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OpcodeDispatcher: optimize LOOP/N/E #3503

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Mar 22, 2024
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OpcodeDispatcher: optimize LOOP/N/E #3503

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29 changes: 10 additions & 19 deletions FEXCore/Source/Interface/Core/OpcodeDispatcher.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1056,41 +1056,32 @@ void OpDispatchBuilder::LoopOp(OpcodeArgs) {
bool CheckZF = Op->OP != 0xE2;
bool ZFTrue = Op->OP == 0xE1;

// If LOOPE then jumps to target if RCX != 0 && ZF == 1
// If LOOPNE then jumps to target if RCX != 0 && ZF == 0
OrderedNode *AndCondWith = nullptr;
if (CheckZF)
AndCondWith = GetRFLAG(FEXCore::X86State::RFLAG_ZF_RAW_LOC, !ZFTrue);

BlockSetRIP = true;
auto ZeroConst = _Constant(0);
IRPair<IROp_Header> SrcCond;

IRPair<IROp_Constant> TakeBranch = _Constant(1);
IRPair<IROp_Constant> DoNotTakeBranch = _Constant(0);

uint32_t SrcSize = (Op->Flags & X86Tables::DecodeFlags::FLAG_ADDRESS_SIZE) ? 4 : 8;

LOGMAN_THROW_A_FMT(Op->Src[1].IsLiteral(), "Src1 needs to be literal here");

uint64_t Target = Op->PC + Op->InstSize + Op->Src[1].Data.Literal.Value;

auto OpSize = SrcSize == 8 ? OpSize::i64Bit : OpSize::i32Bit;
OrderedNode *CondReg = LoadSource(GPRClass, Op, Op->Src[0], Op->Flags);
CondReg = _Sub(SrcSize == 8 ? OpSize::i64Bit : OpSize::i32Bit, CondReg, _Constant(SrcSize * 8, 1));
CondReg = _Sub(OpSize, CondReg, _Constant(SrcSize * 8, 1));
StoreResult(GPRClass, Op, Op->Src[0], CondReg, -1);

SrcCond = _Select(FEXCore::IR::COND_NEQ,
CondReg, ZeroConst, TakeBranch, DoNotTakeBranch);

if (AndCondWith)
SrcCond = _And(OpSize::i64Bit, SrcCond, AndCondWith);
// If LOOPE then jumps to target if RCX != 0 && ZF == 1
// If LOOPNE then jumps to target if RCX != 0 && ZF == 0
//
// To handle efficiently, smash RCX to zero if ZF is wrong (1 csel).
if (CheckZF) {
CondReg = _NZCVSelect(OpSize, {ZFTrue ? COND_EQ : COND_NEQ}, CondReg, _Constant(0));
}

CalculateDeferredFlags();
auto TrueBlock = JumpTargets.find(Target);
auto FalseBlock = JumpTargets.find(Op->PC + Op->InstSize);

{
auto CondJump_ = CondJump(SrcCond);
auto CondJump_ = CondJump(CondReg);

// Taking branch block
if (TrueBlock != JumpTargets.end()) {
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