c-family: Implement __has_feature and __has_extension [PR60512]

This patch implements clang's __has_feature and __has_extension in GCC.
Currently the patch aims to implement all documented features (and some
undocumented ones) following the documentation at
https://clang.llvm.org/docs/LanguageExtensions.html with the exception
of the legacy features for C++ type traits.  These are omitted, since as
the clang documentation notes, __has_builtin is the correct "modern" way
to query for these (which GCC already implements).

gcc/c-family/ChangeLog:

	PR c++/60512
	* c-common.cc (struct hf_feature_info): New.
	(c_common_register_feature): New.
	(init_has_feature): New.
	(has_feature_p): New.
	* c-common.h (c_common_has_feature): New.
	(c_family_register_lang_features): New.
	(c_common_register_feature): New.
	(has_feature_p): New.
	* c-lex.cc (init_c_lex): Plumb through has_feature callback.
	(c_common_has_builtin): Generalize and move common part ...
	(c_common_lex_availability_macro): ... here.
	(c_common_has_feature): New.
	* c-ppoutput.cc (init_pp_output): Plumb through has_feature.

gcc/c/ChangeLog:

	PR c++/60512
	* c-lang.cc (c_family_register_lang_features): New.
	* c-objc-common.cc (struct c_feature_info): New.
	(c_register_features): New.
	* c-objc-common.h (c_register_features): New.

gcc/cp/ChangeLog:

	PR c++/60512
	* cp-lang.cc (c_family_register_lang_features): New.
	* cp-objcp-common.cc (struct cp_feature_selector): New.
	(cp_feature_selector::has_feature): New.
	(struct cp_feature_info): New.
	(cp_register_features): New.
	* cp-objcp-common.h (cp_register_features): New.

gcc/ChangeLog:

	PR c++/60512
	* doc/cpp.texi: Document __has_{feature,extension}.

gcc/objc/ChangeLog:

	PR c++/60512
	* objc-act.cc (struct objc_feature_info): New.
	(objc_nonfragile_abi_p): New.
	(objc_common_register_features): New.
	* objc-act.h (objc_common_register_features): New.
	* objc-lang.cc (c_family_register_lang_features): New.

gcc/objcp/ChangeLog:

	PR c++/60512
	* objcp-lang.cc (c_family_register_lang_features): New.

libcpp/ChangeLog:

	PR c++/60512
	* include/cpplib.h (struct cpp_callbacks): Add has_feature.
	(enum cpp_builtin_type): Add BT_HAS_{FEATURE,EXTENSION}.
	* init.cc: Add __has_{feature,extension}.
	* macro.cc (_cpp_builtin_macro_text): Handle
	BT_HAS_{FEATURE,EXTENSION}.

gcc/testsuite/ChangeLog:

	PR c++/60512
	* c-c++-common/has-feature-common.c: New test.
	* c-c++-common/has-feature-pedantic.c: New test.
	* g++.dg/ext/has-feature.C: New test.
	* gcc.dg/asan/has-feature-asan.c: New test.
	* gcc.dg/has-feature.c: New test.
	* gcc.dg/ubsan/has-feature-ubsan.c: New test.
	* obj-c++.dg/has-feature.mm: New test.
	* objc.dg/has-feature.m: New test.

Co-Authored-By: Iain Sandoe <[email protected]>

Author: acoplan-arm

gcc/c-family/c-common.cc

@@ -311,6 +311,44 @@ const struct fname_var_t fname_vars[] =
   {NULL, 0, 0},
 };
 
+/* Flags to restrict availability of generic features that
+   are known to __has_{feature,extension}.  */
+
+enum
+{
+  HF_FLAG_NONE = 0,
+  HF_FLAG_EXT = 1,	/* Available only as an extension.  */
+  HF_FLAG_SANITIZE = 2, /* Availability depends on sanitizer flags.  */
+};
+
+/* Info for generic features which can be queried through
+   __has_{feature,extension}.  */
+
+struct hf_feature_info
+{
+  const char *ident;
+  unsigned flags;
+  unsigned mask;
+};
+
+/* Table of generic features which can be queried through
+   __has_{feature,extension}.  */
+
+static constexpr hf_feature_info has_feature_table[] =
+{
+  { "address_sanitizer",	    HF_FLAG_SANITIZE, SANITIZE_ADDRESS },
+  { "thread_sanitizer",		    HF_FLAG_SANITIZE, SANITIZE_THREAD },
+  { "leak_sanitizer",		    HF_FLAG_SANITIZE, SANITIZE_LEAK },
+  { "hwaddress_sanitizer",	    HF_FLAG_SANITIZE, SANITIZE_HWADDRESS },
+  { "undefined_behavior_sanitizer", HF_FLAG_SANITIZE, SANITIZE_UNDEFINED },
+  { "attribute_deprecated_with_message",  HF_FLAG_NONE, 0 },
+  { "attribute_unavailable_with_message", HF_FLAG_NONE, 0 },
+  { "enumerator_attributes",		  HF_FLAG_NONE, 0 },
+  { "tls",				  HF_FLAG_NONE, 0 },
+  { "gnu_asm_goto_with_outputs",	  HF_FLAG_EXT, 0 },
+  { "gnu_asm_goto_with_outputs_full",	  HF_FLAG_EXT, 0 }
+};
+
 /* Global visibility options.  */
 struct visibility_flags visibility_options;
 
@@ -9891,4 +9929,63 @@ c_strict_flex_array_level_of (tree array_field)
   return strict_flex_array_level;
 }
 
+/* Map from identifiers to booleans.  Value is true for features, and
+   false for extensions.  Used to implement __has_{feature,extension}.  */
+
+using feature_map_t = hash_map <tree, bool>;
+static feature_map_t *feature_map;
+
+/* Register a feature for __has_{feature,extension}.  FEATURE_P is true
+   if the feature identified by NAME is a feature (as opposed to an
+   extension).  */
+
+void
+c_common_register_feature (const char *name, bool feature_p)
+{
+  bool dup = feature_map->put (get_identifier (name), feature_p);
+  gcc_checking_assert (!dup);
+}
+
+/* Lazily initialize hash table for __has_{feature,extension},
+   dispatching to the appropriate front end to register language-specific
+   features.  */
+
+static void
+init_has_feature ()
+{
+  gcc_checking_assert (!feature_map);
+  feature_map = new feature_map_t;
+
+  for (unsigned i = 0; i < ARRAY_SIZE (has_feature_table); i++)
+    {
+      const hf_feature_info *info = has_feature_table + i;
+
+      if ((info->flags & HF_FLAG_SANITIZE) && !(flag_sanitize & info->mask))
+	continue;
+
+      const bool feature_p = !(info->flags & HF_FLAG_EXT);
+      c_common_register_feature (info->ident, feature_p);
+    }
+
+  /* Register language-specific features.  */
+  c_family_register_lang_features ();
+}
+
+/* If STRICT_P is true, evaluate __has_feature (IDENT).
+   Otherwise, evaluate __has_extension (IDENT).  */
+
+bool
+has_feature_p (const char *ident, bool strict_p)
+{
+  if (!feature_map)
+    init_has_feature ();
+
+  tree name = canonicalize_attr_name (get_identifier (ident));
+  bool *feat_p = feature_map->get (name);
+  if (!feat_p)
+    return false;
+
+  return !strict_p || *feat_p;
+}
+
 #include "gt-c-family-c-common.h"

gcc/c-family/c-common.h

@@ -1126,6 +1126,14 @@ extern bool c_cpp_diagnostic (cpp_reader *, enum cpp_diagnostic_level,
      ATTRIBUTE_GCC_DIAG(5,0);
 extern int c_common_has_attribute (cpp_reader *, bool);
 extern int c_common_has_builtin (cpp_reader *);
+extern int c_common_has_feature (cpp_reader *, bool);
+
+/* Implemented by each front end in *-lang.cc.  */
+extern void c_family_register_lang_features ();
+
+/* Implemented in c-family/c-common.cc.  */
+extern void c_common_register_feature (const char *, bool);
+extern bool has_feature_p (const char *, bool);
 
 extern bool parse_optimize_options (tree, bool);
 

gcc/c-family/c-lex.cc

@@ -83,6 +83,7 @@ init_c_lex (void)
   cb->read_pch = c_common_read_pch;
   cb->has_attribute = c_common_has_attribute;
   cb->has_builtin = c_common_has_builtin;
+  cb->has_feature = c_common_has_feature;
   cb->get_source_date_epoch = cb_get_source_date_epoch;
   cb->get_suggestion = cb_get_suggestion;
   cb->remap_filename = remap_macro_filename;
@@ -452,16 +453,16 @@ c_common_has_attribute (cpp_reader *pfile, bool std_syntax)
   return result;
 }
 
-/* Callback for has_builtin.  */
+/* Helper for __has_{builtin,feature,extension}.  */
 
-int
-c_common_has_builtin (cpp_reader *pfile)
+static const char *
+c_common_lex_availability_macro (cpp_reader *pfile, const char *builtin)
 {
   const cpp_token *token = get_token_no_padding (pfile);
   if (token->type != CPP_OPEN_PAREN)
     {
       cpp_error (pfile, CPP_DL_ERROR,
-		 "missing '(' after \"__has_builtin\"");
+		 "missing '(' after \"__has_%s\"", builtin);
       return 0;
     }
 
@@ -481,7 +482,7 @@ c_common_has_builtin (cpp_reader *pfile)
   else
     {
       cpp_error (pfile, CPP_DL_ERROR,
-		 "macro \"__has_builtin\" requires an identifier");
+		 "macro \"__has_%s\" requires an identifier", builtin);
       if (token->type == CPP_CLOSE_PAREN)
 	return 0;
     }
@@ -500,9 +501,38 @@ c_common_has_builtin (cpp_reader *pfile)
 	break;
     }
 
+  return name;
+}
+
+/* Callback for has_builtin.  */
+
+int
+c_common_has_builtin (cpp_reader *pfile)
+{
+  const char *name = c_common_lex_availability_macro (pfile, "builtin");
+  if (!name)
+    return 0;
+
   return names_builtin_p (name);
 }
 
+/* Callback for has_feature.  STRICT_P is true for has_feature and false
+   for has_extension.  */
+
+int
+c_common_has_feature (cpp_reader *pfile, bool strict_p)
+{
+  const char *builtin = strict_p ? "feature" : "extension";
+  const char *name = c_common_lex_availability_macro (pfile, builtin);
+  if (!name)
+    return 0;
+
+  /* If -pedantic-errors is given, __has_extension is equivalent to
+     __has_feature.  */
+  strict_p |= flag_pedantic_errors;
+  return has_feature_p (name, strict_p);
+}
+
 
 /* Read a token and return its type.  Fill *VALUE with its value, if
    applicable.  Fill *CPP_FLAGS with the token's flags, if it is

gcc/c-family/c-ppoutput.cc

@@ -162,6 +162,7 @@ init_pp_output (FILE *out_stream)
 
   cb->has_attribute = c_common_has_attribute;
   cb->has_builtin = c_common_has_builtin;
+  cb->has_feature = c_common_has_feature;
   cb->get_source_date_epoch = cb_get_source_date_epoch;
   cb->remap_filename = remap_macro_filename;
 

gcc/c/c-lang.cc

@@ -63,6 +63,15 @@ c_get_sarif_source_language (const char *)
   return "c";
 }
 
+/* Implement c-family hook to register language-specific features for
+   __has_{feature,extension}.  */
+
+void
+c_family_register_lang_features ()
+{
+  c_register_features ();
+}
+
 #if CHECKING_P
 
 namespace selftest {

gcc/c/c-objc-common.cc

@@ -34,6 +34,39 @@ along with GCC; see the file COPYING3.  If not see
 static bool c_tree_printer (pretty_printer *, text_info *, const char *,
 			    int, bool, bool, bool, bool *, const char **);
 
+/* Info for C language features which can be queried through
+   __has_{feature,extension}.  */
+
+struct c_feature_info
+{
+  const char *ident;
+  const int *enable_flag;
+};
+
+static const c_feature_info c_feature_table[] =
+{
+  { "c_alignas", &flag_isoc11 },
+  { "c_alignof", &flag_isoc11 },
+  { "c_atomic", &flag_isoc11 },
+  { "c_generic_selections", &flag_isoc11 },
+  { "c_static_assert", &flag_isoc11 },
+  { "c_thread_local", &flag_isoc11 },
+  { "cxx_binary_literals", &flag_isoc23 }
+};
+
+/* Register features specific to the C language.  */
+
+void
+c_register_features ()
+{
+  for (unsigned i = 0; i < ARRAY_SIZE (c_feature_table); i++)
+    {
+      const c_feature_info *info = c_feature_table + i;
+      const bool feat_p = !info->enable_flag || *info->enable_flag;
+      c_common_register_feature (info->ident, feat_p);
+    }
+}
+
 bool
 c_missing_noreturn_ok_p (tree decl)
 {

gcc/c/c-objc-common.h

@@ -21,6 +21,9 @@ along with GCC; see the file COPYING3.  If not see
 #ifndef GCC_C_OBJC_COMMON
 #define GCC_C_OBJC_COMMON
 
+/* Implemented in c-objc-common.cc.  */
+extern void c_register_features ();
+
 /* Lang hooks that are shared between C and ObjC are defined here.  Hooks
    specific to C or ObjC go in c-lang.cc and objc/objc-lang.cc, respectively.  */
 

gcc/cp/cp-lang.cc

@@ -119,6 +119,15 @@ objcp_tsubst_expr (tree /*t*/, tree /*args*/, tsubst_flags_t /*complain*/,
   return NULL_TREE;
 }
 
+/* Implement c-family hook to add language-specific features
+   for __has_{feature,extension}.  */
+
+void
+c_family_register_lang_features ()
+{
+  cp_register_features ();
+}
+
 static const char *
 cxx_dwarf_name (tree t, int verbosity)
 {