xilinx: Add xilinx_dffopt pass (#1557)

6 files changed, 389 insertions, 22 deletions

diff --git a/techlibs/xilinx/Makefile.inc b/techlibs/xilinx/Makefile.inc
index 3ebc72fe8..3f2fbcc85 100644
--- a/techlibs/xilinx/Makefile.inc
+++ b/techlibs/xilinx/Makefile.inc
@@ -1,5 +1,6 @@
 
 OBJS += techlibs/xilinx/synth_xilinx.o
+OBJS += techlibs/xilinx/xilinx_dffopt.o
 
 GENFILES += techlibs/xilinx/brams_init_36.vh
 GENFILES += techlibs/xilinx/brams_init_32.vh
diff --git a/techlibs/xilinx/cells_sim.v b/techlibs/xilinx/cells_sim.v
index f9ce496ff..cf7923777 100644
--- a/techlibs/xilinx/cells_sim.v
+++ b/techlibs/xilinx/cells_sim.v
@@ -329,6 +329,41 @@ module FDSE (
   endcase endgenerate
 endmodule
 
+module FDRSE (
+  output reg Q,
+  (* clkbuf_sink *)
+  (* invertible_pin = "IS_C_INVERTED" *)
+  input C,
+  (* invertible_pin = "IS_CE_INVERTED" *)
+  input CE,
+  (* invertible_pin = "IS_D_INVERTED" *)
+  input D,
+  (* invertible_pin = "IS_R_INVERTED" *)
+  input R,
+  (* invertible_pin = "IS_S_INVERTED" *)
+  input S
+);
+  parameter [0:0] INIT = 1'b0;
+  parameter [0:0] IS_C_INVERTED = 1'b0;
+  parameter [0:0] IS_CE_INVERTED = 1'b0;
+  parameter [0:0] IS_D_INVERTED = 1'b0;
+  parameter [0:0] IS_R_INVERTED = 1'b0;
+  parameter [0:0] IS_S_INVERTED = 1'b0;
+  initial Q <= INIT;
+  wire c = C ^ IS_C_INVERTED;
+  wire ce = CE ^ IS_CE_INVERTED;
+  wire d = D ^ IS_D_INVERTED;
+  wire r = R ^ IS_R_INVERTED;
+  wire s = S ^ IS_S_INVERTED;
+  always @(posedge c)
+    if (r)
+      Q <= 0;
+    else if (s)
+      Q <= 1;
+    else if (ce)
+      Q <= d;
+endmodule
+
 module FDCE (
   (* abc9_arrival=303 *)
   output reg Q,
diff --git a/techlibs/xilinx/cells_xtra.py b/techlibs/xilinx/cells_xtra.py
index e4c580b9d..6d5adf1aa 100644
--- a/techlibs/xilinx/cells_xtra.py
+++ b/techlibs/xilinx/cells_xtra.py
@@ -66,7 +66,7 @@ CELLS = [
     # CLB -- registers/latches.
     # Virtex 1/2/4/5, Spartan 3.
     Cell('FDCPE', port_attrs={'C': ['clkbuf_sink']}),
-    Cell('FDRSE', port_attrs={'C': ['clkbuf_sink']}),
+    # Cell('FDRSE', port_attrs={'C': ['clkbuf_sink']}),
     Cell('LDCPE', port_attrs={'C': ['clkbuf_sink']}),
     # Virtex 6, Spartan 6, Series 7, Ultrascale.
     # Cell('FDCE'),
diff --git a/techlibs/xilinx/cells_xtra.v b/techlibs/xilinx/cells_xtra.v
index 8ac596459..66b7c583f 100644
--- a/techlibs/xilinx/cells_xtra.v
+++ b/techlibs/xilinx/cells_xtra.v
@@ -17,27 +17,6 @@ module FDCPE (...);
     input PRE;
 endmodule
 
-module FDRSE (...);
-    parameter [0:0] INIT = 1'b0;
-    parameter [0:0] IS_C_INVERTED = 1'b0;
-    parameter [0:0] IS_CE_INVERTED = 1'b0;
-    parameter [0:0] IS_D_INVERTED = 1'b0;
-    parameter [0:0] IS_R_INVERTED = 1'b0;
-    parameter [0:0] IS_S_INVERTED = 1'b0;
-    output Q;
-    (* clkbuf_sink *)
-    (* invertible_pin = "IS_C_INVERTED" *)
-    input C;
-    (* invertible_pin = "IS_CE_INVERTED" *)
-    input CE;
-    (* invertible_pin = "IS_D_INVERTED" *)
-    input D;
-    (* invertible_pin = "IS_R_INVERTED" *)
-    input R;
-    (* invertible_pin = "IS_S_INVERTED" *)
-    input S;
-endmodule
-
 module LDCPE (...);
     parameter [0:0] INIT = 1'b0;
     parameter [0:0] IS_CLR_INVERTED = 1'b0;
diff --git a/techlibs/xilinx/synth_xilinx.cc b/techlibs/xilinx/synth_xilinx.cc
index a061c8dc0..971089b28 100644
--- a/techlibs/xilinx/synth_xilinx.cc
+++ b/techlibs/xilinx/synth_xilinx.cc
@@ -570,6 +570,7 @@ struct SynthXilinxPass : public ScriptPass
 			else
 				techmap_args += " -map " + ff_map_file;
 			run("techmap " + techmap_args);
+			run("xilinx_dffopt");
 			run("clean");
 		}
 
diff --git a/techlibs/xilinx/xilinx_dffopt.cc b/techlibs/xilinx/xilinx_dffopt.cc
new file mode 100644
index 000000000..1256a08cb
--- /dev/null
+++ b/techlibs/xilinx/xilinx_dffopt.cc
@@ -0,0 +1,351 @@
+/*
+ *  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/sigtools.h"
+
+USING_YOSYS_NAMESPACE
+PRIVATE_NAMESPACE_BEGIN
+
+typedef std::pair<Const, std::vector<SigBit>> LutData;
+
+// Compute a LUT implementing (select ^ select_inv) ? alt_data : data.  Returns true if successful.
+bool merge_lut(LutData &result, const LutData &data, const LutData select, bool select_inv, SigBit alt_data, int max_lut_size) {
+	// First, gather input signals.
+	result.second = data.second;
+	int idx_alt = -1;
+	if (alt_data.wire) {
+		// Check if we already have it.
+		for (int i = 0; i < GetSize(result.second); i++)
+			if (result.second[i] == alt_data)
+				idx_alt = i;
+		// If not, add it.
+		if (idx_alt == -1) {
+			idx_alt = GetSize(result.second);
+			result.second.push_back(alt_data);
+		}
+	}
+	std::vector<int> idx_sel;
+	for (auto bit : select.second) {
+		int idx = -1;
+		for (int i = 0; i < GetSize(result.second); i++)
+			if (result.second[i] == bit)
+				idx = i;
+		if (idx == -1) {
+			idx = GetSize(result.second);
+			result.second.push_back(bit);
+		}
+		idx_sel.push_back(idx);
+	}
+
+	// If LUT would be too large, bail.
+	if (GetSize(result.second) > max_lut_size)
+		return false;
+
+	// Okay, we're doing it — compute the LUT mask.
+	result.first = Const(0, 1 << GetSize(result.second));
+	for (int i = 0; i < GetSize(result.first); i++) {
+		int sel_lut_idx = 0;
+		for (int j = 0; j < GetSize(select.second); j++)
+			if (i & 1 << idx_sel[j])
+				sel_lut_idx |= 1 << j;
+		bool select_val = (select.first.bits[sel_lut_idx] == State::S1);
+		bool new_bit;
+		if (select_val ^ select_inv) {
+			// Use alt_data.
+			if (alt_data.wire)
+				new_bit = (i & 1 << idx_alt) != 0;
+			else
+				new_bit = alt_data.data == State::S1;
+		} else {
+			// Use original LUT.
+			int lut_idx = i & ((1 << GetSize(data.second)) - 1);
+			new_bit = data.first.bits[lut_idx] == State::S1;
+		}
+		result.first.bits[i] = new_bit ? State::S1 : State::S0;
+	}
+	return true;
+}
+
+struct XilinxDffOptPass : public Pass {
+	XilinxDffOptPass() : Pass("xilinx_dffopt", "Xilinx: optimize FF control signal usage") { }
+	void help() YS_OVERRIDE
+	{
+		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
+		log("\n");
+		log("    xilinx_dffopt [options] [selection]\n");
+		log("\n");
+		log("Converts hardware clock enable and set/reset signals on FFs to emulation\n");
+		log("using LUTs, if doing so would improve area.  Operates on post-techmap Xilinx\n");
+		log("cells (LUT*, FD*).\n");
+		log("\n");
+		log("    -lut4\n");
+		log("        Assume a LUT4-based device (instead of a LUT6-based device).\n");
+		log("\n");
+	}
+	void execute(std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE
+	{
+		log_header(design, "Executing XILINX_DFFOPT pass (optimize FF control signal usage).\n");
+
+		size_t argidx;
+		int max_lut_size = 6;
+		for (argidx = 1; argidx < args.size(); argidx++)
+		{
+			if (args[argidx] == "-lut4") {
+				max_lut_size = 4;
+				continue;
+			}
+			break;
+		}
+		extra_args(args, argidx, design);
+
+		for (auto module : design->selected_modules())
+		{
+			log("Optimizing FFs in %s.\n", log_id(module));
+
+			SigMap sigmap(module);
+			dict<SigBit, pair<LutData, Cell *>> bit_to_lut;
+			dict<SigBit, int> bit_uses;
+
+			// Gather LUTs.
+			for (auto cell : module->selected_cells())
+			{
+				for (auto port : cell->connections())
+					for (auto bit : port.second)
+						bit_uses[sigmap(bit)]++;
+				if (cell->get_bool_attribute(ID::keep))
+					continue;
+				if (cell->type == ID(INV)) {
+					SigBit sigout = sigmap(cell->getPort(ID(O)));
+					SigBit sigin = sigmap(cell->getPort(ID(I)));
+					bit_to_lut[sigout] = make_pair(LutData(Const(1, 2), {sigin}), cell);
+				} else if (cell->type.in(ID(LUT1), ID(LUT2), ID(LUT3), ID(LUT4), ID(LUT5), ID(LUT6))) {
+					SigBit sigout = sigmap(cell->getPort(ID(O)));
+					const Const &init = cell->getParam(ID(INIT));
+					std::vector<SigBit> sigin;
+					sigin.push_back(sigmap(cell->getPort(ID(I0))));
+					if (cell->type == ID(LUT1))
+						goto lut_sigin_done;
+					sigin.push_back(sigmap(cell->getPort(ID(I1))));
+					if (cell->type == ID(LUT2))
+						goto lut_sigin_done;
+					sigin.push_back(sigmap(cell->getPort(ID(I2))));
+					if (cell->type == ID(LUT3))
+						goto lut_sigin_done;
+					sigin.push_back(sigmap(cell->getPort(ID(I3))));
+					if (cell->type == ID(LUT4))
+						goto lut_sigin_done;
+					sigin.push_back(sigmap(cell->getPort(ID(I4))));
+					if (cell->type == ID(LUT5))
+						goto lut_sigin_done;
+					sigin.push_back(sigmap(cell->getPort(ID(I5))));
+lut_sigin_done:
+					bit_to_lut[sigout] = make_pair(LutData(init, sigin), cell);
+				}
+			}
+			for (auto wire : module->wires())
+				if (wire->port_output || wire->port_input)
+					for (int i = 0; i < GetSize(wire); i++)
+						bit_uses[sigmap(SigBit(wire, i))]++;
+
+			// Iterate through FFs.
+			for (auto cell : module->selected_cells())
+			{
+				bool has_s = false, has_r = false;
+				if (cell->type.in(ID(FDCE), ID(FDPE), ID(FDCPE), ID(FDCE_1), ID(FDPE_1), ID(FDCPE_1))) {
+					// Async reset.
+				} else if (cell->type.in(ID(FDRE), ID(FDRE_1))) {
+					has_r = true;
+				} else if (cell->type.in(ID(FDSE), ID(FDSE_1))) {
+					has_s = true;
+				} else if (cell->type.in(ID(FDRSE), ID(FDRSE_1))) {
+					has_r = true;
+					has_s = true;
+				} else {
+					// Not a FF.
+					continue;
+				}
+				if (cell->get_bool_attribute(ID::keep))
+					continue;
+
+				// Don't bother if D has more than one use.
+				SigBit sig_D = sigmap(cell->getPort(ID(D)));
+				if (bit_uses[sig_D] > 2)
+					continue;
+
+				// Find the D LUT.
+				auto it_D = bit_to_lut.find(sig_D);
+				if (it_D == bit_to_lut.end())
+					continue;
+				LutData lut_d = it_D->second.first;
+				Cell *cell_d = it_D->second.second;
+				if (cell->hasParam(ID(IS_D_INVERTED)) && cell->getParam(ID(IS_D_INVERTED)).as_bool()) {
+					// Flip all bits in the LUT.
+					for (int i = 0; i < GetSize(lut_d.first); i++)
+						lut_d.first.bits[i] = (lut_d.first.bits[i] == State::S1) ? State::S0 : State::S1;
+				}
+
+				LutData lut_d_post_ce;
+				LutData lut_d_post_s;
+				LutData lut_d_post_r;
+				bool worthy_post_ce = false;
+				bool worthy_post_s = false;
+				bool worthy_post_r = false;
+
+				// First, unmap CE.
+				SigBit sig_Q = sigmap(cell->getPort(ID(Q)));
+				SigBit sig_CE = sigmap(cell->getPort(ID(CE)));
+				LutData lut_ce = LutData(Const(2, 2), {sig_CE});
+				auto it_CE = bit_to_lut.find(sig_CE);
+				if (it_CE != bit_to_lut.end())
+					lut_ce = it_CE->second.first;
+				if (sig_CE.wire) {
+					// Merge CE LUT and D LUT into one.  If it cannot be done, nothing to do about this FF.
+					if (!merge_lut(lut_d_post_ce, lut_d, lut_ce, true, sig_Q, max_lut_size))
+						continue;
+
+					// If this gets rid of a CE LUT, it's worth it.  If not, it still may be worth it, if we can remove set/reset as well.
+					if (it_CE != bit_to_lut.end())
+						worthy_post_ce = true;
+				} else if (sig_CE.data != State::S1) {
+					// Strange.  Should not happen in a reasonable flow, so bail.
+					continue;
+				} else {
+					lut_d_post_ce = lut_d;
+				}
+
+				// Second, unmap S, if any.
+				lut_d_post_s = lut_d_post_ce;
+				if (has_s) {
+					SigBit sig_S = sigmap(cell->getPort(ID(S)));
+					LutData lut_s = LutData(Const(2, 2), {sig_S});
+					bool inv_s = cell->hasParam(ID(IS_S_INVERTED)) && cell->getParam(ID(IS_S_INVERTED)).as_bool();
+					auto it_S = bit_to_lut.find(sig_S);
+					if (it_S != bit_to_lut.end())
+						lut_s = it_S->second.first;
+					if (sig_S.wire) {
+						// Merge S LUT and D LUT into one.  If it cannot be done, try to at least merge CE.
+						if (!merge_lut(lut_d_post_s, lut_d_post_ce, lut_s, inv_s, SigBit(State::S1), max_lut_size))
+							goto unmap;
+						// If this gets rid of an S LUT, it's worth it.
+						if (it_S != bit_to_lut.end())
+							worthy_post_s = true;
+					} else if (sig_S.data != (inv_s ? State::S1 : State::S0)) {
+						// Strange.  Should not happen in a reasonable flow, so bail.
+						continue;
+					}
+				}
+
+				// Third, unmap R, if any.
+				lut_d_post_r = lut_d_post_s;
+				if (has_r) {
+					SigBit sig_R = sigmap(cell->getPort(ID(R)));
+					LutData lut_r = LutData(Const(2, 2), {sig_R});
+					bool inv_r = cell->hasParam(ID(IS_R_INVERTED)) && cell->getParam(ID(IS_R_INVERTED)).as_bool();
+					auto it_R = bit_to_lut.find(sig_R);
+					if (it_R != bit_to_lut.end())
+						lut_r = it_R->second.first;
+					if (sig_R.wire) {
+						// Merge R LUT and D LUT into one.  If it cannot be done, try to at least merge CE/S.
+						if (!merge_lut(lut_d_post_r, lut_d_post_s, lut_r, inv_r, SigBit(State::S0), max_lut_size))
+							goto unmap;
+						// If this gets rid of an S LUT, it's worth it.
+						if (it_R != bit_to_lut.end())
+							worthy_post_r = true;
+					} else if (sig_R.data != (inv_r ? State::S1 : State::S0)) {
+						// Strange.  Should not happen in a reasonable flow, so bail.
+						continue;
+					}
+				}
+
+unmap:
+				LutData final_lut;
+				if (worthy_post_r) {
+					final_lut = lut_d_post_r;
+					log("  Merging R LUT for %s/%s (%d -> %d)\n", log_id(cell), log_id(sig_Q.wire), GetSize(lut_d.second), GetSize(final_lut.second));
+				} else if (worthy_post_s) {
+					final_lut = lut_d_post_s;
+					log("  Merging S LUT for %s/%s (%d -> %d)\n", log_id(cell), log_id(sig_Q.wire), GetSize(lut_d.second), GetSize(final_lut.second));
+				} else if (worthy_post_ce) {
+					final_lut = lut_d_post_ce;
+					log("  Merging CE LUT for %s/%s (%d -> %d)\n", log_id(cell), log_id(sig_Q.wire), GetSize(lut_d.second), GetSize(final_lut.second));
+				} else {
+					// Nothing to do here.
+					continue;
+				}
+
+				// Okay, we're doing it.  Unmap ports.
+				if (worthy_post_r) {
+					cell->unsetParam(ID(IS_R_INVERTED));
+					cell->setPort(ID(R), Const(0, 1));
+				}
+				if (has_s && (worthy_post_r || worthy_post_s)) {
+					cell->unsetParam(ID(IS_S_INVERTED));
+					cell->setPort(ID(S), Const(0, 1));
+				}
+				cell->setPort(ID(CE), Const(1, 1));
+				cell->unsetParam(ID(IS_D_INVERTED));
+
+				// Create the new LUT.
+				Cell *lut_cell = 0;
+				switch (GetSize(final_lut.second)) {
+					case 1:
+						lut_cell = module->addCell(NEW_ID, ID(LUT1));
+						break;
+					case 2:
+						lut_cell = module->addCell(NEW_ID, ID(LUT2));
+						break;
+					case 3:
+						lut_cell = module->addCell(NEW_ID, ID(LUT3));
+						break;
+					case 4:
+						lut_cell = module->addCell(NEW_ID, ID(LUT4));
+						break;
+					case 5:
+						lut_cell = module->addCell(NEW_ID, ID(LUT5));
+						break;
+					case 6:
+						lut_cell = module->addCell(NEW_ID, ID(LUT6));
+						break;
+					default:
+						log_assert(!"unknown lut size");
+				}
+				lut_cell->attributes = cell_d->attributes;
+				Wire *lut_out = module->addWire(NEW_ID);
+				lut_cell->setParam(ID(INIT), final_lut.first);
+				cell->setPort(ID(D), lut_out);
+				lut_cell->setPort(ID(O), lut_out);
+				lut_cell->setPort(ID(I0), final_lut.second[0]);
+				if (GetSize(final_lut.second) >= 2)
+					lut_cell->setPort(ID(I1), final_lut.second[1]);
+				if (GetSize(final_lut.second) >= 3)
+					lut_cell->setPort(ID(I2), final_lut.second[2]);
+				if (GetSize(final_lut.second) >= 4)
+					lut_cell->setPort(ID(I3), final_lut.second[3]);
+				if (GetSize(final_lut.second) >= 5)
+					lut_cell->setPort(ID(I4), final_lut.second[4]);
+				if (GetSize(final_lut.second) >= 6)
+					lut_cell->setPort(ID(I5), final_lut.second[5]);
+			}
+		}
+	}
+} XilinxDffOptPass;
+
+PRIVATE_NAMESPACE_END
+