Re: CFGs vs. "declare variable before use"

glen herrmannsfeldt <gah@ugcs.caltech.edu>
31 May 2005 21:42:19 -0400

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From: glen herrmannsfeldt <gah@ugcs.caltech.edu>
Newsgroups: comp.compilers
Date: 31 May 2005 21:42:19 -0400
Organization: Compilers Central
References: 05-05-216 05-05-221
Keywords: parse

Torben Ęgidius Mogensen wrote:
(snip)


> CFG's can be used to guarantee that declarations precede use: If the
> declaration dominates every use, then a variable is bound to be
> declared before use.


It seems that verilog is one language that doesn't require a variable
to be declared before it is used. (I found this out accidentally
after reporting a bug. It seems that one system would compile such
code, but the optimizer made some bad assumptions.)


In the case of verilog, though, where statements are not necessarily
executed sequentially, it isn't so obvious what "use" means.


-- glen


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