From 1d0f0d668ade740c928c66c400476924abf62384 Mon Sep 17 00:00:00 2001
From: Clifford Wolf <clifford@clifford.at>
Date: Thu, 31 Mar 2016 08:43:28 +0200
Subject: [PATCH] Renamed opt_const to opt_expr

---
 backends/btor/verilog2btor.sh            |  2 +-
 manual/APPNOTE_012_Verilog_to_BTOR.tex   |  4 +-
 manual/CHAPTER_Optimize.tex              | 16 ++---
 manual/CHAPTER_Overview.tex              |  2 +-
 manual/PRESENTATION_ExSyn.tex            |  6 +-
 passes/opt/Makefile.inc                  |  2 +-
 passes/opt/opt.cc                        | 28 ++++-----
 passes/opt/{opt_const.cc => opt_expr.cc} | 75 ++++++++++++------------
 passes/sat/miter.cc                      |  8 +--
 techlibs/common/prep.cc                  |  4 +-
 techlibs/common/synth.cc                 |  4 +-
 techlibs/common/techmap.v                |  4 +-
 techlibs/ice40/ice40_opt.cc              |  8 +--
 techlibs/ice40/synth_ice40.cc            |  4 +-
 14 files changed, 84 insertions(+), 83 deletions(-)
 rename passes/opt/{opt_const.cc => opt_expr.cc} (93%)

diff --git a/backends/btor/verilog2btor.sh b/backends/btor/verilog2btor.sh
index 1c537d5bd..dfd7f1a85 100755
--- a/backends/btor/verilog2btor.sh
+++ b/backends/btor/verilog2btor.sh
@@ -22,7 +22,7 @@ hierarchy -top $3;
 hierarchy -libdir $DIR;
 hierarchy -check;
 proc;
-opt; opt_const -mux_undef; opt;
+opt; opt_expr -mux_undef; opt;
 rename -hide;;;
 #techmap -map +/pmux2mux.v;;
 splice; opt;
diff --git a/manual/APPNOTE_012_Verilog_to_BTOR.tex b/manual/APPNOTE_012_Verilog_to_BTOR.tex
index 245a6b0b8..1bc277876 100644
--- a/manual/APPNOTE_012_Verilog_to_BTOR.tex
+++ b/manual/APPNOTE_012_Verilog_to_BTOR.tex
@@ -208,7 +208,7 @@ read_verilog -sv $1;
 hierarchy -top $3; hierarchy -libdir $DIR;
 hierarchy -check;
 proc; opt;
-opt_const -mux_undef; opt;
+opt_expr -mux_undef; opt;
 rename -hide;;;
 splice; opt;
 memory_dff -wr_only; memory_collect;;
@@ -263,7 +263,7 @@ read_verilog -sv $1;
 hierarchy -top $3; hierarchy -libdir $DIR;
 hierarchy -check;
 proc; opt;
-opt_const -mux_undef; opt;
+opt_expr -mux_undef; opt;
 rename -hide;;;
 splice; opt;
 memory;;
diff --git a/manual/CHAPTER_Optimize.tex b/manual/CHAPTER_Optimize.tex
index d09b3c478..07f5a26e6 100644
--- a/manual/CHAPTER_Optimize.tex
+++ b/manual/CHAPTER_Optimize.tex
@@ -15,7 +15,7 @@ passes that each perform a simple optimization:
 \begin{itemize}
 \item Once at the beginning of {\tt opt}:
 \begin{itemize}
-\item {\tt opt\_const}
+\item {\tt opt\_expr}
 \item {\tt opt\_share -nomux}
 \end{itemize}
 \item Repeat until result is stable:
@@ -25,13 +25,13 @@ passes that each perform a simple optimization:
 \item {\tt opt\_share}
 \item {\tt opt\_rmdff}
 \item {\tt opt\_clean}
-\item {\tt opt\_const}
+\item {\tt opt\_expr}
 \end{itemize}
 \end{itemize}
 
 The following section describes each of the {\tt opt\_*} passes.
 
-\subsection{The opt\_const pass}
+\subsection{The opt\_expr pass}
 
 This pass performs const folding on the internal combinational cell types
 described in Chap.~\ref{chapter:celllib}. This means a cell with all constant
@@ -57,11 +57,11 @@ this pass can also optimize cells with some constant inputs.
 		$a$ &   1 & $a$ \\
 		  1 & $b$ & $b$ \\
 	\end{tabular}
-	\caption{Const folding rules for {\tt\$\_AND\_} cells as used in {\tt opt\_const}.}
-	\label{tab:opt_const_and}
+	\caption{Const folding rules for {\tt\$\_AND\_} cells as used in {\tt opt\_expr}.}
+	\label{tab:opt_expr_and}
 \end{table}
 
-Table~\ref{tab:opt_const_and} shows the replacement rules used for optimizing
+Table~\ref{tab:opt_expr_and} shows the replacement rules used for optimizing
 an {\tt\$\_AND\_} gate. The first three rules implement the obvious const folding
 rules. Note that `any' might include dynamic values calculated by other parts
 of the circuit. The following three lines propagate undef (X) states.
@@ -76,10 +76,10 @@ an undef value or a 1 and therefore the output can be set to undef.
 The last two lines simply replace an {\tt\$\_AND\_} gate with one constant-1
 input with a buffer.
 
-Besides this basic const folding the {\tt opt\_const} pass can replace 1-bit wide
+Besides this basic const folding the {\tt opt\_expr} pass can replace 1-bit wide
 {\tt \$eq} and {\tt \$ne} cells with buffers or not-gates if one input is constant.
 
-The {\tt opt\_const} pass is very conservative regarding optimizing {\tt \$mux} cells,
+The {\tt opt\_expr} pass is very conservative regarding optimizing {\tt \$mux} cells,
 as these cells are often used to model decision-trees and breaking these trees can
 interfere with other optimizations.
 
diff --git a/manual/CHAPTER_Overview.tex b/manual/CHAPTER_Overview.tex
index 032c0f8c3..4ce314825 100644
--- a/manual/CHAPTER_Overview.tex
+++ b/manual/CHAPTER_Overview.tex
@@ -488,7 +488,7 @@ select.cc}, {\tt show.cc}, \dots) and a couple of other small utility libraries.
 \item {\tt passes/} \\
 This directory contains a subdirectory for each pass or group of passes. For example as
 of this writing the directory {\tt passes/opt/} contains the code for seven
-passes: {\tt opt}, {\tt opt\_const}, {\tt opt\_muxtree}, {\tt opt\_reduce},
+passes: {\tt opt}, {\tt opt\_expr}, {\tt opt\_muxtree}, {\tt opt\_reduce},
 {\tt opt\_rmdff}, {\tt opt\_rmunused} and {\tt opt\_share}.
 
 \item {\tt techlibs/} \\
diff --git a/manual/PRESENTATION_ExSyn.tex b/manual/PRESENTATION_ExSyn.tex
index 1b56374d6..b57063c9c 100644
--- a/manual/PRESENTATION_ExSyn.tex
+++ b/manual/PRESENTATION_ExSyn.tex
@@ -144,7 +144,7 @@ The {\tt opt} command implements a series of simple optimizations. It also
 is a macro command that calls other commands:
 
 \begin{lstlisting}[xleftmargin=0.5cm, basicstyle=\ttfamily\fontsize{8pt}{10pt}\selectfont, language=ys]
-opt_const               # const folding
+opt_expr                # const folding and simple expression rewriting
 opt_share -nomux        # merging identical cells
 
 do
@@ -153,7 +153,7 @@ do
     opt_share           # merging identical cells
     opt_rmdff           # remove/simplify registers with constant inputs
     opt_clean           # remove unused objects (cells, wires) from design
-    opt_const           # const folding
+    opt_expr            # const folding and simple expression rewriting
 while [changed design]
 \end{lstlisting}
 
@@ -161,7 +161,7 @@ The command {\tt clean} can be used as alias for {\tt opt\_clean}. And {\tt ;;}
 can be used as shortcut for {\tt clean}. For example:
 
 \begin{lstlisting}[xleftmargin=0.5cm, basicstyle=\ttfamily\fontsize{8pt}{10pt}\selectfont, language=ys]
-proc; opt; memory; opt_const;; fsm;;
+proc; opt; memory; opt_expr;; fsm;;
 \end{lstlisting}
 \end{frame}
 
diff --git a/passes/opt/Makefile.inc b/passes/opt/Makefile.inc
index 43defb788..dd9088a66 100644
--- a/passes/opt/Makefile.inc
+++ b/passes/opt/Makefile.inc
@@ -5,7 +5,7 @@ OBJS += passes/opt/opt_muxtree.o
 OBJS += passes/opt/opt_reduce.o
 OBJS += passes/opt/opt_rmdff.o
 OBJS += passes/opt/opt_clean.o
-OBJS += passes/opt/opt_const.o
+OBJS += passes/opt/opt_expr.o
 
 ifneq ($(SMALL),1)
 OBJS += passes/opt/share.o
diff --git a/passes/opt/opt.cc b/passes/opt/opt.cc
index f5389d8ee..db35a1775 100644
--- a/passes/opt/opt.cc
+++ b/passes/opt/opt.cc
@@ -37,7 +37,7 @@ struct OptPass : public Pass {
 		log("a series of trivial optimizations and cleanups. This pass executes the other\n");
 		log("passes in the following order:\n");
 		log("\n");
-		log("    opt_const [-mux_undef] [-mux_bool] [-undriven] [-clkinv] [-fine] [-full] [-keepdc]\n");
+		log("    opt_expr [-mux_undef] [-mux_bool] [-undriven] [-clkinv] [-fine] [-full] [-keepdc]\n");
 		log("    opt_share [-share_all] -nomux\n");
 		log("\n");
 		log("    do\n");
@@ -46,13 +46,13 @@ struct OptPass : public Pass {
 		log("        opt_share [-share_all]\n");
 		log("        opt_rmdff\n");
 		log("        opt_clean [-purge]\n");
-		log("        opt_const [-mux_undef] [-mux_bool] [-undriven] [-clkinv] [-fine] [-full] [-keepdc]\n");
+		log("        opt_expr [-mux_undef] [-mux_bool] [-undriven] [-clkinv] [-fine] [-full] [-keepdc]\n");
 		log("    while <changed design>\n");
 		log("\n");
 		log("When called with -fast the following script is used instead:\n");
 		log("\n");
 		log("    do\n");
-		log("        opt_const [-mux_undef] [-mux_bool] [-undriven] [-clkinv] [-fine] [-full] [-keepdc]\n");
+		log("        opt_expr [-mux_undef] [-mux_bool] [-undriven] [-clkinv] [-fine] [-full] [-keepdc]\n");
 		log("        opt_share [-share_all]\n");
 		log("        opt_rmdff\n");
 		log("        opt_clean [-purge]\n");
@@ -66,7 +66,7 @@ struct OptPass : public Pass {
 	virtual void execute(std::vector<std::string> args, RTLIL::Design *design)
 	{
 		std::string opt_clean_args;
-		std::string opt_const_args;
+		std::string opt_expr_args;
 		std::string opt_reduce_args;
 		std::string opt_share_args;
 		bool fast_mode = false;
@@ -81,33 +81,33 @@ struct OptPass : public Pass {
 				continue;
 			}
 			if (args[argidx] == "-mux_undef") {
-				opt_const_args += " -mux_undef";
+				opt_expr_args += " -mux_undef";
 				continue;
 			}
 			if (args[argidx] == "-mux_bool") {
-				opt_const_args += " -mux_bool";
+				opt_expr_args += " -mux_bool";
 				continue;
 			}
 			if (args[argidx] == "-undriven") {
-				opt_const_args += " -undriven";
+				opt_expr_args += " -undriven";
 				continue;
 			}
 			if (args[argidx] == "-clkinv") {
-				opt_const_args += " -clkinv";
+				opt_expr_args += " -clkinv";
 				continue;
 			}
 			if (args[argidx] == "-fine") {
-				opt_const_args += " -fine";
+				opt_expr_args += " -fine";
 				opt_reduce_args += " -fine";
 				continue;
 			}
 			if (args[argidx] == "-full") {
-				opt_const_args += " -full";
+				opt_expr_args += " -full";
 				opt_reduce_args += " -full";
 				continue;
 			}
 			if (args[argidx] == "-keepdc") {
-				opt_const_args += " -keepdc";
+				opt_expr_args += " -keepdc";
 				continue;
 			}
 			if (args[argidx] == "-share_all") {
@@ -125,7 +125,7 @@ struct OptPass : public Pass {
 		if (fast_mode)
 		{
 			while (1) {
-				Pass::call(design, "opt_const" + opt_const_args);
+				Pass::call(design, "opt_expr" + opt_expr_args);
 				Pass::call(design, "opt_share" + opt_share_args);
 				design->scratchpad_unset("opt.did_something");
 				Pass::call(design, "opt_rmdff");
@@ -138,7 +138,7 @@ struct OptPass : public Pass {
 		}
 		else
 		{
-			Pass::call(design, "opt_const" + opt_const_args);
+			Pass::call(design, "opt_expr" + opt_expr_args);
 			Pass::call(design, "opt_share -nomux" + opt_share_args);
 			while (1) {
 				design->scratchpad_unset("opt.did_something");
@@ -147,7 +147,7 @@ struct OptPass : public Pass {
 				Pass::call(design, "opt_share" + opt_share_args);
 				Pass::call(design, "opt_rmdff");
 				Pass::call(design, "opt_clean" + opt_clean_args);
-				Pass::call(design, "opt_const" + opt_const_args);
+				Pass::call(design, "opt_expr" + opt_expr_args);
 				if (design->scratchpad_get_bool("opt.did_something") == false)
 					break;
 				log_header("Rerunning OPT passes. (Maybe there is more to do..)\n");
diff --git a/passes/opt/opt_const.cc b/passes/opt/opt_expr.cc
similarity index 93%
rename from passes/opt/opt_const.cc
rename to passes/opt/opt_expr.cc
index 0fcacf0a8..09dacf394 100644
--- a/passes/opt/opt_const.cc
+++ b/passes/opt/opt_expr.cc
@@ -179,7 +179,7 @@ bool group_cell_inputs(RTLIL::Module *module, RTLIL::Cell *cell, bool commutativ
 		log("\n");
 	}
 
-	cover_list("opt.opt_const.fine.group", "$not", "$pos", "$and", "$or", "$xor", "$xnor", cell->type.str());
+	cover_list("opt.opt_expr.fine.group", "$not", "$pos", "$and", "$or", "$xor", "$xnor", cell->type.str());
 
 	module->remove(cell);
 	did_something = true;
@@ -304,7 +304,7 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 
 	for (auto cell : cells.sorted)
 	{
-#define ACTION_DO(_p_, _s_) do { cover("opt.opt_const.action_" S__LINE__); replace_cell(assign_map, module, cell, input.as_string(), _p_, _s_); goto next_cell; } while (0)
+#define ACTION_DO(_p_, _s_) do { cover("opt.opt_expr.action_" S__LINE__); replace_cell(assign_map, module, cell, input.as_string(), _p_, _s_); goto next_cell; } while (0)
 #define ACTION_DO_Y(_v_) ACTION_DO("\\Y", RTLIL::SigSpec(RTLIL::State::S ## _v_))
 
 		if (clkinv)
@@ -366,7 +366,7 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 					}
 
 				if (new_a != RTLIL::State::Sm && RTLIL::SigSpec(new_a) != sig_a) {
-					cover("opt.opt_const.fine.$reduce_and");
+					cover("opt.opt_expr.fine.$reduce_and");
 					log("Replacing port A of %s cell `%s' in module `%s' with constant driver: %s -> %s\n",
 							cell->type.c_str(), cell->name.c_str(), module->name.c_str(), log_signal(sig_a), log_signal(new_a));
 					cell->setPort("\\A", sig_a = new_a);
@@ -392,7 +392,7 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 					}
 
 				if (new_a != RTLIL::State::Sm && RTLIL::SigSpec(new_a) != sig_a) {
-					cover_list("opt.opt_const.fine.A", "$logic_not", "$logic_and", "$logic_or", "$reduce_or", "$reduce_bool", cell->type.str());
+					cover_list("opt.opt_expr.fine.A", "$logic_not", "$logic_and", "$logic_or", "$reduce_or", "$reduce_bool", cell->type.str());
 					log("Replacing port A of %s cell `%s' in module `%s' with constant driver: %s -> %s\n",
 							cell->type.c_str(), cell->name.c_str(), module->name.c_str(), log_signal(sig_a), log_signal(new_a));
 					cell->setPort("\\A", sig_a = new_a);
@@ -418,7 +418,7 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 					}
 
 				if (new_b != RTLIL::State::Sm && RTLIL::SigSpec(new_b) != sig_b) {
-					cover_list("opt.opt_const.fine.B", "$logic_and", "$logic_or", cell->type.str());
+					cover_list("opt.opt_expr.fine.B", "$logic_and", "$logic_or", cell->type.str());
 					log("Replacing port B of %s cell `%s' in module `%s' with constant driver: %s -> %s\n",
 							cell->type.c_str(), cell->name.c_str(), module->name.c_str(), log_signal(sig_b), log_signal(new_b));
 					cell->setPort("\\B", sig_b = new_b);
@@ -429,13 +429,13 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 		}
 
 		if (cell->type == "$logic_or" && (assign_map(cell->getPort("\\A")) == RTLIL::State::S1 || assign_map(cell->getPort("\\B")) == RTLIL::State::S1)) {
-			cover("opt.opt_const.one_high");
+			cover("opt.opt_expr.one_high");
 			replace_cell(assign_map, module, cell, "one high", "\\Y", RTLIL::State::S1);
 			goto next_cell;
 		}
 
 		if (cell->type == "$logic_and" && (assign_map(cell->getPort("\\A")) == RTLIL::State::S0 || assign_map(cell->getPort("\\B")) == RTLIL::State::S0)) {
-			cover("opt.opt_const.one_low");
+			cover("opt.opt_expr.one_low");
 			replace_cell(assign_map, module, cell, "one low", "\\Y", RTLIL::State::S0);
 			goto next_cell;
 		}
@@ -462,7 +462,7 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 
 			if (0) {
 		found_the_x_bit:
-				cover_list("opt.opt_const.xbit", "$reduce_xor", "$reduce_xnor", "$shl", "$shr", "$sshl", "$sshr", "$shift", "$shiftx",
+				cover_list("opt.opt_expr.xbit", "$reduce_xor", "$reduce_xnor", "$shl", "$shr", "$sshl", "$sshr", "$shift", "$shiftx",
 						"$lt", "$le", "$ge", "$gt", "$neg", "$add", "$sub", "$mul", "$div", "$mod", "$pow", cell->type.str());
 				if (cell->type == "$reduce_xor" || cell->type == "$reduce_xnor" ||
 						cell->type == "$lt" || cell->type == "$le" || cell->type == "$ge" || cell->type == "$gt")
@@ -475,13 +475,13 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 
 		if ((cell->type == "$_NOT_" || cell->type == "$not" || cell->type == "$logic_not") && cell->getPort("\\Y").size() == 1 &&
 				invert_map.count(assign_map(cell->getPort("\\A"))) != 0) {
-			cover_list("opt.opt_const.invert.double", "$_NOT_", "$not", "$logic_not", cell->type.str());
+			cover_list("opt.opt_expr.invert.double", "$_NOT_", "$not", "$logic_not", cell->type.str());
 			replace_cell(assign_map, module, cell, "double_invert", "\\Y", invert_map.at(assign_map(cell->getPort("\\A"))));
 			goto next_cell;
 		}
 
 		if ((cell->type == "$_MUX_" || cell->type == "$mux") && invert_map.count(assign_map(cell->getPort("\\S"))) != 0) {
-			cover_list("opt.opt_const.invert.muxsel", "$_MUX_", "$mux", cell->type.str());
+			cover_list("opt.opt_expr.invert.muxsel", "$_MUX_", "$mux", cell->type.str());
 			log("Optimizing away select inverter for %s cell `%s' in module `%s'.\n", log_id(cell->type), log_id(cell), log_id(module));
 			RTLIL::SigSpec tmp = cell->getPort("\\A");
 			cell->setPort("\\A", cell->getPort("\\B"));
@@ -564,7 +564,7 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 			if (input.match("  1")) ACTION_DO("\\Y", input.extract(1, 1));
 			if (input.match("01 ")) ACTION_DO("\\Y", input.extract(0, 1));
 			if (input.match("10 ")) {
-				cover("opt.opt_const.mux_to_inv");
+				cover("opt.opt_expr.mux_to_inv");
 				cell->type = "$_NOT_";
 				cell->setPort("\\A", input.extract(0, 1));
 				cell->unsetPort("\\B");
@@ -599,7 +599,7 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 			log_assert(GetSize(a) == GetSize(b));
 			for (int i = 0; i < GetSize(a); i++) {
 				if (a[i].wire == NULL && b[i].wire == NULL && a[i] != b[i] && a[i].data <= RTLIL::State::S1 && b[i].data <= RTLIL::State::S1) {
-					cover_list("opt.opt_const.eqneq.isneq", "$eq", "$ne", "$eqx", "$nex", cell->type.str());
+					cover_list("opt.opt_expr.eqneq.isneq", "$eq", "$ne", "$eqx", "$nex", cell->type.str());
 					RTLIL::SigSpec new_y = RTLIL::SigSpec((cell->type == "$eq" || cell->type == "$eqx") ?  RTLIL::State::S0 : RTLIL::State::S1);
 					new_y.extend_u0(cell->parameters["\\Y_WIDTH"].as_int(), false);
 					replace_cell(assign_map, module, cell, "isneq", "\\Y", new_y);
@@ -612,7 +612,7 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 			}
 
 			if (new_a.size() == 0) {
-				cover_list("opt.opt_const.eqneq.empty", "$eq", "$ne", "$eqx", "$nex", cell->type.str());
+				cover_list("opt.opt_expr.eqneq.empty", "$eq", "$ne", "$eqx", "$nex", cell->type.str());
 				RTLIL::SigSpec new_y = RTLIL::SigSpec((cell->type == "$eq" || cell->type == "$eqx") ?  RTLIL::State::S1 : RTLIL::State::S0);
 				new_y.extend_u0(cell->parameters["\\Y_WIDTH"].as_int(), false);
 				replace_cell(assign_map, module, cell, "empty", "\\Y", new_y);
@@ -620,7 +620,7 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 			}
 
 			if (new_a.size() < a.size() || new_b.size() < b.size()) {
-				cover_list("opt.opt_const.eqneq.resize", "$eq", "$ne", "$eqx", "$nex", cell->type.str());
+				cover_list("opt.opt_expr.eqneq.resize", "$eq", "$ne", "$eqx", "$nex", cell->type.str());
 				cell->setPort("\\A", new_a);
 				cell->setPort("\\B", new_b);
 				cell->parameters["\\A_WIDTH"] = new_a.size();
@@ -635,7 +635,7 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 			RTLIL::SigSpec b = assign_map(cell->getPort("\\B"));
 
 			if (a.is_fully_const() && !b.is_fully_const()) {
-				cover_list("opt.opt_const.eqneq.swapconst", "$eq", "$ne", cell->type.str());
+				cover_list("opt.opt_expr.eqneq.swapconst", "$eq", "$ne", cell->type.str());
 				cell->setPort("\\A", b);
 				cell->setPort("\\B", a);
 				std::swap(a, b);
@@ -646,7 +646,7 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 					RTLIL::SigSpec input = b;
 					ACTION_DO("\\Y", cell->getPort("\\A"));
 				} else {
-					cover_list("opt.opt_const.eqneq.isnot", "$eq", "$ne", cell->type.str());
+					cover_list("opt.opt_expr.eqneq.isnot", "$eq", "$ne", cell->type.str());
 					log("Replacing %s cell `%s' in module `%s' with inverter.\n", log_id(cell->type), log_id(cell), log_id(module));
 					cell->type = "$not";
 					cell->parameters.erase("\\B_WIDTH");
@@ -661,7 +661,7 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 		if ((cell->type == "$eq" || cell->type == "$ne") &&
 				(assign_map(cell->getPort("\\A")).is_fully_zero() || assign_map(cell->getPort("\\B")).is_fully_zero()))
 		{
-			cover_list("opt.opt_const.eqneq.cmpzero", "$eq", "$ne", cell->type.str());
+			cover_list("opt.opt_expr.eqneq.cmpzero", "$eq", "$ne", cell->type.str());
 			log("Replacing %s cell `%s' in module `%s' with %s.\n", log_id(cell->type), log_id(cell),
 					log_id(module), "$eq" ? "$logic_not" : "$reduce_bool");
 			cell->type = cell->type == "$eq" ? "$logic_not" : "$reduce_bool";
@@ -699,7 +699,7 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 					sig_y[i] = sig_a[GetSize(sig_a)-1];
 			}
 
-			cover_list("opt.opt_const.constshift", "$shl", "$shr", "$sshl", "$sshr", "$shift", "$shiftx", cell->type.str());
+			cover_list("opt.opt_expr.constshift", "$shl", "$shr", "$sshl", "$sshr", "$shift", "$shiftx", cell->type.str());
 
 			log("Replacing %s cell `%s' (B=%s, SHR=%d) in module `%s' with fixed wiring: %s\n",
 					log_id(cell->type), log_id(cell), log_signal(assign_map(cell->getPort("\\B"))), shift_bits, log_id(module), log_signal(sig_y));
@@ -760,9 +760,9 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 			if (identity_wrt_a || identity_wrt_b)
 			{
 				if (identity_wrt_a)
-					cover_list("opt.opt_const.identwrt.a", "$add", "$sub", "$or", "$xor", "$shl", "$shr", "$sshl", "$sshr", "$shift", "$shiftx", "$mul", "$div", cell->type.str());
+					cover_list("opt.opt_expr.identwrt.a", "$add", "$sub", "$or", "$xor", "$shl", "$shr", "$sshl", "$sshr", "$shift", "$shiftx", "$mul", "$div", cell->type.str());
 				if (identity_wrt_b)
-					cover_list("opt.opt_const.identwrt.b", "$add", "$sub", "$or", "$xor", "$shl", "$shr", "$sshl", "$sshr", "$shift", "$shiftx", "$mul", "$div", cell->type.str());
+					cover_list("opt.opt_expr.identwrt.b", "$add", "$sub", "$or", "$xor", "$shl", "$shr", "$sshl", "$sshr", "$shift", "$shiftx", "$mul", "$div", cell->type.str());
 
 				log("Replacing %s cell `%s' in module `%s' with identity for port %c.\n",
 					cell->type.c_str(), cell->name.c_str(), module->name.c_str(), identity_wrt_a ? 'A' : 'B');
@@ -786,14 +786,14 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 
 		if (mux_bool && (cell->type == "$mux" || cell->type == "$_MUX_") &&
 				cell->getPort("\\A") == RTLIL::SigSpec(0, 1) && cell->getPort("\\B") == RTLIL::SigSpec(1, 1)) {
-			cover_list("opt.opt_const.mux_bool", "$mux", "$_MUX_", cell->type.str());
+			cover_list("opt.opt_expr.mux_bool", "$mux", "$_MUX_", cell->type.str());
 			replace_cell(assign_map, module, cell, "mux_bool", "\\Y", cell->getPort("\\S"));
 			goto next_cell;
 		}
 
 		if (mux_bool && (cell->type == "$mux" || cell->type == "$_MUX_") &&
 				cell->getPort("\\A") == RTLIL::SigSpec(1, 1) && cell->getPort("\\B") == RTLIL::SigSpec(0, 1)) {
-			cover_list("opt.opt_const.mux_invert", "$mux", "$_MUX_", cell->type.str());
+			cover_list("opt.opt_expr.mux_invert", "$mux", "$_MUX_", cell->type.str());
 			log("Replacing %s cell `%s' in module `%s' with inverter.\n", log_id(cell->type), log_id(cell), log_id(module));
 			cell->setPort("\\A", cell->getPort("\\S"));
 			cell->unsetPort("\\B");
@@ -812,7 +812,7 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 		}
 
 		if (consume_x && mux_bool && (cell->type == "$mux" || cell->type == "$_MUX_") && cell->getPort("\\A") == RTLIL::SigSpec(0, 1)) {
-			cover_list("opt.opt_const.mux_and", "$mux", "$_MUX_", cell->type.str());
+			cover_list("opt.opt_expr.mux_and", "$mux", "$_MUX_", cell->type.str());
 			log("Replacing %s cell `%s' in module `%s' with and-gate.\n", log_id(cell->type), log_id(cell), log_id(module));
 			cell->setPort("\\A", cell->getPort("\\S"));
 			cell->unsetPort("\\S");
@@ -832,7 +832,7 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 		}
 
 		if (consume_x && mux_bool && (cell->type == "$mux" || cell->type == "$_MUX_") && cell->getPort("\\B") == RTLIL::SigSpec(1, 1)) {
-			cover_list("opt.opt_const.mux_or", "$mux", "$_MUX_", cell->type.str());
+			cover_list("opt.opt_expr.mux_or", "$mux", "$_MUX_", cell->type.str());
 			log("Replacing %s cell `%s' in module `%s' with or-gate.\n", log_id(cell->type), log_id(cell), log_id(module));
 			cell->setPort("\\B", cell->getPort("\\S"));
 			cell->unsetPort("\\S");
@@ -856,7 +856,7 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 			int width = cell->getPort("\\A").size();
 			if ((cell->getPort("\\A").is_fully_undef() && cell->getPort("\\B").is_fully_undef()) ||
 					cell->getPort("\\S").is_fully_undef()) {
-				cover_list("opt.opt_const.mux_undef", "$mux", "$pmux", cell->type.str());
+				cover_list("opt.opt_expr.mux_undef", "$mux", "$pmux", cell->type.str());
 				replace_cell(assign_map, module, cell, "mux_undef", "\\Y", cell->getPort("\\A"));
 				goto next_cell;
 			}
@@ -875,17 +875,17 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 				new_s = new_s.extract(0, new_s.size()-1);
 			}
 			if (new_s.size() == 0) {
-				cover_list("opt.opt_const.mux_empty", "$mux", "$pmux", cell->type.str());
+				cover_list("opt.opt_expr.mux_empty", "$mux", "$pmux", cell->type.str());
 				replace_cell(assign_map, module, cell, "mux_empty", "\\Y", new_a);
 				goto next_cell;
 			}
 			if (new_a == RTLIL::SigSpec(RTLIL::State::S0) && new_b == RTLIL::SigSpec(RTLIL::State::S1)) {
-				cover_list("opt.opt_const.mux_sel01", "$mux", "$pmux", cell->type.str());
+				cover_list("opt.opt_expr.mux_sel01", "$mux", "$pmux", cell->type.str());
 				replace_cell(assign_map, module, cell, "mux_sel01", "\\Y", new_s);
 				goto next_cell;
 			}
 			if (cell->getPort("\\S").size() != new_s.size()) {
-				cover_list("opt.opt_const.mux_reduce", "$mux", "$pmux", cell->type.str());
+				cover_list("opt.opt_expr.mux_reduce", "$mux", "$pmux", cell->type.str());
 				log("Optimized away %d select inputs of %s cell `%s' in module `%s'.\n",
 						GetSize(cell->getPort("\\S")) - GetSize(new_s), log_id(cell->type), log_id(cell), log_id(module));
 				cell->setPort("\\A", new_a);
@@ -911,7 +911,7 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 				RTLIL::SigSpec y(RTLIL::const_ ## _t(a.as_const(), dummy_arg, \
 						cell->parameters["\\A_SIGNED"].as_bool(), false, \
 						cell->parameters["\\Y_WIDTH"].as_int())); \
-				cover("opt.opt_const.const.$" #_t); \
+				cover("opt.opt_expr.const.$" #_t); \
 				replace_cell(assign_map, module, cell, stringf("%s", log_signal(a)), "\\Y", y); \
 				goto next_cell; \
 			} \
@@ -926,7 +926,7 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 						cell->parameters["\\A_SIGNED"].as_bool(), \
 						cell->parameters["\\B_SIGNED"].as_bool(), \
 						cell->parameters["\\Y_WIDTH"].as_int())); \
-				cover("opt.opt_const.const.$" #_t); \
+				cover("opt.opt_expr.const.$" #_t); \
 				replace_cell(assign_map, module, cell, stringf("%s, %s", log_signal(a), log_signal(b)), "\\Y", y); \
 				goto next_cell; \
 			} \
@@ -1002,7 +1002,7 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 
 				if (a_val == 0)
 				{
-					cover("opt.opt_const.mul_shift.zero");
+					cover("opt.opt_expr.mul_shift.zero");
 
 					log("Replacing multiply-by-zero cell `%s' in module `%s' with zero-driver.\n",
 							cell->name.c_str(), module->name.c_str());
@@ -1018,9 +1018,9 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 					if (a_val == (1 << i))
 					{
 						if (swapped_ab)
-							cover("opt.opt_const.mul_shift.swapped");
+							cover("opt.opt_expr.mul_shift.swapped");
 						else
-							cover("opt.opt_const.mul_shift.unswapped");
+							cover("opt.opt_expr.mul_shift.unswapped");
 
 						log("Replacing multiply-by-%d cell `%s' in module `%s' with shift-by-%d.\n",
 								a_val, cell->name.c_str(), module->name.c_str(), i);
@@ -1056,15 +1056,16 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 	}
 }
 
-struct OptConstPass : public Pass {
-	OptConstPass() : Pass("opt_const", "perform const folding") { }
+struct OptExprPass : public Pass {
+	OptExprPass() : Pass("opt_expr", "perform const folding and simple expression rewriting") { }
 	virtual void help()
 	{
 		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
 		log("\n");
-		log("    opt_const [options] [selection]\n");
+		log("    opt_expr [options] [selection]\n");
 		log("\n");
 		log("This pass performs const folding on internal cell types with constant inputs.\n");
+		log("It also performs some simple expression rewritring.\n");
 		log("\n");
 		log("    -mux_undef\n");
 		log("        remove 'undef' inputs from $mux, $pmux and $_MUX_ cells\n");
@@ -1158,6 +1159,6 @@ struct OptConstPass : public Pass {
 
 		log_pop();
 	}
-} OptConstPass;
+} OptExprPass;
 
 PRIVATE_NAMESPACE_END
diff --git a/passes/sat/miter.cc b/passes/sat/miter.cc
index 682299ef2..e809425c8 100644
--- a/passes/sat/miter.cc
+++ b/passes/sat/miter.cc
@@ -254,7 +254,7 @@ void create_miter_equiv(struct Pass *that, std::vector<std::string> args, RTLIL:
 
 	if (flag_flatten) {
 		log_push();
-		Pass::call_on_module(design, miter_module, "flatten; opt_const -keepdc -undriven;;");
+		Pass::call_on_module(design, miter_module, "flatten; opt_expr -keepdc -undriven;;");
 		log_pop();
 	}
 }
@@ -327,7 +327,7 @@ void create_miter_assert(struct Pass *that, std::vector<std::string> args, RTLIL
 
 	if (flag_flatten) {
 		log_push();
-		Pass::call_on_module(design, module, "opt_const -keepdc -undriven;;");
+		Pass::call_on_module(design, module, "opt_expr -keepdc -undriven;;");
 		log_pop();
 	}
 }
@@ -361,7 +361,7 @@ struct MiterPass : public Pass {
 		log("        also create an 'assert' cell that checks if trigger is always low.\n");
 		log("\n");
 		log("    -flatten\n");
-		log("        call 'flatten; opt_const -keepdc -undriven;;' on the miter circuit.\n");
+		log("        call 'flatten; opt_expr -keepdc -undriven;;' on the miter circuit.\n");
 		log("\n");
 		log("\n");
 		log("    miter -assert [options] module [miter_name]\n");
@@ -375,7 +375,7 @@ struct MiterPass : public Pass {
 		log("        keep module output ports.\n");
 		log("\n");
 		log("    -flatten\n");
-		log("        call 'flatten; opt_const -keepdc -undriven;;' on the miter circuit.\n");
+		log("        call 'flatten; opt_expr -keepdc -undriven;;' on the miter circuit.\n");
 		log("\n");
 	}
 	virtual void execute(std::vector<std::string> args, RTLIL::Design *design)
diff --git a/techlibs/common/prep.cc b/techlibs/common/prep.cc
index 8bae920d0..911737947 100644
--- a/techlibs/common/prep.cc
+++ b/techlibs/common/prep.cc
@@ -69,7 +69,7 @@ struct PrepPass : public Pass {
 		log("\n");
 		log("    prep:\n");
 		log("        proc\n");
-		log("        opt_const\n");
+		log("        opt_expr -keepdc\n");
 		log("        opt_clean\n");
 		log("        check\n");
 		log("        opt -keepdc\n");
@@ -134,7 +134,7 @@ struct PrepPass : public Pass {
 		if (check_label(active, run_from, run_to, "coarse"))
 		{
 			Pass::call(design, "proc");
-			Pass::call(design, "opt_const");
+			Pass::call(design, "opt_expr -keepdc");
 			Pass::call(design, "opt_clean");
 			Pass::call(design, "check");
 			Pass::call(design, "opt -keepdc");
diff --git a/techlibs/common/synth.cc b/techlibs/common/synth.cc
index 83d00f328..c837e1378 100644
--- a/techlibs/common/synth.cc
+++ b/techlibs/common/synth.cc
@@ -81,7 +81,7 @@ struct SynthPass : public Pass {
 		log("\n");
 		log("    coarse:\n");
 		log("        proc\n");
-		log("        opt_const\n");
+		log("        opt_expr\n");
 		log("        opt_clean\n");
 		log("        check\n");
 		log("        opt\n");
@@ -180,7 +180,7 @@ struct SynthPass : public Pass {
 		if (check_label(active, run_from, run_to, "coarse"))
 		{
 			Pass::call(design, "proc");
-			Pass::call(design, "opt_const");
+			Pass::call(design, "opt_expr");
 			Pass::call(design, "opt_clean");
 			Pass::call(design, "check");
 			Pass::call(design, "opt");
diff --git a/techlibs/common/techmap.v b/techlibs/common/techmap.v
index ae08c3d17..a623bb516 100644
--- a/techlibs/common/techmap.v
+++ b/techlibs/common/techmap.v
@@ -93,7 +93,7 @@ module _90_shift_ops_shr_shl_sshl_sshr (A, B, Y);
 	localparam BB_WIDTH = `MIN($clog2(shift_left ? Y_WIDTH : A_SIGNED ? WIDTH : A_WIDTH) + 1, B_WIDTH);
 
 	wire [1023:0] _TECHMAP_DO_00_ = "proc;;";
-	wire [1023:0] _TECHMAP_DO_01_ = "RECURSION; CONSTMAP; opt_muxtree; opt_const -mux_undef -mux_bool -fine;;;";
+	wire [1023:0] _TECHMAP_DO_01_ = "RECURSION; CONSTMAP; opt_muxtree; opt_expr -mux_undef -mux_bool -fine;;;";
 
 	integer i;
 	reg [WIDTH-1:0] buffer;
@@ -136,7 +136,7 @@ module _90_shift_shiftx (A, B, Y);
 	localparam extbit = _TECHMAP_CELLTYPE_ == "$shift" ? 1'b0 : 1'bx;
 
 	wire [1023:0] _TECHMAP_DO_00_ = "proc;;";
-	wire [1023:0] _TECHMAP_DO_01_ = "CONSTMAP; opt_muxtree; opt_const -mux_undef -mux_bool -fine;;;";
+	wire [1023:0] _TECHMAP_DO_01_ = "CONSTMAP; opt_muxtree; opt_expr -mux_undef -mux_bool -fine;;;";
 
 	integer i;
 	reg [WIDTH-1:0] buffer;
diff --git a/techlibs/ice40/ice40_opt.cc b/techlibs/ice40/ice40_opt.cc
index 677ac8d77..69c222808 100644
--- a/techlibs/ice40/ice40_opt.cc
+++ b/techlibs/ice40/ice40_opt.cc
@@ -127,7 +127,7 @@ struct Ice40OptPass : public Pass {
 		log("\n");
 		log("    do\n");
 		log("        <ice40 specific optimizations>\n");
-		log("        opt_const -mux_undef -undriven [-full]\n");
+		log("        opt_expr -mux_undef -undriven [-full]\n");
 		log("        opt_share\n");
 		log("        opt_rmdff\n");
 		log("        opt_clean\n");
@@ -136,14 +136,14 @@ struct Ice40OptPass : public Pass {
 	}
 	virtual void execute(std::vector<std::string> args, RTLIL::Design *design)
 	{
-		string opt_const_args = "-mux_undef -undriven";
+		string opt_expr_args = "-mux_undef -undriven";
 		log_header("Executing ICE40_OPT pass (performing simple optimizations).\n");
 		log_push();
 
 		size_t argidx;
 		for (argidx = 1; argidx < args.size(); argidx++) {
 			if (args[argidx] == "-full") {
-				opt_const_args += " -full";
+				opt_expr_args += " -full";
 				continue;
 			}
 			break;
@@ -158,7 +158,7 @@ struct Ice40OptPass : public Pass {
 			for (auto module : design->selected_modules())
 				run_ice40_opts(module);
 
-			Pass::call(design, "opt_const " + opt_const_args);
+			Pass::call(design, "opt_expr " + opt_expr_args);
 			Pass::call(design, "opt_share");
 			Pass::call(design, "opt_rmdff");
 			Pass::call(design, "opt_clean");
diff --git a/techlibs/ice40/synth_ice40.cc b/techlibs/ice40/synth_ice40.cc
index 92d53f4ab..f24d31a8c 100644
--- a/techlibs/ice40/synth_ice40.cc
+++ b/techlibs/ice40/synth_ice40.cc
@@ -106,7 +106,7 @@ struct SynthIce40Pass : public Pass {
 		log("        dffsr2dff\n");
 		log("        dff2dffe -direct-match $_DFF_*\n");
 		log("        techmap -map +/ice40/cells_map.v\n");
-		log("        opt_const -mux_undef\n");
+		log("        opt_expr -mux_undef\n");
 		log("        simplemap\n");
 		log("        ice40_ffinit\n");
 		log("        ice40_ffssr\n");
@@ -247,7 +247,7 @@ struct SynthIce40Pass : public Pass {
 			Pass::call(design, "dffsr2dff");
 			Pass::call(design, "dff2dffe -direct-match $_DFF_*");
 			Pass::call(design, "techmap -map +/ice40/cells_map.v");
-			Pass::call(design, "opt_const -mux_undef");
+			Pass::call(design, "opt_expr -mux_undef");
 			Pass::call(design, "simplemap");
 			Pass::call(design, "ice40_ffinit");
 			Pass::call(design, "ice40_ffssr");