On Wed, 10 Sep 2025, Nathaniel Shead wrote:
> Does this fix seem reasonable, or is there something I've missed?
>
> My change to g++.dg/lto/pr101396_0.C also causes it to fail link with
> some flags on my machine, with:
>
> FAIL: g++.dg/lto/pr101396 cp_lto_pr101396_0.o-cp_lto_pr101396_1.o link, -O0
> -flto -flto-partition=none -fuse-linker-plugin
> FAIL: g++.dg/lto/pr101396 cp_lto_pr101396_0.o-cp_lto_pr101396_1.o link, -O0
> -flto -flto-partition=1to1 -fno-use-linker-plugin
> FAIL: g++.dg/lto/pr101396 cp_lto_pr101396_0.o-cp_lto_pr101396_1.o link, -O0
> -flto -fuse-linker-plugin -fno-fat-lto-objects
>
> But the logs doesn't indicate exactly what failed with the link, and
> when I try running the commands from the log myself it works fine (exit
> status 0, executable generated and can be ran, etc.). This seems to
> happen also on a clean tree without my changes, so not sure if this is a
> bug or I've misconfigured something or what; any hints?
>
> Other than that failure, successfully bootstrapped and regtested on
> x86_64-pc-linux-gnu.
>
> -- >8 --
>
> On a DECL, TREE_CHAIN will find any other declarations in the same
> binding level. This caused an ICE in PR121865 because the next entity
> in the binding level was the uninstantiated unique friend 'foo', for
> which after being found the compiler tries to generate a mangled name
> for it and crashes.
>
> This didn't happen in non-modules testcases only because normally the
> unique friend function would have been chained after its template_decl,
> and find_decl_types_r bails on lang-specific nodes so it never saw the
> uninstantiated decl. With modules however the order of chaining
> changed, causing the error.
So it didn't visit TREE_CHAIN of a lang specific thing? That would
have been a bug I think. Btw, what context was this chained in?
I suppose we could change things like
fld_worklist_push (TYPE_ATTRIBUTES (t), fld);
to be
fld_worklist_push_{chain,list}
(note there's also TREE_PURPOSE and TREE_VALUE on list nodes). The
way we exempt field/type decls is definitely a bit vague (I'll note
we also have LABEL_DECLs at least).
>
> I don't think it's ever necessary to walk into the TREE_CHAIN, from what
> I can see; other cases where it might be useful (block vars or type
> fields) are already handled explicitly elsewhere, and only one test
> fails because of the change, due to accidentally relying on this "walk
> into the next in-scope declaration" behaviour.
We have various tree lists for which this is necessary, for example
DECL/TYPE_ATTRIBUTES. So I think this is wrong.
> PR c++/121865
>
> gcc/ChangeLog:
>
> * ipa-free-lang-data.cc (find_decls_types_r): Don't walk into
> TREE_CHAINs of DECLs.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/lto/pr101396_0.C: Ensure A will be walked into (and
> isn't constant-folded out of the GIMPLE for the function).
> * g++.dg/modules/lto-4_a.C: New test.
> * g++.dg/modules/lto-4_b.C: New test.
>
> Signed-off-by: Nathaniel Shead <nathanielosh...@gmail.com>
> ---
> gcc/ipa-free-lang-data.cc | 3 ---
> gcc/testsuite/g++.dg/lto/pr101396_0.C | 3 ++-
> gcc/testsuite/g++.dg/modules/lto-4_a.C | 10 ++++++++++
> gcc/testsuite/g++.dg/modules/lto-4_b.C | 8 ++++++++
> 4 files changed, 20 insertions(+), 4 deletions(-)
> create mode 100644 gcc/testsuite/g++.dg/modules/lto-4_a.C
> create mode 100644 gcc/testsuite/g++.dg/modules/lto-4_b.C
>
> diff --git a/gcc/ipa-free-lang-data.cc b/gcc/ipa-free-lang-data.cc
> index 8c4fb3c6b64..41afc6ec82f 100644
> --- a/gcc/ipa-free-lang-data.cc
> +++ b/gcc/ipa-free-lang-data.cc
> @@ -750,9 +750,6 @@ find_decls_types_r (tree *tp, int *ws, void *data)
> && DECL_HAS_VALUE_EXPR_P (t))
> fld_worklist_push (DECL_VALUE_EXPR (t), fld);
>
> - if (TREE_CODE (t) != FIELD_DECL
> - && TREE_CODE (t) != TYPE_DECL)
> - fld_worklist_push (TREE_CHAIN (t), fld);
> *ws = 0;
> }
> else if (TYPE_P (t))
> diff --git a/gcc/testsuite/g++.dg/lto/pr101396_0.C
> b/gcc/testsuite/g++.dg/lto/pr101396_0.C
> index b7a2947a880..d26174df8e0 100644
> --- a/gcc/testsuite/g++.dg/lto/pr101396_0.C
> +++ b/gcc/testsuite/g++.dg/lto/pr101396_0.C
> @@ -8,5 +8,6 @@ enum A : __UINT32_TYPE__ { // { dg-lto-warning "6: type 'A'
> violates the C\\+\\+
>
> int main()
> {
> - return (int) A::a;
> + enum A x = A::a;
> + return (int) x;
> }
> diff --git a/gcc/testsuite/g++.dg/modules/lto-4_a.C
> b/gcc/testsuite/g++.dg/modules/lto-4_a.C
> new file mode 100644
> index 00000000000..16629158dc2
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/modules/lto-4_a.C
> @@ -0,0 +1,10 @@
> +// PR c++/121865
> +// { dg-require-effective-target lto }
> +// { dg-additional-options "-fmodules -flto" }
> +
> +export module M;
> +export template <typename T> struct S;
> +export template <typename T> void foo(S<T>) {}
> +template <typename T> struct S {
> + friend void foo<>(S);
> +};
> diff --git a/gcc/testsuite/g++.dg/modules/lto-4_b.C
> b/gcc/testsuite/g++.dg/modules/lto-4_b.C
> new file mode 100644
> index 00000000000..0322855caf4
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/modules/lto-4_b.C
> @@ -0,0 +1,8 @@
> +// PR c++/121865
> +// { dg-module-do link }
> +// { dg-require-effective-target lto }
> +// { dg-additional-options "-fmodules -flto" }
> +
> +import M;
> +template struct S<int>;
> +int main() {}
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)
