From: Jeff Law <law@redhat.com>
To: Richard Guenther <richard.guenther@gmail.com>
Cc: Jiangning Liu <jiangning.liu@arm.com>, gcc@gcc.gnu.org
Subject: Re: A case that PRE optimization hurts performance
Date: Tue, 27 Sep 2011 18:59:00 -0000 [thread overview]
Message-ID: <4E81E406.4090305@redhat.com> (raw)
In-Reply-To: <CAFiYyc3_iMCX37w0nFmUBHx1n9Gp-DztdM24jGTxPbZ-c6ff8g@mail.gmail.com>
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On 09/27/11 01:30, Richard Guenther wrote:
>
>> It knows something about prephitmp.6_1 and thus could simplify
>> D.2734_9 = prephitmp_6.1 & D.2732_7; to D.2734_9 = D.2732_7; But
>> admittedly I have no idea if DOM tries to simplify things other
>> than comparisons within the jump threading machinery ... (the
>> above block basically ends in if (D.2729_6 != 0 &&
>> prephitmp_6.1), so I'd guess it's worth to simplify the (complex)
>> conditional expression).
Jump threading will enter simplified expressions into the hash tables
for every statement in the block in an effort to utilize any
information available to determine the result of the comparison.
However, those simplifications aren't ever reflected back into the IL.
The thing to remember is jump threading is tasked detecting cases
where the control statement has a predetermined destination utilizing
path sensitive information. Expanding it to do general path
sensitive optimizations is possible, but at even greater cost.
jeff
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next prev parent reply other threads:[~2011-09-27 14:56 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <4e3762ed.030d440a.1143.2af2SMTPIN_ADDED@mx.google.com>
2011-08-02 9:23 ` Richard Guenther
2011-09-16 2:01 ` Jiangning Liu
[not found] ` <4e72add8.c9d0e30a.142a.ffffe60eSMTPIN_ADDED@mx.google.com>
2011-09-23 20:25 ` Richard Guenther
2011-09-26 8:34 ` Jiangning Liu
[not found] ` <4e802c3d.94ebd80a.4b1f.ffff8101SMTPIN_ADDED@mx.google.com>
2011-09-26 14:33 ` Richard Guenther
2011-09-27 7:30 ` Jeff Law
2011-09-27 11:15 ` Jiangning Liu
2011-09-27 13:44 ` Richard Guenther
2011-09-27 18:59 ` Jeff Law [this message]
2011-09-27 18:59 ` Richard Guenther
2011-09-27 21:56 ` Jeff Law
2011-08-02 2:37 Jiangning Liu
2011-08-15 8:40 ` Václav Zeman
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