1 files changed, 133 insertions, 0 deletions
diff --git a/manual/CHAPTER_Prog/stubnets.cc b/manual/CHAPTER_Prog/stubnets.cc
new file mode 100644
index 000000000..1c71f78b8
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+++ b/manual/CHAPTER_Prog/stubnets.cc
@@ -0,0 +1,133 @@
+// This is free and unencumbered software released into the public domain.
+// 
+// Anyone is free to copy, modify, publish, use, compile, sell, or
+// distribute this software, either in source code form or as a compiled
+// binary, for any purpose, commercial or non-commercial, and by any
+// means.
+
+#include "kernel/rtlil.h"
+#include "kernel/register.h"
+#include "kernel/sigtools.h"
+#include "kernel/log.h"
+
+#include <string>
+#include <map>
+#include <set>
+
+// this function is called for each module in the design
+static void find_stub_nets(RTLIL::Design *design, RTLIL::Module *module, bool report_bits)
+{
+	// use a SigMap to convert nets to a unique representation
+	SigMap sigmap(module);
+
+	// count how many times a single-bit signal is used
+	std::map<RTLIL::SigSpec, int> bit_usage_count;
+
+	// count ouput lines for this module (needed only for summary output at the end)
+	int line_count = 0;
+
+	log("Looking for stub wires in module %s:\n", RTLIL::id2cstr(module->name));
+
+	// For all ports on all cells
+	for (auto &cell_iter : module->cells)
+	for (auto &conn : cell_iter.second->connections)
+	{
+		// Get the signals on the port
+		// (use sigmap to get a uniqe signal name)
+		RTLIL::SigSpec sig = sigmap(conn.second);
+
+		// split the signal up into single-bit chunks
+		sig.expand();
+
+		// add each chunk to bit_usage_count, unless it is a constant
+		for (auto &c : sig.chunks)
+			if (c.wire != NULL)
+				bit_usage_count[c]++;
+	}
+
+	// for each wire in the module
+	for (auto &wire_iter : module->wires)
+	{
+		RTLIL::Wire *wire = wire_iter.second;
+
+		// .. but only selected wires
+		if (!design->selected(module, wire))
+			continue;
+
+		// add +1 usage if this wire actually is a port
+		int usage_offset = wire->port_id > 0 ? 1 : 0;
+
+		// we will record which bits of the (possibly multi-bit) wire are stub signals
+		std::set<int> stub_bits;
+
+		// get a signal description for this wire and split it into seperate bits
+		RTLIL::SigSpec sig = sigmap(wire);
+		sig.expand();
+
+		// for each bit (unless it is a constant):
+		// check if it is used at least two times and add to stub_bits otherwise
+		for (size_t i = 0; i < sig.chunks.size(); i++)
+			if (sig.chunks[i].wire != NULL && (bit_usage_count[sig.chunks[i]] +
+					usage_offset) < 2)
+				stub_bits.insert(i);
+
+		// continue if no stub bits found
+		if (stub_bits.size() == 0)
+			continue;
+
+		// report stub bits and/or stub wires, don't report single bits
+		// if called with report_bits set to false.
+		if (int(stub_bits.size()) == sig.width) {
+			log("  found stub wire: %s\n", RTLIL::id2cstr(wire->name));
+		} else {
+			if (!report_bits)
+				continue;
+			log("  found wire with stub bits: %s [", RTLIL::id2cstr(wire->name));
+			for (int bit : stub_bits)
+				log("%s%d", bit == *stub_bits.begin() ? "" : ", ", bit);
+			log("]\n");
+		}
+
+		// we have outputted a line, increment summary counter
+		line_count++;
+	}
+
+	// report summary
+	if (report_bits)
+		log("  found %d stub wires or wires with stub bits.\n", line_count);
+	else
+		log("  found %d stub wires.\n", line_count);
+}
+
+// each pass contains a singleton object that is derived from Pass
+struct StubnetsPass : public Pass {
+	StubnetsPass() : Pass("stubnets") { }
+	virtual void execute(std::vector<std::string> args, RTLIL::Design *design)
+	{
+		// variables to mirror information from passed options
+		bool report_bits = 0;
+
+		log_header("Executing STUBNETS pass (find stub nets).\n");
+
+		// parse options
+		size_t argidx;
+		for (argidx = 1; argidx < args.size(); argidx++) {
+			std::string arg = args[argidx];
+			if (arg == "-report_bits") {
+				report_bits = true;
+				continue;
+			}
+			break;
+		}
+
+		// handle extra options (e.g. selection)
+		extra_args(args, argidx, design);
+
+		// call find_stub_nets() for each module that is either
+		// selected as a whole or contains selected objects.
+		for (auto &it : design->modules)
+			if (design->selected_module(it.first))
+				find_stub_nets(design, it.second, report_bits);
+	}
+} StubnetsPass;
+