[PATCH] c++: Fix up CONSTRUCTOR_PLACEHOLDER_BOUNDARY handling [PR105256]

[PATCH] c++: Fix up CONSTRUCTOR_PLACEHOLDER_BOUNDARY handling [PR105256]

[Jakub Jelinek]

Hi!

The CONSTRUCTOR_PLACEHOLDER_BOUNDARY bit is supposed to separate
PLACEHOLDER_EXPRs that should be replaced by one object or subobjects of it
(variable, TARGET_EXPR slot, ...) from other PLACEHOLDER_EXPRs that should
be replaced by different objects or subobjects.
The bit is set when finding PLACEHOLDER_EXPRs inside of a CONSTRUCTOR, not
looking into nested CONSTRUCTOR_PLACEHOLDER_BOUNDARY ctors, and we prevent
elision of TARGET_EXPRs (through TARGET_EXPR_NO_ELIDE) whose initializer
is a CONSTRUCTOR_PLACEHOLDER_BOUNDARY ctor.  The following testcase ICEs
though, we don't replace the placeholders in there at all, because
CONSTRUCTOR_PLACEHOLDER_BOUNDARY isn't set on the TARGET_EXPR_INITIAL
ctor, but on a ctor nested in such a ctor.  replace_placeholders should be
run on the whole TARGET_EXPR slot.

So, the following patch fixes it by moving the CONSTRUCTOR_PLACEHOLDER_BOUNDARY
bit from nested CONSTRUCTORs to the CONSTRUCTOR containing those (but only
if it is closely nested, if there is some other tree sandwiched in between,
it doesn't do it).

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2022-04-15  Jakub Jelinek  <jakub@redhat.com>

	PR c++/105256
	* typeck2.cc (process_init_constructor_array,
	process_init_constructor_record, process_init_constructor_union): Move
	CONSTRUCTOR_PLACEHOLDER_BOUNDARY flag from CONSTRUCTOR elements to the
	containing CONSTRUCTOR.

	* g++.dg/cpp0x/pr105256.C: New test.

--- gcc/cp/typeck2.cc.jj	2022-04-07 09:09:54.432995137 +0200
+++ gcc/cp/typeck2.cc	2022-04-14 16:02:12.438432494 +0200
@@ -1515,6 +1515,14 @@ process_init_constructor_array (tree typ
 	      strip_array_types (TREE_TYPE (ce->value)))));
 
       picflags |= picflag_from_initializer (ce->value);
+      /* Propagate CONSTRUCTOR_PLACEHOLDER_BOUNDARY to outer
+	 CONSTRUCTOR.  */
+      if (TREE_CODE (ce->value) == CONSTRUCTOR
+	  && CONSTRUCTOR_PLACEHOLDER_BOUNDARY (ce->value))
+	{
+	  CONSTRUCTOR_PLACEHOLDER_BOUNDARY (init) = 1;
+	  CONSTRUCTOR_PLACEHOLDER_BOUNDARY (ce->value) = 0;
+	}
     }
 
   /* No more initializers. If the array is unbounded, we are done. Otherwise,
@@ -1560,6 +1568,14 @@ process_init_constructor_array (tree typ
 	      }
 
 	    picflags |= picflag_from_initializer (next);
+	    /* Propagate CONSTRUCTOR_PLACEHOLDER_BOUNDARY to outer
+	       CONSTRUCTOR.  */
+	    if (TREE_CODE (next) == CONSTRUCTOR
+		&& CONSTRUCTOR_PLACEHOLDER_BOUNDARY (next))
+	      {
+		CONSTRUCTOR_PLACEHOLDER_BOUNDARY (init) = 1;
+		CONSTRUCTOR_PLACEHOLDER_BOUNDARY (next) = 0;
+	      }
 	    if (len > i+1)
 	      {
 		tree range = build2 (RANGE_EXPR, size_type_node,
@@ -1754,6 +1770,13 @@ process_init_constructor_record (tree ty
       if (fldtype != TREE_TYPE (field))
 	next = cp_convert_and_check (TREE_TYPE (field), next, complain);
       picflags |= picflag_from_initializer (next);
+      /* Propagate CONSTRUCTOR_PLACEHOLDER_BOUNDARY to outer CONSTRUCTOR.  */
+      if (TREE_CODE (next) == CONSTRUCTOR
+	  && CONSTRUCTOR_PLACEHOLDER_BOUNDARY (next))
+	{
+	  CONSTRUCTOR_PLACEHOLDER_BOUNDARY (init) = 1;
+	  CONSTRUCTOR_PLACEHOLDER_BOUNDARY (next) = 0;
+	}
       CONSTRUCTOR_APPEND_ELT (v, field, next);
     }
 
@@ -1894,6 +1917,14 @@ process_init_constructor_union (tree typ
     ce->value = massage_init_elt (TREE_TYPE (ce->index), ce->value, nested,
 				  flags, complain);
 
+  /* Propagate CONSTRUCTOR_PLACEHOLDER_BOUNDARY to outer CONSTRUCTOR.  */
+  if (ce->value
+      && TREE_CODE (ce->value) == CONSTRUCTOR
+      && CONSTRUCTOR_PLACEHOLDER_BOUNDARY (ce->value))
+    {
+      CONSTRUCTOR_PLACEHOLDER_BOUNDARY (init) = 1;
+      CONSTRUCTOR_PLACEHOLDER_BOUNDARY (ce->value) = 0;
+    }
   return picflag_from_initializer (ce->value);
 }
 
--- gcc/testsuite/g++.dg/cpp0x/pr105256.C.jj	2022-04-14 16:04:30.518518875 +0200
+++ gcc/testsuite/g++.dg/cpp0x/pr105256.C	2022-04-14 16:03:53.264035175 +0200
@@ -0,0 +1,18 @@
+// PR c++/105256
+// { dg-do compile { target c++11 } }
+
+int bar (int &);
+
+struct S {
+  struct T {
+    struct U {
+      int i = bar (i);
+    } u;
+  };
+};
+
+void
+foo (S::T *p)
+{
+  *p = {};
+};

	Jakub

Re: [PATCH] c++: Fix up CONSTRUCTOR_PLACEHOLDER_BOUNDARY handling [PR105256]

[Jason Merrill]

On 4/15/22 07:22, Jakub Jelinek wrote:
> Hi!
> 
> The CONSTRUCTOR_PLACEHOLDER_BOUNDARY bit is supposed to separate
> PLACEHOLDER_EXPRs that should be replaced by one object or subobjects of it
> (variable, TARGET_EXPR slot, ...) from other PLACEHOLDER_EXPRs that should
> be replaced by different objects or subobjects.
> The bit is set when finding PLACEHOLDER_EXPRs inside of a CONSTRUCTOR, not
> looking into nested CONSTRUCTOR_PLACEHOLDER_BOUNDARY ctors, and we prevent
> elision of TARGET_EXPRs (through TARGET_EXPR_NO_ELIDE) whose initializer
> is a CONSTRUCTOR_PLACEHOLDER_BOUNDARY ctor.  The following testcase ICEs
> though, we don't replace the placeholders in there at all, because
> CONSTRUCTOR_PLACEHOLDER_BOUNDARY isn't set on the TARGET_EXPR_INITIAL
> ctor, but on a ctor nested in such a ctor.  replace_placeholders should be
> run on the whole TARGET_EXPR slot.
> 
> So, the following patch fixes it by moving the CONSTRUCTOR_PLACEHOLDER_BOUNDARY
> bit from nested CONSTRUCTORs to the CONSTRUCTOR containing those (but only
> if it is closely nested, if there is some other tree sandwiched in between,
> it doesn't do it).

Hmm, Patrick made a similar change and then reverted it for PR90996. 
But it makes sense to me; when we replace placeholders, it's appropriate 
to look at the whole aggregate initialization rather than the innermost 
CONSTRUCTOR that has DMIs.  Patrick, was there a reason that change 
seemed wrong to you, or was it just unnecessary for the bug you were 
working on?

> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
> 
> 2022-04-15  Jakub Jelinek  <jakub@redhat.com>
> 
> 	PR c++/105256
> 	* typeck2.cc (process_init_constructor_array,
> 	process_init_constructor_record, process_init_constructor_union): Move
> 	CONSTRUCTOR_PLACEHOLDER_BOUNDARY flag from CONSTRUCTOR elements to the
> 	containing CONSTRUCTOR.
> 
> 	* g++.dg/cpp0x/pr105256.C: New test.
> 
> --- gcc/cp/typeck2.cc.jj	2022-04-07 09:09:54.432995137 +0200
> +++ gcc/cp/typeck2.cc	2022-04-14 16:02:12.438432494 +0200
> @@ -1515,6 +1515,14 @@ process_init_constructor_array (tree typ
>   	      strip_array_types (TREE_TYPE (ce->value)))));
>   
>         picflags |= picflag_from_initializer (ce->value);
> +      /* Propagate CONSTRUCTOR_PLACEHOLDER_BOUNDARY to outer
> +	 CONSTRUCTOR.  */
> +      if (TREE_CODE (ce->value) == CONSTRUCTOR
> +	  && CONSTRUCTOR_PLACEHOLDER_BOUNDARY (ce->value))
> +	{
> +	  CONSTRUCTOR_PLACEHOLDER_BOUNDARY (init) = 1;
> +	  CONSTRUCTOR_PLACEHOLDER_BOUNDARY (ce->value) = 0;
> +	}
>       }
>   
>     /* No more initializers. If the array is unbounded, we are done. Otherwise,
> @@ -1560,6 +1568,14 @@ process_init_constructor_array (tree typ
>   	      }
>   
>   	    picflags |= picflag_from_initializer (next);
> +	    /* Propagate CONSTRUCTOR_PLACEHOLDER_BOUNDARY to outer
> +	       CONSTRUCTOR.  */
> +	    if (TREE_CODE (next) == CONSTRUCTOR
> +		&& CONSTRUCTOR_PLACEHOLDER_BOUNDARY (next))
> +	      {
> +		CONSTRUCTOR_PLACEHOLDER_BOUNDARY (init) = 1;
> +		CONSTRUCTOR_PLACEHOLDER_BOUNDARY (next) = 0;
> +	      }
>   	    if (len > i+1)
>   	      {
>   		tree range = build2 (RANGE_EXPR, size_type_node,
> @@ -1754,6 +1770,13 @@ process_init_constructor_record (tree ty
>         if (fldtype != TREE_TYPE (field))
>   	next = cp_convert_and_check (TREE_TYPE (field), next, complain);
>         picflags |= picflag_from_initializer (next);
> +      /* Propagate CONSTRUCTOR_PLACEHOLDER_BOUNDARY to outer CONSTRUCTOR.  */
> +      if (TREE_CODE (next) == CONSTRUCTOR
> +	  && CONSTRUCTOR_PLACEHOLDER_BOUNDARY (next))
> +	{
> +	  CONSTRUCTOR_PLACEHOLDER_BOUNDARY (init) = 1;
> +	  CONSTRUCTOR_PLACEHOLDER_BOUNDARY (next) = 0;
> +	}
>         CONSTRUCTOR_APPEND_ELT (v, field, next);
>       }
>   
> @@ -1894,6 +1917,14 @@ process_init_constructor_union (tree typ
>       ce->value = massage_init_elt (TREE_TYPE (ce->index), ce->value, nested,
>   				  flags, complain);
>   
> +  /* Propagate CONSTRUCTOR_PLACEHOLDER_BOUNDARY to outer CONSTRUCTOR.  */
> +  if (ce->value
> +      && TREE_CODE (ce->value) == CONSTRUCTOR
> +      && CONSTRUCTOR_PLACEHOLDER_BOUNDARY (ce->value))
> +    {
> +      CONSTRUCTOR_PLACEHOLDER_BOUNDARY (init) = 1;
> +      CONSTRUCTOR_PLACEHOLDER_BOUNDARY (ce->value) = 0;
> +    }
>     return picflag_from_initializer (ce->value);
>   }
>   
> --- gcc/testsuite/g++.dg/cpp0x/pr105256.C.jj	2022-04-14 16:04:30.518518875 +0200
> +++ gcc/testsuite/g++.dg/cpp0x/pr105256.C	2022-04-14 16:03:53.264035175 +0200
> @@ -0,0 +1,18 @@
> +// PR c++/105256
> +// { dg-do compile { target c++11 } }
> +
> +int bar (int &);
> +
> +struct S {
> +  struct T {
> +    struct U {
> +      int i = bar (i);
> +    } u;
> +  };
> +};
> +
> +void
> +foo (S::T *p)
> +{
> +  *p = {};
> +};
> 
> 	Jakub
> 

Re: [PATCH] c++: Fix up CONSTRUCTOR_PLACEHOLDER_BOUNDARY handling [PR105256]

[Patrick Palka]

On Sun, Apr 17, 2022 at 6:24 PM Jason Merrill <jason@redhat.com> wrote:
>
> On 4/15/22 07:22, Jakub Jelinek wrote:
> > Hi!
> >
> > The CONSTRUCTOR_PLACEHOLDER_BOUNDARY bit is supposed to separate
> > PLACEHOLDER_EXPRs that should be replaced by one object or subobjects of it
> > (variable, TARGET_EXPR slot, ...) from other PLACEHOLDER_EXPRs that should
> > be replaced by different objects or subobjects.
> > The bit is set when finding PLACEHOLDER_EXPRs inside of a CONSTRUCTOR, not
> > looking into nested CONSTRUCTOR_PLACEHOLDER_BOUNDARY ctors, and we prevent
> > elision of TARGET_EXPRs (through TARGET_EXPR_NO_ELIDE) whose initializer
> > is a CONSTRUCTOR_PLACEHOLDER_BOUNDARY ctor.  The following testcase ICEs
> > though, we don't replace the placeholders in there at all, because
> > CONSTRUCTOR_PLACEHOLDER_BOUNDARY isn't set on the TARGET_EXPR_INITIAL
> > ctor, but on a ctor nested in such a ctor.  replace_placeholders should be
> > run on the whole TARGET_EXPR slot.
> >
> > So, the following patch fixes it by moving the CONSTRUCTOR_PLACEHOLDER_BOUNDARY
> > bit from nested CONSTRUCTORs to the CONSTRUCTOR containing those (but only
> > if it is closely nested, if there is some other tree sandwiched in between,
> > it doesn't do it).
>
> Hmm, Patrick made a similar change and then reverted it for PR90996.
> But it makes sense to me; when we replace placeholders, it's appropriate
> to look at the whole aggregate initialization rather than the innermost
> CONSTRUCTOR that has DMIs.  Patrick, was there a reason that change
> seemed wrong to you, or was it just unnecessary for the bug you were
> working on?

That change was just not strictly necessary for PR90996 I think.  For
that testcase:

struct S {
  int &&a = 2;
  int b[1] {a};
};

S c[] {{2}};

we first call replace_placeholders from store_init_value for the
overall initiializer for c

  {{.a=(int &) &_ZGR1c_, .b={*(&<PLACEHOLDER_EXPR struct S>)->a}}

but CONSTRUCTOR_PLACEHOLDER_BOUNDARY set on the middle pair of {}
prevents the placeholder from being resolved to c[0].  The reverted
change would have allowed us to resolve the placeholder at this point,
since the flag would have been moved to the outermost {} IIUC.

But fortunately split_nonconstant_init then factors out the
initialization of c[0].b into an INIT_EXPR:

  c[0].b[0] = *(&<PLACEHOLDER_EXPR struct S>)->a;

during gimplification of which we attempt replace_placeholders again
which succeeds this time at resolving the placeholder, due to the
other change in r10-7587 that made replace_placeholders look through
all handled components, not just COMPONENT_REF (mirroring
replace_placeholders_r).

So I reverted the rest of r10-7587 after Martin noticed it had no
effect: https://gcc.gnu.org/pipermail/gcc-patches/2020-April/543918.html

The reverted change and Jakub's more general patch seem right/safe to
me FWIW, I just couldn't come up with a testcase that demonstrated its
need at the time unfortunately.



>
> > Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
> >
> > 2022-04-15  Jakub Jelinek  <jakub@redhat.com>
> >
> >       PR c++/105256
> >       * typeck2.cc (process_init_constructor_array,
> >       process_init_constructor_record, process_init_constructor_union): Move
> >       CONSTRUCTOR_PLACEHOLDER_BOUNDARY flag from CONSTRUCTOR elements to the
> >       containing CONSTRUCTOR.
> >
> >       * g++.dg/cpp0x/pr105256.C: New test.
> >
> > --- gcc/cp/typeck2.cc.jj      2022-04-07 09:09:54.432995137 +0200
> > +++ gcc/cp/typeck2.cc 2022-04-14 16:02:12.438432494 +0200
> > @@ -1515,6 +1515,14 @@ process_init_constructor_array (tree typ
> >             strip_array_types (TREE_TYPE (ce->value)))));
> >
> >         picflags |= picflag_from_initializer (ce->value);
> > +      /* Propagate CONSTRUCTOR_PLACEHOLDER_BOUNDARY to outer
> > +      CONSTRUCTOR.  */
> > +      if (TREE_CODE (ce->value) == CONSTRUCTOR
> > +       && CONSTRUCTOR_PLACEHOLDER_BOUNDARY (ce->value))
> > +     {
> > +       CONSTRUCTOR_PLACEHOLDER_BOUNDARY (init) = 1;
> > +       CONSTRUCTOR_PLACEHOLDER_BOUNDARY (ce->value) = 0;
> > +     }
> >       }
> >
> >     /* No more initializers. If the array is unbounded, we are done. Otherwise,
> > @@ -1560,6 +1568,14 @@ process_init_constructor_array (tree typ
> >             }
> >
> >           picflags |= picflag_from_initializer (next);
> > +         /* Propagate CONSTRUCTOR_PLACEHOLDER_BOUNDARY to outer
> > +            CONSTRUCTOR.  */
> > +         if (TREE_CODE (next) == CONSTRUCTOR
> > +             && CONSTRUCTOR_PLACEHOLDER_BOUNDARY (next))
> > +           {
> > +             CONSTRUCTOR_PLACEHOLDER_BOUNDARY (init) = 1;
> > +             CONSTRUCTOR_PLACEHOLDER_BOUNDARY (next) = 0;
> > +           }
> >           if (len > i+1)
> >             {
> >               tree range = build2 (RANGE_EXPR, size_type_node,
> > @@ -1754,6 +1770,13 @@ process_init_constructor_record (tree ty
> >         if (fldtype != TREE_TYPE (field))
> >       next = cp_convert_and_check (TREE_TYPE (field), next, complain);
> >         picflags |= picflag_from_initializer (next);
> > +      /* Propagate CONSTRUCTOR_PLACEHOLDER_BOUNDARY to outer CONSTRUCTOR.  */
> > +      if (TREE_CODE (next) == CONSTRUCTOR
> > +       && CONSTRUCTOR_PLACEHOLDER_BOUNDARY (next))
> > +     {
> > +       CONSTRUCTOR_PLACEHOLDER_BOUNDARY (init) = 1;
> > +       CONSTRUCTOR_PLACEHOLDER_BOUNDARY (next) = 0;
> > +     }
> >         CONSTRUCTOR_APPEND_ELT (v, field, next);
> >       }
> >
> > @@ -1894,6 +1917,14 @@ process_init_constructor_union (tree typ
> >       ce->value = massage_init_elt (TREE_TYPE (ce->index), ce->value, nested,
> >                                 flags, complain);
> >
> > +  /* Propagate CONSTRUCTOR_PLACEHOLDER_BOUNDARY to outer CONSTRUCTOR.  */
> > +  if (ce->value
> > +      && TREE_CODE (ce->value) == CONSTRUCTOR
> > +      && CONSTRUCTOR_PLACEHOLDER_BOUNDARY (ce->value))
> > +    {
> > +      CONSTRUCTOR_PLACEHOLDER_BOUNDARY (init) = 1;
> > +      CONSTRUCTOR_PLACEHOLDER_BOUNDARY (ce->value) = 0;
> > +    }
> >     return picflag_from_initializer (ce->value);
> >   }
> >
> > --- gcc/testsuite/g++.dg/cpp0x/pr105256.C.jj  2022-04-14 16:04:30.518518875 +0200
> > +++ gcc/testsuite/g++.dg/cpp0x/pr105256.C     2022-04-14 16:03:53.264035175 +0200
> > @@ -0,0 +1,18 @@
> > +// PR c++/105256
> > +// { dg-do compile { target c++11 } }
> > +
> > +int bar (int &);
> > +
> > +struct S {
> > +  struct T {
> > +    struct U {
> > +      int i = bar (i);
> > +    } u;
> > +  };
> > +};
> > +
> > +void
> > +foo (S::T *p)
> > +{
> > +  *p = {};
> > +};
> >
> >       Jakub
> >
>

Re: [PATCH] c++: Fix up CONSTRUCTOR_PLACEHOLDER_BOUNDARY handling [PR105256]

[Jakub Jelinek]

On Mon, Apr 18, 2022 at 09:57:12AM -0400, Patrick Palka wrote:
> > Hmm, Patrick made a similar change and then reverted it for PR90996.
> > But it makes sense to me; when we replace placeholders, it's appropriate
> > to look at the whole aggregate initialization rather than the innermost
> > CONSTRUCTOR that has DMIs.  Patrick, was there a reason that change
> > seemed wrong to you, or was it just unnecessary for the bug you were
> > working on?
> 
> The reverted change and Jakub's more general patch seem right/safe to
> me FWIW, I just couldn't come up with a testcase that demonstrated its
> need at the time unfortunately.

So is the patch ok for trunk then?
Apparently it is also a recent regression on 11 branch (since Marek's
r11-9711) when compiling firefox, ok for 11.3 as well?

> > > 2022-04-15  Jakub Jelinek  <jakub@redhat.com>
> > >
> > >       PR c++/105256
> > >       * typeck2.cc (process_init_constructor_array,
> > >       process_init_constructor_record, process_init_constructor_union): Move
> > >       CONSTRUCTOR_PLACEHOLDER_BOUNDARY flag from CONSTRUCTOR elements to the
> > >       containing CONSTRUCTOR.
> > >
> > >       * g++.dg/cpp0x/pr105256.C: New test.

	Jakub

Re: [PATCH] c++: Fix up CONSTRUCTOR_PLACEHOLDER_BOUNDARY handling [PR105256]

[Jason Merrill]

On Tue, Apr 19, 2022, 6:53 AM Jakub Jelinek <jakub@redhat.com> wrote:

> On Mon, Apr 18, 2022 at 09:57:12AM -0400, Patrick Palka wrote:
> > > Hmm, Patrick made a similar change and then reverted it for PR90996.
> > > But it makes sense to me; when we replace placeholders, it's
> appropriate
> > > to look at the whole aggregate initialization rather than the innermost
> > > CONSTRUCTOR that has DMIs.  Patrick, was there a reason that change
> > > seemed wrong to you, or was it just unnecessary for the bug you were
> > > working on?
> >
> > The reverted change and Jakub's more general patch seem right/safe to
> > me FWIW, I just couldn't come up with a testcase that demonstrated its
> > need at the time unfortunately.
>
> So is the patch ok for trunk then?
> Apparently it is also a recent regression on 11 branch (since Marek's
> r11-9711) when compiling firefox, ok for 11.3 as well?
>

Ok for both.

> > > 2022-04-15  Jakub Jelinek  <jakub@redhat.com>
> > > >
> > > >       PR c++/105256
> > > >       * typeck2.cc (process_init_constructor_array,
> > > >       process_init_constructor_record,
> process_init_constructor_union): Move
> > > >       CONSTRUCTOR_PLACEHOLDER_BOUNDARY flag from CONSTRUCTOR
> elements to the
> > > >       containing CONSTRUCTOR.
> > > >
> > > >       * g++.dg/cpp0x/pr105256.C: New test.
>
>         Jakub
>
>