From 592ba31e224c062fe558dad21d2f605196df0b31 Mon Sep 17 00:00:00 2001
From: Bram Speeckaert <bram.speeckaert@gmail.com>
Date: Tue, 1 Nov 2022 11:51:57 +0100
Subject: [PATCH] JitArm64: cmp - Optimize a == 0 case

By explicitly handling this, we can avoid materializing zero in a
register and generate more efficient code altogether.

Before:
0x52800016   mov    w22, #0x0
0xb94093b5   ldr    w21, [x29, #0x90]
0x93407ed7   sxtw   x23, w22
0x93407eb9   sxtw   x25, w21
0xcb1902f9   sub    x25, x23, x25

After:
0xb94093b7   ldr    w23, [x29, #0x90]
0x4b1703f9   neg    w25, w23
0x93407f39   sxtw   x25, w25
---
 Source/Core/Core/PowerPC/JitArm64/JitArm64_Integer.cpp | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/Source/Core/Core/PowerPC/JitArm64/JitArm64_Integer.cpp b/Source/Core/Core/PowerPC/JitArm64/JitArm64_Integer.cpp
index 2b46e80e70..2166a1427d 100644
--- a/Source/Core/Core/PowerPC/JitArm64/JitArm64_Integer.cpp
+++ b/Source/Core/Core/PowerPC/JitArm64/JitArm64_Integer.cpp
@@ -579,6 +579,11 @@ void JitArm64::cmp(UGeckoInstruction inst)
     s64 B = static_cast<s32>(gpr.GetImm(b));
     MOVI2R(CR, A - B);
   }
+  else if (gpr.IsImm(a) && !gpr.GetImm(a))
+  {
+    NEG(EncodeRegTo32(CR), gpr.R(b));
+    SXTW(CR, EncodeRegTo32(CR));
+  }
   else if (gpr.IsImm(b) && !gpr.GetImm(b))
   {
     SXTW(CR, gpr.R(a));