8315934: RISC-V: Disable conservative fences per vendor

Reviewed-by: rehn, mli, fyang

Author: luhenry

src/hotspot/cpu/riscv/vm_version_riscv.cpp

@@ -99,6 +99,17 @@ void VM_Version::initialize() {
     }
   }
 
+  // Enable vendor specific features
+
+  if (mvendorid.enabled()) {
+    // Rivos
+    if (mvendorid.value() == RIVOS) {
+      if (FLAG_IS_DEFAULT(UseConservativeFence)) {
+        FLAG_SET_DEFAULT(UseConservativeFence, false);
+      }
+    }
+  }
+
   if (UseZic64b) {
     if (CacheLineSize != 64) {
       assert(!FLAG_IS_DEFAULT(CacheLineSize), "default cache line size should be 64 bytes");

src/hotspot/cpu/riscv/vm_version_riscv.hpp

@@ -40,6 +40,12 @@ class RiscvHwprobe;
 class VM_Version : public Abstract_VM_Version {
   friend RiscvHwprobe;
  private:
+
+  // JEDEC encoded as ((bank - 1) << 7) | (0x7f & JEDEC)
+  enum VendorId {
+    RIVOS = 0x6cf, // JEDEC: 0x4f, Bank: 14
+  };
+
   class RVFeatureValue {
     const char* const _pretty;
     const bool        _feature_string;

src/hotspot/os_cpu/linux_riscv/vm_version_linux_riscv.cpp

@@ -208,14 +208,11 @@ char* VM_Version::os_uarch_additional_features() {
 }
 
 void VM_Version::vendor_features() {
-  // JEDEC encoded as ((bank - 1) << 7) | (0x7f & JEDEC)
-  static constexpr int RIVOS_MVENDORID = 0x6cf; // JEDEC: 0x4f, Bank: 14
-
   if (!mvendorid.enabled()) {
     return;
   }
   switch (mvendorid.value()) {
-    case RIVOS_MVENDORID:
+    case RIVOS:
     rivos_features();
     break;
     default: