From 2309459605b262040f7bea84e6d935d2838686d5 Mon Sep 17 00:00:00 2001
From: Eddie Hung <eddie@fpgeh.com>
Date: Sat, 15 Jun 2019 19:36:55 -0700
Subject: [PATCH] Do not treat $__ABC_FF_ as a user cell

---
 backends/aiger/xaiger.cc | 18 +++++++++---------
 passes/techmap/abc9.cc   | 27 ++++++---------------------
 2 files changed, 15 insertions(+), 30 deletions(-)

diff --git a/backends/aiger/xaiger.cc b/backends/aiger/xaiger.cc
index ce2f6e571..923ba3da8 100644
--- a/backends/aiger/xaiger.cc
+++ b/backends/aiger/xaiger.cc
@@ -222,15 +222,15 @@ struct XAigerWriter
 
 			log_assert(!holes_mode);
 
-			// FIXME: Should short here, rather than provide $__ABC_FF_
-			//        to ABC like a user cell
-			//if (cell->type == "$__ABC_FF_")
-			//{
-			//	SigBit D = sigmap(cell->getPort("\\D").as_bit());
-			//	SigBit Q = sigmap(cell->getPort("\\Q").as_bit());
-			//	alias_map[Q] = D;
-			//	continue;
-			//}
+			if (cell->type == "$__ABC_FF_")
+			{
+				SigBit D = sigmap(cell->getPort("\\D").as_bit());
+				SigBit Q = sigmap(cell->getPort("\\Q").as_bit());
+				unused_bits.erase(D);
+				undriven_bits.erase(Q);
+				alias_map[Q] = D;
+				continue;
+			}
 
 			RTLIL::Module* inst_module = !holes_mode ? module->design->module(cell->type) : nullptr;
 			bool inst_flop = inst_module ? inst_module->attributes.count("\\abc_flop") : false;
diff --git a/passes/techmap/abc9.cc b/passes/techmap/abc9.cc
index e13cd0eef..decf5a6aa 100644
--- a/passes/techmap/abc9.cc
+++ b/passes/techmap/abc9.cc
@@ -512,26 +512,18 @@ void abc9_module(RTLIL::Design *design, RTLIL::Module *current_module, std::stri
 			}
 		}
 
-		// Remove all AND, NOT, and ABC box instances
-		// in preparation for stitching mapped_mod in
-		// Short $_FF_ cells used by ABC (FIXME)
 		dict<IdString, decltype(RTLIL::Cell::parameters)> erased_boxes;
-		std::vector<RTLIL::Cell*> abc_dff;
 		for (auto it = module->cells_.begin(); it != module->cells_.end(); ) {
 			RTLIL::Cell* cell = it->second;
-			if (cell->type.in("$_AND_", "$_NOT_")) {
+			if (cell->type.in("$_AND_", "$_NOT_", "$__ABC_FF_")) {
 				it = module->cells_.erase(it);
 				continue;
 			}
-			if (cell->type.in("$__ABC_FF_"))
-				abc_dff.emplace_back(cell);
-			else {
-				RTLIL::Module* box_module = design->module(cell->type);
-				if (box_module && box_module->attributes.count("\\abc_box_id")) {
-					erased_boxes.insert(std::make_pair(it->first, std::move(cell->parameters)));
-					it = module->cells_.erase(it);
-					continue;
-				}
+			RTLIL::Module* box_module = design->module(cell->type);
+			if (box_module && box_module->attributes.count("\\abc_box_id")) {
+				erased_boxes.insert(std::make_pair(it->first, std::move(cell->parameters)));
+				it = module->cells_.erase(it);
+				continue;
 			}
 			++it;
 		}
@@ -695,13 +687,6 @@ void abc9_module(RTLIL::Design *design, RTLIL::Module *current_module, std::stri
 			}
 		}
 
-		for (auto cell : abc_dff) {
-			RTLIL::SigBit D = cell->getPort("\\D");
-			RTLIL::SigBit Q = cell->getPort("\\Q");
-			module->connect(Q, D);
-			module->remove(cell);
-		}
-
 		//log("ABC RESULTS:        internal signals: %8d\n", int(signal_list.size()) - in_wires - out_wires);
 		log("ABC RESULTS:           input signals: %8d\n", in_wires);
 		log("ABC RESULTS:          output signals: %8d\n", out_wires);
-- 
2.30.2