Add -match-init option to dff2dffs.

3 files changed, 77 insertions, 3 deletions

diff --git a/CHANGELOG b/CHANGELOG
index e416d152c..890fad978 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -39,6 +39,7 @@ Yosys 0.9 .. Yosys 0.9-dev
     - Added "xilinx_srl" for Xilinx shift register extraction
     - Removed "shregmap -tech xilinx" (superseded by "xilinx_srl")
     - Added "_TECHMAP_WIREINIT_*_" attribute and "_TECHMAP_REMOVEINIT_*_" wire for "techmap" pass
+    - Added "-match-init" option to "dff2dffs" pass
 
 Yosys 0.8 .. Yosys 0.9
 ----------------------
diff --git a/passes/techmap/dff2dffs.cc b/passes/techmap/dff2dffs.cc
index 0ea033513..3fa1ed5cf 100644
--- a/passes/techmap/dff2dffs.cc
+++ b/passes/techmap/dff2dffs.cc
@@ -34,11 +34,16 @@ struct Dff2dffsPass : public Pass {
 		log("Merge synchronous set/reset $_MUX_ cells to create $__DFFS_[NP][NP][01], to be run before\n");
 		log("dff2dffe for SR over CE priority.\n");
 		log("\n");
+		log("    -match-init\n");
+		log("        Disallow merging synchronous set/reset that has polarity opposite of the\n");
+		log("        output wire's init attribute (if any).\n");
+		log("\n");
 	}
 	void execute(std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE
 	{
 		log_header(design, "Executing dff2dffs pass (merge synchronous set/reset into FF cells).\n");
 
+		bool match_init = false;
 		size_t argidx;
 		for (argidx = 1; argidx < args.size(); argidx++)
 		{
@@ -46,6 +51,10 @@ struct Dff2dffsPass : public Pass {
 			// 	singleton_mode = true;
 			// 	continue;
 			// }
+			if (args[argidx] == "-match-init") {
+				match_init = true;
+				continue;
+			}
 			break;
 		}
 		extra_args(args, argidx, design);
@@ -96,9 +105,6 @@ struct Dff2dffsPass : public Pass {
 				SigBit bit_b = sigmap(mux_cell->getPort(ID::B));
 				SigBit bit_s = sigmap(mux_cell->getPort(ID(S)));
 
-				log("  Merging %s (A=%s, B=%s, S=%s) into %s (%s).\n", log_id(mux_cell),
-						log_signal(bit_a), log_signal(bit_b), log_signal(bit_s), log_id(cell), log_id(cell->type));
-
 				SigBit sr_val, sr_sig;
 				bool invert_sr;
 				sr_sig = bit_s;
@@ -113,6 +119,23 @@ struct Dff2dffsPass : public Pass {
 					invert_sr = false;
 				}
 
+				if (match_init) {
+					SigBit bit_q = cell->getPort(ID(Q));
+					if (bit_q.wire) {
+						auto it = bit_q.wire->attributes.find(ID(init));
+						if (it != bit_q.wire->attributes.end()) {
+							auto init_val = it->second[bit_q.offset];
+							if (init_val == State::S1 && sr_val != State::S1)
+								continue;
+							if (init_val == State::S0 && sr_val != State::S0)
+								continue;
+						}
+					}
+				}
+
+				log("  Merging %s (A=%s, B=%s, S=%s) into %s (%s).\n", log_id(mux_cell),
+						log_signal(bit_a), log_signal(bit_b), log_signal(bit_s), log_id(cell), log_id(cell->type));
+
 				if (sr_val == State::S1) {
 					if (cell->type == ID($_DFF_N_)) {
 						if (invert_sr) cell->type = ID($__DFFS_NN1_);
diff --git a/tests/techmap/dff2dffs.ys b/tests/techmap/dff2dffs.ys
new file mode 100644
index 000000000..13f1a3cf3
--- /dev/null
+++ b/tests/techmap/dff2dffs.ys
@@ -0,0 +1,50 @@
+read_verilog << EOT
+module top(...);
+input clk;
+input d;
+input sr;
+output reg q0, q1, q2, q3, q4, q5;
+
+initial q0 = 1'b0;
+initial q1 = 1'b0;
+initial q2 = 1'b1;
+initial q3 = 1'b1;
+initial q4 = 1'bx;
+initial q5 = 1'bx;
+
+always @(posedge clk) begin
+	q0 <= sr ? 1'b0 : d;
+	q1 <= sr ? 1'b1 : d;
+	q2 <= sr ? 1'b0 : d;
+	q3 <= sr ? 1'b1 : d;
+	q4 <= sr ? 1'b0 : d;
+	q5 <= sr ? 1'b1 : d;
+end
+
+endmodule
+EOT
+
+proc
+simplemap
+design -save ref
+
+dff2dffs
+clean
+
+select -assert-count 1 w:q0 %x t:$__DFFS_PP0_ %i
+select -assert-count 1 w:q1 %x t:$__DFFS_PP1_ %i
+select -assert-count 1 w:q2 %x t:$__DFFS_PP0_ %i
+select -assert-count 1 w:q3 %x t:$__DFFS_PP1_ %i
+select -assert-count 1 w:q4 %x t:$__DFFS_PP0_ %i
+select -assert-count 1 w:q5 %x t:$__DFFS_PP1_ %i
+
+design -load ref
+dff2dffs -match-init
+clean
+
+select -assert-count 1 w:q0 %x t:$__DFFS_PP0_ %i
+select -assert-count 0 w:q1 %x t:$__DFFS_PP1_ %i
+select -assert-count 0 w:q2 %x t:$__DFFS_PP0_ %i
+select -assert-count 1 w:q3 %x t:$__DFFS_PP1_ %i
+select -assert-count 1 w:q4 %x t:$__DFFS_PP0_ %i
+select -assert-count 1 w:q5 %x t:$__DFFS_PP1_ %i