8255401: Shenandoah: Allow oldval and newval registers to overlap in cmpxchg_oop()

Reviewed-by: roland

Author: rkennke

src/hotspot/cpu/aarch64/gc/shenandoah/shenandoahBarrierSetAssembler_aarch64.cpp

@@ -477,7 +477,8 @@ void ShenandoahBarrierSetAssembler::cmpxchg_oop(MacroAssembler* masm,
   bool is_narrow = UseCompressedOops;
   Assembler::operand_size size = is_narrow ? Assembler::word : Assembler::xword;
 
-  assert_different_registers(addr, expected, new_val, tmp1, tmp2);
+  assert_different_registers(addr, expected, tmp1, tmp2);
+  assert_different_registers(addr, new_val,  tmp1, tmp2);
 
   Label step4, done;
 

src/hotspot/cpu/x86/gc/shenandoah/shenandoahBarrierSetAssembler_x86.cpp

@@ -638,7 +638,8 @@ void ShenandoahBarrierSetAssembler::cmpxchg_oop(MacroAssembler* masm,
                                                 bool exchange, Register tmp1, Register tmp2) {
   assert(ShenandoahCASBarrier, "Should only be used when CAS barrier is enabled");
   assert(oldval == rax, "must be in rax for implicit use in cmpxchg");
-  assert_different_registers(oldval, newval, tmp1, tmp2);
+  assert_different_registers(oldval, tmp1, tmp2);
+  assert_different_registers(newval, tmp1, tmp2);
 
   Label L_success, L_failure;