8318776: Require supports_cx8 to always be true

Reviewed-by: eosterlund, shade, dcubed

Author: David Holmes

make/data/hotspot-symbols/symbols-unix

@@ -203,7 +203,6 @@ JVM_SetStackWalkContinuation
 JVM_SetThreadPriority
 JVM_SleepNanos
 JVM_StartThread
-JVM_SupportsCX8
 JVM_TotalMemory
 JVM_UnloadLibrary
 JVM_WaitForReferencePendingList

src/hotspot/cpu/aarch64/c1_LIRAssembler_aarch64.cpp

@@ -1511,7 +1511,6 @@ void LIR_Assembler::casl(Register addr, Register newval, Register cmpval) {
 
 
 void LIR_Assembler::emit_compare_and_swap(LIR_OpCompareAndSwap* op) {
-  assert(VM_Version::supports_cx8(), "wrong machine");
   Register addr;
   if (op->addr()->is_register()) {
     addr = as_reg(op->addr());

src/hotspot/cpu/aarch64/vm_version_aarch64.cpp

@@ -68,7 +68,6 @@ static SpinWait get_spin_wait_desc() {
 }
 
 void VM_Version::initialize() {
-  _supports_cx8 = true;
   _supports_atomic_getset4 = true;
   _supports_atomic_getadd4 = true;
   _supports_atomic_getset8 = true;

src/hotspot/cpu/arm/c1_LIRAssembler_arm.cpp

@@ -1385,7 +1385,6 @@ void LIR_Assembler::emit_compare_and_swap(LIR_OpCompareAndSwap* op) {
     __ mov(dest, 1, eq);
     __ mov(dest, 0, ne);
   } else if (op->code() == lir_cas_long) {
-    assert(VM_Version::supports_cx8(), "wrong machine");
     Register cmp_value_lo = op->cmp_value()->as_register_lo();
     Register cmp_value_hi = op->cmp_value()->as_register_hi();
     Register new_value_lo = op->new_value()->as_register_lo();

src/hotspot/cpu/arm/vm_version_arm_32.cpp

@@ -128,10 +128,16 @@ void VM_Version::early_initialize() {
   // use proper dmb instruction
   get_os_cpu_info();
 
+  // Future cleanup: if SUPPORTS_NATIVE_CX8 is defined then we should not need
+  // any alternative solutions. At present this allows for the theoretical
+  // possibility of building for ARMv7 and then running on ARMv5 or 6. If that
+  // is impossible then the ARM port folk should clean this up.
   _kuser_helper_version = *(int*)KUSER_HELPER_VERSION_ADDR;
+#ifndef SUPPORTS_NATIVE_CX8
   // armv7 has the ldrexd instruction that can be used to implement cx8
   // armv5 with linux >= 3.1 can use kernel helper routine
   _supports_cx8 = (supports_ldrexd() || supports_kuser_cmpxchg64());
+#endif
 }
 
 void VM_Version::initialize() {
@@ -278,7 +284,7 @@ void VM_Version::initialize() {
   _supports_atomic_getadd8 = supports_ldrexd();
 
 #ifdef COMPILER2
-  assert(_supports_cx8 && _supports_atomic_getset4 && _supports_atomic_getadd4
+  assert(supports_cx8() && _supports_atomic_getset4 && _supports_atomic_getadd4
          && _supports_atomic_getset8 && _supports_atomic_getadd8, "C2: atomic operations must be supported");
 #endif
   char buf[512];

src/hotspot/cpu/ppc/vm_version_ppc.cpp

@@ -200,10 +200,6 @@ void VM_Version::initialize() {
     print_features();
   }
 
-  // PPC64 supports 8-byte compare-exchange operations (see Atomic::cmpxchg)
-  // and 'atomic long memory ops' (see Unsafe_GetLongVolatile).
-  _supports_cx8 = true;
-
   // Used by C1.
   _supports_atomic_getset4 = true;
   _supports_atomic_getadd4 = true;

src/hotspot/cpu/riscv/c1_LIRAssembler_riscv.cpp

@@ -1251,7 +1251,6 @@ void LIR_Assembler::emit_opTypeCheck(LIR_OpTypeCheck* op) {
 }
 
 void LIR_Assembler::emit_compare_and_swap(LIR_OpCompareAndSwap* op) {
-  assert(VM_Version::supports_cx8(), "wrong machine");
   Register addr;
   if (op->addr()->is_register()) {
     addr = as_reg(op->addr());

src/hotspot/cpu/riscv/vm_version_riscv.cpp

@@ -46,7 +46,6 @@ RV_FEATURE_FLAGS(ADD_RV_FEATURE_IN_LIST)
   nullptr};
 
 void VM_Version::initialize() {
-  _supports_cx8 = true;
   _supports_atomic_getset4 = true;
   _supports_atomic_getadd4 = true;
   _supports_atomic_getset8 = true;

src/hotspot/cpu/s390/c1_LIRAssembler_s390.cpp

@@ -2670,7 +2670,6 @@ void LIR_Assembler::emit_compare_and_swap(LIR_OpCompareAndSwap* op) {
   Register addr = op->addr()->as_pointer_register();
   Register t1_cmp = Z_R1_scratch;
   if (op->code() == lir_cas_long) {
-    assert(VM_Version::supports_cx8(), "wrong machine");
     Register cmp_value_lo = op->cmp_value()->as_register_lo();
     Register new_value_lo = op->new_value()->as_register_lo();
     __ z_lgr(t1_cmp, cmp_value_lo);

src/hotspot/cpu/s390/vm_version_s390.cpp

@@ -287,11 +287,6 @@ void VM_Version::initialize() {
     FLAG_SET_DEFAULT(UsePopCountInstruction, true);
   }
 
-  // z/Architecture supports 8-byte compare-exchange operations
-  // (see Atomic::cmpxchg)
-  // and 'atomic long memory ops' (see Unsafe_GetLongVolatile).
-  _supports_cx8 = true;
-
   _supports_atomic_getadd4 = VM_Version::has_LoadAndALUAtomicV1();
   _supports_atomic_getadd8 = VM_Version::has_LoadAndALUAtomicV1();