c++: Move consteval folding to cp_fold_r

In the review of P2564: <https://gcc.gnu.org/pipermail/gcc-patches/2023-August/628747.html> it turned out that in order to correctly handle an example in the paper, we should stop doing immediate evaluation in build_over_call and bot_replace, and instead do it in cp_fold_r. This patch does that. Another benefit is that this is a pretty significant simplification, at least in my opinion. Also, this fixes the c++/110997 ICE (but the test doesn't compile yet). The main drawback seems to be that cp_fold_r doesn't process uninstantiated templates. We still have to handle things like "false ? foo () : 1". To that end, I've added cp_fold_immediate, called on dead branches in cxx_eval_conditional_expression. You'll see that I've reintroduced ADDR_EXPR_DENOTES_CALL_P here. This is to detect *(&foo)) () (s.*&S::foo) () which were deemed ill-formed. gcc/cp/ChangeLog: * call.cc (build_over_call): Set ADDR_EXPR_DENOTES_CALL_P. Don't handle immediate_invocation_p here. * constexpr.cc (cxx_eval_call_expression): Use mce_true for DECL_IMMEDIATE_FUNCTION_P. (cxx_eval_conditional_expression): Call cp_fold_immediate. * cp-gimplify.cc (enum fold_flags): Add ff_fold_immediate. (maybe_replace_decl): Make static. (cp_fold_r): Expand immediate invocations. (cp_fold_immediate_r): New. (cp_fold_immediate): New. * cp-tree.h (ADDR_EXPR_DENOTES_CALL_P): Define. (cp_fold_immediate): Declare. * tree.cc (bot_replace): Don't handle immediate invocations here. libstdc++-v3/ChangeLog: * testsuite/20_util/allocator/105975.cc: Add dg-error. gcc/testsuite/ChangeLog: * g++.dg/cpp23/consteval-if2.C: Add xfail. * g++.dg/cpp2a/consteval-memfn1.C: Adjust. * g++.dg/cpp2a/consteval11.C: Remove dg-message. * g++.dg/cpp2a/consteval3.C: Remove dg-message and dg-error. * g++.dg/cpp2a/consteval9.C: Remove dg-message. * g++.dg/cpp2a/consteval32.C: New test. * g++.dg/cpp2a/consteval33.C: New test. * g++.dg/cpp2a/consteval34.C: New test. * g++.dg/cpp2a/consteval35.C: New test.
2023-08-31 20:11:50 -04:00 · 2023-08-31 20:11:50 -04:00 · 6851e3423c
commit 6851e3423c
parent f25960b038
15 changed files with 288 additions and 133 deletions
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@ -10434,6 +10434,10 @@ build_over_call (struct z_candidate *cand, int flags, tsubst_flags_t complain)
      fn = build_addr_func (fn, complain);
      if (fn == error_mark_node)
 	return error_mark_node;
+
+      /* We're actually invoking the function.  (Immediate functions get an
+	 & when invoking it even though the user didn't use &.)  */
+      ADDR_EXPR_DENOTES_CALL_P (fn) = true;
    }

  tree call = build_cxx_call (fn, nargs, argarray, complain|decltype_flag);
@ -10451,41 +10455,7 @@ build_over_call (struct z_candidate *cand, int flags, tsubst_flags_t complain)
      if (TREE_CODE (c) == CALL_EXPR)
 	suppress_warning (c /* Suppress all warnings.  */);
    }
-  if (TREE_CODE (fn) == ADDR_EXPR)
-    {
-      tree fndecl = STRIP_TEMPLATE (TREE_OPERAND (fn, 0));
-      if (immediate_invocation_p (fndecl))
-	{
-	  tree obj_arg = NULL_TREE;
-	  /* Undo convert_from_reference called by build_cxx_call.  */
-	  if (REFERENCE_REF_P (call))
-	    call = TREE_OPERAND (call, 0);
-	  if (DECL_CONSTRUCTOR_P (fndecl))
-	    obj_arg = cand->first_arg ? cand->first_arg : (*args)[0];
-	  if (obj_arg && is_dummy_object (obj_arg))
-	    {
-	      call = build_cplus_new (DECL_CONTEXT (fndecl), call, complain);
-	      obj_arg = NULL_TREE;
-	    }
-	  /* Look through *(const T *)&obj.  */
-	  else if (obj_arg && INDIRECT_REF_P (obj_arg))
-	    {
-	      tree addr = TREE_OPERAND (obj_arg, 0);
-	      STRIP_NOPS (addr);
-	      if (TREE_CODE (addr) == ADDR_EXPR)
-		{
-		  tree typeo = TREE_TYPE (obj_arg);
-		  tree typei = TREE_TYPE (TREE_OPERAND (addr, 0));
-		  if (same_type_ignoring_top_level_qualifiers_p (typeo, typei))
-		    obj_arg = TREE_OPERAND (addr, 0);
-		}
-	    }
-	  call = cxx_constant_value (call, obj_arg, complain);
-	  if (obj_arg && !error_operand_p (call))
-	    call = cp_build_init_expr (obj_arg, call);
-	  call = convert_from_reference (call);
-	}
-    }
+
  return call;
 }

--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@ -3135,6 +3135,11 @@ cxx_eval_call_expression (const constexpr_ctx *ctx, tree t,
 	  unsigned save_heap_alloc_count = ctx->global->heap_vars.length ();
 	  unsigned save_heap_dealloc_count = ctx->global->heap_dealloc_count;

+	  /* Make sure we fold std::is_constant_evaluated to true in an
+	     immediate function.  */
+	  if (DECL_IMMEDIATE_FUNCTION_P (fun))
+	    call_ctx.manifestly_const_eval = mce_true;
+
 	  /* If this is a constexpr destructor, the object's const and volatile
 	     semantics are no longer in effect; see [class.dtor]p5.  */
 	  if (new_obj && DECL_DESTRUCTOR_P (fun))
@ -3807,8 +3812,7 @@ cxx_eval_binary_expression (const constexpr_ctx *ctx, tree t,
 }

 /* Subroutine of cxx_eval_constant_expression.
-   Attempt to evaluate condition expressions.  Dead branches are not
-   looked into.  */
+   Attempt to evaluate condition expressions.  */

 static tree
 cxx_eval_conditional_expression (const constexpr_ctx *ctx, tree t,
@ -3837,12 +3841,25 @@ cxx_eval_conditional_expression (const constexpr_ctx *ctx, tree t,
 				   boolean_type_node);
    }
  /* Don't VERIFY_CONSTANT the other operands.  */
-  if (integer_zerop (val))
+  const bool zero_p = integer_zerop (val);
+  if (zero_p)
    val = TREE_OPERAND (t, 2);
  else
    val = TREE_OPERAND (t, 1);
  if (TREE_CODE (t) == IF_STMT && !val)
    val = void_node;
+
+  /* P2564: a subexpression of a manifestly constant-evaluated expression
+     or conversion is an immediate function context.  */
+  if (ctx->manifestly_const_eval != mce_true
+      && !in_immediate_context ()
+      && cp_fold_immediate (&TREE_OPERAND (t, zero_p ? 1 : 2),
+			    ctx->manifestly_const_eval))
+    {
+      *non_constant_p = true;
+      return t;
+    }
+
  /* A TARGET_EXPR may be nested inside another TARGET_EXPR, but still
     serve as the initializer for the same object as the outer TARGET_EXPR,
     as in
--- a/gcc/cp/cp-gimplify.cc
+++ b/gcc/cp/cp-gimplify.cc
@ -53,6 +53,8 @@ enum fold_flags {
     definitely not in a manifestly constant-evaluated
     context.  */
  ff_mce_false = 1 << 1,
+  /* Whether we're being called from cp_fold_immediate.  */
+  ff_fold_immediate = 1 << 2,
 };

 using fold_flags_t = int;
@ -1000,7 +1002,7 @@ cp_genericize_target_expr (tree *stmt_p)
   replacement when cp_folding TARGET_EXPR to preserve the invariant that
   AGGR_INIT_EXPR_SLOT agrees with the enclosing TARGET_EXPR_SLOT.  */

-bool
+static bool
 maybe_replace_decl (tree *tp, tree decl, tree replacement)
 {
  if (!*tp || !VOID_TYPE_P (TREE_TYPE (*tp)))
@ -1029,6 +1031,123 @@ struct cp_genericize_data
  bool handle_invisiref_parm_p;
 };

+/* A subroutine of cp_fold_r to handle immediate functions.  */
+
+static tree
+cp_fold_immediate_r (tree *stmt_p, int *walk_subtrees, void *data_)
+{
+  auto data = static_cast<cp_fold_data *>(data_);
+  tree stmt = *stmt_p;
+  /* The purpose of this is not to emit errors for mce_unknown.  */
+  const tsubst_flags_t complain = (data->flags & ff_mce_false
+				   ? tf_error : tf_none);
+
+  /* No need to look into types or unevaluated operands.
+     NB: This affects cp_fold_r as well.  */
+  if (TYPE_P (stmt) || unevaluated_p (TREE_CODE (stmt)))
+    {
+      *walk_subtrees = 0;
+      return NULL_TREE;
+    }
+
+  switch (TREE_CODE (stmt))
+    {
+    /* Unfortunately we must handle code like
+	 false ? bar () : 42
+       where we have to check bar too.  The cp_fold call in cp_fold_r could
+       fold the ?: into a constant before we see it here.  */
+    case COND_EXPR:
+      /* If we are called from cp_fold_immediate, we don't need to worry about
+	 cp_fold folding away the COND_EXPR.  */
+      if (data->flags & ff_fold_immediate)
+	break;
+      if (TREE_OPERAND (stmt, 1)
+	  && cp_walk_tree (&TREE_OPERAND (stmt, 1), cp_fold_immediate_r, data,
+			   nullptr))
+	return error_mark_node;
+      if (TREE_OPERAND (stmt, 2)
+	  && cp_walk_tree (&TREE_OPERAND (stmt, 2), cp_fold_immediate_r, data,
+			   nullptr))
+	return error_mark_node;
+      /* We're done here.  Don't clear *walk_subtrees here though: we're called
+	 from cp_fold_r and we must let it recurse on the expression with
+	 cp_fold.  */
+      break;
+    case PTRMEM_CST:
+      if (TREE_CODE (PTRMEM_CST_MEMBER (stmt)) == FUNCTION_DECL
+	  && DECL_IMMEDIATE_FUNCTION_P (PTRMEM_CST_MEMBER (stmt)))
+	{
+	  if (!data->pset.add (stmt) && (complain & tf_error))
+	    {
+	      error_at (PTRMEM_CST_LOCATION (stmt),
+			"taking address of an immediate function %qD",
+			PTRMEM_CST_MEMBER (stmt));
+	      *stmt_p = build_zero_cst (TREE_TYPE (stmt));
+	    }
+	  return error_mark_node;
+	}
+      break;
+
+    /* Expand immediate invocations.  */
+    case CALL_EXPR:
+    case AGGR_INIT_EXPR:
+      if (tree fn = cp_get_callee (stmt))
+	if (TREE_CODE (fn) != ADDR_EXPR || ADDR_EXPR_DENOTES_CALL_P (fn))
+	  if (tree fndecl = cp_get_fndecl_from_callee (fn, /*fold*/false))
+	    if (DECL_IMMEDIATE_FUNCTION_P (fndecl))
+	      {
+		stmt = cxx_constant_value (stmt, complain);
+		if (stmt == error_mark_node)
+		  {
+		    if (complain & tf_error)
+		      *stmt_p = error_mark_node;
+		    return error_mark_node;
+		  }
+		*stmt_p = stmt;
+	      }
+      break;
+
+    case ADDR_EXPR:
+      if (TREE_CODE (TREE_OPERAND (stmt, 0)) == FUNCTION_DECL
+	  && DECL_IMMEDIATE_FUNCTION_P (TREE_OPERAND (stmt, 0))
+	  && !ADDR_EXPR_DENOTES_CALL_P (stmt))
+	{
+	  if (complain & tf_error)
+	    {
+	      error_at (EXPR_LOCATION (stmt),
+			"taking address of an immediate function %qD",
+			TREE_OPERAND (stmt, 0));
+	      *stmt_p = build_zero_cst (TREE_TYPE (stmt));
+	    }
+	  return error_mark_node;
+	}
+      break;
+
+    default:
+      break;
+    }
+
+  return NULL_TREE;
+}
+
+/* A wrapper around cp_fold_immediate_r.  Return true if we found
+   a non-constant immediate function, or taking the address of an
+   immediate function.  */
+
+bool
+cp_fold_immediate (tree *tp, mce_value manifestly_const_eval)
+{
+  if (cxx_dialect <= cxx17)
+    return false;
+
+  fold_flags_t flags = ff_fold_immediate;
+  if (manifestly_const_eval == mce_false)
+    flags |= ff_mce_false;
+
+  cp_fold_data data (flags);
+  return !!cp_walk_tree_without_duplicates (tp, cp_fold_immediate_r, &data);
+}
+
 /* Perform any pre-gimplification folding of C++ front end trees to
   GENERIC.
   Note:  The folding of non-omp cases is something to move into
@ -1043,36 +1162,8 @@ cp_fold_r (tree *stmt_p, int *walk_subtrees, void *data_)
  tree stmt = *stmt_p;
  enum tree_code code = TREE_CODE (stmt);

-  switch (code)
-    {
-    case PTRMEM_CST:
-      if (TREE_CODE (PTRMEM_CST_MEMBER (stmt)) == FUNCTION_DECL
-	  && DECL_IMMEDIATE_FUNCTION_P (PTRMEM_CST_MEMBER (stmt)))
-	{
-	  if (!data->pset.add (stmt))
-	    error_at (PTRMEM_CST_LOCATION (stmt),
-		      "taking address of an immediate function %qD",
-		      PTRMEM_CST_MEMBER (stmt));
-	  stmt = *stmt_p = build_zero_cst (TREE_TYPE (stmt));
-	  break;
-	}
-      break;
-
-    case ADDR_EXPR:
-      if (TREE_CODE (TREE_OPERAND (stmt, 0)) == FUNCTION_DECL
-	  && DECL_IMMEDIATE_FUNCTION_P (TREE_OPERAND (stmt, 0)))
-	{
-	  error_at (EXPR_LOCATION (stmt),
-		    "taking address of an immediate function %qD",
-		    TREE_OPERAND (stmt, 0));
-	  stmt = *stmt_p = build_zero_cst (TREE_TYPE (stmt));
-	  break;
-	}
-      break;
-
-    default:
-      break;
-    }
+  if (cxx_dialect > cxx17)
+    cp_fold_immediate_r (stmt_p, walk_subtrees, data);

  *stmt_p = stmt = cp_fold (*stmt_p, data->flags);

@ -1084,7 +1175,7 @@ cp_fold_r (tree *stmt_p, int *walk_subtrees, void *data_)
 	 always the same tree, which the first time cp_fold_r has been
 	 called on it had the subtrees walked.  */
      *walk_subtrees = 0;
-      return NULL;
+      return NULL_TREE;
    }

  code = TREE_CODE (stmt);
@ -1136,7 +1227,7 @@ cp_fold_r (tree *stmt_p, int *walk_subtrees, void *data_)
 	}
      cp_walk_tree (&OMP_FOR_PRE_BODY (stmt), cp_fold_r, data, NULL);
      *walk_subtrees = 0;
-      return NULL;
+      return NULL_TREE;

    case IF_STMT:
      if (IF_STMT_CONSTEVAL_P (stmt))
@ -1146,7 +1237,7 @@ cp_fold_r (tree *stmt_p, int *walk_subtrees, void *data_)
 	  cp_walk_tree (&ELSE_CLAUSE (stmt), cp_fold_r, data, NULL);
 	  cp_walk_tree (&IF_SCOPE (stmt), cp_fold_r, data, NULL);
 	  *walk_subtrees = 0;
-	  return NULL;
+	  return NULL_TREE;
 	}
      break;

@ -1183,7 +1274,7 @@ cp_fold_r (tree *stmt_p, int *walk_subtrees, void *data_)
      break;
    }

-  return NULL;
+  return NULL_TREE;
 }

 /* Fold ALL the trees!  FIXME we should be able to remove this, but
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@ -4784,6 +4784,11 @@ get_vec_init_expr (tree t)
 #define PTRMEM_OK_P(NODE) \
  TREE_LANG_FLAG_0 (TREE_CHECK3 ((NODE), ADDR_EXPR, OFFSET_REF, SCOPE_REF))

+/* True if this ADDR_EXPR denotes a function call; that is, it's
+   fn() rather than &fn.  */
+#define ADDR_EXPR_DENOTES_CALL_P(NODE) \
+  (ADDR_EXPR_CHECK(NODE)->base.protected_flag)
+
 /* Get the POINTER_TYPE to the METHOD_TYPE associated with this
   pointer to member function.  TYPE_PTRMEMFUNC_P _must_ be true,
   before using this macro.  */
@ -6580,6 +6585,24 @@ extern int class_dump_id;
 extern int module_dump_id;
 extern int raw_dump_id;

+/* Whether the current context is manifestly constant-evaluated.
+   Used by the constexpr machinery to control folding of
+   __builtin_is_constant_evaluated.  */
+
+enum class mce_value
+{
+  /* Unknown, so treat __builtin_is_constant_evaluated as non-constant.  */
+  mce_unknown = 0,
+  /* Fold it to true.  */
+  mce_true = 1,
+  /* Fold it to false.  Primarily used during cp_fold_function and
+     cp_fully_fold_init.  */
+  mce_false = -1,
+};
+constexpr mce_value mce_unknown = mce_value::mce_unknown;
+constexpr mce_value mce_true = mce_value::mce_true;
+constexpr mce_value mce_false = mce_value::mce_false;
+
 /* in call.cc */
 extern bool check_dtor_name			(tree, tree);
 int magic_varargs_p				(tree);
@ -8354,6 +8377,7 @@ extern tree process_stmt_assume_attribute	(tree, tree, location_t);
 extern bool simple_empty_class_p		(tree, tree, tree_code);
 extern tree fold_builtin_source_location	(const_tree);
 extern tree get_source_location_impl_type	();
+extern bool cp_fold_immediate			(tree *, mce_value);

 /* in name-lookup.cc */
 extern tree strip_using_decl                    (tree);
@ -8515,24 +8539,6 @@ struct GTY((for_user)) constexpr_fundef {
  tree result;
 };

-/* Whether the current context is manifestly constant-evaluated.
-   Used by the constexpr machinery to control folding of
-   __builtin_is_constant_evaluated.  */
-
-enum class mce_value
-{
-  /* Unknown, so treat __builtin_is_constant_evaluated as non-constant.  */
-  mce_unknown = 0,
-  /* Fold it to true.  */
-  mce_true = 1,
-  /* Fold it to false.  Primarily used during cp_fold_function and
-     cp_fully_fold_init.  */
-  mce_false = -1,
-};
-constexpr mce_value mce_unknown = mce_value::mce_unknown;
-constexpr mce_value mce_true = mce_value::mce_true;
-constexpr mce_value mce_false = mce_value::mce_false;
-
 extern void fini_constexpr			(void);
 extern bool literal_type_p                      (tree);
 extern void maybe_save_constexpr_fundef		(tree);
--- a/gcc/cp/tree.cc
+++ b/gcc/cp/tree.cc
@ -3254,7 +3254,7 @@ bot_manip (tree* tp, int* walk_subtrees, void* data_)
   variables.  */

 static tree
-bot_replace (tree* t, int* walk_subtrees, void* data_)
+bot_replace (tree* t, int */*walk_subtrees*/, void* data_)
 {
  bot_data &data = *(bot_data*)data_;
  splay_tree target_remap = data.target_remap;
@ -3284,27 +3284,6 @@ bot_replace (tree* t, int* walk_subtrees, void* data_)
 			    /*check_access=*/false, /*nonnull=*/true,
 			    tf_warning_or_error);
    }
-  else if (cxx_dialect >= cxx20
-	   && (TREE_CODE (*t) == CALL_EXPR
-	       || TREE_CODE (*t) == AGGR_INIT_EXPR)
-	   && !in_immediate_context ())
-    {
-      /* Expand immediate invocations.  */
-      if (tree fndecl = cp_get_callee_fndecl_nofold (*t))
-	if (DECL_IMMEDIATE_FUNCTION_P (fndecl))
-	  {
-	    /* Make in_immediate_context true within the args.  */
-	    in_consteval_if_p_temp_override ito;
-	    in_consteval_if_p = true;
-	    int nargs = call_expr_nargs (*t);
-	    for (int i = 0; i < nargs; ++i)
-	      cp_walk_tree (&get_nth_callarg (*t, i), bot_replace, data_, NULL);
-	    *t = cxx_constant_value (*t);
-	    if (*t == error_mark_node)
-	      return error_mark_node;
-	    *walk_subtrees = 0;
-	  }
-    }

  return NULL_TREE;
 }
--- a/gcc/testsuite/g++.dg/cpp23/consteval-if2.C
+++ b/gcc/testsuite/g++.dg/cpp23/consteval-if2.C
@ -58,6 +58,7 @@ baz (int x)
  return r;
 }

+// This function is not instantiated so NDR.
 template <typename T>
 constexpr int
 qux (int x)
@ -65,7 +66,7 @@ qux (int x)
  int r = 0;
  if not consteval	// { dg-warning "'if consteval' only available with" "" { target c++20_only } }
    {
-      r += foo (x);	// { dg-error "'x' is not a constant expression" }
+      r += foo (x);	// { dg-error "'x' is not a constant expression" "" { xfail *-*-* } }
    }
  else
    {
--- a/gcc/testsuite/g++.dg/cpp2a/consteval-memfn1.C
+++ b/gcc/testsuite/g++.dg/cpp2a/consteval-memfn1.C
@ -25,3 +25,10 @@ void VerifyHash(fixed_string s) {
  fixed_string::size_static(-1); // { dg-message "expansion of" }
  s(); // { dg-bogus "" }
 }
+
+void
+do_test ()
+{
+  fixed_string f;
+  VerifyHash<int>(f);
+}
--- a/gcc/testsuite/g++.dg/cpp2a/consteval11.C
+++ b/gcc/testsuite/g++.dg/cpp2a/consteval11.C
@ -5,21 +5,21 @@ consteval int bar (int i) { if (i != 1) throw 1; return 0; }	// { dg-error "is n

 constexpr int a = bar (1);
 constexpr int b = bar (2);		// { dg-message "in 'constexpr' expansion of" }
-constexpr int c = 0 ? bar (3) : 1;	// { dg-message "in 'constexpr' expansion of" }
+constexpr int c = 0 ? bar (3) : 1;
 const int d = bar (4);			// { dg-message "in 'constexpr' expansion of" }
-const int e = 0 ? bar (5) : 1;		// { dg-message "in 'constexpr' expansion of" }
+const int e = 0 ? bar (5) : 1;
 int f = bar (1);
 int g = bar (6);			// { dg-message "in 'constexpr' expansion of" }
-int h = 0 ? bar (7) : 1;		// { dg-message "in 'constexpr' expansion of" }
+int h = 0 ? bar (7) : 1;

 void
 foo ()
 {
  constexpr int a = bar (1);
  constexpr int b = bar (2);		// { dg-message "in 'constexpr' expansion of" }
-  constexpr int c = 0 ? bar (3) : 1;	// { dg-message "in 'constexpr' expansion of" }
+  constexpr int c = 0 ? bar (3) : 1;
  const int d = bar (4);		// { dg-message "in 'constexpr' expansion of" }
-  const int e = 0 ? bar (5) : 1;	// { dg-message "in 'constexpr' expansion of" }
+  const int e = 0 ? bar (5) : 1;
  int f = bar (1);
  int g = bar (6);			// { dg-message "in 'constexpr' expansion of" }
  int h = 0 ? bar (7) : 1;		// { dg-message "in 'constexpr' expansion of" }
@ -33,13 +33,13 @@ foo ()
  else
    bar (12);				// { dg-message "in 'constexpr' expansion of" }
  if constexpr (0)
-    bar (13);				// { dg-message "in 'constexpr' expansion of" }
+    bar (13);
  else
    bar (14);				// { dg-message "in 'constexpr' expansion of" }
  if constexpr (1)
    bar (15);				// { dg-message "in 'constexpr' expansion of" }
  else
-    bar (16);				// { dg-message "in 'constexpr' expansion of" }
+    bar (16);
 }

 consteval int
@ -77,22 +77,25 @@ template <typename T>
 void
 qux ()
 {
+  // Used to give errors errors here, but not since we moved consteval
+  // function folding to cp_fold_r which isn't called on uninstantiated
+  // templates.
  if (0)
-    bar (2);				// { dg-message "in 'constexpr' expansion of" }
+    bar (2);
  else
-    bar (3);				// { dg-message "in 'constexpr' expansion of" }
+    bar (3);
  if (1)
-    bar (4);				// { dg-message "in 'constexpr' expansion of" }
+    bar (4);
  else
-    bar (5);				// { dg-message "in 'constexpr' expansion of" }
+    bar (5);
  if constexpr (0)
-    bar (6);				// { dg-message "in 'constexpr' expansion of" }
+    bar (6);
  else
-    bar (7);				// { dg-message "in 'constexpr' expansion of" }
+    bar (7);
  if constexpr (1)
-    bar (8);				// { dg-message "in 'constexpr' expansion of" }
+    bar (8);
  else
-    bar (9);				// { dg-message "in 'constexpr' expansion of" }
+    bar (9);
  if (0)
    bar ((T) 2);
  else
--- a/gcc/testsuite/g++.dg/cpp2a/consteval3.C
+++ b/gcc/testsuite/g++.dg/cpp2a/consteval3.C
@ -18,8 +18,7 @@ consteval int f6 (int x) { return x; }
 int d = 6;		// { dg-message "'int d' is not const" }
 int e = f6 (d);		// { dg-error "the value of 'd' is not usable in a constant expression" }
 constexpr int f7 (int x) { return f6 (x); }	// { dg-error "'x' is not a constant expression" }
-constexpr int f = f7 (5);	// { dg-error "" }
-				// { dg-message "in 'constexpr' expansion of" "" { target *-*-* } .-1 }
+constexpr int f = f7 (5);
 using fnptr = int (int);
 fnptr *g = f6;		// { dg-error "taking address of an immediate function 'consteval int f6\\(int\\)'" }
 int f8 (fnptr *);
--- a/gcc/testsuite/g++.dg/cpp2a/consteval32.C
+++ b/gcc/testsuite/g++.dg/cpp2a/consteval32.C
@ -0,0 +1,4 @@
+// { dg-do compile { target c++20 } }
+
+consteval int foo ()  { return 42; }
+int bar () { return (*(&foo)) (); } // { dg-error "taking address" }
--- a/gcc/testsuite/g++.dg/cpp2a/consteval33.C
+++ b/gcc/testsuite/g++.dg/cpp2a/consteval33.C
@ -0,0 +1,34 @@
+// { dg-do compile { target c++20 } }
+
+consteval int id (int i) { return i; }
+consteval int add (int i, int j) { return i + j; }
+
+constexpr int
+foo (int i = id (42))
+{
+  return i + id (id (id (0)));
+}
+
+constexpr int
+bar (int i = id (id (id (42))))
+{
+  return i;
+}
+
+constexpr int
+baz (int i = add (add (id (1), id (2)), id (3)))
+{
+  return i;
+}
+
+void
+g ()
+{
+  foo ();
+  bar ();
+  baz ();
+}
+
+static_assert (foo () == 42);
+static_assert (bar () == 42);
+static_assert (baz () == 6);
--- a/gcc/testsuite/g++.dg/cpp2a/consteval34.C
+++ b/gcc/testsuite/g++.dg/cpp2a/consteval34.C
@ -0,0 +1,33 @@
+// { dg-do compile { target c++20 } }
+
+consteval int bar (int i) { if (i != 1) throw 1; return 0; }	// { dg-error "is not a constant expression" }
+
+constexpr int
+foo (bool b)
+{
+  return b ? bar (3) : 2; // { dg-message "in .constexpr. expansion" }
+}
+
+static_assert (foo (false) == 2);
+
+__extension__ constexpr int g1 = false ?: bar (2); // { dg-message "in .constexpr. expansion" }
+__extension__ constexpr int g2 = false ?: (1 + bar (2)); // { dg-message "in .constexpr. expansion" }
+__extension__ constexpr int g3 = true ?: bar (2);
+__extension__ constexpr int g4 = true ?: (1 + bar (2));
+constexpr int g5 = bar (2) ? 1 : 2; // { dg-message "in .constexpr. expansion" }
+constexpr int g6 = bar (2) - 1 ? 1 : 2; // { dg-message "in .constexpr. expansion" }
+
+void
+g ()
+{
+  __extension__ int a1[bar(3)]; // { dg-message "in .constexpr. expansion" }
+  int a2[sizeof (bar(3))];
+
+  int a3 = false ? (1 + bar (8)) : 1; // { dg-message "in .constexpr. expansion" }
+  a3 += false ? (1 + bar (8)) : 1; // { dg-message "in .constexpr. expansion" }
+
+  __extension__ int a4 = false ?: (1 + bar (8)); // { dg-message "in .constexpr. expansion" }
+  __extension__ int a5 = true ?: (1 + bar (8)); // { dg-message "in .constexpr. expansion" }
+  int a6 = bar (2) ? 1 : 2; // { dg-message "in .constexpr. expansion" }
+  int a7 = bar (2) - 1 ? 1 : 2; // { dg-message "in .constexpr. expansion" }
+}
--- a/gcc/testsuite/g++.dg/cpp2a/consteval35.C
+++ b/gcc/testsuite/g++.dg/cpp2a/consteval35.C
@ -0,0 +1,10 @@
+// { dg-do compile { target c++20 } }
+
+template <typename T, typename F>
+constexpr bool is_not(T t, F f) {
+     return not f(t);
+}
+
+consteval bool is_even(int i) { return i % 2 == 0; }
+
+static_assert(is_not(5, is_even)); // ok
--- a/gcc/testsuite/g++.dg/cpp2a/consteval9.C
+++ b/gcc/testsuite/g++.dg/cpp2a/consteval9.C
@ -15,10 +15,11 @@ void qux ()
  int a = bar (N);	// { dg-message "in 'constexpr' expansion of 'bar\\(2\\)'" }
 }

+// This function is not instantiated so NDR.
 template <int N>
 void quux ()
 {
-  int a = bar (5);	// { dg-message "in 'constexpr' expansion of 'bar\\(5\\)'" }
+  int a = bar (5);
 }

 void
--- a/libstdc++-v3/testsuite/20_util/allocator/105975.cc
+++ b/libstdc++-v3/testsuite/20_util/allocator/105975.cc
@ -13,6 +13,6 @@ consteval bool test_pr105957()
  a.deallocate(p, n);
  return true;
 }
-static_assert( test_pr105957() );
+static_assert( test_pr105957() ); // { dg-error "non-constant" }

 // { dg-error "throw_bad_array_new_length" "" { target *-*-* } 0 }