https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119608
--- Comment #2 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Nathaniel Shead <nsh...@gcc.gnu.org>: https://gcc.gnu.org/g:b8e8829cfb73d7aa009d387ab09bdbab221930d7 commit r15-9217-gb8e8829cfb73d7aa009d387ab09bdbab221930d7 Author: Nathaniel Shead <nathanielosh...@gmail.com> Date: Fri Apr 4 11:56:53 2025 +1100 c++/modules: Fix divergence in streaming/non-streaming tree walks [PR119608] Modules streaming walks decls multiple times, first as a non-streaming walk to find dependencies, and then later to actually emit the decls. The first walk needs to be done to note locations that will be emitted. In the PR we are getting a checking ICE because we are streaming a decl that we didn't initially walk when collecting dependencies, so the location isn't in the noted locations map. This is because in decl_node we have a branch where a PARM_DECL that hasn't previously been referenced gets walked by value only if 'streaming_p ()' is true. The true root cause here is that the decltype(v) in the testcase refers to a different PARM_DECL from the one in the declaration that we're streaming; it's the PARM_DECL from the initial forward-declaration, that we're not streaming. A proper fix would be to ensure that it gets remapped to the decl in the definition we're actually emitting, but for now this workaround fixes the bug (and any other bugs that might manifest similarly). PR c++/119608 gcc/cp/ChangeLog: * module.cc (trees_out::decl_node): Maybe require by-value walking not just when streaming. gcc/testsuite/ChangeLog: * g++.dg/modules/pr119608_a.C: New test. * g++.dg/modules/pr119608_b.C: New test. Signed-off-by: Nathaniel Shead <nathanielosh...@gmail.com> Reviewed-by: Jason Merrill <ja...@redhat.com>
