From 7ce7da629e8059a7c819ea26436f4426648d22b5 Mon Sep 17 00:00:00 2001
From: Sintendo <3380580+Sintendo@users.noreply.github.com>
Date: Sat, 1 Feb 2025 22:02:43 +0100
Subject: [PATCH] JitArm64_Integer: cmpl - Subtract shifted 12-bit constant

You can encode a shifted 12-bit immediate in a SUB instruction on ARM64.
We 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:
0x52a00218   mov    w24, #0x100000            ; =1048576
0xcb180379   sub    x25, x27, x24

After:
0xd1440379   sub    x25, x27, #0x100, lsl #12 ; =0x100000
---
 Source/Core/Core/PowerPC/JitArm64/JitArm64_Integer.cpp | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/Source/Core/Core/PowerPC/JitArm64/JitArm64_Integer.cpp b/Source/Core/Core/PowerPC/JitArm64/JitArm64_Integer.cpp
index ef44a72efd..58fab5cfea 100644
--- a/Source/Core/Core/PowerPC/JitArm64/JitArm64_Integer.cpp
+++ b/Source/Core/Core/PowerPC/JitArm64/JitArm64_Integer.cpp
@@ -736,6 +736,10 @@ void JitArm64::cmpl(UGeckoInstruction inst)
     else
       SUB(CR, EncodeRegTo64(gpr.R(a)), imm);
   }
+  else if (gpr.IsImm(b) && (gpr.GetImm(b) & 0xFFF000) == gpr.GetImm(b))
+  {
+    SUB(CR, EncodeRegTo64(gpr.R(a)), gpr.GetImm(b) >> 12, true);
+  }
   else
   {
     SUB(CR, EncodeRegTo64(gpr.R(a)), EncodeRegTo64(gpr.R(b)));