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çå: [4.8 & 4.9] Backport of r211885


> > > > 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. 



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