[Bug target/103622] ICE: Segmentation fault (in altivec_resolve_new_overloaded_builtin)

["linkw at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103622

--- Comment #3 from Kewen Lin <linkw at gcc dot gnu.org> ---

> One thought seems to check instance->fntype first and take (skip) it as
> mismatch if it's NULL.

This looks like a bad idea, to use long double as the type instead of float128
when type float128 isn't supported might be better.

diff --git a/gcc/config/rs6000/rs6000-gen-builtins.c
b/gcc/config/rs6000/rs6000-gen-builtins.c
index d2e9c4ce547..2b87eef1412 100644
--- a/gcc/config/rs6000/rs6000-gen-builtins.c
+++ b/gcc/config/rs6000/rs6000-gen-builtins.c
@@ -2473,6 +2473,39 @@ write_fntype_init (char *str)
       fprintf (init_file, ",\n\t\t\t\t");
     }
   fprintf (init_file, "NULL_TREE);\n");
+
+  /* Use long_double_type_node instead if float128_type_node isn't
+     supported, it's to avoid unexpected function types.  */
+  if (tf_found)
+    {
+      char *buf1 = strdup (str);
+      fprintf (init_file, "  else\n  ");
+      fprintf (init_file, "  %s\n    = build_function_type_list (", buf1);
+      tok = strtok (buf1, "_");
+      if (!strcmp ("tf", tok))
+       write_type_node ("ld", true);
+      else
+       write_type_node (tok, true);
+      tok = strtok (0, "_");
+      tok = strtok (0, "_");
+      if (tok)
+       fprintf (init_file, ",\n\t\t\t\t");
+
+      /* Note:  A function with no arguments ends with '_ftype_v'.  */
+      while (tok && strcmp (tok, "v"))
+       {
+         if (!strcmp ("tf", tok))
+           write_type_node ("ld", true);
+         else
+           write_type_node (tok, true);
+         tok = strtok (0, "_");
+         fprintf (init_file, ",\n\t\t\t\t");
+       }
+      fprintf (init_file, "NULL_TREE);\n");
+
+      free (buf1);
+    }
+
   free (buf);
 }

The above hacking make the segfault gone and it will emit:

test.c: In function ‘get_float128_exponent’:
test.c:6:5: error: ‘__builtin_vsx_scalar_extract_expq’ requires ISA 3.0 IEEE
128-bit floating point
    6 |     return __builtin_vec_scalar_extract_exp (a);
      |     ^~~~~~
test.c:6:5: note: overloaded builtin ‘__builtin_vec_scalar_extract_exp’ is
implemented by builtin ‘__builtin_vsx_scalar_extract_expq’