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6502-cpp/include/optimizer.hpp

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#ifndef INC_6502_CPP_OPTIMIZER_HPP
#define INC_6502_CPP_OPTIMIZER_HPP
#include "6502.hpp"
#include "personality.hpp"
#include <span>
#include <vector>
constexpr bool consume_directives(auto &begin, const auto &end)
{
if (begin != end && begin->type == ASMLine::Type::Directive) {
++begin;
return true;
}
return false;
}
constexpr bool consume_labels(auto &begin, const auto &end)
{
if (begin != end && begin->type == ASMLine::Type::Label) {
++begin;
return true;
}
return false;
}
constexpr bool is_opcode(const mos6502 &op, const auto... opcodes) { return ((op.opcode == opcodes) || ...); }
constexpr bool is_end_of_block(const auto &begin)
{
if (begin->text.ends_with("__optimizable") || begin->op.value.ends_with("__optimizable")) {
return false;
}
if (begin->type == ASMLine::Type::Label) { return true; }
return is_opcode(*begin,
mos6502::OpCode::jsr,
mos6502::OpCode::jmp,
mos6502::OpCode::bcc,
mos6502::OpCode::bcs,
mos6502::OpCode::beq,
mos6502::OpCode::bne,
mos6502::OpCode::bpl);
}
constexpr bool consume_end_of_block(auto &begin, const auto &end)
{
if (begin != end && is_end_of_block(begin)) {
++begin;
return true;
}
return false;
}
static std::vector<std::span<mos6502>> get_optimizable_blocks(std::vector<mos6502> &statements)
{
std::vector<std::span<mos6502>> blocks;
auto begin = std::begin(statements);
auto end = std::end(statements);
const auto find_end_of_block = [](auto &find_begin, const auto &find_end) {
while (find_begin != find_end) {
if (is_end_of_block(find_begin)) { return; }
++find_begin;
}
};
while (begin != end) {
while (consume_end_of_block(begin, end) || consume_directives(begin, end) || consume_labels(begin, end)) {}
const auto block_start = begin;
find_end_of_block(begin, end);
blocks.emplace_back(block_start, begin);
}
return blocks;
}
static bool is_virtual_register_op(const mos6502 &op, const Personality &personality)
{
for (int i = 0; i < 32; ++i) {
if (personality.get_register(i).value == op.op.value) { return true; }
}
return false;
}
static bool optimize_dead_tax(std::span<mos6502> &block)
{
for (auto itr = block.begin(); itr != block.end(); ++itr) {
if (is_opcode(*itr, mos6502::OpCode::tax, mos6502::OpCode::tsx, mos6502::OpCode::ldx)) {
for (auto inner = std::next(itr); inner != block.end(); ++inner) {
if (is_opcode(*inner,
mos6502::OpCode::txa,
mos6502::OpCode::txs,
mos6502::OpCode::stx,
mos6502::OpCode::inx,
mos6502::OpCode::dex,
mos6502::OpCode::cpx)) {
break;
}
if (is_opcode(*inner, mos6502::OpCode::tax, mos6502::OpCode::tsx, mos6502::OpCode::ldx)) {
// redundant store found
*itr = mos6502(ASMLine::Type::Directive, "; removed dead load of X: " + itr->to_string());
return true;
}
}
}
}
return false;
}
bool optimize_dead_sta(std::span<mos6502> &block, const Personality &personality)
{
for (auto itr = block.begin(); itr != block.end(); ++itr) {
if (itr->opcode == mos6502::OpCode::sta && is_virtual_register_op(*itr, personality)) {
for (auto inner = std::next(itr); inner != block.end(); ++inner) {
if (not inner->op.value.starts_with("#<(") && inner->op.value.find('(') != std::string::npos) {
// this is an indexed operation, which is risky to optimize a sta around on the virtual registers,
// so we'll skip this block
break;
}
if (inner->op.value == itr->op.value) {
if (is_opcode(*inner, mos6502::OpCode::sta)) {
// redundant store found
*itr = mos6502(ASMLine::Type::Directive, "; removed dead store of a: " + itr->to_string());
return true;
} else {
// someone else is operating on us, time to abort
break;
}
}
}
}
}
return false;
}
bool optimize_redundant_ldy(std::span<mos6502> &block)
{
for (auto itr = block.begin(); itr != block.end(); ++itr) {
if (itr->opcode == mos6502::OpCode::ldy && itr->op.value.starts_with('#')) {
for (auto inner = std::next(itr); inner != block.end(); ++inner) {
if (is_opcode(*inner,
mos6502::OpCode::cpy,
mos6502::OpCode::tya,
mos6502::OpCode::tay,
mos6502::OpCode::sty,
mos6502::OpCode::iny,
mos6502::OpCode::dey)) {
break;// break, these all operate on Y
}
// we found a matching ldy
if (is_opcode(*inner, mos6502::OpCode::ldy)) {
// with the same value
// note: this operation is only safe because we know that our system only uses Y
// for index operations and we don't rely (or even necessarily *want* the changes to N,Z)
if (inner->op.value == itr->op.value) {
*inner = mos6502(ASMLine::Type::Directive, "; removed redundant ldy: " + inner->to_string());
return true;
} else {
break;
}
}
}
}
}
return false;
}
bool optimize_redundant_lda(std::span<mos6502> &block, const Personality &personality)
{
// look for a literal or virtual register load into A
// that is redundant later
for (auto itr = block.begin(); itr != block.end(); ++itr) {
if (itr->opcode == mos6502::OpCode::lda
&& (itr->op.value.starts_with('#') || is_virtual_register_op(*itr, personality))) {
for (auto inner = std::next(itr); inner != block.end(); ++inner) {
if (is_opcode(*inner,
mos6502::OpCode::tay,
mos6502::OpCode::tax,
mos6502::OpCode::sta,
mos6502::OpCode::pha,
mos6502::OpCode::nop)) {
continue;// OK to skip instructions that don't modify A or change flags
}
if (inner->type == ASMLine::Type::Directive) {
continue;// OK to skip directives
}
if (is_opcode(*inner, mos6502::OpCode::lda)) {
if (inner->op == itr->op) {
// we found a matching lda, after an sta, we can remove it
*inner = mos6502(ASMLine::Type::Directive, "; removed redundant lda: " + inner->to_string());
return true;
} else {
break;
}
}
break;// we can only optimize around tax and comments right now
}
}
}
return false;
}
bool optimize_redundant_lda_after_sta(std::span<mos6502> &block)
{
for (auto itr = block.begin(); itr != block.end(); ++itr) {
if (itr->opcode == mos6502::OpCode::sta) {
for (auto inner = std::next(itr); inner != block.end(); ++inner) {
if (is_opcode(*inner,
mos6502::OpCode::tax,
mos6502::OpCode::tay,
mos6502::OpCode::clc,
mos6502::OpCode::sec,
mos6502::OpCode::sta,
mos6502::OpCode::pha,
mos6502::OpCode::txs,
mos6502::OpCode::php,
mos6502::OpCode::sty,
mos6502::OpCode::nop)) {
continue;// OK to skip instructions that don't modify A or change flags
}
if (inner->type == ASMLine::Type::Directive) {
continue;// OK to skip directives
}
if (is_opcode(*inner, mos6502::OpCode::lda)) {
if (inner->op == itr->op) {
// we found a matching lda, after a sta, we can remove it
*inner = mos6502(ASMLine::Type::Directive, "; removed redundant lda: " + inner->to_string());
return true;
} else {
break;
}
}
break;// we can only optimize around tax and comments right now
}
}
}
return false;
}
bool optimize(std::vector<mos6502> &instructions, [[maybe_unused]] const Personality &personality)
{
// remove unused flag-fix-up blocks
// it might make sense in the future to only insert these if determined they are needed?
for (size_t op = 10; op < instructions.size(); ++op) {
if (instructions[op].opcode == mos6502::OpCode::lda || instructions[op].opcode == mos6502::OpCode::bcc
|| instructions[op].opcode == mos6502::OpCode::bcs || instructions[op].opcode == mos6502::OpCode::ldy
|| instructions[op].opcode == mos6502::OpCode::inc || instructions[op].opcode == mos6502::OpCode::clc
|| instructions[op].opcode == mos6502::OpCode::sec || instructions[op].text.starts_with("; Handle N / S")) {
if (instructions[op - 1].text == "; END remove if next is lda, bcc, bcs, ldy, inc, clc, sec"
|| (instructions[op - 2].text == "; END remove if next is lda, bcc, bcs, ldy, inc, clc, sec"
&& instructions[op - 1].type == ASMLine::Type::Directive)) {
for (size_t inner_op = op - 1; inner_op > 1; --inner_op) {
instructions[inner_op] =
mos6502(ASMLine::Type::Directive, "; removed unused flag fix-up: " + instructions[inner_op].to_string());
if (instructions[inner_op].text.find("; BEGIN") != std::string::npos) { return true; }
}
}
}
}
// replace use of __zero_reg__ with literal 0
for (auto &op : instructions) {
if (op.type == ASMLine::Type::Instruction && op.op.type == Operand::Type::literal
&& op.op.value == personality.get_register(1).value && op.opcode != mos6502::OpCode::sta) {
// replace use of zero reg with literal 0
const auto old_string = op.to_string();
op.op.value = "#0";
op.comment = "replaced use of register 1 with a literal 0, because of AVR GCC __zero_reg__ ; " + old_string;
}
}
bool optimizer_run = false;
for (auto &block : get_optimizable_blocks(instructions)) {
const bool block_optimized = optimize_redundant_lda_after_sta(block)
|| optimize_dead_sta(block, personality) || optimize_dead_tax(block)
|| optimize_redundant_ldy(block) || optimize_redundant_lda(block, personality);
optimizer_run = optimizer_run || block_optimized;
}
return optimizer_run;
}
#endif// INC_6502_CPP_OPTIMIZER_HPP
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