From 693d86dd675aab51a9a55a58b57afffdb111032c Mon Sep 17 00:00:00 2001
From: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Date: Mon, 25 Mar 2024 12:59:19 -0400
Subject: [PATCH] OpcodeDispatcher: add SetAFAndFixup helper

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
---
 FEXCore/Source/Interface/Core/OpcodeDispatcher.h    |  1 +
 .../Interface/Core/OpcodeDispatcher/Flags.cpp       | 13 +++++++++++++
 2 files changed, 14 insertions(+)

diff --git a/FEXCore/Source/Interface/Core/OpcodeDispatcher.h b/FEXCore/Source/Interface/Core/OpcodeDispatcher.h
index 167ecb2a2..360bdf323 100644
--- a/FEXCore/Source/Interface/Core/OpcodeDispatcher.h
+++ b/FEXCore/Source/Interface/Core/OpcodeDispatcher.h
@@ -1764,6 +1764,7 @@ private:
   OrderedNode *LoadPFRaw();
   OrderedNode *LoadAF();
   void FixupAF();
+  void SetAFAndFixup(OrderedNode *AF);
   void CalculatePF(OrderedNode *Res);
   void CalculateAF(OrderedNode *Src1, OrderedNode *Src2);
 
diff --git a/FEXCore/Source/Interface/Core/OpcodeDispatcher/Flags.cpp b/FEXCore/Source/Interface/Core/OpcodeDispatcher/Flags.cpp
index 67e51966d..b8aa8371f 100644
--- a/FEXCore/Source/Interface/Core/OpcodeDispatcher/Flags.cpp
+++ b/FEXCore/Source/Interface/Core/OpcodeDispatcher/Flags.cpp
@@ -277,6 +277,19 @@ void OpDispatchBuilder::FixupAF() {
   SetRFLAG<FEXCore::X86State::RFLAG_AF_RAW_LOC>(XorRes);
 }
 
+void OpDispatchBuilder::SetAFAndFixup(OrderedNode *AF) {
+  // We have a value of AF, we shift into AF[4].  We need to fixup AF[4] so that
+  // we get the right value when we XOR in PF[4] later. The easiest solution is
+  // to XOR by PF[4], since:
+  //
+  //  (AF[4] ^ PF[4]) ^ PF[4] = AF[4]
+
+  auto PFRaw = GetRFLAG(FEXCore::X86State::RFLAG_PF_RAW_LOC);
+
+  OrderedNode *XorRes = _XorShift(OpSize::i32Bit, PFRaw, AF, ShiftType::LSL, 4);
+  SetRFLAG<FEXCore::X86State::RFLAG_AF_RAW_LOC>(XorRes);
+}
+
 void OpDispatchBuilder::CalculatePF(OrderedNode *Res) {
   // Calculation is entirely deferred until load, just store the 8-bit result.
   SetRFLAG<FEXCore::X86State::RFLAG_PF_RAW_LOC>(Res);