From 95db5a9d3899973c0c7bcfa887f8404ac017d53f Mon Sep 17 00:00:00 2001 From: Jannis Harder Date: Fri, 5 Aug 2022 15:43:08 +0200 Subject: [PATCH] formalff: New -setundef option Find FFs with undefined initialization values for which changing the initialization does not change the observable behavior and initialize them. For -ff2anyinit, this reduces the number of generated $anyinit cells that drive wires with private names. --- passes/sat/formalff.cc | 335 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 335 insertions(+) diff --git a/passes/sat/formalff.cc b/passes/sat/formalff.cc index 0c85c3442..209486a37 100644 --- a/passes/sat/formalff.cc +++ b/passes/sat/formalff.cc @@ -21,10 +21,302 @@ #include "kernel/sigtools.h" #include "kernel/ffinit.h" #include "kernel/ff.h" +#include "kernel/modtools.h" USING_YOSYS_NAMESPACE PRIVATE_NAMESPACE_BEGIN + +// Finds signal values with known constant or known unused values in the initial state +struct InitValWorker +{ + Module *module; + + ModWalker modwalker; + SigMap &sigmap; + FfInitVals initvals; + + dict initconst_bits; + dict used_bits; + + InitValWorker(Module *module) : module(module), modwalker(module->design), sigmap(modwalker.sigmap) + { + modwalker.setup(module); + initvals.set(&modwalker.sigmap, module); + + for (auto wire : module->wires()) + if (wire->name.isPublic() || wire->get_bool_attribute(ID::keep)) + for (auto bit : SigSpec(wire)) + used_bits[sigmap(bit)] = true; + } + + // Sign/Zero-extended indexing of individual port bits + static SigBit bit_in_port(RTLIL::Cell *cell, RTLIL::IdString port, RTLIL::IdString sign, int index) + { + auto sig_port = cell->getPort(port); + if (index < GetSize(sig_port)) + return sig_port[index]; + else if (cell->getParam(sign).as_bool()) + return GetSize(sig_port) > 0 ? sig_port[GetSize(sig_port) - 1] : State::Sx; + else + return State::S0; + } + + // Has the signal a known constant value in the initial state? + // + // For sync-only FFs outputs, this is their initval. For logic loops, + // multiple drivers or unknown cells this is Sx. For a small number of + // handled cells we recurse through their inputs. All results are cached. + RTLIL::State initconst(SigBit bit) + { + sigmap.apply(bit); + + if (!bit.is_wire()) + return bit.data; + + auto it = initconst_bits.find(bit); + if (it != initconst_bits.end()) + return it->second; + + // Setting this temporarily to x takes care of any logic loops + initconst_bits[bit] = State::Sx; + + pool portbits; + modwalker.get_drivers(portbits, {bit}); + + if (portbits.size() != 1) + return State::Sx; + + ModWalker::PortBit portbit = *portbits.begin(); + RTLIL::Cell *cell = portbit.cell; + + if (RTLIL::builtin_ff_cell_types().count(cell->type)) + { + FfData ff(&initvals, cell); + + if (ff.has_aload || ff.has_sr || ff.has_arst || (!ff.has_clk && !ff.has_gclk)) { + for (auto bit_q : ff.sig_q) { + initconst_bits[sigmap(bit_q)] = State::Sx; + } + return State::Sx; + } + + for (int i = 0; i < ff.width; i++) { + initconst_bits[sigmap(ff.sig_q[i])] = ff.val_init[i]; + } + + return ff.val_init[portbit.offset]; + } + + if (cell->type.in(ID($mux), ID($and), ID($or), ID($eq), ID($eqx), ID($initstate))) + { + if (cell->type == ID($mux)) + { + SigBit sig_s = sigmap(cell->getPort(ID::S)); + State init_s = initconst(sig_s); + State init_y; + + if (init_s == State::S0) { + init_y = initconst(cell->getPort(ID::A)[portbit.offset]); + } else if (init_s == State::S1) { + init_y = initconst(cell->getPort(ID::B)[portbit.offset]); + } else { + State init_a = initconst(cell->getPort(ID::A)[portbit.offset]); + State init_b = initconst(cell->getPort(ID::B)[portbit.offset]); + init_y = init_a == init_b ? init_a : State::Sx; + } + initconst_bits[bit] = init_y; + return init_y; + } + + if (cell->type.in(ID($and), ID($or))) + { + State init_a = initconst(bit_in_port(cell, ID::A, ID::A_SIGNED, portbit.offset)); + State init_b = initconst(bit_in_port(cell, ID::B, ID::B_SIGNED, portbit.offset)); + State init_y; + if (init_a == init_b) + init_y = init_a; + else if (cell->type == ID($and) && (init_a == State::S0 || init_b == State::S0)) + init_y = State::S0; + else if (cell->type == ID($or) && (init_a == State::S1 || init_b == State::S1)) + init_y = State::S1; + else + init_y = State::Sx; + + initconst_bits[bit] = init_y; + return init_y; + } + + if (cell->type.in(ID($eq), ID($eqx))) // Treats $eqx as $eq + { + if (portbit.offset > 0) { + initconst_bits[bit] = State::S0; + return State::S0; + } + + SigSpec sig_a = cell->getPort(ID::A); + SigSpec sig_b = cell->getPort(ID::B); + + State init_y = State::S1; + + for (int i = 0; init_y != State::S0 && i < GetSize(sig_a); i++) { + State init_ai = initconst(bit_in_port(cell, ID::A, ID::A_SIGNED, i)); + if (init_ai == State::Sx) { + init_y = State::Sx; + continue; + } + State init_bi = initconst(bit_in_port(cell, ID::B, ID::B_SIGNED, i)); + if (init_bi == State::Sx) + init_y = State::Sx; + else if (init_ai != init_bi) + init_y = State::S0; + } + + initconst_bits[bit] = init_y; + return init_y; + } + + if (cell->type == ID($initstate)) + { + initconst_bits[bit] = State::S1; + return State::S1; + } + + log_assert(false); + } + + return State::Sx; + } + + RTLIL::Const initconst(SigSpec sig) + { + std::vector bits; + for (auto bit : sig) + bits.push_back(initconst(bit)); + return bits; + } + + // Is the initial value of this signal used? + // + // An initial value of a signal is considered as used if it a) aliases a + // wire with a public name, an output wire or with a keep attribute b) + // combinationally drives such a wire or c) drive an input to an unknown + // cell. + // + // This recurses into driven cells for a small number of known handled + // celltypes. Results are cached and initconst is used to detect unused + // inputs for the handled celltypes. + bool is_initval_used(SigBit bit) + { + if (!bit.is_wire()) + return false; + + auto it = used_bits.find(bit); + if (it != used_bits.end()) + return it->second; + + used_bits[bit] = true; // Temporarily set to guard against logic loops + + pool portbits; + modwalker.get_consumers(portbits, {bit}); + + for (auto portbit : portbits) { + RTLIL::Cell *cell = portbit.cell; + if (!cell->type.in(ID($mux), ID($and), ID($or), ID($mem_v2)) && !RTLIL::builtin_ff_cell_types().count(cell->type)) { + return true; + } + } + + for (auto portbit : portbits) + { + RTLIL::Cell *cell = portbit.cell; + if (RTLIL::builtin_ff_cell_types().count(cell->type)) + { + FfData ff(&initvals, cell); + if (ff.has_aload || ff.has_sr || ff.has_arst || ff.has_gclk || !ff.has_clk) + return true; + if (ff.has_ce && initconst(ff.sig_ce.as_bit()) == (ff.pol_ce ? State::S0 : State::S1)) + continue; + if (ff.has_srst && initconst(ff.sig_ce.as_bit()) == (ff.pol_srst ? State::S1 : State::S0)) + continue; + + return true; + } + else if (cell->type == ID($mux)) + { + State init_s = initconst(cell->getPort(ID::S).as_bit()); + if (init_s == State::S0 && portbit.port == ID::B) + continue; + if (init_s == State::S1 && portbit.port == ID::A) + continue; + auto sig_y = cell->getPort(ID::Y); + + if (is_initval_used(sig_y[portbit.offset])) + return true; + } + else if (cell->type.in(ID($and), ID($or))) + { + auto sig_a = cell->getPort(ID::A); + auto sig_b = cell->getPort(ID::B); + auto sig_y = cell->getPort(ID::Y); + if (GetSize(sig_y) != GetSize(sig_a) || GetSize(sig_y) != GetSize(sig_b)) + return true; // TODO handle more of this + State absorbing = cell->type == ID($and) ? State::S0 : State::S1; + if (portbit.port == ID::A && initconst(sig_b[portbit.offset]) == absorbing) + continue; + if (portbit.port == ID::B && initconst(sig_a[portbit.offset]) == absorbing) + continue; + + if (is_initval_used(sig_y[portbit.offset])) + return true; + } + else if (cell->type == ID($mem_v2)) + { + // TODO Use mem.h instead to uniformily cover all cases, most + // likely requires processing all memories when initializing + // the worker + if (!portbit.port.in(ID::WR_DATA, ID::WR_ADDR, ID::RD_ADDR)) + return true; + + if (portbit.port == ID::WR_DATA) + { + if (initconst(cell->getPort(ID::WR_EN)[portbit.offset]) == State::S0) + continue; + } + else if (portbit.port == ID::WR_ADDR) + { + int port = portbit.offset / cell->getParam(ID::ABITS).as_int(); + auto sig_en = cell->getPort(ID::WR_EN); + int width = cell->getParam(ID::WIDTH).as_int(); + + for (int i = port * width; i < (port + 1) * width; i++) + if (initconst(sig_en[i]) != State::S0) + return true; + + continue; + } + else if (portbit.port == ID::RD_ADDR) + { + int port = portbit.offset / cell->getParam(ID::ABITS).as_int(); + auto sig_en = cell->getPort(ID::RD_EN); + + if (initconst(sig_en[port]) != State::S0) + return true; + + continue; + } + else + return true; + } + else + log_assert(false); + } + + used_bits[bit] = false; + return false; + } +}; + struct FormalFfPass : public Pass { FormalFfPass() : Pass("formalff", "prepare FFs for formal") { } void help() override @@ -64,6 +356,12 @@ struct FormalFfPass : public Pass { log(" Emit fine-grained $_FF_ cells instead of coarse-grained $ff cells for\n"); log(" -anyinit2ff. Cannot be combined with -clk2ff or -ff2anyinit.\n"); log("\n"); + log(" -setundef\n"); + log(" Find FFs with undefined initialization values for which changing the\n"); + log(" initialization does not change the observable behavior and initialize\n"); + log(" them. For -ff2anyinit, this reduces the number of generated $anyinit\n"); + log(" cells that drive wires with private names.\n"); + log("\n"); // TODO: An option to check whether all FFs use the same clock before changing it to the global clock } @@ -73,6 +371,7 @@ struct FormalFfPass : public Pass { bool flag_ff2anyinit = false; bool flag_anyinit2ff = false; bool flag_fine = false; + bool flag_setundef = false; log_header(design, "Executing FORMALFF pass.\n"); @@ -95,6 +394,10 @@ struct FormalFfPass : public Pass { flag_fine = true; continue; } + if (args[argidx] == "-setundef") { + flag_setundef = true; + continue; + } break; } extra_args(args, argidx, design); @@ -113,6 +416,38 @@ struct FormalFfPass : public Pass { for (auto module : design->selected_modules()) { + if (flag_setundef) + { + InitValWorker worker(module); + + for (auto cell : module->selected_cells()) + { + if (RTLIL::builtin_ff_cell_types().count(cell->type)) + { + FfData ff(&worker.initvals, cell); + if (ff.has_aload || ff.has_sr || ff.has_arst || ff.val_init.is_fully_def()) + continue; + + if (ff.has_ce && // CE can make the initval stick around + worker.initconst(ff.sig_ce.as_bit()) != (ff.pol_ce ? State::S1 : State::S0) && // unless it's known active + (!ff.has_srst || ff.ce_over_srst || + worker.initconst(ff.sig_srst.as_bit()) != (ff.pol_srst ? State::S1 : State::S0))) // or a srst with priority is known active + continue; + + auto before = ff.val_init; + for (int i = 0; i < ff.width; i++) + if (ff.val_init[i] == State::Sx && !worker.is_initval_used(ff.sig_q[i])) + ff.val_init[i] = State::S0; + + if (ff.val_init != before) { + log("Setting unused undefined initial value of %s.%s (%s) from %s to %s\n", + log_id(module), log_id(cell), log_id(cell->type), + log_const(before), log_const(ff.val_init)); + worker.initvals.set_init(ff.sig_q, ff.val_init); + } + } + } + } SigMap sigmap(module); FfInitVals initvals(&sigmap, module);