Re: Java Compilers and Tail Recursion

Jason Karney <jkarney@netgenics.com> asked:
| Is the current crop of Java compilers smart enough to optimize tail
| recursion? I am specifically wondering about Symantec and Sun's JDK
| compilers.


Tail-recursion elimination is prohibited by the implementation of the
Java SecurityMangler. See definitions of getClassContext(),
classDepth(), inClass(), classLoaderDepth() etc. (section 20.17.* in
the language spec)


So the answer is you can't do it _and_ support the ClassLoader/
SecurityManager protocol. This is (in my opinion) because that
protocol is an inelegant hack.


It would not be at all difficult to do the elimination, it doesn't
even need a compiler to do it either, an interpreter can just check
for a suitable return bytecode after an invoke opcode (and you have to
check for being in a synchronized method too). It's a simple peephole
optimization, because the method-invocation and return byte codes are
at a high-enough level.


__Mark
[ markt@harlequin.co.uk | http://www.harlequin.co.uk/ | +44(0)1954 785433 ]
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