Some improvements in opt_rmdff

diff --git a/passes/opt/opt_rmdff.cc b/passes/opt/opt_rmdff.cc
index 4870f76b673a5872200a10ff8f12822e1862e9d4..a1a9e7f3b7f680509c37fc3e2b1f52b77e78d1e5 100644 (file)
--- a/passes/opt/opt_rmdff.cc
+++ b/passes/opt/opt_rmdff.cc
@@ -25,6 +25,7 @@
 #include <stdio.h>
 
 static SigMap assign_map;
+static SigSet<RTLIL::Cell*> mux_drivers;
 
 static bool handle_dff(RTLIL::Module *mod, RTLIL::Cell *dff)
 {
@@ -66,19 +67,42 @@ static bool handle_dff(RTLIL::Module *mod, RTLIL::Cell *dff)
        }
        else
                log_error("abort.");
-       
+
        assign_map.apply(sig_d);
        assign_map.apply(sig_q);
        assign_map.apply(sig_c);
        assign_map.apply(sig_r);
 
+       if (dff->type == "$dff" && mux_drivers.has(sig_d)) {
+               std::set<RTLIL::Cell*> muxes;
+               mux_drivers.find(sig_d, muxes);
+               for (auto mux : muxes) {
+                       RTLIL::SigSpec sig_a = assign_map(mux->connections.at("\\A"));
+                       RTLIL::SigSpec sig_b = assign_map(mux->connections.at("\\B"));
+                       if (sig_a == sig_q && sig_b.is_fully_const()) {
+                               RTLIL::SigSig conn(sig_q, sig_b);
+                               mod->connections.push_back(conn);
+                               goto delete_dff;
+                       }
+                       if (sig_b == sig_q && sig_a.is_fully_const()) {
+                               RTLIL::SigSig conn(sig_q, sig_a);
+                               mod->connections.push_back(conn);
+                               goto delete_dff;
+                       }
+               }
+       }
+
        if (sig_d.is_fully_const() && sig_r.width == 0) {
                RTLIL::SigSig conn(sig_q, sig_d);
                mod->connections.push_back(conn);
                goto delete_dff;
        }
 
-       if (sig_d == sig_q && sig_r.width == 0) {
+       if (sig_d == sig_q) {
+               if (sig_r.width > 0) {
+                       RTLIL::SigSig conn(sig_q, val_rv);
+                       mod->connections.push_back(conn);
+               }
                goto delete_dff;
        }
 
@@ -117,9 +141,15 @@ struct OptRmdffPass : public Pass {
                                continue;
 
                        assign_map.set(mod_it.second);
+                       mux_drivers.clear();
 
                        std::vector<std::string> dff_list;
                        for (auto &it : mod_it.second->cells) {
+                               if (it.second->type == "$mux" || it.second->type == "$pmux") {
+                                       if (it.second->connections.at("\\A").width == it.second->connections.at("\\B").width)
+                                               mux_drivers.insert(assign_map(it.second->connections.at("\\Y")), it.second);
+                                       continue;
+                               }
                                if (!design->selected(mod_it.second, it.second))
                                        continue;
                                if (it.second->type == "$_DFF_N_") dff_list.push_back(it.first);
@@ -144,6 +174,7 @@ struct OptRmdffPass : public Pass {
                }
 
                assign_map.clear();
+               mux_drivers.clear();
                log("Replaced %d DFF cells.\n", total_count);
        }
 } OptRmdffPass;