Merge pull request #1085 from YosysHQ/eddie/shregmap_improve

Improve shregmap to handle case where first flop is common to two chains

passes/techmap/shregmap.cc

@@ -293,10 +293,22 @@ struct ShregmapWorker
 
 				if (opts.init || sigbit_init.count(q_bit) == 0)
 				{
-					if (sigbit_chain_next.count(d_bit)) {
+					auto r = sigbit_chain_next.insert(std::make_pair(d_bit, cell));
+					if (!r.second) {
+						// Insertion not successful means that d_bit is already
+						// connected to another register, thus mark it as a
+						// non chain user ...
 						sigbit_with_non_chain_users.insert(d_bit);
-					} else
-						sigbit_chain_next[d_bit] = cell;
+						// ... and clone d_bit into another wire, and use that
+						// wire as a different key in the d_bit-to-cell dictionary
+						// so that it can be identified as another chain
+						// (omitting this common flop)
+						// Link: https://github.com/YosysHQ/yosys/pull/1085
+						Wire *wire = module->addWire(NEW_ID);
+						module->connect(wire, d_bit);
+						sigmap.add(wire, d_bit);
+						sigbit_chain_next.insert(std::make_pair(wire, cell));
+					}
 
 					sigbit_chain_prev[q_bit] = cell;
 					continue;

tests/various/shregmap.v

@@ -0,0 +1,48 @@
+module shregmap_static_test(input i, clk, output [1:0] q);
+reg head = 1'b0;
+reg [3:0] shift1 = 4'b0000;
+reg [3:0] shift2 = 4'b0000;
+
+always @(posedge clk) begin
+    head <= i;
+    shift1 <= {shift1[2:0], head};
+    shift2 <= {shift2[2:0], head};
+end
+
+assign q = {shift2[3], shift1[3]};
+endmodule
+
+module $__SHREG_DFF_P_(input C, D, output Q);
+parameter DEPTH = 1;
+parameter [DEPTH-1:0] INIT = {DEPTH{1'b0}};
+reg [DEPTH-1:0] r = INIT;
+always @(posedge C) 
+    r <= { r[DEPTH-2:0], D };
+assign Q = r[DEPTH-1];
+endmodule
+
+module shregmap_variable_test(input i, clk, input [1:0] l1, l2, output [1:0] q);
+reg head = 1'b0;
+reg [3:0] shift1 = 4'b0000;
+reg [3:0] shift2 = 4'b0000;
+
+always @(posedge clk) begin
+    head <= i;
+    shift1 <= {shift1[2:0], head};
+    shift2 <= {shift2[2:0], head};
+end
+
+assign q = {shift2[l2], shift1[l1]};
+endmodule
+
+module $__XILINX_SHREG_(input C, D, input [1:0] L, output Q);
+parameter CLKPOL = 1;
+parameter ENPOL = 1;
+parameter DEPTH = 1;
+parameter [DEPTH-1:0] INIT = {DEPTH{1'b0}};
+reg [DEPTH-1:0] r = INIT;
+wire clk = C ^ CLKPOL;
+always @(posedge C)
+    r <= { r[DEPTH-2:0], D };
+assign Q = r[L];
+endmodule

tests/various/shregmap.ys

@@ -0,0 +1,66 @@
+read_verilog shregmap.v
+design -save read
+
+design -copy-to model $__SHREG_DFF_P_
+hierarchy -top shregmap_static_test
+prep
+design -save gold
+
+techmap
+shregmap -init
+
+opt
+
+stat
+# show -width
+select -assert-count 1 t:$_DFF_P_
+select -assert-count 2 t:$__SHREG_DFF_P_
+
+design -stash gate
+
+design -import gold -as gold
+design -import gate -as gate
+design -copy-from model -as $__SHREG_DFF_P_ \$__SHREG_DFF_P_
+prep
+
+miter -equiv -flatten -make_assert -make_outputs gold gate miter
+sat -verify -prove-asserts -show-ports -seq 5 miter
+
+design -load gold
+stat
+
+design -load gate
+stat
+
+##########
+
+design -load read
+design -copy-to model $__XILINX_SHREG_
+hierarchy -top shregmap_variable_test
+prep
+design -save gold
+
+simplemap t:$dff t:$dffe
+shregmap -tech xilinx
+
+stat
+# show -width
+write_verilog -noexpr -norename
+select -assert-count 1 t:$_DFF_P_
+select -assert-count 2 t:$__XILINX_SHREG_
+
+design -stash gate
+
+design -import gold -as gold
+design -import gate -as gate
+design -copy-from model -as $__XILINX_SHREG_ \$__XILINX_SHREG_
+prep
+
+miter -equiv -flatten -make_assert -make_outputs gold gate miter
+sat -verify -prove-asserts -show-ports -seq 5 miter
+
+design -load gold
+stat
+
+design -load gate
+stat