From d905990d0194decb9f673ccf10aa488820816b87 Mon Sep 17 00:00:00 2001
From: =?utf8?q?Marcelina=20Ko=C5=9Bcielnicka?= <mwk@0x04.net>
Date: Sun, 23 May 2021 15:42:51 +0200
Subject: [PATCH] memory_share: Split off feedback path finding as a separate
 pass.

memory_share is actually three passes in a trenchcoat.  Split off the
one that has the least in common with the other two as a separate pass.
---
 passes/memory/memory.cc        |   4 +-
 passes/memory/memory_share.cc  | 247 +-----------------------
 passes/opt/Makefile.inc        |   1 +
 passes/opt/opt_mem_feedback.cc | 333 +++++++++++++++++++++++++++++++++
 4 files changed, 343 insertions(+), 242 deletions(-)
 create mode 100644 passes/opt/opt_mem_feedback.cc

diff --git a/passes/memory/memory.cc b/passes/memory/memory.cc
index 9dec05db8..57e436943 100644
--- a/passes/memory/memory.cc
+++ b/passes/memory/memory.cc
@@ -38,9 +38,10 @@ struct MemoryPass : public Pass {
 		log("    opt_mem\n");
 		log("    memory_dff                          (skipped if called with -nordff or -memx)\n");
 		log("    opt_clean\n");
+		log("    opt_mem_feedback\n");
 		log("    memory_share\n");
-		log("    opt_clean\n");
 		log("    memory_memx                         (when called with -memx)\n");
+		log("    opt_clean\n");
 		log("    memory_collect\n");
 		log("    memory_bram -rules <bram_rules>     (when called with -bram)\n");
 		log("    memory_map                          (skipped if called with -nomap)\n");
@@ -86,6 +87,7 @@ struct MemoryPass : public Pass {
 		if (!flag_nordff)
 			Pass::call(design, "memory_dff");
 		Pass::call(design, "opt_clean");
+		Pass::call(design, "opt_mem_feedback");
 		Pass::call(design, "memory_share");
 		if (flag_memx)
 			Pass::call(design, "memory_memx");
diff --git a/passes/memory/memory_share.cc b/passes/memory/memory_share.cc
index 7315aeae1..22227bf2b 100644
--- a/passes/memory/memory_share.cc
+++ b/passes/memory/memory_share.cc
@@ -25,12 +25,8 @@
 USING_YOSYS_NAMESPACE
 PRIVATE_NAMESPACE_BEGIN
 
-bool memcells_cmp(RTLIL::Cell *a, RTLIL::Cell *b)
+bool memwr_cmp(RTLIL::Cell *a, RTLIL::Cell *b)
 {
-	if (a->type == ID($memrd) && b->type == ID($memrd))
-		return a->name < b->name;
-	if (a->type == ID($memrd) || b->type == ID($memrd))
-		return (a->type == ID($memrd)) < (b->type == ID($memrd));
 	return a->parameters.at(ID::PRIORITY).as_int() < b->parameters.at(ID::PRIORITY).as_int();
 }
 
@@ -42,219 +38,6 @@ struct MemoryShareWorker
 	ModWalker modwalker;
 	CellTypes cone_ct;
 
-	std::map<RTLIL::SigBit, std::pair<RTLIL::Cell*, int>> sig_to_mux;
-	std::map<pair<std::set<std::map<SigBit, bool>>, SigBit>, SigBit> conditions_logic_cache;
-
-
-	// -----------------------------------------------------------------
-	// Converting feedbacks to async read ports to proper enable signals
-	// -----------------------------------------------------------------
-
-	bool find_data_feedback(const std::set<RTLIL::SigBit> &async_rd_bits, RTLIL::SigBit sig,
-			std::map<RTLIL::SigBit, bool> &state, std::set<std::map<RTLIL::SigBit, bool>> &conditions)
-	{
-		if (async_rd_bits.count(sig)) {
-			conditions.insert(state);
-			return true;
-		}
-
-		if (sig_to_mux.count(sig) == 0)
-			return false;
-
-		RTLIL::Cell *cell = sig_to_mux.at(sig).first;
-		int bit_idx = sig_to_mux.at(sig).second;
-
-		std::vector<RTLIL::SigBit> sig_a = sigmap(cell->getPort(ID::A));
-		std::vector<RTLIL::SigBit> sig_b = sigmap(cell->getPort(ID::B));
-		std::vector<RTLIL::SigBit> sig_s = sigmap(cell->getPort(ID::S));
-		std::vector<RTLIL::SigBit> sig_y = sigmap(cell->getPort(ID::Y));
-		log_assert(sig_y.at(bit_idx) == sig);
-
-		for (int i = 0; i < int(sig_s.size()); i++)
-			if (state.count(sig_s[i]) && state.at(sig_s[i]) == true) {
-				if (find_data_feedback(async_rd_bits, sig_b.at(bit_idx + i*sig_y.size()), state, conditions)) {
-					RTLIL::SigSpec new_b = cell->getPort(ID::B);
-					new_b.replace(bit_idx + i*sig_y.size(), RTLIL::State::Sx);
-					cell->setPort(ID::B, new_b);
-				}
-				return false;
-			}
-
-
-		for (int i = 0; i < int(sig_s.size()); i++)
-		{
-			if (state.count(sig_s[i]) && state.at(sig_s[i]) == false)
-				continue;
-
-			std::map<RTLIL::SigBit, bool> new_state = state;
-			new_state[sig_s[i]] = true;
-
-			if (find_data_feedback(async_rd_bits, sig_b.at(bit_idx + i*sig_y.size()), new_state, conditions)) {
-				RTLIL::SigSpec new_b = cell->getPort(ID::B);
-				new_b.replace(bit_idx + i*sig_y.size(), RTLIL::State::Sx);
-				cell->setPort(ID::B, new_b);
-			}
-		}
-
-		std::map<RTLIL::SigBit, bool> new_state = state;
-		for (int i = 0; i < int(sig_s.size()); i++)
-			new_state[sig_s[i]] = false;
-
-		if (find_data_feedback(async_rd_bits, sig_a.at(bit_idx), new_state, conditions)) {
-			RTLIL::SigSpec new_a = cell->getPort(ID::A);
-			new_a.replace(bit_idx, RTLIL::State::Sx);
-			cell->setPort(ID::A, new_a);
-		}
-
-		return false;
-	}
-
-	RTLIL::SigBit conditions_to_logic(std::set<std::map<RTLIL::SigBit, bool>> &conditions, SigBit olden, int &created_conditions)
-	{
-		auto key = make_pair(conditions, olden);
-
-		if (conditions_logic_cache.count(key))
-			return conditions_logic_cache.at(key);
-
-		RTLIL::SigSpec terms;
-		for (auto &cond : conditions) {
-			RTLIL::SigSpec sig1, sig2;
-			for (auto &it : cond) {
-				sig1.append(it.first);
-				sig2.append(it.second ? RTLIL::State::S1 : RTLIL::State::S0);
-			}
-			terms.append(module->Ne(NEW_ID, sig1, sig2));
-			created_conditions++;
-		}
-
-		if (olden.wire != nullptr || olden != State::S1)
-			terms.append(olden);
-
-		if (GetSize(terms) == 0)
-			terms = State::S1;
-
-		if (GetSize(terms) > 1)
-			terms = module->ReduceAnd(NEW_ID, terms);
-
-		return conditions_logic_cache[key] = terms;
-	}
-
-	void translate_rd_feedback_to_en(std::string memid, std::vector<RTLIL::Cell*> &rd_ports, std::vector<RTLIL::Cell*> &wr_ports)
-	{
-		std::map<RTLIL::SigSpec, std::vector<std::set<RTLIL::SigBit>>> async_rd_bits;
-		std::map<RTLIL::SigBit, std::set<RTLIL::SigBit>> muxtree_upstream_map;
-		std::set<RTLIL::SigBit> non_feedback_nets;
-
-		for (auto wire : module->wires())
-			if (wire->port_output) {
-				std::vector<RTLIL::SigBit> bits = sigmap(wire);
-				non_feedback_nets.insert(bits.begin(), bits.end());
-			}
-
-		for (auto cell : module->cells())
-		{
-			bool ignore_data_port = false;
-
-			if (cell->type.in(ID($mux), ID($pmux)))
-			{
-				std::vector<RTLIL::SigBit> sig_a = sigmap(cell->getPort(ID::A));
-				std::vector<RTLIL::SigBit> sig_b = sigmap(cell->getPort(ID::B));
-				std::vector<RTLIL::SigBit> sig_s = sigmap(cell->getPort(ID::S));
-				std::vector<RTLIL::SigBit> sig_y = sigmap(cell->getPort(ID::Y));
-
-				non_feedback_nets.insert(sig_s.begin(), sig_s.end());
-
-				for (int i = 0; i < int(sig_y.size()); i++) {
-					muxtree_upstream_map[sig_y[i]].insert(sig_a[i]);
-					for (int j = 0; j < int(sig_s.size()); j++)
-						muxtree_upstream_map[sig_y[i]].insert(sig_b[i + j*sig_y.size()]);
-				}
-
-				continue;
-			}
-
-			if (cell->type.in(ID($memwr), ID($memrd)) &&
-					cell->parameters.at(ID::MEMID).decode_string() == memid)
-				ignore_data_port = true;
-
-			for (auto conn : cell->connections())
-			{
-				if (ignore_data_port && conn.first == ID::DATA)
-					continue;
-				std::vector<RTLIL::SigBit> bits = sigmap(conn.second);
-				non_feedback_nets.insert(bits.begin(), bits.end());
-			}
-		}
-
-		std::set<RTLIL::SigBit> expand_non_feedback_nets = non_feedback_nets;
-		while (!expand_non_feedback_nets.empty())
-		{
-			std::set<RTLIL::SigBit> new_expand_non_feedback_nets;
-
-			for (auto &bit : expand_non_feedback_nets)
-				if (muxtree_upstream_map.count(bit))
-					for (auto &new_bit : muxtree_upstream_map.at(bit))
-						if (!non_feedback_nets.count(new_bit)) {
-							non_feedback_nets.insert(new_bit);
-							new_expand_non_feedback_nets.insert(new_bit);
-						}
-
-			expand_non_feedback_nets.swap(new_expand_non_feedback_nets);
-		}
-
-		for (auto cell : rd_ports)
-		{
-			if (cell->parameters.at(ID::CLK_ENABLE).as_bool())
-				continue;
-
-			RTLIL::SigSpec sig_addr = sigmap(cell->getPort(ID::ADDR));
-			std::vector<RTLIL::SigBit> sig_data = sigmap(cell->getPort(ID::DATA));
-
-			for (int i = 0; i < int(sig_data.size()); i++)
-				if (non_feedback_nets.count(sig_data[i]))
-					goto not_pure_feedback_port;
-
-			async_rd_bits[sig_addr].resize(max(async_rd_bits.size(), sig_data.size()));
-			for (int i = 0; i < int(sig_data.size()); i++)
-				async_rd_bits[sig_addr][i].insert(sig_data[i]);
-
-		not_pure_feedback_port:;
-		}
-
-		if (async_rd_bits.empty())
-			return;
-
-		log("Populating enable bits on write ports of memory %s.%s with aync read feedback:\n", log_id(module), log_id(memid));
-
-		for (auto cell : wr_ports)
-		{
-			RTLIL::SigSpec sig_addr = sigmap_xmux(cell->getPort(ID::ADDR));
-			if (!async_rd_bits.count(sig_addr))
-				continue;
-
-			log("  Analyzing write port %s.\n", log_id(cell));
-
-			std::vector<RTLIL::SigBit> cell_data = cell->getPort(ID::DATA);
-			std::vector<RTLIL::SigBit> cell_en = cell->getPort(ID::EN);
-
-			int created_conditions = 0;
-			for (int i = 0; i < int(cell_data.size()); i++)
-				if (cell_en[i] != RTLIL::SigBit(RTLIL::State::S0))
-				{
-					std::map<RTLIL::SigBit, bool> state;
-					std::set<std::map<RTLIL::SigBit, bool>> conditions;
-
-					find_data_feedback(async_rd_bits.at(sig_addr).at(i), cell_data[i], state, conditions);
-					cell_en[i] = conditions_to_logic(conditions, cell_en[i], created_conditions);
-				}
-
-			if (created_conditions) {
-				log("    Added enable logic for %d different cases.\n", created_conditions);
-				cell->setPort(ID::EN, cell_en);
-			}
-		}
-	}
-
 
 	// ------------------------------------------------------
 	// Consolidate write ports that write to the same address
@@ -669,21 +452,16 @@ struct MemoryShareWorker
 
 	void operator()(RTLIL::Module* module)
 	{
-		std::map<std::string, std::pair<std::vector<RTLIL::Cell*>, std::vector<RTLIL::Cell*>>> memindex;
+		std::map<std::string, std::vector<RTLIL::Cell*>> memindex;
 
 		this->module = module;
 		sigmap.set(module);
-		sig_to_mux.clear();
-		conditions_logic_cache.clear();
 
 		sigmap_xmux = sigmap;
 		for (auto cell : module->cells())
 		{
-			if (cell->type == ID($memrd))
-				memindex[cell->parameters.at(ID::MEMID).decode_string()].first.push_back(cell);
-
 			if (cell->type == ID($memwr))
-				memindex[cell->parameters.at(ID::MEMID).decode_string()].second.push_back(cell);
+				memindex[cell->parameters.at(ID::MEMID).decode_string()].push_back(cell);
 
 			if (cell->type == ID($mux))
 			{
@@ -695,20 +473,11 @@ struct MemoryShareWorker
 				else if (sig_b.is_fully_undef())
 					sigmap_xmux.add(cell->getPort(ID::Y), sig_a);
 			}
-
-			if (cell->type.in(ID($mux), ID($pmux)))
-			{
-				std::vector<RTLIL::SigBit> sig_y = sigmap(cell->getPort(ID::Y));
-				for (int i = 0; i < int(sig_y.size()); i++)
-					sig_to_mux[sig_y[i]] = std::pair<RTLIL::Cell*, int>(cell, i);
-			}
 		}
 
 		for (auto &it : memindex) {
-			std::sort(it.second.first.begin(), it.second.first.end(), memcells_cmp);
-			std::sort(it.second.second.begin(), it.second.second.end(), memcells_cmp);
-			translate_rd_feedback_to_en(it.first, it.second.first, it.second.second);
-			consolidate_wr_by_addr(it.first, it.second.second);
+			std::sort(it.second.begin(), it.second.end(), memwr_cmp);
+			consolidate_wr_by_addr(it.first, it.second);
 		}
 
 		cone_ct.setup_internals();
@@ -728,7 +497,7 @@ struct MemoryShareWorker
 		modwalker.setup(module, &cone_ct);
 
 		for (auto &it : memindex)
-			consolidate_wr_using_sat(it.first, it.second.second);
+			consolidate_wr_using_sat(it.first, it.second);
 	}
 };
 
@@ -744,10 +513,6 @@ struct MemorySharePass : public Pass {
 		log("\n");
 		log("The following methods are used to consolidate the number of memory ports:\n");
 		log("\n");
-		log("  - When write ports are connected to async read ports accessing the same\n");
-		log("    address, then this feedback path is converted to a write port with\n");
-		log("    byte/part enable signals.\n");
-		log("\n");
 		log("  - When multiple write ports access the same address then this is converted\n");
 		log("    to a single write port with a more complex data and/or enable logic path.\n");
 		log("\n");
diff --git a/passes/opt/Makefile.inc b/passes/opt/Makefile.inc
index 4ae9b8895..b0192235b 100644
--- a/passes/opt/Makefile.inc
+++ b/passes/opt/Makefile.inc
@@ -2,6 +2,7 @@
 OBJS += passes/opt/opt.o
 OBJS += passes/opt/opt_merge.o
 OBJS += passes/opt/opt_mem.o
+OBJS += passes/opt/opt_mem_feedback.o
 OBJS += passes/opt/opt_muxtree.o
 OBJS += passes/opt/opt_reduce.o
 OBJS += passes/opt/opt_dff.o
diff --git a/passes/opt/opt_mem_feedback.cc b/passes/opt/opt_mem_feedback.cc
new file mode 100644
index 000000000..75e244514
--- /dev/null
+++ b/passes/opt/opt_mem_feedback.cc
@@ -0,0 +1,333 @@
+/*
+ *  yosys -- Yosys Open SYnthesis Suite
+ *
+ *  Copyright (C) 2012  Clifford Wolf <clifford@clifford.at>
+ *
+ *  Permission to use, copy, modify, and/or distribute this software for any
+ *  purpose with or without fee is hereby granted, provided that the above
+ *  copyright notice and this permission notice appear in all copies.
+ *
+ *  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ *  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ *  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ *  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ *  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ *  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ *  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ *
+ */
+
+#include "kernel/yosys.h"
+#include "kernel/satgen.h"
+#include "kernel/sigtools.h"
+#include "kernel/modtools.h"
+
+USING_YOSYS_NAMESPACE
+PRIVATE_NAMESPACE_BEGIN
+
+bool memrd_cmp(RTLIL::Cell *a, RTLIL::Cell *b)
+{
+	return a->name < b->name;
+}
+
+bool memwr_cmp(RTLIL::Cell *a, RTLIL::Cell *b)
+{
+	return a->parameters.at(ID::PRIORITY).as_int() < b->parameters.at(ID::PRIORITY).as_int();
+}
+
+struct OptMemFeedbackWorker
+{
+	RTLIL::Design *design;
+	RTLIL::Module *module;
+	SigMap sigmap, sigmap_xmux;
+
+	std::map<RTLIL::SigBit, std::pair<RTLIL::Cell*, int>> sig_to_mux;
+	std::map<pair<std::set<std::map<SigBit, bool>>, SigBit>, SigBit> conditions_logic_cache;
+
+
+	// -----------------------------------------------------------------
+	// Converting feedbacks to async read ports to proper enable signals
+	// -----------------------------------------------------------------
+
+	bool find_data_feedback(const std::set<RTLIL::SigBit> &async_rd_bits, RTLIL::SigBit sig,
+			std::map<RTLIL::SigBit, bool> &state, std::set<std::map<RTLIL::SigBit, bool>> &conditions)
+	{
+		if (async_rd_bits.count(sig)) {
+			conditions.insert(state);
+			return true;
+		}
+
+		if (sig_to_mux.count(sig) == 0)
+			return false;
+
+		RTLIL::Cell *cell = sig_to_mux.at(sig).first;
+		int bit_idx = sig_to_mux.at(sig).second;
+
+		std::vector<RTLIL::SigBit> sig_a = sigmap(cell->getPort(ID::A));
+		std::vector<RTLIL::SigBit> sig_b = sigmap(cell->getPort(ID::B));
+		std::vector<RTLIL::SigBit> sig_s = sigmap(cell->getPort(ID::S));
+		std::vector<RTLIL::SigBit> sig_y = sigmap(cell->getPort(ID::Y));
+		log_assert(sig_y.at(bit_idx) == sig);
+
+		for (int i = 0; i < int(sig_s.size()); i++)
+			if (state.count(sig_s[i]) && state.at(sig_s[i]) == true) {
+				if (find_data_feedback(async_rd_bits, sig_b.at(bit_idx + i*sig_y.size()), state, conditions)) {
+					RTLIL::SigSpec new_b = cell->getPort(ID::B);
+					new_b.replace(bit_idx + i*sig_y.size(), RTLIL::State::Sx);
+					cell->setPort(ID::B, new_b);
+				}
+				return false;
+			}
+
+
+		for (int i = 0; i < int(sig_s.size()); i++)
+		{
+			if (state.count(sig_s[i]) && state.at(sig_s[i]) == false)
+				continue;
+
+			std::map<RTLIL::SigBit, bool> new_state = state;
+			new_state[sig_s[i]] = true;
+
+			if (find_data_feedback(async_rd_bits, sig_b.at(bit_idx + i*sig_y.size()), new_state, conditions)) {
+				RTLIL::SigSpec new_b = cell->getPort(ID::B);
+				new_b.replace(bit_idx + i*sig_y.size(), RTLIL::State::Sx);
+				cell->setPort(ID::B, new_b);
+			}
+		}
+
+		std::map<RTLIL::SigBit, bool> new_state = state;
+		for (int i = 0; i < int(sig_s.size()); i++)
+			new_state[sig_s[i]] = false;
+
+		if (find_data_feedback(async_rd_bits, sig_a.at(bit_idx), new_state, conditions)) {
+			RTLIL::SigSpec new_a = cell->getPort(ID::A);
+			new_a.replace(bit_idx, RTLIL::State::Sx);
+			cell->setPort(ID::A, new_a);
+		}
+
+		return false;
+	}
+
+	RTLIL::SigBit conditions_to_logic(std::set<std::map<RTLIL::SigBit, bool>> &conditions, SigBit olden, int &created_conditions)
+	{
+		auto key = make_pair(conditions, olden);
+
+		if (conditions_logic_cache.count(key))
+			return conditions_logic_cache.at(key);
+
+		RTLIL::SigSpec terms;
+		for (auto &cond : conditions) {
+			RTLIL::SigSpec sig1, sig2;
+			for (auto &it : cond) {
+				sig1.append(it.first);
+				sig2.append(it.second ? RTLIL::State::S1 : RTLIL::State::S0);
+			}
+			terms.append(module->Ne(NEW_ID, sig1, sig2));
+			created_conditions++;
+		}
+
+		if (olden.wire != nullptr || olden != State::S1)
+			terms.append(olden);
+
+		if (GetSize(terms) == 0)
+			terms = State::S1;
+
+		if (GetSize(terms) > 1)
+			terms = module->ReduceAnd(NEW_ID, terms);
+
+		return conditions_logic_cache[key] = terms;
+	}
+
+	void translate_rd_feedback_to_en(std::string memid, std::vector<RTLIL::Cell*> &rd_ports, std::vector<RTLIL::Cell*> &wr_ports)
+	{
+		std::map<RTLIL::SigSpec, std::vector<std::set<RTLIL::SigBit>>> async_rd_bits;
+		std::map<RTLIL::SigBit, std::set<RTLIL::SigBit>> muxtree_upstream_map;
+		std::set<RTLIL::SigBit> non_feedback_nets;
+
+		for (auto wire : module->wires())
+			if (wire->port_output) {
+				std::vector<RTLIL::SigBit> bits = sigmap(wire);
+				non_feedback_nets.insert(bits.begin(), bits.end());
+			}
+
+		for (auto cell : module->cells())
+		{
+			bool ignore_data_port = false;
+
+			if (cell->type.in(ID($mux), ID($pmux)))
+			{
+				std::vector<RTLIL::SigBit> sig_a = sigmap(cell->getPort(ID::A));
+				std::vector<RTLIL::SigBit> sig_b = sigmap(cell->getPort(ID::B));
+				std::vector<RTLIL::SigBit> sig_s = sigmap(cell->getPort(ID::S));
+				std::vector<RTLIL::SigBit> sig_y = sigmap(cell->getPort(ID::Y));
+
+				non_feedback_nets.insert(sig_s.begin(), sig_s.end());
+
+				for (int i = 0; i < int(sig_y.size()); i++) {
+					muxtree_upstream_map[sig_y[i]].insert(sig_a[i]);
+					for (int j = 0; j < int(sig_s.size()); j++)
+						muxtree_upstream_map[sig_y[i]].insert(sig_b[i + j*sig_y.size()]);
+				}
+
+				continue;
+			}
+
+			if (cell->type.in(ID($memwr), ID($memrd)) &&
+					cell->parameters.at(ID::MEMID).decode_string() == memid)
+				ignore_data_port = true;
+
+			for (auto conn : cell->connections())
+			{
+				if (ignore_data_port && conn.first == ID::DATA)
+					continue;
+				std::vector<RTLIL::SigBit> bits = sigmap(conn.second);
+				non_feedback_nets.insert(bits.begin(), bits.end());
+			}
+		}
+
+		std::set<RTLIL::SigBit> expand_non_feedback_nets = non_feedback_nets;
+		while (!expand_non_feedback_nets.empty())
+		{
+			std::set<RTLIL::SigBit> new_expand_non_feedback_nets;
+
+			for (auto &bit : expand_non_feedback_nets)
+				if (muxtree_upstream_map.count(bit))
+					for (auto &new_bit : muxtree_upstream_map.at(bit))
+						if (!non_feedback_nets.count(new_bit)) {
+							non_feedback_nets.insert(new_bit);
+							new_expand_non_feedback_nets.insert(new_bit);
+						}
+
+			expand_non_feedback_nets.swap(new_expand_non_feedback_nets);
+		}
+
+		for (auto cell : rd_ports)
+		{
+			if (cell->parameters.at(ID::CLK_ENABLE).as_bool())
+				continue;
+
+			RTLIL::SigSpec sig_addr = sigmap(cell->getPort(ID::ADDR));
+			std::vector<RTLIL::SigBit> sig_data = sigmap(cell->getPort(ID::DATA));
+
+			for (int i = 0; i < int(sig_data.size()); i++)
+				if (non_feedback_nets.count(sig_data[i]))
+					goto not_pure_feedback_port;
+
+			async_rd_bits[sig_addr].resize(max(async_rd_bits.size(), sig_data.size()));
+			for (int i = 0; i < int(sig_data.size()); i++)
+				async_rd_bits[sig_addr][i].insert(sig_data[i]);
+
+		not_pure_feedback_port:;
+		}
+
+		if (async_rd_bits.empty())
+			return;
+
+		log("Populating enable bits on write ports of memory %s.%s with aync read feedback:\n", log_id(module), log_id(memid));
+
+		for (auto cell : wr_ports)
+		{
+			RTLIL::SigSpec sig_addr = sigmap_xmux(cell->getPort(ID::ADDR));
+			if (!async_rd_bits.count(sig_addr))
+				continue;
+
+			log("  Analyzing write port %s.\n", log_id(cell));
+
+			std::vector<RTLIL::SigBit> cell_data = cell->getPort(ID::DATA);
+			std::vector<RTLIL::SigBit> cell_en = cell->getPort(ID::EN);
+
+			int created_conditions = 0;
+			for (int i = 0; i < int(cell_data.size()); i++)
+				if (cell_en[i] != RTLIL::SigBit(RTLIL::State::S0))
+				{
+					std::map<RTLIL::SigBit, bool> state;
+					std::set<std::map<RTLIL::SigBit, bool>> conditions;
+
+					find_data_feedback(async_rd_bits.at(sig_addr).at(i), cell_data[i], state, conditions);
+					cell_en[i] = conditions_to_logic(conditions, cell_en[i], created_conditions);
+				}
+
+			if (created_conditions) {
+				log("    Added enable logic for %d different cases.\n", created_conditions);
+				cell->setPort(ID::EN, cell_en);
+			}
+		}
+	}
+
+	// -------------
+	// Setup and run
+	// -------------
+
+	OptMemFeedbackWorker(RTLIL::Design *design) : design(design) {}
+
+	void operator()(RTLIL::Module* module)
+	{
+		std::map<std::string, std::pair<std::vector<RTLIL::Cell*>, std::vector<RTLIL::Cell*>>> memindex;
+
+		this->module = module;
+		sigmap.set(module);
+		sig_to_mux.clear();
+		conditions_logic_cache.clear();
+
+		sigmap_xmux = sigmap;
+		for (auto cell : module->cells())
+		{
+			if (cell->type == ID($memrd))
+				memindex[cell->parameters.at(ID::MEMID).decode_string()].first.push_back(cell);
+
+			if (cell->type == ID($memwr))
+				memindex[cell->parameters.at(ID::MEMID).decode_string()].second.push_back(cell);
+
+			if (cell->type == ID($mux))
+			{
+				RTLIL::SigSpec sig_a = sigmap_xmux(cell->getPort(ID::A));
+				RTLIL::SigSpec sig_b = sigmap_xmux(cell->getPort(ID::B));
+
+				if (sig_a.is_fully_undef())
+					sigmap_xmux.add(cell->getPort(ID::Y), sig_b);
+				else if (sig_b.is_fully_undef())
+					sigmap_xmux.add(cell->getPort(ID::Y), sig_a);
+			}
+
+			if (cell->type.in(ID($mux), ID($pmux)))
+			{
+				std::vector<RTLIL::SigBit> sig_y = sigmap(cell->getPort(ID::Y));
+				for (int i = 0; i < int(sig_y.size()); i++)
+					sig_to_mux[sig_y[i]] = std::pair<RTLIL::Cell*, int>(cell, i);
+			}
+		}
+
+		for (auto &it : memindex) {
+			std::sort(it.second.first.begin(), it.second.first.end(), memrd_cmp);
+			std::sort(it.second.second.begin(), it.second.second.end(), memwr_cmp);
+			translate_rd_feedback_to_en(it.first, it.second.first, it.second.second);
+		}
+	}
+};
+
+struct OptMemFeedbackPass : public Pass {
+	OptMemFeedbackPass() : Pass("opt_mem_feedback", "convert memory read-to-write port feedback paths to write enables") { }
+	void help() override
+	{
+		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
+		log("\n");
+		log("    opt_mem_feedback [selection]\n");
+		log("\n");
+		log("This pass detects cases where an asynchronous read port is connected via\n");
+		log("a mux tree to a write port with the same address.  When such a path is\n");
+		log("found, it is replaced with a new condition on an enable signal, possibly\n");
+		log("allowing for removal of the read port.\n");
+		log("\n");
+	}
+	void execute(std::vector<std::string> args, RTLIL::Design *design) override {
+		log_header(design, "Executing OPT_MEM_FEEDBACK pass (finding memory read-to-write feedback paths).\n");
+		extra_args(args, 1, design);
+		OptMemFeedbackWorker worker(design);
+
+		for (auto module : design->selected_modules())
+			worker(module);
+	}
+} OptMemFeedbackPass;
+
+PRIVATE_NAMESPACE_END
+
-- 
2.30.2