From: "Joseph S. Myers" <joseph@codesourcery.com>
To: Andrew Stubbs <ams@codesourcery.com>
Cc: Bernd Schmidt <bernds@codesourcery.com>,
Richard Earnshaw <rearnsha@arm.com>,
gcc-patches@gcc.gnu.org
Subject: Re: [patch][simplify-rtx] Fix 16-bit -> 64-bit multiply and accumulate
Date: Wed, 25 May 2011 12:34:00 -0000 [thread overview]
Message-ID: <Pine.LNX.4.64.1105251013410.31877@digraph.polyomino.org.uk> (raw)
In-Reply-To: <4DDCBE2A.6020006@codesourcery.com>
On Wed, 25 May 2011, Andrew Stubbs wrote:
> So, you're saying that promoting a regular multiply to a widening multiply
> isn't a valid transformation anyway? I suppose that does make sense. I knew
In general, yes. RTL always has modulo semantics (except for division and
remainder by -1); all optimizations based on undefinedness of overflow (in
the absence of -fwrapv) happen at tree/GIMPLE level, where signed and
unsigned types are still distinct. (So you could promote a regular
multiply of signed types at GIMPLE level in the absence of
-fwrapv/-ftrapv, but not at RTL level and not for unsigned types at GIMPLE
level.)
--
Joseph S. Myers
joseph@codesourcery.com
next prev parent reply other threads:[~2011-05-25 10:16 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-12-09 16:45 [patch][ARM] " Andrew Stubbs
2011-01-27 2:09 ` Ramana Radhakrishnan
2011-01-27 10:46 ` Andrew Stubbs
2011-01-27 19:22 ` Richard Earnshaw
2011-01-28 13:06 ` Andrew Stubbs
2011-01-28 15:08 ` Richard Earnshaw
2011-01-28 15:55 ` Andrew Stubbs
2011-01-28 16:01 ` Richard Earnshaw
2011-03-25 16:27 ` Andrew Stubbs
2011-04-15 11:23 ` Andrew Stubbs
2011-05-03 9:08 ` Bernd Schmidt
2011-05-03 9:36 ` Andrew Stubbs
2011-05-18 15:32 ` [patch][combine] " Andrew Stubbs
2011-05-19 13:06 ` Bernd Schmidt
2011-05-24 17:51 ` [patch][simplify-rtx] " Andrew Stubbs
2011-05-24 21:00 ` Joseph S. Myers
2011-05-25 9:47 ` Andrew Stubbs
2011-05-25 12:34 ` Joseph S. Myers [this message]
2011-05-25 13:42 ` Andrew Stubbs
2011-05-25 13:48 ` Joseph S. Myers
2011-05-25 14:01 ` Andrew Stubbs
2011-05-25 14:27 ` Joseph S. Myers
2011-05-26 13:57 ` Andrew Stubbs
2011-05-26 14:47 ` Joseph S. Myers
2011-06-02 9:46 ` Richard Earnshaw
2011-06-07 11:05 ` Andrew Stubbs
2011-02-09 6:31 ` [patch][ARM] " Hans-Peter Nilsson
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