Merge pull request #1035 from YosysHQ/eddie/opt_rmdff

opt_rmdff to work on $dffe and $_DFFE_*

3 files changed, 144 insertions, 4 deletions

diff --git a/passes/opt/opt_rmdff.cc b/passes/opt/opt_rmdff.cc
index e8570f0eb..2abffa2a9 100644
--- a/passes/opt/opt_rmdff.cc
+++ b/passes/opt/opt_rmdff.cc
@@ -260,8 +260,8 @@ delete_dlatch:
 
 bool handle_dff(RTLIL::Module *mod, RTLIL::Cell *dff)
 {
-	RTLIL::SigSpec sig_d, sig_q, sig_c, sig_r;
-	RTLIL::Const val_cp, val_rp, val_rv;
+	RTLIL::SigSpec sig_d, sig_q, sig_c, sig_r, sig_e;
+	RTLIL::Const val_cp, val_rp, val_rv, val_ep;
 
 	if (dff->type == "$_FF_") {
 		sig_d = dff->getPort("\\D");
@@ -285,6 +285,16 @@ bool handle_dff(RTLIL::Module *mod, RTLIL::Cell *dff)
 		val_rp = RTLIL::Const(dff->type[7] == 'P', 1);
 		val_rv = RTLIL::Const(dff->type[8] == '1', 1);
 	}
+	else if (dff->type.substr(0,7) == "$_DFFE_" && dff->type.substr(9) == "_" &&
+			(dff->type[7] == 'N' || dff->type[7] == 'P') &&
+			(dff->type[8] == 'N' || dff->type[8] == 'P')) {
+		sig_d = dff->getPort("\\D");
+		sig_q = dff->getPort("\\Q");
+		sig_c = dff->getPort("\\C");
+		sig_e = dff->getPort("\\E");
+		val_cp = RTLIL::Const(dff->type[6] == 'P', 1);
+		val_ep = RTLIL::Const(dff->type[7] == 'P', 1);
+	}
 	else if (dff->type == "$ff") {
 		sig_d = dff->getPort("\\D");
 		sig_q = dff->getPort("\\Q");
@@ -295,6 +305,14 @@ bool handle_dff(RTLIL::Module *mod, RTLIL::Cell *dff)
 		sig_c = dff->getPort("\\CLK");
 		val_cp = RTLIL::Const(dff->parameters["\\CLK_POLARITY"].as_bool(), 1);
 	}
+	else if (dff->type == "$dffe") {
+		sig_e = dff->getPort("\\EN");
+		sig_d = dff->getPort("\\D");
+		sig_q = dff->getPort("\\Q");
+		sig_c = dff->getPort("\\CLK");
+		val_cp = RTLIL::Const(dff->parameters["\\CLK_POLARITY"].as_bool(), 1);
+		val_ep = RTLIL::Const(dff->parameters["\\EN_POLARITY"].as_bool(), 1);
+	}
 	else if (dff->type == "$adff") {
 		sig_d = dff->getPort("\\D");
 		sig_q = dff->getPort("\\Q");
@@ -337,39 +355,60 @@ bool handle_dff(RTLIL::Module *mod, RTLIL::Cell *dff)
 		}
 	}
 
+	// If clock is driven by a constant and (i) no reset signal
+	//                                      (ii) Q has no initial value
+	//                                      (iii) initial value is same as reset value
 	if (!sig_c.empty() && sig_c.is_fully_const() && (!sig_r.size() || !has_init || val_init == val_rv)) {
 		if (val_rv.bits.size() == 0)
 			val_rv = val_init;
+		// Q is permanently reset value or initial value
 		mod->connect(sig_q, val_rv);
 		goto delete_dff;
 	}
 
+	// If D is fully undefined and reset signal present and (i) Q has no initial value
+	//                                                     (ii) initial value is same as reset value
 	if (sig_d.is_fully_undef() && sig_r.size() && (!has_init || val_init == val_rv)) {
+		// Q is permanently reset value
 		mod->connect(sig_q, val_rv);
 		goto delete_dff;
 	}
 
+	// If D is fully undefined and no reset signal and Q has an initial value
 	if (sig_d.is_fully_undef() && !sig_r.size() && has_init) {
+		// Q is permanently initial value
 		mod->connect(sig_q, val_init);
 		goto delete_dff;
 	}
 
+	// If D is fully constant and (i) no reset signal
+	//                            (ii) reset value is same as constant D
+	//                        and (a) has no initial value
+	//                            (b) initial value same as constant D
 	if (sig_d.is_fully_const() && (!sig_r.size() || val_rv == sig_d.as_const()) && (!has_init || val_init == sig_d.as_const())) {
+		// Q is permanently D
 		mod->connect(sig_q, sig_d);
 		goto delete_dff;
 	}
 
+	// If D input is same as Q output and (i) no reset signal
+	//                                    (ii) no initial signal
+	//                                    (iii) initial value is same as reset value
 	if (sig_d == sig_q && (sig_r.empty() || !has_init || val_init == val_rv)) {
+		// Q is permanently reset value or initial value
 		if (sig_r.size())
 			mod->connect(sig_q, val_rv);
-		if (has_init)
+		else if (has_init)
 			mod->connect(sig_q, val_init);
 		goto delete_dff;
 	}
 
+	// If reset signal is present, and is fully constant
 	if (!sig_r.empty() && sig_r.is_fully_const())
 	{
+		// If reset value is permanently active or if reset is undefined
 		if (sig_r == val_rp || sig_r.is_fully_undef()) {
+			// Q is permanently reset value
 			mod->connect(sig_q, val_rv);
 			goto delete_dff;
 		}
@@ -389,6 +428,30 @@ bool handle_dff(RTLIL::Module *mod, RTLIL::Cell *dff)
 		dff->unsetPort("\\R");
 	}
 
+	// If enable signal is present, and is fully constant
+	if (!sig_e.empty() && sig_e.is_fully_const())
+	{
+		// If enable value is permanently inactive
+		if (sig_e != val_ep) {
+			// Q is permanently initial value
+			mod->connect(sig_q, val_init);
+			goto delete_dff;
+		}
+
+		log("Removing unused enable from %s (%s) from module %s.\n", log_id(dff), log_id(dff->type), log_id(mod));
+
+		if (dff->type == "$dffe") {
+			dff->type = "$dff";
+			dff->unsetPort("\\EN");
+			dff->unsetParam("\\EN_POLARITY");
+			return true;
+		}
+
+		log_assert(dff->type.substr(0,7) == "$_DFFE_");
+		dff->type = stringf("$_DFF_%c_", + dff->type[7]);
+		dff->unsetPort("\\E");
+	}
+
 	return false;
 
 delete_dff:
@@ -489,7 +552,8 @@ struct OptRmdffPass : public Pass {
 				if (cell->type.in("$_FF_", "$_DFF_N_", "$_DFF_P_",
 						"$_DFF_NN0_", "$_DFF_NN1_", "$_DFF_NP0_", "$_DFF_NP1_",
 						"$_DFF_PN0_", "$_DFF_PN1_", "$_DFF_PP0_", "$_DFF_PP1_",
-						"$ff", "$dff", "$adff"))
+						"$_DFFE_NN_", "$_DFFE_NP_", "$_DFFE_PN_", "$_DFFE_PP_",
+						"$ff", "$dff", "$dffe", "$adff"))
 					dff_list.push_back(cell->name);
 
 				if (cell->type.in("$dlatch", "$_DLATCH_P_", "$_DLATCH_N_"))
diff --git a/tests/various/opt_rmdff.v b/tests/various/opt_rmdff.v
new file mode 100644
index 000000000..b1c06703c
--- /dev/null
+++ b/tests/various/opt_rmdff.v
@@ -0,0 +1,50 @@
+module opt_rmdff_test (input C, input D, input E, output [29:0] Q);
+\$dffe #(.WIDTH(1), .CLK_POLARITY(1), .EN_POLARITY(1)) remove0 (.CLK(C), .D(D), .EN(1'b0), .Q(Q[0])); // EN is never active
+(* init = "1'b1" *) wire Q1; assign Q[1] = Q1;
+\$dffe #(.WIDTH(1), .CLK_POLARITY(1), .EN_POLARITY(1)) remove1 (.CLK(C), .D(D), .EN(1'b0), .Q(Q1)); // EN is never active
+\$dffe #(.WIDTH(1), .CLK_POLARITY(1), .EN_POLARITY(1)) remove2 (.CLK(C), .D(D), .EN(1'bx), .Q(Q[2])); // EN is don't care
+\$dffe #(.WIDTH(1), .CLK_POLARITY(1), .EN_POLARITY(1)) keep3 (.CLK(C), .D(D), .EN(1'b1), .Q(Q[3])); // EN is always active
+(* init = "1'b0" *) wire Q4; assign Q[4] = Q4;
+\$dffe #(.WIDTH(1), .CLK_POLARITY(0), .EN_POLARITY(1)) keep4 (.CLK(C), .D(D), .EN(1'b1), .Q(Q4)); // EN is always active
+\$dffe #(.WIDTH(1), .CLK_POLARITY(1), .EN_POLARITY(0)) remove5 (.CLK(C), .D(D), .EN(1'b1), .Q(Q[5])); // EN is never active
+\$dffe #(.WIDTH(1), .CLK_POLARITY(1), .EN_POLARITY(0)) remove6 (.CLK(C), .D(D), .EN(1'bx), .Q(Q[6])); // EN is don't care
+(* init = "1'b0" *) wire Q7; assign Q[7] = Q7;
+\$dffe #(.WIDTH(1), .CLK_POLARITY(0), .EN_POLARITY(0)) keep7 (.CLK(C), .D(D), .EN(E), .Q(Q7)); // EN is non constant
+
+\$_DFFE_PP_ remove8 (.C(C), .D(D), .E(1'b0), .Q(Q[8])); // EN is never active
+(* init = "1'b1" *) wire Q9; assign Q[9] = Q9;
+\$_DFFE_PP_ remove9 (.C(C), .D(D), .E(1'b0), .Q(Q9)); // EN is never active
+\$_DFFE_PP_ remove10 (.C(C), .D(D), .E(1'bx), .Q(Q[10])); // EN is don't care
+\$_DFFE_PP_ keep11 (.C(C), .D(D), .E(1'b1), .Q(Q[11])); // EN is always active
+(* init = "1'b0" *) wire Q12; assign Q[12] = Q12;
+\$_DFFE_PP_ keep12 (.C(C), .D(D), .E(1'b1), .Q(Q12)); // EN is always active
+
+\$_DFFE_NN_ remove13 (.C(C), .D(D), .E(1'b1), .Q(Q[13])); // EN is never active
+(* init = "1'b1" *) wire Q14; assign Q[14] = Q14;
+\$_DFFE_NN_ remove14 (.C(C), .D(D), .E(1'b1), .Q(Q14)); // EN is never active
+\$_DFFE_NN_ remove15 (.C(C), .D(D), .E(1'bx), .Q(Q[15])); // EN is don't care
+\$_DFFE_NN_ keep16 (.C(C), .D(D), .E(1'b0), .Q(Q[16])); // EN is always active
+(* init = "1'b0" *) wire Q17; assign Q[17] = Q17;
+\$_DFFE_NN_ keep17 (.C(C), .D(D), .E(1'b0), .Q(Q17)); // EN is always active
+
+\$dffe #(.WIDTH(1), .CLK_POLARITY(1), .EN_POLARITY(1)) remove18 (.CLK(1'b0), .D(D), .EN(E), .Q(Q[18])); // CLK is constant
+(* init = "1'b1" *) wire Q19; assign Q[19] = Q19;
+\$dffe #(.WIDTH(1), .CLK_POLARITY(1), .EN_POLARITY(1)) remove19 (.CLK(1'b1), .D(D), .EN(E), .Q(Q19)); // CLK is constant
+\$dffe #(.WIDTH(1), .CLK_POLARITY(1), .EN_POLARITY(1)) remove20 (.CLK(C), .D(1'bx), .EN(E), .Q(Q[20])); // D is undriven, Q has no initial value
+(* init = "1'b0" *) wire Q21; assign Q[21] = Q21;
+\$dffe #(.WIDTH(1), .CLK_POLARITY(1), .EN_POLARITY(1)) keep21 (.CLK(C), .D(1'bx), .EN(E), .Q(Q21)); // D is undriven, Q has initial value
+//\$dffe #(.WIDTH(1), .CLK_POLARITY(0), .EN_POLARITY(1)) remove22 (.CLK(C), .D(1'b0), .EN(1'b1), .Q(Q[22])); // D is constant, no initial Q value, EN is always active
+//                                                                                                           // (TODO, Q starts with 1'bx and becomes 1'b0)
+(* init = "1'b0" *) wire Q23; assign Q[23] = Q23;
+\$dffe #(.WIDTH(1), .CLK_POLARITY(1), .EN_POLARITY(1)) noenable23 (.CLK(C), .D(1'b0), .EN(1'b1), .Q(Q23)); // D is constant, initial Q value same as D, EN is always active
+(* init = "1'b1" *) wire Q24; assign Q[24] = Q24;
+\$dffe #(.WIDTH(1), .CLK_POLARITY(1), .EN_POLARITY(0)) keep24 (.CLK(C), .D(1'b0), .EN(1'b0), .Q(Q24)); // D is constant, initial Q value NOT same as D, EN is always active
+(* init = "1'b1" *) wire Q25; assign Q[25] = Q25;
+\$dffe #(.WIDTH(1), .CLK_POLARITY(1), .EN_POLARITY(0)) remove25 (.CLK(C), .D(1'b0), .EN(1'b1), .Q(Q25)); // D is constant, EN is never active
+\$dffe #(.WIDTH(1), .CLK_POLARITY(1), .EN_POLARITY(1)) remove26 (.CLK(C), .D(Q[26]), .EN(1'b1), .Q(Q[26])); // D is Q, EN is always active
+\$dffe #(.WIDTH(1), .CLK_POLARITY(1), .EN_POLARITY(0)) remove27 (.CLK(C), .D(Q[27]), .EN(1'b1), .Q(Q[27])); // D is Q, EN is never active, but no initial value
+\$dffe #(.WIDTH(1), .CLK_POLARITY(1), .EN_POLARITY(0)) remove28 (.CLK(C), .D(Q[28]), .EN(E), .Q(Q[28])); // EN is nonconst, but no initial value
+(* init = "1'b1" *) wire Q29; assign Q[29] = Q29;
+\$dffe #(.WIDTH(1), .CLK_POLARITY(1), .EN_POLARITY(1)) keep29 (.CLK(C), .D(Q[29]), .EN(1'b1), .Q(Q29)); // EN is always active, but with initial value
+
+endmodule
diff --git a/tests/various/opt_rmdff.ys b/tests/various/opt_rmdff.ys
new file mode 100644
index 000000000..081f81782
--- /dev/null
+++ b/tests/various/opt_rmdff.ys
@@ -0,0 +1,26 @@
+read_verilog -icells opt_rmdff.v
+prep
+design -stash gold
+read_verilog -icells opt_rmdff.v
+proc
+opt_rmdff
+
+select -assert-count 0 c:remove*
+select -assert-min 7 c:keep*
+select -assert-count 0  t:$dffe 7:$_DFFE_* %u c:noenable* %i
+
+design -stash gate
+
+design -import gold -as gold
+design -import gate -as gate
+
+equiv_make gold gate equiv
+hierarchy -top equiv
+equiv_simple -undef
+equiv_status -assert
+
+design -load gold
+stat
+
+design -load gate
+stat