6502/6502-cpp
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Automatically reroute long branch instructions

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This commit is contained in:
Jason Turner 2016-08-06 21:01:01 -06:00
parent d59fbdaf4c
commit 6dcb39e300
1 changed files with 38 additions and 1 deletions
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39
src/main.cpp
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@ -276,7 +276,7 @@ struct mos6502 : ASMLine
{
switch (type) {
case ASMLine::Type::Label:
return text + ':';
return text; // + ':';
case ASMLine::Type::Directive:
case ASMLine::Type::Instruction:
return '\t' + text + ' ' + op.value;
@ -748,6 +748,37 @@ bool optimize(std::vector<mos6502> &instructions)
return false;
}
bool fix_long_branches(std::vector<mos6502> &instructions, int &branch_patch_count)
{
std::map<std::string, size_t> labels;
for (size_t op = 0; op < instructions.size(); ++op)
{
if (instructions[op].type == ASMLine::Type::Label) {
labels[instructions[op].text] = op;
}
}
for (size_t op = 0; op < instructions.size(); ++op)
{
if (instructions[op].is_branch && std::abs(static_cast<int>(labels[instructions[op].op.value]) - static_cast<int>(op)) * 3 > 255)
{
++branch_patch_count;
const auto going_to = instructions[op].op.value;
const auto new_pos = "branch_patch_" + std::to_string(branch_patch_count);
// uh-oh too long of a branch, have to convert this to a jump...
if (instructions[op].opcode == mos6502::OpCode::bne) {
instructions[op] = mos6502(mos6502::OpCode::beq, Operand(Operand::Type::literal, new_pos));
instructions.insert(std::next(std::begin(instructions), op + 1), mos6502(mos6502::OpCode::jmp, Operand(Operand::Type::literal, going_to)));
instructions.insert(std::next(std::begin(instructions), op + 2), mos6502(ASMLine::Type::Label, new_pos));
return true;
} else {
throw std::runtime_error("Don't know how to reorg this branch");
}
}
}
return false;
}
bool fix_overwritten_flags(std::vector<mos6502> &instructions)
{
@ -944,6 +975,12 @@ int main()
// do it however many times it takes
}
int branch_patch_count = 0;
while (fix_long_branches(new_instructions, branch_patch_count))
{
// do it however many times it takes
}
for (const auto i : new_instructions)
{