From b0be20560f0ec41173ac4593aebbf6ef5f940536 Mon Sep 17 00:00:00 2001
From: Sintendo <bram.speeckaert@gmail.com>
Date: Mon, 4 Jan 2021 23:56:58 +0100
Subject: [PATCH] Jit64: subfx - Special case b == 0

Happens in Super Mario Sunshine. You could probably do something similar
for b == -1 (like we do for subfic), but I couldn't find any titles that
do this.

- Case 1: d == a

Before:
41 8B C7             mov         eax,r15d
41 BF 00 00 00 00    mov         r15d,0
44 2B F8             sub         r15d,eax

After:
41 F7 DF             neg         r15d

- Case 2: d != a

Before:
BF 00 00 00 00       mov         edi,0
41 2B FD             sub         edi,r13d

After:
41 8B FD             mov         edi,r13d
F7 DF                neg         edi
---
 Source/Core/Core/PowerPC/Jit64/Jit_Integer.cpp | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/Source/Core/Core/PowerPC/Jit64/Jit_Integer.cpp b/Source/Core/Core/PowerPC/Jit64/Jit_Integer.cpp
index a654b4d776..e90859d270 100644
--- a/Source/Core/Core/PowerPC/Jit64/Jit_Integer.cpp
+++ b/Source/Core/Core/PowerPC/Jit64/Jit_Integer.cpp
@@ -980,6 +980,18 @@ void Jit64::subfx(UGeckoInstruction inst)
         GenerateOverflow();
     }
   }
+  else if (gpr.IsImm(b) && gpr.Imm32(b) == 0)
+  {
+    RCOpArg Ra = gpr.Use(a, RCMode::Read);
+    RCX64Reg Rd = gpr.Bind(d, RCMode::Write);
+    RegCache::Realize(Ra, Rd);
+
+    if (d != a)
+      MOV(32, Rd, Ra);
+    NEG(32, Rd);
+    if (inst.OE)
+      GenerateOverflow();
+  }
   else
   {
     RCOpArg Ra = gpr.Use(a, RCMode::Read);