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198 lines
5.9 KiB
C++
198 lines
5.9 KiB
C++
//
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// CachingExecutor.hpp
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// Clock Signal
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//
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// Created by Thomas Harte on 16/01/2021.
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// Copyright © 2021 Thomas Harte. All rights reserved.
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//
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#pragma once
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#include "../Numeric/Sizes.hpp"
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#include <array>
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#include <cstdint>
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#include <limits>
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#include <list>
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#include <map>
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#include <queue>
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#include <unordered_map>
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namespace InstructionSet {
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/*!
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A caching executor makes use of an instruction set-specific executor to cache 'performers' (i.e. function pointers)
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that result from decoding.
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In other words, it's almost a JIT compiler, but producing threaded code (in the Forth sense) and then incurring whatever
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costs sit behind using the C ABI for calling. Since there'll always be exactly one parameter, being the specific executor,
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hopefully the calling costs are acceptable.
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Intended usage is for specific executors to subclass from this and declare it a friend.
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TODO: determine promises re: interruption, amongst other things.
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*/
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template <
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/// Indicates the Executor for this platform.
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typename Executor,
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/// Indicates the greatest value the program counter might take.
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uint64_t max_address,
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/// Indicates the maximum number of potential performers that will be provided.
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uint64_t max_performer_count,
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/// Provides the type of Instruction to expect.
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typename InstructionType,
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/// Indicates whether instructions should be treated as ephemeral or included in the cache.
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bool retain_instructions
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> class CachingExecutor {
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public:
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using Performer = void (Executor::*)();
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using PerformerIndex = typename MinIntTypeValue<max_performer_count>::type;
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using ProgramCounterType = typename MinIntTypeValue<max_address>::type;
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// MARK: - Parser call-ins.
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void announce_overflow(ProgramCounterType) {
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/*
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Should be impossible for now; this is intended to provide information
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when page caching.
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*/
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}
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void announce_instruction(ProgramCounterType, InstructionType instruction) {
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// Dutifully map the instruction to a performer and keep it.
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program_.push_back(static_cast<Executor *>(this)->action_for(instruction));
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if constexpr (retain_instructions) {
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// TODO.
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}
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}
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protected:
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// Storage for the statically-allocated list of performers. It's a bit more
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// work for executors to fill this array, but subsequently performers can be
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// indexed by array position, which is a lot more compact than a generic pointer.
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std::array<Performer, max_performer_count+1> performers_;
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ProgramCounterType program_counter_;
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/*!
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Moves the current point of execution to @c address, updating necessary performer caches
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and doing any translation as is necessary.
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*/
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void set_program_counter(ProgramCounterType address) {
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// Set flag to terminate any inner loop currently running through
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// previously-parsed content.
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has_branched_ = true;
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program_counter_ = address;
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// Temporary implementation: just interpret.
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program_.clear();
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program_index_ = 0;
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static_cast<Executor *>(this)->parse(address, ProgramCounterType(max_address));
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// const auto page = find_page(address);
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// const auto entry = page->entry_points.find(address);
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// if(entry == page->entry_points.end()) {
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// // Requested segment wasn't found; check whether it was
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// // within the recently translated list and otherwise
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// // translate it.
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// }
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}
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/*!
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Indicates whether the processor is currently 'stopped', i.e. whether all attempts to run
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should produce no activity. Some processors have such a state when waiting for
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interrupts or for a reset.
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*/
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void set_is_stopped(bool) {}
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/*!
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Executes up to the next branch.
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*/
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void run_to_branch() {
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has_branched_ = false;
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for(auto index: program_) {
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const auto performer = performers_[index];
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(static_cast<Executor *>(this)->*performer)();
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if(has_branched_) break;
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}
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}
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/*!
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Runs for @c duration; the intention is that subclasses provide a method
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that is clear about units, and call this to count down in whatever units they
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count down in.
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*/
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void run_for(int duration) {
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remaining_duration_ += duration;
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while(remaining_duration_ > 0) {
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has_branched_ = false;
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Executor *const executor = static_cast<Executor *>(this);
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while(remaining_duration_ > 0 && !has_branched_) {
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const auto performer = performers_[program_[program_index_]];
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++program_index_;
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(executor->*performer)();
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}
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}
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}
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/*!
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Should be called by a specific executor to subtract from the remaining
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running duration.
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*/
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inline void subtract_duration(int duration) {
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remaining_duration_ -= duration;
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}
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private:
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bool has_branched_ = false;
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int remaining_duration_ = 0;
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std::vector<PerformerIndex> program_;
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size_t program_index_ = 0;
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/* TODO: almost below here can be shoved off into an LRUCache object, or similar. */
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// static constexpr size_t max_cached_pages = 64;
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// struct Page {
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// std::map<ProgramCounterType, PerformerIndex> entry_points;
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// TODO: can I statically these two? Should I?
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// std::vector<PerformerIndex> actions_;
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// std::vector<typename std::enable_if<!std::is_same<InstructionType, void>::value, InstructionType>::type> instructions_;
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// };
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// std::array<Page, max_cached_pages> pages_;
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// Maps from page numbers to pages.
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// std::unordered_map<ProgramCounterType, Page *> cached_pages_;
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// Maintains an LRU of recently-used pages in case of a need for reuse.
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// std::list<ProgramCounterType> touched_pages_;
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/*!
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Finds or creates the page that contains @c address.
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*/
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/* Page *find_page(ProgramCounterType address) {
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// TODO: are 1kb pages always appropriate? Is 64 the correct amount to keep?
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const auto page_address = ProgramCounterType(address >> 10);
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auto page = cached_pages_.find(page_address);
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if(page == cached_pages_.end()) {
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// Page wasn't found; either allocate a new one or
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// reuse one that already exists.
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if(cached_pages_.size() == max_cached_pages) {
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} else {
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}
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} else {
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// Page was found; LRU shuffle it.
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}
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return nullptr;
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}*/
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};
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}
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