On 1/8/24 10:27, Patrick Palka wrote:
On Mon, 8 Jan 2024, Nathaniel Shead wrote:
On Thu, Jan 04, 2024 at 03:39:15PM -0500, Patrick Palka wrote:
On Sun, 3 Dec 2023, Nathaniel Shead wrote:
The TYPE_DECL_SUPPRESS_DEBUG and DECL_EXTERNAL flags use the same
underlying bit. This is causing confusion when attempting to determine
the interface for a streamed-in class type, since the modules code
currently assumes that all DECL_EXTERNAL types are extern templates.
However, when -g is specified then TYPE_DECL_SUPPRESS_DEBUG (and hence
DECL_EXTERNAL) is marked on various other kinds of declarations, such as
vtables, which causes them to never be emitted.
But a vtable isn't a TYPE_DECL?
I suspect what you mean is that maybe_suppress_debug_info is setting
TYPE_DECL_SUPPRESS_DEBUG to try to avoid duplication of debug info for
classes with vtables, and then the modules code is wrongly assuming that
you can check DECL_EXTERNAL for TYPE_DECL, and that it's set only if
CLASSTYPE_INTERFACE_ONLY is also set, which is wrong in this case, so we
avoid emitting the vtable or anything else for that class.
It seems unnecessary to start setting DECL_EXTERNAL on the TYPE_DECL to
mean the exact same thing as CLASSTYPE_INTERFACE_ONLY. Rather, the
modules code should stop trying to check DECL_EXTERNAL on a TYPE_DECL.
Under what circumstances does it make sense for CLASSTYPE_INTERFACE_ONLY
to be set in the context of modules, anyway? We probably want to
propagate it for things in the global module so that various libstdc++
explicit instantiations work the same with import std.
For an class imported from a named module, this ties into the earlier
discussion about vtables and inlines that hasn't resolved yet in the ABI
committee. But it's certainly significantly interface-like. And I
would expect maybe_suppress_debug_info to suppress the debug info for
such a class on the assumption that the module unit has the needed debug
info.
Jason
