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OpcodeDispatcher: Defer second XOR for AF

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AF is calculated as:

  ((Src1 ^ Src2) ^ Res)[4]

Due to the extract, this is equivalent to

  ((Src1 ^ Src2) ^ (Res ^ 1))[4]

We already store (Res ^ 1) as the PF byte. So, it suffices to store

  AF Byte = Src1 ^ Src2

and then we can recover the flag value

  AF = (AF Byte ^ PF Byte)[4]

This saves an instruction from the AF calculation. It does couple PF/AF writes.
In practice, most instructions fall into one of these categories:

  * Both PF and AF written together, the coupling is correct.
  * PF written but AF invalidated, irrelevant.
  * Both invalidated, irrelevant.

None of these require special handling. Where we do need special handling is
when we want to write them separately, in which case we can fix-up the value of
AF as appropriate.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
This commit is contained in:
Alyssa Rosenzweig committed 2023-09-05 14:21:18 -04:00
1 parent 80ac824dd9
commit 02c864d837
4 files changed
+56 -22
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FEXCore/Source/Interface/Core/OpcodeDispatcher.cpp
+4
View File
@@ -3485,6 +3485,7 @@ void OpDispatchBuilder::DAAOp(OpcodeArgs) {
SetRFLAG<FEXCore::X86State::RFLAG_SF_LOC>(_Select(FEXCore::IR::COND_UGE, _And(OpSize::i64Bit, AL, _Constant(0x80)), _Constant(0), _Constant(1), _Constant(0)));
SetRFLAG<FEXCore::X86State::RFLAG_ZF_LOC>(_Select(FEXCore::IR::COND_EQ, _And(OpSize::i64Bit, AL, _Constant(0xFF)), _Constant(0), _Constant(1), _Constant(0)));
CalculatePFUncheckedABI(AL);
FixupAF();
}
void OpDispatchBuilder::DASOp(OpcodeArgs) {
@@ -3557,6 +3558,7 @@ void OpDispatchBuilder::DASOp(OpcodeArgs) {
SetRFLAG<FEXCore::X86State::RFLAG_SF_LOC>(_Select(FEXCore::IR::COND_UGE, _And(OpSize::i64Bit, AL, _Constant(0x80)), _Constant(0), _Constant(1), _Constant(0)));
SetRFLAG<FEXCore::X86State::RFLAG_ZF_LOC>(_Select(FEXCore::IR::COND_EQ, _And(OpSize::i64Bit, AL, _Constant(0xFF)), _Constant(0), _Constant(1), _Constant(0)));
CalculatePFUncheckedABI(AL);
FixupAF();
}
void OpDispatchBuilder::AAAOp(OpcodeArgs) {
@@ -3653,6 +3655,7 @@ void OpDispatchBuilder::AAMOp(OpcodeArgs) {
SetRFLAG<FEXCore::X86State::RFLAG_SF_LOC>(_Select(FEXCore::IR::COND_UGE, _And(OpSize::i64Bit, AL, _Constant(0x80)), _Constant(0), _Constant(1), _Constant(0)));
SetRFLAG<FEXCore::X86State::RFLAG_ZF_LOC>(_Select(FEXCore::IR::COND_EQ, _And(OpSize::i64Bit, AL, _Constant(0xFF)), _Constant(0), _Constant(1), _Constant(0)));
CalculatePFUncheckedABI(AL);
_InvalidateFlags(1u << X86State::RFLAG_AF_LOC);
}
void OpDispatchBuilder::AADOp(OpcodeArgs) {
@@ -3670,6 +3673,7 @@ void OpDispatchBuilder::AADOp(OpcodeArgs) {
SetRFLAG<FEXCore::X86State::RFLAG_SF_LOC>(_Select(FEXCore::IR::COND_UGE, _And(OpSize::i64Bit, AL, _Constant(0x80)), _Constant(0), _Constant(1), _Constant(0)));
SetRFLAG<FEXCore::X86State::RFLAG_ZF_LOC>(_Select(FEXCore::IR::COND_EQ, _And(OpSize::i64Bit, AL, _Constant(0xFF)), _Constant(0), _Constant(1), _Constant(0)));
CalculatePFUncheckedABI(AL);
_InvalidateFlags(1u << X86State::RFLAG_AF_LOC);
}
void OpDispatchBuilder::XLATOp(OpcodeArgs) {