ASM not reporting constant instructions

I'm trying to use the ASM library to read byte code and translate it into a different format. Starting off with a simple test class containing this method:

public static double square(double a) {
    return a * a;
}

Which compiles to this byte code:

public static double square(double);
Code:
   0: dload_0
   1: dload_0
   2: dmul
   3: dreturn

using this MethodVisitor to read the code:

    return new MethodVisitor(ASM7) {
        @Override
        public void visitInsn(int opcode) {
            System.out.println(String.format("%02x", opcode));
        }

        @Override
        public void visitLdcInsn(Object value) {
            System.out.println(value);
        }
    };

I get this output:

6b
af

Those are the opcodes for dmul and dreturn respectively, so it is traversing the code, but it's not reporting the dload_0 instructions, either by visitInsn or visitLdcInsn.

What am I doing wrong?

ASM expands dload_0 to dload 0. At the same time, when writing, ASM optimizes the byte code instruction back to the short-cut constant when writing it to a ClassWriter. Override visitVarInsn and you will see the output with the byte code as first and the variable index as second argument.

(Edited after Holger's comment.)