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

[Jason Merrill <jason@redhat.com>]

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);

> 	PR c++/94155 - crash in gimplifier with paren init of aggregates.
> 	* decl.c (check_initializer): Fill in constructor indexes.
> 
> 	* g++.dg/cpp2a/paren-init22.C: New test.
> ---
>   gcc/cp/decl.c                             |  6 ++++++
>   gcc/testsuite/g++.dg/cpp2a/paren-init22.C | 15 +++++++++++++++
>   2 files changed, 21 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..80dd2d8b931 100644
> --- a/gcc/cp/decl.c
> +++ b/gcc/cp/decl.c
> @@ -6754,6 +6754,12 @@ 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.  */
> +	      for (unsigned int i = 0; i < CONSTRUCTOR_NELTS (init); i++)
> +		CONSTRUCTOR_ELT (init, i)->index = size_int (i);
>   	    }
>   	}
>         else if (TREE_CODE (init) == TREE_LIST
> 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: 48e331d63827a0500670d685c0fe7d609e0a807a
>