Re: [PATCH v2] c++: Fix crash in gimplifier with paren init of aggregates [PR94155]

[Marek Polacek <polacek@redhat.com>]

On Fri, Apr 03, 2020 at 10:39:49PM -0400, Jason Merrill via Gcc-patches wrote:
> On 4/3/20 9:08 PM, Marek Polacek wrote:
> > On Fri, Apr 03, 2020 at 03:01:37PM -0400, Jason Merrill via Gcc-patches wrote:
> > > On 3/30/20 4:28 PM, Marek Polacek wrote:
> > > > Here we crash in the gimplifier because gimplify_init_ctor_eval doesn't
> > > > expect null indexes for a constructor:
> > > > 
> > > >         /* ??? Here's to hoping the front end fills in all of the indices,
> > > >            so we don't have to figure out what's missing ourselves.  */
> > > >         gcc_assert (purpose);
> > > > 
> > > > The indexes weren't filled because we never called reshape_init: for
> > > > a constructor that represents parenthesized initialization of an
> > > > aggregate we don't allow brace elision or designated initializers.  So
> > > > fill in the indexes manually, here we have an array, and we can simply
> > > > assign indexes starting from 0.
> > > > 
> > > > Bootstrapped/regtested on x86_64-linux, ok for trunk?
> > > 
> > > Shouldn't digest_init fill in the indexes?  In
> > > process_init_constructor_array I see
> > > 
> > >        if (!ce->index)
> > >          ce->index = size_int (i);
> > 
> > Yes, that works too.  Thus:
> > 
> > Bootstrapped/regtested on x86_64-linux, ok for trunk?
> > 
> > -- >8 --
> > Here we crash in the gimplifier because gimplify_init_ctor_eval doesn't
> > expect null indexes for a constructor:
> > 
> >        /* ??? Here's to hoping the front end fills in all of the indices,
> >           so we don't have to figure out what's missing ourselves.  */
> >        gcc_assert (purpose);
> > 
> > The indexes weren't filled because we never called reshape_init: for
> > a constructor that represents parenthesized initialization of an
> > aggregate we don't allow brace elision or designated initializers.  So
> > call digest_init to fill in the indexes.
> > 
> > Bootstrapped/regtested on x86_64-linux, ok for trunk?
> > 
> > 	PR c++/94155 - crash in gimplifier with paren init of aggregates.
> > 	* decl.c (check_initializer): Call digest_init.
> > 
> > 	* g++.dg/cpp2a/paren-init22.C: New test.
> > ---
> >   gcc/cp/decl.c                             |  5 +++++
> >   gcc/testsuite/g++.dg/cpp2a/paren-init22.C | 15 +++++++++++++++
> >   2 files changed, 20 insertions(+)
> >   create mode 100644 gcc/testsuite/g++.dg/cpp2a/paren-init22.C
> > 
> > diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
> > index 69a238997b4..63e7bda09f5 100644
> > --- a/gcc/cp/decl.c
> > +++ b/gcc/cp/decl.c
> > @@ -6754,6 +6754,11 @@ check_initializer (tree decl, tree init, int flags, vec<tree, va_gc> **cleanups)
> >   	      init = build_constructor_from_list (init_list_type_node, init);
> >   	      CONSTRUCTOR_IS_DIRECT_INIT (init) = true;
> >   	      CONSTRUCTOR_IS_PAREN_INIT (init) = true;
> > +	      /* The gimplifier expects that the front end fills in all of the
> > +		 indices.  Normally, reshape_init_array fills these in, but we
> > +		 don't call reshape_init because that does nothing when it gets
> > +		 CONSTRUCTOR_IS_PAREN_INIT.  */
> > +	      init = digest_init (type, init, tf_warning_or_error);
> 
> But why weren't we already calling digest_init in store_init_value?  Was the
> CONSTRUCTOR making it all the way to gimplification still having
> init_list_type_node?

It's because we set LOOKUP_ALREADY_DIGESTED a few lines below:
 6813               /* Don't call digest_init; it's unnecessary and will complain
 6814                  about aggregate initialization of non-aggregate classes.  */
 6815               flags |= LOOKUP_ALREADY_DIGESTED;
and so store_init_value doesn't digest.  Given the comment I'd be nervous about
not setting that flag here.

Marek