Re: i++ in Java

Eddy Truyen wrote:


> Hi there,
>
> javac compiles statements like i++, i-- and similar to optimized byte
> code. This means that the resulting bytecodes are not the same when
> compiling i=i+1;
> Is their anyway to turn this off?
> I looked and at first glance their seems to be an option -O to optimize
> the compiler, but no option that leads to compiling only 'clean' code
> without dupx statements that insert elements within the Java stack




Dupx statements are used for more than just optimizations. say you
have the sequence:


new java/lang/String
dup
invokevirtual (some string function) // note invokevirtual takes the object
off the stack
invokevirtual (some other string function)


The only way I can think of to perform the same optimization is:


new java/lang/String
astore_0
aload_0
invokevirtual (Some string function)
aload_0
invokevirtual (some other string function)


I don't really think that's any cleaner, so I doubt there is an option
to do that. Java Bytecode is a stack based architecture, so naturally
the generated code is stack like and doesn't do all that loading and
storing that is common in load/store architectures.


As far as i++ goes, iinc (the optimized bytecode you refer to)is
pretty straightforward. You are correct though. I was surprised that
i = i + 1 is not translated to the same thing as i++. javac is not
known for its powerful optimization though.


STEVE

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