diff --git a/passes/opt/Makefile.inc b/passes/opt/Makefile.inc
index a145cf946..639dc6590 100644
--- a/passes/opt/Makefile.inc
+++ b/passes/opt/Makefile.inc
@@ -6,6 +6,7 @@ OBJS += passes/opt/opt_reduce.o
OBJS += passes/opt/opt_rmdff.o
OBJS += passes/opt/opt_clean.o
OBJS += passes/opt/opt_expr.o
+OBJS += passes/opt/opt_demorgan.o
OBJS += passes/opt/rmports.o
ifneq ($(SMALL),1)
diff --git a/passes/opt/opt_demorgan.cc b/passes/opt/opt_demorgan.cc
new file mode 100644
index 000000000..62d65dea7
--- /dev/null
+++ b/passes/opt/opt_demorgan.cc
@@ -0,0 +1,202 @@
+/*
+ * yosys -- Yosys Open SYnthesis Suite
+ *
+ * Copyright (C) 2017 Clifford Wolf <clifford@clifford.at>
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ *
+ */
+
+#include "kernel/yosys.h"
+#include "kernel/sigtools.h"
+#include "kernel/modtools.h"
+
+USING_YOSYS_NAMESPACE
+PRIVATE_NAMESPACE_BEGIN
+
+void demorgan_worker(
+ ModIndex& index,
+ Cell *cell,
+ unsigned int& cells_changed)
+{
+ SigMap& sigmap = index.sigmap;
+ auto m = cell->module;
+
+ //TODO: Add support for reduce_xor
+ //DeMorgan of XOR is either XOR (if even number of inputs) or XNOR (if odd number)
+
+ if( (cell->type != "$reduce_and") && (cell->type != "$reduce_or") )
+ return;
+
+ auto insig = sigmap(cell->getPort("\\A"));
+ log("Inspecting %s cell %s (%d inputs)\n", log_id(cell->type), log_id(cell->name), insig.size());
+ int num_inverted = 0;
+ for(int i=0; i<insig.size(); i++)
+ {
+ auto b = insig[i];
+
+ //See if this bit is driven by a $not cell
+ //TODO: do other stuff like nor/nand?
+ pool<ModIndex::PortInfo> ports = index.query_ports(b);
+ bool inverted = false;
+ for(auto x : ports)
+ {
+ if(x.port == "\\Y" && x.cell->type == "$_NOT_")
+ {
+ inverted = true;
+ break;
+ }
+ }
+
+ if(inverted)
+ num_inverted ++;
+ }
+
+ //Stop if less than half of the inputs are inverted
+ if(num_inverted*2 < insig.size())
+ {
+ log(" %d / %d inputs are inverted, not pushing\n", num_inverted, insig.size());
+ return;
+ }
+
+ //More than half of the inputs are inverted! Push through
+ cells_changed ++;
+ log(" %d / %d inputs are inverted, pushing inverter through reduction\n", num_inverted, insig.size());
+
+ //For each input, either add or remove the inverter as needed
+ //TODO: this duplicates the loop up above, can we refactor it?
+ for(int i=0; i<insig.size(); i++)
+ {
+ auto b = insig[i];
+
+ //See if this bit is driven by a $not cell
+ //TODO: do other stuff like nor/nand?
+ pool<ModIndex::PortInfo> ports = index.query_ports(b);
+ RTLIL::Cell* srcinv = NULL;
+ for(auto x : ports)
+ {
+ if(x.port == "\\Y" && x.cell->type == "$_NOT_")
+ {
+ srcinv = x.cell;
+ break;
+ }
+ }
+
+ //We are NOT inverted! Add an inverter
+ if(!srcinv)
+ {
+ auto inverted_b = m->addWire(NEW_ID);
+ m->addNot(NEW_ID, RTLIL::SigSpec(b), RTLIL::SigSpec(inverted_b));
+ insig[i] = inverted_b;
+ }
+
+ //We ARE inverted - bypass it
+ //Don't automatically delete the inverter since other stuff might still use it
+ else
+ insig[i] = srcinv->getPort("\\A");
+ }
+
+ //Cosmetic fixup: If our input is just a scrambled version of one bus, rearrange it
+ //Reductions are all commutative, so there's no point in having them in a weird order
+ bool same_signal = true;
+ RTLIL::Wire* srcwire = insig[0].wire;
+ std::map<int, int> seen_bits;
+ for(int i=0; i<insig.size(); i++)
+ seen_bits[i] = 0;
+ for(int i=0; i<insig.size(); i++)
+ {
+ seen_bits[insig[i].offset] ++;
+ if(insig[i].wire != srcwire)
+ {
+ same_signal = false;
+ break;
+ }
+ }
+ if(same_signal)
+ {
+ //Make sure we've seen every bit exactly once
+ bool every_bit_once = true;
+ for(int i=0; i<insig.size(); i++)
+ {
+ if(seen_bits[i] != 1)
+ {
+ every_bit_once = false;
+ break;
+ }
+ }
+
+ //All good? Just use the whole wire as-is without any reordering
+ //We do have to swap MSB to LSB b/c that's the way the reduction cells seem to work?
+ //Unclear on why this isn't sorting properly
+ //TODO: can we do SigChunks instead of single bits if we have subsets of a bus?
+ if(every_bit_once && (insig.size() == srcwire->width) )
+ {
+ log("Rearranging bits\n");
+ RTLIL::SigSpec newsig;
+ for(int i=0; i<insig.size(); i++)
+ newsig.append(RTLIL::SigBit(srcwire, insig.size() - i - 1));
+ insig = newsig;
+ insig.sort();
+ }
+ }
+
+ //Push the new input signal back to the reduction (after bypassing/adding inverters)
+ cell->setPort("\\A", insig);
+
+ //Change the cell type
+ if(cell->type == "$reduce_and")
+ cell->type = "$reduce_or";
+ else if(cell->type == "$reduce_or")
+ cell->type = "$reduce_and";
+ //don't change XOR
+
+ //Add an inverter to the output
+ auto inverted_output = cell->getPort("\\Y");
+ auto uninverted_output = m->addWire(NEW_ID);
+ m->addNot(NEW_ID, RTLIL::SigSpec(uninverted_output), inverted_output);
+ cell->setPort("\\Y", uninverted_output);
+}
+
+struct OptDemorganPass : public Pass {
+ OptDemorganPass() : Pass("opt_demorgan", "Optimize reductions with DeMorgan equivalents") { }
+ virtual void help()
+ {
+ // |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
+ log("\n");
+ log(" opt_demorgan [selection]\n");
+ log("\n");
+ log("This pass pushes inverters through $reduce_* cells if this will reduce the\n");
+ log("overall gate count of the circuit\n");
+ log("\n");
+ }
+ virtual void execute(std::vector<std::string> /*args*/, RTLIL::Design *design)
+ {
+ log_header(design, "Executing OPT_DEMORGAN pass (push inverters through $reduce_* cells).\n");
+
+ //int argidx = 0;
+ //extra_args(args, argidx, design);
+
+ unsigned int cells_changed = 0;
+ for (auto module : design->selected_modules())
+ {
+ ModIndex index(module);
+ for (auto cell : module->selected_cells())
+ demorgan_worker(index, cell, cells_changed);
+ }
+
+ if(cells_changed)
+ log("Pushed inverters through %u reductions\n", cells_changed);
+ }
+} OptDemorganPass;
+
+PRIVATE_NAMESPACE_END