--- old/src/hotspot/cpu/aarch64/macroAssembler_aarch64.cpp	2018-10-24 13:35:04.641868308 +0200
+++ new/src/hotspot/cpu/aarch64/macroAssembler_aarch64.cpp	2018-10-24 13:34:55.881847972 +0200
@@ -2367,21 +2367,18 @@
                              bool weak,
                              Register result) {
   if (result == noreg)  result = rscratch1;
+  BLOCK_COMMENT("cmpxchg {");
   if (UseLSE) {
     mov(result, expected);
     lse_cas(result, new_val, addr, size, acquire, release, /*not_pair*/ true);
-    cmp(result, expected);
+    compare_eq(result, expected, size);
   } else {
-    BLOCK_COMMENT("cmpxchg {");
     Label retry_load, done;
     if ((VM_Version::features() & VM_Version::CPU_STXR_PREFETCH))
       prfm(Address(addr), PSTL1STRM);
     bind(retry_load);
     load_exclusive(result, addr, size, acquire);
-    if (size == xword)
-      cmp(result, expected);
-    else
-      cmpw(result, expected);
+    compare_eq(result, expected, size);
     br(Assembler::NE, done);
     store_exclusive(rscratch1, new_val, addr, size, release);
     if (weak) {
@@ -2390,10 +2387,28 @@
       cbnzw(rscratch1, retry_load);
     }
     bind(done);
-    BLOCK_COMMENT("} cmpxchg");
   }
+  BLOCK_COMMENT("} cmpxchg");
 }
 
+// A generic comparison. Only compares for equality, clobbers rscratch1.
+void MacroAssembler::compare_eq(Register rm, Register rn, enum operand_size size) {
+  if (size == xword) {
+    cmp(rm, rn);
+  } else if (size == word) {
+    cmpw(rm, rn);
+  } else if (size == halfword) {
+    eorw(rscratch1, rm, rn);
+    ands(zr, rscratch1, 0xffff);
+  } else if (size == byte) {
+    eorw(rscratch1, rm, rn);
+    ands(zr, rscratch1, 0xff);
+  } else {
+    ShouldNotReachHere();
+  }
+}
+
+
 static bool different(Register a, RegisterOrConstant b, Register c) {
   if (b.is_constant())
     return a != c;