On Fri, 20 Oct 2023, Nathan Sidwell wrote:
> Thanks for looking at this, but your patch is essentially papering over the
> problem.
>
> It took me a while to figure out, but the clue was that things like
> 'decltype(f()).m' worked, but 'decltype(f()){0}' did not. The CONSTRUCTOR
> node is the exception to the rule that required an expression node's type to
> be streamed after the node's operands. We want the opposite for CTORS.
>
> I'll commit this once bootstrapped.
Very interesting, thanks a lot! It's awesome that both testcases could
be fixed simultaneously after all :)
>
> nathan
>
> On 10/18/23 12:28, Patrick Palka wrote:
> > Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> > trunk?
> >
> > -- >8 --
> >
> > For a local variable initialized by a lambda:
> >
> > auto f = []{};
> >
> > The corresponding BLOCK_VARS contains the variable declaration first,
> > followed by the closure type declaration, consistent with the
> > syntactical order. This however means that a use of the closure type
> > appears (in the variable type/initializer) before the declaration of the
> > type. This ends up causing an ICE when streaming the BLOCK_VARS of f1
> > below because we stream (by value) the CONSTRUCTOR initializer of g1 --
> > which contains components of the closure type -- before we've streamed
> > the declaration defining the closure type. The following comment in
> > module.cc seems relevant:
> >
> > /* We want to stream the type of a expression-like nodes /after/
> > we've streamed the operands. The type often contains (bits
> > of the) types of the operands, and with things like decltype
> > and noexcept in play, we really want to stream the decls
> > defining the type before we try and stream the type on its
> > own. Otherwise we can find ourselves trying to read in a
> > decl, when we're already partially reading in a component of
> > its type. And that's bad. */
> >
> > This patch narrowly fixes this issue by special casing closure type
> > declarations in add_decl_to_level. (A loop is needed since there could
> > be multiple variable declarations with an unprocessed initializer in
> > light of structured bindings.)
> >
> > PR c++/105322
> >
> > gcc/cp/ChangeLog:
> >
> > * name-lookup.cc (add_decl_to_level): When adding a closure
> > type declaration to a block scope, add it before rather than
> > after any variable declarations whose initializer we're still
> > processing.
> >
> > gcc/testsuite/ChangeLog:
> >
> > * g++.dg/modules/lambda-5_a.C: New test.
> > * g++.dg/modules/lambda-5_b.C: New test.
> > ---
> > gcc/cp/name-lookup.cc | 19 ++++++++++++++++---
> > gcc/testsuite/g++.dg/modules/lambda-5_a.C | 23 +++++++++++++++++++++++
> > gcc/testsuite/g++.dg/modules/lambda-5_b.C | 10 ++++++++++
> > 3 files changed, 49 insertions(+), 3 deletions(-)
> > create mode 100644 gcc/testsuite/g++.dg/modules/lambda-5_a.C
> > create mode 100644 gcc/testsuite/g++.dg/modules/lambda-5_b.C
> >
> > diff --git a/gcc/cp/name-lookup.cc b/gcc/cp/name-lookup.cc
> > index a8b9229b29e..bb00baaf9f4 100644
> > --- a/gcc/cp/name-lookup.cc
> > +++ b/gcc/cp/name-lookup.cc
> > @@ -391,9 +391,22 @@ add_decl_to_level (cp_binding_level *b, tree decl)
> > gcc_assert (b->names != decl);
> > /* We build up the list in reverse order, and reverse it later if
> > - necessary. */
> > - TREE_CHAIN (decl) = b->names;
> > - b->names = decl;
> > + necessary. If we're adding a lambda closure type to a block
> > + scope as part of a local variable initializer, then make sure
> > + we declare the type before the variable; modules expects that
> > + we see a type declaration before a use of the type. */
> > + tree *prev = &b->names;
> > + if (b->kind == sk_block
> > + && !processing_template_decl
> > + && TREE_CODE (decl) == TYPE_DECL
> > + && LAMBDA_TYPE_P (TREE_TYPE (decl)))
> > + while (*prev && VAR_P (*prev)
> > + && !DECL_EXTERNAL (*prev)
> > + && !DECL_INITIALIZED_P (*prev))
> > + prev = &TREE_CHAIN (*prev);
> > +
> > + TREE_CHAIN (decl) = *prev;
> > + *prev = decl;
> > /* If appropriate, add decl to separate list of statics. We include
> > extern variables because they might turn out to be static later.
> > diff --git a/gcc/testsuite/g++.dg/modules/lambda-5_a.C
> > b/gcc/testsuite/g++.dg/modules/lambda-5_a.C
> > new file mode 100644
> > index 00000000000..6b54c8e3173
> > --- /dev/null
> > +++ b/gcc/testsuite/g++.dg/modules/lambda-5_a.C
> > @@ -0,0 +1,23 @@
> > +// PR c++/105322
> > +// { dg-additional-options -fmodules-ts }
> > +// { dg-module-cmi pr105322 }
> > +
> > +export module pr105322;
> > +
> > +struct A { };
> > +
> > +export
> > +inline void f1() {
> > + A a;
> > + auto g1 = [a] { }; // used to ICE here during stream out
> > +}
> > +
> > +export
> > +template<class...>
> > +void f2() {
> > + A a;
> > + auto g2 = [a] { };
> > +}
> > +
> > +export
> > +inline auto g3 = [a=A{}] { };
> > diff --git a/gcc/testsuite/g++.dg/modules/lambda-5_b.C
> > b/gcc/testsuite/g++.dg/modules/lambda-5_b.C
> > new file mode 100644
> > index 00000000000..e25a913b726
> > --- /dev/null
> > +++ b/gcc/testsuite/g++.dg/modules/lambda-5_b.C
> > @@ -0,0 +1,10 @@
> > +// PR c++/105322
> > +// { dg-additional-options -fmodules-ts }
> > +
> > +import pr105322;
> > +
> > +int main() {
> > + f1();
> > + f2();
> > + g3();
> > +}
>
> --
> Nathan Sidwell
>
