flatten, techmap: don't canonicalize tpl driven bits via sigmap.

For connection `assign a = b;`, `sigmap(a)` returns `b`. This is
exactly the opposite of the desired canonicalization for driven bits.
Consider the following code:

    module foo(inout a, b);
      assign a = b;
    endmodule
    module bar(output c);
      foo f(c, 1'b0);
    endmodule

Before this commit, the inout ports would be swapped after flattening
(and cause a crash while attempting to drive a constant value).

This issue was introduced in 9f772eb9.

Fixes #2183.

passes/techmap/flatten.cc

@@ -152,15 +152,14 @@ struct FlattenWorker
 
 		// Attach port connections of the flattened cell
 
-		SigMap tpl_sigmap(tpl);
 		pool<SigBit> tpl_driven;
 		for (auto tpl_cell : tpl->cells())
 			for (auto &tpl_conn : tpl_cell->connections())
 				if (tpl_cell->output(tpl_conn.first))
-					for (auto bit : tpl_sigmap(tpl_conn.second))
+					for (auto bit : tpl_conn.second)
 						tpl_driven.insert(bit);
 		for (auto &tpl_conn : tpl->connections())
-			for (auto bit : tpl_sigmap(tpl_conn.first))
+			for (auto bit : tpl_conn.first)
 				tpl_driven.insert(bit);
 
 		SigMap sigmap(module);
@@ -190,7 +189,7 @@ struct FlattenWorker
 			} else {
 				SigSpec sig_tpl = tpl_wire, sig_mod = port_it.second;
 				for (int i = 0; i < GetSize(sig_tpl) && i < GetSize(sig_mod); i++) {
-					if (tpl_driven.count(tpl_sigmap(sig_tpl[i]))) {
+					if (tpl_driven.count(sig_tpl[i])) {
 						new_conn.first.append(sig_mod[i]);
 						new_conn.second.append(sig_tpl[i]);
 					} else {

passes/techmap/techmap.cc

@@ -233,16 +233,14 @@ struct TechmapWorker
 			}
 		}
 
-		SigMap tpl_sigmap(tpl);
 		pool<SigBit> tpl_written_bits;
-
 		for (auto tpl_cell : tpl->cells())
 		for (auto &conn : tpl_cell->connections())
 			if (tpl_cell->output(conn.first))
-				for (auto bit : tpl_sigmap(conn.second))
+				for (auto bit : conn.second)
 					tpl_written_bits.insert(bit);
 		for (auto &conn : tpl->connections())
-			for (auto bit : tpl_sigmap(conn.first))
+			for (auto bit : conn.first)
 				tpl_written_bits.insert(bit);
 
 		SigMap port_signal_map;
@@ -280,7 +278,7 @@ struct TechmapWorker
 				SigSpec sig_tpl = w, sig_tpl_pf = w, sig_mod = it.second;
 				apply_prefix(cell->name, sig_tpl_pf, module);
 				for (int i = 0; i < GetSize(sig_tpl) && i < GetSize(sig_mod); i++) {
-					if (tpl_written_bits.count(tpl_sigmap(sig_tpl[i]))) {
+					if (tpl_written_bits.count(sig_tpl[i])) {
 						c.first.append(sig_mod[i]);
 						c.second.append(sig_tpl_pf[i]);
 					} else {

tests/techmap/bug2183.ys

@@ -0,0 +1,11 @@
+read_verilog <<EOT
+module foo(inout a, b);
+  assign a = b;
+endmodule
+module bar(output c);
+  foo f(c, 1'b0);
+endmodule
+EOT
+
+hierarchy -auto-top
+flatten