From fa13457abbf4bf194b4c5b8b0d5ff86fc2862ae7 Mon Sep 17 00:00:00 2001
From: Sintendo <3380580+Sintendo@users.noreply.github.com>
Date: Sat, 28 Dec 2024 20:18:09 +0100
Subject: [PATCH] JitArm64_Integer: subfex - Optimize InHostCarry case for -1

The result is either -1 or 0 depending on the state of the carry flag.
This can be done with a csetm instruction.

Before:
0x1280001a   mov    w26, #-0x1                ; =-1
0x1a1f035a   adc    w26, w26, wzr

After:
0x5a9f23fa   csetm  w26, lo
---
 .../Core/PowerPC/JitArm64/JitArm64_Integer.cpp     | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/Source/Core/Core/PowerPC/JitArm64/JitArm64_Integer.cpp b/Source/Core/Core/PowerPC/JitArm64/JitArm64_Integer.cpp
index 3b6aef8788..ed59599cff 100644
--- a/Source/Core/Core/PowerPC/JitArm64/JitArm64_Integer.cpp
+++ b/Source/Core/Core/PowerPC/JitArm64/JitArm64_Integer.cpp
@@ -1244,8 +1244,18 @@ void JitArm64::subfex(UGeckoInstruction inst)
     {
       gpr.BindToRegister(d, false);
       ARM64Reg RD = gpr.R(d);
-      MOVI2R(RD, imm);
-      ADC(RD, RD, ARM64Reg::WZR);
+      if (is_all_ones)
+      {
+        // RD = -1 + carry = carry ? 0 : -1
+        // CSETM sets the destination to -1 if the condition is true, 0
+        // otherwise. Hence, the condition must be carry clear.
+        CSETM(RD, CC_CC);
+      }
+      else
+      {
+        MOVI2R(RD, imm);
+        ADC(RD, RD, ARM64Reg::WZR);
+      }
       break;
     }
     case CarryFlag::ConstantTrue: