From 5fe0ffe30f315d50b2405c2d436ad8e7ca9ba2f6 Mon Sep 17 00:00:00 2001 From: whitequark Date: Mon, 8 Jul 2019 15:19:01 +0000 Subject: [PATCH 1/2] proc_prune: new pass. The proc_prune pass is similar in nature to proc_rmdead pass: while proc_rmdead removes branches that never become active because another branch preempts it, proc_prune removes assignments that never become active because another assignment preempts them. Genrtlil contains logic similar to the proc_prune pass, but their purpose is different: genrtlil has to prune assignments to adapt the semantics of blocking assignments in HDLs (latest assignment wins) to semantics of assignments in RTLIL processes (assignment in the most specific case wins). On the other hand proc_prune is a general purpose RTLIL simplification that benefits all frontends, even those not using the Yosys AST library. The proc_prune pass is added to the proc script after proc_rmdead, since it gives better results with fewer branches. --- passes/proc/Makefile.inc | 2 +- passes/proc/proc.cc | 2 + passes/proc/proc_prune.cc | 135 ++++++++++++++++++++++++++++++++++++++ 3 files changed, 138 insertions(+), 1 deletion(-) create mode 100644 passes/proc/proc_prune.cc diff --git a/passes/proc/Makefile.inc b/passes/proc/Makefile.inc index 397fe46a1..4b56979f8 100644 --- a/passes/proc/Makefile.inc +++ b/passes/proc/Makefile.inc @@ -1,5 +1,6 @@ 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 @@ -7,4 +8,3 @@ OBJS += passes/proc/proc_arst.o OBJS += passes/proc/proc_mux.o OBJS += passes/proc/proc_dlatch.o OBJS += passes/proc/proc_dff.o - diff --git a/passes/proc/proc.cc b/passes/proc/proc.cc index ef7cb0f71..a5b4a3112 100644 --- a/passes/proc/proc.cc +++ b/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"); diff --git a/passes/proc/proc_prune.cc b/passes/proc/proc_prune.cc new file mode 100644 index 000000000..7222d414d --- /dev/null +++ b/passes/proc/proc_prune.cc @@ -0,0 +1,135 @@ +/* + * yosys -- Yosys Open SYnthesis Suite + * + * Copyright (C) 2019 whitequark + * + * 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 +#include + +USING_YOSYS_NAMESPACE +PRIVATE_NAMESPACE_BEGIN + +struct PruneWorker +{ + RTLIL::Module *module; + SigMap sigmap; + + int count = 0; + + PruneWorker(RTLIL::Module *mod) : module(mod), sigmap(mod) {} + + pool do_switch(RTLIL::SwitchRule *sw, pool assigned) + { + pool 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 case_assigned = do_case(it, assigned); + 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 do_case(RTLIL::CaseRule *cs, pool assigned) + { + for (auto it = cs->switches.rbegin(); it != cs->switches.rend(); ++it) { + pool sw_assigned = do_switch((*it), assigned); + assigned.insert(sw_assigned.begin(), sw_assigned.end()); + } + pool 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) + remove.insert(*it); + else { + for (auto &bit : lhs) + if (bit.wire) + assigned.insert(bit); + } + } + for (auto it = cs->actions.begin(); it != cs->actions.end(); ) { + if (remove[*it]) { + it = cs->actions.erase(it); + count++; + } else it++; + } + return assigned; + } + + void do_process(RTLIL::Process *pr) + { + do_case(&pr->root_case, {}); + } +}; + +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 args, RTLIL::Design *design) YS_OVERRIDE + { + int total_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_count += worker.count; + } + + log("Removed %d redundant assignment%s.\n", total_count, total_count == 1 ? "" : "s"); + } +} ProcPrunePass; + +PRIVATE_NAMESPACE_END From 44bcb7a187ffa00921cb14fa50428ce272ce3b6b Mon Sep 17 00:00:00 2001 From: whitequark Date: Tue, 9 Jul 2019 08:14:52 +0000 Subject: [PATCH 2/2] proc_prune: promote assigns to module connections when legal. This can pave the way for further transformations by exposing identities that were previously hidden in a process to any pass that uses SigMap. Indeed, this commit removes some ad-hoc logic from proc_init that appears to have been tailored to the output of genrtlil in favor of using `SigMap.apply()`. (This removal is not optional, as the ad-hoc logic cannot cope with the result of running proc_prune; a similar issue was fixed in proc_arst.) --- passes/proc/proc_arst.cc | 2 +- passes/proc/proc_init.cc | 26 +++++----------------- passes/proc/proc_prune.cc | 47 +++++++++++++++++++++++++++++---------- 3 files changed, 42 insertions(+), 33 deletions(-) diff --git a/passes/proc/proc_arst.cc b/passes/proc/proc_arst.cc index b69eba3f9..d069f152a 100644 --- a/passes/proc/proc_arst.cc +++ b/passes/proc/proc_arst.cc @@ -172,7 +172,7 @@ restart_proc_arst: 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) diff --git a/passes/proc/proc_init.cc b/passes/proc/proc_init.cc index e2dc07e53..462a384b7 100644 --- a/passes/proc/proc_init.cc +++ b/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; diff --git a/passes/proc/proc_prune.cc b/passes/proc/proc_prune.cc index 7222d414d..9e00b0a8a 100644 --- a/passes/proc/proc_prune.cc +++ b/passes/proc/proc_prune.cc @@ -31,11 +31,11 @@ struct PruneWorker RTLIL::Module *module; SigMap sigmap; - int count = 0; + int removed_count = 0, promoted_count = 0; PruneWorker(RTLIL::Module *mod) : module(mod), sigmap(mod) {} - pool do_switch(RTLIL::SwitchRule *sw, pool assigned) + pool do_switch(RTLIL::SwitchRule *sw, pool assigned, pool &affected) { pool all_assigned; bool full_case = sw->get_bool_attribute("\\full_case"); @@ -43,7 +43,7 @@ struct PruneWorker for (auto it : sw->cases) { if (it->compare.empty()) full_case = true; - pool case_assigned = do_case(it, assigned); + pool case_assigned = do_case(it, assigned, affected); if (first) { first = false; all_assigned = case_assigned; @@ -58,10 +58,11 @@ struct PruneWorker return assigned; } - pool do_case(RTLIL::CaseRule *cs, pool assigned) + pool do_case(RTLIL::CaseRule *cs, pool assigned, pool &affected, + bool root = false) { for (auto it = cs->switches.rbegin(); it != cs->switches.rend(); ++it) { - pool sw_assigned = do_switch((*it), assigned); + pool sw_assigned = do_switch((*it), assigned, affected); assigned.insert(sw_assigned.begin(), sw_assigned.end()); } pool remove; @@ -74,18 +75,35 @@ struct PruneWorker break; } } - if (redundant) + if (redundant) { + removed_count++; remove.insert(*it); - else { + } 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); - count++; } else it++; } return assigned; @@ -93,7 +111,8 @@ struct PruneWorker void do_process(RTLIL::Process *pr) { - do_case(&pr->root_case, {}); + pool affected; + do_case(&pr->root_case, {}, affected, /*root=*/true); } }; @@ -111,7 +130,7 @@ struct ProcPrunePass : public Pass { } void execute(std::vector args, RTLIL::Design *design) YS_OVERRIDE { - int total_count = 0; + 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); @@ -125,10 +144,14 @@ struct ProcPrunePass : public Pass { continue; worker.do_process(proc_it.second); } - total_count += worker.count; + total_removed_count += worker.removed_count; + total_promoted_count += worker.promoted_count; } - log("Removed %d redundant assignment%s.\n", total_count, total_count == 1 ? "" : "s"); + 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;