[PATCH, 4.4, PR 52430] IPA-CP has to clone or leave alone externally_visible nodes

[Maxim Kuvyrkov]

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;

Thanks,

--
Maxim Kuvyrkov
CodeSourcery / Mentor Graphics