c++, v3: Emit fundamental tinfos for _Float16/decltype(0.0bf16) types on ia32 with -mno-sse2 [PR108883]

_Float16 and decltype(0.0bf16) types are on x86 supported only with
-msse2.  On x86_64 that is the default, but on ia32 it is not.
We should still emit fundamental type tinfo for those types in
libsupc++.a/libstdc++.*, regardless of whether libsupc++/libstdc++
is compiled with -msse2 or not, as user programs can be compiled
with different ISA flags from libsupc++/libstdc++ and if they
are compiled with -msse2 and use std::float16_t or std::bfloat16_t
and need RTTI for it, it should work out of the box.  Furthermore,
libstdc++ ABI on ia32 shouldn't depend on whether the library
is compiled with -mno-sse or -msse2.

Unfortunately, just hacking up libsupc++ Makefile/configure so that
a single source is compiled with -msse2 isn't appropriate, because
that TU emits also code and the code should be able to run on CPUs
which libstdc++ supports.  We could add [[gnu::attribute ("no-sse2")]]
there perhaps conditionally, but it all gets quite ugly.

The following patch instead adds a target hook which allows the backend
to temporarily tweak registered types such that emit_support_tinfos
emits whatever is needed.

Additionally, it makes emit_support_tinfos_1 call emit_tinfo_decl
immediately, so that temporarily created dummy types for emit_support_tinfo
purposes only can be nullified again afterwards.  And removes the
previous fallback_* types used for dfloat*_type_node tinfos even when
decimal types aren't supported.

2023-03-03  Jakub Jelinek  <jakub@redhat.com>

	PR target/108883
gcc/
	* target.h (emit_support_tinfos_callback): New typedef.
	* targhooks.h (default_emit_support_tinfos): Declare.
	* targhooks.cc (default_emit_support_tinfos): New function.
	* target.def (emit_support_tinfos): New target hook.
	* doc/tm.texi.in (emit_support_tinfos): Document it.
	* doc/tm.texi: Regenerated.
	* config/i386/i386.cc (ix86_emit_support_tinfos): New function.
	(TARGET_EMIT_SUPPORT_TINFOS): Redefine.
gcc/cp/
	* cp-tree.h (enum cp_tree_index): Remove CPTI_FALLBACK_DFLOAT*_TYPE
	enumerators.
	(fallback_dfloat32_type, fallback_dfloat64_type,
	fallback_dfloat128_type): Remove.
	* rtti.cc (emit_support_tinfo_1): If not emitted already, call
	emit_tinfo_decl and remove from unemitted_tinfo_decls right away.
	(emit_support_tinfos): Move &dfloat*_type_node from fundamentals array
	into new fundamentals_with_fallback array.  Call emit_support_tinfo_1
	on elements of that array too, with the difference that if
	the type is NULL, use a fallback REAL_TYPE for it temporarily.
	Drop the !targetm.decimal_float_supported_p () handling.  Call
	targetm.emit_support_tinfos at the end.
	* mangle.cc (write_builtin_type): Remove references to
	fallback_dfloat*_type.  Handle bfloat16_type_node mangling.

gcc/config/i386/i386.cc

@@ -22775,6 +22775,27 @@ ix86_mangle_type (const_tree type)
     }
 }
 
+/* Create C++ tinfo symbols for only conditionally available fundamental
+   types.  */
+
+static void
+ix86_emit_support_tinfos (emit_support_tinfos_callback callback)
+{
+  extern tree ix86_float16_type_node;
+  extern tree ix86_bf16_type_node;
+
+  if (!TARGET_SSE2)
+    {
+      gcc_checking_assert (!float16_type_node && !bfloat16_type_node);
+      float16_type_node = ix86_float16_type_node;
+      bfloat16_type_node = ix86_bf16_type_node;
+      callback (float16_type_node);
+      callback (bfloat16_type_node);
+      float16_type_node = NULL_TREE;
+      bfloat16_type_node = NULL_TREE;
+    }
+}
+
 static GTY(()) tree ix86_tls_stack_chk_guard_decl;
 
 static tree
@@ -24954,6 +24975,9 @@ ix86_libgcc_floating_mode_supported_p
 #undef TARGET_MANGLE_TYPE
 #define TARGET_MANGLE_TYPE ix86_mangle_type
 
+#undef TARGET_EMIT_SUPPORT_TINFOS
+#define TARGET_EMIT_SUPPORT_TINFOS ix86_emit_support_tinfos
+
 #undef TARGET_STACK_PROTECT_GUARD
 #define TARGET_STACK_PROTECT_GUARD ix86_stack_protect_guard
 

gcc/cp/cp-tree.h

@@ -235,10 +235,6 @@ enum cp_tree_index
 
     CPTI_PSEUDO_CONTRACT_VIOLATION,
 
-    CPTI_FALLBACK_DFLOAT32_TYPE,
-    CPTI_FALLBACK_DFLOAT64_TYPE,
-    CPTI_FALLBACK_DFLOAT128_TYPE,
-
     CPTI_MAX
 };
 
@@ -397,13 +393,6 @@ extern GTY(()) tree cp_global_trees[CPTI_MAX];
    access nodes in tree.h.  */
 
 #define access_default_node		null_node
-
-/* Variant of dfloat{32,64,128}_type_node only used for fundamental
-   rtti purposes if DFP is disabled.  */
-#define fallback_dfloat32_type		cp_global_trees[CPTI_FALLBACK_DFLOAT32_TYPE]
-#define fallback_dfloat64_type		cp_global_trees[CPTI_FALLBACK_DFLOAT64_TYPE]
-#define fallback_dfloat128_type		cp_global_trees[CPTI_FALLBACK_DFLOAT128_TYPE]
-
 
 #include "name-lookup.h"
 

gcc/cp/mangle.cc

@@ -2732,11 +2732,11 @@ write_builtin_type (tree type)
 	write_char ('d');
       else if (type == long_double_type_node)
 	write_char ('e');
-      else if (type == dfloat32_type_node || type == fallback_dfloat32_type)
+      else if (type == dfloat32_type_node)
 	write_string ("Df");
-      else if (type == dfloat64_type_node || type == fallback_dfloat64_type)
+      else if (type == dfloat64_type_node)
 	write_string ("Dd");
-      else if (type == dfloat128_type_node || type == fallback_dfloat128_type)
+      else if (type == dfloat128_type_node)
 	write_string ("De");
       else if (type == float16_type_node)
 	write_string ("DF16_");
@@ -2752,6 +2752,8 @@ write_builtin_type (tree type)
 	write_string ("DF64x");
       else if (type == float128x_type_node)
 	write_string ("DF128x");
+      else if (type == bfloat16_type_node)
+	write_string ("DF16b");
       else
 	gcc_unreachable ();
       break;

gcc/cp/rtti.cc

@@ -1577,6 +1577,15 @@ emit_support_tinfo_1 (tree bltn)
 	  gcc_assert (TREE_PUBLIC (tinfo) && !DECL_COMDAT (tinfo));
 	  DECL_INTERFACE_KNOWN (tinfo) = 1;
 	}
+
+      /* Emit it right away if not emitted already.  */
+      if (DECL_INITIAL (tinfo) == NULL_TREE)
+	{
+	  gcc_assert (unemitted_tinfo_decls->last () == tinfo);
+	  bool ok = emit_tinfo_decl (tinfo);
+	  gcc_assert (ok);
+	  unemitted_tinfo_decls->pop ();
+	}
     }
 }
 
@@ -1602,12 +1611,18 @@ emit_support_tinfos (void)
     &long_integer_type_node, &long_unsigned_type_node,
     &long_long_integer_type_node, &long_long_unsigned_type_node,
     &float_type_node, &double_type_node, &long_double_type_node,
-    &dfloat32_type_node, &dfloat64_type_node, &dfloat128_type_node,
     &bfloat16_type_node, &float16_type_node, &float32_type_node,
     &float64_type_node, &float128_type_node, &float32x_type_node,
     &float64x_type_node, &float128x_type_node, &nullptr_type_node,
     0
   };
+  /* Similar, but for floating point types only which should get type info
+     regardless whether they are non-NULL or NULL.  */
+  static tree *const fundamentals_with_fallback[] =
+  {
+    &dfloat32_type_node, &dfloat64_type_node, &dfloat128_type_node,
+    0
+  };
   int ix;
 
   /* Look for a defined class.  */
@@ -1627,8 +1642,20 @@ emit_support_tinfos (void)
   location_t saved_loc = input_location;
   input_location = BUILTINS_LOCATION;
   doing_runtime = 1;
+  tree fallback = NULL_TREE;
   for (ix = 0; fundamentals[ix]; ix++)
     emit_support_tinfo_1 (*fundamentals[ix]);
+  for (ix = 0; fundamentals_with_fallback[ix]; ix++)
+    if (*fundamentals_with_fallback[ix])
+      emit_support_tinfo_1 (*fundamentals_with_fallback[ix]);
+    else
+      {
+	if (fallback == NULL_TREE)
+	  fallback = make_node (REAL_TYPE);
+	*fundamentals_with_fallback[ix] = fallback;
+	emit_support_tinfo_1 (fallback);
+	*fundamentals_with_fallback[ix] = NULL_TREE;
+      }
   for (ix = 0; ix < NUM_INT_N_ENTS; ix ++)
     if (int_n_enabled_p[ix])
       {
@@ -1637,20 +1664,10 @@ emit_support_tinfos (void)
       }
   for (tree t = registered_builtin_types; t; t = TREE_CHAIN (t))
     emit_support_tinfo_1 (TREE_VALUE (t));
-  /* For compatibility, emit DFP typeinfos even when DFP isn't enabled,
-     because we've emitted that in the past.  */
-  if (!targetm.decimal_float_supported_p ())
-    {
-      gcc_assert (dfloat32_type_node == NULL_TREE
-		  && dfloat64_type_node == NULL_TREE
-		  && dfloat128_type_node == NULL_TREE);
-      fallback_dfloat32_type = make_node (REAL_TYPE);
-      fallback_dfloat64_type = make_node (REAL_TYPE);
-      fallback_dfloat128_type = make_node (REAL_TYPE);
-      emit_support_tinfo_1 (fallback_dfloat32_type);
-      emit_support_tinfo_1 (fallback_dfloat64_type);
-      emit_support_tinfo_1 (fallback_dfloat128_type);
-    }
+
+  /* Emit additional typeinfos as requested by target.  */
+  targetm.emit_support_tinfos (emit_support_tinfo_1);
+
   input_location = saved_loc;
 }
 

gcc/doc/tm.texi

@@ -1525,6 +1525,15 @@ appropriate for a target that does not define any new fundamental
 types.
 @end deftypefn
 
+@deftypefn {Target Hook} void TARGET_EMIT_SUPPORT_TINFOS (emit_support_tinfos_callback @var{callback})
+If your target defines any fundamental types which depend on ISA flags,
+they might need C++ tinfo symbols in libsupc++/libstdc++ regardless of
+ISA flags the library is compiled with.
+This hook allows creating tinfo symbols even for those cases, by temporarily
+creating each corresponding fundamental type trees, calling the
+@var{callback} function on it and setting the type back to @code{nullptr}.
+@end deftypefn
+
 @node Type Layout
 @section Layout of Source Language Data Types
 

gcc/doc/tm.texi.in

@@ -1286,6 +1286,8 @@ pattern needs to support both a 32- and a 64-bit mode.
 
 @hook TARGET_MANGLE_TYPE
 
+@hook TARGET_EMIT_SUPPORT_TINFOS
+
 @node Type Layout
 @section Layout of Source Language Data Types
 

gcc/target.def

@@ -2606,6 +2606,19 @@ types.",
  const char *, (const_tree type),
  hook_constcharptr_const_tree_null)
 
+/* Temporarily add conditional target specific types for the purpose of
+   emitting C++ fundamental type tinfos.  */
+DEFHOOK
+(emit_support_tinfos,
+ "If your target defines any fundamental types which depend on ISA flags,\n\
+they might need C++ tinfo symbols in libsupc++/libstdc++ regardless of\n\
+ISA flags the library is compiled with.\n\
+This hook allows creating tinfo symbols even for those cases, by temporarily\n\
+creating each corresponding fundamental type trees, calling the\n\
+@var{callback} function on it and setting the type back to @code{nullptr}.",
+ void, (emit_support_tinfos_callback callback),
+ default_emit_support_tinfos)
+
 /* Make any adjustments to libfunc names needed for this target.  */
 DEFHOOK
 (init_libfuncs,

gcc/target.h

@@ -260,6 +260,8 @@ enum poly_value_estimate_kind
   POLY_VALUE_LIKELY
 };
 
+typedef void (*emit_support_tinfos_callback) (tree);
+
 extern bool verify_type_context (location_t, type_context_kind, const_tree,
 				 bool = false);
 

gcc/targhooks.cc

@@ -752,6 +752,11 @@ default_builtin_reciprocal (tree)
   return NULL_TREE;
 }
 
+void
+default_emit_support_tinfos (emit_support_tinfos_callback)
+{
+}
+
 bool
 hook_bool_CUMULATIVE_ARGS_arg_info_false (cumulative_args_t,
 					  const function_arg_info &)

gcc/targhooks.h

@@ -98,6 +98,8 @@ extern int default_builtin_vectorization_cost (enum vect_cost_for_stmt, tree, in
 
 extern tree default_builtin_reciprocal (tree);
 
+extern void default_emit_support_tinfos (emit_support_tinfos_callback);
+
 extern HOST_WIDE_INT default_static_rtx_alignment (machine_mode);
 extern HOST_WIDE_INT default_constant_alignment (const_tree, HOST_WIDE_INT);
 extern HOST_WIDE_INT constant_alignment_word_strings (const_tree,