C++ PATCH for c++/80095, ICE with this pointer in NSDMI

Marek Polacek polacek@redhat.com
Wed Apr 5 09:49:00 GMT 2017


Ping.

On Wed, Mar 29, 2017 at 11:32:39PM +0200, Marek Polacek wrote:
> On Wed, Mar 29, 2017 at 02:56:51PM -0400, Jason Merrill wrote:
> > On Wed, Mar 29, 2017 at 12:38 PM, Marek Polacek <polacek@redhat.com> wrote:
> > > Here we have a reference initialization with NSDMI and *this.  We are crashing
> > > because a PLACEHOLDER_EXPR crept into the gimplifier.
> > >
> > > This happens since r218653 where set_up_extended_ref_temp was changed to
> > > use split_nonconstant_init.  As a consequence, cp_gimplify_init_expr might
> > > now be receiving
> > >
> > >   D.2051.p = (void *) &<PLACEHOLDER_EXPR struct A>
> > >
> > > instead of
> > >
> > >   D.2051 = {.p = (void *) &<PLACEHOLDER_EXPR struct A>}
> > >
> > > where the RHS was a CONSTRUCTOR.  It no longer is, so replace_placeholders is
> > > not called anymore.  It occurred to me that we should use the same check as in
> > > store_init_value (i.e. check that the object to be used in the substitution is
> > > a class), but given what split_nonconstant_init might produce, handle
> > > COMPONENT_REFs specially.
> > >
> > > Bootstrapped/regtested on x86_64-linux, ok for trunk and 6?
> > >
> > > 2017-03-29  Marek Polacek  <polacek@redhat.com>
> > >
> > >         PR c++/80095 - ICE with this pointer in NSDMI.
> > >         * cp-gimplify.c (cp_gimplify_init_expr): Call replace_placeholders
> > >         when TO is a class.
> > >
> > >         * g++.dg/cpp1y/nsdmi-aggr8.C: New test.
> > >
> > > diff --git gcc/cp/cp-gimplify.c gcc/cp/cp-gimplify.c
> > > index 354ae1a..e530daf 100644
> > > --- gcc/cp/cp-gimplify.c
> > > +++ gcc/cp/cp-gimplify.c
> > > @@ -496,7 +496,16 @@ cp_gimplify_init_expr (tree *expr_p)
> > >             TREE_TYPE (from) = void_type_node;
> > >         }
> > >
> > > -      if (cxx_dialect >= cxx14 && TREE_CODE (sub) == CONSTRUCTOR)
> > > +      /* split_nonconstant_init might've produced something like
> > > +        D.2051.p = (void *) &<PLACEHOLDER_EXPR struct A>
> > > +        in which case we want to substitute the placeholder with
> > > +        D.2051.  */
> > > +      tree op0 = to;
> > > +      while (TREE_CODE (op0) == COMPONENT_REF)
> > > +       op0 = TREE_OPERAND (op0, 0);
> > > +      tree type = TREE_TYPE (op0);
> > > +
> > > +      if (cxx_dialect >= cxx14 && CLASS_TYPE_P (strip_array_types (type)))
> > 
> > How about doing this checking in replace_placeholders, instead?  That
> > is, if the object isn't a (member of a) class, just return.
> 
> Sure.  I also moved the C++14 check into replace_placeholders, although maybe
> I shouldn't have.
> 
> Bootstrapped/regtested on x86_64-linux, ok for trunk and 6?
> 
> 2017-03-29  Marek Polacek  <polacek@redhat.com>
> 
> 	PR c++/80095
> 	* call.c (build_over_call): Don't check cxx_dialect.
> 	* cp-gimplify.c (cp_gimplify_init_expr): Don't check cxx_dialect nor
> 	whether SUB is a CONSTRUCTOR.
> 	* init.c (build_new_1): Don't check cxx_dialect.
> 	* tree.c (replace_placeholders): Add a function comment.  Return if
> 	not in C++14, or if the object isn't a (member of a) class.
> 	* typeck2.c (store_init_value): Don't check cxx_dialect nor whether
> 	TYPE is CLASS_TYPE_P.
> 
> 	* g++.dg/cpp1y/nsdmi-aggr8.C: New test.
> 
> diff --git gcc/cp/call.c gcc/cp/call.c
> index 803fbd4..c15b8e4 100644
> --- gcc/cp/call.c
> +++ gcc/cp/call.c
> @@ -8047,9 +8047,8 @@ build_over_call (struct z_candidate *cand, int flags, tsubst_flags_t complain)
>  	{
>  	  arg = cp_build_indirect_ref (arg, RO_NULL, complain);
>  	  val = build2 (MODIFY_EXPR, TREE_TYPE (to), to, arg);
> -	  if (cxx_dialect >= cxx14)
> -	    /* Handle NSDMI that refer to the object being initialized.  */
> -	    replace_placeholders (arg, to);
> +	  /* Handle NSDMI that refer to the object being initialized.  */
> +	  replace_placeholders (arg, to);
>  	}
>        else
>  	{
> diff --git gcc/cp/cp-gimplify.c gcc/cp/cp-gimplify.c
> index 354ae1a..3f91c35 100644
> --- gcc/cp/cp-gimplify.c
> +++ gcc/cp/cp-gimplify.c
> @@ -496,9 +496,8 @@ cp_gimplify_init_expr (tree *expr_p)
>  	    TREE_TYPE (from) = void_type_node;
>  	}
>  
> -      if (cxx_dialect >= cxx14 && TREE_CODE (sub) == CONSTRUCTOR)
> -	/* Handle aggregate NSDMI.  */
> -	replace_placeholders (sub, to);
> +      /* Handle aggregate NSDMI.  */
> +      replace_placeholders (sub, to);
>  
>        if (t == sub)
>  	break;
> diff --git gcc/cp/init.c gcc/cp/init.c
> index 7732795..6a70955 100644
> --- gcc/cp/init.c
> +++ gcc/cp/init.c
> @@ -3373,8 +3373,7 @@ build_new_1 (vec<tree, va_gc> **placement, tree type, tree nelts,
>  	     object being initialized, replace them now and don't try to
>  	     preevaluate.  */
>  	  bool had_placeholder = false;
> -	  if (cxx_dialect >= cxx14
> -	      && !processing_template_decl
> +	  if (!processing_template_decl
>  	      && TREE_CODE (init_expr) == INIT_EXPR)
>  	    TREE_OPERAND (init_expr, 1)
>  	      = replace_placeholders (TREE_OPERAND (init_expr, 1),
> diff --git gcc/cp/tree.c gcc/cp/tree.c
> index 2757af6..9939135 100644
> --- gcc/cp/tree.c
> +++ gcc/cp/tree.c
> @@ -2813,9 +2813,23 @@ replace_placeholders_r (tree* t, int* walk_subtrees, void* data_)
>    return NULL_TREE;
>  }
>  
> +/* Replace PLACEHOLDER_EXPRs in EXP with object OBJ.  SEEN_P is set if
> +   a PLACEHOLDER_EXPR has been encountered.  */
> +
>  tree
>  replace_placeholders (tree exp, tree obj, bool *seen_p)
>  {
> +  /* This is only relevant for C++14.  */
> +  if (cxx_dialect < cxx14)
> +    return exp;
> +
> +  /* If the object isn't a (member of a) class, do nothing.  */
> +  tree op0 = obj;
> +  while (TREE_CODE (op0) == COMPONENT_REF)
> +    op0 = TREE_OPERAND (op0, 0);
> +  if (!CLASS_TYPE_P (strip_array_types (TREE_TYPE (op0))))
> +    return exp;
> +
>    tree *tp = &exp;
>    replace_placeholders_t data = { obj, false };
>    if (TREE_CODE (exp) == TARGET_EXPR)
> diff --git gcc/cp/typeck2.c gcc/cp/typeck2.c
> index 58a01c9..67fbaea 100644
> --- gcc/cp/typeck2.c
> +++ gcc/cp/typeck2.c
> @@ -836,9 +836,8 @@ store_init_value (tree decl, tree init, vec<tree, va_gc>** cleanups, int flags)
>      }
>    value = cp_fully_fold (value);
>  
> -  if (cxx_dialect >= cxx14 && CLASS_TYPE_P (strip_array_types (type)))
> -    /* Handle aggregate NSDMI in non-constant initializers, too.  */
> -    value = replace_placeholders (value, decl);
> +  /* Handle aggregate NSDMI in non-constant initializers, too.  */
> +  value = replace_placeholders (value, decl);
>  
>    /* DECL may change value; purge caches.  */
>    clear_cv_and_fold_caches ();
> diff --git gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr8.C gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr8.C
> index e69de29..8c99ffb 100644
> --- gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr8.C
> +++ gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr8.C
> @@ -0,0 +1,16 @@
> +// PR c++/80095
> +// { dg-do compile { target c++14 } }
> +
> +struct A
> +{
> +  void* p = this;
> +};
> +
> +void
> +foo ()
> +{
> +  const A& a = A{};
> +  A&& a2 = A{};
> +  const A& a3{};
> +  A&& a4{};
> +}
> 
> 	Marek

	Marek



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