From d877cfa4e2c3baf3cb8b8449d1608e1c2f05208c Mon Sep 17 00:00:00 2001
From: Sintendo <3380580+Sintendo@users.noreply.github.com>
Date: Wed, 26 Jun 2024 00:07:20 +0200
Subject: [PATCH] JitArm64_Integer: Optimize subfic for zero
When the immediate value is zero, we can do a negation. On ARM64 the NEG
/NEGS instructions are just an alias for SUB/SUBS with a hardcoded WZR.
Before:
```
ldr w22, [x29, #0x28]
mov w21, #0x0 ; =0
subs w22, w21, w22
```
After:
```
ldr w22, [x29, #0x28]
negs w22, w22
```
---
.../Core/PowerPC/JitArm64/JitArm64_Integer.cpp | 14 ++++++++++----
1 file changed, 10 insertions(+), 4 deletions(-)
diff --git a/Source/Core/Core/PowerPC/JitArm64/JitArm64_Integer.cpp b/Source/Core/Core/PowerPC/JitArm64/JitArm64_Integer.cpp
index 7e5817ac0c..f3d263379c 100644
--- a/Source/Core/Core/PowerPC/JitArm64/JitArm64_Integer.cpp
+++ b/Source/Core/Core/PowerPC/JitArm64/JitArm64_Integer.cpp
@@ -1392,13 +1392,19 @@ void JitArm64::subfic(UGeckoInstruction inst)
}
else
{
- const bool allocate_reg = d == a;
- gpr.BindToRegister(d, allocate_reg);
+ const bool will_read = d == a;
+ const bool is_zero = imm == 0;
+ const bool allocate_reg = will_read && !is_zero;
+ gpr.BindToRegister(d, will_read);
// d = imm - a
ARM64Reg RD = gpr.R(d);
- ARM64Reg WA = allocate_reg ? gpr.GetReg() : RD;
- MOVI2R(WA, imm);
+ ARM64Reg WA = ARM64Reg::WZR;
+ if (!is_zero)
+ {
+ WA = will_read ? gpr.GetReg() : RD;
+ MOVI2R(WA, imm);
+ }
CARRY_IF_NEEDED(SUB, SUBS, RD, WA, gpr.R(a));
if (allocate_reg)