From 76228fa4824359a98f8d6139f507b5ce190c827a Mon Sep 17 00:00:00 2001
From: JosJuice <josjuice@gmail.com>
Date: Mon, 29 Jun 2020 18:17:19 +0200
Subject: [PATCH] Jit64: Implement low DCBZ hack

I was hoping this would improve the performance of Cars 2 by
avoiding interpreter fallbacks, but it doesn't seem to have
made any measurable impact.
---
 Source/Core/Core/PowerPC/Jit64/Jit_LoadStore.cpp | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/Source/Core/Core/PowerPC/Jit64/Jit_LoadStore.cpp b/Source/Core/Core/PowerPC/Jit64/Jit_LoadStore.cpp
index 4fae084339..6d98aa9738 100644
--- a/Source/Core/Core/PowerPC/Jit64/Jit_LoadStore.cpp
+++ b/Source/Core/Core/PowerPC/Jit64/Jit_LoadStore.cpp
@@ -290,7 +290,6 @@ void Jit64::dcbz(UGeckoInstruction inst)
 {
   INSTRUCTION_START
   JITDISABLE(bJITLoadStoreOff);
-  FALLBACK_IF(SConfig::GetInstance().bLowDCBZHack);
 
   int a = inst.RA;
   int b = inst.RB;
@@ -304,6 +303,14 @@ void Jit64::dcbz(UGeckoInstruction inst)
     AND(32, R(RSCRATCH), Imm32(~31));
   }
 
+  FixupBranch end_dcbz_hack;
+  if (SConfig::GetInstance().bLowDCBZHack)
+  {
+    // HACK: Don't clear any memory in the [0x8000'0000, 0x8000'8000) region.
+    CMP(32, R(RSCRATCH), Imm32(0x8000'8000));
+    end_dcbz_hack = J_CC(CC_L);
+  }
+
   bool emit_fast_path = MSR.DR && m_jit.jo.fastmem_arena;
 
   if (emit_fast_path)
@@ -333,10 +340,13 @@ void Jit64::dcbz(UGeckoInstruction inst)
 
   if (emit_fast_path)
   {
-    FixupBranch end = J(true);
+    FixupBranch end_far_code = J(true);
     SwitchToNearCode();
-    SetJumpTarget(end);
+    SetJumpTarget(end_far_code);
   }
+
+  if (SConfig::GetInstance().bLowDCBZHack)
+    SetJumpTarget(end_dcbz_hack);
 }
 
 void Jit64::stX(UGeckoInstruction inst)