Re: Improved C warning messages

> [ re not generating useless errors for widened and narrowed types ]
>In the parse tree at each node, you could maintain in addition to the type of
>the expression, the smallest data type that is known to hold the value without
>losing any information. This can then be used to decide on whether or not
>a particular warning should be issued.


Yes. A fairly straight-forward analysis using _abstract
interpretation_ will yield that information. (If you don't know what
abstract interpretation is, a web search will probably pull up some
useful references.) It might be better to use integer ranges for your
abstract domain, rather than using data types, because integer range
information is often useful for optimization purposes too, for example
for omitting array bounds checks. But using data types for your
abstract domain does make it easy to keep a simple and clean
separation between the front-end and the back-end.


--
Fergus Henderson <fjh@cs.mu.oz.au>
WWW: <http://www.cs.mu.oz.au/~fjh>
PGP: finger fjh@128.250.37.3

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