From: Bernd Schmidt <bernds@codesourcery.com>
To: Jakub Jelinek <jakub@redhat.com>
Cc: Eric Botcazou <ebotcazou@adacore.com>,
Richard Sandiford <richard.sandiford@linaro.org>,
Richard Henderson <rth@redhat.com>,
GCC Patches <gcc-patches@gcc.gnu.org>
Subject: Re: Add __builtin_clrsb, similar to clz/ctz
Date: Tue, 23 Aug 2011 10:08:00 -0000 [thread overview]
Message-ID: <4E53744B.6040502@codesourcery.com> (raw)
In-Reply-To: <20110823090549.GC2687@tyan-ft48-01.lab.bos.redhat.com>
On 08/23/11 11:05, Jakub Jelinek wrote:
> On Mon, Jun 20, 2011 at 09:38:22PM +0200, Bernd Schmidt wrote:
>> D'oh. Blackfin has a (clrsb:HI (operand:SI)) instruction, so adding this
>> showed a problem with some of the existing simplify_const_unop cases:
>> for ffs/clz/ctz/clrsb/parity/popcount, we should look at the mode of the
>> operand, rather than the mode of the operation. This limits what we can
>> do in that function, since op_mode is sometimes VOIDmode - we really
>> should add builtin folders for these at some point.
>
>> * simplify-rtx.c (simplify_const_unary_operation): Likewise.
>> Use op_mode rather than mode when optimizing ffs, clz, ctz, parity
>> and popcount.
>
> This change is IMHO wrong,
Conceptually, I think it is exactly right. It may however be
inconvenient in some cases.
> see e.g.
> PR50161 where we have (subreg:SI (popcount:DI (const_int -1))). This
> is supposed to yield 64, but with your changes
> it yields 128 - the op_mode here is VOIDmode,
This is what shouldn't happen.
> cse_process_notes_1
> perhaps could be changed for VOIDmode new_rtx to try to
> simplify_replace_rtx it...
Is this where the problem came from? Sounds like it's worth a try.
Wasn't Richard S. working on a patch to give constants modes?
Bernd
next prev parent reply other threads:[~2011-08-23 9:37 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-06-16 13:06 Bernd Schmidt
2011-06-16 13:10 ` Georg-Johann Lay
2011-06-16 13:56 ` Laurent Desnogues
2011-06-16 13:59 ` Bernd Schmidt
2011-06-16 17:03 ` Richard Henderson
2011-06-20 20:32 ` Bernd Schmidt
2011-06-20 20:48 ` Richard Henderson
2011-06-21 16:39 ` [PATCH] Fix __bultin_clrsb* (PR middle-end/49489) Jakub Jelinek
2011-06-21 16:46 ` Bernd Schmidt
2011-06-23 6:23 ` Add __builtin_clrsb, similar to clz/ctz H.J. Lu
2011-07-12 3:50 ` Hans-Peter Nilsson
2011-08-23 10:07 ` Jakub Jelinek
2011-08-23 10:08 ` Bernd Schmidt [this message]
2011-08-23 10:19 ` Richard Guenther
2011-08-23 10:25 ` Jakub Jelinek
2011-08-23 10:34 ` Bernd Schmidt
2011-08-23 13:43 ` [PATCH] For FFS/CLZ/CTZ/CLRSB/POPCOUNT/PARITY/BSWAP require operand mode equal to operation mode (or VOIDmode) (PR middle-end/50161) Jakub Jelinek
2011-08-23 14:54 ` Georg-Johann Lay
2011-08-23 15:58 ` Jakub Jelinek
2011-08-23 16:16 ` Bernd Schmidt
2011-08-23 10:45 ` Add __builtin_clrsb, similar to clz/ctz Richard Sandiford
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