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From "Mikhail Loenko" <mloe...@gmail.com>
Subject Re: verification of unreachable code
Date Fri, 06 Apr 2007 01:37:25 GMT
missed example?

2007/4/5, Alexei Fedotov <alexei.fedotov@gmail.com>:
> Folks,
> Thank you for expressing your thoughts - this is very useful. I agree
> with performance reasoning to skip dead code verification.
>
> Here is one more example:
>
>
>
> On 4/2/07, Mikhail Loenko <mloenko@gmail.com> wrote:
> > 02 Apr 2007 01:57:39 +0400, Egor Pasko <egor.pasko@gmail.com>:
> > > On the 0x2AB day of Apache Harmony Alexei Fedotov wrote:
> > > > Hello, Pavel, community,
> > > >
> > > > Could you here help me to understand the following issue? Consider the
> > > > following example:
> > > > ;
> > > > ; test method
> > > > .method public test([Ljava/lang/String;)I
> > > >    .limit stack 3
> > > >    .limit locals 2
> > > >
> > > >
> > > >    sipush 555
> > > >    iconst_1 ; push int 1
> > > >    iconst_2 ; push int 2
> > > >    if_icmplt Next
> > > > Next:
> > > >    sipush 555
> > > >    if_icmpne Fail
> > > >    ; pass
> > > >    sipush 104
> > > >    ireturn
> > > >
> > > >  Fail:
> > > >    sipush 105
> > > >    ireturn // <<<<<< look here
> > > >
> > > >
> > > >    return // <<<<<< look here
> > > > .end method
> > > >
> > > > In VM validation test suite we have a big number of tests like this
> > > > which have several different return instructions one method. JVM spec
> > > > says about this: "Each return instruction must match its method's
> > > > return type." Strangely, Sun's verifier allows this code to pass
> > > > verification, probably due to the fact that invalid "return" statement
> > > > is unreachable.
> > > >
> > > > Do you think we should be compatible with Sun on this issue?
> > >
> > > I think, skipping analysis of unreachable code pieces would make
> > > verification easier and faster not sacrificing JVM security, real apps
> > > and such. JIT does not touch unreachable code too. So, let's decide if
> > > real TCK/compat issues appear and forget unreachable code until then.
> >
> > +1
> >
> > Thanks,
> > Mikhail
> >
> >
> > >
> > > --
> > > Egor Pasko
> > >
> > >
> >
>
>
> --
> With best regards,
> Alexei,
> ESSD, Intel
>

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