Re: [PATCH] Check DECL_CONTEXT of new/delete operators.

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

On Mon, Mar 30, 2020 at 10:41 AM Martin Liška <mliska@suse.cz> wrote:
>
> Hi.
>
> The patch ensures that a deleted new/delete pair has a same context.
> That will fix the issue presented in the PR.
>
> Patch can bootstrap on x86_64-linux-gnu and survives regression tests.

I think this will break the DCE with LTO since we strip quite some
DECL_CONTEXT in free-lang-data.

Honza - do you remember why we strip DECL_CONTEXT for methods
which will most likely keep their containing record types live through
their this
arguments?  Quoting:

  /* We need to keep field decls associated with their trees. Otherwise tree
     merging may merge some fileds and keep others disjoint wich in turn will
     not do well with TREE_CHAIN pointers linking them.

     Also do not drop containing types for virtual methods and tables because
     these are needed by devirtualization.
     C++ destructors are special because C++ frontends sometimes produces
     virtual destructor as an alias of non-virtual destructor.  In
     devirutalization code we always walk through aliases and we need
     context to be preserved too.  See PR89335  */
  if (TREE_CODE (decl) != FIELD_DECL
      && ((TREE_CODE (decl) != VAR_DECL && TREE_CODE (decl) != FUNCTION_DECL)
          || (!DECL_VIRTUAL_P (decl)
              && (TREE_CODE (decl) != FUNCTION_DECL
                  || !DECL_CXX_DESTRUCTOR_P (decl)))))
    DECL_CONTEXT (decl) = fld_decl_context (DECL_CONTEXT (decl));

and fld_decl_context stripping up to the next non-TYPE context (unless VLA).

Richard.

> Ready to be installed?
> Thanks,
> Martin
>
> gcc/ChangeLog:
>
> 2020-03-30  Martin Liska  <mliska@suse.cz>
>
>         PR c++/94314
>         * tree-ssa-dce.c (propagate_necessity): Verify that
>         DECL_CONTEXT of a new/delete operators do match.
>
> gcc/testsuite/ChangeLog:
>
> 2020-03-30  Martin Liska  <mliska@suse.cz>
>
>         PR c++/94314
>         * g++.dg/pr94314.C: New test.
> ---
>   gcc/testsuite/g++.dg/pr94314.C | 84 ++++++++++++++++++++++++++++++++++
>   gcc/tree-ssa-dce.c             | 31 +++++++++----
>   2 files changed, 105 insertions(+), 10 deletions(-)
>   create mode 100644 gcc/testsuite/g++.dg/pr94314.C
>
>