diff --git a/vlib/strings/builder.v b/vlib/strings/builder.v
index 610c933515..a70d30bb53 100644
--- a/vlib/strings/builder.v
+++ b/vlib/strings/builder.v
@@ -32,6 +32,7 @@ pub fn (mut b Builder) write_b(data byte) {
 	b.len++
 }
 
+[inline]
 pub fn (mut b Builder) write(s string) {
 	if s == '' {
 		return
@@ -77,6 +78,7 @@ pub fn (mut b Builder) go_back_to(pos int) {
 	b.len = pos
 }
 
+[inline]
 pub fn (mut b Builder) writeln(s string) {
 	// for c in s {
 	// b.buf << c
diff --git a/vlib/v/gen/cgen.v b/vlib/v/gen/cgen.v
index ae4a8d74fc..07ce6b467c 100644
--- a/vlib/v/gen/cgen.v
+++ b/vlib/v/gen/cgen.v
@@ -3599,9 +3599,8 @@ fn (mut g Gen) write_expr_to_string(expr ast.Expr) string {
 	return g.out.cut_last(g.out.buf.len - pos)
 }
 
-fn (mut g Gen) start_tmp() {
-}
-
+// fn (mut g Gen) start_tmp() {
+// }
 // If user is accessing the return value eg. in assigment, pass the variable name.
 // If the user is not using the optional return value. We need to pass a temp var
 // to access its fields (`.ok`, `.error` etc)
diff --git a/vlib/v/gen/fn.v b/vlib/v/gen/fn.v
index f2b83d0810..a4bf180a30 100644
--- a/vlib/v/gen/fn.v
+++ b/vlib/v/gen/fn.v
@@ -28,7 +28,7 @@ fn (mut g Gen) gen_fn_decl(it ast.FnDecl) {
 		g.cur_generic_type = 0
 		return
 	}
-	//g.cur_fn = it
+	// g.cur_fn = it
 	fn_start_pos := g.out.len
 	msvc_attrs := g.write_fn_attrs()
 	// Live
@@ -270,7 +270,13 @@ fn (mut g Gen) call_expr(node ast.CallExpr) {
 		g.write('$styp $tmp_opt = ')
 	}
 	if node.is_method {
-		g.method_call(node)
+		if node.name == 'writeln' && g.pref.show_cc &&
+			node.args.len > 0 && node.args[0].expr is ast.StringInterLiteral &&
+			g.table.get_type_symbol(node.receiver_type).name == 'strings.Builder' {
+			g.string_inter_literal_sb_optimized(node)
+		} else {
+			g.method_call(node)
+		}
 	} else {
 		g.fn_call(node)
 	}
diff --git a/vlib/v/gen/str.v b/vlib/v/gen/str.v
index e49bcf7f82..93b81906b9 100644
--- a/vlib/v/gen/str.v
+++ b/vlib/v/gen/str.v
@@ -138,13 +138,61 @@ fn (mut g Gen) string_literal(node ast.StringLiteral) {
 	}
 }
 
+// optimize string interpolation in string builders:
+// `sb.writeln('a=$a')` =>
+// `sb.writeln('a='); sb.writeln(a.str())`
+fn (mut g Gen) string_inter_literal_sb_optimized(call_expr ast.CallExpr) {
+	node := call_expr.args[0].expr as ast.StringInterLiteral
+	// sb_name := g.cur_call_expr.left
+	// g.go_before_stmt(0)
+	g.writeln('// sb inter opt')
+	write := 'writeln'
+	/*
+	if node.vals.len != node.exprs.len {
+		println('NOPE')
+		println(node.vals)
+		println('==========')
+		println(node.exprs)
+	}
+	*/
+	for i, val in node.vals {
+		escaped_val := val.replace_each(['"', '\\"', '\r\n', '\\n', '\n', '\\n', '%', '%%'])
+		// if val == '' {
+		// break
+		// continue
+		// }
+		g.write('strings__Builder_${write}(&')
+		g.expr(call_expr.left)
+		g.write(', tos_lit("')
+		g.write(escaped_val)
+		g.writeln('"));')
+		//
+		if i >= node.exprs.len {
+			break
+		}
+		// if node.expr_types.len <= i || node.exprs.len <= i {
+		// continue
+		// }
+		g.write('strings__Builder_${write}(&')
+		g.expr(call_expr.left)
+		g.write(', ')
+		g.write(g.typ(node.expr_types[i]))
+		g.write('_str(')
+		g.expr(node.exprs[i])
+		g.writeln('));')
+	}
+	g.writeln('')
+	// println(node.vals)
+	return
+}
+
 fn (mut g Gen) string_inter_literal(node ast.StringInterLiteral) {
 	mut cur_line := ''
 	mut tmp := ''
 	free := g.pref.autofree && g.inside_call && !g.inside_return &&
-		g.inside_ternary == 0 && !g.inside_const 
-		//&& g.cur_fn != 0 &&
-		//g.cur_fn.name != ''
+		g.inside_ternary == 0 && !g.inside_const
+	// && g.cur_fn != 0 &&
+	// g.cur_fn.name != ''
 	if free {
 		// Save the string expr in a temporary variable, so that it can be removed after the call.
 		tmp = g.new_tmp_var()