prefer instanceOf instead of getClass() (#9366)
Motivation:
`instanceOf` doesn't perform null check like `getClass()` does. So `instanceOf` may be faster. However, it not true for all cases, as C2 could eliminate these null checks for `getClass()`.
Modification:
Replaced `string.getClass() == AsciiString.class` with `string instanceof AsciiString`.
Proof:
```
@BenchmarkMode(Mode.Throughput)
@Fork(value = 1)
@State(Scope.Thread)
@Warmup(iterations = 5, time = 1, batchSize = 1000)
@Measurement(iterations = 10, time = 1, batchSize = 1000)
public class GetClassInstanceOf {
Object key;
@Setup
public void setup() {
key = "123";
}
@Benchmark
public boolean getClassEquals() {
return key.getClass() == String.class;
}
@Benchmark
public boolean instanceOf() {
return key instanceof String;
}
}
```
```
Benchmark Mode Cnt Score Error Units
GetClassInstanceOf.getClassEquals thrpt 10 401863.130 ± 3092.568 ops/s
GetClassInstanceOf.instanceOf thrpt 10 421386.176 ± 4317.328 ops/s
```
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