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Decode the real delay slot when a function's final branch has its slot at the next function #415

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Decode the real delay slot when a function's final branch has its slot at the next function #415

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649956f
Decode the real delay slot when a function's final branch has its slo…
0xLeathery Oct 29, 2026
9a73ddc
Test that function-final branches run their real delay slot
0xLeathery Oct 29, 2026
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108 changes: 67 additions & 41 deletions ps2xRecomp/src/lib/ps2_recompiler.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2120,62 +2120,67 @@ namespace ps2recomp
uint32_t start = function.start;
uint32_t end = function.end;

for (uint32_t address = start; address < end; address += 4)
auto decodeInstructionAt = [&](uint32_t address) -> Instruction
{
try
{
if (!m_elfParser->isValidAddress(address))
{
{
std::ostringstream msg;
msg << "Invalid address 0x" << std::hex << address << " (truncating decode)";
m_reporter.warningAt("decode", function.name, address, msg.str());
}
truncated = true;
break;
}

uint32_t rawInstruction = m_elfParser->readWord(address);
const uint32_t originalInstruction = rawInstruction;
uint32_t rawInstruction = m_elfParser->readWord(address);
const uint32_t originalInstruction = rawInstruction;

auto patchIt = m_config.patches.find(address);
if (patchIt != m_config.patches.end())
auto patchIt = m_config.patches.find(address);
if (patchIt != m_config.patches.end())
{
const PatchClass patchClass = classifyPatchedInstruction(originalInstruction);
if (shouldApplyConfiguredPatch(patchClass, m_config))
{
const PatchClass patchClass = classifyPatchedInstruction(originalInstruction);
if (shouldApplyConfiguredPatch(patchClass, m_config))
try
{
try
rawInstruction = std::stoul(patchIt->second, nullptr, 0);
{
rawInstruction = std::stoul(patchIt->second, nullptr, 0);
{
std::ostringstream msg;
msg << "Applied patch at 0x" << std::hex << address;
m_reporter.info("patch", msg.str());
}
std::ostringstream msg;
msg << "Applied patch at 0x" << std::hex << address;
m_reporter.info("patch", msg.str());
}
catch (const std::exception &e)
}
catch (const std::exception &e)
{
{
{
std::ostringstream msg;
msg << "Invalid patch value at 0x" << std::hex << address
<< " (" << patchIt->second << "): " << e.what()
<< ". Using original instruction.";
m_reporter.warningAt("patch", function.name, address, msg.str());
}
std::ostringstream msg;
msg << "Invalid patch value at 0x" << std::hex << address
<< " (" << patchIt->second << "): " << e.what()
<< ". Using original instruction.";
m_reporter.warningAt("patch", function.name, address, msg.str());
}
}
}
}

Instruction inst = m_decoder->decodeInstruction(address, rawInstruction, !m_config.lowMemoryMode);

auto mmioIt = m_config.mmioByInstructionAddress.find(address);
if (mmioIt != m_config.mmioByInstructionAddress.end())
{
inst.isMmio = true;
inst.mmioAddress = mmioIt->second;
}

Instruction inst = m_decoder->decodeInstruction(address, rawInstruction, !m_config.lowMemoryMode);
return inst;
};

auto mmioIt = m_config.mmioByInstructionAddress.find(address);
if (mmioIt != m_config.mmioByInstructionAddress.end())
for (uint32_t address = start; address < end; address += 4)
{
try
{
if (!m_elfParser->isValidAddress(address))
{
inst.isMmio = true;
inst.mmioAddress = mmioIt->second;
{
std::ostringstream msg;
msg << "Invalid address 0x" << std::hex << address << " (truncating decode)";
m_reporter.warningAt("decode", function.name, address, msg.str());
}
truncated = true;
break;
}

instructions.push_back(inst);
instructions.push_back(decodeInstructionAt(address));
}
catch (const std::exception &e)
{
Expand Down Expand Up @@ -2204,6 +2209,27 @@ namespace ps2recomp
function.end = instructions.back().address + 4;
}

// When another function starts at the final branch's delay slot, decode the real slot past
// function.end so the branch runs it instead of a synthetic NOP.
const bool delaySlotPastEnd = !truncated && instructions.back().hasDelaySlot &&
instructions.back().address + 4u == function.end &&
m_elfParser->isValidAddress(function.end);
if (delaySlotPastEnd)
{
try
{
instructions.push_back(decodeInstructionAt(function.end));
}
catch (const std::exception &e)
{
{
std::ostringstream msg;
msg << "Error decoding delay slot past function end: " << e.what() << " (using NOP)";
m_reporter.warningAt("decode", function.name, function.end, msg.str());
}
}
}

m_decodedFunctions.insert_or_assign(function.start, std::move(instructions));

return true;
Expand Down
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