From 01eed0a7585fbd3031e850ee8f14778e9e46a0e4 Mon Sep 17 00:00:00 2001
From: Sintendo <3380580+Sintendo@users.noreply.github.com>
Date: Sat, 1 Feb 2025 17:02:10 +0100
Subject: [PATCH] JitArm64_Integer: cmp - Add 12-bit constant

You can encode a 12-bit immediate in an ADD instruction on ARM64. If the
negated constant fits in this range, we can exploit this to avoid
materializing the immediate.

This approach saves an instruction if it does not need to be
materialized in a register afterwards. Otherwise, we just materialize
it later and the total number of instructions stays the same.

Before:
0x12800019   mov    w25, #-0x1                ; =-1
0x93407f5b   sxtw   x27, w26
0xcb39c37b   sub    x27, x27, w25, sxtw

After:
0x93407f5b   sxtw   x27, w26
0x9100077b   add    x27, x27, #0x1
---
 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 3a56e58b84..2175f9a219 100644
--- a/Source/Core/Core/PowerPC/JitArm64/JitArm64_Integer.cpp
+++ b/Source/Core/Core/PowerPC/JitArm64/JitArm64_Integer.cpp
@@ -663,6 +663,11 @@ void JitArm64::cmp(UGeckoInstruction inst)
     SXTW(CR, gpr.R(a));
     SUB(CR, CR, gpr.GetImm(b) >> 12, true);
   }
+  else if (gpr.IsImm(b) && (((~gpr.GetImm(b) + 1) & 0xFFF) == (~gpr.GetImm(b) + 1)))
+  {
+    SXTW(CR, gpr.R(a));
+    ADD(CR, CR, ~gpr.GetImm(b) + 1);
+  }
   else
   {
     ARM64Reg RA = gpr.R(a);