[PATCH] c++: implement P2564, consteval needs to propagate up [PR107687]

[Marek Polacek <polacek@redhat.com>]

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

-- >8 --

This patch implements P2564, described at <wg21.link/p2564>, whereby
certain functions are promoted to consteval.  For example:

  consteval int id(int i) { return i; }

  template <typename T>
  constexpr int f(T t)
  {
    return t + id(t); // id causes f<int> to be promoted to consteval
  }

  void g(int i)
  {
    f (3);
  }

now compiles.  Previously the code was ill-formed: we would complain
that 't' in 'f' is not a constant expression.  Since 'f' is now
consteval, it means that the call to id(t) is in an immediate context,
so doesn't have to produce a constant -- this is how we allow consteval
functions composition.  But making 'f<int>' consteval also means that
the call to 'f' in 'g' must yield a constant; failure to do so results
in an error.  I made the effort to have cc1plus explain to us what's
going on.  For example, calling f(i) produces this neat diagnostic:

q.C: In function 'void g(int)':
q.C:11:5: error: call to consteval function 'f<int>(i)' is not a constant expression
   11 |   f (i);
      |   ~~^~~
q.C:6:16: note: 'constexpr int f(T) [with T = int]' was promoted to an immediate function because its body contains an immediate-escalating expression 'id(t)'
    6 |   return t + id(t);
      |              ~~^~~

which hopefully makes it clear what's going on.

Implementing this proposal has been tricky.  One problem was delayed
instantiation: instantiating a function can set off a domino effect
where one call promotes a function to consteval but that then means
that another function should also be promoted, etc.  I previously
thought that I could get past that by implementing the propagation in
cp_gimplify_expr at which point we have already instantiated everything
via instantiate_pending_templates.  But I realized that we don't
gimplify e.g.

  static auto p = &id;

and so we'd never detect taking the address of a consteval function.
Therefore this patch instantiates immediate-escalating functions
beforehand.  And as usual, there were a lot of other things to
handle.  It's not just calls to consteval functions that we must
detect, we also have to look for id-expressions that denote an
immediate function.

I discovered two crashes:
<https://gcc.gnu.org/PR110997>, ICE-on-valid with NSDMI
<https://gcc.gnu.org/PR111106>, missing ; causes an ICE
which this patch doesn't address, but adds a dg-ice test for the former.

I left one FIXME in the patch because I'm unclear on how to properly fix
the modules problem.

	PR c++/107687

gcc/c-family/ChangeLog:

	* c-cppbuiltin.cc (c_cpp_builtins): Update __cpp_consteval.

gcc/cp/ChangeLog:

	* call.cc (immediate_invocation_p): No longer static.
	(immediate_escalating_function_p): New.
	(maybe_promote_function_to_consteval): New.
	(build_over_call): Set ADDR_EXPR_DENOTES_CALL_P.  Maybe promote
	current_function_decl to consteval.
	* constexpr.cc (instantiate_cx_fn_r): No longer static.
	* cp-gimplify.cc (struct find_escalating_expr_t): New.
	(find_escalating_expr_r): New.
	(maybe_explain_promoted_consteval): New.
	(maybe_escalate_decl_and_cfun): New.
	(cp_fold_r) <case PTRMEM_CST>: Handle promoting functions to consteval.
	<case CALL_EXPR>: New case, handle promoting functions to consteval.
	<case ADDR_EXPR>: Handle promoting functions to consteval.
	* cp-tree.h (ADDR_EXPR_DENOTES_CALL_P): Define.
	(immediate_invocation_p): Declare.
	(immediate_escalating_function_p): Declare.
	(maybe_promote_function_to_consteval): Declare.
	(instantiate_constexpr_fns): Declare.
	* typeck.cc (cp_build_addr_expr_1): SET_EXPR_LOCATION on constexpr
	functions as well.

libstdc++-v3/ChangeLog:

	* testsuite/20_util/integer_comparisons/greater_equal_neg.cc: Adjust
	expected diagnostic.
	* testsuite/20_util/integer_comparisons/greater_neg.cc: Likewise.
	* testsuite/20_util/integer_comparisons/less_equal_neg.cc: Likewise.
	* testsuite/20_util/optional/monadic/or_else_neg.cc: Likewise.
	* testsuite/23_containers/array/creation/3_neg.cc: Likewise.
	* testsuite/23_containers/span/first_neg.cc: Likewise.
	* testsuite/23_containers/span/last_neg.cc: Likewise.
	* testsuite/23_containers/span/subspan_neg.cc: Likewise.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/constexpr-inst1.C: Add dg-error.
	* g++.dg/cpp23/consteval-if10.C: Remove dg-error.
	* g++.dg/cpp23/consteval-if2.C: Likewise.
	* g++.dg/cpp23/feat-cxx2b.C: Adjust expected value of __cpp_consteval.
	* g++.dg/cpp26/feat-cxx26.C: Likewise.
	* g++.dg/cpp2a/feat-cxx2a.C: Likewise.
	* g++.dg/cpp2a/consteval-prop1.C: New test.
	* g++.dg/cpp2a/consteval-prop10.C: New test.
	* g++.dg/cpp2a/consteval-prop11.C: New test.
	* g++.dg/cpp2a/consteval-prop12.C: New test.
	* g++.dg/cpp2a/consteval-prop13.C: New test.
	* g++.dg/cpp2a/consteval-prop14.C: New test.
	* g++.dg/cpp2a/consteval-prop15.C: New test.
	* g++.dg/cpp2a/consteval-prop16.C: New test.
	* g++.dg/cpp2a/consteval-prop17.C: New test.
	* g++.dg/cpp2a/consteval-prop2.C: New test.
	* g++.dg/cpp2a/consteval-prop3.C: New test.
	* g++.dg/cpp2a/consteval-prop4.C: New test.
	* g++.dg/cpp2a/consteval-prop5.C: New test.
	* g++.dg/cpp2a/consteval-prop6.C: New test.
	* g++.dg/cpp2a/consteval-prop7.C: New test.
	* g++.dg/cpp2a/consteval-prop8.C: New test.
	* g++.dg/cpp2a/consteval-prop9.C: New test.
---
 gcc/c-family/c-cppbuiltin.cc                  |   2 +-
 gcc/cp/call.cc                                |  74 +++++-
 gcc/cp/constexpr.cc                           |   2 +-
 gcc/cp/cp-gimplify.cc                         | 223 ++++++++++++++++--
 gcc/cp/cp-tree.h                              |   9 +
 gcc/cp/typeck.cc                              |   4 +-
 gcc/testsuite/g++.dg/cpp0x/constexpr-inst1.C  |   5 +-
 gcc/testsuite/g++.dg/cpp23/consteval-if10.C   |   7 +-
 gcc/testsuite/g++.dg/cpp23/consteval-if2.C    |  10 +-
 gcc/testsuite/g++.dg/cpp23/feat-cxx2b.C       |   4 +-
 gcc/testsuite/g++.dg/cpp26/feat-cxx26.C       |   4 +-
 gcc/testsuite/g++.dg/cpp2a/consteval-prop1.C  | 149 ++++++++++++
 gcc/testsuite/g++.dg/cpp2a/consteval-prop10.C |   9 +
 gcc/testsuite/g++.dg/cpp2a/consteval-prop11.C |  48 ++++
 gcc/testsuite/g++.dg/cpp2a/consteval-prop12.C |  30 +++
 gcc/testsuite/g++.dg/cpp2a/consteval-prop13.C |  23 ++
 gcc/testsuite/g++.dg/cpp2a/consteval-prop14.C |  72 ++++++
 gcc/testsuite/g++.dg/cpp2a/consteval-prop15.C |  81 +++++++
 gcc/testsuite/g++.dg/cpp2a/consteval-prop16.C |  73 ++++++
 gcc/testsuite/g++.dg/cpp2a/consteval-prop17.C |  32 +++
 gcc/testsuite/g++.dg/cpp2a/consteval-prop2.C  |  54 +++++
 gcc/testsuite/g++.dg/cpp2a/consteval-prop3.C  |  31 +++
 gcc/testsuite/g++.dg/cpp2a/consteval-prop4.C  |  32 +++
 gcc/testsuite/g++.dg/cpp2a/consteval-prop5.C  |  27 +++
 gcc/testsuite/g++.dg/cpp2a/consteval-prop6.C  |  58 +++++
 gcc/testsuite/g++.dg/cpp2a/consteval-prop7.C  |  76 ++++++
 gcc/testsuite/g++.dg/cpp2a/consteval-prop8.C  |  71 ++++++
 gcc/testsuite/g++.dg/cpp2a/consteval-prop9.C  |  67 ++++++
 gcc/testsuite/g++.dg/cpp2a/feat-cxx2a.C       |   4 +-
 .../integer_comparisons/greater_equal_neg.cc  |  24 +-
 .../integer_comparisons/greater_neg.cc        |  24 +-
 .../integer_comparisons/less_equal_neg.cc     |  24 +-
 .../20_util/optional/monadic/or_else_neg.cc   |  10 +-
 .../23_containers/array/creation/3_neg.cc     |  14 +-
 .../testsuite/23_containers/span/first_neg.cc |   4 +-
 .../testsuite/23_containers/span/last_neg.cc  |   4 +-
 .../23_containers/span/subspan_neg.cc         |  12 +-
 37 files changed, 1306 insertions(+), 91 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/consteval-prop1.C
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/consteval-prop10.C
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/consteval-prop11.C
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/consteval-prop12.C
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/consteval-prop13.C
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/consteval-prop14.C
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/consteval-prop15.C
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/consteval-prop16.C
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/consteval-prop17.C
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/consteval-prop2.C
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/consteval-prop3.C
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/consteval-prop4.C
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/consteval-prop5.C
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/consteval-prop6.C
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/consteval-prop7.C
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/consteval-prop8.C
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/consteval-prop9.C

diff --git a/gcc/c-family/c-cppbuiltin.cc b/gcc/c-family/c-cppbuiltin.cc
index f2b12fd63db..8f8ebc7e4bb 100644
--- a/gcc/c-family/c-cppbuiltin.cc
+++ b/gcc/c-family/c-cppbuiltin.cc
@@ -1058,7 +1058,7 @@ c_cpp_builtins (cpp_reader *pfile)
 	    cpp_define (pfile, "__cpp_constexpr=202002L");
 	  cpp_define (pfile, "__cpp_constexpr_in_decltype=201711L");
 	  cpp_define (pfile, "__cpp_conditional_explicit=201806L");
-	  cpp_define (pfile, "__cpp_consteval=201811L");
+	  cpp_define (pfile, "__cpp_consteval=202211L");
 	  cpp_define (pfile, "__cpp_constinit=201907L");
 	  cpp_define (pfile, "__cpp_deduction_guides=201907L");
 	  cpp_define (pfile, "__cpp_nontype_template_args=201911L");
diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
index 673ec91d60e..31f78b71fe1 100644
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -9735,7 +9735,9 @@ build_trivial_dtor_call (tree instance, bool no_ptr_deref)
 
 /* Return true if in an immediate function context, or an unevaluated operand,
    or a default argument/member initializer, or a subexpression of an immediate
-   invocation.  */
+   invocation.
+   ??? P2564 says that "a subexpression of a manifestly constant-evaluated
+   expression or conversion" is also an immediate function context.  */
 
 bool
 in_immediate_context ()
@@ -9754,7 +9756,7 @@ in_immediate_context ()
 /* Return true if a call to FN with number of arguments NARGS
    is an immediate invocation.  */
 
-static bool
+bool
 immediate_invocation_p (tree fn)
 {
   return (TREE_CODE (fn) == FUNCTION_DECL
@@ -9762,6 +9764,54 @@ immediate_invocation_p (tree fn)
 	  && !in_immediate_context ());
 }
 
+/* Return true if FN is an immediate-escalating function.  */
+
+bool
+immediate_escalating_function_p (tree fn)
+{
+  if (!fn)
+    return false;
+
+  gcc_checking_assert (TREE_CODE (fn) == FUNCTION_DECL);
+
+  /* An immediate-escalating function is
+      -- the call operator of a lambda that is not declared with the consteval
+	 specifier  */
+  if (LAMBDA_FUNCTION_P (fn) && !DECL_IMMEDIATE_FUNCTION_P (fn))
+    return true;
+  /* -- a defaulted special member function that is not declared with the
+	consteval specifier  */
+  special_function_kind sfk = special_memfn_p (fn);
+  if (sfk != sfk_none
+      && DECL_DEFAULTED_FN (fn)
+      && !DECL_IMMEDIATE_FUNCTION_P (fn))
+    return true;
+  /* -- a function that results from the instantiation of a templated entity
+	defined with the constexpr specifier.  */
+  return is_instantiation_of_constexpr (fn);
+}
+
+/* Promote FN to an immediate function, including its clones, if it is
+   an immediate-escalating function.  Return true if we did promote;
+   false otherwise.  */
+
+bool
+maybe_promote_function_to_consteval (tree fn)
+{
+  if (fn
+      && !DECL_IMMEDIATE_FUNCTION_P (fn)
+      && immediate_escalating_function_p (fn))
+    {
+      SET_DECL_IMMEDIATE_FUNCTION_P (fn);
+      tree clone;
+      FOR_EACH_CLONE (clone, fn)
+	SET_DECL_IMMEDIATE_FUNCTION_P (clone);
+      return true;
+    }
+
+  return false;
+}
+
 /* Subroutine of the various build_*_call functions.  Overload resolution
    has chosen a winning candidate CAND; build up a CALL_EXPR accordingly.
    ARGS is a TREE_LIST of the unconverted arguments to the call.  FLAGS is a
@@ -10460,6 +10510,10 @@ build_over_call (struct z_candidate *cand, int flags, tsubst_flags_t complain)
 				   UNAVAILABLE_DEPRECATED_SUPPRESS);
 
       fn = build_addr_func (fn, complain);
+      /* 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;
+
       if (fn == error_mark_node)
 	return error_mark_node;
     }
@@ -10484,6 +10538,7 @@ build_over_call (struct z_candidate *cand, int flags, tsubst_flags_t complain)
       tree fndecl = STRIP_TEMPLATE (TREE_OPERAND (fn, 0));
       if (immediate_invocation_p (fndecl))
 	{
+	  tree orig_call = call;
 	  tree obj_arg = NULL_TREE;
 	  /* Undo convert_from_reference called by build_cxx_call.  */
 	  if (REFERENCE_REF_P (call))
@@ -10508,6 +10563,21 @@ build_over_call (struct z_candidate *cand, int flags, tsubst_flags_t complain)
 		    obj_arg = TREE_OPERAND (addr, 0);
 		}
 	    }
+
+	  /* [expr.const]p16 "An expression or conversion is
+	     immediate-escalating if it is not initially in an immediate
+	     function context and it is either
+	      -- an immediate invocation that is not a constant expression and
+	      is not a subexpression of an immediate invocation."
+
+	      If we are in an immediate-escalating function, the
+	      immediate-escalating expression or conversion makes it an
+	      immediate function.  So CALL does not need to produce a constant
+	      expression.  ??? It's ugly to call cxx_constant_value twice in
+	      some cases.  */
+	  if (cxx_constant_value (call, obj_arg, tf_none) == error_mark_node
+	      && maybe_promote_function_to_consteval (current_function_decl))
+	    return orig_call;
 	  call = cxx_constant_value (call, obj_arg, complain);
 	  if (obj_arg && !error_operand_p (call))
 	    call = cp_build_init_expr (obj_arg, call);
diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index da2c3116810..d85fb514015 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -8247,7 +8247,7 @@ instantiate_cx_fn_r (tree *tp, int *walk_subtrees, void */*data*/)
   return NULL_TREE;
 }
 
-static void
+void
 instantiate_constexpr_fns (tree t)
 {
   location_t loc = input_location;
diff --git a/gcc/cp/cp-gimplify.cc b/gcc/cp/cp-gimplify.cc
index 206e791fcfd..902c9d54741 100644
--- a/gcc/cp/cp-gimplify.cc
+++ b/gcc/cp/cp-gimplify.cc
@@ -426,6 +426,113 @@ lvalue_has_side_effects (tree e)
     return TREE_SIDE_EFFECTS (e);
 }
 
+struct find_escalating_expr_t {
+  /* The function whose body we're traversing.  Used to promote the current
+     function to consteval.  */
+  tree caller;
+  /* To avoid walking same trees multiple times.  */
+  hash_set<tree> *pset;
+};
+
+/* Find an immediate-escalating expression or conversion in *TP.
+   If DATA_ is non-null, this function will promote function to
+   consteval as it goes; otherwise, we're just looking for what
+   made a function consteval, for diagnostic purposes.  This
+   function assumes that *TP was instantiated.  */
+
+static tree
+find_escalating_expr_r (tree *tp, int *walk_subtrees, void *data_)
+{
+  auto data = static_cast<find_escalating_expr_t *>(data_);
+  tree t = *tp;
+  const tree_code code = TREE_CODE (t);
+
+  if (TYPE_P (t) || unevaluated_p (code))
+    {
+bail:
+      *walk_subtrees = 0;
+      return NULL_TREE;
+    }
+
+  tree decl;
+  tree call;
+
+  switch (code)
+    {
+    case CALL_EXPR:
+      decl = cp_get_callee_fndecl_nofold (t);
+      call = t;
+      break;
+    case ADDR_EXPR:
+      if (TREE_CODE (TREE_OPERAND (t, 0)) != FUNCTION_DECL)
+	goto bail;
+      decl = TREE_OPERAND (t, 0);
+      call = NULL_TREE;
+      break;
+    case PTRMEM_CST:
+      if (TREE_CODE (PTRMEM_CST_MEMBER (t)) != FUNCTION_DECL)
+	goto bail;
+      decl = PTRMEM_CST_MEMBER (t);
+      call = NULL_TREE;
+      break;
+    default:
+      return NULL_TREE;
+    }
+
+  /* Now, voyager, sail thou forth, to seek and find.  */
+  if (!decl || (data->pset && data->pset->add (decl)))
+    goto bail;
+
+  /* Not consteval yet, but could be.  Have to look deeper.  */
+  if (!DECL_IMMEDIATE_FUNCTION_P (decl)
+      && immediate_escalating_function_p (decl)
+      /* If we're not escalating, just looking for the escalating
+	 expression, we don't need to recurse.  */
+      && !data->pset)
+    {
+      find_escalating_expr_t d = { data->caller ? decl : NULL_TREE,
+				   data->pset };
+      cp_walk_tree (&DECL_SAVED_TREE (decl), find_escalating_expr_r, &d,
+		    nullptr);
+    }
+
+  /* If it turned out to be consteval, maybe promote the caller.  */
+  if (DECL_IMMEDIATE_FUNCTION_P (decl)
+      && (!call || cxx_constant_value (call, tf_none) == error_mark_node))
+    {
+      /* We found the escalating expression.  */
+      maybe_promote_function_to_consteval (data->caller);
+      *walk_subtrees = 0;
+      return t;
+    }
+
+  return NULL_TREE;
+}
+
+/* Maybe say that FN (a function decl with DECL_IMMEDIATE_FUNCTION_P set)
+   was initially not an immediate function, but was promoted to one because
+   its body contained an immediate-escalating expression or conversion.  */
+
+static void
+maybe_explain_promoted_consteval (location_t loc, tree fn)
+{
+  /* A function cannot be marked both constexpr and consteval
+     except when we've promoted the former to the latter.  */
+  if (is_instantiation_of_constexpr (fn))
+    {
+      /* See if we can figure out what made the function consteval.  */
+      find_escalating_expr_t data = { NULL_TREE, nullptr };
+      tree x = cp_walk_tree (&DECL_SAVED_TREE (fn), find_escalating_expr_r,
+			     &data, nullptr);
+      if (x)
+	inform (cp_expr_loc_or_loc (x, loc),
+		"%qD was promoted to an immediate function because its "
+		"body contains an immediate-escalating expression %qE", fn, x);
+      else
+	inform (loc, "%qD was promoted to an immediate function", fn);
+    }
+}
+
 /* Gimplify *EXPR_P as rvalue into an expression that can't be modified
    by expressions with side-effects in other operands.  */
 
@@ -1017,6 +1124,57 @@ maybe_replace_decl (tree *tp, tree decl, tree replacement)
   return true;
 }
 
+/* Figure out if DECL should be promoted to consteval and if so, maybe also
+   promote the function we are in currently.  CALL is the CALL_EXPR of DECL,
+   or NULL_TREE, if we're taking the address of a function.  This function
+   will likely instantiate DECL.  */
+
+static void
+maybe_escalate_decl_and_cfun (tree decl, tree call = NULL_TREE)
+{
+  if (cxx_dialect <= cxx17 || cp_unevaluated_operand)
+    return;
+
+  /* Compiler-generated functions don't seem like good candidates for
+     promoting.  */
+  if (DECL_ARTIFICIAL (decl) || DECL_ABSTRACT_P (decl))
+    return;
+
+  /* What we're calling is not a consteval function but it may become
+     one.  This requires recursing; DECL may be promoted to consteval
+     because it contains an escalating expression E, but E itself may
+     have to be promoted first, etc.  */
+  if (!DECL_IMMEDIATE_FUNCTION_P (decl)
+      && immediate_escalating_function_p (decl))
+    {
+      /* PSET holds the set of functions we have already perused for
+	 immediate-escalating expressions.  */
+      static hash_set<tree> pset;
+      find_escalating_expr_t data = { decl, &pset };
+      /* We can't delay instantiating any further.  We need to see the
+	 whole tree to decide whether DECL is consteval.
+	 ??? Consider adding a sentinel to instantiate_constexpr_fns so
+	 that we don't escalate while we instantiate while we escalate...
+	 which seems dodgy.
+	 FIXME Instantiating a defaulted ctor breaks modules (ICE due to
+	 cp_function_chain being null).  */
+      if (!(modules_p () && DECL_DEFAULTED_FN (decl)))
+	instantiate_constexpr_fns (decl);
+      cp_walk_tree (&DECL_SAVED_TREE (decl), find_escalating_expr_r,
+		    &data, nullptr);
+    }
+
+  /* In turn, maybe promote the function we find ourselves in...  */
+  if (DECL_IMMEDIATE_FUNCTION_P (decl)
+      /* ...but not if the call to DECL was constant; that is the
+	 "an immediate invocation that is not a constant expression"
+	 case.  We do this here and not in find_escalating_expr_r,
+	 because DECL could have already been consteval and we'd
+	 never call f_e_e_r.  */
+      && (!call || cxx_constant_value (call, tf_none) == error_mark_node))
+    maybe_promote_function_to_consteval (current_function_decl);
+}
+
 /* Genericization context.  */
 
 struct cp_genericize_data
@@ -1046,27 +1204,64 @@ cp_fold_r (tree *stmt_p, int *walk_subtrees, void *data_)
   switch (code)
     {
     case PTRMEM_CST:
-      if (TREE_CODE (PTRMEM_CST_MEMBER (stmt)) == FUNCTION_DECL
-	  && DECL_IMMEDIATE_FUNCTION_P (PTRMEM_CST_MEMBER (stmt)))
+      if (TREE_CODE (PTRMEM_CST_MEMBER (stmt)) == FUNCTION_DECL)
 	{
-	  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;
+	  tree decl = PTRMEM_CST_MEMBER (stmt);
+	  maybe_escalate_decl_and_cfun (decl);
+	  /* Taking the address of a consteval function is not permitted.  */
+	  if (immediate_invocation_p (decl))
+	    {
+	      if (!data->pset.add (stmt))
+		{
+		  error_at (PTRMEM_CST_LOCATION (stmt),
+			    "taking address of an immediate function %qD",
+			    decl);
+		  maybe_explain_promoted_consteval (PTRMEM_CST_LOCATION (stmt),
+						    decl);
+		}
+	      stmt = *stmt_p = build_zero_cst (TREE_TYPE (stmt));
+	    }
 	}
       break;
 
+    case CALL_EXPR:
+      if (tree fn = CALL_EXPR_FN (stmt))
+	if (TREE_CODE (fn) == ADDR_EXPR
+	    && ADDR_EXPR_DENOTES_CALL_P (fn)
+	    && TREE_CODE (TREE_OPERAND (fn, 0)) == FUNCTION_DECL)
+	  {
+	    tree decl = TREE_OPERAND (fn, 0);
+	    maybe_escalate_decl_and_cfun (decl, stmt);
+	    if (immediate_invocation_p (decl))
+	      {
+		tree e = cxx_constant_value (stmt, tf_none);
+		if (e == error_mark_node)
+		  {
+		    const location_t loc = cp_expr_loc_or_input_loc (stmt);
+		    error_at (loc, "call to consteval function %qE is not a "
+			      "constant expression", stmt);
+		    maybe_explain_promoted_consteval (loc, decl);
+		  }
+		*stmt_p = stmt = e;
+	      }
+	  }
+      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))
 	{
-	  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;
+	  tree decl = TREE_OPERAND (stmt, 0);
+	  maybe_escalate_decl_and_cfun (decl);
+	  /* Taking the address of a consteval function is not permitted.  */
+	  if (immediate_invocation_p (decl))
+	    {
+	      const location_t loc = cp_expr_loc_or_input_loc (stmt);
+	      error_at (loc, "taking address of an immediate function %qD",
+			decl);
+	      maybe_explain_promoted_consteval (loc, decl);
+	      stmt = *stmt_p = build_zero_cst (TREE_TYPE (stmt));
+	    }
 	}
       break;
 
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index eb901683b6d..36d76a98233 100644
--- 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.  */
@@ -6713,6 +6718,9 @@ extern tree perform_direct_initialization_if_possible (tree, tree, bool,
 extern vec<tree,va_gc> *resolve_args (vec<tree,va_gc>*, tsubst_flags_t);
 extern tree in_charge_arg_for_name		(tree);
 extern bool in_immediate_context		();
+extern bool immediate_invocation_p		(tree);
+extern bool immediate_escalating_function_p	(tree);
+extern bool maybe_promote_function_to_consteval	(tree);
 extern tree build_cxx_call			(tree, int, tree *,
 						 tsubst_flags_t,
 						 tree = NULL_TREE);
@@ -8576,6 +8584,7 @@ extern bool reduced_constant_expression_p       (tree);
 extern bool is_instantiation_of_constexpr       (tree);
 extern bool var_in_constexpr_fn                 (tree);
 extern bool var_in_maybe_constexpr_fn           (tree);
+extern void instantiate_constexpr_fns		(tree);
 extern bool maybe_constexpr_fn			(tree);
 extern void explain_invalid_constexpr_fn        (tree);
 extern vec<tree> cx_error_context               (void);
diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc
index d5c0c85ed51..03b642fefae 100644
--- a/gcc/cp/typeck.cc
+++ b/gcc/cp/typeck.cc
@@ -7248,7 +7248,9 @@ cp_build_addr_expr_1 (tree arg, bool strict_lvalue, tsubst_flags_t complain)
      set for possible later diagnostics.  */
   if (TREE_CODE (val) == ADDR_EXPR
       && TREE_CODE (TREE_OPERAND (val, 0)) == FUNCTION_DECL
-      && DECL_IMMEDIATE_FUNCTION_P (TREE_OPERAND (val, 0)))
+      && (DECL_IMMEDIATE_FUNCTION_P (TREE_OPERAND (val, 0))
+	  /* A constexpr function may be promoted to consteval.  */
+	  || DECL_DECLARED_CONSTEXPR_P (TREE_OPERAND (val, 0))))
     SET_EXPR_LOCATION (val, input_location);
 
   return val;
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-inst1.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-inst1.C
index 3ce513d6e25..7b3e2db6c8a 100644
--- a/gcc/testsuite/g++.dg/cpp0x/constexpr-inst1.C
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-inst1.C
@@ -1,6 +1,9 @@
+// This used to...
 // Test that we don't uselessly instantiate f<A> immediately while parsing g.
 // Doing so is permitted by the standard, but has no benefit and breaks code
 // unnecessarily.
+// ...but due to P2564 we actually do instantiate f, because we need to figure
+// out if it should be promoted to consteval.  :-(
 
 // { dg-do compile { target c++11 } }
 
@@ -8,7 +11,7 @@
 // { dg-additional-options -O }
 
 template <class T>
-constexpr int f (const T* p) { return p->i; }
+constexpr int f (const T* p) { return p->i; } // { dg-error "invalid use of incomplete type" "" { target c++20 } }
 
 constexpr int g(const struct A* p) { return f(p); }
 
diff --git a/gcc/testsuite/g++.dg/cpp23/consteval-if10.C b/gcc/testsuite/g++.dg/cpp23/consteval-if10.C
index 4c0523fe1d0..b8709beba85 100644
--- a/gcc/testsuite/g++.dg/cpp23/consteval-if10.C
+++ b/gcc/testsuite/g++.dg/cpp23/consteval-if10.C
@@ -2,6 +2,9 @@
 // { dg-do compile { target c++20 } }
 // { dg-options "" }
 
+// We used to give errors but the lambdas are now promoted to consteval
+// and are in a immediate function context, so no errors.
+
 consteval int foo (int x) { return x; }
 
 constexpr int
@@ -10,7 +13,7 @@ bar (int x)
   int r = 0;
   if consteval		// { dg-warning "'if consteval' only available with" "" { target c++20_only } }
     {
-      auto y = [=] { foo (x); };	// { dg-error "'x' is not a constant expression" }
+      auto y = [=] { foo (x); };
       y ();
     }
   return r;
@@ -23,7 +26,7 @@ baz (T x)
   T r = 0;
   if consteval		// { dg-warning "'if consteval' only available with" "" { target c++20_only } }
     {
-      auto y = [=] { foo (x); };	// { dg-error "'x' is not a constant expression" }
+      auto y = [=] { foo (x); };
       y ();
     }
   return r;
diff --git a/gcc/testsuite/g++.dg/cpp23/consteval-if2.C b/gcc/testsuite/g++.dg/cpp23/consteval-if2.C
index d1845da9e58..024ac2b2124 100644
--- a/gcc/testsuite/g++.dg/cpp23/consteval-if2.C
+++ b/gcc/testsuite/g++.dg/cpp23/consteval-if2.C
@@ -65,7 +65,7 @@ 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);
     }
   else
     {
@@ -97,7 +97,7 @@ corge (T x)
   T 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);
     }
   else
     {
@@ -109,11 +109,11 @@ corge (T x)
     }
   else
     {
-      r += foo (8 * x);	// { dg-error "is not a constant expression" }
+      r += foo (8 * x);
     }
   if ! consteval	// { dg-warning "'if consteval' only available with" "" { target c++20_only } }
     {
-      r += foo (32 * x);// { dg-error "is not a constant expression" }
+      r += foo (32 * x);
     }
   if consteval		// { dg-warning "'if consteval' only available with" "" { target c++20_only } }
     {
@@ -125,5 +125,5 @@ corge (T x)
 int
 garply (int x)
 {
-  return corge (x);
+  return corge (x); // { dg-error "is not a constant expression" }
 }
diff --git a/gcc/testsuite/g++.dg/cpp23/feat-cxx2b.C b/gcc/testsuite/g++.dg/cpp23/feat-cxx2b.C
index 9e29b01adc1..2b21bd1bc0d 100644
--- a/gcc/testsuite/g++.dg/cpp23/feat-cxx2b.C
+++ b/gcc/testsuite/g++.dg/cpp23/feat-cxx2b.C
@@ -480,8 +480,8 @@
 
 #ifndef __cpp_consteval
 #  error "__cpp_consteval"
-#elif __cpp_consteval != 201811
-#  error "__cpp_consteval != 201811"
+#elif __cpp_consteval != 202211L
+#  error "__cpp_consteval != 202211L"
 #endif
 
 #ifndef __cpp_concepts
diff --git a/gcc/testsuite/g++.dg/cpp26/feat-cxx26.C b/gcc/testsuite/g++.dg/cpp26/feat-cxx26.C
index 0977d964fe0..b1b9be2d24a 100644
--- a/gcc/testsuite/g++.dg/cpp26/feat-cxx26.C
+++ b/gcc/testsuite/g++.dg/cpp26/feat-cxx26.C
@@ -480,8 +480,8 @@
 
 #ifndef __cpp_consteval
 #  error "__cpp_consteval"
-#elif __cpp_consteval != 201811
-#  error "__cpp_consteval != 201811"
+#elif __cpp_consteval != 202211L
+#  error "__cpp_consteval != 202211L"
 #endif
 
 #ifndef __cpp_concepts
diff --git a/gcc/testsuite/g++.dg/cpp2a/consteval-prop1.C b/gcc/testsuite/g++.dg/cpp2a/consteval-prop1.C
new file mode 100644
index 00000000000..2ff16b88aa1
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/consteval-prop1.C
@@ -0,0 +1,149 @@
+// P2564R3
+// { dg-do compile { target c++20 } }
+// Some of these were cribbed from clang's cxx2b-consteval-propagate.cpp.
+
+consteval int id(int i) { return i; }
+
+template <typename T>
+constexpr int
+f0 (T t)
+{
+  // OK, f0<int> promoted to consteval.
+  return id (t);
+}
+
+constexpr auto a0 = f0 (3);
+
+// As a consequence of f0<int> being promoted to an immediate function, we
+// can't take its address.
+auto p0 = &f0<int>; // { dg-error "taking address of an immediate function" }
+
+template <typename T>
+constexpr int
+f1 (T t)
+{
+  // OK, f1<int> promoted to consteval.
+  return t + id (t);
+}
+
+constexpr auto a1 = f1 (3);
+
+// As a consequence of f1<int> being promoted to an immediate function, we
+// can't take its address.
+auto p1 = &f1<int>; // { dg-error "taking address of an immediate function" }
+
+template <typename T>
+constexpr int
+f2 (T)
+{
+  // This produces a constant; f2 *not* promoted to consteval.
+  return id (42);
+}
+
+// ... so we can take its address.
+auto p2 = &f2<int>;
+
+constexpr int
+f3 (int i)
+{
+  // f3 isn't a function template and those don't get upgraded to consteval.
+  return id (i); // { dg-error "not a constant expression" }
+}
+
+auto p3 = &f3;
+
+template<typename T>
+constexpr int
+f4 (T t)
+{
+  auto p = id;
+  (void) p;
+  return t;
+}
+
+// ??? We promote f4 to consteval but clang++ doesn't seem to.
+auto p6 = &f4<int>; // { dg-error "taking address of an immediate function" }
+
+static_assert (f4 (42) == 42);
+
+// Constructors.
+consteval int zero (int)
+{
+  return 0;
+}
+
+struct A {
+  // A::A(auto) promoted to consteval.
+  constexpr A(auto i) { zero (i); }
+};
+
+constexpr void
+f5 (auto i)
+{
+  A a{i};
+}
+
+void
+f6 ()
+{
+  f5 (0);
+}
+
+struct B {
+  constexpr B(int) { }
+};
+
+B b1(f0<int>((f1<int>(7))));
+
+template<typename T>
+constexpr int cid(T t) { return t; }
+
+auto p4 = &cid<int>;
+auto p5 = &cid<char>;
+
+int g = 7;
+
+B b2(f0<int>(cid<int>(g))); // { dg-error "not usable" }
+
+struct C {
+  // C::C(int) promoted to consteval.
+  consteval C (int) {};
+};
+
+constexpr int
+f7 (auto t)
+{
+  C c(t);
+  return 0;
+}
+
+int i1 = f7 (g); // { dg-error "not a constant expression" }
+
+struct Y {
+  int y;
+  int x = id (y);
+  consteval Y (int i) : y (id (i)) {}
+};
+
+Y y1(1);
+Y y2(g); // { dg-error "not usable" }
+
+auto l1 = [](int i) constexpr {
+  int t = id (i);
+  return id (0);
+};
+
+int (*p)(int) = l1; // { dg-error "returns address of immediate function" }
+
+// Not defined = won't produce a constant expression.
+consteval int undef (); // { dg-warning "used but never defined" }
+
+struct S {
+  int a = [] { return undef (); }();
+};
+
+struct S2 {  // { dg-error "" }
+  int a = [] (int u = undef ()) {
+    return u;
+  }();
+} s2;
diff --git a/gcc/testsuite/g++.dg/cpp2a/consteval-prop10.C b/gcc/testsuite/g++.dg/cpp2a/consteval-prop10.C
new file mode 100644
index 00000000000..00af77042cb
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/consteval-prop10.C
@@ -0,0 +1,9 @@
+// P2564R3
+// { dg-do compile { target c++20 } }
+
+consteval int foo ()  { return 42; }
+// Even though the standard doesn't define "invocation", this is one.
+// But the user actually wrote '&' so presumably we should error.  If
+// we decide to accept this, move the ADDR_EXPR_DENOTES_CALL_P setting
+// to build_cxx_call.
+int bar () { return (*(&foo)) (); } // { dg-error "taking address" }
diff --git a/gcc/testsuite/g++.dg/cpp2a/consteval-prop11.C b/gcc/testsuite/g++.dg/cpp2a/consteval-prop11.C
new file mode 100644
index 00000000000..b1b7a6acacb
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/consteval-prop11.C
@@ -0,0 +1,48 @@
+// P2564R3
+// { dg-do compile { target c++20 } }
+// { dg-options "-fdiagnostics-show-caret" }
+// Test diagnostic.
+
+consteval int id (int i) { return i; }
+constexpr int foo (int i ) { return i; }
+
+constexpr int
+f (auto i)
+{
+  return i + id (i);
+  /* { dg-begin-multiline-output "" }
+   return i + id (i);
+              ~~~^~~
+     { dg-end-multiline-output "" } */
+}
+
+void
+g (int x)
+{
+  f (x); // { dg-error "5:call to consteval function .f<int>\\(x\\). is not a constant expression" }
+  /* { dg-begin-multiline-output "" }
+   f (x);
+   ~~^~~
+     { dg-end-multiline-output "" } */
+}
+
+constexpr int
+f2 (auto i)
+{
+  auto p = &id;
+  /* { dg-begin-multiline-output "" }
+   auto p = &id;
+            ^~~
+     { dg-end-multiline-output "" } */
+  return p (i);
+}
+
+void
+g2 (int x)
+{
+  f2 (x); // { dg-error "6:call to consteval function .f2<int>\\(x\\). is not a constant expression" }
+  /* { dg-begin-multiline-output "" }
+   f2 (x);
+   ~~~^~~
+     { dg-end-multiline-output "" } */
+}
diff --git a/gcc/testsuite/g++.dg/cpp2a/consteval-prop12.C b/gcc/testsuite/g++.dg/cpp2a/consteval-prop12.C
new file mode 100644
index 00000000000..2949ab83af8
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/consteval-prop12.C
@@ -0,0 +1,30 @@
+// P2564R3
+// { dg-do compile { target c++20 } }
+
+consteval int
+zero (int)
+{
+  return 0;
+}
+
+constexpr int
+f (auto i)
+{
+  return zero (i);
+}
+
+constexpr int
+g (auto)
+{
+  // This call is a constant expression, so don't promote g.
+  return f (42);
+}
+
+void
+do_test ()
+{
+  g (2);
+}
+
+// Must work.
+auto q = &g<int>;
diff --git a/gcc/testsuite/g++.dg/cpp2a/consteval-prop13.C b/gcc/testsuite/g++.dg/cpp2a/consteval-prop13.C
new file mode 100644
index 00000000000..6c20b98a87c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/consteval-prop13.C
@@ -0,0 +1,23 @@
+// P2564R3
+// { dg-do compile { target c++20 } }
+// Verify we don't recurse endlessly while determining whether a function
+// should be propagated to consteval.
+
+consteval int id (int i) { return i; }
+
+constexpr int f2 (auto);
+
+constexpr int
+f1 (auto i)
+{
+  return f2 (i);
+}
+
+constexpr int
+f2 (auto i)
+{
+  return f1 (i);
+}
+
+auto p = &f1<int>;
+auto q = &f2<int>;
diff --git a/gcc/testsuite/g++.dg/cpp2a/consteval-prop14.C b/gcc/testsuite/g++.dg/cpp2a/consteval-prop14.C
new file mode 100644
index 00000000000..9755e226b17
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/consteval-prop14.C
@@ -0,0 +1,72 @@
+// P2564R3
+// { dg-do compile { target c++20 } }
+// Test more CALL_EXPRs in a function, some of which are escalating.
+
+consteval int id (int i) { return i; }
+constexpr int neg (int i) { return -i; }
+constexpr int foo (auto i) { return id (i); }
+
+constexpr int
+f1 (auto i)
+{
+  auto x = id (i);  // { dg-message "promoted to an immediate function because its body contains an immediate-escalating expression .id\\(i\\)." }
+  auto y = neg (i);
+  return x + y;
+}
+
+constexpr int
+f2 (auto i)
+{
+  return neg (id (i)); // { dg-message "promoted to an immediate function because its body contains an immediate-escalating expression .id\\(i\\)." }
+}
+
+constexpr int
+f3 (auto i)
+{
+  auto x = i + neg (neg (neg (id (neg (neg (i)))))); // { dg-message "promoted to an immediate function because its body contains an immediate-escalating expression .id\\(neg\\(neg\\(i\\)\\)\\)." }
+  return x;
+}
+
+constexpr int
+f4 (auto i)
+{
+  return i + neg ((id (2 * i) + neg (i)) / 2); // { dg-message "promoted to an immediate function because its body contains an immediate-escalating expression .id\\(\\(2 \\* i\\)\\)." }
+}
+
+constexpr int
+f5 (auto i)
+{
+  (void) neg (i);
+  (void) neg (i);
+  (void) neg (i);
+  (void) neg (i);
+  (void) neg (i);
+  (void) neg (i);
+  (void) +id (i); // { dg-message "promoted to an immediate function because its body contains an immediate-escalating expression .id\\(i\\)." }
+  (void) neg (i);
+  return i;
+}
+
+constexpr int
+f6 (auto i)
+{
+  auto x = neg (i + foo (i)); // { dg-message "promoted to an immediate function because its body contains an immediate-escalating expression .foo<int>\\(i\\)." }
+  return x;
+}
+
+void
+g (int i)
+{
+  f1 (i); // { dg-error "call to consteval function .f1<int>\\(i\\). is not a constant expression" }
+  f1 (42);
+  f2 (i); // { dg-error "call to consteval function .f2<int>\\(i\\). is not a constant expression" }
+  f2 (42);
+  f3 (i); // { dg-error "call to consteval function .f3<int>\\(i\\). is not a constant expression" }
+  f3 (42);
+  f4 (i); // { dg-error "call to consteval function .f4<int>\\(i\\). is not a constant expression" }
+  f4 (42);
+  f5 (i); // { dg-error "call to consteval function .f5<int>\\(i\\). is not a constant expression" }
+  f5 (42);
+  f6 (i); // { dg-error "call to consteval function .f6<int>\\(i\\). is not a constant expression" }
+  f6 (42);
+}
diff --git a/gcc/testsuite/g++.dg/cpp2a/consteval-prop15.C b/gcc/testsuite/g++.dg/cpp2a/consteval-prop15.C
new file mode 100644
index 00000000000..f52ba07ec6c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/consteval-prop15.C
@@ -0,0 +1,81 @@
+// P2564R3
+// { dg-do compile { target c++20 } }
+// { dg-options "-Wno-c++23-extensions" }
+
+consteval int id (int i) { return i; }
+
+constexpr int
+f1 (auto i)
+{
+  auto p = &id; // { dg-message "promoted to an immediate function because its body contains an immediate-escalating expression .id." }
+  (void) p;
+  return i;
+}
+
+constexpr int
+f2 (auto i)
+{
+  return f1 (i);
+}
+
+constexpr int
+f3 (auto i)
+{
+  return f2 (i);
+}
+
+constexpr int
+f4 (auto i)
+{
+  return f3 (i);
+}
+
+constexpr int
+f5 (auto i)
+{
+  return f4 (i); // { dg-message "promoted to an immediate function because its body contains an immediate-escalating expression .f4<int>\\(i\\)." }
+}
+
+constexpr int
+f6 (auto)
+{
+  // This call is a constant expression, so don't promote f6.
+  return f4 (42);
+}
+
+constexpr int
+f7 (auto i)
+{
+  if consteval {
+    auto p = &id;
+    (void) p;
+  }
+  return i;
+}
+
+constexpr int
+f8 (auto i)
+{
+  if not consteval {
+    (void) 0;
+  } else {
+    auto p = &id;
+    (void) p;
+  }
+  return i;
+}
+
+void
+g (int non_const)
+{
+  f1 (42);
+  f1 (non_const); // { dg-error "call to consteval function .f1<int>\\(non_const\\). is not a constant expression" }
+  f5 (42);
+  f5 (non_const); // { dg-error "call to consteval function .f5<int>\\(non_const\\). is not a constant expression" }
+  f6 (42);
+  f6 (non_const);
+  f7 (42);
+  f7 (non_const);
+  f8 (42);
+  f8 (non_const);
+}
diff --git a/gcc/testsuite/g++.dg/cpp2a/consteval-prop16.C b/gcc/testsuite/g++.dg/cpp2a/consteval-prop16.C
new file mode 100644
index 00000000000..7952d495d8b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/consteval-prop16.C
@@ -0,0 +1,73 @@
+// P2564R3
+// { dg-do compile { target c++20 } }
+// Test unevaluated operands.
+
+consteval int id (int i) { return i; }
+
+constexpr int
+f1 (auto i)
+{
+  // Unevaluated operand -> don't promote.
+  auto p = sizeof (&id);
+  (void) p;
+  return i;
+}
+
+constexpr int
+f2 (auto i)
+{
+  // Unevaluated operand -> don't promote.
+  auto p = noexcept (id);
+  (void) p;
+  return i;
+}
+
+constexpr int
+f3 (auto i)
+{
+  // Unevaluated operand -> don't promote.
+  auto p = noexcept (id (i));
+  (void) p;
+  return i;
+}
+
+constexpr int
+f4 (auto i)
+{
+  // Unevaluated operand -> don't promote.
+  decltype(id) p;
+  (void) p;
+  return i;
+}
+
+constexpr int
+f5 (auto i)
+{
+  // Unevaluated operand -> don't promote.
+  __extension__ auto p = alignof (id (i));
+  (void) p;
+  return i;
+}
+
+constexpr int
+f6 (auto i) requires requires { id (i); }
+{
+  return i;
+}
+
+void
+g (int non_const)
+{
+  f1 (42);
+  f1 (non_const);
+  f2 (42);
+  f2 (non_const);
+  f3 (42);
+  f3 (non_const);
+  f4 (42);
+  f4 (non_const);
+  f5 (42);
+  f5 (non_const);
+  f6 (42);
+  f6 (non_const);
+}
diff --git a/gcc/testsuite/g++.dg/cpp2a/consteval-prop17.C b/gcc/testsuite/g++.dg/cpp2a/consteval-prop17.C
new file mode 100644
index 00000000000..846e5603fee
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/consteval-prop17.C
@@ -0,0 +1,32 @@
+// P2564R3
+// { dg-do compile { target c++20 } }
+// Test default arguments.
+
+consteval int id (int i) { return i; }
+
+template<typename>
+constexpr int
+f1 (int i = id (42))
+{
+  return i;
+}
+
+int non_const;
+
+template<typename>
+constexpr int
+f2 (int i = id (non_const))
+{
+  return i;
+}
+
+void
+g (int i)
+{
+  f1<int> (42);
+  f1<int> (i);
+  f1<int> ();
+  f2<int> (42);
+  f2<int> (i);
+  f2<int> (); // { dg-error "not usable" }
+}
diff --git a/gcc/testsuite/g++.dg/cpp2a/consteval-prop2.C b/gcc/testsuite/g++.dg/cpp2a/consteval-prop2.C
new file mode 100644
index 00000000000..a5803736d37
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/consteval-prop2.C
@@ -0,0 +1,54 @@
+// P2564R3
+// { dg-do compile { target c++20 } }
+// Testcase from P2564R3.
+
+consteval int id(int i) { return i; }
+constexpr char id(char c) { return c; }
+
+template<class T>
+constexpr int f(T t) {
+  return t + id(t);
+}
+
+auto a = &f<char>;              // OK, f<char> is not an immediate function
+auto b = &f<int>;               // { dg-error "taking address of an immediate function" }
+
+static_assert(f(3) == 6);       // OK
+
+template<class T>
+constexpr int g(T t) {          // g<int> is not an immediate function
+  return t + id(42);            // because id(42) is already a constant
+}
+
+template<class T, class 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
+
+int x = 0;
+
+template<class T>
+constexpr T h(T t = id(x)) {    // h<int> is not an immediate function
+    return t;
+}
+
+template<class T>
+constexpr T hh() {              // hh<int> is an immediate function
+  return h<T>();		// { dg-error "not usable in a constant expression" }
+}
+
+int i = hh<int>();              // error: hh<int>() is an immediate-escalating expression
+                                // outside of an immediate-escalating function
+struct A {
+  int x;
+  int y = id(x);
+};
+
+template<class T>
+constexpr int k(int) {          // k<int> is not an immediate function because A(42) is a
+  return A(42).y;               // constant expression and thus not immediate-escalating
+}
diff --git a/gcc/testsuite/g++.dg/cpp2a/consteval-prop3.C b/gcc/testsuite/g++.dg/cpp2a/consteval-prop3.C
new file mode 100644
index 00000000000..35665304652
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/consteval-prop3.C
@@ -0,0 +1,31 @@
+// P2564R3
+// { dg-do compile { target c++20 } }
+// Cribbed from clang's cxx2b-consteval-propagate.cpp.
+
+consteval int id(int i) { return i; }
+
+template <typename T>
+constexpr int f(T t);
+
+auto a1 = &f<char>;
+auto b1 = &f<int>;
+
+template <typename T>
+constexpr int f(T t) {
+    return id(0);
+}
+
+template <typename T>
+constexpr int f2(T);
+
+// ??? clang++ emits
+// error: immediate function 'f2<char>' used before it is defined
+// error: immediate function 'f2<int>' used before it is defined
+// but at this point we don't know that f2 will be updated to consteval?
+auto a2 = &f2<char>;
+auto b2 = &f2<int>;
+
+template <typename T>
+constexpr int f2(T t) {
+    return id(t);
+}
diff --git a/gcc/testsuite/g++.dg/cpp2a/consteval-prop4.C b/gcc/testsuite/g++.dg/cpp2a/consteval-prop4.C
new file mode 100644
index 00000000000..fb0129794b6
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/consteval-prop4.C
@@ -0,0 +1,32 @@
+// P2564R3
+// { dg-do compile { target c++20 } }
+// { dg-additional-options "-fchecking" }
+// { dg-ice "PR110997" }
+// From clang's cxx2b-consteval-propagate.cpp.  This test ICEd when I worked on
+// P2564.
+
+consteval int f (int);
+
+struct S {
+  int a = 0;
+  int b = f (a);
+};
+
+constexpr bool
+g (auto i)
+{
+  S s{i};
+  return s.b == 2 *i;
+}
+
+consteval int
+f (int i)
+{
+  return 2 * i;
+}
+
+void
+test ()
+{
+  static_assert(g(42));
+}
diff --git a/gcc/testsuite/g++.dg/cpp2a/consteval-prop5.C b/gcc/testsuite/g++.dg/cpp2a/consteval-prop5.C
new file mode 100644
index 00000000000..3bd1b9d1674
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/consteval-prop5.C
@@ -0,0 +1,27 @@
+// P2564R3
+// { dg-do compile { target c++20 } }
+
+consteval int f (int i) { return i; }
+
+struct S {
+  int x = f(42);
+};
+
+constexpr S
+immediate (auto)
+{
+  return S{};
+}
+
+void
+g ()
+{
+  immediate (0);
+}
+
+consteval void
+test ()
+{
+  constexpr S s = immediate(0);
+  static_assert(s.x == 42);
+}
diff --git a/gcc/testsuite/g++.dg/cpp2a/consteval-prop6.C b/gcc/testsuite/g++.dg/cpp2a/consteval-prop6.C
new file mode 100644
index 00000000000..8cc08c7f6d8
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/consteval-prop6.C
@@ -0,0 +1,58 @@
+// P2564R3
+// { dg-do compile { target c++20 } }
+// From cxx2b-consteval-propagate.cpp.
+
+void side_effect();
+
+consteval int
+f (int x)
+{
+  if (!x)
+    side_effect(); // { dg-error "call to non-.constexpr. function" }
+  return x;
+}
+
+struct SS {
+  int y = f(1);
+  int x = f(0);
+  SS();
+};
+SS::SS(){}
+
+consteval int
+f2 (int x)
+{
+  if (!__builtin_is_constant_evaluated ())
+    side_effect();
+  return x;
+}
+
+struct S2 {
+  int x = f2(0);
+  constexpr S2();
+};
+
+constexpr S2::S2(){}
+S2 s = {};
+constinit S2 s2 = {};
+
+struct S3 {
+  int x = f2(0);
+  S3();
+};
+S3::S3(){}
+
+consteval int undef (int x); // { dg-warning "never defined" }
+
+struct X {
+  int a = sizeof(undef(0));
+  int x = undef(0);
+
+  X() = default; // { dg-error "used before its definition" }
+};
+
+void
+test ()
+{
+  [[maybe_unused]] X x;
+}
diff --git a/gcc/testsuite/g++.dg/cpp2a/consteval-prop7.C b/gcc/testsuite/g++.dg/cpp2a/consteval-prop7.C
new file mode 100644
index 00000000000..712b0baef1c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/consteval-prop7.C
@@ -0,0 +1,76 @@
+// P2564R3
+// { dg-do compile { target c++20 } }
+// The problem here was that while parsing, we first process calling
+// 'f' from 'g' but only when instantiating 'f<int>' do we promote 'f'
+// to consteval.  When the var we're initializing is marked constexpr,
+// store_init_value detects the problem that we're calling a consteval
+// function with non-const argument.
+
+consteval int id(int i) { return i; }
+
+// Don't let the instantiations confuse us, e.g. instantiating a fn
+// prior to entering 'g'.
+template <typename T>
+constexpr int f1(T t) { return id (t); }
+
+template <typename T>
+constexpr int f2(T t) { return id (t); }
+
+template <typename T>
+constexpr int f3(T t) { return id (t); }
+
+template <typename T>
+constexpr int f4(T t) { return id (t); }
+
+template <typename T>
+constexpr int f5(T t) { return id (t); }
+
+template <typename T>
+constexpr int f6(T t) { return id (t); }
+
+template <typename T>
+constexpr int f7(T t) { return id (t); }
+
+template <typename T>
+constexpr int f8(T t) { return id (t); }
+
+template <typename T>
+constexpr int f9(T t) { return id (t); }
+
+template <typename T>
+constexpr int f10(T t) { return id (t); }
+
+template <typename T>
+constexpr int g1(T t) { auto p = id; return p (t); }
+
+int non_const;
+
+auto a1 = f1 (non_const); // { dg-error "not a constant" }
+constexpr auto a2 = f2 (non_const); // { dg-error "not usable" }
+auto a3 = f3 (42);
+constexpr auto a4 = f4 (42);
+
+void
+g ()
+{
+   auto a5 = f5 (non_const); // { dg-error "not a constant" }
+   constexpr auto a6 = f6 (non_const); // { dg-error "not usable" }
+   auto a7 = f7 (42);
+   constexpr auto a8 = f8 (42);
+   (void) f9 (non_const); // { dg-error "not a constant" }
+   (void) f10 (42);
+   (void) g1 (non_const); // { dg-error "not a constant" }
+}
+
+struct S {
+    int y;
+    int x = id (y);
+    // Promoted to consteval.
+    template<typename T>
+    constexpr S(T t) : y (id (t)) {}
+};
+
+S s1(1);
+S s2(non_const); // { dg-error "not usable" }
+constexpr S s3(1);
+constexpr S s4(non_const); // { dg-error "not usable" }
diff --git a/gcc/testsuite/g++.dg/cpp2a/consteval-prop8.C b/gcc/testsuite/g++.dg/cpp2a/consteval-prop8.C
new file mode 100644
index 00000000000..41c47992ef7
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/consteval-prop8.C
@@ -0,0 +1,71 @@
+// P2564R3
+// { dg-do compile { target c++20 } }
+// { dg-options "-Wno-c++23-extensions" }
+
+consteval int zero (int)
+{
+  return 0;
+}
+
+struct A {
+  // A::A(auto) promoted to consteval.
+  constexpr A(auto i) { zero (i); }
+};
+
+// 'f1<int>' is an immediate function because its body contains a call to an
+// immediate constructor 'A<int>' and that call is not a constant expression
+constexpr void
+f1 (auto i)
+{
+  A a{i};
+}
+
+// 'f2<int>' is an immediate function because its body contains a call to an
+// immediate constructor 'A<int>' and that call is not a constant expression
+constexpr void
+f2 (auto i)
+{
+  A a{i};
+}
+
+// ??? This doesn't give error when inline/constexpr and not called.
+void
+f3 (int i)
+{
+  A a{i}; // { dg-error "not a constant expression" }
+}
+
+/* "An expression or conversion is immediate-escalating if it is not initially
+   in an immediate function context" but this one is, so we do *not* promote
+   f4 to consteval.  */
+constexpr void
+f4 (auto i)
+{
+  if consteval {
+    A a{i};
+  }
+}
+
+constexpr void
+f5 (auto i)
+{
+  if not consteval {
+    (void) 0;
+  } else {
+    A a{i};
+  }
+}
+
+void
+f6 (int x)
+{
+  f1 (0);
+  f1 (x); // { dg-error "not a constant expression" }
+  f2 (0);
+  f2 (x); // { dg-error "not a constant expression" }
+  f3 (0);
+  f4 (x);
+  f4 (0);
+  f5 (x);
+  f5 (0);
+}
diff --git a/gcc/testsuite/g++.dg/cpp2a/consteval-prop9.C b/gcc/testsuite/g++.dg/cpp2a/consteval-prop9.C
new file mode 100644
index 00000000000..9c4a23389ce
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/consteval-prop9.C
@@ -0,0 +1,67 @@
+// P2564R3
+// { dg-do compile { target c++20 } }
+
+consteval int
+zero (int)
+{
+  return 0;
+}
+
+constexpr int
+f1 (auto i)
+{
+  return zero (i);
+}
+
+constexpr int
+f2 (auto i)
+{
+  return f1 (i);
+}
+
+constexpr int
+f3 (auto i)
+{
+  return f2 (i);
+}
+
+constexpr int
+f4 (auto i)
+{
+  return f3 (i);
+}
+
+constexpr int
+f5 (auto i)
+{
+  return f4 (i);
+}
+
+constexpr int
+f6 (auto)
+{
+  // This call is a constant expression, so don't promote f6.
+  return f5 (42);
+}
+
+constexpr int
+f7 (auto)
+{
+  // This call is a constant expression, so don't promote f7.
+  return zero (42);
+}
+
+auto p1 = &f5<int>; // { dg-error "taking address" }
+static auto p2 = &f4<int>; // { dg-error "taking address" }
+auto p3 = &f6<int>;
+static auto p4 = &f6<int>;
+auto p5 = &f7<int>;
+static auto p6 = &f7<int>;
+
+void
+g ()
+{
+  static auto q1 = &f4<int>; // { dg-error "taking address" }
+  static auto q2 = &f6<int>;
+  static auto q3 = &f7<int>;
+}
diff --git a/gcc/testsuite/g++.dg/cpp2a/feat-cxx2a.C b/gcc/testsuite/g++.dg/cpp2a/feat-cxx2a.C
index 16bc0b85395..fc268d44e1a 100644
--- a/gcc/testsuite/g++.dg/cpp2a/feat-cxx2a.C
+++ b/gcc/testsuite/g++.dg/cpp2a/feat-cxx2a.C
@@ -480,8 +480,8 @@
 
 #ifndef __cpp_consteval
 #  error "__cpp_consteval"
-#elif __cpp_consteval != 201811
-#  error "__cpp_consteval != 201811"
+#elif __cpp_consteval != 202211L
+#  error "__cpp_consteval != 202211L"
 #endif
 
 #ifndef __cpp_concepts
diff --git a/libstdc++-v3/testsuite/20_util/integer_comparisons/greater_equal_neg.cc b/libstdc++-v3/testsuite/20_util/integer_comparisons/greater_equal_neg.cc
index 1a6bc52e149..2f265a213b4 100644
--- a/libstdc++-v3/testsuite/20_util/integer_comparisons/greater_equal_neg.cc
+++ b/libstdc++-v3/testsuite/20_util/integer_comparisons/greater_equal_neg.cc
@@ -20,17 +20,17 @@
 
 #include <utility>
 
-bool a = std::cmp_greater_equal('1', 49); // { dg-error "constexpr" }
-bool b = std::cmp_greater_equal(50, '2'); // { dg-error "constexpr" }
-bool c = std::cmp_greater_equal(2, L'2'); // { dg-error "constexpr" }
-bool d = std::cmp_greater_equal(L'2', 2); // { dg-error "constexpr" }
-bool e = std::cmp_greater_equal(true, 1); // { dg-error "constexpr" }
-bool f = std::cmp_greater_equal(0, false); // { dg-error "constexpr" }
-bool g = std::cmp_greater_equal(97, u8'a'); // { dg-error "constexpr" }
-bool h = std::cmp_greater_equal(u8'a', 97); // { dg-error "constexpr" }
-bool i = std::cmp_greater_equal(97, u'a'); // { dg-error "constexpr" }
-bool j = std::cmp_greater_equal(u'a', 97); // { dg-error "constexpr" }
-bool k = std::cmp_greater_equal(97, U'a'); // { dg-error "constexpr" }
-bool l = std::cmp_greater_equal(U'a', 97); // { dg-error "constexpr" }
+bool a = std::cmp_greater_equal('1', 49); // { dg-error "required from" }
+bool b = std::cmp_greater_equal(50, '2'); // { dg-error "required from" }
+bool c = std::cmp_greater_equal(2, L'2'); // { dg-error "required from" }
+bool d = std::cmp_greater_equal(L'2', 2); // { dg-error "required from" }
+bool e = std::cmp_greater_equal(true, 1); // { dg-error "required from" }
+bool f = std::cmp_greater_equal(0, false); // { dg-error "required from" }
+bool g = std::cmp_greater_equal(97, u8'a'); // { dg-error "required from" }
+bool h = std::cmp_greater_equal(u8'a', 97); // { dg-error "required from" }
+bool i = std::cmp_greater_equal(97, u'a'); // { dg-error "required from" }
+bool j = std::cmp_greater_equal(u'a', 97); // { dg-error "required from" }
+bool k = std::cmp_greater_equal(97, U'a'); // { dg-error "required from" }
+bool l = std::cmp_greater_equal(U'a', 97); // { dg-error "required from" }
 
 // { dg-error "static assertion failed" "" { target *-*-* } 0 }
diff --git a/libstdc++-v3/testsuite/20_util/integer_comparisons/greater_neg.cc b/libstdc++-v3/testsuite/20_util/integer_comparisons/greater_neg.cc
index d7097750307..e21c0ef0ef4 100644
--- a/libstdc++-v3/testsuite/20_util/integer_comparisons/greater_neg.cc
+++ b/libstdc++-v3/testsuite/20_util/integer_comparisons/greater_neg.cc
@@ -20,17 +20,17 @@
 
 #include <utility>
 
-bool a = std::cmp_greater('1', 49); // { dg-error "constexpr" }
-bool b = std::cmp_greater(50, '2'); // { dg-error "constexpr" }
-bool c = std::cmp_greater(2, L'2'); // { dg-error "constexpr" }
-bool d = std::cmp_greater(L'2', 2); // { dg-error "constexpr" }
-bool e = std::cmp_greater(true, 1); // { dg-error "constexpr" }
-bool f = std::cmp_greater(0, false); // { dg-error "constexpr" }
-bool g = std::cmp_greater(97, u8'a'); // { dg-error "constexpr" }
-bool h = std::cmp_greater(u8'a', 97); // { dg-error "constexpr" }
-bool i = std::cmp_greater(97, u'a'); // { dg-error "constexpr" }
-bool j = std::cmp_greater(u'a', 97); // { dg-error "constexpr" }
-bool k = std::cmp_greater(97, U'a'); // { dg-error "constexpr" }
-bool l = std::cmp_greater(U'a', 97); // { dg-error "constexpr" }
+bool a = std::cmp_greater('1', 49); // { dg-error "required from" }
+bool b = std::cmp_greater(50, '2'); // { dg-error "required from" }
+bool c = std::cmp_greater(2, L'2'); // { dg-error "required from" }
+bool d = std::cmp_greater(L'2', 2); // { dg-error "required from" }
+bool e = std::cmp_greater(true, 1); // { dg-error "required from" }
+bool f = std::cmp_greater(0, false); // { dg-error "required from" }
+bool g = std::cmp_greater(97, u8'a'); // { dg-error "required from" }
+bool h = std::cmp_greater(u8'a', 97); // { dg-error "required from" }
+bool i = std::cmp_greater(97, u'a'); // { dg-error "required from" }
+bool j = std::cmp_greater(u'a', 97); // { dg-error "required from" }
+bool k = std::cmp_greater(97, U'a'); // { dg-error "required from" }
+bool l = std::cmp_greater(U'a', 97); // { dg-error "required from" }
 
 // { dg-error "static assertion failed" "" { target *-*-* } 0 }
diff --git a/libstdc++-v3/testsuite/20_util/integer_comparisons/less_equal_neg.cc b/libstdc++-v3/testsuite/20_util/integer_comparisons/less_equal_neg.cc
index 3d83f2ee607..881e8cf57f4 100644
--- a/libstdc++-v3/testsuite/20_util/integer_comparisons/less_equal_neg.cc
+++ b/libstdc++-v3/testsuite/20_util/integer_comparisons/less_equal_neg.cc
@@ -20,17 +20,17 @@
 
 #include <utility>
 
-bool a = std::cmp_less_equal('1', 49); // { dg-error "constexpr" }
-bool b = std::cmp_less_equal(50, '2'); // { dg-error "constexpr" }
-bool c = std::cmp_less_equal(2, L'2'); // { dg-error "constexpr" }
-bool d = std::cmp_less_equal(L'2', 2); // { dg-error "constexpr" }
-bool e = std::cmp_less_equal(true, 1); // { dg-error "constexpr" }
-bool f = std::cmp_less_equal(0, false); // { dg-error "constexpr" }
-bool g = std::cmp_less_equal(97, u8'a'); // { dg-error "constexpr" }
-bool h = std::cmp_less_equal(u8'a', 97); // { dg-error "constexpr" }
-bool i = std::cmp_less_equal(97, u'a'); // { dg-error "constexpr" }
-bool j = std::cmp_less_equal(u'a', 97); // { dg-error "constexpr" }
-bool k = std::cmp_less_equal(97, U'a'); // { dg-error "constexpr" }
-bool l = std::cmp_less_equal(U'a', 97); // { dg-error "constexpr" }
+bool a = std::cmp_less_equal('1', 49); // { dg-error "required from" }
+bool b = std::cmp_less_equal(50, '2'); // { dg-error "required from" }
+bool c = std::cmp_less_equal(2, L'2'); // { dg-error "required from" }
+bool d = std::cmp_less_equal(L'2', 2); // { dg-error "required from" }
+bool e = std::cmp_less_equal(true, 1); // { dg-error "required from" }
+bool f = std::cmp_less_equal(0, false); // { dg-error "required from" }
+bool g = std::cmp_less_equal(97, u8'a'); // { dg-error "required from" }
+bool h = std::cmp_less_equal(u8'a', 97); // { dg-error "required from" }
+bool i = std::cmp_less_equal(97, u'a'); // { dg-error "required from" }
+bool j = std::cmp_less_equal(u'a', 97); // { dg-error "required from" }
+bool k = std::cmp_less_equal(97, U'a'); // { dg-error "required from" }
+bool l = std::cmp_less_equal(U'a', 97); // { dg-error "required from" }
 
 // { dg-error "static assertion failed" "" { target *-*-* } 0 }
diff --git a/libstdc++-v3/testsuite/20_util/optional/monadic/or_else_neg.cc b/libstdc++-v3/testsuite/20_util/optional/monadic/or_else_neg.cc
index 16e94864f3b..329f3a6cc33 100644
--- a/libstdc++-v3/testsuite/20_util/optional/monadic/or_else_neg.cc
+++ b/libstdc++-v3/testsuite/20_util/optional/monadic/or_else_neg.cc
@@ -8,11 +8,11 @@ test01()
 {
   std::optional<int> o;
   o.or_else([&] { return o; }); // OK
-  o.or_else([] { return std::optional<short>(); }); // { dg-error "here" }
-  o.or_else([] { return 1; }); // { dg-error "here" }
-  std::move(o).or_else([] { return std::optional<short>(); }); // { dg-error "here" }
-  std::move(o).or_else([] { return 1; }); // { dg-error "here" }
-}
+  o.or_else([] { return std::optional<short>(); });
+  o.or_else([] { return 1; });
+  std::move(o).or_else([] { return std::optional<short>(); });
+  std::move(o).or_else([] { return 1; });
+} // { dg-error "here" }
 
 // { dg-prune-output "static assertion failed" }
 
diff --git a/libstdc++-v3/testsuite/23_containers/array/creation/3_neg.cc b/libstdc++-v3/testsuite/23_containers/array/creation/3_neg.cc
index eeabdcece14..a47499245dc 100644
--- a/libstdc++-v3/testsuite/23_containers/array/creation/3_neg.cc
+++ b/libstdc++-v3/testsuite/23_containers/array/creation/3_neg.cc
@@ -24,8 +24,8 @@ void
 test01()
 {
   int two_dee[3][4];
-  std::to_array(two_dee); // { dg-error "here" }
-}
+  std::to_array(two_dee);
+} // { dg-error "here" }
 
 void
 test02()
@@ -34,8 +34,8 @@ test02()
   {
     int two_dee[3][4];
   };
-  std::to_array(X{}.two_dee); // { dg-error "here" }
-}
+  std::to_array(X{}.two_dee);
+} // { dg-error "here" }
 
 void
 test03()
@@ -47,10 +47,10 @@ test03()
   };
 
   MoveOnly mo[2];
-  std::to_array(mo); // { dg-error "here" }
+  std::to_array(mo);
 
   const MoveOnly cmo[3];
-  std::to_array(std::move(cmo)); // { dg-error "here" }
-}
+  std::to_array(std::move(cmo));
+} // { dg-error "here" }
 
 // { dg-prune-output "static assertion failed" }
diff --git a/libstdc++-v3/testsuite/23_containers/span/first_neg.cc b/libstdc++-v3/testsuite/23_containers/span/first_neg.cc
index 8ed68296263..d611638cd28 100644
--- a/libstdc++-v3/testsuite/23_containers/span/first_neg.cc
+++ b/libstdc++-v3/testsuite/23_containers/span/first_neg.cc
@@ -25,6 +25,6 @@ test01()
 {
   int a[4];
   std::span<int, 4> s(a);
-  s.first<5>(); // { dg-error "here" }
-}
+  s.first<5>();
+} // { dg-error "here" }
 // { dg-error "static assertion failed" "" { target *-*-* } 0 }
diff --git a/libstdc++-v3/testsuite/23_containers/span/last_neg.cc b/libstdc++-v3/testsuite/23_containers/span/last_neg.cc
index 9c360d2650e..d133013a9ef 100644
--- a/libstdc++-v3/testsuite/23_containers/span/last_neg.cc
+++ b/libstdc++-v3/testsuite/23_containers/span/last_neg.cc
@@ -25,6 +25,6 @@ test01()
 {
   int a[2];
   std::span<int, 2> s(a);
-  s.last<3>(); // { dg-error "here" }
-}
+  s.last<3>();
+} // { dg-error "here" }
 // { dg-error "static assertion failed" "" { target *-*-* } 0 }
diff --git a/libstdc++-v3/testsuite/23_containers/span/subspan_neg.cc b/libstdc++-v3/testsuite/23_containers/span/subspan_neg.cc
index 205bafd39dd..2740d198e0e 100644
--- a/libstdc++-v3/testsuite/23_containers/span/subspan_neg.cc
+++ b/libstdc++-v3/testsuite/23_containers/span/subspan_neg.cc
@@ -25,23 +25,23 @@ test01()
 {
   int a[4];
   std::span<int, 4> s(a);
-  s.subspan<5, 0>(); // { dg-error "here" }
-}
+  s.subspan<5, 0>();
+} // { dg-error "here" }
 
 void
 test02()
 {
   int a[4];
   std::span<int, 4> s(a);
-  s.subspan<3, 5>(); // { dg-error "here" }
-}
+  s.subspan<3, 5>();
+} // { dg-error "here" }
 
 void
 test03()
 {
   int a[4];
   std::span<int, 4> s(a);
-  s.subspan<3, 2>(); // { dg-error "here" }
-}
+  s.subspan<3, 2>();
+} // { dg-error "here" }
 
 // { dg-error "static assertion failed" "" { target *-*-* } 0 }

base-commit: 0cfc9c953d0221ec3971a25e6509ebe1041f142e
-- 
2.41.0