22 files changed, 1303 insertions, 30 deletions
diff --git a/tests/opt/.gitignore b/tests/opt/.gitignore
index 397b4a762..8355de9dc 100644
--- a/tests/opt/.gitignore
+++ b/tests/opt/.gitignore
@@ -1 +1,2 @@
 *.log
+run-test.mk
diff --git a/tests/opt/bug2221.ys b/tests/opt/bug2221.ys
new file mode 100644
index 000000000..8ac380243
--- /dev/null
+++ b/tests/opt/bug2221.ys
@@ -0,0 +1,16 @@
+read_verilog <<EOT
+module test (
+        input [1:0] a,
+        input [1:0] b,
+        output [5:0] y
+);
+
+wire [5:0] aa = {a, 4'h0};
+wire [5:0] bb = {b, 4'h0};
+
+assign y = aa * bb;
+
+endmodule
+EOT
+
+equiv_opt -assert opt_expr
diff --git a/tests/opt/bug2311.ys b/tests/opt/bug2311.ys
new file mode 100644
index 000000000..455147cd3
--- /dev/null
+++ b/tests/opt/bug2311.ys
@@ -0,0 +1,14 @@
+read_verilog -icells << EOT
+
+module top(...);
+
+input A;
+output Y;
+
+$_XNOR_ x (.A(A), .B(A), .Y(Y));
+
+endmodule
+
+EOT
+
+equiv_opt -assert opt_expr
diff --git a/tests/opt/bug2318.ys b/tests/opt/bug2318.ys
new file mode 100644
index 000000000..9de6f88ec
--- /dev/null
+++ b/tests/opt/bug2318.ys
@@ -0,0 +1,12 @@
+read_verilog <<EOT
+module t(input [3:0] A, input [3:0] B, output signed [3:0] Y);
+
+wire [7:0] P = A * B;
+wire signed [7:0] SP = P;
+wire signed [3:0] SB = B;
+assign Y = SP / SB;
+
+endmodule
+EOT
+
+equiv_opt -assert peepopt
diff --git a/tests/opt/opt_clean_mem.ys b/tests/opt/opt_clean_mem.ys
new file mode 100644
index 000000000..b35b15871
--- /dev/null
+++ b/tests/opt/opt_clean_mem.ys
@@ -0,0 +1,49 @@
+read_verilog <<EOT
+module top(...);
+
+input [7:0] wa;
+input [7:0] ra1;
+input [7:0] ra2;
+input [7:0] wd;
+input clk;
+wire [7:0] rd1;
+wire [7:0] rd2;
+
+reg [7:0] mem[0:7];
+
+always @(posedge clk)
+	mem[wa] <= wd;
+assign rd1 = mem[ra1];
+assign rd2 = mem[ra2];
+
+initial mem[8'h12] = 8'h34;
+
+endmodule
+EOT
+
+proc
+memory_dff
+
+select -assert-count 2 t:$memrd
+select -assert-count 1 t:$memwr
+select -assert-count 1 t:$meminit
+design -save orig
+
+opt_clean
+select -assert-none t:$memrd
+select -assert-none t:$memwr
+select -assert-none t:$meminit
+
+design -load orig
+expose top/rd1
+opt_clean
+select -assert-count 1 t:$memrd
+select -assert-count 1 t:$memwr
+select -assert-count 1 t:$meminit
+
+design -load orig
+expose top/rd1 top/rd2
+opt_clean
+select -assert-count 2 t:$memrd
+select -assert-count 1 t:$memwr
+select -assert-count 1 t:$meminit
diff --git a/tests/opt/opt_dff_arst.ys b/tests/opt/opt_dff_arst.ys
new file mode 100644
index 000000000..2aa3b7a26
--- /dev/null
+++ b/tests/opt/opt_dff_arst.ys
@@ -0,0 +1,101 @@
+### Always-active ARST removal.
+
+read_verilog -icells <<EOT
+
+module top(...);
+
+input CLK;
+input [1:0] D;
+output [11:0] Q;
+input ARST;
+input EN;
+
+$adff #(.CLK_POLARITY(1'b1), .ARST_POLARITY(1'b1), .ARST_VALUE(2'h2), .WIDTH(2)) ff0 (.CLK(CLK), .ARST(1'b1), .D(D), .Q(Q[1:0]));
+$adffe #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b1), .ARST_POLARITY(1'b0), .ARST_VALUE(2'h2), .WIDTH(2)) ff1 (.CLK(CLK), .ARST(1'b0), .EN(EN), .D(D), .Q(Q[3:2]));
+$adlatch #(.EN_POLARITY(1'b1), .ARST_POLARITY(1'b1), .ARST_VALUE(2'h2), .WIDTH(2)) ff2 (.EN(EN), .ARST(1'b1), .D(D), .Q(Q[5:4]));
+$adff #(.CLK_POLARITY(1'b1), .ARST_POLARITY(1'b1), .ARST_VALUE(2'h2), .WIDTH(2)) ff3 (.CLK(CLK), .ARST(1'bx), .D(D), .Q(Q[7:6]));
+$adffe #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b1), .ARST_POLARITY(1'b0), .ARST_VALUE(2'h2), .WIDTH(2)) ff4 (.CLK(CLK), .ARST(1'bx), .EN(EN), .D(D), .Q(Q[9:8]));
+$adlatch #(.EN_POLARITY(1'b1), .ARST_POLARITY(1'b1), .ARST_VALUE(2'h2), .WIDTH(2)) ff5 (.EN(EN), .ARST(1'bx), .D(D), .Q(Q[11:10]));
+
+
+endmodule
+
+EOT
+
+design -save orig
+
+equiv_opt -undef -assert -multiclock opt_dff
+design -load postopt
+select -assert-none t:*
+
+design -load orig
+
+equiv_opt -undef -assert -multiclock opt_dff -keepdc
+design -load postopt
+select -assert-count 1 t:$adff
+select -assert-count 1 t:$adffe
+select -assert-count 1 t:$adlatch
+
+design -load orig
+simplemap
+
+equiv_opt -undef -assert -multiclock opt_dff
+design -load postopt
+select -assert-none t:*
+
+design -load orig
+simplemap
+
+equiv_opt -undef -assert -multiclock opt_dff -keepdc
+design -load postopt
+select -assert-count 2 t:$_DFF_???_
+select -assert-count 2 t:$_DFFE_????_
+select -assert-count 2 t:$_DLATCH_???_
+
+design -reset
+
+
+### Never-active ARST removal.
+
+read_verilog -icells <<EOT
+
+module top(...);
+
+input CLK;
+input [1:0] D;
+output [5:0] Q;
+input ARST;
+input EN;
+
+$adff #(.CLK_POLARITY(1'b1), .ARST_POLARITY(1'b1), .ARST_VALUE(2'h2), .WIDTH(2)) ff0 (.CLK(CLK), .ARST(1'b0), .D(D), .Q(Q[1:0]));
+$adffe #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b1), .ARST_POLARITY(1'b0), .ARST_VALUE(2'h2), .WIDTH(2)) ff1 (.CLK(CLK), .ARST(1'b1), .EN(EN), .D(D), .Q(Q[3:2]));
+$adlatch #(.EN_POLARITY(1'b1), .ARST_POLARITY(1'b1), .ARST_VALUE(2'h2), .WIDTH(2)) ff2 (.EN(EN), .ARST(1'b0), .D(D), .Q(Q[5:4]));
+
+endmodule
+
+EOT
+
+design -save orig
+
+equiv_opt -undef -assert -multiclock opt_dff
+design -load postopt
+select -assert-none t:$adff
+select -assert-none t:$adffe
+select -assert-none t:$adlatch
+select -assert-count 1 t:$dff
+select -assert-count 1 t:$dffe
+select -assert-count 1 t:$dlatch
+
+design -load orig
+simplemap
+
+equiv_opt -undef -assert -multiclock opt_dff
+design -load postopt
+select -assert-none t:$_DFF_???_
+select -assert-none t:$_DFFE_????_
+select -assert-none t:$_DLATCH_???_
+select -assert-count 2 t:$_DFF_P_
+select -assert-count 2 t:$_DFFE_PP_
+select -assert-count 2 t:$_DLATCH_P_
+
+design -reset
diff --git a/tests/opt/opt_dff_clk.ys b/tests/opt/opt_dff_clk.ys
new file mode 100644
index 000000000..f3aefa406
--- /dev/null
+++ b/tests/opt/opt_dff_clk.ys
@@ -0,0 +1,45 @@
+### Never-toggling CLK removal.
+
+read_verilog -icells <<EOT
+
+module top(...);
+
+input EN;
+input [1:0] D;
+(* init = 18'h15555 *)
+output [17:0] Q;
+input SRST;
+input ARST;
+input [1:0] CLR;
+input [1:0] SET;
+
+$dff #(.CLK_POLARITY(1'b1), .WIDTH(2)) ff0 (.CLK(1'b0), .D(D), .Q(Q[1:0]));
+$dffe #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b1), .WIDTH(2)) ff1 (.CLK(1'b1), .EN(EN), .D(D), .Q(Q[3:2]));
+$adff #(.CLK_POLARITY(1'b1), .ARST_POLARITY(1'b1), .ARST_VALUE(2'h2), .WIDTH(2)) ff2 (.CLK(1'bx), .ARST(ARST), .D(D), .Q(Q[5:4]));
+$adffe #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b0), .ARST_POLARITY(1'b1), .ARST_VALUE(2'h2), .WIDTH(2)) ff3 (.CLK(1'b0), .EN(EN), .ARST(ARST), .D(D), .Q(Q[7:6]));
+$sdff #(.CLK_POLARITY(1'b1), .SRST_POLARITY(1'b1), .SRST_VALUE(2'h2), .WIDTH(2)) ff4 (.CLK(1'b1), .SRST(SRST), .D(D), .Q(Q[9:8]));
+$sdffe #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b1), .SRST_POLARITY(1'b1), .SRST_VALUE(2'h2), .WIDTH(2)) ff5 (.CLK(1'bx), .EN(EN), .SRST(SRST), .D(D), .Q(Q[11:10]));
+$sdffce #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b1), .SRST_POLARITY(1'b1), .SRST_VALUE(2'h2), .WIDTH(2)) ff6 (.CLK(1'bx), .EN(EN), .SRST(SRST), .D(D), .Q(Q[13:12]));
+$dffsr #(.CLK_POLARITY(1'b1), .CLR_POLARITY(1'b1), .SET_POLARITY(1'b0), .WIDTH(2)) ff7 (.CLK(1'b1), .SET(SET), .CLR(CLR), .D(D), .Q(Q[15:14]));
+$dffsre #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b0), .CLR_POLARITY(1'b1), .SET_POLARITY(1'b0), .WIDTH(2)) ff8 (.CLK(1'bx), .EN(EN), .SET(SET), .CLR(CLR), .D(D), .Q(Q[17:16]));
+
+endmodule
+
+EOT
+
+design -save orig
+
+equiv_opt -undef -assert -multiclock opt_dff -keepdc
+design -load postopt
+select -assert-count 2 t:$dlatch
+select -assert-count 2 t:$sr
+select -assert-none t:$dlatch t:$sr %% %n t:* %i
+
+design -load orig
+simplemap
+
+equiv_opt -undef -assert -multiclock opt_dff -keepdc
+design -load postopt
+select -assert-count 4 t:$_DLATCH_?_
+select -assert-count 4 t:$_SR_??_
+select -assert-none t:$_DLATCH_?_ t:$_SR_??_ %% %n t:* %i
diff --git a/tests/opt/opt_dff_const.ys b/tests/opt/opt_dff_const.ys
new file mode 100644
index 000000000..6a7dec7fa
--- /dev/null
+++ b/tests/opt/opt_dff_const.ys
@@ -0,0 +1,49 @@
+### Replace FFs with a const.
+
+read_verilog -icells <<EOT
+
+module top(...);
+
+input CLK;
+input EN;
+(* init=84'haaaaaaaaaaaaaaaaaaaaa *)
+output [83:0] Q;
+input SRST;
+input ARST;
+input [3:0] CLR;
+input [3:0] SET;
+
+$dff #(.CLK_POLARITY(1'b1), .WIDTH(4)) ff0 (.CLK(CLK), .D(4'hc), .Q(Q[3:0]));
+$dffe #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b1), .WIDTH(4)) ff1 (.CLK(CLK), .EN(EN), .D(4'hc), .Q(Q[7:4]));
+$adff #(.CLK_POLARITY(1'b1), .ARST_POLARITY(1'b1), .ARST_VALUE(8'hf0), .WIDTH(8)) ff2 (.CLK(CLK), .ARST(ARST), .D(8'hcc), .Q(Q[15:8]));
+$adffe #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b0), .ARST_POLARITY(1'b1), .ARST_VALUE(8'hf0), .WIDTH(8)) ff3 (.CLK(CLK), .EN(EN), .ARST(ARST), .D(8'hcc), .Q(Q[23:16]));
+$sdff #(.CLK_POLARITY(1'b1), .SRST_POLARITY(1'b1), .SRST_VALUE(8'hf0), .WIDTH(8)) ff4 (.CLK(CLK), .SRST(SRST), .D(8'hcc), .Q(Q[31:24]));
+$sdffe #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b1), .SRST_POLARITY(1'b1), .SRST_VALUE(8'hf0), .WIDTH(8)) ff5 (.CLK(CLK), .EN(EN), .SRST(SRST), .D(8'hcc), .Q(Q[39:32]));
+$sdffce #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b1), .SRST_POLARITY(1'b1), .SRST_VALUE(8'hf0), .WIDTH(8)) ff6 (.CLK(CLK), .EN(EN), .SRST(SRST), .D(8'hcc), .Q(Q[47:40]));
+$dffsr #(.CLK_POLARITY(1'b1), .CLR_POLARITY(1'b1), .SET_POLARITY(1'b0), .WIDTH(8)) ff7 (.CLK(CLK), .SET({SET, 4'hf}), .CLR({4'h0, CLR}), .D(8'hcc), .Q(Q[55:48]));
+$dffsre #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b0), .CLR_POLARITY(1'b0), .SET_POLARITY(1'b1), .WIDTH(8)) ff8 (.CLK(CLK), .EN(EN), .SET({SET, 4'h0}), .CLR({4'hf, CLR}), .D(8'hcc), .Q(Q[63:56]));
+
+$dlatch #(.EN_POLARITY(1'b1), .WIDTH(4)) ff9 (.EN(EN), .D(4'hc), .Q(Q[67:64]));
+$adlatch #(.EN_POLARITY(1'b0), .ARST_POLARITY(1'b1), .ARST_VALUE(8'hf0), .WIDTH(8)) ff10 (.EN(EN), .ARST(ARST), .D(8'hcc), .Q(Q[75:68]));
+$dlatchsr #(.EN_POLARITY(1'b0), .CLR_POLARITY(1'b1), .SET_POLARITY(1'b1), .WIDTH(8)) ff11 (.EN(EN), .SET({SET, 4'h0}), .CLR({4'h0, CLR}), .D(8'hcc), .Q(Q[83:76]));
+
+endmodule
+
+EOT
+
+design -save orig
+
+equiv_opt -undef -assert -multiclock opt_dff
+design -load postopt
+select -assert-count 1 t:$dff r:WIDTH=2 %i
+select -assert-count 1 t:$dffe r:WIDTH=2 %i
+select -assert-count 1 t:$adff r:WIDTH=6 %i
+select -assert-count 1 t:$adffe r:WIDTH=6 %i
+select -assert-count 1 t:$sdff r:WIDTH=6 %i
+select -assert-count 1 t:$sdffe r:WIDTH=6 %i
+select -assert-count 1 t:$sdffce r:WIDTH=6 %i
+select -assert-count 1 t:$dffsr r:WIDTH=6 %i
+select -assert-count 1 t:$dffsre r:WIDTH=6 %i
+select -assert-count 1 t:$dlatch r:WIDTH=2 %i
+select -assert-count 1 t:$adlatch r:WIDTH=6 %i
+select -assert-count 1 t:$dlatchsr r:WIDTH=6 %i
diff --git a/tests/opt/opt_dff_dffmux.ys b/tests/opt/opt_dff_dffmux.ys
new file mode 100644
index 000000000..43190cc31
--- /dev/null
+++ b/tests/opt/opt_dff_dffmux.ys
@@ -0,0 +1,129 @@
+design -reset
+read_verilog <<EOT
+module opt_dffmuxext_unsigned(input clk, ce, input [1:0] i, output reg [3:0] o);
+    always @(posedge clk) if (ce) o <= i;
+endmodule
+EOT
+
+proc
+equiv_opt -assert opt
+design -load postopt
+select -assert-count 1 t:$dffe r:WIDTH=2 %i
+select -assert-count 0 t:$dffe %% t:* %D
+
+####################
+
+design -reset
+read_verilog <<EOT
+module opt_dffmuxext_signed(input clk, ce, input signed [1:0] i, output reg signed [3:0] o);
+    always @(posedge clk) if (ce) o <= i;
+endmodule
+EOT
+
+proc
+equiv_opt -assert opt
+design -load postopt
+wreduce
+select -assert-count 1 t:$dffe r:WIDTH=2 %i
+select -assert-count 0 t:$dffe %% t:* %D
+
+###################
+
+design -reset
+read_verilog <<EOT
+module opt_dffmuxext_const(input clk, ce, input [1:0] i, output reg [5:0] o);
+    always @(posedge clk) if (ce) o <= {1'b0, i[1], 2'b1x, i[0], 1'bz};
+endmodule
+EOT
+
+proc
+equiv_opt -assert opt
+design -load postopt
+select -assert-count 1 t:$dffe r:WIDTH=2 %i
+select -assert-count 0 t:$dffe %% t:* %D
+
+###################
+
+design -reset
+read_verilog <<EOT
+module opt_dffmuxext_const_init(input clk, ce, input [1:0] i, (* init=6'b0x00x1 *) output reg [5:0] o);
+    always @(posedge clk) if (ce) o <= {1'b0, i[1], 2'b1x, i[0], 1'bz};
+endmodule
+EOT
+
+proc
+equiv_opt -assert opt
+design -load postopt
+select -assert-count 1 t:$dffe r:WIDTH=4 %i
+select -assert-count 0 t:$dffe %% t:* %D
+
+####################
+
+design -reset
+read_verilog <<EOT
+module opt_dffmuxext_unsigned_rst(input clk, ce, rst, input [1:0] i, output reg [3:0] o);
+    always @(posedge clk) if (rst) o <= 0; else if (ce) o <= i;
+endmodule
+EOT
+
+proc
+equiv_opt -assert opt
+design -load postopt
+wreduce
+select -assert-count 1 t:$sdffe r:WIDTH=2 %i
+select -assert-count 0 t:$sdffe %% t:* %D
+
+####################
+
+design -reset
+read_verilog <<EOT
+module opt_dffmuxext_signed_rst(input clk, ce, rstn, input signed [1:0] i, output reg signed [3:0] o);
+    always @(posedge clk) begin
+        if (ce) o <= i;
+        if (!rstn) o <= 4'b1111;
+    end
+endmodule
+EOT
+
+proc
+equiv_opt -assert opt
+design -load postopt
+wreduce
+select -assert-count 1 t:$sdffe r:WIDTH=2 %i
+select -assert-count 0 t:$sdffe %% t:* %D
+
+####################
+
+design -reset
+read_verilog <<EOT
+module opt_dffmuxext_signed_rst_init(input clk, ce, rstn, input signed [1:0] i, output reg signed [3:0] o);
+    initial o <= 4'b0010;
+    always @(posedge clk) begin
+        if (ce) o <= i;
+        if (!rstn) o <= 4'b1111;
+    end
+endmodule
+EOT
+
+proc
+# NB: equiv_opt uses equiv_induct which covers
+#     only the induction half of temporal induction
+#     --- missing the base-case half
+#     This makes it akin to `sat -tempinduct-inductonly`
+#     instead of `sat -tempinduct-baseonly` or
+#     `sat -tempinduct` which is necessary for this
+#     testcase
+#equiv_opt -assert opt
+
+design -save gold
+opt
+wreduce
+design -stash gate
+design -import gold -as gold
+design -import gate -as gate
+miter -equiv -flatten -make_assert -make_outputs gold gate miter
+sat -tempinduct -verify -prove-asserts -show-ports miter
+
+design -load gate
+select -assert-count 1 t:$sdffe r:WIDTH=3 %i
+select -assert-count 0 t:$sdffe %% t:* %D
diff --git a/tests/opt/opt_dff_en.ys b/tests/opt/opt_dff_en.ys
new file mode 100644
index 000000000..06ee6c63d
--- /dev/null
+++ b/tests/opt/opt_dff_en.ys
@@ -0,0 +1,157 @@
+### Always-active EN removal.
+
+read_verilog -icells <<EOT
+
+module top(...);
+
+input CLK;
+input [1:0] D;
+output [15:0] Q;
+input SRST;
+input ARST;
+input [1:0] CLR;
+input [1:0] SET;
+
+$dffe #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b1), .WIDTH(2)) ff0 (.CLK(CLK), .EN(1'b1), .D(D), .Q(Q[1:0]));
+$adffe #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b0), .ARST_POLARITY(1'b1), .ARST_VALUE(2'h2), .WIDTH(2)) ff1 (.CLK(CLK), .EN(1'b0), .ARST(ARST), .D(D), .Q(Q[3:2]));
+$sdffe #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b1), .SRST_POLARITY(1'b1), .SRST_VALUE(2'h2), .WIDTH(2)) ff2 (.CLK(CLK), .EN(1'b1), .SRST(SRST), .D(D), .Q(Q[5:4]));
+$sdffce #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b1), .SRST_POLARITY(1'b1), .SRST_VALUE(2'h2), .WIDTH(2)) ff3 (.CLK(CLK), .EN(1'b1), .SRST(SRST), .D(D), .Q(Q[7:6]));
+$dffsre #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b0), .CLR_POLARITY(1'b1), .SET_POLARITY(1'b0), .WIDTH(2)) ff4 (.CLK(CLK), .EN(1'b0), .SET(SET), .CLR(CLR), .D(D), .Q(Q[9:8]));
+
+$dlatch #(.EN_POLARITY(1'b1), .WIDTH(2)) ff5 (.EN(1'b1), .D(D), .Q(Q[11:10]));
+$adlatch #(.EN_POLARITY(1'b0), .ARST_POLARITY(1'b1), .ARST_VALUE(2'h2), .WIDTH(2)) ff6 (.EN(1'b0), .ARST(ARST), .D(D), .Q(Q[13:12]));
+$dlatchsr #(.EN_POLARITY(1'b0), .CLR_POLARITY(1'b1), .SET_POLARITY(1'b0), .WIDTH(2)) ff7 (.EN(1'b0), .SET(SET), .CLR(CLR), .D(D), .Q(Q[15:14]));
+
+endmodule
+
+EOT
+
+design -save orig
+
+# Equivalence check will fail for unmapped adlatch and dlatchsr due to negative hold hack.
+delete top/ff6 top/ff7
+equiv_opt -undef -assert -multiclock opt_dff
+
+design -load orig
+delete top/ff6 top/ff7
+simplemap
+equiv_opt -undef -assert -multiclock opt_dff
+
+design -load orig
+opt_dff
+select -assert-count 0 t:$dffe
+select -assert-count 0 t:$adffe
+select -assert-count 0 t:$sdffe
+select -assert-count 0 t:$sdffce
+select -assert-count 0 t:$dffsre
+select -assert-count 0 t:$dlatch
+select -assert-count 0 t:$adlatch
+select -assert-count 0 t:$dlatchsr
+select -assert-count 1 t:$dff
+select -assert-count 2 t:$sdff
+select -assert-count 1 t:$adff
+select -assert-count 1 t:$dffsr
+
+design -load orig
+simplemap
+opt_dff
+select -assert-count 0 t:$_DFFE_*
+select -assert-count 0 t:$_SDFFE_*
+select -assert-count 0 t:$_SDFFCE_*
+select -assert-count 0 t:$_DFFSRE_*
+select -assert-count 0 t:$_DLATCH*
+select -assert-count 2 t:$_DFF_P_
+select -assert-count 4 t:$_SDFF_PP?_
+select -assert-count 2 t:$_DFF_PP?_
+select -assert-count 2 t:$_DFFSR_PNP_
+
+design -reset
+
+
+
+### Never-active EN removal.
+
+read_verilog -icells <<EOT
+
+module top(...);
+
+input CLK;
+input [1:0] D;
+(* init = 32'h55555555 *)
+output [31:0] Q;
+input SRST;
+input ARST;
+input [1:0] CLR;
+input [1:0] SET;
+
+$dffe #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b1), .WIDTH(2)) ff0 (.CLK(CLK), .EN(1'b0), .D(D), .Q(Q[1:0]));
+$adffe #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b0), .ARST_POLARITY(1'b1), .ARST_VALUE(2'h2), .WIDTH(2)) ff1 (.CLK(CLK), .EN(1'b1), .ARST(ARST), .D(D), .Q(Q[3:2]));
+$sdffe #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b1), .SRST_POLARITY(1'b1), .SRST_VALUE(2'h2), .WIDTH(2)) ff2 (.CLK(CLK), .EN(1'b0), .SRST(SRST), .D(D), .Q(Q[5:4]));
+$sdffce #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b1), .SRST_POLARITY(1'b1), .SRST_VALUE(2'h2), .WIDTH(2)) ff3 (.CLK(CLK), .EN(1'b0), .SRST(SRST), .D(D), .Q(Q[7:6]));
+$dffsre #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b0), .CLR_POLARITY(1'b1), .SET_POLARITY(1'b0), .WIDTH(2)) ff4 (.CLK(CLK), .EN(1'b1), .SET(SET), .CLR(CLR), .D(D), .Q(Q[9:8]));
+
+$dlatch #(.EN_POLARITY(1'b1), .WIDTH(2)) ff5 (.EN(1'b0), .D(D), .Q(Q[11:10]));
+$adlatch #(.EN_POLARITY(1'b0), .ARST_POLARITY(1'b1), .ARST_VALUE(2'h2), .WIDTH(2)) ff6 (.EN(1'b1), .ARST(ARST), .D(D), .Q(Q[13:12]));
+$dlatchsr #(.EN_POLARITY(1'b0), .CLR_POLARITY(1'b1), .SET_POLARITY(1'b0), .WIDTH(2)) ff7 (.EN(1'b1), .SET(SET), .CLR(CLR), .D(D), .Q(Q[15:14]));
+
+$dffe #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b1), .WIDTH(2)) ff8 (.CLK(CLK), .EN(1'bx), .D(D), .Q(Q[17:16]));
+$adffe #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b0), .ARST_POLARITY(1'b1), .ARST_VALUE(2'h2), .WIDTH(2)) ff9 (.CLK(CLK), .EN(1'bx), .ARST(ARST), .D(D), .Q(Q[19:18]));
+$sdffe #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b1), .SRST_POLARITY(1'b1), .SRST_VALUE(2'h2), .WIDTH(2)) ff10 (.CLK(CLK), .EN(1'bx), .SRST(SRST), .D(D), .Q(Q[21:20]));
+$sdffce #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b1), .SRST_POLARITY(1'b1), .SRST_VALUE(2'h2), .WIDTH(2)) ff11 (.CLK(CLK), .EN(1'bx), .SRST(SRST), .D(D), .Q(Q[23:22]));
+$dffsre #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b0), .CLR_POLARITY(1'b1), .SET_POLARITY(1'b0), .WIDTH(2)) ff12 (.CLK(CLK), .EN(1'bx), .SET(SET), .CLR(CLR), .D(D), .Q(Q[25:24]));
+
+$dlatch #(.EN_POLARITY(1'b1), .WIDTH(2)) ff13 (.EN(1'bx), .D(D), .Q(Q[27:26]));
+$adlatch #(.EN_POLARITY(1'b0), .ARST_POLARITY(1'b1), .ARST_VALUE(2'h2), .WIDTH(2)) ff14 (.EN(1'bx), .ARST(ARST), .D(D), .Q(Q[29:28]));
+$dlatchsr #(.EN_POLARITY(1'b0), .CLR_POLARITY(1'b1), .SET_POLARITY(1'b0), .WIDTH(2)) ff15 (.EN(1'bx), .SET(SET), .CLR(CLR), .D(D), .Q(Q[31:30]));
+
+endmodule
+
+EOT
+
+design -save orig
+
+equiv_opt -undef -assert -multiclock opt_dff
+design -load postopt
+select -assert-count 2 t:$dffe
+select -assert-count 4 t:$dlatch
+select -assert-count 4 t:$sr
+select -assert-none t:$dffe t:$dlatch t:$sr %% %n t:* %i
+
+design -load orig
+
+equiv_opt -undef -assert -multiclock opt_dff -keepdc
+design -load postopt
+select -assert-count 2 t:$dffe
+select -assert-count 1 t:$adffe
+select -assert-count 1 t:$sdffe
+select -assert-count 1 t:$sdffce
+select -assert-count 1 t:$dffsre
+select -assert-count 3 t:$dlatch
+select -assert-count 1 t:$adlatch
+select -assert-count 1 t:$dlatchsr
+select -assert-count 2 t:$sr
+
+design -load orig
+simplemap
+
+equiv_opt -undef -assert -multiclock opt_dff
+design -load postopt
+select -assert-count 4 t:$_DFFE_??_
+select -assert-count 8 t:$_DLATCH_?_
+select -assert-count 8 t:$_SR_??_
+select -assert-none t:$_DFFE_??_ t:$_DLATCH_?_ t:$_SR_??_ %% %n t:* %i
+
+design -load orig
+simplemap
+
+equiv_opt -undef -assert -multiclock opt_dff -keepdc
+design -load postopt
+select -assert-count 4 t:$_DFFE_??_
+select -assert-count 2 t:$_DFFE_????_
+select -assert-count 2 t:$_SDFFE_????_
+select -assert-count 2 t:$_SDFFCE_????_
+select -assert-count 2 t:$_DFFSRE_????_
+select -assert-count 6 t:$_DLATCH_?_
+select -assert-count 2 t:$_DLATCH_???_
+select -assert-count 2 t:$_DLATCHSR_???_
+select -assert-count 4 t:$_SR_??_
diff --git a/tests/opt/opt_dff_mux.ys b/tests/opt/opt_dff_mux.ys
new file mode 100644
index 000000000..ed01bed59
--- /dev/null
+++ b/tests/opt/opt_dff_mux.ys
@@ -0,0 +1,86 @@
+### CE and SRST matching.
+
+read_verilog -icells <<EOT
+
+module top(...);
+
+input CLK;
+input NE, NS;
+input EN;
+output [23:0] Q;
+input [23:0] D;
+input SRST;
+input ARST;
+input [1:0] CLR;
+input [1:0] SET;
+
+$dff #(.CLK_POLARITY(1'b1), .WIDTH(2)) ff0 (.CLK(CLK), .D(NS ? 2'h2 : NE ? D[1:0] : Q[1:0]), .Q(Q[1:0]));
+$dffe #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b1), .WIDTH(2)) ff1 (.CLK(CLK), .EN(EN), .D(NS ? 2'h2 : NE ? D[3:2] : Q[3:2]), .Q(Q[3:2]));
+$adff #(.CLK_POLARITY(1'b1), .ARST_POLARITY(1'b1), .ARST_VALUE(2'h2), .WIDTH(2)) ff2 (.CLK(CLK), .ARST(ARST), .D(NS ? 2'h2 : NE ? D[5:4] : Q[5:4]), .Q(Q[5:4]));
+$adffe #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b0), .ARST_POLARITY(1'b1), .ARST_VALUE(2'h2), .WIDTH(2)) ff3 (.CLK(CLK), .EN(EN), .ARST(ARST), .D(NS ? 2'h2 : NE ? D[7:6] : Q[7:6]), .Q(Q[7:6]));
+$sdff #(.CLK_POLARITY(1'b1), .SRST_POLARITY(1'b1), .SRST_VALUE(2'h2), .WIDTH(2)) ff4 (.CLK(CLK), .SRST(SRST), .D(NS ? 2'h2 : NE ? D[9:8] : Q[9:8]), .Q(Q[9:8]));
+$sdffe #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b1), .SRST_POLARITY(1'b1), .SRST_VALUE(2'h2), .WIDTH(2)) ff5 (.CLK(CLK), .EN(EN), .SRST(SRST), .D(NS ? 2'h2 : NE ? D[11:10] : Q[11:10]), .Q(Q[11:10]));
+$sdffce #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b1), .SRST_POLARITY(1'b1), .SRST_VALUE(2'h2), .WIDTH(2)) ff6 (.CLK(CLK), .EN(EN), .SRST(SRST), .D(NS ? 2'h2 : NE ? D[13:12] : Q[13:12]), .Q(Q[13:12]));
+$dffsr #(.CLK_POLARITY(1'b1), .CLR_POLARITY(1'b1), .SET_POLARITY(1'b0), .WIDTH(2)) ff7 (.CLK(CLK), .SET(SET), .CLR(CLR), .D(NS ? 2'h2 : NE ? D[15:14] : Q[15:14]), .Q(Q[15:14]));
+$dffsre #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b0), .CLR_POLARITY(1'b1), .SET_POLARITY(1'b0), .WIDTH(2)) ff8 (.CLK(CLK), .EN(EN), .SET(SET), .CLR(CLR), .D(NS ? 2'h2 : NE ? D[17:16] : Q[17:16]), .Q(Q[17:16]));
+
+endmodule
+
+EOT
+
+design -save orig
+
+equiv_opt -undef -assert -multiclock opt_dff -keepdc
+design -load postopt
+clean
+select -assert-count 0 t:$dff
+select -assert-count 0 t:$dffe
+select -assert-count 0 t:$adff
+select -assert-count 2 t:$adffe
+select -assert-count 0 t:$dffsr
+select -assert-count 2 t:$dffsre
+select -assert-count 0 t:$sdff
+select -assert-count 3 t:$sdffe
+select -assert-count 2 t:$sdffce
+
+design -load orig
+
+equiv_opt -undef -assert -multiclock opt_dff -nodffe -nosdff
+design -load postopt
+clean
+select -assert-count 1 t:$dff
+select -assert-count 1 t:$dffe
+select -assert-count 1 t:$adff
+select -assert-count 1 t:$adffe
+select -assert-count 1 t:$dffsr
+select -assert-count 1 t:$dffsre
+select -assert-count 1 t:$sdff
+select -assert-count 1 t:$sdffe
+select -assert-count 1 t:$sdffce
+equiv_opt -undef -assert -multiclock opt_dff -nodffe
+design -load postopt
+clean
+select -assert-count 0 t:$dff
+select -assert-count 0 t:$dffe
+select -assert-count 1 t:$adff
+select -assert-count 1 t:$adffe
+select -assert-count 1 t:$dffsr
+select -assert-count 1 t:$dffsre
+select -assert-count 2 t:$sdff
+select -assert-count 1 t:$sdffe
+select -assert-count 2 t:$sdffce
+
+design -load orig
+
+equiv_opt -undef -assert -multiclock opt_dff -nosdff
+design -load postopt
+clean
+select -assert-count 0 t:$dff
+select -assert-count 2 t:$dffe
+select -assert-count 0 t:$adff
+select -assert-count 2 t:$adffe
+select -assert-count 0 t:$dffsr
+select -assert-count 2 t:$dffsre
+select -assert-count 0 t:$sdff
+select -assert-count 2 t:$sdffe
+select -assert-count 1 t:$sdffce
diff --git a/tests/opt/opt_dff_qd.ys b/tests/opt/opt_dff_qd.ys
new file mode 100644
index 000000000..afc96c42f
--- /dev/null
+++ b/tests/opt/opt_dff_qd.ys
@@ -0,0 +1,56 @@
+### Q = D case.
+
+read_verilog -icells <<EOT
+
+module top(...);
+
+input CLK;
+input EN;
+(* init = 24'h555555 *)
+output [23:0] Q;
+input SRST;
+input ARST;
+input [1:0] CLR;
+input [1:0] SET;
+
+$dff #(.CLK_POLARITY(1'b1), .WIDTH(2)) ff0 (.CLK(CLK), .D(Q[1:0]), .Q(Q[1:0]));
+$dffe #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b1), .WIDTH(2)) ff1 (.CLK(CLK), .EN(EN), .D(Q[3:2]), .Q(Q[3:2]));
+$adff #(.CLK_POLARITY(1'b1), .ARST_POLARITY(1'b1), .ARST_VALUE(2'h2), .WIDTH(2)) ff2 (.CLK(CLK), .ARST(ARST), .D(Q[5:4]), .Q(Q[5:4]));
+$adffe #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b0), .ARST_POLARITY(1'b1), .ARST_VALUE(2'h2), .WIDTH(2)) ff3 (.CLK(CLK), .EN(EN), .ARST(ARST), .D(Q[7:6]), .Q(Q[7:6]));
+$sdff #(.CLK_POLARITY(1'b1), .SRST_POLARITY(1'b1), .SRST_VALUE(2'h2), .WIDTH(2)) ff4 (.CLK(CLK), .SRST(SRST), .D(Q[9:8]), .Q(Q[9:8]));
+$sdffe #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b1), .SRST_POLARITY(1'b1), .SRST_VALUE(2'h2), .WIDTH(2)) ff5 (.CLK(CLK), .EN(EN), .SRST(SRST), .D(Q[11:10]), .Q(Q[11:10]));
+$sdffce #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b1), .SRST_POLARITY(1'b1), .SRST_VALUE(2'h2), .WIDTH(2)) ff6 (.CLK(CLK), .EN(EN), .SRST(SRST), .D(Q[13:12]), .Q(Q[13:12]));
+$dffsr #(.CLK_POLARITY(1'b1), .CLR_POLARITY(1'b1), .SET_POLARITY(1'b0), .WIDTH(2)) ff7 (.CLK(CLK), .SET(SET), .CLR(CLR), .D(Q[15:14]), .Q(Q[15:14]));
+$dffsre #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b0), .CLR_POLARITY(1'b1), .SET_POLARITY(1'b0), .WIDTH(2)) ff8 (.CLK(CLK), .EN(EN), .SET(SET), .CLR(CLR), .D(Q[17:16]), .Q(Q[17:16]));
+
+$dlatch #(.EN_POLARITY(1'b1), .WIDTH(2)) ff9 (.EN(EN), .D(Q[19:18]), .Q(Q[19:18]));
+$adlatch #(.EN_POLARITY(1'b0), .ARST_POLARITY(1'b1), .ARST_VALUE(2'h2), .WIDTH(2)) ff10 (.EN(EN), .ARST(ARST), .D(Q[21:20]), .Q(Q[21:20]));
+$dlatchsr #(.EN_POLARITY(1'b0), .CLR_POLARITY(1'b1), .SET_POLARITY(1'b0), .WIDTH(2)) ff11 (.EN(EN), .SET(SET), .CLR(CLR), .D(Q[23:22]), .Q(Q[23:22]));
+
+endmodule
+
+EOT
+
+design -save orig
+
+# Equivalence check will fail for unmapped adlatch and dlatchsr due to negative hold hack.
+delete top/ff10 top/ff11
+equiv_opt -undef -assert -multiclock opt_dff -keepdc
+
+design -load orig
+opt_dff -keepdc
+select -assert-count 1 t:$and
+select -assert-count 3 t:$dffe
+select -assert-count 3 t:$dlatch
+select -assert-count 3 t:$sr
+select -assert-none t:$and t:$dffe t:$dlatch t:$sr %% %n t:* %i
+
+design -load orig
+simplemap
+opt_dff -keepdc
+select -assert-count 2 t:$_AND_
+select -assert-count 6 t:$_DFFE_??_
+select -assert-count 6 t:$_DLATCH_?_
+select -assert-count 6 t:$_SR_??_
+select -assert-none t:$_AND_ t:$_DFFE_??_ t:$_DLATCH_?_ t:$_SR_??_ %% %n t:* %i
+
diff --git a/tests/opt/opt_dff_sr.ys b/tests/opt/opt_dff_sr.ys
new file mode 100644
index 000000000..daedb115c
--- /dev/null
+++ b/tests/opt/opt_dff_sr.ys
@@ -0,0 +1,304 @@
+### Always-active SET/CLR removal.
+
+read_verilog -icells <<EOT
+
+module top(...);
+
+input CLK;
+input [5:0] D;
+output [23:0] Q;
+input CLR;
+input SET;
+input EN;
+
+$dffsr #(.CLK_POLARITY(1'b1), .SET_POLARITY(1'b1), .CLR_POLARITY(1'b1), .WIDTH(6)) ff0 (.CLK(CLK), .CLR({CLR, CLR, CLR, 1'b1, 1'b0, 1'bx}), .SET({1'b1, 1'b0, 1'bx, SET, SET, SET}), .D(D), .Q(Q[5:0]));
+$dffsre #(.CLK_POLARITY(1'b1), .SET_POLARITY(1'b0), .CLR_POLARITY(1'b0), .EN_POLARITY(1'b1), .WIDTH(6)) ff1 (.CLK(CLK), .EN(EN), .CLR({CLR, CLR, CLR, 1'b1, 1'b0, 1'bx}), .SET({1'b1, 1'b0, 1'bx, SET, SET, SET}), .D(D), .Q(Q[11:6]));
+$dlatchsr #(.SET_POLARITY(1'b0), .CLR_POLARITY(1'b1), .EN_POLARITY(1'b1), .WIDTH(6)) ff2 (.EN(EN), .CLR({CLR, CLR, CLR, 1'b1, 1'b0, 1'bx}), .SET({1'b1, 1'b0, 1'bx, SET, SET, SET}), .D(D), .Q(Q[17:12]));
+$sr #(.SET_POLARITY(1'b1), .CLR_POLARITY(1'b0), .WIDTH(6)) ff3 (.CLR({CLR, CLR, CLR, 1'b1, 1'b0, 1'bx}), .SET({1'b1, 1'b0, 1'bx, SET, SET, SET}), .Q(Q[23:18]));
+
+endmodule
+
+EOT
+
+design -save orig
+
+equiv_opt -undef -assert -multiclock opt_dff
+design -load postopt
+select -assert-count 1 t:$dffsr
+select -assert-count 1 t:$dffsr r:WIDTH=2 %i
+select -assert-count 1 t:$dffsre
+select -assert-count 1 t:$dffsre r:WIDTH=2 %i
+select -assert-count 1 t:$dlatchsr
+select -assert-count 1 t:$dlatchsr r:WIDTH=2 %i
+select -assert-none t:$sr
+
+design -load orig
+
+equiv_opt -undef -assert -multiclock opt_dff -keepdc
+design -load postopt
+select -assert-count 1 t:$dffsr
+select -assert-count 1 t:$dffsr r:WIDTH=4 %i
+select -assert-count 1 t:$dffsre
+select -assert-count 1 t:$dffsre r:WIDTH=4 %i
+select -assert-count 1 t:$dlatchsr
+select -assert-count 1 t:$dlatchsr r:WIDTH=4 %i
+select -assert-count 1 t:$sr
+select -assert-count 1 t:$sr r:WIDTH=4 %i
+
+design -load orig
+simplemap
+
+equiv_opt -undef -assert -multiclock opt_dff
+design -load postopt
+select -assert-count 1 t:$_DFF_PP0_
+select -assert-count 1 t:$_DFF_PP1_
+select -assert-count 1 t:$_DFFE_PN0P_
+select -assert-count 1 t:$_DFFE_PN1P_
+select -assert-count 1 t:$_DLATCH_PP0_
+select -assert-count 1 t:$_DLATCH_PN1_
+select -assert-none t:$_DFF_PP0_ t:$_DFF_PP1_ t:$_DFFE_PN0P_ t:$_DFFE_PN1P_ t:$_DLATCH_PP0_ t:$_DLATCH_PN1_ t:$_NOT_ %% %n t:* %i
+
+design -load orig
+simplemap
+
+equiv_opt -undef -assert -multiclock opt_dff -keepdc
+design -load postopt
+select -assert-count 1 t:$_DFF_PP0_
+select -assert-count 1 t:$_DFF_PP1_
+select -assert-count 2 t:$_DFFSR_PPP_
+select -assert-count 1 t:$_DFFE_PN0P_
+select -assert-count 1 t:$_DFFE_PN1P_
+select -assert-count 2 t:$_DFFSRE_PNNP_
+select -assert-count 1 t:$_DLATCH_PP0_
+select -assert-count 1 t:$_DLATCH_PN1_
+select -assert-count 2 t:$_DLATCHSR_PNP_
+select -assert-count 1 t:$_DLATCH_P_
+select -assert-count 1 t:$_DLATCH_N_
+select -assert-count 2 t:$_SR_PN_
+select -assert-none t:$_DFF_PP0_ t:$_DFF_PP1_ t:$_DFFSR_PPP_ t:$_DFFE_PN0P_ t:$_DFFE_PN1P_ t:$_DFFSRE_PNNP_ t:$_DLATCH_PP0_ t:$_DLATCH_PN1_ t:$_DLATCHSR_PNP_ t:$_NOT_ t:$_DLATCH_N_ t:$_DLATCH_P_ t:$_SR_PN_ %% %n t:* %i
+
+design -reset
+
+
+
+### Never-active CLR removal.
+
+read_verilog -icells <<EOT
+
+module top(...);
+
+input CLK;
+input [5:0] D;
+output [23:0] Q;
+input CLR;
+input SET;
+input EN;
+
+$dffsr #(.CLK_POLARITY(1'b1), .SET_POLARITY(1'b1), .CLR_POLARITY(1'b1), .WIDTH(6)) ff0 (.CLK(CLK), .CLR(6'h00), .SET({6{SET}}), .D(D), .Q(Q[5:0]));
+$dffsre #(.CLK_POLARITY(1'b1), .SET_POLARITY(1'b0), .CLR_POLARITY(1'b0), .EN_POLARITY(1'b1), .WIDTH(6)) ff1 (.CLK(CLK), .EN(EN), .D(D), .CLR(6'h3f), .SET({6{SET}}), .Q(Q[11:6]));
+$dlatchsr #(.SET_POLARITY(1'b0), .CLR_POLARITY(1'b1), .EN_POLARITY(1'b1), .WIDTH(6)) ff2 (.EN(EN), .D(D), .CLR(6'h00), .SET({6{SET}}), .Q(Q[17:12]));
+$sr #(.SET_POLARITY(1'b1), .CLR_POLARITY(1'b0), .WIDTH(6)) ff3 (.CLR(6'h3f), .SET({6{SET}}), .Q(Q[23:18]));
+
+endmodule
+
+EOT
+
+design -save orig
+
+equiv_opt -undef -assert -multiclock opt_dff -keepdc
+design -load postopt
+select -assert-count 0 t:$dffsr
+select -assert-count 0 t:$dffsre
+select -assert-count 0 t:$dlatchsr
+select -assert-count 0 t:$sr
+select -assert-count 1 t:$adff
+select -assert-count 1 t:$adffe
+select -assert-count 1 t:$adlatch
+select -assert-count 1 t:$dlatch
+
+design -reset
+
+
+
+### Never-active CLR removal (not applicable).
+
+read_verilog -icells <<EOT
+
+module top(...);
+
+input CLK;
+input [5:0] D;
+output [23:0] Q;
+input CLR;
+input SET;
+input ALT;
+input EN;
+
+$dffsr #(.CLK_POLARITY(1'b1), .SET_POLARITY(1'b1), .CLR_POLARITY(1'b1), .WIDTH(6)) ff0 (.CLK(CLK), .CLR(6'h00), .SET({{5{SET}}, ALT}), .D(D), .Q(Q[5:0]));
+$dffsre #(.CLK_POLARITY(1'b1), .SET_POLARITY(1'b0), .CLR_POLARITY(1'b0), .EN_POLARITY(1'b1), .WIDTH(6)) ff1 (.CLK(CLK), .EN(EN), .D(D), .CLR(6'h3f), .SET({{5{SET}}, ALT}), .Q(Q[11:6]));
+$dlatchsr #(.SET_POLARITY(1'b0), .CLR_POLARITY(1'b1), .EN_POLARITY(1'b1), .WIDTH(6)) ff2 (.EN(EN), .D(D), .CLR(6'h00), .SET({{5{SET}}, ALT}), .Q(Q[17:12]));
+$sr #(.SET_POLARITY(1'b1), .CLR_POLARITY(1'b0), .WIDTH(6)) ff3 (.CLR(6'h3f), .SET({{5{SET}}, ALT}), .Q(Q[23:18]));
+
+endmodule
+
+EOT
+
+design -save orig
+
+equiv_opt -undef -assert -multiclock opt_dff -keepdc
+design -load postopt
+select -assert-count 1 t:$dffsr
+select -assert-count 1 t:$dffsre
+select -assert-count 1 t:$dlatchsr
+select -assert-count 1 t:$sr
+select -assert-count 0 t:$adff
+select -assert-count 0 t:$adffe
+select -assert-count 0 t:$adlatch
+select -assert-count 0 t:$dlatch
+
+design -load orig
+simplemap
+
+equiv_opt -undef -assert -multiclock opt_dff -keepdc
+design -load postopt
+select -assert-count 0 t:$_DFFSR_*
+select -assert-count 0 t:$_DFFSRE_*
+select -assert-count 0 t:$_DLATCHSR_*
+select -assert-count 0 t:$_SR_*
+select -assert-count 6 t:$_DFF_PP1_
+select -assert-count 6 t:$_DFFE_PN1P_
+select -assert-count 6 t:$_DLATCH_PN1_
+select -assert-count 6 t:$_DLATCH_P_
+
+design -reset
+
+
+
+### Never-active SET removal.
+
+read_verilog -icells <<EOT
+
+module top(...);
+
+input CLK;
+input [5:0] D;
+output [23:0] Q;
+input CLR;
+input SET;
+input EN;
+
+$dffsr #(.CLK_POLARITY(1'b1), .SET_POLARITY(1'b1), .CLR_POLARITY(1'b1), .WIDTH(6)) ff0 (.CLK(CLK), .CLR({6{CLR}}), .SET(6'h00), .D(D), .Q(Q[5:0]));
+$dffsre #(.CLK_POLARITY(1'b1), .SET_POLARITY(1'b0), .CLR_POLARITY(1'b0), .EN_POLARITY(1'b1), .WIDTH(6)) ff1 (.CLK(CLK), .EN(EN), .D(D), .CLR({6{CLR}}), .SET(6'h3f), .Q(Q[11:6]));
+$dlatchsr #(.SET_POLARITY(1'b0), .CLR_POLARITY(1'b1), .EN_POLARITY(1'b1), .WIDTH(6)) ff2 (.EN(EN), .D(D), .CLR({6{CLR}}), .SET(6'h3f), .Q(Q[17:12]));
+$sr #(.SET_POLARITY(1'b1), .CLR_POLARITY(1'b0), .WIDTH(6)) ff3 (.CLR({6{CLR}}), .SET(6'h00), .Q(Q[23:18]));
+
+endmodule
+
+EOT
+
+design -save orig
+
+equiv_opt -undef -assert -multiclock opt_dff -keepdc
+design -load postopt
+select -assert-count 0 t:$dffsr
+select -assert-count 0 t:$dffsre
+select -assert-count 0 t:$dlatchsr
+select -assert-count 0 t:$sr
+select -assert-count 1 t:$adff
+select -assert-count 1 t:$adffe
+select -assert-count 1 t:$adlatch
+select -assert-count 1 t:$dlatch
+
+design -reset
+
+
+
+### Never-active CLR removal (not applicable).
+
+read_verilog -icells <<EOT
+
+module top(...);
+
+input CLK;
+input [5:0] D;
+output [23:0] Q;
+input CLR;
+input SET;
+input ALT;
+input EN;
+
+$dffsr #(.CLK_POLARITY(1'b1), .SET_POLARITY(1'b1), .CLR_POLARITY(1'b1), .WIDTH(6)) ff0 (.CLK(CLK), .CLR({{5{CLR}}, ALT}), .SET(6'h00), .D(D), .Q(Q[5:0]));
+$dffsre #(.CLK_POLARITY(1'b1), .SET_POLARITY(1'b0), .CLR_POLARITY(1'b0), .EN_POLARITY(1'b1), .WIDTH(6)) ff1 (.CLK(CLK), .EN(EN), .D(D), .CLR({{5{CLR}}, ALT}), .SET(6'h3f), .Q(Q[11:6]));
+$dlatchsr #(.SET_POLARITY(1'b0), .CLR_POLARITY(1'b1), .EN_POLARITY(1'b1), .WIDTH(6)) ff2 (.EN(EN), .D(D), .CLR({{5{CLR}}, ALT}), .SET(6'h3f), .Q(Q[17:12]));
+$sr #(.SET_POLARITY(1'b1), .CLR_POLARITY(1'b0), .WIDTH(6)) ff3 (.CLR({{5{CLR}}, ALT}), .SET(6'h00), .Q(Q[23:18]));
+
+endmodule
+
+EOT
+
+design -save orig
+
+equiv_opt -undef -assert -multiclock opt_dff -keepdc
+design -load postopt
+select -assert-count 1 t:$dffsr
+select -assert-count 1 t:$dffsre
+select -assert-count 1 t:$dlatchsr
+select -assert-count 1 t:$sr
+select -assert-count 0 t:$adff
+select -assert-count 0 t:$adffe
+select -assert-count 0 t:$adlatch
+select -assert-count 0 t:$dlatch
+
+design -load orig
+simplemap
+
+equiv_opt -undef -assert -multiclock opt_dff -keepdc
+design -load postopt
+select -assert-count 0 t:$_DFFSR_*
+select -assert-count 0 t:$_DFFSRE_*
+select -assert-count 0 t:$_DLATCHSR_*
+select -assert-count 0 t:$_SR_*
+select -assert-count 6 t:$_DFF_PP0_
+select -assert-count 6 t:$_DFFE_PN0P_
+select -assert-count 6 t:$_DLATCH_PP0_
+select -assert-count 6 t:$_DLATCH_N_
+
+design -reset
+
+
+
+### SET/CLR merge into ARST.
+
+read_verilog -icells <<EOT
+
+module top(...);
+
+input CLK;
+input [5:0] D;
+output [23:0] Q;
+input ARST;
+input EN;
+
+$dffsr #(.CLK_POLARITY(1'b1), .SET_POLARITY(1'b1), .CLR_POLARITY(1'b1), .WIDTH(6)) ff0 (.CLK(CLK), .CLR({ARST, 5'h00}), .SET({1'b0, {5{ARST}}}), .D(D), .Q(Q[5:0]));
+$dffsre #(.CLK_POLARITY(1'b1), .SET_POLARITY(1'b0), .CLR_POLARITY(1'b0), .EN_POLARITY(1'b1), .WIDTH(6)) ff1 (.CLK(CLK), .EN(EN), .D(D), .CLR({ARST, 5'h1f}), .SET({1'b1, {5{ARST}}}), .Q(Q[11:6]));
+$dlatchsr #(.SET_POLARITY(1'b0), .CLR_POLARITY(1'b1), .EN_POLARITY(1'b1), .WIDTH(6)) ff2 (.EN(EN), .D(D), .CLR({ARST, 5'h00}), .SET({1'b1, {5{ARST}}}), .Q(Q[17:12]));
+$sr #(.SET_POLARITY(1'b1), .CLR_POLARITY(1'b0), .WIDTH(6)) ff3 (.CLR({ARST, 5'h1f}), .SET({1'b0, {5{ARST}}}), .Q(Q[23:18]));
+
+endmodule
+
+EOT
+
+design -save orig
+
+equiv_opt -undef -assert -multiclock opt_dff -keepdc
+design -load postopt
+select -assert-count 0 t:$dffsr
+select -assert-count 0 t:$dffsre
+select -assert-count 1 t:$dlatchsr
+select -assert-count 1 t:$sr
+select -assert-count 1 t:$adff
+select -assert-count 1 t:$adff r:ARST_VALUE=6'h1f %i
+select -assert-count 1 t:$adffe
+select -assert-count 1 t:$adffe r:ARST_VALUE=6'h1f %i
+select -assert-count 0 t:$adlatch
+select -assert-count 0 t:$dlatch
diff --git a/tests/opt/opt_dff_srst.ys b/tests/opt/opt_dff_srst.ys
new file mode 100644
index 000000000..4a77de0b8
--- /dev/null
+++ b/tests/opt/opt_dff_srst.ys
@@ -0,0 +1,113 @@
+### Always-active SRST removal.
+
+read_verilog -icells <<EOT
+
+module top(...);
+
+input CLK;
+input [1:0] D;
+(* init=12'h555 *)
+output [11:0] Q;
+input SRST;
+input EN;
+
+$sdff #(.CLK_POLARITY(1'b1), .SRST_POLARITY(1'b1), .SRST_VALUE(2'h2), .WIDTH(2)) ff0 (.CLK(CLK), .SRST(1'b1), .D(D), .Q(Q[1:0]));
+$sdffe #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b1), .SRST_POLARITY(1'b0), .SRST_VALUE(2'h2), .WIDTH(2)) ff1 (.CLK(CLK), .SRST(1'b0), .EN(EN), .D(D), .Q(Q[3:2]));
+$sdffce #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b1), .SRST_POLARITY(1'b0), .SRST_VALUE(2'h2), .WIDTH(2)) ff2 (.CLK(CLK), .SRST(1'b0), .EN(EN), .D(D), .Q(Q[5:4]));
+$sdff #(.CLK_POLARITY(1'b1), .SRST_POLARITY(1'b1), .SRST_VALUE(2'h2), .WIDTH(2)) ff3 (.CLK(CLK), .SRST(1'bx), .D(D), .Q(Q[7:6]));
+$sdffe #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b1), .SRST_POLARITY(1'b0), .SRST_VALUE(2'h2), .WIDTH(2)) ff4 (.CLK(CLK), .SRST(1'bx), .EN(EN), .D(D), .Q(Q[9:8]));
+$sdffce #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b1), .SRST_POLARITY(1'b0), .SRST_VALUE(2'h2), .WIDTH(2)) ff5 (.CLK(CLK), .SRST(1'bx), .EN(EN), .D(D), .Q(Q[11:10]));
+
+
+endmodule
+
+EOT
+
+design -save orig
+
+equiv_opt -undef -assert -multiclock opt_dff
+design -load postopt
+select -assert-count 0 t:$sdff
+select -assert-count 0 t:$sdffe
+select -assert-count 0 t:$sdffce
+select -assert-count 4 t:$dff
+select -assert-count 2 t:$dffe
+
+design -load orig
+
+equiv_opt -undef -assert -multiclock opt_dff -keepdc
+design -load postopt
+select -assert-count 1 t:$sdff
+select -assert-count 1 t:$sdffe
+select -assert-count 1 t:$sdffce
+select -assert-count 2 t:$dff
+select -assert-count 1 t:$dffe
+
+design -load orig
+simplemap
+
+equiv_opt -undef -assert -multiclock opt_dff
+design -load postopt
+select -assert-none t:$_SDFF_???_
+select -assert-none t:$_SDFFE_????_
+select -assert-none t:$_SDFFCE_????_
+select -assert-count 8 t:$_DFF_?_
+select -assert-count 4 t:$_DFFE_??_
+
+design -load orig
+simplemap
+
+equiv_opt -undef -assert -multiclock opt_dff -keepdc
+design -load postopt
+select -assert-count 2 t:$_SDFF_???_
+select -assert-count 2 t:$_SDFFE_????_
+select -assert-count 2 t:$_SDFFCE_????_
+select -assert-count 4 t:$_DFF_?_
+select -assert-count 2 t:$_DFFE_??_
+
+design -reset
+
+
+### Never-active SRST removal.
+
+read_verilog -icells <<EOT
+
+module top(...);
+
+input CLK;
+input [1:0] D;
+output [5:0] Q;
+input SRST;
+input EN;
+
+$sdff #(.CLK_POLARITY(1'b1), .SRST_POLARITY(1'b1), .SRST_VALUE(2'h2), .WIDTH(2)) ff0 (.CLK(CLK), .SRST(1'b0), .D(D), .Q(Q[1:0]));
+$sdffe #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b1), .SRST_POLARITY(1'b0), .SRST_VALUE(2'h2), .WIDTH(2)) ff1 (.CLK(CLK), .SRST(1'b1), .EN(EN), .D(D), .Q(Q[3:2]));
+$sdffce #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b1), .SRST_POLARITY(1'b0), .SRST_VALUE(2'h2), .WIDTH(2)) ff2 (.CLK(CLK), .SRST(1'b1), .EN(EN), .D(D), .Q(Q[5:4]));
+
+endmodule
+
+EOT
+
+design -save orig
+
+equiv_opt -undef -assert -multiclock opt_dff
+design -load postopt
+select -assert-none t:$sdff
+select -assert-none t:$sdffe
+select -assert-none t:$sdffce
+select -assert-count 1 t:$dff
+select -assert-count 2 t:$dffe
+
+design -load orig
+simplemap
+
+equiv_opt -undef -assert -multiclock opt_dff
+design -load postopt
+select -assert-none t:$_SDFF_???_
+select -assert-none t:$_SDFFE_????_
+select -assert-none t:$_SDFFCE_????_
+select -assert-count 2 t:$_DFF_P_
+select -assert-count 4 t:$_DFFE_PP_
+
+design -reset
+
diff --git a/tests/opt/opt_expr_combined_assign.ys b/tests/opt/opt_expr_combined_assign.ys
new file mode 100644
index 000000000..b18923c7b
--- /dev/null
+++ b/tests/opt/opt_expr_combined_assign.ys
@@ -0,0 +1,83 @@
+read_verilog -sv <<EOT
+module opt_expr_or_test(input [3:0] i, input [7:0] j, output [8:0] o);
+wire[8:0] a = 8'b0;
+initial begin
+	a |= i;
+	a |= j;
+end
+    assign o = a;
+endmodule
+EOT
+proc
+equiv_opt -assert opt_expr -fine
+design -load postopt
+
+select -assert-count 1 t:$or r:A_WIDTH=4 r:B_WIDTH=4 r:Y_WIDTH=4 %i %i %i
+
+design -reset
+read_verilog -sv <<EOT
+module opt_expr_add_test(input [3:0] i, input [7:0] j, output [8:0] o);
+wire[8:0] a = 8'b0;
+initial begin
+        a += i;
+        a += j;
+end
+    assign o = a;
+endmodule
+EOT
+proc
+equiv_opt -assert opt_expr -fine
+design -load postopt
+
+select -assert-count 1 t:$add r:A_WIDTH=9 r:B_WIDTH=8 r:Y_WIDTH=9 %i %i %i
+
+design -reset
+read_verilog -sv <<EOT
+module opt_expr_xor_test(input [3:0] i, input [7:0] j, output [8:0] o);
+wire[8:0] a = 8'b0;
+initial begin
+        a ^= i;
+        a ^= j;
+end
+    assign o = a;
+endmodule
+EOT
+proc
+equiv_opt -assert opt_expr -fine
+design -load postopt
+
+select -assert-count 1 t:$xor r:A_WIDTH=4 r:B_WIDTH=4 r:Y_WIDTH=4 %i %i %i
+
+design -reset
+read_verilog -sv <<EOT
+module opt_expr_sub_test(input [3:0] i, input [7:0] j, output [8:0] o);
+wire[8:0] a = 8'b0;
+initial begin
+        a -= i;
+        a -= j;
+end
+    assign o = a;
+endmodule
+EOT
+proc
+equiv_opt -assert opt_expr -fine
+design -load postopt
+
+select -assert-count 1 t:$sub r:A_WIDTH=9 r:B_WIDTH=8 r:Y_WIDTH=9 %i %i %i
+
+design -reset
+read_verilog -sv <<EOT
+module opt_expr_and_test(input [3:0] i, input [7:0] j, output [8:0] o);
+wire[8:0] a = 8'b11111111;
+initial begin
+        a &= i;
+        a &= j;
+end
+    assign o = a;
+endmodule
+EOT
+proc
+equiv_opt -assert opt_expr -fine
+design -load postopt
+
+select -assert-count 1 t:$and r:A_WIDTH=4 r:B_WIDTH=4 r:Y_WIDTH=4 %i %i %i
diff --git a/tests/opt/opt_rmdff.v b/tests/opt/opt_rmdff.v
index b1c06703c..536bf1d4e 100644
--- a/tests/opt/opt_rmdff.v
+++ b/tests/opt/opt_rmdff.v
@@ -1,50 +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;
+(* 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;
+(* 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;
+(* 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;
+(* 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;
+(* 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;
+(* 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;
+(* 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;
+(* 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;
+(* 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;
+(* 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;
+(* 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;
+(* 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;
+(* 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/opt/opt_rmdff.ys b/tests/opt/opt_rmdff.ys
index 83a162f44..998414597 100644
--- a/tests/opt/opt_rmdff.ys
+++ b/tests/opt/opt_rmdff.ys
@@ -1,9 +1,10 @@
 read_verilog -icells opt_rmdff.v
 prep
 design -stash gold
+
 read_verilog -icells opt_rmdff.v
 proc
-opt_rmdff
+opt_dff
 
 select -assert-count 0 c:remove*
 select -assert-min 7 c:keep*
@@ -14,13 +15,18 @@ 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
+cd gold
+# fix up the "EN is don't care" cases, so that the gold output can't
+# become defined by using the properties of an undefined enable. (Both
+# remove6 and remove15 have active-low enables.)
+connect -port remove6 EN 1'b1
+connect -port remove15 E 1'b1
+cd ..
+
+clk2fflogic
+opt_clean
+
+miter -equiv -ignore_gold_x -make_assert -make_outputs -make_outcmp -flatten gold gate miter
+hierarchy -top miter
 
-#design -load gold
-#stat
-#
-#design -load gate
-#stat
+sat -verify -prove-asserts -enable_undef -set-init-undef -seq 10 -show-public miter
diff --git a/tests/opt/opt_rmdff_sat.ys b/tests/opt/opt_rmdff_sat.ys
index 1c3dd9c05..231c43ecb 100644
--- a/tests/opt/opt_rmdff_sat.ys
+++ b/tests/opt/opt_rmdff_sat.ys
@@ -1,5 +1,5 @@
 read_verilog opt_rmdff_sat.v
 prep -flatten
-opt_rmdff -sat
-synth
+opt_dff -sat -nosdff
+simplemap
 select -assert-count 5 t:$_DFF_P_
diff --git a/tests/opt/opt_share_bug2334.ys b/tests/opt/opt_share_bug2334.ys
new file mode 100644
index 000000000..004d98349
--- /dev/null
+++ b/tests/opt/opt_share_bug2334.ys
@@ -0,0 +1,13 @@
+read_verilog <<EOT
+
+module t(input [3:0] A, input [3:0] B, input [3:0] C, input S, output [3:0] Y);
+
+wire [3:0] t = A + C;
+
+assign Y = S ? A + B : {4{t[0]}};
+
+endmodule
+
+EOT
+
+equiv_opt -assert opt_share
diff --git a/tests/opt/opt_share_bug2335.ys b/tests/opt/opt_share_bug2335.ys
new file mode 100644
index 000000000..0846a9ec3
--- /dev/null
+++ b/tests/opt/opt_share_bug2335.ys
@@ -0,0 +1,27 @@
+read_verilog <<EOT
+
+module top(...);
+
+input [3:0] A, B, C;
+input S;
+input [1:0] T;
+output [3:0] X;
+output reg [3:0] Y;
+
+wire [3:0] D = A + B;
+
+assign X = S ? D : A + C;
+always @* begin
+        case(T)
+        2'b01: Y <= A;
+        2'b10: Y <= B;
+        default: Y <= D;
+        endcase
+end
+
+endmodule
+
+EOT
+
+proc
+equiv_opt -assert opt_share
diff --git a/tests/opt/opt_share_bug2336.ys b/tests/opt/opt_share_bug2336.ys
new file mode 100644
index 000000000..cd472ef46
--- /dev/null
+++ b/tests/opt/opt_share_bug2336.ys
@@ -0,0 +1,14 @@
+read_verilog <<EOT
+
+module top(input [3:0] A, B, C, input S, output [2:0] O);
+
+wire [3:0] tb = A + B;
+wire [3:0] tc = A + C;
+
+assign O = S ? tb[3:1] : tc[3:1];
+
+endmodule
+
+EOT
+
+equiv_opt -assert opt_share
diff --git a/tests/opt/run-test.sh b/tests/opt/run-test.sh
index 44ce7e674..2007cd6e4 100755
--- a/tests/opt/run-test.sh
+++ b/tests/opt/run-test.sh
@@ -1,6 +1,4 @@
 #!/bin/bash
-set -e
-for x in *.ys; do
-  echo "Running $x.."
-  ../../yosys -ql ${x%.ys}.log $x
-done
+set -eu
+source ../gen-tests-makefile.sh
+run_tests --yosys-scripts