The predicate "(this == null)" is always false in a valid Java program, and therefore, it should be folded to "false". While the pattern is almost never explicitly appear in Java programs, it may effectively manifest after inlining, e.g. like:

    @Benchmark
    @CompilerControl(CompilerControl.Mode.DONT_INLINE)
    public void test() {
        m(this);
    }

    private void m(Object o) {
        if (o == null) {
            throw new IllegalArgumentException();
        }
    }

A real-life case is java.util.concurrent.atomic.A*FU checks. C2 optimizes these cases nicely. C1 does not optimize it, but it really should.

Benchmark:
 http://cr.openjdk.java.net/~shade/8141044/ThisNull.java

C1 perfasm, notice the null check in org.openjdk.ThisNull::test:
 http://cr.openjdk.java.net/~shade/8141044/c1.perfasm

C2 perfasm, notice the absence of null check:
 http://cr.openjdk.java.net/~shade/8141044/c2.perfasm