From 41c0183c0774f48c02a13c2f875d284e88e38693 Mon Sep 17 00:00:00 2001
From: krk <keremkat@gmail.com>
Date: Thu, 12 Dec 2024 13:52:55 +0000
Subject: [PATCH] Backport 3c60f0b2bb75150d49da9ab94d88b767275de5e2

---
 src/hotspot/cpu/aarch64/register_aarch64.hpp  |  8 +++++++-
 .../cpu/aarch64/vm_version_aarch64.cpp        | 20 ++++++++++++++++---
 2 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/src/hotspot/cpu/aarch64/register_aarch64.hpp b/src/hotspot/cpu/aarch64/register_aarch64.hpp
index 5a152d62777..459e24639fd 100644
--- a/src/hotspot/cpu/aarch64/register_aarch64.hpp
+++ b/src/hotspot/cpu/aarch64/register_aarch64.hpp
@@ -140,7 +140,13 @@ class FloatRegisterImpl: public AbstractRegisterImpl {
     max_slots_per_register = 8,
     save_slots_per_register = 2,
     slots_per_neon_register = 4,
-    extra_save_slots_per_neon_register = slots_per_neon_register - save_slots_per_register
+    extra_save_slots_per_neon_register = slots_per_neon_register - save_slots_per_register,
+    neon_vl = 16,
+    // VLmax: The maximum sve vector length is determined by the hardware
+    // sve_vl_min <= VLmax <= sve_vl_max.
+    sve_vl_min = 16,
+    // Maximum supported vector length across all CPUs
+    sve_vl_max = 256
   };
 
   // construction
diff --git a/src/hotspot/cpu/aarch64/vm_version_aarch64.cpp b/src/hotspot/cpu/aarch64/vm_version_aarch64.cpp
index c5046582a61..0bba64e1f45 100644
--- a/src/hotspot/cpu/aarch64/vm_version_aarch64.cpp
+++ b/src/hotspot/cpu/aarch64/vm_version_aarch64.cpp
@@ -24,6 +24,7 @@
  */
 
 #include "precompiled.hpp"
+#include "register_aarch64.hpp"
 #include "runtime/arguments.hpp"
 #include "runtime/globals_extension.hpp"
 #include "runtime/java.hpp"
@@ -414,14 +415,27 @@ void VM_Version::initialize() {
     if (FLAG_IS_DEFAULT(UseSVE)) {
       FLAG_SET_DEFAULT(UseSVE, (_features & CPU_SVE2) ? 2 : 1);
     }
-    if (UseSVE > 0) {
-      _initial_sve_vector_length = get_current_sve_vector_length();
-    }
   } else if (UseSVE > 0) {
     warning("UseSVE specified, but not supported on current CPU. Disabling SVE.");
     FLAG_SET_DEFAULT(UseSVE, 0);
   }
 
+  if (UseSVE > 0) {
+    int vl = get_current_sve_vector_length();
+    if (vl < 0) {
+      warning("Unable to get SVE vector length on this system. "
+              "Disabling SVE. Specify -XX:UseSVE=0 to shun this warning.");
+      FLAG_SET_DEFAULT(UseSVE, 0);
+    } else if ((vl == 0) || ((vl % FloatRegisterImpl::sve_vl_min) != 0) || !is_power_of_2(vl)) {
+      warning("Detected SVE vector length (%d) should be a power of two and a multiple of %d. "
+              "Disabling SVE. Specify -XX:UseSVE=0 to shun this warning.",
+              vl, FloatRegisterImpl::sve_vl_min);
+      FLAG_SET_DEFAULT(UseSVE, 0);
+    } else {
+      _initial_sve_vector_length = vl;
+    }
+  }
+
   // This machine allows unaligned memory accesses
   if (FLAG_IS_DEFAULT(UseUnalignedAccesses)) {
     FLAG_SET_DEFAULT(UseUnalignedAccesses, true);