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From: "rguenther at suse dot de" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/37242] missed FRE opportunity because of signedness of addition
Date: Wed, 27 Aug 2008 19:13:00 -0000 [thread overview]
Message-ID: <20080827191222.8992.qmail@sourceware.org> (raw)
In-Reply-To: <bug-37242-7849@http.gcc.gnu.org/bugzilla/>
------- Comment #9 from rguenther at suse dot de 2008-08-27 19:12 -------
Subject: Re: missed FRE opportunity because of
signedness of addition
On Wed, 27 Aug 2008, bonzini at gnu dot org wrote:
> ------- Comment #8 from bonzini at gnu dot org 2008-08-27 17:50 -------
> Subject: Re: missed FRE opportunity because
> of signedness of addition
>
> Maybe we can lookup the non-GIMPLE operands in simplify_unary_expression
> and replace them with existing SSA_NAMES if they have been value numbered.
So when we see
pretmp.36_86 = (unsigned int) maxIdx_24;
we do not even simplify it to (unsigned int)maxIdx_59 + 1.
So much for the fold theory... instead we come from
#9 0x080b75dd in pointer_int_sum (resultcode=PLUS_EXPR, ptrop=0xb7c9d57c,
intop=0xb7ca37a0) at /home/richard/src/trunk/gcc/c-common.c:3361
3361 ret = fold_build2 (POINTER_PLUS_EXPR, result_type, ptrop,
intop);
(gdb) call debug_generic_expr (ptrop)
y + 4
(gdb) call debug_generic_expr (intop)
(unsigned int) ((unsigned int) x * 4)
go through y p+ (4 + (unsigned int) ((unsigned int) x * 4)) which we
fold by fold_plusminus_mult_expr to ((unsigned int) x + 1) * 4.
I saw your patch that adds this folding. And indeed we should
be able to lookup (unsigned int) x + 1 in two steps.
I may look into this at some point.
Richard.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37242
next prev parent reply other threads:[~2008-08-27 19:13 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-08-26 11:55 [Bug tree-optimization/37242] New: missed load PRE-like opportunity bonzini at gnu dot org
2008-08-26 11:57 ` [Bug tree-optimization/37242] " bonzini at gnu dot org
2008-08-26 12:03 ` [Bug tree-optimization/37242] missed FRE opportunity bonzini at gnu dot org
2008-08-26 21:17 ` [Bug tree-optimization/37242] missed FRE opportunity because of signedness of addition pinskia at gcc dot gnu dot org
2008-08-27 6:42 ` bonzini at gnu dot org
2008-08-27 7:16 ` bonzini at gnu dot org
2008-08-27 7:16 ` bonzini at gnu dot org
2008-08-27 9:42 ` rguenther at suse dot de
2008-08-27 17:51 ` bonzini at gnu dot org
2008-08-27 19:13 ` rguenther at suse dot de [this message]
2008-08-27 19:55 ` bonzini at gnu dot org
2008-08-27 20:18 ` rguenther at suse dot de
2008-08-28 6:10 ` bonzini at gnu dot org
2008-08-28 6:18 ` bonzini at gnu dot org
2008-08-28 8:03 ` rguenther at suse dot de
2008-08-28 8:43 ` bonzini at gnu dot org
2008-08-28 8:47 ` rguenther at suse dot de
2008-08-28 8:58 ` bonzini at gnu dot org
2008-08-28 8:59 ` bonzini at gnu dot org
2008-08-29 4:39 ` pinskia at gcc dot gnu dot org
[not found] <bug-37242-4@http.gcc.gnu.org/bugzilla/>
2011-04-27 17:57 ` matt at use dot net
2011-04-28 9:53 ` rguenth at gcc dot gnu.org
2012-04-18 22:51 ` pinskia at gcc dot gnu.org
2012-06-29 0:20 ` matt at use dot net
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