SetUsed();
 	}
 
+// This isn't in-lined to avoid needing to pull in ID.h.
+IDPtr NameExpr::IdPtr()
+	{
+	return id;
+	}
+
 ValPtr NameExpr::Eval(Frame* f) const
 	{
 	ValPtr v;
@@ -436,7 +590,14 @@ ValPtr UnaryExpr::Eval(Frame* f) const
 	if ( ! v )
 		return nullptr;
 
-	if ( is_vector(v) && Tag() != EXPR_IS && Tag() != EXPR_CAST )
+	if ( is_vector(v) && Tag() != EXPR_IS && Tag() != EXPR_CAST &&
+	     // The following allows passing vectors-by-reference to
+	     // functions that use vector-of-any for generic vector
+	     // manipulation ...
+	     Tag() != EXPR_TO_ANY_COERCE &&
+	     // ... and the following to avoid vectorizing operations
+	     // on vector-of-any's
+	     Tag() != EXPR_FROM_ANY_COERCE )
 		{
 		VectorVal* v_op = v->AsVectorVal();
 		VectorTypePtr out_t;
@@ -457,9 +618,7 @@ ValPtr UnaryExpr::Eval(Frame* f) const
 		return result;
 		}
 	else
-		{
 		return Fold(v.get());
-		}
 	}
 
 bool UnaryExpr::IsPure() const
@@ -2129,7 +2288,8 @@ void RefExpr::Assign(Frame* f, ValPtr v)
 AssignExpr::AssignExpr(ExprPtr arg_op1,
                        ExprPtr arg_op2,
                        bool arg_is_init, ValPtr arg_val,
-                       const AttributesPtr& attrs)
+                       const AttributesPtr& attrs,
+                       bool typecheck)
 	: BinaryExpr(EXPR_ASSIGN, arg_is_init ?
 	             std::move(arg_op1) : arg_op1->MakeLvalue(),
 	             std::move(arg_op2))
@@ -2152,9 +2312,10 @@ AssignExpr::AssignExpr(ExprPtr arg_op1,
 		return;
 		}
 
-	// We discard the status from TypeCheck since it has already
+	if ( typecheck )
-	// generated error messages.
+		// We discard the status from TypeCheck since it has already
-	(void) TypeCheck(attrs);
+		// generated error messages.
+		(void) TypeCheck(attrs);
 
 	val = std::move(arg_val);
 
@@ -2754,16 +2915,6 @@ ValPtr IndexExpr::Eval(Frame* f) const
 		return Fold(v1.get(), v2.get());
 	}
 
-static int get_slice_index(int idx, int len)
-	{
-	if ( abs(idx) > len )
-		idx = idx > 0 ? len : 0; // Clamp maximum positive/negative indices.
-	else if ( idx < 0 )
-		idx += len;  // Map to a positive index.
-
-	return idx;
-	}
-
 ValPtr IndexExpr::Fold(Val* v1, Val* v2) const
 	{
 	if ( IsError() )
@@ -2855,105 +3006,9 @@ void IndexExpr::Assign(Frame* f, ValPtr v)
 		return;
 
 	auto v1 = op1->Eval(f);
-
-	if ( ! v1 )
-		return;
-
 	auto v2 = op2->Eval(f);
 
-	if ( ! v1 || ! v2 )
+	AssignToIndex(v1, v2, v);
-		return;
-
-	// Hold an extra reference to 'arg_v' in case the ownership transfer to
-	// the table/vector goes wrong and we still want to obtain diagnostic info
-	// from the original value after the assignment already unref'd.
-	auto v_extra = v;
-
-	switch ( v1->GetType()->Tag() ) {
-	case TYPE_VECTOR:
-		{
-		const ListVal* lv = v2->AsListVal();
-		VectorVal* v1_vect = v1->AsVectorVal();
-
-		if ( lv->Length() > 1 )
-			{
-			auto len = v1_vect->Size();
-			bro_int_t first = get_slice_index(lv->Idx(0)->CoerceToInt(), len);
-			bro_int_t last = get_slice_index(lv->Idx(1)->CoerceToInt(), len);
-
-			// Remove the elements from the vector within the slice
-			for ( auto idx = first; idx < last; idx++ )
-				v1_vect->Remove(first);
-
-			// Insert the new elements starting at the first position
-			VectorVal* v_vect = v->AsVectorVal();
-
-			for ( auto idx = 0u; idx < v_vect->Size(); idx++, first++ )
-				v1_vect->Insert(first, v_vect->At(idx));
-			}
-		else if ( ! v1_vect->Assign(lv->Idx(0)->CoerceToUnsigned(), std::move(v)) )
-			{
-			v = std::move(v_extra);
-
-			if ( v )
-				{
-				ODesc d;
-				v->Describe(&d);
-				const auto& vt = v->GetType();
-				auto vtt = vt->Tag();
-				std::string tn = vtt == TYPE_RECORD ? vt->GetName() : type_name(vtt);
-				RuntimeErrorWithCallStack(util::fmt(
-				  "vector index assignment failed for invalid type '%s', value: %s",
-				  tn.data(), d.Description()));
-				}
-			else
-				RuntimeErrorWithCallStack("assignment failed with null value");
-			}
-		break;
-		}
-
-	case TYPE_TABLE:
-		{
-		bool iterators_invalidated = false;
-
-		if ( ! v1->AsTableVal()->Assign(std::move(v2), std::move(v), true, &iterators_invalidated) )
-			{
-			v = std::move(v_extra);
-
-			if ( v )
-				{
-				ODesc d;
-				v->Describe(&d);
-				const auto& vt = v->GetType();
-				auto vtt = vt->Tag();
-				std::string tn = vtt == TYPE_RECORD ? vt->GetName() : type_name(vtt);
-				RuntimeErrorWithCallStack(util::fmt(
-				  "table index assignment failed for invalid type '%s', value: %s",
-				  tn.data(), d.Description()));
-				}
-			else
-				RuntimeErrorWithCallStack("assignment failed with null value");
-			}
-
-		if ( iterators_invalidated )
-			{
-			ODesc d;
-			Describe(&d);
-			reporter->PushLocation(GetLocationInfo());
-			reporter->Warning("possible loop/iterator invalidation caused by expression: %s", d.Description());
-			reporter->PopLocation();
-			}
-		}
-		break;
-
-	case TYPE_STRING:
-		RuntimeErrorWithCallStack("assignment via string index accessor not allowed");
-		break;
-
-	default:
-		RuntimeErrorWithCallStack("bad index expression type in assignment");
-		break;
-	}
 	}
 
 void IndexExpr::ExprDescribe(ODesc* d) const
@@ -5168,7 +5223,16 @@ bool check_and_promote_args(ListExpr* const args, RecordType* types)
 				return false;
 				}
 
-			def_elements.push_front(def_attr->GetExpr().get());
+			// Don't use the default expression directly, as
+			// doing so will wind up sharing its code across
+			// different invocations that use the default
+			// argument.  That works okay for the interpreter,
+			// but if we transform the code we want that done
+			// separately for each instance, rather than
+			// one instance inheriting the transformed version
+			// from another.
+			auto e = def_attr->GetExpr();
+			def_elements.push_front(e->Duplicate().release());
 			}
 
 		for ( const auto& elem : def_elements )

src/Expr.h

@@ -68,6 +68,15 @@ enum BroExprTag : int {
 	EXPR_IS,
 	EXPR_INDEX_SLICE_ASSIGN,
 	EXPR_INLINE,
+
+	// The following types of expressions are only created for
+	// ASTs transformed to reduced form; they aren't germane for
+	// ASTs produced by parsing .zeek script files.
+	EXPR_INDEX_ASSIGN, EXPR_FIELD_LHS_ASSIGN,
+	EXPR_APPEND_TO,
+	EXPR_TO_ANY_COERCE, EXPR_FROM_ANY_COERCE,
+	EXPR_ANY_INDEX,
+
 	EXPR_NOP,
 
 #define NUM_EXPRS (int(EXPR_NOP) + 1)
@@ -75,18 +84,27 @@ enum BroExprTag : int {
 
 extern const char* expr_name(BroExprTag t);
 
-class ListExpr;
-class NameExpr;
-class ConstExpr;
-class IndexExpr;
 class AssignExpr;
 class CallExpr;
+class ConstExpr;
 class EventExpr;
-class Stmt;
+class FieldAssignExpr;
+class FieldExpr;
+class ForExpr;
+class IndexExpr;
+class ListExpr;
+class NameExpr;
+class RefExpr;
 
 class Expr;
-using ExprPtr = IntrusivePtr<Expr>;
+using CallExprPtr = IntrusivePtr<CallExpr>;
+using ConstExprPtr = IntrusivePtr<ConstExpr>;
 using EventExprPtr = IntrusivePtr<EventExpr>;
+using ExprPtr = IntrusivePtr<Expr>;
+using NameExprPtr = IntrusivePtr<NameExpr>;
+using RefExprPtr = IntrusivePtr<RefExpr>;
+
+class Stmt;
 using StmtPtr = IntrusivePtr<Stmt>;
 
 class Expr : public Obj {
@@ -182,13 +200,17 @@ public:
 	ctype* As ## ctype (); \
 	IntrusivePtr<ctype> As ## ctype ## Ptr ();
 
+	ZEEK_EXPR_ACCESSOR_DECLS(AssignExpr)
+	ZEEK_EXPR_ACCESSOR_DECLS(CallExpr)
+	ZEEK_EXPR_ACCESSOR_DECLS(ConstExpr)
+	ZEEK_EXPR_ACCESSOR_DECLS(EventExpr)
+	ZEEK_EXPR_ACCESSOR_DECLS(FieldAssignExpr)
+	ZEEK_EXPR_ACCESSOR_DECLS(FieldExpr)
+	ZEEK_EXPR_ACCESSOR_DECLS(ForExpr)
+	ZEEK_EXPR_ACCESSOR_DECLS(IndexExpr)
 	ZEEK_EXPR_ACCESSOR_DECLS(ListExpr)
 	ZEEK_EXPR_ACCESSOR_DECLS(NameExpr)
-	ZEEK_EXPR_ACCESSOR_DECLS(ConstExpr)
+	ZEEK_EXPR_ACCESSOR_DECLS(RefExpr)
-	ZEEK_EXPR_ACCESSOR_DECLS(CallExpr)
-	ZEEK_EXPR_ACCESSOR_DECLS(AssignExpr)
-	ZEEK_EXPR_ACCESSOR_DECLS(IndexExpr)
-	ZEEK_EXPR_ACCESSOR_DECLS(EventExpr)
 
 	void Describe(ODesc* d) const override final;
 
@@ -200,6 +222,117 @@ public:
 	// Recursively traverses the AST to inline eligible function calls.
 	virtual ExprPtr Inline(Inliner* inl)	{ return ThisPtr(); }
 
+	// True if the expression can serve as an operand to a reduced
+	// expression.
+	bool IsSingleton(Reducer* r) const
+		{
+		return (tag == EXPR_NAME && IsReduced(r)) || tag == EXPR_CONST;
+		}
+
+	// True if the expression has no side effects, false otherwise.
+	virtual bool HasNoSideEffects() const	{ return IsPure(); }
+
+	// True if the expression is in fully reduced form: a singleton
+	// or an assignment to an operator with singleton operands.
+	virtual bool IsReduced(Reducer* c) const;
+
+	// True if the expression's operands are singletons.
+	virtual bool HasReducedOps(Reducer* c) const;
+
+	// True if (a) the expression has at least one operand, and (b) all
+	// of its operands are constant.
+	bool HasConstantOps() const
+		{
+		return GetOp1() && GetOp1()->IsConst() &&
+			(! GetOp2() ||
+			 (GetOp2()->IsConst() &&
+			  (! GetOp3() || GetOp3()->IsConst())));
+		}
+
+	// True if the expression is reduced to a form that can be
+	// used in a conditional.
+	bool IsReducedConditional(Reducer* c) const;
+
+	// True if the expression is reduced to a form that can be
+	// used in a field assignment.
+	bool IsReducedFieldAssignment(Reducer* c) const;
+
+	// True if this expression can be the RHS for a field assignment.
+	bool IsFieldAssignable(const Expr* e) const;
+
+	// True if the expression will transform to one of another type
+	// upon reduction, for non-constant operands.  "Transform" means
+	// something beyond assignment to a temporary.  Necessary so that
+	// we know to fully reduce such expressions if they're the RHS
+	// of an assignment.
+	virtual bool WillTransform(Reducer* c) const	{ return false; }
+
+	// The same, but for the expression when used in a conditional context.
+	virtual bool WillTransformInConditional(Reducer* c) const
+		{ return false; }
+
+	// Returns the current expression transformed into "new_me".
+	// Takes a bare pointer for "new_me" since often it's newly
+	// allocated.
+	ExprPtr TransformMe(Expr* new_me, Reducer* c, StmtPtr& red_stmt);
+	ExprPtr TransformMe(ExprPtr new_me, Reducer* c, StmtPtr& red_stmt)
+		{ return TransformMe(new_me.get(), c, red_stmt); }
+
+	// Returns a set of predecessor statements in red_stmt (which might
+	// be nil if no reduction necessary), and the reduced version of
+	// the expression, suitable for replacing previous uses.  The
+	// second version always yields a singleton suitable for use
+	// as an operand.  The first version does this too except
+	// for assignment statements; thus, its form is not guarantee
+	// suitable for use as an operand.
+	virtual ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt);
+	virtual ExprPtr ReduceToSingleton(Reducer* c, StmtPtr& red_stmt)
+		{ return Reduce(c, red_stmt); }
+
+	// Reduces the expression to one whose operands are singletons.
+	// Returns a predecessor statement (which might be a StmtList), if any.
+	virtual StmtPtr ReduceToSingletons(Reducer* c);
+
+	// Reduces the expression to one that can appear as a conditional.
+	ExprPtr ReduceToConditional(Reducer* c, StmtPtr& red_stmt);
+
+	// Reduces the expression to one that can appear as a field
+	// assignment.
+	ExprPtr ReduceToFieldAssignment(Reducer* c, StmtPtr& red_stmt);
+
+	// Helper function for factoring out complexities related to
+	// index-based assignment.
+	void AssignToIndex(ValPtr v1, ValPtr v2, ValPtr v3) const;
+
+	// Returns a new expression corresponding to a temporary
+	// that's been assigned to the given expression via red_stmt.
+	ExprPtr AssignToTemporary(ExprPtr e, Reducer* c, StmtPtr& red_stmt);
+	// Same but for this expression.
+	ExprPtr AssignToTemporary(Reducer* c, StmtPtr& red_stmt)
+		{ return AssignToTemporary(ThisPtr(), c, red_stmt); }
+
+	// If the expression always evaluates to the same value, returns
+	// that value.  Otherwise, returns nullptr.
+	virtual ValPtr FoldVal() const	{ return nullptr; }
+
+	// Returns a Val or a constant Expr corresponding to zero.
+	ValPtr MakeZero(TypeTag t) const;
+	ConstExprPtr MakeZeroExpr(TypeTag t) const;
+
+	// Returns the expression's operands, or nil if it doesn't
+	// have the given operand.
+	virtual ExprPtr GetOp1() const;
+	virtual ExprPtr GetOp2() const;
+	virtual ExprPtr GetOp3() const;
+
+	// Sets the operands to new values.
+	virtual void SetOp1(ExprPtr new_op);
+	virtual void SetOp2(ExprPtr new_op);
+	virtual void SetOp3(ExprPtr new_op);
+
+	// Helper function to reduce boring code runs.
+	StmtPtr MergeStmts(StmtPtr s1, StmtPtr s2, StmtPtr s3 = nullptr) const;
+
 	// Access to the original expression from which this one is derived,
 	// or this one if we don't have an original.  Returns a bare pointer
 	// rather than an ExprPtr to emphasize that the access is read-only.
@@ -272,6 +405,7 @@ public:
 	explicit NameExpr(IDPtr id, bool const_init = false);
 
 	ID* Id() const		{ return id.get(); }
+	IDPtr IdPtr();
 
 	ValPtr Eval(Frame* f) const override;
 	void Assign(Frame* f, ValPtr v) override;
@@ -282,10 +416,20 @@ public:
 
 	// Optimization-related:
 	ExprPtr Duplicate() override;
+	bool HasNoSideEffects() const override	{ return true; }
+	bool IsReduced(Reducer* c) const override;
+	bool HasReducedOps(Reducer* c) const override	{ return IsReduced(c); }
+	bool WillTransform(Reducer* c) const override	{ return ! IsReduced(c); }
+	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
+	ValPtr FoldVal() const override;
 
 protected:
 	void ExprDescribe(ODesc* d) const override;
 
+	// Returns true if our identifier is a global with a constant value
+	// that can be propagated; used for optimization.
+	bool FoldableGlobal() const;
+
 	IDPtr id;
 	bool in_const_init;
 };
@@ -303,6 +447,7 @@ public:
 
 	// Optimization-related:
 	ExprPtr Duplicate() override;
+	ValPtr FoldVal() const override	{ return val; }
 
 protected:
 	void ExprDescribe(ODesc* d) const override;
@@ -325,6 +470,14 @@ public:
 	// Optimization-related:
 	ExprPtr Inline(Inliner* inl) override;
 
+	bool HasNoSideEffects() const override;
+	bool IsReduced(Reducer* c) const override;
+	bool HasReducedOps(Reducer* c) const override;
+	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
+
+	ExprPtr GetOp1() const override final	{ return op; }
+	void SetOp1(ExprPtr _op) override final	{ op = std::move(_op); }
+
 protected:
 	UnaryExpr(BroExprTag arg_tag, ExprPtr arg_op);
 
@@ -353,6 +506,17 @@ public:
 	// Optimization-related:
 	ExprPtr Inline(Inliner* inl) override;
 
+	bool HasNoSideEffects() const override;
+	bool IsReduced(Reducer* c) const override;
+	bool HasReducedOps(Reducer* c) const override;
+	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
+
+	ExprPtr GetOp1() const override final	{ return op1; }
+	ExprPtr GetOp2() const override final	{ return op2; }
+
+	void SetOp1(ExprPtr _op) override final	{ std::move(op1 = _op); }
+	void SetOp2(ExprPtr _op) override final	{ std::move(op2 = _op); }
+
 protected:
 	BinaryExpr(BroExprTag arg_tag,
 	           ExprPtr arg_op1, ExprPtr arg_op2)
@@ -425,6 +589,12 @@ public:
 
 	// Optimization-related:
 	ExprPtr Duplicate() override;
+	bool HasNoSideEffects() const override;
+	bool WillTransform(Reducer* c) const override	{ return true; }
+	bool IsReduced(Reducer* c) const override;
+	bool HasReducedOps(Reducer* c) const override	{ return false; }
+	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
+	ExprPtr ReduceToSingleton(Reducer* c, StmtPtr& red_stmt) override;
 };
 
 class ComplementExpr final : public UnaryExpr {
@@ -433,6 +603,8 @@ public:
 
 	// Optimization-related:
 	ExprPtr Duplicate() override;
+	bool WillTransform(Reducer* c) const override;
+	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
 
 protected:
 	ValPtr Fold(Val* v) const override;
@@ -444,6 +616,8 @@ public:
 
 	// Optimization-related:
 	ExprPtr Duplicate() override;
+	bool WillTransform(Reducer* c) const override;
+	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
 
 protected:
 	ValPtr Fold(Val* v) const override;
@@ -455,6 +629,8 @@ public:
 
 	// Optimization-related:
 	ExprPtr Duplicate() override;
+	bool WillTransform(Reducer* c) const override;
+	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
 
 protected:
 	ValPtr Fold(Val* v) const override;
@@ -466,6 +642,8 @@ public:
 
 	// Optimization-related:
 	ExprPtr Duplicate() override;
+	bool WillTransform(Reducer* c) const override;
+	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
 
 protected:
 	ValPtr Fold(Val* v) const override;
@@ -490,6 +668,11 @@ public:
 
 	// Optimization-related:
 	ExprPtr Duplicate() override;
+	bool WillTransform(Reducer* c) const override;
+	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
+
+protected:
+	ExprPtr BuildSub(const ExprPtr& op1, const ExprPtr& op2);
 };
 
 class AddToExpr final : public BinaryExpr {
@@ -499,6 +682,8 @@ public:
 
 	// Optimization-related:
 	ExprPtr Duplicate() override;
+	bool WillTransform(Reducer* c) const override	{ return true; }
+	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
 };
 
 class RemoveFromExpr final : public BinaryExpr {
@@ -508,6 +693,8 @@ public:
 
 	// Optimization-related:
 	ExprPtr Duplicate() override;
+	bool WillTransform(Reducer* c) const override	{ return true; }
+	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
 };
 
 class SubExpr final : public BinaryExpr {
@@ -516,6 +703,8 @@ public:
 
 	// Optimization-related:
 	ExprPtr Duplicate() override;
+	bool WillTransform(Reducer* c) const override;
+	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
 };
 
 class TimesExpr final : public BinaryExpr {
@@ -525,6 +714,8 @@ public:
 
 	// Optimization-related:
 	ExprPtr Duplicate() override;
+	bool WillTransform(Reducer* c) const override;
+	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
 };
 
 class DivideExpr final : public BinaryExpr {
@@ -533,6 +724,8 @@ public:
 
 	// Optimization-related:
 	ExprPtr Duplicate() override;
+	bool WillTransform(Reducer* c) const override;
+	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
 
 protected:
 	ValPtr AddrFold(Val* v1, Val* v2) const override;
@@ -555,6 +748,13 @@ public:
 
 	// Optimization-related:
 	ExprPtr Duplicate() override;
+	bool WillTransform(Reducer* c) const override	{ return true; }
+	bool WillTransformInConditional(Reducer* c) const override;
+	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
+
+protected:
+	bool IsTrue(const ExprPtr& e) const;
+	bool IsFalse(const ExprPtr& e) const;
 };
 
 class BitExpr final : public BinaryExpr {
@@ -563,6 +763,8 @@ public:
 
 	// Optimization-related:
 	ExprPtr Duplicate() override;
+	bool WillTransform(Reducer* c) const override;
+	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
 };
 
 class EqExpr final : public BinaryExpr {
@@ -572,6 +774,8 @@ public:
 
 	// Optimization-related:
 	ExprPtr Duplicate() override;
+	bool WillTransform(Reducer* c) const override;
+	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
 
 protected:
 	ValPtr Fold(Val* v1, Val* v2) const override;
@@ -584,6 +788,8 @@ public:
 
 	// Optimization-related:
 	ExprPtr Duplicate() override;
+	bool WillTransform(Reducer* c) const override;
+	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
 };
 
 class CondExpr final : public Expr {
@@ -603,6 +809,20 @@ public:
 	ExprPtr Duplicate() override;
 	ExprPtr Inline(Inliner* inl) override;
 
+	bool WillTransform(Reducer* c) const override;
+	bool IsReduced(Reducer* c) const override;
+	bool HasReducedOps(Reducer* c) const override;
+	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
+	StmtPtr ReduceToSingletons(Reducer* c) override;
+
+	ExprPtr GetOp1() const override final	{ return op1; }
+	ExprPtr GetOp2() const override final	{ return op2; }
+	ExprPtr GetOp3() const override final	{ return op3; }
+
+	void SetOp1(ExprPtr _op) override final	{ op1 = std::move(_op); }
+	void SetOp2(ExprPtr _op) override final	{ op2 = std::move(_op); }
+	void SetOp3(ExprPtr _op) override final	{ op3 = std::move(_op); }
+
 protected:
 	void ExprDescribe(ODesc* d) const override;
 
@@ -620,6 +840,14 @@ public:
 
 	// Optimization-related:
 	ExprPtr Duplicate() override;
+
+	bool WillTransform(Reducer* c) const override;
+	bool IsReduced(Reducer* c) const override;
+	bool HasReducedOps(Reducer* c) const override;
+	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
+
+	// Reduce to simplifed LHS form, i.e., a reference to only a name.
+	StmtPtr ReduceToLHS(Reducer* c);
 };
 
 class AssignExpr : public BinaryExpr {
@@ -628,7 +856,8 @@ public:
 	// yet still perform the assignment.  Used for triggers.
 	AssignExpr(ExprPtr op1, ExprPtr op2, bool is_init,
 	           ValPtr val = nullptr,
-	           const AttributesPtr& attrs = nullptr);
+	           const AttributesPtr& attrs = nullptr,
+		   bool type_check = true);
 
 	ValPtr Eval(Frame* f) const override;
 	void EvalIntoAggregate(const zeek::Type* t, Val* aggr, Frame* f) const override;
@@ -637,20 +866,29 @@ public:
 	ValPtr InitVal(const zeek::Type* t, ValPtr aggr) const override;
 	bool IsPure() const override;
 
-	void SetOp2(ExprPtr e)
-		{
-		op2 = std::move(e);
-		}
-
 	// Optimization-related:
 	ExprPtr Duplicate() override;
 
+	bool HasNoSideEffects() const override;
+	bool WillTransform(Reducer* c) const override	{ return true; }
+	bool IsReduced(Reducer* c) const override;
+	bool HasReducedOps(Reducer* c) const override;
+	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
+	ExprPtr ReduceToSingleton(Reducer* c, StmtPtr& red_stmt) override;
+
+	// Whether this is an assignment to a temporary.
+	bool IsTemp() const	{ return is_temp; }
+	void SetIsTemp()	{ is_temp = true; }
+
 protected:
 	bool TypeCheck(const AttributesPtr& attrs = nullptr);
 	bool TypeCheckArithmetics(TypeTag bt1, TypeTag bt2);
 
 	bool is_init;
 	ValPtr val;	// optional
+
+	// Optimization-related:
+	bool is_temp = false;
 };
 
 class IndexSliceAssignExpr final : public AssignExpr {
@@ -688,6 +926,9 @@ public:
 	// Optimization-related:
 	ExprPtr Duplicate() override;
 
+	bool HasReducedOps(Reducer* c) const override;
+	StmtPtr ReduceToSingletons(Reducer* c) override;
+
 protected:
 	ValPtr Fold(Val* v1, Val* v2) const override;
 
@@ -797,6 +1038,10 @@ public:
 	// Optimization-related:
 	ExprPtr Duplicate() override;
 
+	bool HasReducedOps(Reducer* c) const override;
+	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
+	StmtPtr ReduceToSingletons(Reducer* c) override;
+
 protected:
 	ValPtr InitVal(const zeek::Type* t, ValPtr aggr) const override;
 
@@ -823,6 +1068,10 @@ public:
 	// Optimization-related:
 	ExprPtr Duplicate() override;
 
+	bool HasReducedOps(Reducer* c) const override;
+	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
+	StmtPtr ReduceToSingletons(Reducer* c) override;
+
 protected:
 	ValPtr InitVal(const zeek::Type* t, ValPtr aggr) const override;
 
@@ -849,6 +1098,10 @@ public:
 	// Optimization-related:
 	ExprPtr Duplicate() override;
 
+	bool HasReducedOps(Reducer* c) const override;
+	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
+	StmtPtr ReduceToSingletons(Reducer* c) override;
+
 protected:
 	ValPtr InitVal(const zeek::Type* t, ValPtr aggr) const override;
 
@@ -867,6 +1120,8 @@ public:
 	// Optimization-related:
 	ExprPtr Duplicate() override;
 
+	bool HasReducedOps(Reducer* c) const override;
+
 protected:
 	ValPtr InitVal(const zeek::Type* t, ValPtr aggr) const override;
 
@@ -885,6 +1140,9 @@ public:
 	// Optimization-related:
 	ExprPtr Duplicate() override;
 
+	bool WillTransform(Reducer* c) const override	{ return true; }
+	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
+
 protected:
 	void ExprDescribe(ODesc* d) const override;
 
@@ -898,6 +1156,9 @@ public:
 	// Optimization-related:
 	ExprPtr Duplicate() override;
 
+	bool WillTransform(Reducer* c) const override;
+	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
+
 protected:
 	ValPtr FoldSingleVal(Val* v, InternalTypeTag t) const;
 	ValPtr Fold(Val* v) const override;
@@ -974,6 +1235,16 @@ public:
 	ExprPtr Duplicate() override;
 	ExprPtr Inline(Inliner* inl) override;
 
+	bool IsReduced(Reducer* c) const override;
+	bool HasReducedOps(Reducer* c) const override;
+	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
+
+	ExprPtr GetOp1() const override final;
+	ExprPtr GetOp2() const override final;
+
+	void SetOp1(ExprPtr _op) override final;
+	void SetOp2(ExprPtr _op) override final;
+
 protected:
 	void ExprDescribe(ODesc* d) const override;
 
@@ -988,6 +1259,8 @@ public:
 	// Optimization-related:
 	ExprPtr Duplicate() override;
 
+	bool HasReducedOps(Reducer* c) const override;
+
 protected:
 	ValPtr Fold(Val* v1, Val* v2) const override;
 
@@ -1011,6 +1284,11 @@ public:
 	ExprPtr Duplicate() override;
 	ExprPtr Inline(Inliner* inl) override;
 
+	bool IsReduced(Reducer* c) const override;
+	bool HasReducedOps(Reducer* c) const override;
+	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
+	StmtPtr ReduceToSingletons(Reducer* c) override;
+
 protected:
 	void ExprDescribe(ODesc* d) const override;
 
@@ -1038,6 +1316,8 @@ public:
 	ExprPtr Duplicate() override;
 	ExprPtr Inline(Inliner* inl) override;
 
+	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
+
 protected:
 	void ExprDescribe(ODesc* d) const override;
 
@@ -1048,30 +1328,8 @@ private:
 	std::string my_name;
 };
 
-class EventExpr final : public Expr {
+// This comes before EventExpr so that EventExpr::GetOp1 can return its
-public:
+// arguments as convertible to ExprPtr.
-	EventExpr(const char* name, ListExprPtr args);
-
-	const char* Name() const	{ return name.c_str(); }
-	ListExpr* Args() const		{ return args.get(); }
-	EventHandlerPtr Handler()  const	{ return handler; }
-
-	ValPtr Eval(Frame* f) const override;
-
-	TraversalCode Traverse(TraversalCallback* cb) const override;
-
-	// Optimization-related:
-	ExprPtr Duplicate() override;
-	ExprPtr Inline(Inliner* inl) override;
-
-protected:
-	void ExprDescribe(ODesc* d) const override;
-
-	std::string name;
-	EventHandlerPtr handler;
-	ListExprPtr args;
-};
-
 class ListExpr : public Expr {
 public:
 	ListExpr();
@@ -1099,6 +1357,11 @@ public:
 	ExprPtr Duplicate() override;
 	ExprPtr Inline(Inliner* inl) override;
 
+	bool IsReduced(Reducer* c) const override;
+	bool HasReducedOps(Reducer* c) const override;
+	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
+	StmtPtr ReduceToSingletons(Reducer* c) override;
+
 protected:
 	ValPtr AddSetInit(const zeek::Type* t, ValPtr aggr) const;
 
@@ -1107,6 +1370,38 @@ protected:
 	ExprPList exprs;
 };
 
+class EventExpr final : public Expr {
+public:
+	EventExpr(const char* name, ListExprPtr args);
+
+	const char* Name() const	{ return name.c_str(); }
+	ListExpr* Args() const		{ return args.get(); }
+	EventHandlerPtr Handler()  const	{ return handler; }
+
+	ValPtr Eval(Frame* f) const override;
+
+	TraversalCode Traverse(TraversalCallback* cb) const override;
+
+	// Optimization-related:
+	ExprPtr Duplicate() override;
+	ExprPtr Inline(Inliner* inl) override;
+
+	bool IsReduced(Reducer* c) const override;
+	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
+	StmtPtr ReduceToSingletons(Reducer* c) override;
+
+	ExprPtr GetOp1() const override final	{ return args; }
+	void SetOp1(ExprPtr _op) override final
+		{ args = {NewRef{}, _op->AsListExpr()}; }
+
+protected:
+	void ExprDescribe(ODesc* d) const override;
+
+	std::string name;
+	EventHandlerPtr handler;
+	ListExprPtr args;
+};
+
 
 class RecordAssignExpr final : public ListExpr {
 public:
@@ -1155,6 +1450,9 @@ public:
 
 	ExprPtr Duplicate() override;
 
+	bool IsReduced(Reducer* c) const override;
+	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
+
 	TraversalCode Traverse(TraversalCallback* cb) const override;
 
 protected:
@@ -1166,6 +1464,134 @@ protected:
 	StmtPtr body;
 };
 
+// A companion to AddToExpr that's for vector-append, instantiated during
+// the reduction process.
+class AppendToExpr : public BinaryExpr {
+public:
+	AppendToExpr(ExprPtr op1, ExprPtr op2);
+	ValPtr Eval(Frame* f) const override;
+
+	bool IsReduced(Reducer* c) const override;
+	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
+
+	ExprPtr Duplicate() override;
+};
+
+// An internal class for reduced form.
+class IndexAssignExpr : public BinaryExpr {
+public:
+	// "op1[op2] = op3", all reduced.
+	IndexAssignExpr(ExprPtr op1, ExprPtr op2, ExprPtr op3);
+
+	ValPtr Eval(Frame* f) const override;
+
+	ExprPtr Duplicate() override;
+
+	bool IsReduced(Reducer* c) const override;
+	bool HasReducedOps(Reducer* c) const override;
+	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
+	ExprPtr ReduceToSingleton(Reducer* c, StmtPtr& red_stmt) override;
+
+	ExprPtr GetOp3() const override final	{ return op3; }
+	void SetOp3(ExprPtr _op) override final { op3 = _op; }
+
+	TraversalCode Traverse(TraversalCallback* cb) const override;
+
+protected:
+	void ExprDescribe(ODesc* d) const override;
+
+	ExprPtr op3;	// assignment RHS
+};
+
+// An internal class for reduced form.
+class FieldLHSAssignExpr : public BinaryExpr {
+public:
+	// "op1$field = RHS", where RHS is reduced with respect to
+	// ReduceToFieldAssignment().
+	FieldLHSAssignExpr(ExprPtr op1, ExprPtr op2, const char* field_name,
+				int field);
+
+	const char* FieldName() const	{ return field_name; }
+	int Field() const		{ return field; }
+
+	ValPtr Eval(Frame* f) const override;
+
+	ExprPtr Duplicate() override;
+
+	bool IsReduced(Reducer* c) const override;
+	bool HasReducedOps(Reducer* c) const override;
+	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
+	ExprPtr ReduceToSingleton(Reducer* c, StmtPtr& red_stmt) override;
+
+protected:
+	void ExprDescribe(ODesc* d) const override;
+
+	const char* field_name;
+	int field;
+};
+
+// Expression to explicitly capture conversion to an "any" type, rather
+// than it occurring implicitly during script interpretation.
+class CoerceToAnyExpr : public UnaryExpr {
+public:
+	CoerceToAnyExpr(ExprPtr op);
+
+protected:
+	ValPtr Fold(Val* v) const override;
+
+	ExprPtr Duplicate() override;
+};
+
+// Same, but for conversion from an "any" type.
+class CoerceFromAnyExpr : public UnaryExpr {
+public:
+	CoerceFromAnyExpr(ExprPtr op, TypePtr to_type);
+
+protected:
+	ValPtr Fold(Val* v) const override;
+
+	ExprPtr Duplicate() override;
+};
+
+// Expression used to explicitly capture [a, b, c, ...] = x assignments.
+class AnyIndexExpr : public UnaryExpr {
+public:
+	AnyIndexExpr(ExprPtr op, int index);
+
+	int Index() const	{ return index; }
+
+protected:
+	ValPtr Fold(Val* v) const override;
+
+	void ExprDescribe(ODesc* d) const override;
+
+	ExprPtr Duplicate() override;
+	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
+
+	int index;
+};
+
+// Used internally for optimization, when a placeholder is needed.
+class NopExpr : public Expr {
+public:
+	explicit NopExpr() : Expr(EXPR_NOP) { }
+
+	ValPtr Eval(Frame* f) const override;
+
+	ExprPtr Duplicate() override;
+
+	TraversalCode Traverse(TraversalCallback* cb) const override;
+
+protected:
+	void ExprDescribe(ODesc* d) const override;
+};
+
+
+// Assigns v1[v2] = v3.  Returns an error message, or nullptr on success.
+// Factored out so that compiled code can call it as well as the interpreter.
+extern const char* assign_to_index(ValPtr v1, ValPtr v2, ValPtr v3,
+					bool& iterators_invalidated);
+
 
 inline Val* Expr::ExprVal() const
 	{

src/Stmt.h

@@ -11,9 +11,12 @@
 #include "zeek/ID.h"
 
 ZEEK_FORWARD_DECLARE_NAMESPACED(CompositeHash, zeek::detail);
+ZEEK_FORWARD_DECLARE_NAMESPACED(NameExpr, zeek::detail);
 
 namespace zeek::detail {
 
+using NameExprPtr = IntrusivePtr<zeek::detail::NameExpr>;
+
 class ExprListStmt : public Stmt {
 public:
 	const ListExpr* ExprList() const	{ return l.get(); }
@@ -366,6 +369,11 @@ public:
 	StmtPtr Duplicate() override;
 	void Inline(Inliner* inl) override;
 
+	// Idioms commonly used in reduction.
+	StmtList(StmtPtr s1, Stmt* s2);
+	StmtList(StmtPtr s1, StmtPtr s2);
+	StmtList(StmtPtr s1, StmtPtr s2, StmtPtr s3);
+
 protected:
 	bool IsPure() const override;
 
@@ -439,6 +447,74 @@ protected:
 	bool is_return;
 };
 
+
+// Internal statement used for inlining.  Executes a block and stops
+// the propagation of any "return" inside the block.  Generated in
+// an already-reduced state.
+class CatchReturnStmt : public Stmt {
+public:
+	explicit CatchReturnStmt(StmtPtr block, NameExprPtr ret_var);
+
+	StmtPtr Block() const	{ return block; }
+
+	// This returns a bare pointer rather than a NameExprPtr only
+	// because we don't want to have to include Expr.h in this header.
+	const NameExpr* RetVar() const		{ return ret_var.get(); }
+
+	// The assignment statement this statement transformed into,
+	// or nil if it hasn't (the common case).
+	StmtPtr AssignStmt() const	{ return assign_stmt; }
+
+	ValPtr Exec(Frame* f, StmtFlowType& flow) const override;
+
+	bool IsPure() const override;
+
+	// Even though these objects are generated in reduced form, we still
+	// have a reduction method to support the subsequent optimizer pass.
+	StmtPtr DoReduce(Reducer* c) override;
+
+	// Note, no need for a NoFlowAfter() method because anything that
+	// has "NoFlowAfter" inside the body still gets caught and we
+	// continue afterwards.
+
+	StmtPtr Duplicate() override;
+
+	void StmtDescribe(ODesc* d) const override;
+
+	TraversalCode Traverse(TraversalCallback* cb) const override;
+
+protected:
+	// The inlined function body.
+	StmtPtr block;
+
+	// Expression that holds the return value.  Only used for compiling.
+	NameExprPtr ret_var;
+
+	// If this statement transformed into an assignment, that
+	// corresponding statement.
+	StmtPtr assign_stmt;
+};
+
+// Statement that makes sure at run-time that an "any" type has the
+// correct number of (list) entries to enable sub-assigning to it via
+// statements like "[a, b, c] = x;".  Generated in an already-reduced state.
+class CheckAnyLenStmt : public ExprStmt {
+public:
+	explicit CheckAnyLenStmt(ExprPtr e, int expected_len);
+
+	ValPtr Exec(Frame* f, StmtFlowType& flow) const override;
+
+	StmtPtr Duplicate() override;
+
+	bool IsReduced(Reducer* c) const override;
+	StmtPtr DoReduce(Reducer* c) override;
+
+	void StmtDescribe(ODesc* d) const override;
+
+protected:
+	int expected_len;
+};
+
 } // namespace zeek::detail
 
 using ExprListStmt [[deprecated("Remove in v4.1. Use zeek::detail::ExprListStmt instead.")]] = zeek::detail::ExprListStmt;

src/StmtBase.h

@@ -24,11 +24,13 @@ using ValPtr = IntrusivePtr<Val>;
 
 namespace zeek::detail {
 
-class StmtList;
+class ExprStmt;
 class ForStmt;
 class InitStmt;
-class WhenStmt;
+class ReturnStmt;
+class StmtList;
 class SwitchStmt;
+class WhenStmt;
 
 class EventExpr;
 class ListExpr;
@@ -37,6 +39,7 @@ using EventExprPtr = IntrusivePtr<EventExpr>;
 using ListExprPtr = IntrusivePtr<ListExpr>;
 
 class Inliner;
+class Reducer;
 
 class Stmt;
 using StmtPtr = IntrusivePtr<Stmt>;
@@ -50,6 +53,7 @@ public:
 	virtual ValPtr Exec(Frame* f, StmtFlowType& flow) const = 0;
 
 	Stmt* Ref()			{ zeek::Ref(this); return this; }
+	StmtPtr ThisPtr()		{ return {NewRef{}, this}; }
 
 	bool SetLocationInfo(const Location* loc) override
 		{ return Stmt::SetLocationInfo(loc, loc); }
@@ -64,7 +68,9 @@ public:
 	ForStmt* AsForStmt();
 	const ForStmt* AsForStmt() const;
 
+	const ExprStmt* AsExprStmt() const;
 	const InitStmt* AsInitStmt() const;
+	const ReturnStmt* AsReturnStmt() const;
 	const WhenStmt* AsWhenStmt() const;
 	const SwitchStmt* AsSwitchStmt() const;
 
@@ -81,12 +87,37 @@ public:
 
 	virtual TraversalCode Traverse(TraversalCallback* cb) const = 0;
 
-	// Returns a duplicate of the statement.
+	// Returns a duplicate of the statement so that modifications
+	// can be made to statements from inlining function bodies - or
+	// to the originals - without affecting other instances.
+	//
+	// It's tempting to think that there are some statements that
+	// are safe to share across multiple functions and could just
+	// return references to themselves - but since we associate
+	// information for script optimization with individual statements
+	// nodes, even these need to be duplicated.
 	virtual StmtPtr Duplicate() = 0;
 
 	// Recursively traverses the AST to inline eligible function calls.
 	virtual void Inline(Inliner* inl)	{ }
 
+	// True if the statement is in reduced form.
+	virtual bool IsReduced(Reducer* c) const;
+
+	// Returns a reduced version of the statement, as managed by
+	// the given Reducer.
+	StmtPtr Reduce(Reducer* c);
+	virtual StmtPtr DoReduce(Reducer* c)	{ return ThisPtr(); }
+
+	// True if there's definitely no control flow past the statement.
+	// The argument governs whether to ignore "break" statements, given
+	// they mean two different things depending on whether they're in
+	// a loop or a switch.  Also, if we want to know whether flow reaches
+	// the *end* of a loop, then we also want to ignore break's, as
+	// in that case, they do lead to flow reaching the end.
+	virtual bool NoFlowAfter(bool ignore_break) const
+		{ return false; }
+
 	// Access to the original statement from which this one is derived,
 	// or this one if we don't have an original.  Returns a bare pointer
 	// rather than a StmtPtr to emphasize that the access is read-only.
@@ -124,6 +155,11 @@ public:
 protected:
 	explicit Stmt(StmtTag arg_tag);
 
+	// Helper function called after reductions to perform canonical
+	// actions.  Takes a bare pointer for new_me because usually
+	// it's been newly new'd, so this keeps down code clutter.
+	StmtPtr TransformMe(Stmt* new_me, Reducer* c);
+
 	void AddTag(ODesc* d) const;
 	virtual void StmtDescribe(ODesc* d) const;
 	void DescribeDone(ODesc* d) const;

src/script_opt/Reduce.h

@@ -0,0 +1,186 @@
+// See the file "COPYING" in the main distribution directory for copyright.
+
+#pragma once
+
+#include "zeek/IntrusivePtr.h"
+
+namespace zeek::detail {
+
+class Expr;
+class TempVar;
+class ProfileFunc;
+
+class Reducer {
+public:
+	Reducer(Scope* s);
+	~Reducer();
+
+	StmtPtr Reduce(StmtPtr s)
+		{
+		return s->Reduce(this);
+		}
+
+	ExprPtr GenTemporaryExpr(const TypePtr& t, ExprPtr rhs);
+
+	NameExpr* UpdateName(NameExpr* n);
+	bool NameIsReduced(const NameExpr* n) const;
+
+	void UpdateIDs(IDPList* ids);
+	bool IDsAreReduced(const IDPList* ids) const;
+
+	void UpdateIDs(std::vector<IDPtr>& ids);
+	bool IDsAreReduced(const std::vector<IDPtr>& ids) const;
+
+	IDPtr UpdateID(IDPtr id);
+	bool ID_IsReduced(const IDPtr& id) const
+		{ return ID_IsReduced(id.get()); }
+	bool ID_IsReduced(const ID* id) const;
+
+	// This is called *prior* to pushing a new inline block, in
+	// order to generate the equivalent of function parameters.
+	NameExprPtr GenInlineBlockName(IDPtr id);
+
+	int NumNewLocals() const	{ return new_locals.size(); }
+
+	// Returns the name of a temporary for holding the return
+	// value of the block, or nil if the type indicates there's
+	// o return value.
+	NameExprPtr PushInlineBlock(TypePtr type);
+	void PopInlineBlock();
+
+	// Whether it's okay to split a statement into two copies for if-else
+	// expansion.  We only allow this to a particular depth because
+	// beyond that a function body can get too large to analyze.
+	bool BifurcationOkay() const	{ return bifurcation_level <= 12; }
+	int BifurcationLevel() const	{ return bifurcation_level; }
+
+	void PushBifurcation()		{ ++bifurcation_level; }
+	void PopBifurcation()		{ --bifurcation_level; }
+
+	int NumTemps() const		{ return temps.length(); }
+
+	// True if this name already reflects the replacement.
+	bool IsNewLocal(const NameExpr* n) const
+		{ return IsNewLocal(n->Id()); }
+	bool IsNewLocal(const ID* id) const;
+
+	bool IsTemporary(const ID* id) const
+		{ return FindTemporary(id) != nullptr; }
+
+	// This is a stub for now, since it's not relevant for AST
+	// reduction by itself.  However, many of the Reduce methods
+	// ultimately will call this predicate to control how they
+	// function during the second traversal used to optimize
+	// the reduced form, so we provide the hook now.
+	bool Optimizing() const	{ return false; }
+
+	// A stub for now, but ultimately a predicate that indicates whether
+	// a given reduction pass is being made to prune unused statements.
+	bool IsPruning() const		{ return false; }
+
+	// A stub for now, ultimately a predicate that returns true if
+	// the given statement should be removed due to AST optimization.
+	bool ShouldOmitStmt(const StmtPtr& s) const	{ return false; }
+
+	// A stub for now, ultimately provides a replacement for the
+	// given statement due to AST optimization, or nil if there's
+	// no replacement.
+	StmtPtr ReplacementStmt(const StmtPtr& s) const	{ return nullptr; }
+
+	// NOT YET IMPLEMENTED, SO CURRENTLY A STUB:
+	// Given the LHS and RHS of an assignment, returns true
+	// if the RHS is a common subexpression (meaning that the
+	// current assignment statement should be deleted).  In
+	// that case, has the side effect of associating an alias
+	// for the LHS with the temporary holding the equivalent RHS.
+	//
+	// Assumes reduction (including alias propagation) has
+	// already been applied.
+	bool IsCSE(const AssignExpr* a, const NameExpr* lhs, const Expr* rhs)
+		{ return false; }
+
+	// Given an lhs=rhs statement followed by succ_stmt, returns
+	// a (new) merge of the two if they're of the form tmp=rhs, var=tmp;
+	// otherwise, nil.
+	Stmt* MergeStmts(const NameExpr* lhs, ExprPtr rhs, Stmt* succ_stmt);
+
+	// The following two methods will, in the future, update expressions
+	// with optimized versions.  They are distinct because the first
+	// one (meant for calls in a Stmt reduction context) will also Reduce
+	// the expression, whereas the second one (meant for calls in an Expr
+	// context) does not, to avoid circularity.
+	//
+	// For now, they are stubs.
+	//
+	// These two are used for use in optimizing expressions that appear in
+	// a Stmt context.
+	ExprPtr OptExpr(Expr* e)	{ return {NewRef{}, e}; }
+	ExprPtr OptExpr(ExprPtr e)	{ return e; }
+	// This one for expressions appearing in an Expr context.
+	ExprPtr UpdateExpr(ExprPtr e)	{ return e; }
+
+	const Scope* FuncScope() const	{ return scope; }
+
+protected:
+	bool SameVal(const Val* v1, const Val* v2) const;
+
+	IDPtr GenTemporary(const TypePtr& t, ExprPtr rhs);
+	TempVar* FindTemporary(const ID* id) const;
+
+	// Retrieve the identifier corresponding to the new local for
+	// the given expression.  Creates the local if necessary.
+	IDPtr FindNewLocal(ID* id);
+	IDPtr FindNewLocal(const NameExpr* n)
+		{ return FindNewLocal(n->Id()); }
+
+	// Generate a new local to use in lieu of the original (seen
+	// in an inlined block).  The difference is that the new
+	// version has a distinct name and has a correct frame offset
+	// for the current function.
+	IDPtr GenLocal(ID* orig);
+
+	// Track that we're replacing instances of "orig" with a new
+	// expression.  This allows us to locate the RDs associated
+	// with "orig" in the context of the new expression, without
+	// requiring an additional RD propagation pass.
+	void TrackExprReplacement(const Expr* orig, const Expr* e);
+
+	Scope* scope;
+	PList<TempVar> temps;
+
+	// Temps for which we've processed their associated expression
+	// (and they didn't wind up being aliases).
+	PList<TempVar> expr_temps;
+
+	// Let's us go from an identifier to an associated temporary
+	// variable, if it corresponds to one.
+	std::unordered_map<const ID*, TempVar*> ids_to_temps;
+
+	std::unordered_set<ID*> new_locals;
+	std::unordered_map<const ID*, IDPtr> orig_to_new_locals;
+
+	// Tracks whether we're inside an inline block, and if so then
+	// how deeply.
+	int inline_block_level = 0;
+
+	// Tracks how deeply we are in "bifurcation", i.e., duplicating
+	// code for if-else cascades.  We need to cap this at a certain
+	// depth or else we can get functions whose size blows up
+	// exponentially.
+	int bifurcation_level = 0;
+
+	// For a new expression we've created, map it to the expression
+	// it's replacing.  This allows us to locate the RDs associated
+	// with the usage.
+	std::unordered_map<const Expr*, const Expr*> new_expr_to_orig;
+};
+
+// Used for debugging, to communicate which expression wasn't
+// reduced when we expected them all to be.
+extern const Expr* non_reduced_perp;
+extern bool checking_reduction;
+
+// Used to report a non-reduced expression.
+extern bool NonReduced(const Expr* perp);
+
+} // zeek::detail

src/script_opt/TempVar.cc

@@ -1,7 +1,7 @@
 // See the file "COPYING" in the main distribution directory for copyright.
 
-#include "TempVar.h"
+#include "zeek/script_opt/TempVar.h"
-#include "Reporter.h"
+#include "zeek/Reporter.h"
 
 
 namespace zeek::detail {

src/script_opt/TempVar.h

@@ -5,8 +5,8 @@
 // Class for managing temporary variables created during statement reduction
 // for compilation.
 
-#include "ID.h"
+#include "zeek/ID.h"
-#include "Expr.h"
+#include "zeek/Expr.h"
 
 
 namespace zeek::detail {