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Re: [PATCH] Make attribute functions pure

From: Robert Dewar <dewar at gnat dot com>
To: Laurent GUERBY <laurent at guerby dot net>
Cc: Jakub Jelinek <jakub at redhat dot com>,Richard Kenner <kenner at vlsi1 dot ultra dot nyu dot edu>, paul at codesourcery dot com,gcc-patches at gcc dot gnu dot org, gcc at gcc dot gnu dot org
Date: Sun, 25 Jul 2004 21:56:54 +0100
Subject: Re: [PATCH] Make attribute functions pure
References: <10407231255.AA27336@vlsi1.ultra.nyu.edu> <20040723111335.GU30497@sunsite.ms.mff.cuni.cz> <1090602836.10860.205.camel@pc.site>

Laurent GUERBY wrote:

Interesting, I assume GNAT is not mapping the Ada pragma Pure
to the same thing as the GNU C pure attribute, since Ada
semantics allow the compiler only to remove a call to a Pure function
(reusing previous call result when arguments are provably not changing),
not to move it around. Otherwise it's a bug.


Actually that's not clear ... it is definitely an ARG issue. If
there are no side effects, then obviously the call can be moved
around. The intention of the design was not to allow side effects,
so it is not really clear what transformations are or are not
allowed. I would guess the ARG would be inclined to be permissive,
i.e. to allow any optimization which would be valid in the absence
of side effects.

Laurent

Follow-Ups:
- Re: [PATCH] Make attribute functions pure
  - From: Laurent GUERBY

References:
- Re: [PATCH] Make attribute functions pure
  - From: Richard Kenner
- Re: [PATCH] Make attribute functions pure
  - From: Jakub Jelinek
- Re: [PATCH] Make attribute functions pure
  - From: Laurent GUERBY

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