JitArm64_Integer: subfzex - Optimize a == 0 with in-host carry

Before:
0x52800019   mov    w25, #0x0                 ; =0
0x7a1903f9   ngcs   w25, w25
0x1a9f37f5   cset   w21, hs
0x390bd3b5   strb   w21, [x29, #0x2f4]

After:
0x5a9f23f9   csetm  w25, lo

1 files changed, 9 insertions, 0 deletions

diff --git a/Source/Core/Core/PowerPC/JitArm64/JitArm64_Integer.cpp b/Source/Core/Core/PowerPC/JitArm64/JitArm64_Integer.cpp
index e82db40756..3cf4175b72 100644
--- a/Source/Core/Core/PowerPC/JitArm64/JitArm64_Integer.cpp
+++ b/Source/Core/Core/PowerPC/JitArm64/JitArm64_Integer.cpp
@@ -1326,6 +1326,15 @@ void JitArm64::subfzex(UGeckoInstruction inst)
     gpr.SetImmediate(d, imm + carry);
     ComputeCarry(Interpreter::Helper_Carry(imm, carry));
   }
+  else if (gpr.IsImm(a, 0) && js.carryFlag == CarryFlag::InHostCarry)
+  {
+    gpr.BindToRegister(d, false);
+    // RD = ~0 + carry = -1 + carry = carry ? 0 : -1
+    // Note that CSETM sets the destination to -1 if the condition is true,
+    // and 0 otherwise. Hence, the condition must be carry clear.
+    CSETM(gpr.R(d), CC_CC);
+    // Carry remains unchanged.
+  }
   else
   {
     gpr.BindToRegister(d, d == a);