From: whitequark <whitequark@whitequark.org>
Date: Tue, 21 Apr 2020 14:49:36 +0000 (+0000)
Subject: cxxrtl: unbuffer module input wires.
X-Git-Tag: working-ls180~602^2~7
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=06985c3afdba579d0bba266bb6daba0101358ad5;p=yosys.git

cxxrtl: unbuffer module input wires.

Module input wires are never set by the module, so it is unnecessary
to buffer them. Although important for all inputs, this is especially
critical for clocks, since after this commit, hierarchy levels no
longer add delta cycles. As a result, Minerva SRAM SoC runs ~73%
faster when flattened, and ~264% (!!) faster when hierarchical.
---

diff --git a/backends/cxxrtl/cxxrtl.cc b/backends/cxxrtl/cxxrtl.cc
index 89b059504..f5a8e18b5 100644
--- a/backends/cxxrtl/cxxrtl.cc
+++ b/backends/cxxrtl/cxxrtl.cc
@@ -360,6 +360,11 @@ struct FlowGraph {
 	}
 };
 
+bool is_input_wire(const RTLIL::Wire *wire)
+{
+	return wire->port_input && !wire->port_output;
+}
+
 bool is_cxxrtl_blackbox_cell(const RTLIL::Cell *cell)
 {
 	RTLIL::Module *cell_module = cell->module->design->module(cell->type);
@@ -685,7 +690,7 @@ struct CxxrtlWorker {
 					default:
 						log_assert(false);
 				}
-			} else if (localized_wires[chunk.wire]) {
+			} else if (localized_wires[chunk.wire] || is_input_wire(chunk.wire)) {
 				f << mangle(chunk.wire);
 			} else {
 				f << mangle(chunk.wire) << (is_lhs ? ".next" : ".curr");
@@ -1093,7 +1098,11 @@ struct CxxrtlWorker {
 			log_assert(cell->known());
 			const char *access = is_cxxrtl_blackbox_cell(cell) ? "->" : ".";
 			for (auto conn : cell->connections())
-				if (cell->input(conn.first)) {
+				if (cell->input(conn.first) && !cell->output(conn.first)) {
+					f << indent << mangle(cell) << access << mangle_wire_name(conn.first) << " = ";
+					dump_sigspec_rhs(conn.second);
+					f << ";\n";
+				} else if (cell->input(conn.first)) {
 					f << indent << mangle(cell) << access << mangle_wire_name(conn.first) << ".next = ";
 					dump_sigspec_rhs(conn.second);
 					f << ";\n";
@@ -1258,21 +1267,17 @@ struct CxxrtlWorker {
 		}
 	}
 
-	void dump_wire(const RTLIL::Wire *wire, bool is_local)
+	void dump_wire(const RTLIL::Wire *wire, bool is_local_context)
 	{
 		if (elided_wires.count(wire))
 			return;
+		if (localized_wires.count(wire) != is_local_context)
+			return;
 
-		if (is_local) {
-			if (!localized_wires.count(wire))
-				return;
-
+		if (is_local_context) {
 			dump_attrs(wire);
 			f << indent << "value<" << wire->width << "> " << mangle(wire) << ";\n";
 		} else {
-			if (localized_wires.count(wire))
-				return;
-
 			std::string width;
 			if (wire->module->has_attribute(ID(cxxrtl.blackbox)) && wire->has_attribute(ID(cxxrtl.width))) {
 				width = wire->get_string_attribute(ID(cxxrtl.width));
@@ -1281,29 +1286,44 @@ struct CxxrtlWorker {
 			}
 
 			dump_attrs(wire);
-			f << indent << "wire<" << width << "> " << mangle(wire);
+			f << indent << (is_input_wire(wire) ? "value" : "wire") << "<" << width << "> " << mangle(wire);
 			if (wire->has_attribute(ID::init)) {
 				f << " ";
 				dump_const_init(wire->attributes.at(ID::init));
 			}
 			f << ";\n";
 			if (sync_wires[wire]) {
+				if (is_input_wire(wire)) {
+					f << indent << "value<" << width << "> prev_" << mangle(wire);
+					if (wire->has_attribute(ID::init)) {
+						f << " ";
+						dump_const_init(wire->attributes.at(ID::init));
+					}
+					f << ";\n";
+				}
 				for (auto sync_type : sync_types) {
 					if (sync_type.first.wire == wire) {
+						std::string prev, next;
+						if (is_input_wire(wire)) {
+							prev = "prev_" + mangle(sync_type.first.wire);
+							next =           mangle(sync_type.first.wire);
+						} else {
+							prev = mangle(sync_type.first.wire) + ".curr";
+							next = mangle(sync_type.first.wire) + ".next";
+						}
+						prev += ".slice<" + std::to_string(sync_type.first.offset) + ">().val()";
+						next += ".slice<" + std::to_string(sync_type.first.offset) + ">().val()";
 						if (sync_type.second != RTLIL::STn) {
 							f << indent << "bool posedge_" << mangle(sync_type.first) << "() const {\n";
 							inc_indent();
-								f << indent << "return ";
-								f << "!" << mangle(sync_type.first.wire) << ".curr.slice<" << sync_type.first.offset << ">().val() && ";
-								f <<        mangle(sync_type.first.wire) << ".next.slice<" << sync_type.first.offset << ">().val();\n";
+								f << indent << "return !" << prev << " && " << next << ";\n";
 							dec_indent();
 							f << indent << "}\n";
-						} else {
+						}
+						if (sync_type.second != RTLIL::STp) {
 							f << indent << "bool negedge_" << mangle(sync_type.first) << "() const {\n";
 							inc_indent();
-								f << indent << "return ";
-								f <<        mangle(sync_type.first.wire) << ".curr.slice<" << sync_type.first.offset << ">().val() && ";
-								f << "!" << mangle(sync_type.first.wire) << ".next.slice<" << sync_type.first.offset << ">().val();\n";
+								f << indent << "return " << prev << " && !" << next << ";\n";
 							dec_indent();
 							f << indent << "}\n";
 						}
@@ -1363,7 +1383,7 @@ struct CxxrtlWorker {
 		inc_indent();
 			if (!module->get_bool_attribute(ID(cxxrtl.blackbox))) {
 				for (auto wire : module->wires())
-					dump_wire(wire, /*is_local=*/true);
+					dump_wire(wire, /*is_local_context=*/true);
 				for (auto node : schedule[module]) {
 					switch (node.type) {
 						case FlowGraph::Node::Type::CONNECT:
@@ -1388,6 +1408,11 @@ struct CxxrtlWorker {
 			for (auto wire : module->wires()) {
 				if (elided_wires.count(wire) || localized_wires.count(wire))
 					continue;
+				if (is_input_wire(wire)) {
+					if (sync_wires[wire])
+						f << indent << "prev_" << mangle(wire) << " = " << mangle(wire) << ";\n";
+					continue;
+				}
 				if (!module->get_bool_attribute(ID(cxxrtl.blackbox)) || wire->port_id != 0)
 					f << indent << "changed |= " << mangle(wire) << ".commit();\n";
 			}
@@ -1445,7 +1470,7 @@ struct CxxrtlWorker {
 			inc_indent();
 				for (auto wire : module->wires()) {
 					if (wire->port_id != 0)
-						dump_wire(wire, /*is_local=*/false);
+						dump_wire(wire, /*is_local_context=*/false);
 				}
 				f << "\n";
 				f << indent << "void eval() override {\n";
@@ -1485,7 +1510,7 @@ struct CxxrtlWorker {
 			f << indent << "struct " << mangle(module) << " : public module {\n";
 			inc_indent();
 				for (auto wire : module->wires())
-					dump_wire(wire, /*is_local=*/false);
+					dump_wire(wire, /*is_local_context=*/false);
 				f << "\n";
 				bool has_memories = false;
 				for (auto memory : module->memories) {
@@ -1948,9 +1973,9 @@ struct CxxrtlBackend : public Backend {
 		log("      top.step();\n");
 		log("      while (1) {\n");
 		log("        /* user logic */\n");
-		log("        top.p_clk.next = value<1> {0u};\n");
+		log("        top.p_clk = value<1> {0u};\n");
 		log("        top.step();\n");
-		log("        top.p_clk.next = value<1> {1u};\n");
+		log("        top.p_clk = value<1> {1u};\n");
 		log("        top.step();\n");
 		log("      }\n");
 		log("    }\n");
@@ -1972,16 +1997,18 @@ struct CxxrtlBackend : public Backend {
 		log("    module debug(...);\n");
 		log("      (* cxxrtl.edge = \"p\" *) input clk;\n");
 		log("      input en;\n");
-		log("      input [7:0] data;\n");
+		log("      input [7:0] i_data;\n");
+		log("      output [7:0] o_data;\n");
 		log("    endmodule\n");
 		log("\n");
 		log("For this HDL interface, this backend will generate the following C++ interface:\n");
 		log("\n");
 		log("    struct bb_p_debug : public module {\n");
-		log("      wire<1> p_clk;\n");
+		log("      value<1> p_clk;\n");
 		log("      bool posedge_p_clk() const { /* ... */ }\n");
-		log("      wire<1> p_en;\n");
-		log("      wire<8> p_data;\n");
+		log("      value<1> p_en;\n");
+		log("      value<8> p_i_data;\n");
+		log("      wire<8> p_o_data;\n");
 		log("\n");
 		log("      void eval() override;\n");
 		log("      bool commit() override;\n");
@@ -1997,8 +2024,9 @@ struct CxxrtlBackend : public Backend {
 		log("\n");
 		log("    struct stderr_debug : public bb_p_debug {\n");
 		log("      void eval() override {\n");
-		log("        if (posedge_p_clk() && p_en.curr)\n");
-		log("          fprintf(stderr, \"debug: %%02x\\n\", p_data.curr.data[0]);\n");
+		log("        if (posedge_p_clk() && p_en)\n");
+		log("          fprintf(stderr, \"debug: %%02x\\n\", p_i_data.data[0]);\n");
+		log("        p_o_data.next = p_i_data;\n");
 		log("        bb_p_debug::eval();\n");
 		log("      }\n");
 		log("    };\n");
@@ -2020,7 +2048,8 @@ struct CxxrtlBackend : public Backend {
 		log("      parameter WIDTH = 8;\n");
 		log("      (* cxxrtl.edge = \"p\" *) input clk;\n");
 		log("      input en;\n");
-		log("      (* cxxrtl.width = \"WIDTH\" *) input [WIDTH - 1:0] data;\n");
+		log("      (* cxxrtl.width = \"WIDTH\" *) input [WIDTH - 1:0] i_data;\n");
+		log("      (* cxxrtl.width = \"WIDTH\" *) output [WIDTH - 1:0] o_data;\n");
 		log("    endmodule\n");
 		log("\n");
 		log("For this parametric HDL interface, this backend will generate the following C++\n");
@@ -2029,7 +2058,8 @@ struct CxxrtlBackend : public Backend {
 		log("    template<size_t WIDTH>\n");
 		log("    struct bb_p_debug : public module {\n");
 		log("      // ...\n");
-		log("      wire<WIDTH> p_data;\n");
+		log("      value<WIDTH> p_i_data;\n");
+		log("      wire<WIDTH> p_o_data;\n");
 		log("      // ...\n");
 		log("      static std::unique_ptr<bb_p_debug<WIDTH>>\n");
 		log("      create(std::string name, metadata_map parameters, metadata_map attributes);\n");