Build a temporary SigChunk list in the iterator in the cases where that's needed

backends/rtlil/rtlil_backend.cc

@@ -121,7 +121,8 @@ void RTLIL_BACKEND::dump_sigspec(std::ostream &f, const RTLIL::SigSpec &sig, boo
 		dump_sigchunk(f, sig.as_chunk(), autoint);
 	} else {
 		f << stringf("{ ");
-		for (const auto& chunk : reversed(sig.chunks())) {
+		auto chunks = sig.chunks();
+		for (const auto& chunk : reversed(chunks)) {
 			dump_sigchunk(f, chunk, false);
 			f << stringf(" ");
 		}

backends/verilog/verilog_backend.cc

@@ -382,8 +382,9 @@ void dump_sigspec(std::ostream &f, const RTLIL::SigSpec &sig)
 		dump_sigchunk(f, sig.as_chunk());
 	} else {
 		f << stringf("{ ");
-		for (auto it = sig.chunks().rbegin(); it != sig.chunks().rend(); ++it) {
-			if (it != sig.chunks().rbegin())
+		auto chunks = sig.chunks();
+		for (auto it = chunks.rbegin(); it != chunks.rend(); ++it) {
+			if (it != chunks.rbegin())
 				f << stringf(", ");
 			dump_sigchunk(f, *it, true);
 		}

kernel/rtlil.h

@@ -1276,8 +1276,7 @@ public:
 	SigSpec &operator=(SigSpec &&rhs) = default;
 
 	struct Chunks {
-		const SigSpec &spec;
-
+		Chunks(const SigSpec &spec) : spec(spec) {}
 		struct const_iterator {
 			using iterator_category = std::forward_iterator_tag;
 			using value_type = const SigChunk &;
@@ -1320,26 +1319,43 @@ public:
 			it.bit_index = spec.size();
 			return it;
 		}
-		std::vector<RTLIL::SigChunk>::const_reverse_iterator rbegin() const {
-			spec.pack();
-			return spec.chunks_.rbegin();
+		// Later we should deprecate these and remove their in-tree calls,
+		// so we can eventually remove chunk_vector.
+		std::vector<RTLIL::SigChunk>::const_reverse_iterator rbegin() {
+			ensure_chunk_vector();
+			return chunk_vector.rbegin();
 		}
-		std::vector<RTLIL::SigChunk>::const_reverse_iterator rend() const {
-			spec.pack();
-			return spec.chunks_.rend();
+		std::vector<RTLIL::SigChunk>::const_reverse_iterator rend() {
+			ensure_chunk_vector();
+			return chunk_vector.rend();
+		}
+		int size() {
+			ensure_chunk_vector();
+			return chunk_vector.size();
 		}
 		int size() const {
-			spec.pack();
-			return spec.chunks_.size();
+			int result = 0;
+			for (const SigChunk &_: *this)
+				++result;
+			return result;
 		}
-		const SigChunk &at(int index) const {
-			spec.pack();
-			return spec.chunks_.at(index);
+		const SigChunk &at(int index) {
+			ensure_chunk_vector();
+			return chunk_vector.at(index);
 		}
-		operator const std::vector<RTLIL::SigChunk>&() const {
-			spec.pack();
-			return spec.chunks_;
+		operator const std::vector<RTLIL::SigChunk>&() {
+			ensure_chunk_vector();
+			return chunk_vector;
 		}
+	private:
+		void ensure_chunk_vector() {
+			if (spec.size() > 0 && chunk_vector.empty()) {
+				for (const RTLIL::SigChunk &c : *this)
+					chunk_vector.push_back(c);
+			}
+		}
+		const SigSpec &spec;
+		std::vector<RTLIL::SigChunk> chunk_vector;
 	};
 	friend struct Chunks::const_iterator;
 

kernel/utils.h

@@ -277,14 +277,26 @@ inline int ceil_log2(int x)
 #endif
 }
 
+template <typename T>
+auto reversed(T& container) {
+	struct reverse_view {
+		reverse_view(T& container) : container(container) {}
+		auto begin() const { return container.rbegin(); }
+		auto end() const { return container.rend(); }
+		T& container;
+	};
+	return reverse_view{container};
+}
+
 template <typename T>
 auto reversed(const T& container) {
-    struct reverse_view {
-        const T& cont;
-        auto begin() const { return cont.rbegin(); }
-        auto end() const { return cont.rend(); }
-    };
-    return reverse_view{container};
+	struct reverse_view {
+		reverse_view(const T& container) : container(container) {}
+		auto begin() const { return container.rbegin(); }
+		auto end() const { return container.rend(); }
+		const T& container;
+	};
+	return reverse_view{container};
 }
 
 YOSYS_NAMESPACE_END