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Re: [PATCH] Fix up ICEs with TREE_CONSTANT references (PR c++/78373)
- From: Jakub Jelinek <jakub at redhat dot com>
- To: Jason Merrill <jason at redhat dot com>
- Cc: Richard Biener <rguenther at suse dot de>, gcc-patches List <gcc-patches at gcc dot gnu dot org>
- Date: Wed, 16 Nov 2016 22:55:03 +0100
- Subject: Re: [PATCH] Fix up ICEs with TREE_CONSTANT references (PR c++/78373)
- Authentication-results: sourceware.org; auth=none
- References: <20161116210027.GB3541@tucnak.redhat.com> <CADzB+2=BD1qvEJ1MCBd8H0S64OsJTVHv_ZGfR+4xBB83g7jW=A@mail.gmail.com>
- Reply-to: Jakub Jelinek <jakub at redhat dot com>
On Wed, Nov 16, 2016 at 04:26:36PM -0500, Jason Merrill wrote:
> On Wed, Nov 16, 2016 at 4:00 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> > Jason's recent patch to turn reference vars initialized with invariant
> > addresses broke the first testcase below, because &self->singleton
> > is considered TREE_CONSTANT (because self is TREE_CONSTANT VAR_DECL and
> > singleton field has constant offset), but after going into SSA form
> > it is not supposed to be TREE_CONSTANT anymore (&self_2->singleton),
> > because SSA_NAMEs don't have TREE_CONSTANT set on them.
> >
> > The following patch fixes it by gimplifying such vars into their
> > DECL_INITIAL unless in OpenMP regions, where such folding is deferred
> > until omplower pass finishes.
>
> Hmm, this seems like a workaround; why don't we see the same problem
> with constant pointer variables?
Dunno, tried to construct a testcase, but it doesn't fail. If it is e.g.
TREE_CONSTANT because of being constexpr, then the FE already replaces it
by its initializer.
> A simpler workaround would be to not set TREE_CONSTANT on references
> in the first place, since the constexpr code doesn't need it. What do
> you think?
If the FE doesn't need it, indeed it would be simpler this way.
> commit 6cdd28bb152fcb07a7eb6c9f053cd435cf719a20
> Author: Jason Merrill <jason@redhat.com>
> Date: Wed Nov 16 16:13:25 2016 -0500
>
> ref
>
> diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
> index c54a2de..87db589 100644
> --- a/gcc/cp/decl.c
> +++ b/gcc/cp/decl.c
> @@ -6839,7 +6839,8 @@ cp_finish_decl (tree decl, tree init, bool init_const_expr_p,
> /* Set these flags now for templates. We'll update the flags in
> store_init_value for instantiations. */
> DECL_INITIALIZED_BY_CONSTANT_EXPRESSION_P (decl) = 1;
> - if (decl_maybe_constant_var_p (decl))
> + if (decl_maybe_constant_var_p (decl)
> + && TREE_CODE (type) != REFERENCE_TYPE)
> TREE_CONSTANT (decl) = 1;
> }
> }
> diff --git a/gcc/cp/typeck2.c b/gcc/cp/typeck2.c
> index 022a478..dcdb710 100644
> --- a/gcc/cp/typeck2.c
> +++ b/gcc/cp/typeck2.c
> @@ -824,7 +824,8 @@ store_init_value (tree decl, tree init, vec<tree, va_gc>** cleanups, int flags)
> const_init = (reduced_constant_expression_p (value)
> || error_operand_p (value));
> DECL_INITIALIZED_BY_CONSTANT_EXPRESSION_P (decl) = const_init;
> - TREE_CONSTANT (decl) = const_init && decl_maybe_constant_var_p (decl);
> + if (TREE_CODE (type) != REFERENCE_TYPE)
> + TREE_CONSTANT (decl) = const_init && decl_maybe_constant_var_p (decl);
> }
> value = cp_fully_fold (value);
>
Jakub