Re: Semantical checks that involve flow of execution of the program

"John Max Skaller" <skaller@nospam.com.au>
21 Oct 2004 22:21:10 -0400

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Related articles
Semantical checks that involve flow of execution of the program lujoplujop@gmail.com (Lujop) (2004-10-17)
Re: Semantical checks that involve flow of execution of the program skaller@nospam.com.au (John Max Skaller) (2004-10-21)
Re: Semantical checks that involve flow of execution of the program choksheak@yahoo.com (ChokSheak Lau) (2004-10-21)
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From: "John Max Skaller" <skaller@nospam.com.au>
Newsgroups: comp.compilers
Date: 21 Oct 2004 22:21:10 -0400
Organization: Compilers Central
References: 04-10-122
Keywords: semantics
Posted-Date: 21 Oct 2004 22:21:10 EDT

On Sun, 17 Oct 2004 16:09:46 -0400, Lujop wrote:


> //var a is not inicialized
> ...
> if codition1 then
> a <- 1
> else if codition2 then
> b <-2
> else
> a <- 1
>
> With this example Java says that 'a' is possibly not initialized
> because branch 2 don't assign any value in a.


If your representation is a node


Cond (c,yes,no)


then you can just use


a_is_init (yes) and a_is_init (no)


For sequential statements:


Seq(first,next)


you can use


a_is_init(first) or a_is_init(next)


These are synthetic attributes -- you can calculate bottom up
directly in the parser, or using simple recursive descent.


In practice you would not use a function just checking for
one variable 'a'. Instead, you'd calculate *all* the variables
initialised at once, using a set. Then the rules would be like:


init (Cond (c, yes, no) ==> init(yes) intersect init (no)


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