From: Clifford Wolf <clifford@clifford.at>
Date: Tue, 29 Jul 2014 12:42:33 +0000 (+0200)
Subject: Added $shift and $shiftx cell types (needed for correct part select behavior)
X-Git-Tag: yosys-0.4~371
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=397b00252dc0c4af725614bd12fc299147ba8efa;p=yosys.git

Added $shift and $shiftx cell types (needed for correct part select behavior)
---

diff --git a/CHECKLISTS b/CHECKLISTS
index 3f824fc28..8a149a539 100644
--- a/CHECKLISTS
+++ b/CHECKLISTS
@@ -123,6 +123,8 @@ Things to do right away:
 
 	- Add to kernel/celltypes.h (incl. eval() handling for non-mem cells)
 	- Add to InternalCellChecker::check() in kernel/rtlil.cc
+	- Add to techlibs/common/simlib.v
+	- Add to techlibs/common/stdcells.v
 
 Things to do after finalizing the cell interface:
 
diff --git a/backends/btor/btor.cc b/backends/btor/btor.cc
index f721fdc99..43c036690 100644
--- a/backends/btor/btor.cc
+++ b/backends/btor/btor.cc
@@ -111,6 +111,8 @@ struct BtorDumper
 		cell_type_translation["$shl"] = "sll";
 		cell_type_translation["$sshr"] = "sra";
 		cell_type_translation["$sshl"] = "sll";
+		cell_type_translation["$shift"] = "srl";
+		cell_type_translation["$shiftx"] = "srl";
 		cell_type_translation["$lt"] = "ult";
 		cell_type_translation["$le"] = "ulte";
 		cell_type_translation["$gt"] = "ugt";
@@ -540,7 +542,7 @@ struct BtorDumper
 				}
 				line_ref[cell->name]=line_num;
 			}
-			else if(cell->type == "$shr" || cell->type == "$shl" || cell->type == "$sshr" || cell->type == "$sshl")
+			else if(cell->type == "$shr" || cell->type == "$shl" || cell->type == "$sshr" || cell->type == "$sshl" || cell->type == "$shift" || cell->type == "$shiftx")
 			{
 				log("writing binary cell - %s\n", cstr(cell->type));
 				int output_width = cell->parameters.at(RTLIL::IdString("\\Y_WIDTH")).as_int();
diff --git a/frontends/ast/genrtlil.cc b/frontends/ast/genrtlil.cc
index cb666679b..b7f336354 100644
--- a/frontends/ast/genrtlil.cc
+++ b/frontends/ast/genrtlil.cc
@@ -917,11 +917,17 @@ RTLIL::SigSpec AstNode::genRTLIL(int width_hint, bool sign_hint)
 							children[0]->children[1]->clone() : children[0]->children[0]->clone());
 					fake_ast->children[0]->delete_children();
 					RTLIL::SigSpec shift_val = fake_ast->children[1]->genRTLIL();
-					if (id2ast->range_right != 0)
-						shift_val = current_module->Sub(NEW_ID, shift_val, id2ast->range_right);
-					if (id2ast->range_swapped)
-						shift_val = current_module->Sub(NEW_ID, RTLIL::SigSpec(source_width - width), shift_val);
-					RTLIL::SigSpec sig = binop2rtlil(fake_ast, "$shr", width, fake_ast->children[0]->genRTLIL(), shift_val);
+					if (id2ast->range_right != 0) {
+						shift_val = current_module->Sub(NEW_ID, shift_val, id2ast->range_right, fake_ast->children[1]->is_signed);
+						fake_ast->children[1]->is_signed = true;
+					}
+					if (id2ast->range_swapped) {
+						shift_val = current_module->Sub(NEW_ID, RTLIL::SigSpec(source_width - width), shift_val, fake_ast->children[1]->is_signed);
+						fake_ast->children[1]->is_signed = true;
+					}
+					if (SIZE(shift_val) >= 32)
+						fake_ast->children[1]->is_signed = true;
+					RTLIL::SigSpec sig = binop2rtlil(fake_ast, "$shiftx", width, fake_ast->children[0]->genRTLIL(), shift_val);
 					delete left_at_zero_ast;
 					delete right_at_zero_ast;
 					delete fake_ast;
diff --git a/kernel/calc.cc b/kernel/calc.cc
index b413760d1..b3ff3cf2a 100644
--- a/kernel/calc.cc
+++ b/kernel/calc.cc
@@ -276,7 +276,7 @@ RTLIL::Const RTLIL::const_logic_or(const RTLIL::Const &arg1, const RTLIL::Const
 	return result;
 }
 
-static RTLIL::Const const_shift(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool sign_ext, int direction, int result_len)
+static RTLIL::Const const_shift_worker(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool sign_ext, int direction, int result_len)
 {
 	int undef_bit_pos = -1;
 	BigInteger offset = const2big(arg2, false, undef_bit_pos) * direction;
@@ -305,28 +305,61 @@ RTLIL::Const RTLIL::const_shl(const RTLIL::Const &arg1, const RTLIL::Const &arg2
 {
 	RTLIL::Const arg1_ext = arg1;
 	extend_u0(arg1_ext, result_len, signed1);
-	return const_shift(arg1_ext, arg2, false, -1, result_len);
+	return const_shift_worker(arg1_ext, arg2, false, -1, result_len);
 }
 
 RTLIL::Const RTLIL::const_shr(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool, int result_len)
 {
 	RTLIL::Const arg1_ext = arg1;
 	extend_u0(arg1_ext, result_len, signed1);
-	return const_shift(arg1_ext, arg2, false, +1, result_len);
+	return const_shift_worker(arg1_ext, arg2, false, +1, result_len);
 }
 
 RTLIL::Const RTLIL::const_sshl(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool signed2, int result_len)
 {
 	if (!signed1)
 		return const_shl(arg1, arg2, signed1, signed2, result_len);
-	return const_shift(arg1, arg2, true, -1, result_len);
+	return const_shift_worker(arg1, arg2, true, -1, result_len);
 }
 
 RTLIL::Const RTLIL::const_sshr(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool signed2, int result_len)
 {
 	if (!signed1)
 		return const_shr(arg1, arg2, signed1, signed2, result_len);
-	return const_shift(arg1, arg2, true, +1, result_len);
+	return const_shift_worker(arg1, arg2, true, +1, result_len);
+}
+
+static RTLIL::Const const_shift_shiftx(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool, bool signed2, int result_len, RTLIL::State other_bits)
+{
+	int undef_bit_pos = -1;
+	BigInteger offset = const2big(arg2, signed2, undef_bit_pos);
+
+	if (result_len < 0)
+		result_len = arg1.bits.size();
+
+	RTLIL::Const result(RTLIL::State::Sx, result_len);
+	if (undef_bit_pos >= 0)
+		return result;
+
+	for (int i = 0; i < result_len; i++) {
+		BigInteger pos = BigInteger(i) + offset;
+		if (pos < 0 || pos >= arg1.bits.size())
+			result.bits[i] = other_bits;
+		else
+			result.bits[i] = arg1.bits[pos.toInt()];
+	}
+
+	return result;
+}
+
+RTLIL::Const RTLIL::const_shift(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool signed2, int result_len)
+{
+	return const_shift_shiftx(arg1, arg2, signed1, signed2, result_len, RTLIL::State::S0);
+}
+
+RTLIL::Const RTLIL::const_shiftx(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool signed2, int result_len)
+{
+	return const_shift_shiftx(arg1, arg2, signed1, signed2, result_len, RTLIL::State::Sx);
 }
 
 RTLIL::Const RTLIL::const_lt(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool signed2, int result_len)
diff --git a/kernel/celltypes.h b/kernel/celltypes.h
index 43c23add3..e1a1110d3 100644
--- a/kernel/celltypes.h
+++ b/kernel/celltypes.h
@@ -75,6 +75,8 @@ struct CellTypes
 		cell_types.insert("$shr");
 		cell_types.insert("$sshl");
 		cell_types.insert("$sshr");
+		cell_types.insert("$shift");
+		cell_types.insert("$shiftx");
 		cell_types.insert("$lt");
 		cell_types.insert("$le");
 		cell_types.insert("$eq");
@@ -224,7 +226,7 @@ struct CellTypes
 		if (type == "$sshl" && !signed1)
 			type = "$shl";
 
-		if (type != "$sshr" && type != "$sshl" && type != "$shr" && type != "$shl" &&
+		if (type != "$sshr" && type != "$sshl" && type != "$shr" && type != "$shl" && type != "$shift" && type != "$shiftx" &&
 				type != "$pos" && type != "$neg" && type != "$not" && type != "$bu0") {
 			if (!signed1 || !signed2)
 				signed1 = false, signed2 = false;
@@ -248,6 +250,8 @@ struct CellTypes
 		HANDLE_CELL_TYPE(shr)
 		HANDLE_CELL_TYPE(sshl)
 		HANDLE_CELL_TYPE(sshr)
+		HANDLE_CELL_TYPE(shift)
+		HANDLE_CELL_TYPE(shiftx)
 		HANDLE_CELL_TYPE(lt)
 		HANDLE_CELL_TYPE(le)
 		HANDLE_CELL_TYPE(eq)
diff --git a/kernel/rtlil.cc b/kernel/rtlil.cc
index b562e2afb..83bbd7b17 100644
--- a/kernel/rtlil.cc
+++ b/kernel/rtlil.cc
@@ -474,7 +474,8 @@ namespace {
 				return;
 			}
 
-			if (cell->type == "$shl" || cell->type == "$shr" || cell->type == "$sshl" || cell->type == "$sshr") {
+			if (cell->type == "$shl" || cell->type == "$shr" || cell->type == "$sshl" || cell->type == "$sshr" ||
+					cell->type == "$shift" || cell->type == "$shiftx") {
 				param_bool("\\A_SIGNED");
 				param_bool("\\B_SIGNED");
 				port("\\A", param("\\A_WIDTH"));
@@ -1101,6 +1102,8 @@ DEF_METHOD(Shl,      sig_a.size(), "$shl")
 DEF_METHOD(Shr,      sig_a.size(), "$shr")
 DEF_METHOD(Sshl,     sig_a.size(), "$sshl")
 DEF_METHOD(Sshr,     sig_a.size(), "$sshr")
+DEF_METHOD(Shift,    sig_a.size(), "$shift")
+DEF_METHOD(Shiftx,   sig_a.size(), "$shiftx")
 DEF_METHOD(Lt,       1, "$lt")
 DEF_METHOD(Le,       1, "$le")
 DEF_METHOD(Eq,       1, "$eq")
diff --git a/kernel/rtlil.h b/kernel/rtlil.h
index 097af9d28..e8d05e7e4 100644
--- a/kernel/rtlil.h
+++ b/kernel/rtlil.h
@@ -172,6 +172,8 @@ namespace RTLIL
 	RTLIL::Const const_shr         (const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool signed2, int result_len);
 	RTLIL::Const const_sshl        (const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool signed2, int result_len);
 	RTLIL::Const const_sshr        (const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool signed2, int result_len);
+	RTLIL::Const const_shift       (const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool signed2, int result_len);
+	RTLIL::Const const_shiftx      (const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool signed2, int result_len);
 
 	RTLIL::Const const_lt          (const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool signed2, int result_len);
 	RTLIL::Const const_le          (const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool signed2, int result_len);
@@ -474,10 +476,12 @@ public:
 	RTLIL::Cell* addReduceXnor (RTLIL::IdString name, RTLIL::SigSpec sig_a, RTLIL::SigSpec sig_y, bool is_signed = false);
 	RTLIL::Cell* addReduceBool (RTLIL::IdString name, RTLIL::SigSpec sig_a, RTLIL::SigSpec sig_y, bool is_signed = false);
                      
-	RTLIL::Cell* addShl  (RTLIL::IdString name, RTLIL::SigSpec sig_a, RTLIL::SigSpec sig_b, RTLIL::SigSpec sig_y, bool is_signed = false);
-	RTLIL::Cell* addShr  (RTLIL::IdString name, RTLIL::SigSpec sig_a, RTLIL::SigSpec sig_b, RTLIL::SigSpec sig_y, bool is_signed = false);
-	RTLIL::Cell* addSshl (RTLIL::IdString name, RTLIL::SigSpec sig_a, RTLIL::SigSpec sig_b, RTLIL::SigSpec sig_y, bool is_signed = false);
-	RTLIL::Cell* addSshr (RTLIL::IdString name, RTLIL::SigSpec sig_a, RTLIL::SigSpec sig_b, RTLIL::SigSpec sig_y, bool is_signed = false);
+	RTLIL::Cell* addShl    (RTLIL::IdString name, RTLIL::SigSpec sig_a, RTLIL::SigSpec sig_b, RTLIL::SigSpec sig_y, bool is_signed = false);
+	RTLIL::Cell* addShr    (RTLIL::IdString name, RTLIL::SigSpec sig_a, RTLIL::SigSpec sig_b, RTLIL::SigSpec sig_y, bool is_signed = false);
+	RTLIL::Cell* addSshl   (RTLIL::IdString name, RTLIL::SigSpec sig_a, RTLIL::SigSpec sig_b, RTLIL::SigSpec sig_y, bool is_signed = false);
+	RTLIL::Cell* addSshr   (RTLIL::IdString name, RTLIL::SigSpec sig_a, RTLIL::SigSpec sig_b, RTLIL::SigSpec sig_y, bool is_signed = false);
+	RTLIL::Cell* addShift  (RTLIL::IdString name, RTLIL::SigSpec sig_a, RTLIL::SigSpec sig_b, RTLIL::SigSpec sig_y, bool is_signed = false);
+	RTLIL::Cell* addShiftx (RTLIL::IdString name, RTLIL::SigSpec sig_a, RTLIL::SigSpec sig_b, RTLIL::SigSpec sig_y, bool is_signed = false);
                      
 	RTLIL::Cell* addLt  (RTLIL::IdString name, RTLIL::SigSpec sig_a, RTLIL::SigSpec sig_b, RTLIL::SigSpec sig_y, bool is_signed = false);
 	RTLIL::Cell* addLe  (RTLIL::IdString name, RTLIL::SigSpec sig_a, RTLIL::SigSpec sig_b, RTLIL::SigSpec sig_y, bool is_signed = false);
@@ -551,10 +555,12 @@ public:
 	RTLIL::SigSpec ReduceXnor (RTLIL::IdString name, RTLIL::SigSpec sig_a, bool is_signed = false);
 	RTLIL::SigSpec ReduceBool (RTLIL::IdString name, RTLIL::SigSpec sig_a, bool is_signed = false);
 
-	RTLIL::SigSpec Shl  (RTLIL::IdString name, RTLIL::SigSpec sig_a, RTLIL::SigSpec sig_b, bool is_signed = false);
-	RTLIL::SigSpec Shr  (RTLIL::IdString name, RTLIL::SigSpec sig_a, RTLIL::SigSpec sig_b, bool is_signed = false);
-	RTLIL::SigSpec Sshl (RTLIL::IdString name, RTLIL::SigSpec sig_a, RTLIL::SigSpec sig_b, bool is_signed = false);
-	RTLIL::SigSpec Sshr (RTLIL::IdString name, RTLIL::SigSpec sig_a, RTLIL::SigSpec sig_b, bool is_signed = false);
+	RTLIL::SigSpec Shl    (RTLIL::IdString name, RTLIL::SigSpec sig_a, RTLIL::SigSpec sig_b, bool is_signed = false);
+	RTLIL::SigSpec Shr    (RTLIL::IdString name, RTLIL::SigSpec sig_a, RTLIL::SigSpec sig_b, bool is_signed = false);
+	RTLIL::SigSpec Sshl   (RTLIL::IdString name, RTLIL::SigSpec sig_a, RTLIL::SigSpec sig_b, bool is_signed = false);
+	RTLIL::SigSpec Sshr   (RTLIL::IdString name, RTLIL::SigSpec sig_a, RTLIL::SigSpec sig_b, bool is_signed = false);
+	RTLIL::SigSpec Shift  (RTLIL::IdString name, RTLIL::SigSpec sig_a, RTLIL::SigSpec sig_b, bool is_signed = false);
+	RTLIL::SigSpec Shiftx (RTLIL::IdString name, RTLIL::SigSpec sig_a, RTLIL::SigSpec sig_b, bool is_signed = false);
 
 	RTLIL::SigSpec Lt  (RTLIL::IdString name, RTLIL::SigSpec sig_a, RTLIL::SigSpec sig_b, bool is_signed = false);
 	RTLIL::SigSpec Le  (RTLIL::IdString name, RTLIL::SigSpec sig_a, RTLIL::SigSpec sig_b, bool is_signed = false);
diff --git a/kernel/satgen.h b/kernel/satgen.h
index 27a29cb57..a079b42f0 100644
--- a/kernel/satgen.h
+++ b/kernel/satgen.h
@@ -597,7 +597,7 @@ struct SatGen
 			return true;
 		}
 
-		if (cell->type == "$shl" || cell->type == "$shr" || cell->type == "$sshl" || cell->type == "$sshr")
+		if (cell->type == "$shl" || cell->type == "$shr" || cell->type == "$sshl" || cell->type == "$sshr" || cell->type == "$shift" || cell->type == "$shiftx")
 		{
 			std::vector<int> a = importDefSigSpec(cell->get("\\A"), timestep);
 			std::vector<int> b = importDefSigSpec(cell->get("\\B"), timestep);
@@ -605,6 +605,7 @@ struct SatGen
 
 			char shift_left = cell->type == "$shl" || cell->type == "$sshl";
 			bool sign_extend = cell->type == "$sshr" && cell->parameters["\\A_SIGNED"].as_bool();
+			bool shift_shiftx = cell->type == "$shift" || cell->type == "$shiftx";
 
 			while (y.size() < a.size())
 				y.push_back(ez->literal());
@@ -616,9 +617,13 @@ struct SatGen
 			std::vector<int> tmp = a;
 			for (size_t i = 0; i < b.size(); i++)
 			{
+				bool shift_left_this = shift_left;
+				if (shift_shiftx && i == b.size()-1 && cell->parameters["\\B_SIGNED"].as_bool())
+					shift_left_this = true;
+
 				std::vector<int> tmp_shifted(tmp.size());
 				for (size_t j = 0; j < tmp.size(); j++) {
-					int idx = j + (1 << (i > 30 ? 30 : i)) * (shift_left ? -1 : +1);
+					int idx = j + (1 << (i > 30 ? 30 : i)) * (shift_left_this ? -1 : +1);
 					tmp_shifted.at(j) = (0 <= idx && idx < int(tmp.size())) ? tmp.at(idx) : sign_extend ? tmp.back() : ez->FALSE;
 				}
 				tmp = ez->vec_ite(b.at(i), tmp_shifted, tmp);
@@ -639,10 +644,15 @@ struct SatGen
 				tmp = undef_a;
 				for (size_t i = 0; i < b.size(); i++)
 				{
+					bool shift_left_this = shift_left;
+					if (shift_shiftx && i == b.size()-1 && cell->parameters["\\B_SIGNED"].as_bool())
+						shift_left_this = true;
+
 					std::vector<int> tmp_shifted(tmp.size());
 					for (size_t j = 0; j < tmp.size(); j++) {
-						int idx = j + (1 << (i > 30 ? 30 : i)) * (shift_left ? -1 : +1);
-						tmp_shifted.at(j) = (0 <= idx && idx < int(tmp.size())) ? tmp.at(idx) : sign_extend ? tmp.back() : ez->FALSE;
+						int idx = j + (1 << (i > 30 ? 30 : i)) * (shift_left_this ? -1 : +1);
+						tmp_shifted.at(j) = (0 <= idx && idx < int(tmp.size())) ? tmp.at(idx) :
+								sign_extend ? tmp.back() : cell->type == "$shiftx" ? ez->TRUE : ez->FALSE;
 					}
 					tmp = ez->vec_ite(b.at(i), tmp_shifted, tmp);
 				}
diff --git a/passes/memory/memory_share.cc b/passes/memory/memory_share.cc
index e61661a20..b1629b7c4 100644
--- a/passes/memory/memory_share.cc
+++ b/passes/memory/memory_share.cc
@@ -695,6 +695,8 @@ struct MemoryShareWorker
 		cone_ct.cell_types.erase("$shr");
 		cone_ct.cell_types.erase("$sshl");
 		cone_ct.cell_types.erase("$sshr");
+		cone_ct.cell_types.erase("$shift");
+		cone_ct.cell_types.erase("$shiftx");
 
 		modwalker.setup(design, module, &cone_ct);
 
diff --git a/passes/opt/opt_const.cc b/passes/opt/opt_const.cc
index 254fe5bb4..3e7487c39 100644
--- a/passes/opt/opt_const.cc
+++ b/passes/opt/opt_const.cc
@@ -338,7 +338,7 @@ static void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bo
 			goto next_cell;
 		}
 
-		if (cell->type == "$reduce_xor" || cell->type == "$reduce_xnor" ||
+		if (cell->type == "$reduce_xor" || cell->type == "$reduce_xnor" || cell->type == "$shift" || cell->type == "$shiftx" ||
 				cell->type == "$shl" || cell->type == "$shr" || cell->type == "$sshl" || cell->type == "$sshr" ||
 				cell->type == "$lt" || cell->type == "$le" || cell->type == "$ge" || cell->type == "$gt" ||
 				cell->type == "$neg" || cell->type == "$add" || cell->type == "$sub" ||
@@ -347,7 +347,7 @@ static void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bo
 			RTLIL::SigSpec sig_a = assign_map(cell->get("\\A"));
 			RTLIL::SigSpec sig_b = cell->has("\\B") ? assign_map(cell->get("\\B")) : RTLIL::SigSpec();
 
-			if (cell->type == "$shl" || cell->type == "$shr" || cell->type == "$sshl" || cell->type == "$sshr")
+			if (cell->type == "$shl" || cell->type == "$shr" || cell->type == "$sshl" || cell->type == "$sshr" || cell->type == "$shift" || cell->type == "$shiftx")
 				sig_a = RTLIL::SigSpec();
 
 			for (auto &bit : sig_a.to_sigbit_vector())
@@ -360,8 +360,8 @@ static void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bo
 
 			if (0) {
 		found_the_x_bit:
-				cover_list("opt.opt_const.xbit", "$reduce_xor", "$reduce_xnor", "$shl", "$shr", "$sshl", "$sshr", "$lt", "$le", "$ge", "$gt",
-						"$neg", "$add", "$sub", "$mul", "$div", "$mod", "$pow", cell->type);
+				cover_list("opt.opt_const.xbit", "$reduce_xor", "$reduce_xnor", "$shl", "$shr", "$sshl", "$sshr", "$shift", "$shiftx",
+						"$lt", "$le", "$ge", "$gt", "$neg", "$add", "$sub", "$mul", "$div", "$mod", "$pow", cell->type);
 				if (cell->type == "$reduce_xor" || cell->type == "$reduce_xnor" ||
 						cell->type == "$lt" || cell->type == "$le" || cell->type == "$ge" || cell->type == "$gt")
 					replace_cell(assign_map, module, cell, "x-bit in input", "\\Y", RTLIL::State::Sx);
@@ -572,7 +572,7 @@ static void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bo
 					identity_wrt_a = true;
 			}
 
-			if (cell->type == "$shl" || cell->type == "$shr" || cell->type == "$sshl" || cell->type == "$sshr")
+			if (cell->type == "$shl" || cell->type == "$shr" || cell->type == "$sshl" || cell->type == "$sshr" || cell->type == "$shift" || cell->type == "$shiftx")
 			{
 				RTLIL::SigSpec b = assign_map(cell->get("\\B"));
 
@@ -603,9 +603,9 @@ static void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bo
 			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", "$mul", "$div", cell->type);
+					cover_list("opt.opt_const.identwrt.a", "$add", "$sub", "$or", "$xor", "$shl", "$shr", "$sshl", "$sshr", "$shift", "$shiftx", "$mul", "$div", cell->type);
 				if (identity_wrt_b)
-					cover_list("opt.opt_const.identwrt.b", "$add", "$sub", "$or", "$xor", "$shl", "$shr", "$sshl", "$sshr", "$mul", "$div", cell->type);
+					cover_list("opt.opt_const.identwrt.b", "$add", "$sub", "$or", "$xor", "$shl", "$shr", "$sshl", "$sshr", "$shift", "$shiftx", "$mul", "$div", cell->type);
 
 				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');
@@ -792,6 +792,8 @@ static void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bo
 		FOLD_2ARG_CELL(shr)
 		FOLD_2ARG_CELL(sshl)
 		FOLD_2ARG_CELL(sshr)
+		FOLD_2ARG_CELL(shift)
+		FOLD_2ARG_CELL(shiftx)
 
 		FOLD_2ARG_CELL(lt)
 		FOLD_2ARG_CELL(le)
diff --git a/techlibs/common/simlib.v b/techlibs/common/simlib.v
index 1b50959c9..76aa4a52d 100644
--- a/techlibs/common/simlib.v
+++ b/techlibs/common/simlib.v
@@ -418,6 +418,54 @@ endmodule
 
 // --------------------------------------------------------
 
+module \$shift (A, B, Y);
+
+parameter A_SIGNED = 0;
+parameter B_SIGNED = 0;
+parameter A_WIDTH = 0;
+parameter B_WIDTH = 0;
+parameter Y_WIDTH = 0;
+
+input [A_WIDTH-1:0] A;
+input [B_WIDTH-1:0] B;
+output [Y_WIDTH-1:0] Y;
+
+generate
+	if (B_SIGNED) begin:BLOCK1
+		assign Y = $signed(B) < 0 ? A << -B : A >> B;
+	end else begin:BLOCK2
+		assign Y = A >> B;
+	end
+endgenerate
+
+endmodule
+
+// --------------------------------------------------------
+
+module \$shiftx (A, B, Y);
+
+parameter A_SIGNED = 0;
+parameter B_SIGNED = 0;
+parameter A_WIDTH = 0;
+parameter B_WIDTH = 0;
+parameter Y_WIDTH = 0;
+
+input [A_WIDTH-1:0] A;
+input [B_WIDTH-1:0] B;
+output [Y_WIDTH-1:0] Y;
+
+generate
+	if (B_SIGNED) begin:BLOCK1
+		assign Y = A[$signed(B) +: Y_WIDTH];
+	end else begin:BLOCK2
+		assign Y = A[B +: Y_WIDTH];
+	end
+endgenerate
+
+endmodule
+
+// --------------------------------------------------------
+
 module \$lt (A, B, Y);
 
 parameter A_SIGNED = 0;
diff --git a/techlibs/common/stdcells.v b/techlibs/common/stdcells.v
index a05ea2786..ee59048c3 100644
--- a/techlibs/common/stdcells.v
+++ b/techlibs/common/stdcells.v
@@ -129,12 +129,12 @@ endmodule
 
 // --------------------------------------------------------
 
-module \$__shift (X, A, Y);
+module \$__shift (XL, XR, A, Y);
 
 parameter WIDTH = 1;
 parameter SHIFT = 0;
 
-input X;
+input XL, XR;
 input [WIDTH-1:0] A;
 output [WIDTH-1:0] Y;
 
@@ -142,12 +142,12 @@ genvar i;
 generate
 	for (i = 0; i < WIDTH; i = i + 1) begin:V
 		if (i+SHIFT < 0) begin
-			assign Y[i] = 0;
+			assign Y[i] = XR;
 		end else
 		if (i+SHIFT < WIDTH) begin
 			assign Y[i] = A[i+SHIFT];
 		end else begin
-			assign Y[i] = X;
+			assign Y[i] = XL;
 		end
 	end
 endgenerate
@@ -196,7 +196,8 @@ generate
 			.WIDTH(WIDTH),
 			.SHIFT(0 - (2 ** (i > 30 ? 30 : i)))
 		) sh (
-			.X(0),
+			.XL(1'b0),
+			.XR(1'b0),
 			.A(unshifted),
 			.Y(shifted)
 		);
@@ -255,7 +256,8 @@ generate
 			.WIDTH(WIDTH),
 			.SHIFT(2 ** (i > 30 ? 30 : i))
 		) sh (
-			.X(0),
+			.XL(1'b0),
+			.XR(1'b0),
 			.A(unshifted),
 			.Y(shifted)
 		);
@@ -314,7 +316,8 @@ generate
 			.WIDTH(WIDTH),
 			.SHIFT(0 - (2 ** (i > 30 ? 30 : i)))
 		) sh (
-			.X(0),
+			.XL(1'b0),
+			.XR(1'b0),
 			.A(unshifted),
 			.Y(shifted)
 		);
@@ -382,7 +385,8 @@ generate
 			.WIDTH(WIDTH),
 			.SHIFT(2 ** (i > 30 ? 30 : i))
 		) sh (
-			.X(A_SIGNED && A[A_WIDTH-1]),
+			.XL(A_SIGNED && A[A_WIDTH-1]),
+			.XR(1'b0),
 			.A(unshifted),
 			.Y(shifted)
 		);
@@ -401,6 +405,58 @@ endmodule
 
 // --------------------------------------------------------
 
+module \$shift (A, B, Y);
+
+parameter A_SIGNED = 0;
+parameter B_SIGNED = 0;
+parameter A_WIDTH = 1;
+parameter B_WIDTH = 1;
+parameter Y_WIDTH = 1;
+
+input [A_WIDTH-1:0] A;
+input [B_WIDTH-1:0] B;
+output [Y_WIDTH-1:0] Y;
+
+generate
+	if (B_SIGNED) begin:BLOCK1
+		assign Y = $signed(B) < 0 ? A << -B : A >> B;
+	end else begin:BLOCK2
+		assign Y = A >> B;
+	end
+endgenerate
+
+endmodule
+
+// --------------------------------------------------------
+
+module \$shiftx (A, B, Y);
+
+parameter A_SIGNED = 0;
+parameter B_SIGNED = 0;
+parameter A_WIDTH = 1;
+parameter B_WIDTH = 1;
+parameter Y_WIDTH = 1;
+
+input [A_WIDTH-1:0] A;
+input [B_WIDTH-1:0] B;
+output [Y_WIDTH-1:0] Y;
+
+\$shift #(
+	.A_SIGNED(A_SIGNED),
+	.B_SIGNED(B_SIGNED),
+	.A_WIDTH(A_WIDTH),
+	.B_WIDTH(B_WIDTH),
+	.Y_WIDTH(Y_WIDTH),
+) sh (
+	.A(A),
+	.B(B),
+	.Y(Y)
+);
+
+endmodule
+
+// --------------------------------------------------------
+
 module \$__fulladd (A, B, C, X, Y);
 
 // {X, Y} = A + B + C