From ed519f578eb965f9976931c817aa54e3cd89710d Mon Sep 17 00:00:00 2001
From: Clifford Wolf <clifford@clifford.at>
Date: Fri, 30 Sep 2016 17:02:38 +0200
Subject: [PATCH] Added "opt_rmdff -keepdc"

---
 passes/opt/opt.cc       | 10 ++++++----
 passes/opt/opt_rmdff.cc | 17 ++++++++++++++---
 2 files changed, 20 insertions(+), 7 deletions(-)

diff --git a/passes/opt/opt.cc b/passes/opt/opt.cc
index 13ea5469b..021c1a03f 100644
--- a/passes/opt/opt.cc
+++ b/passes/opt/opt.cc
@@ -44,7 +44,7 @@ struct OptPass : public Pass {
 		log("        opt_muxtree\n");
 		log("        opt_reduce [-fine] [-full]\n");
 		log("        opt_merge [-share_all]\n");
-		log("        opt_rmdff\n");
+		log("        opt_rmdff [-keepdc]\n");
 		log("        opt_clean [-purge]\n");
 		log("        opt_expr [-mux_undef] [-mux_bool] [-undriven] [-clkinv] [-fine] [-full] [-keepdc]\n");
 		log("    while <changed design>\n");
@@ -54,7 +54,7 @@ struct OptPass : public Pass {
 		log("    do\n");
 		log("        opt_expr [-mux_undef] [-mux_bool] [-undriven] [-clkinv] [-fine] [-full] [-keepdc]\n");
 		log("        opt_merge [-share_all]\n");
-		log("        opt_rmdff\n");
+		log("        opt_rmdff [-keepdc]\n");
 		log("        opt_clean [-purge]\n");
 		log("    while <changed design in opt_rmdff>\n");
 		log("\n");
@@ -69,6 +69,7 @@ struct OptPass : public Pass {
 		std::string opt_expr_args;
 		std::string opt_reduce_args;
 		std::string opt_merge_args;
+		std::string opt_rmdff_args;
 		bool fast_mode = false;
 
 		log_header(design, "Executing OPT pass (performing simple optimizations).\n");
@@ -108,6 +109,7 @@ struct OptPass : public Pass {
 			}
 			if (args[argidx] == "-keepdc") {
 				opt_expr_args += " -keepdc";
+				opt_rmdff_args += " -keepdc";
 				continue;
 			}
 			if (args[argidx] == "-share_all") {
@@ -128,7 +130,7 @@ struct OptPass : public Pass {
 				Pass::call(design, "opt_expr" + opt_expr_args);
 				Pass::call(design, "opt_merge" + opt_merge_args);
 				design->scratchpad_unset("opt.did_something");
-				Pass::call(design, "opt_rmdff");
+				Pass::call(design, "opt_rmdff" + opt_rmdff_args);
 				if (design->scratchpad_get_bool("opt.did_something") == false)
 					break;
 				Pass::call(design, "opt_clean" + opt_clean_args);
@@ -145,7 +147,7 @@ struct OptPass : public Pass {
 				Pass::call(design, "opt_muxtree");
 				Pass::call(design, "opt_reduce" + opt_reduce_args);
 				Pass::call(design, "opt_merge" + opt_merge_args);
-				Pass::call(design, "opt_rmdff");
+				Pass::call(design, "opt_rmdff" + opt_rmdff_args);
 				Pass::call(design, "opt_clean" + opt_clean_args);
 				Pass::call(design, "opt_expr" + opt_expr_args);
 				if (design->scratchpad_get_bool("opt.did_something") == false)
diff --git a/passes/opt/opt_rmdff.cc b/passes/opt/opt_rmdff.cc
index fa954afac..7e87d1adc 100644
--- a/passes/opt/opt_rmdff.cc
+++ b/passes/opt/opt_rmdff.cc
@@ -29,6 +29,7 @@ PRIVATE_NAMESPACE_BEGIN
 SigMap assign_map, dff_init_map;
 SigSet<RTLIL::Cell*> mux_drivers;
 dict<SigBit, pool<SigBit>> init_attributes;
+bool keepdc;
 
 void remove_init_attr(SigSpec sig)
 {
@@ -115,7 +116,7 @@ bool handle_dff(RTLIL::Module *mod, RTLIL::Cell *dff)
 	bool has_init = false;
 	RTLIL::Const val_init;
 	for (auto bit : dff_init_map(sig_q).to_sigbit_vector()) {
-		if (bit.wire == NULL)
+		if (bit.wire == NULL || keepdc)
 			has_init = true;
 		val_init.bits.push_back(bit.wire == NULL ? bit.data : RTLIL::State::Sx);
 	}
@@ -182,7 +183,7 @@ struct OptRmdffPass : public Pass {
 	{
 		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
 		log("\n");
-		log("    opt_rmdff [selection]\n");
+		log("    opt_rmdff [-keepdc] [selection]\n");
 		log("\n");
 		log("This pass identifies flip-flops with constant inputs and replaces them with\n");
 		log("a constant driver.\n");
@@ -193,7 +194,17 @@ struct OptRmdffPass : public Pass {
 		int total_count = 0, total_initdrv = 0;
 		log_header(design, "Executing OPT_RMDFF pass (remove dff with constant values).\n");
 
-		extra_args(args, 1, design);
+		keepdc = false;
+
+		size_t argidx;
+		for (argidx = 1; argidx < args.size(); argidx++) {
+			if (args[argidx] == "-keepdc") {
+				keepdc = true;
+				continue;
+			}
+			break;
+		}
+		extra_args(args, argidx, design);
 
 		for (auto module : design->selected_modules())
 		{
-- 
2.30.2