Fix zero-clearing instruction on aarch64

Author: rkennke

compiler/src/jdk.graal.compiler/src/jdk/graal/compiler/hotspot/aarch64/shenandoah/AArch64HotSpotShenandoahCompareAndSwapOp.java

@@ -195,8 +195,9 @@ public void emitCode(CompilationResultBuilder crb, AArch64MacroAssembler masm) {
 
             if (setConditionFlags) {
                 masm.bind(resultNullFailure);
-                // Clear zero flag to indicate failure.
-                masm.subs(32, zr, zr, 1);
+                // Clear zero flag to indicate failure. We come here knowing that result is null,
+                // so comparing it to 1 results in the zero (EQ) flag getting cleared.
+                masm.subs(32, zr, result,1);
                 masm.jmp(done);
             }
         });