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-rw-r--r--passes/pmgen/Makefile.inc6
-rw-r--r--passes/pmgen/xilinx_srl.cc270
-rw-r--r--passes/pmgen/xilinx_srl.pmg244
3 files changed, 520 insertions, 0 deletions
diff --git a/passes/pmgen/Makefile.inc b/passes/pmgen/Makefile.inc
index 8e0cbdca8..e73a7b1c9 100644
--- a/passes/pmgen/Makefile.inc
+++ b/passes/pmgen/Makefile.inc
@@ -30,3 +30,9 @@ PEEPOPT_PATTERN += passes/pmgen/peepopt_muldiv.pmg
passes/pmgen/peepopt_pm.h: passes/pmgen/pmgen.py $(PEEPOPT_PATTERN)
$(P) mkdir -p passes/pmgen && python3 $< -o $@ -p peepopt $(filter-out $<,$^)
+
+# --------------------------------------
+
+OBJS += passes/pmgen/xilinx_srl.o
+passes/pmgen/xilinx_srl.o: passes/pmgen/xilinx_srl_pm.h
+$(eval $(call add_extra_objs,passes/pmgen/xilinx_srl_pm.h))
diff --git a/passes/pmgen/xilinx_srl.cc b/passes/pmgen/xilinx_srl.cc
new file mode 100644
index 000000000..c332ccb9f
--- /dev/null
+++ b/passes/pmgen/xilinx_srl.cc
@@ -0,0 +1,270 @@
+/*
+ * yosys -- Yosys Open SYnthesis Suite
+ *
+ * Copyright (C) 2012 Clifford Wolf <clifford@clifford.at>
+ * (C) 2019 Eddie Hung <eddie@fpgeh.com>
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ *
+ */
+
+#include "kernel/yosys.h"
+#include "kernel/sigtools.h"
+
+USING_YOSYS_NAMESPACE
+PRIVATE_NAMESPACE_BEGIN
+
+// for peepopt_pm
+bool did_something;
+
+#include "passes/pmgen/xilinx_srl_pm.h"
+#include "passes/pmgen/ice40_dsp_pm.h"
+#include "passes/pmgen/peepopt_pm.h"
+
+void run_fixed(xilinx_srl_pm &pm)
+{
+ auto &st = pm.st_fixed;
+ auto &ud = pm.ud_fixed;
+ auto param_def = [&ud](Cell *cell, IdString param) {
+ auto def = ud.default_params.at(std::make_pair(cell->type,param));
+ return cell->parameters.at(param, def);
+ };
+
+ log("Found fixed chain of length %d (%s):\n", GetSize(ud.longest_chain), log_id(st.first->type));
+
+ auto first_cell = ud.longest_chain.back();
+
+ SigSpec initval;
+ for (auto cell : ud.longest_chain) {
+ log_debug(" %s\n", log_id(cell));
+ if (cell->type.in(ID($_DFF_N_), ID($_DFF_P_), ID($_DFFE_NN_), ID($_DFFE_NP_), ID($_DFFE_PN_), ID($_DFFE_PP_))) {
+ SigBit Q = cell->getPort(ID(Q));
+ log_assert(Q.wire);
+ auto it = Q.wire->attributes.find(ID(init));
+ if (it != Q.wire->attributes.end()) {
+ auto &i = it->second[Q.offset];
+ initval.append(i);
+ i = State::Sx;
+ }
+ else
+ initval.append(State::Sx);
+ }
+ else if (cell->type.in(ID(FDRE), ID(FDRE_1)))
+ initval.append(param_def(cell, ID(INIT)));
+ else
+ log_abort();
+ if (cell != first_cell)
+ pm.autoremove(cell);
+ }
+
+ auto last_cell = ud.longest_chain.front();
+ Cell *c = pm.module->addCell(NEW_ID, ID($__XILINX_SHREG_));
+ pm.module->swap_names(c, first_cell);
+
+ if (first_cell->type.in(ID($_DFF_N_), ID($_DFF_P_), ID($_DFFE_NN_), ID($_DFFE_NP_), ID($_DFFE_PN_), ID($_DFFE_PP_), ID(FDRE), ID(FDRE_1))) {
+ c->setParam(ID(DEPTH), GetSize(ud.longest_chain));
+ c->setParam(ID(INIT), initval.as_const());
+ if (first_cell->type.in(ID($_DFF_P_), ID($_DFFE_PN_), ID($_DFFE_PP_)))
+ c->setParam(ID(CLKPOL), 1);
+ else if (first_cell->type.in(ID($_DFF_N_), ID($DFFE_NN_), ID($_DFFE_NP_), ID(FDRE_1)))
+ c->setParam(ID(CLKPOL), 0);
+ else if (first_cell->type.in(ID(FDRE)))
+ c->setParam(ID(CLKPOL), param_def(first_cell, ID(IS_C_INVERTED)).as_bool() ? 0 : 1);
+ else
+ log_abort();
+ if (first_cell->type.in(ID($_DFFE_NP_), ID($_DFFE_PP_)))
+ c->setParam(ID(ENPOL), 1);
+ else if (first_cell->type.in(ID($_DFFE_NN_), ID($_DFFE_PN_)))
+ c->setParam(ID(ENPOL), 0);
+ else
+ c->setParam(ID(ENPOL), 2);
+
+ c->setPort(ID(C), first_cell->getPort(ID(C)));
+ c->setPort(ID(D), first_cell->getPort(ID(D)));
+ c->setPort(ID(Q), last_cell->getPort(ID(Q)));
+ c->setPort(ID(L), GetSize(ud.longest_chain)-1);
+ if (first_cell->type.in(ID($_DFF_N_), ID($_DFF_P_)))
+ c->setPort(ID(E), State::S1);
+ else if (first_cell->type.in(ID($_DFFE_NN_), ID($_DFFE_NP_), ID($_DFFE_PN_), ID($_DFFE_PP_)))
+ c->setPort(ID(E), first_cell->getPort(ID(E)));
+ else if (first_cell->type.in(ID(FDRE), ID(FDRE_1)))
+ c->setPort(ID(E), first_cell->getPort(ID(CE)));
+ else
+ log_abort();
+ }
+ else
+ log_abort();
+
+ log(" -> %s (%s)\n", log_id(c), log_id(c->type));
+}
+
+void run_variable(xilinx_srl_pm &pm)
+{
+ auto &st = pm.st_variable;
+ auto &ud = pm.ud_variable;
+
+ log("Found variable chain of length %d (%s):\n", GetSize(ud.chain), log_id(st.first->type));
+
+ auto first_cell = ud.chain.back().first;
+ auto first_slice = ud.chain.back().second;
+
+ SigSpec initval;
+ for (const auto &i : ud.chain) {
+ auto cell = i.first;
+ auto slice = i.second;
+ log_debug(" %s\n", log_id(cell));
+ if (cell->type.in(ID($_DFF_N_), ID($_DFF_P_), ID($_DFFE_NN_), ID($_DFFE_NP_), ID($_DFFE_PN_), ID($_DFFE_PP_), ID($dff), ID($dffe))) {
+ SigBit Q = cell->getPort(ID(Q))[slice];
+ log_assert(Q.wire);
+ auto it = Q.wire->attributes.find(ID(init));
+ if (it != Q.wire->attributes.end()) {
+ auto &i = it->second[Q.offset];
+ initval.append(i);
+ i = State::Sx;
+ }
+ else
+ initval.append(State::Sx);
+ }
+ else
+ log_abort();
+ if (cell != first_cell)
+ cell->connections_.at(ID(Q))[slice] = pm.module->addWire(NEW_ID);
+ }
+ pm.autoremove(st.shiftx);
+
+ Cell *c = pm.module->addCell(NEW_ID, ID($__XILINX_SHREG_));
+ pm.module->swap_names(c, first_cell);
+
+ if (first_cell->type.in(ID($_DFF_N_), ID($_DFF_P_), ID($_DFFE_NN_), ID($_DFFE_NP_), ID($_DFFE_PN_), ID($_DFFE_PP_), ID($dff), ID($dffe))) {
+ c->setParam(ID(DEPTH), GetSize(ud.chain));
+ c->setParam(ID(INIT), initval.as_const());
+ Const clkpol, enpol;
+ if (first_cell->type.in(ID($_DFF_P_), ID($_DFFE_PN_), ID($_DFFE_PP_)))
+ clkpol = 1;
+ else if (first_cell->type.in(ID($_DFF_N_), ID($DFFE_NN_), ID($_DFFE_NP_)))
+ clkpol = 0;
+ else if (first_cell->type.in(ID($dff), ID($dffe)))
+ clkpol = first_cell->getParam(ID(CLK_POLARITY));
+ else
+ log_abort();
+ if (first_cell->type.in(ID($_DFFE_NP_), ID($_DFFE_PP_)))
+ enpol = 1;
+ else if (first_cell->type.in(ID($_DFFE_NN_), ID($_DFFE_PN_)))
+ enpol = 0;
+ else if (first_cell->type.in(ID($dffe)))
+ enpol = first_cell->getParam(ID(EN_POLARITY));
+ else
+ enpol = 2;
+ c->setParam(ID(CLKPOL), clkpol);
+ c->setParam(ID(ENPOL), enpol);
+
+ if (first_cell->type.in(ID($_DFF_N_), ID($_DFF_P_), ID($_DFFE_NN_), ID($_DFFE_NP_), ID($_DFFE_PN_), ID($_DFFE_PP_)))
+ c->setPort(ID(C), first_cell->getPort(ID(C)));
+ else if (first_cell->type.in(ID($dff), ID($dffe)))
+ c->setPort(ID(C), first_cell->getPort(ID(CLK)));
+ else
+ log_abort();
+ c->setPort(ID(D), first_cell->getPort(ID(D))[first_slice]);
+ c->setPort(ID(Q), st.shiftx->getPort(ID(Y)));
+ c->setPort(ID(L), st.shiftx->getPort(ID(B)));
+ if (first_cell->type.in(ID($_DFF_N_), ID($_DFF_P_), ID($dff)))
+ c->setPort(ID(E), State::S1);
+ else if (first_cell->type.in(ID($_DFFE_NN_), ID($_DFFE_NP_), ID($_DFFE_PN_), ID($_DFFE_PP_)))
+ c->setPort(ID(E), first_cell->getPort(ID(E)));
+ else if (first_cell->type.in(ID($dffe)))
+ c->setPort(ID(E), first_cell->getPort(ID(EN)));
+ else
+ log_abort();
+ }
+ else
+ log_abort();
+
+ log(" -> %s (%s)\n", log_id(c), log_id(c->type));
+}
+
+struct XilinxSrlPass : public Pass {
+ XilinxSrlPass() : Pass("xilinx_srl", "Xilinx shift register extraction") { }
+ void help() YS_OVERRIDE
+ {
+ // |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
+ log("\n");
+ log(" xilinx_srl [options] [selection]\n");
+ log("\n");
+ log("This pass converts chains of built-in flops (bit-level: $_DFF_[NP]_, $_DFFE_*\n");
+ log("and word-level: $dff, $dffe) as well as Xilinx flops (FDRE, FDRE_1) into a\n");
+ log("$__XILINX_SHREG cell. Chains must be of the same cell type, clock, clock polarity,\n");
+ log("enable, and enable polarity (where relevant).\n");
+ log("Flops with resets cannot be mapped to Xilinx devices and will not be inferred.");
+ log("\n");
+ log(" -minlen N\n");
+ log(" min length of shift register (default = 3)\n");
+ log("\n");
+ log(" -fixed\n");
+ log(" infer fixed-length shift registers.\n");
+ log("\n");
+ log(" -variable\n");
+ log(" infer variable-length shift registers (i.e. fixed-length shifts where\n");
+ log(" each element also fans-out to a $shiftx cell.\n");
+ log("\n");
+ }
+
+ void execute(std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE
+ {
+ log_header(design, "Executing XILINX_SRL pass (Xilinx shift register extraction).\n");
+
+ bool fixed = false;
+ bool variable = false;
+ int minlen = 3;
+
+ size_t argidx;
+ for (argidx = 1; argidx < args.size(); argidx++)
+ {
+ if (args[argidx] == "-minlen" && argidx+1 < args.size()) {
+ minlen = atoi(args[++argidx].c_str());
+ continue;
+ }
+ if (args[argidx] == "-fixed") {
+ fixed = true;
+ continue;
+ }
+ if (args[argidx] == "-variable") {
+ variable = true;
+ continue;
+ }
+ break;
+ }
+ extra_args(args, argidx, design);
+
+ if (!fixed && !variable)
+ log_cmd_error("'-fixed' and/or '-variable' must be specified.\n");
+
+ for (auto module : design->selected_modules()) {
+ auto pm = xilinx_srl_pm(module, module->selected_cells());
+ pm.ud_fixed.minlen = minlen;
+ pm.ud_variable.minlen = minlen;
+
+ if (fixed) {
+ // TODO: How to get these automatically?
+ pm.ud_fixed.default_params[std::make_pair(ID(FDRE),ID(INIT))] = State::S0;
+ pm.ud_fixed.default_params[std::make_pair(ID(FDRE),ID(IS_C_INVERTED))] = State::S0;
+ pm.ud_fixed.default_params[std::make_pair(ID(FDRE),ID(IS_D_INVERTED))] = State::S0;
+ pm.ud_fixed.default_params[std::make_pair(ID(FDRE),ID(IS_R_INVERTED))] = State::S0;
+ pm.run_fixed(run_fixed);
+ }
+ if (variable)
+ pm.run_variable(run_variable);
+ }
+ }
+} XilinxSrlPass;
+
+PRIVATE_NAMESPACE_END
diff --git a/passes/pmgen/xilinx_srl.pmg b/passes/pmgen/xilinx_srl.pmg
new file mode 100644
index 000000000..cfa1cacfb
--- /dev/null
+++ b/passes/pmgen/xilinx_srl.pmg
@@ -0,0 +1,244 @@
+pattern fixed
+
+state <IdString> clk_port en_port
+udata <vector<Cell*>> chain longest_chain
+udata <pool<Cell*>> non_first_cells
+udata <int> minlen
+udata <dict<std::pair<IdString,IdString>,Const>> default_params
+
+code
+ non_first_cells.clear();
+ subpattern(setup);
+endcode
+
+match first
+ select first->type.in($_DFF_N_, $_DFF_P_, $_DFFE_NN_, $_DFFE_NP_, $_DFFE_PN_, $_DFFE_PP_, \FDRE, \FDRE_1)
+ select !first->has_keep_attr()
+ select !first->type.in(\FDRE) || !first->hasParam(\IS_R_INVERTED) || !param(first, \IS_R_INVERTED).as_bool()
+ select !first->type.in(\FDRE) || !first->hasParam(\IS_D_INVERTED) || !param(first, \IS_D_INVERTED).as_bool()
+ select !first->type.in(\FDRE, \FDRE_1) || port(first, \R) == State::S0
+ filter !non_first_cells.count(first)
+//generate
+// SigSpec A = module->addWire(NEW_ID);
+// SigSpec B = module->addWire(NEW_ID);
+// SigSpec Y = module->addWire(NEW_ID);
+// switch (rng(3))
+// {
+// case 0:
+// module->addAndGate(NEW_ID, A, B, Y);
+// break;
+// case 1:
+// module->addOrGate(NEW_ID, A, B, Y);
+// break;
+// case 2:
+// module->addXorGate(NEW_ID, A, B, Y);
+// break;
+// }
+endmatch
+
+code clk_port en_port
+ if (first->type.in($_DFF_N_, $_DFF_P_, $_DFFE_NN_, $_DFFE_NP_, $_DFFE_PN_, $_DFFE_PP_, \FDRE, \FDRE_1))
+ clk_port = \C;
+ else log_abort();
+ if (first->type.in($_DFF_N_, $_DFF_P_))
+ en_port = IdString();
+ else if (first->type.in($_DFFE_NN_, $_DFFE_NP_, $_DFFE_PN_, $_DFFE_PP_))
+ en_port = \E;
+ else if (first->type.in(\FDRE, \FDRE_1))
+ en_port = \CE;
+ else log_abort();
+
+ longest_chain.clear();
+ chain.push_back(first);
+ subpattern(tail);
+finally
+ chain.pop_back();
+ log_assert(chain.empty());
+ if (GetSize(longest_chain) >= minlen)
+ accept;
+endcode
+
+// ------------------------------------------------------------------
+
+subpattern setup
+arg clk_port
+arg en_port
+
+match first
+ select first->type.in($_DFF_N_, $_DFF_P_, $_DFFE_NN_, $_DFFE_NP_, $_DFFE_PN_, $_DFFE_PP_, \FDRE, \FDRE_1)
+ select !first->has_keep_attr()
+ select !first->type.in(\FDRE) || !first->hasParam(\IS_R_INVERTED) || !param(first, \IS_R_INVERTED).as_bool()
+ select !first->type.in(\FDRE) || !first->hasParam(\IS_D_INVERTED) || !param(first, \IS_D_INVERTED).as_bool()
+ select !first->type.in(\FDRE, \FDRE_1) || port(first, \R) == State::S0
+endmatch
+
+code clk_port en_port
+ if (first->type.in($_DFF_N_, $_DFF_P_, $_DFFE_NN_, $_DFFE_NP_, $_DFFE_PN_, $_DFFE_PP_, \FDRE, \FDRE_1))
+ clk_port = \C;
+ else log_abort();
+ if (first->type.in($_DFF_N_, $_DFF_P_))
+ en_port = IdString();
+ else if (first->type.in($_DFFE_NN_, $_DFFE_NP_, $_DFFE_PN_, $_DFFE_PP_))
+ en_port = \E;
+ else if (first->type.in(\FDRE, \FDRE_1))
+ en_port = \CE;
+ else log_abort();
+endcode
+
+match next
+ select next->type.in($_DFF_N_, $_DFF_P_, $_DFFE_NN_, $_DFFE_NP_, $_DFFE_PN_, $_DFFE_PP_, \FDRE, \FDRE_1)
+ select !next->has_keep_attr()
+ select !port(next, \D)[0].wire->get_bool_attribute(\keep)
+ select nusers(port(next, \Q)) == 2
+ select !next->type.in(\FDRE, \FDRE_1) || port(next, \R) == State::S0
+ index <IdString> next->type === first->type
+ index <SigBit> port(next, \Q) === port(first, \D)
+ filter port(next, clk_port) == port(first, clk_port)
+ filter en_port == IdString() || port(next, en_port) == port(first, en_port)
+ filter !next->type.in(\FDRE) || !first->hasParam(\IS_C_INVERTED) || (next->hasParam(\IS_C_INVERTED) && param(next, \IS_C_INVERTED).as_bool() == param(first, \IS_C_INVERTED).as_bool())
+ filter !next->type.in(\FDRE) || !first->hasParam(\IS_D_INVERTED) || (next->hasParam(\IS_D_INVERTED) && param(next, \IS_D_INVERTED).as_bool() == param(first, \IS_D_INVERTED).as_bool())
+ filter !next->type.in(\FDRE) || !first->hasParam(\IS_R_INVERTED) || (next->hasParam(\IS_R_INVERTED) && param(next, \IS_R_INVERTED).as_bool() == param(first, \IS_R_INVERTED).as_bool())
+ filter !next->type.in(\FDRE, \FDRE_1) || port(next, \R) == port(first, \R)
+endmatch
+
+code
+ non_first_cells.insert(next);
+endcode
+
+// ------------------------------------------------------------------
+
+subpattern tail
+arg first
+arg clk_port
+arg en_port
+
+match next
+ semioptional
+ select next->type.in($_DFF_N_, $_DFF_P_, $_DFFE_NN_, $_DFFE_NP_, $_DFFE_PN_, $_DFFE_PP_, \FDRE, \FDRE_1)
+ select !next->has_keep_attr()
+ select !port(next, \D)[0].wire->get_bool_attribute(\keep)
+ select nusers(port(next, \Q)) == 2
+ index <IdString> next->type === chain.back()->type
+ index <SigBit> port(next, \Q) === port(chain.back(), \D)
+ filter port(next, clk_port) == port(first, clk_port)
+ filter en_port == IdString() || port(next, en_port) == port(first, en_port)
+ filter !next->type.in(\FDRE) || !first->hasParam(\IS_C_INVERTED) || (next->hasParam(\IS_C_INVERTED) && param(next, \IS_C_INVERTED).as_bool() == param(first, \IS_C_INVERTED).as_bool())
+ filter !next->type.in(\FDRE) || !first->hasParam(\IS_D_INVERTED) || (next->hasParam(\IS_D_INVERTED) && param(next, \IS_D_INVERTED).as_bool() == param(first, \IS_D_INVERTED).as_bool())
+ filter !next->type.in(\FDRE) || !first->hasParam(\IS_R_INVERTED) || (next->hasParam(\IS_R_INVERTED) && param(next, \IS_R_INVERTED).as_bool() == param(first, \IS_R_INVERTED).as_bool())
+ filter !next->type.in(\FDRE, \FDRE_1) || port(next, \R) == port(first, \R)
+//generate 10
+// SigSpec A = module->addWire(NEW_ID);
+// SigSpec B = module->addWire(NEW_ID);
+// SigSpec Y = port(chain.back().first, chain.back().second);
+// Cell *c = module->addAndGate(NEW_ID, A, B, Y);
+// c->type = chain.back().first->type;
+endmatch
+
+code
+ if (next) {
+ chain.push_back(next);
+ subpattern(tail);
+ } else {
+ if (GetSize(chain) > GetSize(longest_chain))
+ longest_chain = chain;
+ }
+finally
+ if (next)
+ chain.pop_back();
+endcode
+
+// -----------
+
+pattern variable
+
+state <IdString> clk_port en_port
+state <int> shiftx_width
+state <int> slice
+udata <int> minlen
+udata <vector<pair<Cell*,int>>> chain
+udata <pool<SigBit>> chain_bits
+
+code
+ chain_bits.clear();
+endcode
+
+match shiftx
+ select shiftx->type.in($shiftx)
+ select !shiftx->has_keep_attr()
+ select param(shiftx, \Y_WIDTH).as_int() == 1
+ filter param(shiftx, \A_WIDTH).as_int() >= minlen
+endmatch
+
+code shiftx_width
+ shiftx_width = param(shiftx, \A_WIDTH).as_int();
+endcode
+
+match first
+ select first->type.in($_DFF_N_, $_DFF_P_, $_DFFE_NN_, $_DFFE_NP_, $_DFFE_PN_, $_DFFE_PP_, $dff, $dffe)
+ select !first->has_keep_attr()
+ select !port(first, \Q)[0].wire->get_bool_attribute(\keep)
+ slice idx GetSize(port(first, \Q))
+ select nusers(port(first, \Q)[idx]) <= 2
+ index <SigBit> port(first, \Q)[idx] === port(shiftx, \A)[shiftx_width-1]
+ set slice idx
+endmatch
+
+code clk_port en_port
+ if (first->type.in($_DFF_N_, $_DFF_P_, $_DFFE_NN_, $_DFFE_NP_, $_DFFE_PN_, $_DFFE_PP_))
+ clk_port = \C;
+ else if (first->type.in($dff, $dffe))
+ clk_port = \CLK;
+ else log_abort();
+ if (first->type.in($_DFF_N_, $_DFF_P_, $dff))
+ en_port = IdString();
+ else if (first->type.in($_DFFE_NN_, $_DFFE_NP_, $_DFFE_PN_, $_DFFE_PP_))
+ en_port = \E;
+ else if (first->type.in($dffe))
+ en_port = \EN;
+ else log_abort();
+
+ chain_bits.insert(port(first, \Q)[slice]);
+ chain.emplace_back(first, slice);
+ subpattern(tail);
+finally
+ if (GetSize(chain) == shiftx_width)
+ accept;
+ chain.clear();
+endcode
+
+// ------------------------------------------------------------------
+
+subpattern tail
+arg first
+arg shiftx
+arg shiftx_width
+arg slice
+arg clk_port
+arg en_port
+
+match next
+ semioptional
+ select next->type.in($_DFF_N_, $_DFF_P_, $_DFFE_NN_, $_DFFE_NP_, $_DFFE_PN_, $_DFFE_PP_, $dff, $dffe)
+ select !next->has_keep_attr()
+ select !port(next, \D)[0].wire->get_bool_attribute(\keep)
+ slice idx GetSize(port(next, \Q))
+ select nusers(port(next, \Q)[idx]) <= 3
+ index <IdString> next->type === chain.back().first->type
+ index <SigBit> port(next, \Q)[idx] === port(chain.back().first, \D)[chain.back().second]
+ index <SigBit> port(next, \Q)[idx] === port(shiftx, \A)[shiftx_width-1-GetSize(chain)]
+ filter port(next, clk_port) == port(first, clk_port)
+ filter en_port == IdString() || port(next, en_port) == port(first, en_port)
+ filter !next->type.in($dff, $dffe) || param(next, \CLK_POLARITY).as_bool() == param(first, \CLK_POLARITY).as_bool()
+ filter !next->type.in($dffe) || param(next, \EN_POLARITY).as_bool() == param(first, \EN_POLARITY).as_bool()
+ filter !chain_bits.count(port(next, \D)[idx])
+ set slice idx
+endmatch
+
+code
+ if (next) {
+ chain_bits.insert(port(next, \Q)[slice]);
+ chain.emplace_back(next, slice);
+ if (GetSize(chain) < shiftx_width)
+ subpattern(tail);
+ }
+endcode