Re: [PATCH v3] c++: Fix crash in gimplifier with paren init of aggregates [PR94155]

[Marek Polacek <polacek@redhat.com>]

On Mon, Apr 06, 2020 at 10:47:49AM -0400, Jason Merrill via Gcc-patches wrote:
> On 4/4/20 1:56 PM, Marek Polacek wrote:
> > 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.
> 
> OK, then why isn't it called by build_aggr_init?  How is the CONSTRUCTOR
> getting a type without this being fixed up?
> 
> ...
> 
> Ah, because build_vec_init builds up a new CONSTRUCTOR and gives it a type
> without setting the indexes like process_init_constructor_array does:
> 
> Jason

> diff --git a/gcc/cp/init.c b/gcc/cp/init.c
> index 27623cf4db1..ea95a3bc910 100644
> --- a/gcc/cp/init.c
> +++ b/gcc/cp/init.c
> @@ -4438,6 +4438,8 @@ build_vec_init (tree base, tree maxindex, tree init,
>  	    errors = true;
>  	  if (try_const)
>  	    {
> +	      if (!field)
> +		field = size_int (idx);
>  	      tree e = maybe_constant_init (one_init);
>  	      if (reduced_constant_expression_p (e))
>  		{

That works, thanks for figuring that out.

Bootstrapped/regtested on x86_64-pc-linux-gnu, 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.

	PR c++/94155 - crash in gimplifier with paren init of aggregates.
	* init.c (build_vec_init): Fill in indexes.

	* g++.dg/cpp2a/paren-init22.C: New test.
---
 gcc/cp/init.c                             |  2 ++
 gcc/testsuite/g++.dg/cpp2a/paren-init22.C | 15 +++++++++++++++
 2 files changed, 17 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/paren-init22.C

diff --git a/gcc/cp/init.c b/gcc/cp/init.c
index 27623cf4db1..ea95a3bc910 100644
--- a/gcc/cp/init.c
+++ b/gcc/cp/init.c
@@ -4438,6 +4438,8 @@ build_vec_init (tree base, tree maxindex, tree init,
 	    errors = true;
 	  if (try_const)
 	    {
+	      if (!field)
+		field = size_int (idx);
 	      tree e = maybe_constant_init (one_init);
 	      if (reduced_constant_expression_p (e))
 		{
diff --git a/gcc/testsuite/g++.dg/cpp2a/paren-init22.C b/gcc/testsuite/g++.dg/cpp2a/paren-init22.C
new file mode 100644
index 00000000000..1b2959e7731
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/paren-init22.C
@@ -0,0 +1,15 @@
+// PR c++/94155 - crash in gimplifier with paren init of aggregates.
+// { dg-do compile { target c++2a } }
+
+struct S { int i, j; };
+
+struct A {
+  S s;
+  constexpr A(S e) : s(e) {}
+};
+
+void
+f()
+{
+  A g[1]({{1, 1}});
+}

base-commit: c72a1b6f8b26de37d1a922a8af143af009747498
-- 
Marek Polacek • Red Hat, Inc. • 300 A St, Boston, MA