From 2b86055848c396591c6ec693a8abd8826b300b2b Mon Sep 17 00:00:00 2001
From: Eddie Hung <eddie@fpgeh.com>
Date: Wed, 4 Sep 2019 12:35:15 -0700
Subject: [PATCH] Add peepopt_dffmuxext

---
 passes/pmgen/Makefile.inc          |  1 +
 passes/pmgen/peepopt.cc            |  1 +
 passes/pmgen/peepopt_dffmuxext.pmg | 58 ++++++++++++++++++++++++++++++
 3 files changed, 60 insertions(+)
 create mode 100644 passes/pmgen/peepopt_dffmuxext.pmg

diff --git a/passes/pmgen/Makefile.inc b/passes/pmgen/Makefile.inc
index 4989c582a..6648e2ec0 100644
--- a/passes/pmgen/Makefile.inc
+++ b/passes/pmgen/Makefile.inc
@@ -27,6 +27,7 @@ $(eval $(call add_extra_objs,passes/pmgen/peepopt_pm.h))
 
 PEEPOPT_PATTERN  = passes/pmgen/peepopt_shiftmul.pmg
 PEEPOPT_PATTERN += passes/pmgen/peepopt_muldiv.pmg
+PEEPOPT_PATTERN += passes/pmgen/peepopt_dffmuxext.pmg
 
 passes/pmgen/peepopt_pm.h: passes/pmgen/pmgen.py $(PEEPOPT_PATTERN)
 	$(P) mkdir -p passes/pmgen && python3 $< -o $@ -p peepopt $(filter-out $<,$^)
diff --git a/passes/pmgen/peepopt.cc b/passes/pmgen/peepopt.cc
index e7f95cf85..b57d26cef 100644
--- a/passes/pmgen/peepopt.cc
+++ b/passes/pmgen/peepopt.cc
@@ -60,6 +60,7 @@ struct PeepoptPass : public Pass {
 				peepopt_pm pm(module, module->selected_cells());
 				pm.run_shiftmul();
 				pm.run_muldiv();
+				pm.run_dffmuxext();
 			}
 		}
 	}
diff --git a/passes/pmgen/peepopt_dffmuxext.pmg b/passes/pmgen/peepopt_dffmuxext.pmg
new file mode 100644
index 000000000..e99ce1602
--- /dev/null
+++ b/passes/pmgen/peepopt_dffmuxext.pmg
@@ -0,0 +1,58 @@
+pattern dffmuxext
+
+state <IdString> muxAB
+
+match dff
+	select dff->type == $dff
+	select GetSize(port(dff, \D)) > 1
+endmatch
+
+match mux
+	select mux->type == $mux
+	select GetSize(port(mux, \Y)) > 1
+	choice <IdString> AB {\A, \B}
+	//select port(mux, AB)[GetSize(port(mux, \Y))-1].wire
+	index <SigSpec> port(mux, \Y) === port(dff, \D)
+	define <IdString> BA (AB == \A ? \B : \A)
+	index <SigSpec> port(mux, BA) === port(dff, \Q)
+	filter port(mux, AB)[GetSize(port(mux, \Y))-1] == port(mux, AB)[GetSize(port(mux, \Y))-2]
+	set muxAB AB
+endmatch
+
+code
+	did_something = true;
+
+	log_cell(dff);
+	log_cell(mux);
+
+	SigSpec &D = mux->connections_.at(muxAB);
+	SigSpec &Q = dff->connections_.at(\Q);
+	int width = GetSize(D);
+
+	SigBit sign = D[width-1];
+	bool is_signed = sign.wire;
+	int i;
+	for (i = width-1; i >= 2; i--) {
+		if (!is_signed) {
+			module->connect(Q[i], sign);
+			if (D[i-1] != sign)
+				break;
+		}
+		else {
+			module->connect(Q[i], Q[i-1]);
+			if (D[i-2] != sign)
+				break;
+		}
+	}
+
+	mux->connections_.at(\A).remove(i, width-i);
+	mux->connections_.at(\B).remove(i, width-i);
+	mux->connections_.at(\Y).remove(i, width-i);
+	mux->fixup_parameters();
+	dff->connections_.at(\D).remove(i, width-i);
+	dff->connections_.at(\Q).remove(i, width-i);
+	dff->fixup_parameters();
+
+	log("dffmuxext pattern in %s: dff=%s, mux=%s; removed top %d bits.\n", log_id(module), log_id(dff), log_id(mux), width-i);
+	accept;
+endcode
-- 
2.30.2