[PATCH] c++, v2: Fix ICE during mangling of a conversion operator function template [PR126093]

[Jakub Jelinek]

On Tue, Aug 11, 2026 at 04:25:19PM -0400, Jason Merrill wrote:
> On 8/7/26 8:45 AM, Jakub Jelinek wrote:
> > We ICE when trying to mangle the TEMPLATE_DECL of a conversion operator,
> > because FNDECL_USED_AUTO macro requires FUNCTION_DECL, but here we
> > have a TEMPLATE_DECL instead.
> > In this case, DECL_CONV_FN_TYPE contains the right type, so this patch
> > just guards the FNDECL_USED_AUTO macro use on FUNCTION_DECLs.
> 
> Hmm, if it's valid to get a TEMPLATE_DECL here I think we want to
> STRIP_TEMPLATE earlier in the function to avoid the need for this; lots of
> other things here seem to assume we're looking at the inner decl.

Ok, here is a different patch then to use STRIP_TEMPLATE before calling
write_unqualified_name in the {class,function,variable,alias} template,
concept, namespace alias and namespace (for the last two STRIP_TEMPLATE
will do nothing, so I haven't moved it to a separate handling).

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2026-08-18  Jakub Jelinek  <ja...@redhat.com>

        PR c++/126093
        * mangle.cc (write_reflection): Call write_unqualified_name on
        STRIP_TEMPLATE (arg) rather than just arg.

        * g++.dg/reflect/mangle1.C: Add 2 new tests for reflections of
        conversion templates.

--- gcc/cp/mangle.cc.jj 2026-08-07 17:33:22.558549077 +0200
+++ gcc/cp/mangle.cc    2026-08-17 19:57:43.384028251 +0200
@@ -4302,7 +4302,7 @@ write_reflection (tree refl)
           || strcmp (prefix, "ns") == 0)
     {
       write_prefix (decl_mangling_context (arg));
-      write_unqualified_name (arg);
+      write_unqualified_name (STRIP_TEMPLATE (arg));
     }
   else if (strcmp (prefix, "ba") == 0)
     {
--- gcc/testsuite/g++.dg/reflect/mangle1.C.jj   2026-08-07 17:33:22.564549003 
+0200
+++ gcc/testsuite/g++.dg/reflect/mangle1.C      2026-08-17 19:56:23.372630344 
+0200
@@ -15,6 +15,10 @@ struct S : B {
   int : 0;
   static int var;
 };
+struct Q {
+  template <typename T>
+  operator T () { return T (); }
+};
 struct W { union {}; union {}; union {}; union {}; };
 template <auto> struct TCls {};
 template <auto> void TFn ();
@@ -65,6 +69,10 @@ namespace NS2 {
   struct Z {
   };
   struct AA { int a, b; };
+  struct Q {
+    template <int N>
+    operator int () { return N; }
+  };
 }
 
 constexpr auto ctx = std::meta::access_context::current ();
@@ -147,6 +155,8 @@ baz (int x)
   bar <241, ^^NS2::TCls> (); // class template
   bar <250, ^^TFn> (); // function template
   bar <251, ^^NS2::TFn> (); // function template
+  bar <252, members_of (^^Q, ctx)[0]> (); // function template
+  bar <253, members_of (^^NS2::Q, ctx)[0]> (); // function template
   bar <260, ^^TVar> (); // variable template
   bar <261, ^^NS2::TVar> (); // variable template
   bar <270, ^^TAlias> (); // alias template
@@ -239,6 +249,8 @@ baz (int x)
 // { dg-final { scan-assembler "_Z3barILi241ELDmct3NS24TClsEEvv" } }
 // { dg-final { scan-assembler "_Z3barILi250ELDmft3TFnEEvv" } }
 // { dg-final { scan-assembler "_Z3barILi251ELDmft3NS23TFnEEvv" } }
+// { dg-final { scan-assembler "_Z3barILi252ELDmft1QcvT_EEvv" } }
+// { dg-final { scan-assembler "_Z3barILi253ELDmft3NS21QcviEEvv" } }
 // { dg-final { scan-assembler "_Z3barILi260ELDmvt4TVarEEvv" } }
 // { dg-final { scan-assembler "_Z3barILi261ELDmvt3NS24TVarEEvv" } }
 // { dg-final { scan-assembler "_Z3barILi270ELDmat6TAliasEEvv" } }


        Jakub