[Bug c++/117397] New: [modules] ICE in binding_cmp with imported deduction guide

[nshead at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117397

            Bug ID: 117397
           Summary: [modules] ICE in binding_cmp with imported deduction
                    guide
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: nshead at gcc dot gnu.org
  Target Milestone: ---

Consider the following:


  // a.h
  template <typename T> struct S;
  template <typename T> S(T) -> S<T>;

  // b.h
  import "a.h";
  template <typename T> struct S;

  // m.cpp
  module;
  template <typename T> struct S;
  export module M;
  import "b.h";
  S<int> foo();


Doing "g++ -fmodules-ts -Wno-global-module -S a.h b.h m.cpp" results in:

m.cpp:3:8: internal compiler error: in binding_cmp, at cp/module.cc:13838
    3 | export module M;
      |        ^~~~~~
0x3bd6ca0 internal_error(char const*, ...)
        ../../gcc/gcc/diagnostic-global-context.cc:518
0x3ba363c fancy_abort(char const*, int, char const*)
        ../../gcc/gcc/diagnostic.cc:1580
0x10bcd9f binding_cmp
        ../../gcc/gcc/cp/module.cc:13838
0x3c2ee06 cmp1<sort_ctx>
        ../../gcc/gcc/sort.cc:151
0x3c2e73e netsort<sort_ctx>
        ../../gcc/gcc/sort.cc:168
0x3c2df7d mergesort<sort_ctx>
        ../../gcc/gcc/sort.cc:205
0x3c2dc4a gcc_qsort(void*, unsigned long, unsigned long, int (*)(void const*,
void const*))
        ../../gcc/gcc/sort.cc:268
0x10bd468 depset::hash::finalize_dependencies()
        ../../gcc/gcc/cp/module.cc:13922
0x10cb34f module_state::write_begin(elf_out*, cpp_reader*,
module_state_config&, unsigned int&)
        ../../gcc/gcc/cp/module.cc:18447
0x10d2e53 finish_module_processing(cpp_reader*)
        ../../gcc/gcc/cp/module.cc:20918
0xff49ff c_parse_final_cleanups()
        ../../gcc/gcc/cp/decl2.cc:5543
0x13c8de2 c_common_parse_file()
        ../../gcc/gcc/c-family/c-opts.cc:1370
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See <https://gcc.gnu.org/bugs/> for instructions.


This appears to be caused by duplicate deduction guides being found by name
lookup when exporting.  The following patch fixes the ICE, but might just be
hiding a more general issue, since I would think that name lookup should have
deduplicated these entries:

diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
index 297ef85bb1e..7133e754271 100644
--- a/gcc/cp/module.cc
+++ b/gcc/cp/module.cc
@@ -13684,19 +13684,26 @@ depset::hash::add_deduction_guides (tree decl)
   if (guides == error_mark_node)
     return;

-  /* We have bindings to add.  */
+  /* We have bindings to add.  Note there could be duplicates in
+     the list of entities found by name lookup.  */
   depset *binding = make_binding (ns, name);
   add_namespace_context (binding, ns);

   depset **slot = binding_slot (ns, name, /*insert=*/true);
   *slot = binding;

-  for (lkp_iterator it (guides); it; ++it)
+  hash_table<named_decl_hash> seen_deps (10);
+  for (tree t : lkp_range (guides))
     {
-      gcc_checking_assert (!TREE_VISITED (*it));
-      depset *dep = make_dependency (*it, EK_FOR_BINDING);
-      binding->deps.safe_push (dep);
-      dep->deps.safe_push (binding);
+      tree *slot = seen_deps.find_slot (t, INSERT);
+      if (!*slot)
+        {
+          gcc_checking_assert (!TREE_VISITED (t));
+          depset *dep = make_dependency (t, EK_FOR_BINDING);
+          binding->deps.safe_push (dep);
+          dep->deps.safe_push (binding);
+          *slot = t;
+        }
     }
 }