From e53fffeb908cf3f6feb11597298b36fbfa9fee37 Mon Sep 17 00:00:00 2001
From: Lioncash <mathew1800@gmail.com>
Date: Wed, 21 Mar 2018 23:51:31 -0400
Subject: [PATCH] PowerPC: Properly unset the overflow bit

The OV bit is non-sticky. Therefore, after an overflow-enabled
instruction executes, if an overflow does *not* occur, then OV is
cleared. SO is sticky however, so it staying set in this case is
correct.
---
 .../Interpreter/Interpreter_Integer.cpp       | 38 +++++++++----------
 Source/Core/Core/PowerPC/PowerPC.h            |  2 +-
 2 files changed, 19 insertions(+), 21 deletions(-)

diff --git a/Source/Core/Core/PowerPC/Interpreter/Interpreter_Integer.cpp b/Source/Core/Core/PowerPC/Interpreter/Interpreter_Integer.cpp
index 8b7a3c8742..7367e85fdc 100644
--- a/Source/Core/Core/PowerPC/Interpreter/Interpreter_Integer.cpp
+++ b/Source/Core/Core/PowerPC/Interpreter/Interpreter_Integer.cpp
@@ -492,16 +492,12 @@ void Interpreter::addzex(UGeckoInstruction inst)
 
 void Interpreter::divwx(UGeckoInstruction inst)
 {
-  s32 a = rGPR[inst.RA];
-  s32 b = rGPR[inst.RB];
+  const s32 a = rGPR[inst.RA];
+  const s32 b = rGPR[inst.RB];
+  const bool overflow = b == 0 || ((u32)a == 0x80000000 && b == -1);
 
-  if (b == 0 || ((u32)a == 0x80000000 && b == -1))
+  if (overflow)
   {
-    if (inst.OE)
-    {
-      SetXER_OV(true);
-    }
-
     if (((u32)a & 0x80000000) && b == 0)
       rGPR[inst.RD] = UINT32_MAX;
     else
@@ -512,22 +508,21 @@ void Interpreter::divwx(UGeckoInstruction inst)
     rGPR[inst.RD] = (u32)(a / b);
   }
 
+  if (inst.OE)
+    SetXER_OV(overflow);
+
   if (inst.Rc)
     Helper_UpdateCR0(rGPR[inst.RD]);
 }
 
 void Interpreter::divwux(UGeckoInstruction inst)
 {
-  u32 a = rGPR[inst.RA];
-  u32 b = rGPR[inst.RB];
+  const u32 a = rGPR[inst.RA];
+  const u32 b = rGPR[inst.RB];
+  const bool overflow = b == 0;
 
-  if (b == 0)
+  if (overflow)
   {
-    if (inst.OE)
-    {
-      SetXER_OV(true);
-    }
-
     rGPR[inst.RD] = 0;
   }
   else
@@ -535,6 +530,9 @@ void Interpreter::divwux(UGeckoInstruction inst)
     rGPR[inst.RD] = a / b;
   }
 
+  if (inst.OE)
+    SetXER_OV(overflow);
+
   if (inst.Rc)
     Helper_UpdateCR0(rGPR[inst.RD]);
 }
@@ -572,8 +570,8 @@ void Interpreter::mullwx(UGeckoInstruction inst)
 
   rGPR[inst.RD] = static_cast<u32>(result);
 
-  if (inst.OE && (result < -0x80000000LL || result > 0x7FFFFFFFLL))
-    SetXER_OV(true);
+  if (inst.OE)
+    SetXER_OV(result < -0x80000000LL || result > 0x7FFFFFFFLL);
 
   if (inst.Rc)
     Helper_UpdateCR0(rGPR[inst.RD]);
@@ -588,8 +586,8 @@ void Interpreter::negx(UGeckoInstruction inst)
   if (inst.Rc)
     Helper_UpdateCR0(rGPR[inst.RD]);
 
-  if (inst.OE && a == 0x80000000)
-    SetXER_OV(true);
+  if (inst.OE)
+    SetXER_OV(a == 0x80000000);
 }
 
 void Interpreter::subfx(UGeckoInstruction inst)
diff --git a/Source/Core/Core/PowerPC/PowerPC.h b/Source/Core/Core/PowerPC/PowerPC.h
index 5b74df1a58..ba838a610d 100644
--- a/Source/Core/Core/PowerPC/PowerPC.h
+++ b/Source/Core/Core/PowerPC/PowerPC.h
@@ -434,7 +434,7 @@ inline u32 GetXER_OV()
 
 inline void SetXER_OV(bool value)
 {
-  PowerPC::ppcState.xer_so_ov |= static_cast<u32>(value);
+  PowerPC::ppcState.xer_so_ov = (PowerPC::ppcState.xer_so_ov & 0xFE) | static_cast<u32>(value);
   SetXER_SO(value);
 }