Re: [PATCH, PR 55264] Do not remove as unreachable any virtual methods before inlining

[Richard Biener <richard.guenther@gmail.com>]

On Wed, Jan 16, 2013 at 11:01 AM, Martin Jambor <mjambor@suse.cz> wrote:
> Hi,
>
> PR 55264 is caused by cgraph machinery thinking it knows all calls to
> a virtual method when that is actually not true.  As discussed with
> Honza, prior to inlining, we should not assume some virtual functions
> (namely those that are neither DECL_COMDAT nor DECL_EXTERNAL) are not
> reachable.

Are they not reachable from the VTABLE which is referenced from all
calls that eventually reach the virtual method?  Thus, isn't the issue that
the VTABLE is not correctly handled by ipa-references code?

> DECL_EXTERNAL however still affects the cgraph_node->local.local flag
> and so in order to avoid some LTO failures, I had to adjust IPA-CP to
> consider such virtual functions non-local so that verification of
> lattice propagation does not complain.  I'm a bit puzzled by the value
> of the flag in this situation but at least it does not seem to cause
> any other problems.
>
> Below is a trunk patch to do all this.  It does not apply to released
> versions which also suffer from the same problem so I'll prepare a
> special version(s) for them once this gets approved.  Bootstrapped and
> tested on x86_64-linux.  OK for trunk?
>
> Thanks,
>
> Martin
>
>
> 2013-01-15  Martin Jambor  <mjambor@suse.cz>
>
>         PR tree-optimizations/55264
>         * ipa-inline-transform.c (can_remove_node_now_p_1): Never return true
>         for virtual methods.
>         * ipa.c (symtab_remove_unreachable_nodes): Never return true for
>         virtual methods before inlining is over.
>         * ipa-cp.c (initialize_node_lattices): Also consider all virtual
>         methods non-local.
>
> testsuite/
>         * g++.dg/ipa/pr55264.C: New test.
>
> Index: src/gcc/ipa-inline-transform.c
> ===================================================================
> --- src.orig/gcc/ipa-inline-transform.c
> +++ src/gcc/ipa-inline-transform.c
> @@ -92,9 +92,7 @@ can_remove_node_now_p_1 (struct cgraph_n
>              those only after all devirtualizable virtual calls are processed.
>              Lacking may edges in callgraph we just preserve them post
>              inlining.  */
> -         && (!DECL_VIRTUAL_P (node->symbol.decl)
> -             || (!DECL_COMDAT (node->symbol.decl)
> -                 && !DECL_EXTERNAL (node->symbol.decl)))
> +         && !DECL_VIRTUAL_P (node->symbol.decl)
>           /* During early inlining some unanalyzed cgraph nodes might be in the
>              callgraph and they might reffer the function in question.  */
>           && !cgraph_new_nodes);
> Index: src/gcc/ipa.c
> ===================================================================
> --- src.orig/gcc/ipa.c
> +++ src/gcc/ipa.c
> @@ -241,8 +241,7 @@ symtab_remove_unreachable_nodes (bool be
>         && (!cgraph_can_remove_if_no_direct_calls_and_refs_p (node)
>             /* Keep around virtual functions for possible devirtualization.  */
>             || (before_inlining_p
> -               && DECL_VIRTUAL_P (node->symbol.decl)
> -               && (DECL_COMDAT (node->symbol.decl) || DECL_EXTERNAL (node->symbol.decl)))))
> +               && DECL_VIRTUAL_P (node->symbol.decl))))
>        {
>          gcc_assert (!node->global.inlined_to);
>         pointer_set_insert (reachable, node);
> Index: src/gcc/testsuite/g++.dg/ipa/pr55264.C
> ===================================================================
> --- /dev/null
> +++ src/gcc/testsuite/g++.dg/ipa/pr55264.C
> @@ -0,0 +1,17 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fno-early-inlining -fno-weak"  } */
> +
> +struct S
> +{
> +  S();
> +  virtual inline void foo ()
> +  {
> +    foo();
> +  }
> +};
> +
> +void
> +B ()
> +{
> +  S().foo ();
> +}
> Index: src/gcc/ipa-cp.c
> ===================================================================
> --- src.orig/gcc/ipa-cp.c
> +++ src/gcc/ipa-cp.c
> @@ -699,7 +699,8 @@ initialize_node_lattices (struct cgraph_
>    int i;
>
>    gcc_checking_assert (cgraph_function_with_gimple_body_p (node));
> -  if (!node->local.local)
> +  if (!node->local.local
> +      || DECL_VIRTUAL_P (node->symbol.decl))
>      {
>        /* When cloning is allowed, we can assume that externally visible
>          functions are not called.  We will compensate this by cloning