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Re: [PATCH, 4.4, PR 52430] IPA-CP has to clone or leave alone externally_visible nodes
Hi,
On Fri, Mar 02, 2012 at 06:54:13PM +1300, Maxim Kuvyrkov wrote:
> On 2/03/2012, at 1:53 AM, Martin Jambor wrote:
>
> > Hi,
> >
> > the following patch backports 4.5 behavior to 4.4 IPA-CP
> > initialization when it decides which nodes need to be duplicated (we
> > often say cloned, but cloning is an overloaded term in gcc) in order
> > to modify them. In 4.5, this is decided by a new predicate called
> > cgraph_only_called_directly_p which checks both node->needed and
> > node->local.externally_visible, whereas 4.4 looks only at the needed
> > flag.
> >
> > As described in the PR, this wrecks havoc for ipcp_update_callgraph
> > which is the stage of the old IPA-CP when it undoes its decisions
> > which turned out not to be safe.
> >
> > Bootstrapped and tested on x86_64-linux, OK for the branch?
> >
> >
> ...
> > Index: gcc/ipa-cp.c
> > ===================================================================
> > --- gcc/ipa-cp.c (revision 184662)
> > +++ gcc/ipa-cp.c (working copy)
> > @@ -508,7 +508,7 @@ ipcp_initialize_node_lattices (struct cg
> >
> > if (ipa_is_called_with_var_arguments (info))
> > type = IPA_BOTTOM;
> > - else if (!node->needed)
> > + else if (!node->needed && !node->local.externally_visible)
> > type = IPA_TOP;
> > /* When cloning is allowed, we can assume that externally visible functions
> > are not called. We will compensate this by cloning later. */
>
> Because this is for a branch, I would be more conservative and avoid any new instances of IPA_TOP -- those that can be obtained from subsequent else-if clauses. I.e.,
>
> else if (!node->needed)
> type = !node->local.externally_visible ? IPA_TOP : IPA_BOTTOM;
>
That would be too conservative because it would mean we would never
duplicate a node and thus never propagate constants into externally
visible functions, even not at -O3 and we do want to keep doing that.
I have committed my patch after it has been approved on IRC by Richi
and Jakub.
Thanks,
Martin