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From: Adam Beneschan <adam@irvine.com>
Newsgroups: comp.lang.ada
Subject: Re: GNAT 4.4.5 order of conditional processing?
Date: Tue, 15 Nov 2011 17:18:30 -0800 (PST)
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Date: 2011-11-15T17:18:30-08:00
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On Nov 15, 3:08=A0pm, Jeffrey Carter
<spam.jrcarter....@spam.not.acm.org> wrote:
>
> Note that the short circuit forms should not be considered optimizations.=
 With
> modern processors, unnecessary short-circuit forms may sometimes be slowe=
r than
> the regular equivalents.

Yeah, but the compiler should be able to figure it out and generate
the best code.  No matter what the Ada language says, if you write "A
and then B" and A and B are Boolean variables, it's perfectly legal
for the compiler to generate an instruction that reads the register
that currently contains B.  (I mean a normal register, not a memory-
mapped I/O register.)  The only time it should be necessary to use
"and" instead of "and then" (on Boolean operands) is if the right side
contains a function call (or, perhaps, a read of a variable that's
mapped to some special hardware address) that you absolutely want to
take place regardless of the left side.

                              -- Adam