Add "opt_expr -fine" feature to remove neutral bits from reduce and logic operators

diff --git a/passes/opt/opt_expr.cc b/passes/opt/opt_expr.cc
index f9e40869d5c28bbe4343d566a58ca6981eca024b..b9aa35a9aeab1ee315bb4c4442c2738a52fc5024 100644 (file)
--- a/passes/opt/opt_expr.cc
+++ b/passes/opt/opt_expr.cc
@@ -449,6 +449,53 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
                                if (group_cell_inputs(module, cell, true, assign_map))
                                        goto next_cell;
 
+                       if (cell->type == "$logic_not" || cell->type == "$logic_and" || cell->type == "$logic_or" ||
+                                       cell->type == "$reduce_or" || cell->type == "$reduce_and" || cell->type == "$reduce_bool")
+                       {
+                               SigBit neutral_bit = cell->type == "$reduce_and" ? State::S1 : State::S0;
+
+                               RTLIL::SigSpec sig_a = assign_map(cell->getPort("\\A"));
+                               RTLIL::SigSpec new_sig_a;
+
+                               for (auto bit : sig_a)
+                                       if (bit != neutral_bit) new_sig_a.append(bit);
+
+                               if (GetSize(new_sig_a) == 0)
+                                       new_sig_a.append(neutral_bit);
+
+                               if (GetSize(new_sig_a) < GetSize(sig_a)) {
+                                       cover_list("opt.opt_expr.fine.neutral_A", "$logic_not", "$logic_and", "$logic_or", "$reduce_or", "$reduce_and", "$reduce_bool", cell->type.str());
+                                       log("Replacing port A of %s cell `%s' in module `%s' with shorter expression: %s -> %s\n",
+                                                       cell->type.c_str(), cell->name.c_str(), module->name.c_str(), log_signal(sig_a), log_signal(new_sig_a));
+                                       cell->setPort("\\A", new_sig_a);
+                                       cell->parameters.at("\\A_WIDTH") = GetSize(new_sig_a);
+                                       did_something = true;
+                               }
+                       }
+
+                       if (cell->type == "$logic_and" || cell->type == "$logic_or")
+                       {
+                               SigBit neutral_bit = State::S0;
+
+                               RTLIL::SigSpec sig_b = assign_map(cell->getPort("\\B"));
+                               RTLIL::SigSpec new_sig_b;
+
+                               for (auto bit : sig_b)
+                                       if (bit != neutral_bit) new_sig_b.append(bit);
+
+                               if (GetSize(new_sig_b) == 0)
+                                       new_sig_b.append(neutral_bit);
+
+                               if (GetSize(new_sig_b) < GetSize(sig_b)) {
+                                       cover_list("opt.opt_expr.fine.neutral_B", "$logic_and", "$logic_or", cell->type.str());
+                                       log("Replacing port B of %s cell `%s' in module `%s' with shorter expression: %s -> %s\n",
+                                                       cell->type.c_str(), cell->name.c_str(), module->name.c_str(), log_signal(sig_b), log_signal(new_sig_b));
+                                       cell->setPort("\\B", new_sig_b);
+                                       cell->parameters.at("\\B_WIDTH") = GetSize(new_sig_b);
+                                       did_something = true;
+                               }
+                       }
+
                        if (cell->type == "$reduce_and")
                        {
                                RTLIL::SigSpec sig_a = assign_map(cell->getPort("\\A"));