From: Ian Lance Taylor <iant@google.com>
To: Adam Nemet <anemet@caviumnetworks.com>
Cc: gcc@gcc.gnu.org, law@redhat.com
Subject: Re: Rationale for an old TRUNCATE patch
Date: Wed, 17 Jun 2009 14:24:00 -0000 [thread overview]
Message-ID: <m3ocsnuef1.fsf@google.com> (raw)
In-Reply-To: <19000.36794.687088.768724@ropi.home> (Adam Nemet's message of "Tue\, 16 Jun 2009 23\:39\:54 -0700")
Adam Nemet <anemet@caviumnetworks.com> writes:
> Ian Lance Taylor writes:
>> truncate has a machine independent meaning.
>
> Yes, I guess with your definition below it does. It's interesting though that
> Jim had said the opposite in the excerpts posted by Jeff:
>
> And a later message from Jim:
>
> Truncate converts a value from a larger to a smaller mode in a machine
> dependent way.
>
> A subreg just chops off the high bits. A truncate does not. The name might
> be a little confusing, but the whole point of truncate is to have something
> that operates differently than a subreg.
>
> Combine is clearly making an invalid transformation.
I'm not entirely sure, but I don't think Jim said the opposite. He said
that the way truncate works is machine dependent. I said that the
output of truncate is machine independent. Since truncate is only
defined for fixed-point modes, I think both statements are true.
Ian
next prev parent reply other threads:[~2009-06-17 14:24 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-06-16 7:12 Adam Nemet
2009-06-16 14:35 ` Ian Lance Taylor
2009-06-16 22:45 ` Adam Nemet
2009-06-17 0:28 ` Ian Lance Taylor
2009-06-17 6:42 ` Adam Nemet
2009-06-17 14:24 ` Ian Lance Taylor [this message]
2009-06-17 15:26 ` Adam Nemet
2009-06-17 15:54 ` Ian Lance Taylor
2009-06-17 2:12 ` Jeff Law
2009-06-17 6:17 ` Adam Nemet
2009-06-17 14:52 ` Jeff Law
2009-06-17 2:10 ` Jeff Law
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