I see the following ICE, it's reduced from icewm package:

$ cat 1.ii
class YWMApp {
public:
  YWMApp(const char *);
};
class YIcon {
public:
  static int getIcon(const char *);
};
YWMApp::YWMApp(const char *) { YIcon::getIcon(""); }
char main_overrideTheme;
main() { YWMApp app(&main_overrideTheme); }

$ cat 2.ii
class mstring {
  public:
  int compareTo(const mstring &) const;
};
int mstring::compareTo(const mstring &) const {}

class refcounted {
public:
  virtual void __destroy();
};
class YIcon;
template < class > class ref {
  YIcon *ptr;

public:
  ~ref() { ptr->__destroy(); }
};
class upath {
public:
  upath(const char *);
  mstring path() { return fPath; }
  mstring fPath;
};
int cacheFind_r;
class YIcon : public refcounted {
  ref< YIcon > getIcon(const char *);
  int cacheFind(upath);

public:
  ref< YIcon > *getItemPtr();
} iconCache;
int YIcon::cacheFind(upath name) {
  ref< YIcon > __trans_tmp_2;
  while (cacheFind_r) {
    {
      __trans_tmp_2 = *getItemPtr();
    }
    ref< YIcon > found = __trans_tmp_2;
    mstring __trans_tmp_1;
    name.path().compareTo(__trans_tmp_1);
  }
}
ref< YIcon > YIcon::getIcon(const char *name) { cacheFind(name); }

$ g++ -O2 -fPIC 1.ii 2.ii -flto=16
1.ii:11:1: warning: ISO C++ forbids declaration of ‘main’ with no type [-Wreturn-type]
   11 | main() { YWMApp app(&main_overrideTheme); }
      | ^~~~
2.ii: In member function ‘int mstring::compareTo(const mstring&) const’:
2.ii:5:48: warning: no return statement in function returning non-void [-Wreturn-type]
    5 | int mstring::compareTo(const mstring &) const {}
      |                                                ^
2.ii: In destructor ‘ref< <template-parameter-1-1> >::~ref()’:
2.ii:16:15: warning: invalid use of incomplete type ‘class YIcon’
   16 |   ~ref() { ptr->__destroy(); }
      |               ^~
2.ii:11:7: note: forward declaration of ‘class YIcon’
   11 | class YIcon;
      |       ^~~~~
2.ii: In member function ‘int YIcon::cacheFind(upath)’:
2.ii:42:1: warning: no return statement in function returning non-void [-Wreturn-type]
   42 | }
      | ^
2.ii: In member function ‘ref<YIcon> YIcon::getIcon(const char*)’:
2.ii:43:66: warning: no return statement in function returning non-void [-Wreturn-type]
   43 | ref< YIcon > YIcon::getIcon(const char *name) { cacheFind(name); }
      |                                                                  ^
1.ii:7:14: warning: ‘getIcon’ violates the C++ One Definition Rule [-Wodr]
    7 |   static int getIcon(const char *);
      |              ^
2.ii:43:14: note: ‘getIcon’ was previously declared here
   43 | ref< YIcon > YIcon::getIcon(const char *name) { cacheFind(name); }
      |              ^
2.ii:43:14: note: code may be misoptimized unless ‘-fno-strict-aliasing’ is used
during IPA pass: inline
2.ii: In function ‘getIcon.constprop.isra’:
2.ii:43:14: internal compiler error: in gimple_phi_arg, at gimple.h:4406
   43 | ref< YIcon > YIcon::getIcon(const char *name) { cacheFind(name); }
      |              ^
0x639113 gimple_phi_arg
	/home/marxin/Programming/gcc/gcc/gimple.h:4406
0x639113 gimple_phi_arg
	/home/marxin/Programming/gcc/gcc/gimple.h:4414
0x639113 gimple_phi_arg_def
	/home/marxin/Programming/gcc/gcc/gimple.h:4457
0x639113 walk_ssa_copies
	/home/marxin/Programming/gcc/gcc/ipa-polymorphic-call.c:835
0xac7f71 ipa_polymorphic_call_context::ipa_polymorphic_call_context(tree_node*, tree_node*, gimple*, tree_node**)
	/home/marxin/Programming/gcc/gcc/ipa-polymorphic-call.c:898
0xa00ed6 possible_polymorphic_call_targets(tree_node*, gimple*, bool*, void**)
	/home/marxin/Programming/gcc/gcc/ipa-utils.h:134
0xa00ed6 gimple_fold_call
	/home/marxin/Programming/gcc/gcc/gimple-fold.c:4348
0xa0176b fold_stmt_1
	/home/marxin/Programming/gcc/gcc/gimple-fold.c:5112
0xd5dea6 fold_marked_statements
	/home/marxin/Programming/gcc/gcc/tree-inline.c:5288
0xd6cbd1 optimize_inline_calls(tree_node*)
	/home/marxin/Programming/gcc/gcc/tree-inline.c:5369
0x15fac04 inline_transform(cgraph_node*)
	/home/marxin/Programming/gcc/gcc/ipa-inline-transform.c:720
0xc0eeaa execute_one_ipa_transform_pass
	/home/marxin/Programming/gcc/gcc/passes.c:2231
0xc0eeaa execute_all_ipa_transforms(bool)
	/home/marxin/Programming/gcc/gcc/passes.c:2270
0x897561 cgraph_node::expand()
	/home/marxin/Programming/gcc/gcc/cgraphunit.c:2189
0x89853b expand_all_functions
	/home/marxin/Programming/gcc/gcc/cgraphunit.c:2335
0x89853b symbol_table::compile()
	/home/marxin/Programming/gcc/gcc/cgraphunit.c:2685
0x7f49e9 lto_main()
	/home/marxin/Programming/gcc/gcc/lto/lto.c:658