[Bug c++/121597] ICE: Segmentation fault, involving nested generic lambda and argument deduction

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121597

--- Comment #1 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Marek Polacek <mpolacek@gcc.gnu.org>:

https://gcc.gnu.org/g:811cc466193d7efcfcc07d2081b1284d97fc91a1

commit r17-1455-g811cc466193d7efcfcc07d2081b1284d97fc91a1
Author: Marek Polacek <polacek@redhat.com>
Date:   Tue May 19 19:03:33 2026 -0400

    c++: recognize more aliases with lambda targs [PR125212]

    This patch introduces a new TYPE_DECL flag so that dependent_opaque_alias_p
    doesn't have to peruse the tree every time it's called to see if there is
    a LAMBDA_EXPR, in which case the alias should be opaque.  Using walk_tree
    in dependent_opaque_alias_p was too expensive, and the special cases we
    had there were fooled by more deeply nested lambdas.

    Compiling range-v3's zip.cpp, perf stat shows:
    this patch: 28.826446158 seconds time elapsed
    trunk:      29.425441889 seconds time elapsed
    so this patch makes the situation marginally better.

            PR c++/121287
            PR c++/125212
            PR c++/105667
            PR c++/121597
            PR c++/110961

    gcc/cp/ChangeLog:

            * cp-tree.h (TYPE_DECL_OPAQUE_ALIAS_P): Define.
            (any_lambdas_p): Declare.
            * decl.cc (grokdeclarator): Set TYPE_DECL_OPAQUE_ALIAS_P.
            * pt.cc (dependent_opaque_alias_p): Refine to check
            TYPE_DECL_OPAQUE_ALIAS_P.
            (tsubst_decl) <case TYPE_DECL>: Set TYPE_DECL_OPAQUE_ALIAS_P.
            (any_lambdas_p): New, factored out of...
            (regenerate_decl_from_template): ...this.  Call it.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp26/lambda-targ1.C: New test.
            * g++.dg/cpp2a/lambda-targ26.C: New test.
            * g++.dg/cpp2a/lambda-targ27.C: New test.
            * g++.dg/cpp2a/lambda-targ28.C: New test.
            * g++.dg/cpp2a/lambda-targ29.C: New test.
            * g++.dg/cpp2a/lambda-targ30.C: New test.
            * g++.dg/cpp2a/lambda-targ31.C: New test.
            * g++.dg/cpp2a/lambda-targ32.C: New test.

    Reviewed-by: Jason Merrill <jason@redhat.com>