c++: Fix usage of CONSTRUCTOR_PLACEHOLDER_BOUNDARY inside array initializers [90996]

This PR reports that since the introduction of the
CONSTRUCTOR_PLACEHOLDER_BOUNDARY flag, we are sometimes failing to resolve
PLACEHOLDER_EXPRs inside array initializers that refer to some inner
constructor.  In the testcase in the PR, we have as the initializer for "S c[];"
the following

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

where CONSTRUCTOR_PLACEHOLDER_BOUNDARY is set on the second outermost
constructor.  However, we pass the whole initializer to replace_placeholders in
store_init_value, and so due to the flag being set on the second outermost ctor
it avoids recursing into the innermost constructor and we fail to resolve the
PLACEHOLDER_EXPR within.

To fix this, we could perhaps either call replace_placeholders in more places,
or we could change where we set CONSTRUCTOR_PLACEHOLDER_BOUNDARY.  This patch
takes the latter approach -- when building up an array initializer, it bubbles
any CONSTRUCTOR_PLACEHOLDER_BOUNDARY flag set on the element initializers up to
the array initializer.  Doing so shouldn't create any new PLACEHOLDER_EXPR
resolution ambiguities because we don't deal with PLACEHOLDER_EXPRs of array
type in the frontend, as far as I can tell.

Does this look OK to comit after testing?

gcc/cp/ChangeLog:

	PR c++/90996
	* tree.c (replace_placeholders): Look through all handled components,
	not just COMPONENT_REFs.
	* typeck2.c (process_init_constructor_array): Propagate
	CONSTRUCTOR_PLACEHOLDER_BOUNDARY up from each element initializer to
	the array initializer.

gcc/testsuite/ChangeLog:

	PR c++/90996
	* g++.dg/cpp1y/pr90996.C: New test.
---
 gcc/cp/tree.c                        |  2 +-
 gcc/cp/typeck2.c                     | 18 ++++++++++++++++++
 gcc/testsuite/g++.dg/cpp1y/pr90996.C | 17 +++++++++++++++++
 3 files changed, 36 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp1y/pr90996.C

On 4/6/20 3:07 PM, Patrick Palka wrote:
> This PR reports that since the introduction of the
> CONSTRUCTOR_PLACEHOLDER_BOUNDARY flag, we are sometimes failing to resolve
> PLACEHOLDER_EXPRs inside array initializers that refer to some inner
> constructor.  In the testcase in the PR, we have as the initializer for "S c[];"
> the following
> 
>    {{.a=(int &) &_ZGR1c_, .b={*(&<PLACEHOLDER_EXPR struct S>)->a}}}
> 
> where CONSTRUCTOR_PLACEHOLDER_BOUNDARY is set on the second outermost
> constructor.  However, we pass the whole initializer to replace_placeholders in
> store_init_value, and so due to the flag being set on the second outermost ctor
> it avoids recursing into the innermost constructor and we fail to resolve the
> PLACEHOLDER_EXPR within.
> 
> To fix this, we could perhaps either call replace_placeholders in more places,
> or we could change where we set CONSTRUCTOR_PLACEHOLDER_BOUNDARY.  This patch
> takes the latter approach -- when building up an array initializer, it bubbles
> any CONSTRUCTOR_PLACEHOLDER_BOUNDARY flag set on the element initializers up to
> the array initializer.  Doing so shouldn't create any new PLACEHOLDER_EXPR
> resolution ambiguities because we don't deal with PLACEHOLDER_EXPRs of array
> type in the frontend, as far as I can tell.

Interesting.  Yes, that sounds like it should work.

> Does this look OK to comit after testing?

Yes.

Though I'm seeing "after testing" a lot; what testing are you doing 
before sending patches?

> gcc/cp/ChangeLog:
> 
> 	PR c++/90996
> 	* tree.c (replace_placeholders): Look through all handled components,
> 	not just COMPONENT_REFs.
> 	* typeck2.c (process_init_constructor_array): Propagate
> 	CONSTRUCTOR_PLACEHOLDER_BOUNDARY up from each element initializer to
> 	the array initializer.
> 
> gcc/testsuite/ChangeLog:
> 
> 	PR c++/90996
> 	* g++.dg/cpp1y/pr90996.C: New test.
> ---
>   gcc/cp/tree.c                        |  2 +-
>   gcc/cp/typeck2.c                     | 18 ++++++++++++++++++
>   gcc/testsuite/g++.dg/cpp1y/pr90996.C | 17 +++++++++++++++++
>   3 files changed, 36 insertions(+), 1 deletion(-)
>   create mode 100644 gcc/testsuite/g++.dg/cpp1y/pr90996.C
> 
> diff --git a/gcc/cp/tree.c b/gcc/cp/tree.c
> index 5eb0dcd717a..d1192b7e094 100644
> --- a/gcc/cp/tree.c
> +++ b/gcc/cp/tree.c
> @@ -3247,7 +3247,7 @@ replace_placeholders (tree exp, tree obj, bool *seen_p /*= NULL*/)
>   
>     /* If the object isn't a (member of a) class, do nothing.  */
>     tree op0 = obj;
> -  while (TREE_CODE (op0) == COMPONENT_REF)
> +  while (handled_component_p (op0))
>       op0 = TREE_OPERAND (op0, 0);
>     if (!CLASS_TYPE_P (strip_array_types (TREE_TYPE (op0))))
>       return exp;
> diff --git a/gcc/cp/typeck2.c b/gcc/cp/typeck2.c
> index cf1cb5ace66..fe844bc08bb 100644
> --- a/gcc/cp/typeck2.c
> +++ b/gcc/cp/typeck2.c
> @@ -1488,6 +1488,17 @@ process_init_constructor_array (tree type, tree init, int nested, int flags,
>   	= massage_init_elt (TREE_TYPE (type), ce->value, nested, flags,
>   			    complain);
>   
> +      if (TREE_CODE (ce->value) == CONSTRUCTOR
> +	  && CONSTRUCTOR_PLACEHOLDER_BOUNDARY (ce->value))
> +	{
> +	  /* Shift CONSTRUCTOR_PLACEHOLDER_BOUNDARY from the element initializer
> +	     up to the array initializer, so that the call to
> +	     replace_placeholders from store_init_value can resolve any
> +	     PLACEHOLDER_EXPRs within this element initializer.  */
> +	  CONSTRUCTOR_PLACEHOLDER_BOUNDARY (ce->value) = 0;
> +	  CONSTRUCTOR_PLACEHOLDER_BOUNDARY (init) = 1;
> +	}
> +
>         gcc_checking_assert
>   	(ce->value == error_mark_node
>   	 || (same_type_ignoring_top_level_qualifiers_p
> @@ -1516,6 +1527,13 @@ process_init_constructor_array (tree type, tree init, int nested, int flags,
>   	      /* The default zero-initialization is fine for us; don't
>   		 add anything to the CONSTRUCTOR.  */
>   	      next = NULL_TREE;
> +	    else if (TREE_CODE (next) == CONSTRUCTOR
> +		     && CONSTRUCTOR_PLACEHOLDER_BOUNDARY (next))
> +	      {
> +		/* As above.  */
> +		CONSTRUCTOR_PLACEHOLDER_BOUNDARY (next) = 0;
> +		CONSTRUCTOR_PLACEHOLDER_BOUNDARY (init) = 1;
> +	      }
>   	  }
>   	else if (!zero_init_p (TREE_TYPE (type)))
>   	  next = build_zero_init (TREE_TYPE (type),
> diff --git a/gcc/testsuite/g++.dg/cpp1y/pr90996.C b/gcc/testsuite/g++.dg/cpp1y/pr90996.C
> new file mode 100644
> index 00000000000..780cbb4e3ac
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp1y/pr90996.C
> @@ -0,0 +1,17 @@
> +// PR c++/90996
> +// { dg-do compile { target c++14 } }
> +
> +struct S
> +{
> +  int &&a = 2;
> +  int b[1] {a};
> +};
> +
> +S c[2][2] {{{5}}};
> +
> +struct T
> +{
> +  S c[2][2] {{{7}}};
> +};
> +
> +T d {};
>

On Mon, 6 Apr 2020, Jason Merrill wrote:

> On 4/6/20 3:07 PM, Patrick Palka wrote:
> > This PR reports that since the introduction of the
> > CONSTRUCTOR_PLACEHOLDER_BOUNDARY flag, we are sometimes failing to resolve
> > PLACEHOLDER_EXPRs inside array initializers that refer to some inner
> > constructor.  In the testcase in the PR, we have as the initializer for "S
> > c[];"
> > the following
> > 
> >    {{.a=(int &) &_ZGR1c_, .b={*(&<PLACEHOLDER_EXPR struct S>)->a}}}
> > 
> > where CONSTRUCTOR_PLACEHOLDER_BOUNDARY is set on the second outermost
> > constructor.  However, we pass the whole initializer to replace_placeholders
> > in
> > store_init_value, and so due to the flag being set on the second outermost
> > ctor
> > it avoids recursing into the innermost constructor and we fail to resolve
> > the
> > PLACEHOLDER_EXPR within.
> > 
> > To fix this, we could perhaps either call replace_placeholders in more
> > places,
> > or we could change where we set CONSTRUCTOR_PLACEHOLDER_BOUNDARY.  This
> > patch
> > takes the latter approach -- when building up an array initializer, it
> > bubbles
> > any CONSTRUCTOR_PLACEHOLDER_BOUNDARY flag set on the element initializers up
> > to
> > the array initializer.  Doing so shouldn't create any new PLACEHOLDER_EXPR
> > resolution ambiguities because we don't deal with PLACEHOLDER_EXPRs of array
> > type in the frontend, as far as I can tell.
> 
> Interesting.  Yes, that sounds like it should work.
> 
> > Does this look OK to comit after testing?
> 
> Yes.
> 
> Though I'm seeing "after testing" a lot; what testing are you doing before
> sending patches?

Sorry for the sloppiness -- I should be writing "after a full
bootstrap/regtest" instead of "after testing" because I do indeed do
some testing before sending a patch.  In particular, I usually run and
inspect the outputs of

    make check RUNTESTFLAGS="dg.exp=*.C"
    make check RUNTESTFLAGS="old-deja.exp=*.C"
    make check RUNTESTFLAGS="conformance.exp=*ranges*"

in a build tree that is configured with --disable-bootstrap, as a quick
smoke test for the patch.  Is this a sufficient amount of testing before
sending a patch for review, or would you prefer that I do a full
bootstrap/regtest beforehand?

In any case, I'll make sure to clearly convey the amount of testing that
was done and is remaining in future patch submissions.

> 
> > gcc/cp/ChangeLog:
> > 
> > 	PR c++/90996
> > 	* tree.c (replace_placeholders): Look through all handled components,
> > 	not just COMPONENT_REFs.
> > 	* typeck2.c (process_init_constructor_array): Propagate
> > 	CONSTRUCTOR_PLACEHOLDER_BOUNDARY up from each element initializer to
> > 	the array initializer.
> > 
> > gcc/testsuite/ChangeLog:
> > 
> > 	PR c++/90996
> > 	* g++.dg/cpp1y/pr90996.C: New test.
> > ---
> >   gcc/cp/tree.c                        |  2 +-
> >   gcc/cp/typeck2.c                     | 18 ++++++++++++++++++
> >   gcc/testsuite/g++.dg/cpp1y/pr90996.C | 17 +++++++++++++++++
> >   3 files changed, 36 insertions(+), 1 deletion(-)
> >   create mode 100644 gcc/testsuite/g++.dg/cpp1y/pr90996.C
> > 
> > diff --git a/gcc/cp/tree.c b/gcc/cp/tree.c
> > index 5eb0dcd717a..d1192b7e094 100644
> > --- a/gcc/cp/tree.c
> > +++ b/gcc/cp/tree.c
> > @@ -3247,7 +3247,7 @@ replace_placeholders (tree exp, tree obj, bool *seen_p
> > /*= NULL*/)
> >       /* If the object isn't a (member of a) class, do nothing.  */
> >     tree op0 = obj;
> > -  while (TREE_CODE (op0) == COMPONENT_REF)
> > +  while (handled_component_p (op0))
> >       op0 = TREE_OPERAND (op0, 0);
> >     if (!CLASS_TYPE_P (strip_array_types (TREE_TYPE (op0))))
> >       return exp;
> > diff --git a/gcc/cp/typeck2.c b/gcc/cp/typeck2.c
> > index cf1cb5ace66..fe844bc08bb 100644
> > --- a/gcc/cp/typeck2.c
> > +++ b/gcc/cp/typeck2.c
> > @@ -1488,6 +1488,17 @@ process_init_constructor_array (tree type, tree init,
> > int nested, int flags,
> >   	= massage_init_elt (TREE_TYPE (type), ce->value, nested, flags,
> >   			    complain);
> >   +      if (TREE_CODE (ce->value) == CONSTRUCTOR
> > +	  && CONSTRUCTOR_PLACEHOLDER_BOUNDARY (ce->value))
> > +	{
> > +	  /* Shift CONSTRUCTOR_PLACEHOLDER_BOUNDARY from the element
> > initializer
> > +	     up to the array initializer, so that the call to
> > +	     replace_placeholders from store_init_value can resolve any
> > +	     PLACEHOLDER_EXPRs within this element initializer.  */
> > +	  CONSTRUCTOR_PLACEHOLDER_BOUNDARY (ce->value) = 0;
> > +	  CONSTRUCTOR_PLACEHOLDER_BOUNDARY (init) = 1;
> > +	}
> > +
> >         gcc_checking_assert
> >   	(ce->value == error_mark_node
> >   	 || (same_type_ignoring_top_level_qualifiers_p
> > @@ -1516,6 +1527,13 @@ process_init_constructor_array (tree type, tree init,
> > int nested, int flags,
> >   	      /* The default zero-initialization is fine for us; don't
> >   		 add anything to the CONSTRUCTOR.  */
> >   	      next = NULL_TREE;
> > +	    else if (TREE_CODE (next) == CONSTRUCTOR
> > +		     && CONSTRUCTOR_PLACEHOLDER_BOUNDARY (next))
> > +	      {
> > +		/* As above.  */
> > +		CONSTRUCTOR_PLACEHOLDER_BOUNDARY (next) = 0;
> > +		CONSTRUCTOR_PLACEHOLDER_BOUNDARY (init) = 1;
> > +	      }
> >   	  }
> >   	else if (!zero_init_p (TREE_TYPE (type)))
> >   	  next = build_zero_init (TREE_TYPE (type),
> > diff --git a/gcc/testsuite/g++.dg/cpp1y/pr90996.C
> > b/gcc/testsuite/g++.dg/cpp1y/pr90996.C
> > new file mode 100644
> > index 00000000000..780cbb4e3ac
> > --- /dev/null
> > +++ b/gcc/testsuite/g++.dg/cpp1y/pr90996.C
> > @@ -0,0 +1,17 @@
> > +// PR c++/90996
> > +// { dg-do compile { target c++14 } }
> > +
> > +struct S
> > +{
> > +  int &&a = 2;
> > +  int b[1] {a};
> > +};
> > +
> > +S c[2][2] {{{5}}};
> > +
> > +struct T
> > +{
> > +  S c[2][2] {{{7}}};
> > +};
> > +
> > +T d {};
> > 
> 
>

On 4/6/20 6:22 PM, Patrick Palka wrote:
> On Mon, 6 Apr 2020, Jason Merrill wrote:
> 
>> On 4/6/20 3:07 PM, Patrick Palka wrote:
>>> This PR reports that since the introduction of the
>>> CONSTRUCTOR_PLACEHOLDER_BOUNDARY flag, we are sometimes failing to resolve
>>> PLACEHOLDER_EXPRs inside array initializers that refer to some inner
>>> constructor.  In the testcase in the PR, we have as the initializer for "S
>>> c[];"
>>> the following
>>>
>>>     {{.a=(int &) &_ZGR1c_, .b={*(&<PLACEHOLDER_EXPR struct S>)->a}}}
>>>
>>> where CONSTRUCTOR_PLACEHOLDER_BOUNDARY is set on the second outermost
>>> constructor.  However, we pass the whole initializer to replace_placeholders
>>> in
>>> store_init_value, and so due to the flag being set on the second outermost
>>> ctor
>>> it avoids recursing into the innermost constructor and we fail to resolve
>>> the
>>> PLACEHOLDER_EXPR within.
>>>
>>> To fix this, we could perhaps either call replace_placeholders in more
>>> places,
>>> or we could change where we set CONSTRUCTOR_PLACEHOLDER_BOUNDARY.  This
>>> patch
>>> takes the latter approach -- when building up an array initializer, it
>>> bubbles
>>> any CONSTRUCTOR_PLACEHOLDER_BOUNDARY flag set on the element initializers up
>>> to
>>> the array initializer.  Doing so shouldn't create any new PLACEHOLDER_EXPR
>>> resolution ambiguities because we don't deal with PLACEHOLDER_EXPRs of array
>>> type in the frontend, as far as I can tell.
>>
>> Interesting.  Yes, that sounds like it should work.
>>
>>> Does this look OK to comit after testing?
>>
>> Yes.
>>
>> Though I'm seeing "after testing" a lot; what testing are you doing before
>> sending patches?
> 
> Sorry for the sloppiness -- I should be writing "after a full
> bootstrap/regtest" instead of "after testing" because I do indeed do
> some testing before sending a patch.  In particular, I usually run and
> inspect the outputs of
> 
>      make check RUNTESTFLAGS="dg.exp=*.C"
>      make check RUNTESTFLAGS="old-deja.exp=*.C"
>      make check RUNTESTFLAGS="conformance.exp=*ranges*"
> 
> in a build tree that is configured with --disable-bootstrap, as a quick
> smoke test for the patch.  Is this a sufficient amount of testing before
> sending a patch for review, or would you prefer that I do a full
> bootstrap/regtest beforehand?

You don't need to do a full bootstrap and run non-C++ testsuites, but 
please run the full libstdc++ testsuite.

Is there a reason you aren't using 'make check-c++'?

> In any case, I'll make sure to clearly convey the amount of testing that
> was done and is remaining in future patch submissions.

Thanks.

Jason

On Wed, 8 Apr 2020, Jason Merrill wrote:
> On 4/6/20 6:22 PM, Patrick Palka wrote:
> > On Mon, 6 Apr 2020, Jason Merrill wrote:
> > 
> > > On 4/6/20 3:07 PM, Patrick Palka wrote:
> > > > This PR reports that since the introduction of the
> > > > CONSTRUCTOR_PLACEHOLDER_BOUNDARY flag, we are sometimes failing to
> > > > resolve
> > > > PLACEHOLDER_EXPRs inside array initializers that refer to some inner
> > > > constructor.  In the testcase in the PR, we have as the initializer for
> > > > "S
> > > > c[];"
> > > > the following
> > > > 
> > > >     {{.a=(int &) &_ZGR1c_, .b={*(&<PLACEHOLDER_EXPR struct S>)->a}}}
> > > > 
> > > > where CONSTRUCTOR_PLACEHOLDER_BOUNDARY is set on the second outermost
> > > > constructor.  However, we pass the whole initializer to
> > > > replace_placeholders
> > > > in
> > > > store_init_value, and so due to the flag being set on the second
> > > > outermost
> > > > ctor
> > > > it avoids recursing into the innermost constructor and we fail to
> > > > resolve
> > > > the
> > > > PLACEHOLDER_EXPR within.
> > > > 
> > > > To fix this, we could perhaps either call replace_placeholders in more
> > > > places,
> > > > or we could change where we set CONSTRUCTOR_PLACEHOLDER_BOUNDARY.  This
> > > > patch
> > > > takes the latter approach -- when building up an array initializer, it
> > > > bubbles
> > > > any CONSTRUCTOR_PLACEHOLDER_BOUNDARY flag set on the element
> > > > initializers up
> > > > to
> > > > the array initializer.  Doing so shouldn't create any new
> > > > PLACEHOLDER_EXPR
> > > > resolution ambiguities because we don't deal with PLACEHOLDER_EXPRs of
> > > > array
> > > > type in the frontend, as far as I can tell.
> > > 
> > > Interesting.  Yes, that sounds like it should work.
> > > 
> > > > Does this look OK to comit after testing?
> > > 
> > > Yes.
> > > 
> > > Though I'm seeing "after testing" a lot; what testing are you doing before
> > > sending patches?
> > 
> > Sorry for the sloppiness -- I should be writing "after a full
> > bootstrap/regtest" instead of "after testing" because I do indeed do
> > some testing before sending a patch.  In particular, I usually run and
> > inspect the outputs of
> > 
> >      make check RUNTESTFLAGS="dg.exp=*.C"
> >      make check RUNTESTFLAGS="old-deja.exp=*.C"
> >      make check RUNTESTFLAGS="conformance.exp=*ranges*"
> > 
> > in a build tree that is configured with --disable-bootstrap, as a quick
> > smoke test for the patch.  Is this a sufficient amount of testing before
> > sending a patch for review, or would you prefer that I do a full
> > bootstrap/regtest beforehand?
> 
> You don't need to do a full bootstrap and run non-C++ testsuites, but please
> run the full libstdc++ testsuite.
> 
> Is there a reason you aren't using 'make check-c++'?

No good reason, I didn't know about "make check-c++" :) Good to know,
thanks!

> 
> > In any case, I'll make sure to clearly convey the amount of testing that
> > was done and is remaining in future patch submissions.
> 
> Thanks.
> 
> Jason
> 
>