System: Refactor main loop

Reduces JIT exits.
Improves runahead performance.

src/common/fastjmp_arm.asm

@@ -0,0 +1,47 @@
+; SPDX-FileCopyrightText: 2021 Connor McLaughlin <stenzek@gmail.com>
+; SPDX-License-Identifier: (GPL-3.0 OR CC-BY-NC-ND-4.0)
+
+#include "ksarm64.h"
+
+  EXPORT fastjmp_set
+  EXPORT fastjmp_jmp
+
+  TEXTAREA
+
+  ; void fastjmp_set(fastjmp_buf*)
+  LEAF_ENTRY fastjmp_set
+    mov x16, sp
+    stp x16, x30, [x0]
+    stp x19, x20, [x0, #16]
+    stp x21, x22, [x0, #32]
+    stp x23, x24, [x0, #48]
+    stp x25, x26, [x0, #64]
+    stp x27, x28, [x0, #80]
+    str x29, [x0, #96]
+    stp d8, d9, [x0, #112]
+    stp d10, d11, [x0, #128]
+    stp d12, d13, [x0, #144]
+    stp d14, d15, [x0, #160]
+    mov w0, wzr
+    br x30
+  LEAF_END
+
+  ; void fastjmp_jmp(fastjmp_buf*, int)
+  LEAF_ENTRY fastjmp_jmp
+    ldp x16, x30, [x0]
+    mov sp, x16
+    ldp x19, x20, [x0, #16]
+    ldp x21, x22, [x0, #32]
+    ldp x23, x24, [x0, #48]
+    ldp x25, x26, [x0, #64]
+    ldp x27, x28, [x0, #80]
+    ldr x29, [x0, #96]
+    ldp d8, d9, [x0, #112]
+    ldp d10, d11, [x0, #128]
+    ldp d12, d13, [x0, #144]
+    ldp d14, d15, [x0, #160]
+    mov w0, w1
+    br x30
+  LEAF_END
+
+  END