Re: Why Virtual Machines? (was: C++ -> Java VM compiler)

{Stuff about bytecodes and intermediate reps elided}


moderator> [I was under the impression that the JVM was designed to
moderator> make it easy to generate efficient code at or just before
moderator> runtime. -John]


Yes, Java byte codes are designed to take advantage of on-the-fly
instruction rewrite. An illustrative example of this is in the section
"Translation to Machine Code" in:


                @Article{Gosling:1995:JIB,
                  author = "James Gosling",
                  title = "{Java} Intermediate Bytecodes",
                  journal = "ACM SIG{\-}PLAN Notices",
                  volume = "30", number = "3", pages = "111--118",
                  month = mar, year = "1995",
                }


BTW, in the Sun interpreter, there is a bytecode-to-bytecode rewrite
optimization called the "quick" instructions. You can read more on
this in "Section 4.1: Use Lossless Quick Opcodes" in the document "The
JIT Compiler Interface Specification" available at:
ftp://ftp.javasoft.com/docs/jit_interface.ps


The JIT interface spec also shows how the JVM can "accomodate"
on-the-fly compilation.


Anand.
--

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