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 {};
> >
>
>
