From 8fe6ef1fa800157f19bfdf87045d906266bc618b Mon Sep 17 00:00:00 2001
From: Stenzek <stenzek@gmail.com>
Date: Thu, 21 Dec 2023 01:53:14 +1000
Subject: [PATCH] CPU/NewRec: Allocate callee-saved registers before
 caller-saved

---
 src/core/cpu_newrec_compiler.cpp | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/src/core/cpu_newrec_compiler.cpp b/src/core/cpu_newrec_compiler.cpp
index 69f4fe4d2..360beeca2 100644
--- a/src/core/cpu_newrec_compiler.cpp
+++ b/src/core/cpu_newrec_compiler.cpp
@@ -525,11 +525,20 @@ u32 CPU::NewRec::Compiler::GetFreeHostReg(u32 flags)
 {
   const u32 req_flags = HR_USABLE | (flags & HR_CALLEE_SAVED);
 
+  u32 fallback = NUM_HOST_REGS;
   for (u32 i = 0; i < NUM_HOST_REGS; i++)
   {
     if ((m_host_regs[i].flags & (req_flags | HR_NEEDED | HR_ALLOCATED)) == req_flags)
-      return i;
+    {
+      // Prefer callee-saved registers.
+      if (m_host_regs[i].flags & HR_CALLEE_SAVED)
+        return i;
+      else if (fallback == NUM_HOST_REGS)
+        fallback = i;
+    }
   }
+  if (fallback != NUM_HOST_REGS)
+    return fallback;
 
   // find register with lowest counter
   u32 lowest = NUM_HOST_REGS;