[PATCH] c++: suppress all warnings on memper pointers to work around dICE [PR101219]

[Sergei Trofimovich]

On Fri, 23 Jul 2021 10:33:09 -0600
Jeff Law <jeffreyalaw@gmail.com> wrote:

> On 7/22/2021 5:15 PM, Sergei Trofimovich via Gcc-patches wrote:
> > From: Sergei Trofimovich <siarheit@google.com>
> >
> > r12-1804 ("cp: add support for per-location warning groups.") among other
> > things removed warning suppression from a few places including ptrmemfuncs.
> >
> > Currently ptrmemfuncs don't have valid BINFO attached which causes ICEs
> > in access checks:
> >
> >      crash_signal
> >          gcc/toplev.c:328
> >      perform_or_defer_access_check(tree_node*, tree_node*, tree_node*, int, access_failure_info*)
> >          gcc/cp/semantics.c:490
> >      finish_non_static_data_member(tree_node*, tree_node*, tree_node*)
> >          gcc/cp/semantics.c:2208
> >      ...
> >
> > The change suppresses warnings again until we provide BINFOs for ptrmemfuncs.
> >
> > 	PR c++/101219
> >
> > gcc/cp/ChangeLog:
> >
> > 	* typeck.c (build_ptrmemfunc_access_expr): Suppress all warnings
> > 	to avoid ICE.
> >
> > gcc/testsuite/ChangeLog:
> >
> > 	* g++.dg/torture/pr101219.C: New test.  
> The C++ maintainers have the final say here, but ISTM that warning 
> suppression shouldn't be used to avoid an ICE, even an ICE within the 
> warning or diagnostic code itself.

Sounds good. I agree fixing it correctly is preferable and should improve
diagnostic on this very test case compared to gcc-11.

I'll need some help plumbing TYPE_BINFO() around build_ptrmemfunc_type().
My attempts to use `xref_basetypes (t, NULL_TREE);` to derive it for a
fresh expression only shuffles ICEs around.

-- 

  Sergei