Re: interactive development and code re-loading

[Per Bothner <per at bothner dot com>]

On 10/14/2015 02:20 AM, Helmut Eller wrote:
> On Wed, Oct 14 2015, Per Bothner wrote:
>
> > I checked in code that defines "interactive mode" as suggested
> > in these emails
>
> Not sure if this was caused by those changes but:
>
>   kawa -e '(eval (call-with-input-string "(define (foo) (foo))" read))'
>
> now gets stuck in an endless loop.

It doesn't appear to have anything with the recent changes.

The reason you have to use the convoluted eval+call-with-input-string
in the test-case is because otherwise line number "fixme" are generated
for the bytecode, and those line number notes "disrupt" the bug.  If you
uncomment the code of CodeAttr#putLineNumber then you get the same
infinite compiler loop for plain:

  kawa -e '(define (foo) (foo))'

The loop happens in processFixups when it is trying to optimize:
  TRANSFER L1; ... L1: GOTO L2
to
  TRANSFER L2; ... L1: GOTO L2
where TRANSFER is a GOTO, conditional goto or certain other instructions.

This optimization gets into an infinite loop when L1==L2.
So (you say): check for L1==L2 - but that doesn't handle longer cycles.

So use a counter to limit the loop to finite number of iterations.
Alas, that triggers a VerifyError - for CodeAttr.class.  (I.e.
it's a bug either in javac or HotSpot.)  I'm having trouble
finding a working fix.  For example completely dropping the
"optimization", or only executing the loop at most once causes other problems.
--
	--Per Bothner
per@bothner.com   http://per.bothner.com/