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Re: çå: [4.8 & 4.9] Backport of r211885
- From: Richard Biener <richard dot guenther at gmail dot com>
- To: "Yangfei (Felix)" <felix dot yang at huawei dot com>
- Cc: Jakub Jelinek <jakub at redhat dot com>, GCC Patches <gcc-patches at gcc dot gnu dot org>, Felix Yang <fei dot yang0953 at gmail dot com>
- Date: Thu, 9 Oct 2014 12:41:15 +0200
- Subject: Re: çå: [4.8 & 4.9] Backport of r211885
- Authentication-results: sourceware.org; auth=none
- References: <CAFc0fxzW0jCw_d1n6fYmmEe+K6SfVn9eekD_M84rtHEpPQAttA at mail dot gmail dot com> <20141009085353 dot GJ1986 at tucnak dot redhat dot com> <DA41BE1DDCA941489001C7FBD7A8820E55547E3A at szxema507-mbx dot china dot huawei dot com> <20141009090729 dot GK1986 at tucnak dot redhat dot com> <DA41BE1DDCA941489001C7FBD7A8820E55547E89 at szxema507-mbx dot china dot huawei dot com>
On Thu, Oct 9, 2014 at 11:35 AM, Yangfei (Felix) <felix.yang@huawei.com> wrote:
>
>> > > > On Thu, Oct 09, 2014 at 09:04:49AM +0000, Yangfei (Felix) wrote:
>> > > > > On Wed, Oct 08, 2014 at 11:00:24PM +0800, Felix Yang wrote:
>> > > > > The enclosed patch for 4.8 & 4.9 branch is a backport of r211885
>> > > > > from
>> > trunk.
>> > > > >
>> > > > > The only change is to use:
>> > > > >
>> > > > > for (def_rec = DF_INSN_INFO_DEFS (insn_info); *def_rec;
>> > > > > def_rec++)
>> > > > >
>> > > > > other than the new FOR_EACH_INSN_INFO_DEF interface.
>> > > > >
>> > > > > Bootstrapped on x86_64-SUSE-Linux for both branches. OK to apply?
>> > > >
>> > > > ChangeLog entry is missing, plus description why do you want to
>> > > > backport
>> > it.
>> > > > If it fixes a bug on the branches, it would be better to have a
>> > > > bugzilla PR for that, and definitely a testcase.
>> > > >
>> > >
>> > > Yeah, I will add a ChangeLog entry for this patch when it is committed.
>> > > I encountered the same issue when working on my local customized
>> > > 4.8/4.9
>> > branches. Not reproduceable with the official 4.8/4.9 branches.
>> > > I thinks it's just an enhancement for the loop invariant pass to
>> > > make it more
>> > versatile. It's better that 4.8/4.9 branches also inlcude this enhancement.
>> > > OK?
>> >
>> > If it is just an enhancement, then those generally are not backported
>> > to release branches (exceptions possible of course, but there needs to be a
>> strong reason).
>> > Each pass has some risk of breaking something, exposing previously
>> > only latent bugs in later passes etc.
>> >
>> > Jakub
>>
>> We can treat it as bugfix, as we got incorrect code when it triggers.
>> It just happens so rarely. Does it worth backporting?
>
> And the patch fix this bug by making the loop invariant pass more conservative.
> I didn't find a PR or testcase on trunk for this patch either.
We at least want a testcase for the "we got incorrect code when it triggers".
Richard.
>