From d703f3ccee0ea66a09954394eebde62882ebc028 Mon Sep 17 00:00:00 2001
From: Ryan Houdek <Sonicadvance1@gmail.com>
Date: Sat, 24 Feb 2024 16:32:25 -0800
Subject: [PATCH] Fixes zero register flag generation

Fixes 140976d322dc5e26c129d1e6448f25f6b2378341

Adds a unit test to ensure it keeps working.
---
 .../Source/Interface/Core/OpcodeDispatcher.cpp  |  5 +++--
 unittests/ASM/FEX_bugs/xor_flags.asm            | 17 +++++++++++++++++
 2 files changed, 20 insertions(+), 2 deletions(-)
 create mode 100644 unittests/ASM/FEX_bugs/xor_flags.asm

diff --git a/FEXCore/Source/Interface/Core/OpcodeDispatcher.cpp b/FEXCore/Source/Interface/Core/OpcodeDispatcher.cpp
index d9269bf5c..59d9e0a85 100644
--- a/FEXCore/Source/Interface/Core/OpcodeDispatcher.cpp
+++ b/FEXCore/Source/Interface/Core/OpcodeDispatcher.cpp
@@ -5138,8 +5138,9 @@ void OpDispatchBuilder::ALUOpImpl(OpcodeArgs, FEXCore::IR::IROps ALUIROp, FEXCor
     Op->Dest.IsGPR() && Op->Src[SrcIdx].IsGPR() &&
     Op->Dest.Data.GPR == Op->Src[SrcIdx].Data.GPR) {
 
-    StoreResult(GPRClass, Op, _Constant(0), -1);
-    ZeroNZCV();
+    auto Result = _Constant(0);
+    StoreResult(GPRClass, Op, Result, -1);
+    GenerateFlags_Logical(Op, Result, Result, Result);
     return;
   }
 
diff --git a/unittests/ASM/FEX_bugs/xor_flags.asm b/unittests/ASM/FEX_bugs/xor_flags.asm
new file mode 100644
index 000000000..c71d2308f
--- /dev/null
+++ b/unittests/ASM/FEX_bugs/xor_flags.asm
@@ -0,0 +1,17 @@
+%ifdef CONFIG
+{
+  "RegData": {
+    "RAX": "0x0000000000004600"
+  }
+}
+%endif
+
+; FEX had a bug where an optimization for canonical zeroing of a register would fail to set flags correctly.
+; This broke `Metal Gear Rising: Revengeance`. The title screen geometry was broken.
+
+mov rax, 0
+mov rbx, 0
+sahf
+xor rbx, rbx
+lahf
+hlt