A new proc_prune pass

passes/proc/Makefile.inc

@@ -1,10 +1,10 @@
 
 OBJS += passes/proc/proc.o
+OBJS += passes/proc/proc_prune.o
 OBJS += passes/proc/proc_clean.o
 OBJS += passes/proc/proc_rmdead.o
 OBJS += passes/proc/proc_init.o
 OBJS += passes/proc/proc_arst.o
 OBJS += passes/proc/proc_mux.o
 OBJS += passes/proc/proc_dlatch.o
 OBJS += passes/proc/proc_dff.o
-

passes/proc/proc.cc

@@ -37,6 +37,7 @@ struct ProcPass : public Pass {
 		log("\n");
 		log("    proc_clean\n");
 		log("    proc_rmdead\n");
+		log("    proc_prune\n");
 		log("    proc_init\n");
 		log("    proc_arst\n");
 		log("    proc_mux\n");
@@ -83,6 +84,7 @@ struct ProcPass : public Pass {
 		Pass::call(design, "proc_clean");
 		if (!ifxmode)
 			Pass::call(design, "proc_rmdead");
+		Pass::call(design, "proc_prune");
 		Pass::call(design, "proc_init");
 		if (global_arst.empty())
 			Pass::call(design, "proc_arst");

passes/proc/proc_arst.cc

@@ -172,7 +172,7 @@ void proc_arst(RTLIL::Module *mod, RTLIL::Process *proc, SigMap &assign_map)
 					sync->type = sync->type == RTLIL::SyncType::STp ? RTLIL::SyncType::ST1 : RTLIL::SyncType::ST0;
 				}
 				for (auto &action : sync->actions) {
-					RTLIL::SigSpec rspec = action.second;
+					RTLIL::SigSpec rspec = assign_map(action.second);
 					RTLIL::SigSpec rval = RTLIL::SigSpec(RTLIL::State::Sm, rspec.size());
 					for (int i = 0; i < GetSize(rspec); i++)
 						if (rspec[i].wire == NULL)

passes/proc/proc_init.cc

@@ -26,21 +26,7 @@
 USING_YOSYS_NAMESPACE
 PRIVATE_NAMESPACE_BEGIN
 
-void proc_get_const(RTLIL::SigSpec &sig, RTLIL::CaseRule &rule)
-{
-	log_assert(rule.compare.size() == 0);
-
-	while (1) {
-		RTLIL::SigSpec tmp = sig;
-		for (auto &it : rule.actions)
-			tmp.replace(it.first, it.second);
-		if (tmp == sig)
-			break;
-		sig = tmp;
-	}
-}
-
-void proc_init(RTLIL::Module *mod, RTLIL::Process *proc)
+void proc_init(RTLIL::Module *mod, SigMap &sigmap, RTLIL::Process *proc)
 {
 	bool found_init = false;
 
@@ -53,9 +39,7 @@ void proc_init(RTLIL::Module *mod, RTLIL::Process *proc)
 			for (auto &action : sync->actions)
 			{
 				RTLIL::SigSpec lhs = action.first;
-				RTLIL::SigSpec rhs = action.second;
-
-				proc_get_const(rhs, proc->root_case);
+				RTLIL::SigSpec rhs = sigmap(action.second);
 
 				if (!rhs.is_fully_const())
 					log_cmd_error("Failed to get a constant init value for %s: %s\n", log_signal(lhs), log_signal(rhs));
@@ -120,10 +104,12 @@ struct ProcInitPass : public Pass {
 		extra_args(args, 1, design);
 
 		for (auto mod : design->modules())
-			if (design->selected(mod))
+			if (design->selected(mod)) {
+				SigMap sigmap(mod);
 				for (auto &proc_it : mod->processes)
 					if (design->selected(mod, proc_it.second))
-						proc_init(mod, proc_it.second);
+						proc_init(mod, sigmap, proc_it.second);
+			}
 	}
 } ProcInitPass;
 

passes/proc/proc_prune.cc

@@ -0,0 +1,158 @@
+/*
+ *  yosys -- Yosys Open SYnthesis Suite
+ *
+ *  Copyright (C) 2019  whitequark <whitequark@whitequark.org>
+ *
+ *  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/register.h"
+#include "kernel/sigtools.h"
+#include "kernel/log.h"
+#include <stdlib.h>
+#include <stdio.h>
+
+USING_YOSYS_NAMESPACE
+PRIVATE_NAMESPACE_BEGIN
+
+struct PruneWorker
+{
+	RTLIL::Module *module;
+	SigMap sigmap;
+
+	int removed_count = 0, promoted_count = 0;
+
+	PruneWorker(RTLIL::Module *mod) : module(mod), sigmap(mod) {}
+
+	pool<RTLIL::SigBit> do_switch(RTLIL::SwitchRule *sw, pool<RTLIL::SigBit> assigned, pool<RTLIL::SigBit> &affected)
+	{
+		pool<RTLIL::SigBit> all_assigned;
+		bool full_case = sw->get_bool_attribute("\\full_case");
+		bool first = true;
+		for (auto it : sw->cases) {
+			if (it->compare.empty())
+				full_case = true;
+			pool<RTLIL::SigBit> case_assigned = do_case(it, assigned, affected);
+			if (first) {
+				first = false;
+				all_assigned = case_assigned;
+			} else {
+				for (auto &bit : all_assigned)
+					if (!case_assigned[bit])
+						all_assigned.erase(bit);
+			}
+		}
+		if (full_case)
+			assigned.insert(all_assigned.begin(), all_assigned.end());
+		return assigned;
+	}
+
+	pool<RTLIL::SigBit> do_case(RTLIL::CaseRule *cs, pool<RTLIL::SigBit> assigned, pool<RTLIL::SigBit> &affected,
+	                            bool root = false)
+	{
+		for (auto it = cs->switches.rbegin(); it != cs->switches.rend(); ++it) {
+			pool<RTLIL::SigBit> sw_assigned = do_switch((*it), assigned, affected);
+			assigned.insert(sw_assigned.begin(), sw_assigned.end());
+		}
+		pool<RTLIL::SigSig> remove;
+		for (auto it = cs->actions.rbegin(); it != cs->actions.rend(); ++it) {
+			RTLIL::SigSpec lhs = sigmap(it->first);
+			bool redundant = true;
+			for (auto &bit : lhs) {
+				if (bit.wire && !assigned[bit]) {
+					redundant = false;
+					break;
+				}
+			}
+			if (redundant) {
+				removed_count++;
+				remove.insert(*it);
+			} else {
+				if (root) {
+					bool promotable = true;
+					for (auto &bit : lhs) {
+						if (bit.wire && affected[bit]) {
+							promotable = false;
+							break;
+						}
+					}
+					if (promotable) {
+						promoted_count++;
+						module->connect(*it);
+						remove.insert(*it);
+					}
+				}
+				for (auto &bit : lhs)
+					if (bit.wire)
+						assigned.insert(bit);
+				for (auto &bit : lhs)
+					if (bit.wire)
+						affected.insert(bit);
+			}
+		}
+		for (auto it = cs->actions.begin(); it != cs->actions.end(); ) {
+			if (remove[*it]) {
+				it = cs->actions.erase(it);
+			} else it++;
+		}
+		return assigned;
+	}
+
+	void do_process(RTLIL::Process *pr)
+	{
+		pool<RTLIL::SigBit> affected;
+		do_case(&pr->root_case, {}, affected, /*root=*/true);
+	}
+};
+
+struct ProcPrunePass : public Pass {
+	ProcPrunePass() : Pass("proc_prune", "remove redundant assignments") { }
+	void help() YS_OVERRIDE
+	{
+		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
+		log("\n");
+		log("    proc_prune [selection]\n");
+		log("\n");
+		log("This pass identifies assignments in processes that are always overwritten by\n");
+		log("a later assignment to the same signal and removes them.\n");
+		log("\n");
+	}
+	void execute(std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE
+	{
+		int total_removed_count = 0, total_promoted_count = 0;
+		log_header(design, "Executing PROC_PRUNE pass (remove redundant assignments in processes).\n");
+
+		extra_args(args, 1, design);
+
+		for (auto mod : design->modules()) {
+			if (!design->selected(mod))
+				continue;
+			PruneWorker worker(mod);
+			for (auto &proc_it : mod->processes) {
+				if (!design->selected(mod, proc_it.second))
+					continue;
+				worker.do_process(proc_it.second);
+			}
+			total_removed_count += worker.removed_count;
+			total_promoted_count += worker.promoted_count;
+		}
+
+		log("Removed %d redundant assignment%s.\n",
+		    total_removed_count, total_removed_count == 1 ? "" : "s");
+		log("Promoted %d assignment%s to connection%s.\n",
+		    total_promoted_count, total_promoted_count == 1 ? "" : "s", total_promoted_count == 1 ? "" : "s");
+	}
+} ProcPrunePass;
+
+PRIVATE_NAMESPACE_END