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From: dewar@merv.cs.nyu.edu (Robert Dewar)
Subject: Re: ADA on the super
Date: 1998/04/21
Message-ID: <dewar.893163240@merv>#1/1
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Andi said

<<It is surprising that Gnat doesn't do this. At least the C frontend of gcc
does a very similar optimization:
>>
No, the optimization you cite is at a radically different semantic level.
There is nothing like dynamic slices and concatenations in C. If you
write Ada code that corresponds to the C code you gave, which is easy
to do, you will of course get identical code.

But there is no C code that is even vaguely like the quoted Ada code.

To get a feel for the issues involved, look at the exp_pakd unit in GNAT,
and also study some -gnatdg output, to understand the general semantic
level of the tree expansions involved here.

Remember that we are talking about very general capabilities here, which
just happen to be used in this particular case to do a rotate.