[PATCH] debug/108772 - ICE with late debug generated with -flto

[Richard Biener <rguenther@suse.de>]

When combining -g1 with -flto we run into the DIE location annotation
machinery for globals calling dwarf2out_late_global_decl but not
having any early generated DIE for function scope statics.  In
this process we'd generate a limbo DIE since also the function scope
doesn't have any early generated DIE.  The limbo handling then tries
to force a DIE for the context chain which ultimatively fails and
ICEs at the std namespace decl because at -g1 we don't represent that.

The following avoids this situation by making sure to never generate
any limbo DIEs from dwarf2out_late_global_decl in the in_lto_p path
but instead for function scope globals rely on DIE generation for
the function to output a DIE for the local static (which doesn't
happen for -g1).

I explored a lot of other options to fix this but in the end this
seems to be the most spot-on fix with the least risk of unwanted
effects.

LTO bootstrapped on x86_64-unknown-linux-gnu (running into PR108984),
bootstrapped and tested on x86_64-unknown-linux-gnu.

OK?

Thanks,
Richard.

	PR debug/108772
	* dwarf2out.cc (dwarf2out_late_global_decl): Do not
	generate a DIE for a function scope static when we do
	not have a DIE for the function already.

	* g++.dg/lto/pr108772_0.C: New testcase.
---
 gcc/dwarf2out.cc                      | 12 ++++++-
 gcc/testsuite/g++.dg/lto/pr108772_0.C | 46 +++++++++++++++++++++++++++
 2 files changed, 57 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/lto/pr108772_0.C

diff --git a/gcc/dwarf2out.cc b/gcc/dwarf2out.cc
index 1f39df3b1e2..6f457ed4472 100644
--- a/gcc/dwarf2out.cc
+++ b/gcc/dwarf2out.cc
@@ -27283,7 +27283,17 @@ dwarf2out_late_global_decl (tree decl)
          was not enabled at compile-time or the target doesn't support
 	 the LTO early debug scheme.  */
       if (! die && in_lto_p)
-	dwarf2out_decl (decl);
+	{
+	  /* Avoid relying on the ability to force context DIEs for
+	     local entities.  Instead if the function context was not
+	     instantiated yet defer to it producing its local DIEs.
+	     See PR108772.  */
+	  dw_die_ref context_die = comp_unit_die ();
+	  if (local_function_static (decl))
+	    context_die = lookup_decl_die (DECL_CONTEXT (decl));
+	  if (context_die)
+	    dwarf2out_decl (decl);
+	}
       else if (die)
 	{
 	  /* We get called via the symtab code invoking late_global_decl
diff --git a/gcc/testsuite/g++.dg/lto/pr108772_0.C b/gcc/testsuite/g++.dg/lto/pr108772_0.C
new file mode 100644
index 00000000000..81f15a90a3e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/lto/pr108772_0.C
@@ -0,0 +1,46 @@
+// { dg-lto-do link }
+// { dg-require-effective-target shared }
+// { dg-require-effective-target fpic }
+// { dg-lto-options { "-flto -fPIC -shared -O1 -fimplicit-constexpr -g1" } }
+// { dg-extra-ld-options "-shared" }
+
+namespace std {
+struct _Sp_counted_base {
+  virtual void *_M_get_deleter(const int &);
+};
+bool _S_eq(int);
+struct _Sp_make_shared_tag {
+  static const int &_S_ti() {
+    static constexpr char __tag{};
+    return reinterpret_cast<const int &>(__tag);
+  }
+};
+struct _Impl {
+  _Impl(int);
+};
+int _Sp_counted_ptr_inplace___a;
+struct _Sp_counted_ptr_inplace : _Sp_counted_base {
+  _Sp_counted_ptr_inplace() : _M_impl(_Sp_counted_ptr_inplace___a) {}
+  void *_M_get_deleter(const int &__ti) {
+    auto __ptr(_M_ptr());
+    &__ti == &_Sp_make_shared_tag::_S_ti() || _S_eq(__ti);
+    return __ptr;
+  }
+  int *_M_ptr();
+  _Impl _M_impl;
+};
+struct __shared_count {
+  __shared_count(int, int) { _Sp_counted_ptr_inplace(); }
+};
+int _M_ptr;
+struct __shared_ptr {
+  template <typename _Alloc>
+  __shared_ptr(_Alloc __tag) : _M_refcount(_M_ptr, __tag) {}
+  __shared_count _M_refcount;
+};
+int shared_ptr___tag;
+struct shared_ptr : __shared_ptr {
+  shared_ptr() : __shared_ptr(shared_ptr___tag) {}
+};
+void ArgEq() { shared_ptr(); }
+} // namespace std
-- 
2.35.3