gcc/cp/constexpr.c

/* Perform -*- C++ -*- constant expression evaluation, including calls to
   constexpr functions.  These routines are used both during actual parsing
   and during the instantiation of template functions.

   Copyright (C) 1998-2019 Free Software Foundation, Inc.

   This file is part of GCC.

   GCC is free software; you can redistribute it and/or modify it
   under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3, or (at your option)
   any later version.

   GCC is distributed in the hope that it will be useful, but
   WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   General Public License for more details.

You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING3.  If not see
<http://www.gnu.org/licenses/>.  */

#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "cp-tree.h"
#include "varasm.h"
#include "c-family/c-objc.h"
#include "tree-iterator.h"
#include "gimplify.h"
#include "builtins.h"
#include "tree-inline.h"
#include "ubsan.h"
#include "gimple-fold.h"
#include "timevar.h"
#include "fold-const-call.h"

static bool verify_constant (tree, bool, bool *, bool *);
#define VERIFY_CONSTANT(X)						\
do {									\
  if (verify_constant ((X), ctx->quiet, non_constant_p, overflow_p)) \
    return t;								\
 } while (0)

static HOST_WIDE_INT find_array_ctor_elt (tree ary, tree dindex,
					  bool insert = false);

/* Returns true iff FUN is an instantiation of a constexpr function
   template or a defaulted constexpr function.  */

bool
is_instantiation_of_constexpr (tree fun)
{
  return ((DECL_TEMPLOID_INSTANTIATION (fun)
	   && DECL_DECLARED_CONSTEXPR_P (DECL_TI_TEMPLATE (fun)))
	  || (DECL_DEFAULTED_FN (fun)
	      && DECL_DECLARED_CONSTEXPR_P (fun)));
}

/* Return true if T is a literal type.   */

bool
literal_type_p (tree t)
{
  if (SCALAR_TYPE_P (t)
      || VECTOR_TYPE_P (t)
      || TYPE_REF_P (t)
      || (VOID_TYPE_P (t) && cxx_dialect >= cxx14))
    return true;
  if (CLASS_TYPE_P (t))
    {
      t = complete_type (t);
      gcc_assert (COMPLETE_TYPE_P (t) || errorcount);
      return CLASSTYPE_LITERAL_P (t);
    }
  if (TREE_CODE (t) == ARRAY_TYPE)
    return literal_type_p (strip_array_types (t));
  return false;
}

/* If DECL is a variable declared `constexpr', require its type
   be literal.  Return error_mark_node if we give an error, the
   DECL otherwise.  */

tree
ensure_literal_type_for_constexpr_object (tree decl)
{
  tree type = TREE_TYPE (decl);
  if (VAR_P (decl)
      && (DECL_DECLARED_CONSTEXPR_P (decl)
	  || var_in_constexpr_fn (decl))
      && !processing_template_decl)
    {
      tree stype = strip_array_types (type);
      if (CLASS_TYPE_P (stype) && !COMPLETE_TYPE_P (complete_type (stype)))
	/* Don't complain here, we'll complain about incompleteness
	   when we try to initialize the variable.  */;
      else if (type_uses_auto (type))
	/* We don't know the actual type yet.  */;
      else if (!literal_type_p (type))
	{
	  if (DECL_DECLARED_CONSTEXPR_P (decl))
	    {
	      auto_diagnostic_group d;
	      error_at (DECL_SOURCE_LOCATION (decl),
			"the type %qT of %<constexpr%> variable %qD "
			"is not literal", type, decl);
	      explain_non_literal_class (type);
	      decl = error_mark_node;
	    }
	  else
	    {
	      if (!is_instantiation_of_constexpr (current_function_decl))
		{
		  auto_diagnostic_group d;
		  error_at (DECL_SOURCE_LOCATION (decl),
			    "variable %qD of non-literal type %qT in "
			    "%<constexpr%> function", decl, type);
		  explain_non_literal_class (type);
		  decl = error_mark_node;
		}
	      cp_function_chain->invalid_constexpr = true;
	    }
	}
      else if (DECL_DECLARED_CONSTEXPR_P (decl)
	       && variably_modified_type_p (type, NULL_TREE))
	{
	  error_at (DECL_SOURCE_LOCATION (decl),
		    "%<constexpr%> variable %qD has variably-modified "
		    "type %qT", decl, type);
	  decl = error_mark_node;
	}
    }
  return decl;
}

/* Representation of entries in the constexpr function definition table.  */

struct GTY((for_user)) constexpr_fundef {
  tree decl;
  tree body;
  tree parms;
  tree result;
};

struct constexpr_fundef_hasher : ggc_ptr_hash<constexpr_fundef>
{
  static hashval_t hash (constexpr_fundef *);
  static bool equal (constexpr_fundef *, constexpr_fundef *);
};

/* This table holds all constexpr function definitions seen in
   the current translation unit.  */

static GTY (()) hash_table<constexpr_fundef_hasher> *constexpr_fundef_table;

/* Utility function used for managing the constexpr function table.
   Return true if the entries pointed to by P and Q are for the
   same constexpr function.  */

inline bool
constexpr_fundef_hasher::equal (constexpr_fundef *lhs, constexpr_fundef *rhs)
{
  return lhs->decl == rhs->decl;
}

/* Utility function used for managing the constexpr function table.
   Return a hash value for the entry pointed to by Q.  */

inline hashval_t
constexpr_fundef_hasher::hash (constexpr_fundef *fundef)
{
  return DECL_UID (fundef->decl);
}

/* Return a previously saved definition of function FUN.   */

static constexpr_fundef *
retrieve_constexpr_fundef (tree fun)
{
  if (constexpr_fundef_table == NULL)
    return NULL;

  constexpr_fundef fundef = { fun, NULL, NULL, NULL };
  return constexpr_fundef_table->find (&fundef);
}

/* Check whether the parameter and return types of FUN are valid for a
   constexpr function, and complain if COMPLAIN.  */

bool
is_valid_constexpr_fn (tree fun, bool complain)
{
  bool ret = true;

  if (DECL_INHERITED_CTOR (fun)
      && TREE_CODE (fun) == TEMPLATE_DECL)
    {
      ret = false;
      if (complain)
	error ("inherited constructor %qD is not %<constexpr%>",
	       DECL_INHERITED_CTOR (fun));
    }
  else
    {
      for (tree parm = FUNCTION_FIRST_USER_PARM (fun);
	   parm != NULL_TREE; parm = TREE_CHAIN (parm))
	if (!literal_type_p (TREE_TYPE (parm)))
	  {
	    ret = false;
	    if (complain)
	      {
		auto_diagnostic_group d;
		error ("invalid type for parameter %d of %<constexpr%> "
		       "function %q+#D", DECL_PARM_INDEX (parm), fun);
		explain_non_literal_class (TREE_TYPE (parm));
	      }
	  }
    }

  if (LAMBDA_TYPE_P (CP_DECL_CONTEXT (fun)) && cxx_dialect < cxx17)
    {
      ret = false;
      if (complain)
	inform (DECL_SOURCE_LOCATION (fun),
		"lambdas are implicitly %<constexpr%> only in C++17 and later");
    }
  else if (!DECL_CONSTRUCTOR_P (fun))
    {
      tree rettype = TREE_TYPE (TREE_TYPE (fun));
      if (!literal_type_p (rettype))
	{
	  ret = false;
	  if (complain)
	    {
	      auto_diagnostic_group d;
	      error ("invalid return type %qT of %<constexpr%> function %q+D",
		     rettype, fun);
	      explain_non_literal_class (rettype);
	    }
	}

      /* C++14 DR 1684 removed this restriction.  */
      if (cxx_dialect < cxx14
	  && DECL_NONSTATIC_MEMBER_FUNCTION_P (fun)
	  && !CLASSTYPE_LITERAL_P (DECL_CONTEXT (fun)))
	{
	  ret = false;
	  if (complain)
	    {
	      auto_diagnostic_group d;
	      if (pedwarn (DECL_SOURCE_LOCATION (fun), OPT_Wpedantic,
			     "enclosing class of %<constexpr%> non-static"
			     " member function %q+#D is not a literal type",
			     fun))
		explain_non_literal_class (DECL_CONTEXT (fun));
	    }
	}
    }
  else if (CLASSTYPE_VBASECLASSES (DECL_CONTEXT (fun)))
    {
      ret = false;
      if (complain)
	error ("%q#T has virtual base classes", DECL_CONTEXT (fun));
    }

  return ret;
}

/* Subroutine of build_data_member_initialization.  MEMBER is a COMPONENT_REF
   for a member of an anonymous aggregate, INIT is the initializer for that
   member, and VEC_OUTER is the vector of constructor elements for the class
   whose constructor we are processing.  Add the initializer to the vector
   and return true to indicate success.  */

static bool
build_anon_member_initialization (tree member, tree init,
				  vec<constructor_elt, va_gc> **vec_outer)
{
  /* MEMBER presents the relevant fields from the inside out, but we need
     to build up the initializer from the outside in so that we can reuse
     previously built CONSTRUCTORs if this is, say, the second field in an
     anonymous struct.  So we use a vec as a stack.  */
  auto_vec<tree, 2> fields;
  do
    {
      fields.safe_push (TREE_OPERAND (member, 1));
      member = TREE_OPERAND (member, 0);
    }
  while (ANON_AGGR_TYPE_P (TREE_TYPE (member))
	 && TREE_CODE (member) == COMPONENT_REF);

  /* VEC has the constructor elements vector for the context of FIELD.
     If FIELD is an anonymous aggregate, we will push inside it.  */
  vec<constructor_elt, va_gc> **vec = vec_outer;
  tree field;
  while (field = fields.pop(),
	 ANON_AGGR_TYPE_P (TREE_TYPE (field)))
    {
      tree ctor;
      /* If there is already an outer constructor entry for the anonymous
	 aggregate FIELD, use it; otherwise, insert one.  */
      if (vec_safe_is_empty (*vec)
	  || (*vec)->last().index != field)
	{
	  ctor = build_constructor (TREE_TYPE (field), NULL);
	  CONSTRUCTOR_APPEND_ELT (*vec, field, ctor);
	}
      else
	ctor = (*vec)->last().value;
      vec = &CONSTRUCTOR_ELTS (ctor);
    }

  /* Now we're at the innermost field, the one that isn't an anonymous
     aggregate.  Add its initializer to the CONSTRUCTOR and we're done.  */
  gcc_assert (fields.is_empty());
  CONSTRUCTOR_APPEND_ELT (*vec, field, init);

  return true;
}

/* Subroutine of  build_constexpr_constructor_member_initializers.
   The expression tree T represents a data member initialization
   in a (constexpr) constructor definition.  Build a pairing of
   the data member with its initializer, and prepend that pair
   to the existing initialization pair INITS.  */

static bool
build_data_member_initialization (tree t, vec<constructor_elt, va_gc> **vec)
{
  tree member, init;
  if (TREE_CODE (t) == CLEANUP_POINT_EXPR)
    t = TREE_OPERAND (t, 0);
  if (TREE_CODE (t) == EXPR_STMT)
    t = TREE_OPERAND (t, 0);
  if (t == error_mark_node)
    return false;
  if (TREE_CODE (t) == STATEMENT_LIST)
    {
      tree_stmt_iterator i;
      for (i = tsi_start (t); !tsi_end_p (i); tsi_next (&i))
	{
	  if (! build_data_member_initialization (tsi_stmt (i), vec))
	    return false;
	}
      return true;
    }
  if (TREE_CODE (t) == CLEANUP_STMT)
    {
      /* We can't see a CLEANUP_STMT in a constructor for a literal class,
	 but we can in a constexpr constructor for a non-literal class.  Just
	 ignore it; either all the initialization will be constant, in which
	 case the cleanup can't run, or it can't be constexpr.
	 Still recurse into CLEANUP_BODY.  */
      return build_data_member_initialization (CLEANUP_BODY (t), vec);
    }
  if (TREE_CODE (t) == CONVERT_EXPR)
    t = TREE_OPERAND (t, 0);
  if (TREE_CODE (t) == INIT_EXPR
      /* vptr initialization shows up as a MODIFY_EXPR.  In C++14 we only
	 use what this function builds for cx_check_missing_mem_inits, and
	 assignment in the ctor body doesn't count.  */
      || (cxx_dialect < cxx14 && TREE_CODE (t) == MODIFY_EXPR))
    {
      member = TREE_OPERAND (t, 0);
      init = break_out_target_exprs (TREE_OPERAND (t, 1));
    }
  else if (TREE_CODE (t) == CALL_EXPR)
    {
      tree fn = get_callee_fndecl (t);
      if (!fn || !DECL_CONSTRUCTOR_P (fn))
	/* We're only interested in calls to subobject constructors.  */
	return true;
      member = CALL_EXPR_ARG (t, 0);
      /* We don't use build_cplus_new here because it complains about
	 abstract bases.  Leaving the call unwrapped means that it has the
	 wrong type, but cxx_eval_constant_expression doesn't care.  */
      init = break_out_target_exprs (t);
    }
  else if (TREE_CODE (t) == BIND_EXPR)
    return build_data_member_initialization (BIND_EXPR_BODY (t), vec);
  else
    /* Don't add anything else to the CONSTRUCTOR.  */
    return true;
  if (INDIRECT_REF_P (member))
    member = TREE_OPERAND (member, 0);
  if (TREE_CODE (member) == NOP_EXPR)
    {
      tree op = member;
      STRIP_NOPS (op);
      if (TREE_CODE (op) == ADDR_EXPR)
	{
	  gcc_assert (same_type_ignoring_top_level_qualifiers_p
		      (TREE_TYPE (TREE_TYPE (op)),
		       TREE_TYPE (TREE_TYPE (member))));
	  /* Initializing a cv-qualified member; we need to look through
	     the const_cast.  */
	  member = op;
	}
      else if (op == current_class_ptr
	       && (same_type_ignoring_top_level_qualifiers_p
		   (TREE_TYPE (TREE_TYPE (member)),
		    current_class_type)))
	/* Delegating constructor.  */
	member = op;
      else
	{
	  /* This is an initializer for an empty base; keep it for now so
	     we can check it in cxx_eval_bare_aggregate.  */
	  gcc_assert (is_empty_class (TREE_TYPE (TREE_TYPE (member))));
	}
    }
  if (TREE_CODE (member) == ADDR_EXPR)
    member = TREE_OPERAND (member, 0);
  if (TREE_CODE (member) == COMPONENT_REF)
    {
      tree aggr = TREE_OPERAND (member, 0);
      if (TREE_CODE (aggr) == VAR_DECL)
	/* Initializing a local variable, don't add anything.  */
	return true;
      if (TREE_CODE (aggr) != COMPONENT_REF)
	/* Normal member initialization.  */
	member = TREE_OPERAND (member, 1);
      else if (ANON_AGGR_TYPE_P (TREE_TYPE (aggr)))
	/* Initializing a member of an anonymous union.  */
	return build_anon_member_initialization (member, init, vec);
      else
	/* We're initializing a vtable pointer in a base.  Leave it as
	   COMPONENT_REF so we remember the path to get to the vfield.  */
	gcc_assert (TREE_TYPE (member) == vtbl_ptr_type_node);
    }

  /* Value-initialization can produce multiple initializers for the
     same field; use the last one.  */
  if (!vec_safe_is_empty (*vec) && (*vec)->last().index == member)
    (*vec)->last().value = init;
  else
    CONSTRUCTOR_APPEND_ELT (*vec, member, init);
  return true;
}

/* Subroutine of check_constexpr_ctor_body_1 and constexpr_fn_retval.
   In C++11 mode checks that the TYPE_DECLs in the BIND_EXPR_VARS of a 
   BIND_EXPR conform to 7.1.5/3/4 on typedef and alias declarations.  */

static bool
check_constexpr_bind_expr_vars (tree t)
{
  gcc_assert (TREE_CODE (t) == BIND_EXPR);

  for (tree var = BIND_EXPR_VARS (t); var; var = DECL_CHAIN (var))
    if (TREE_CODE (var) == TYPE_DECL
	&& DECL_IMPLICIT_TYPEDEF_P (var)
	&& !LAMBDA_TYPE_P (TREE_TYPE (var)))
      return false;
  return true;
}

/* Subroutine of check_constexpr_ctor_body.  */

static bool
check_constexpr_ctor_body_1 (tree last, tree list)
{
  switch (TREE_CODE (list))
    {
    case DECL_EXPR:
      if (TREE_CODE (DECL_EXPR_DECL (list)) == USING_DECL
	  || TREE_CODE (DECL_EXPR_DECL (list)) == TYPE_DECL)
	return true;
      return false;

    case CLEANUP_POINT_EXPR:
      return check_constexpr_ctor_body (last, TREE_OPERAND (list, 0),
					/*complain=*/false);

    case BIND_EXPR:
       if (!check_constexpr_bind_expr_vars (list)
	   || !check_constexpr_ctor_body (last, BIND_EXPR_BODY (list),
					  /*complain=*/false))
	 return false;
       return true;

    case USING_STMT:
    case STATIC_ASSERT:
    case DEBUG_BEGIN_STMT:
      return true;

    default:
      return false;
    }
}

/* Make sure that there are no statements after LAST in the constructor
   body represented by LIST.  */

bool
check_constexpr_ctor_body (tree last, tree list, bool complain)
{
  /* C++14 doesn't require a constexpr ctor to have an empty body.  */
  if (cxx_dialect >= cxx14)
    return true;

  bool ok = true;
  if (TREE_CODE (list) == STATEMENT_LIST)
    {
      tree_stmt_iterator i = tsi_last (list);
      for (; !tsi_end_p (i); tsi_prev (&i))
	{
	  tree t = tsi_stmt (i);
	  if (t == last)
	    break;
	  if (!check_constexpr_ctor_body_1 (last, t))
	    {
	      ok = false;
	      break;
	    }
	}
    }
  else if (list != last
	   && !check_constexpr_ctor_body_1 (last, list))
    ok = false;
  if (!ok)
    {
      if (complain)
	error ("%<constexpr%> constructor does not have empty body");
      DECL_DECLARED_CONSTEXPR_P (current_function_decl) = false;
    }
  return ok;
}

/* V is a vector of constructor elements built up for the base and member
   initializers of a constructor for TYPE.  They need to be in increasing
   offset order, which they might not be yet if TYPE has a primary base
   which is not first in the base-clause or a vptr and at least one base
   all of which are non-primary.  */

static vec<constructor_elt, va_gc> *
sort_constexpr_mem_initializers (tree type, vec<constructor_elt, va_gc> *v)
{
  tree pri = CLASSTYPE_PRIMARY_BINFO (type);
  tree field_type;
  unsigned i;
  constructor_elt *ce;

  if (pri)
    field_type = BINFO_TYPE (pri);
  else if (TYPE_CONTAINS_VPTR_P (type))
    field_type = vtbl_ptr_type_node;
  else
    return v;

  /* Find the element for the primary base or vptr and move it to the
     beginning of the vec.  */
  for (i = 0; vec_safe_iterate (v, i, &ce); ++i)
    if (TREE_TYPE (ce->index) == field_type)
      break;

  if (i > 0 && i < vec_safe_length (v))
    {
      vec<constructor_elt, va_gc> &vref = *v;
      constructor_elt elt = vref[i];
      for (; i > 0; --i)
	vref[i] = vref[i-1];
      vref[0] = elt;
    }

  return v;
}

/* Build compile-time evalable representations of member-initializer list
   for a constexpr constructor.  */

static tree
build_constexpr_constructor_member_initializers (tree type, tree body)
{
  vec<constructor_elt, va_gc> *vec = NULL;
  bool ok = true;
  while (true)
    switch (TREE_CODE (body))
      {
      case MUST_NOT_THROW_EXPR:
      case EH_SPEC_BLOCK:
	body = TREE_OPERAND (body, 0);
	break;

      case STATEMENT_LIST:
	for (tree_stmt_iterator i = tsi_start (body);
	     !tsi_end_p (i); tsi_next (&i))
	  {
	    body = tsi_stmt (i);
	    if (TREE_CODE (body) == BIND_EXPR)
	      break;
	  }
	break;

      case BIND_EXPR:
	body = BIND_EXPR_BODY (body);
	goto found;

      default:
	gcc_unreachable ();
    }
 found:
  if (TREE_CODE (body) == TRY_BLOCK)
    {
      body = TREE_OPERAND (body, 0);
      if (TREE_CODE (body) == BIND_EXPR)
	body = BIND_EXPR_BODY (body);
    }
  if (TREE_CODE (body) == CLEANUP_POINT_EXPR)
    {
      body = TREE_OPERAND (body, 0);
      if (TREE_CODE (body) == EXPR_STMT)
	body = TREE_OPERAND (body, 0);
      if (TREE_CODE (body) == INIT_EXPR
	  && (same_type_ignoring_top_level_qualifiers_p
	      (TREE_TYPE (TREE_OPERAND (body, 0)),
	       current_class_type)))
	{
	  /* Trivial copy.  */
	  return TREE_OPERAND (body, 1);
	}
      ok = build_data_member_initialization (body, &vec);
    }
  else if (TREE_CODE (body) == STATEMENT_LIST)
    {
      tree_stmt_iterator i;
      for (i = tsi_start (body); !tsi_end_p (i); tsi_next (&i))
	{
	  ok = build_data_member_initialization (tsi_stmt (i), &vec);
	  if (!ok)
	    break;
	}
    }
  else if (EXPR_P (body))
    ok = build_data_member_initialization (body, &vec);
  else
    gcc_assert (errorcount > 0);
  if (ok)
    {
      if (vec_safe_length (vec) > 0)
	{
	  /* In a delegating constructor, return the target.  */
	  constructor_elt *ce = &(*vec)[0];
	  if (ce->index == current_class_ptr)
	    {
	      body = ce->value;
	      vec_free (vec);
	      return body;
	    }
	}
      vec = sort_constexpr_mem_initializers (type, vec);
      return build_constructor (type, vec);
    }
  else
    return error_mark_node;
}

/* We have an expression tree T that represents a call, either CALL_EXPR
   or AGGR_INIT_EXPR.  If the call is lexically to a named function,
   retrun the _DECL for that function.  */

static tree
get_function_named_in_call (tree t)
{
  tree fun = cp_get_callee (t);
  if (fun && TREE_CODE (fun) == ADDR_EXPR
      && TREE_CODE (TREE_OPERAND (fun, 0)) == FUNCTION_DECL)
    fun = TREE_OPERAND (fun, 0);
  return fun;
}

/* Subroutine of register_constexpr_fundef.  BODY is the body of a function
   declared to be constexpr, or a sub-statement thereof.  Returns the
   return value if suitable, error_mark_node for a statement not allowed in
   a constexpr function, or NULL_TREE if no return value was found.  */

tree
constexpr_fn_retval (tree body)
{
  switch (TREE_CODE (body))
    {
    case STATEMENT_LIST:
      {
	tree_stmt_iterator i;
	tree expr = NULL_TREE;
	for (i = tsi_start (body); !tsi_end_p (i); tsi_next (&i))
	  {
	    tree s = constexpr_fn_retval (tsi_stmt (i));
	    if (s == error_mark_node)
	      return error_mark_node;
	    else if (s == NULL_TREE)
	      /* Keep iterating.  */;
	    else if (expr)
	      /* Multiple return statements.  */
	      return error_mark_node;
	    else
	      expr = s;
	  }
	return expr;
      }

    case RETURN_EXPR:
      return break_out_target_exprs (TREE_OPERAND (body, 0));

    case DECL_EXPR:
      {
	tree decl = DECL_EXPR_DECL (body);
	if (TREE_CODE (decl) == USING_DECL
	    /* Accept __func__, __FUNCTION__, and __PRETTY_FUNCTION__.  */
	    || DECL_ARTIFICIAL (decl))
	  return NULL_TREE;
	return error_mark_node;
      }

    case CLEANUP_POINT_EXPR:
      return constexpr_fn_retval (TREE_OPERAND (body, 0));

    case BIND_EXPR:
      if (!check_constexpr_bind_expr_vars (body))
	return error_mark_node;
      return constexpr_fn_retval (BIND_EXPR_BODY (body));

    case USING_STMT:
    case DEBUG_BEGIN_STMT:
      return NULL_TREE;

    case CALL_EXPR:
	{
	  tree fun = get_function_named_in_call (body);
	  if (fun != NULL_TREE
	      && fndecl_built_in_p (fun, BUILT_IN_UNREACHABLE))
	    return NULL_TREE;
	}
      /* Fallthru.  */

    default:
      return error_mark_node;
    }
}

/* Subroutine of register_constexpr_fundef.  BODY is the DECL_SAVED_TREE of
   FUN; do the necessary transformations to turn it into a single expression
   that we can store in the hash table.  */

static tree
massage_constexpr_body (tree fun, tree body)
{
  if (DECL_CONSTRUCTOR_P (fun))
    body = build_constexpr_constructor_member_initializers
      (DECL_CONTEXT (fun), body);
  else if (cxx_dialect < cxx14)
    {
      if (TREE_CODE (body) == EH_SPEC_BLOCK)
        body = EH_SPEC_STMTS (body);
      if (TREE_CODE (body) == MUST_NOT_THROW_EXPR)
	body = TREE_OPERAND (body, 0);
      body = constexpr_fn_retval (body);
    }
  return body;
}

/* CTYPE is a type constructed from BODY.  Return true if some
   bases/fields are uninitialized, and complain if COMPLAIN.  */

static bool
cx_check_missing_mem_inits (tree ctype, tree body, bool complain)
{
  unsigned nelts = 0;
  
  if (body)
    {
      if (TREE_CODE (body) != CONSTRUCTOR)
	return false;
      nelts = CONSTRUCTOR_NELTS (body);
    }
  tree field = TYPE_FIELDS (ctype);

  if (TREE_CODE (ctype) == UNION_TYPE)
    {
      if (nelts == 0 && next_initializable_field (field))
	{
	  if (complain)
	    error ("%<constexpr%> constructor for union %qT must "
		   "initialize exactly one non-static data member", ctype);
	  return true;
	}
      return false;
    }

  /* Iterate over the CONSTRUCTOR, checking any missing fields don't
     need an explicit initialization.  */
  bool bad = false;
  for (unsigned i = 0; i <= nelts; ++i)
    {
      tree index = NULL_TREE;
      if (i < nelts)
	{
	  index = CONSTRUCTOR_ELT (body, i)->index;
	  /* Skip base and vtable inits.  */
	  if (TREE_CODE (index) != FIELD_DECL
	      || DECL_ARTIFICIAL (index))
	    continue;
	}

      for (; field != index; field = DECL_CHAIN (field))
	{
	  tree ftype;
	  if (TREE_CODE (field) != FIELD_DECL)
	    continue;
	  if (DECL_UNNAMED_BIT_FIELD (field))
	    continue;
	  if (DECL_ARTIFICIAL (field))
	    continue;
	  if (ANON_AGGR_TYPE_P (TREE_TYPE (field)))
	    {
	      /* Recurse to check the anonummous aggregate member.  */
	      bad |= cx_check_missing_mem_inits
		(TREE_TYPE (field), NULL_TREE, complain);
	      if (bad && !complain)
		return true;
	      continue;
	    }
	  if (DECL_SIZE (field) && integer_zerop (DECL_SIZE (field)))
	    /* An empty field doesn't need an initializer.  */
	    continue;
	  ftype = strip_array_types (TREE_TYPE (field));
	  if (type_has_constexpr_default_constructor (ftype))
	    {
	      /* It's OK to skip a member with a trivial constexpr ctor.
	         A constexpr ctor that isn't trivial should have been
	         added in by now.  */
	      gcc_checking_assert (!TYPE_HAS_COMPLEX_DFLT (ftype)
				   || errorcount != 0);
	      continue;
	    }
	  if (!complain)
	    return true;
	  auto_diagnostic_group d;
	  error ("member %qD must be initialized by mem-initializer "
		 "in %<constexpr%> constructor", field);
	  inform (DECL_SOURCE_LOCATION (field), "declared here");
	  bad = true;
	}
      if (field == NULL_TREE)
	break;

      if (ANON_AGGR_TYPE_P (TREE_TYPE (index)))
	{
	  /* Check the anonymous aggregate initializer is valid.  */
	  bad |= cx_check_missing_mem_inits
	    (TREE_TYPE (index), CONSTRUCTOR_ELT (body, i)->value, complain);
	  if (bad && !complain)
	    return true;
	}
      field = DECL_CHAIN (field);
    }

  return bad;
}

/* We are processing the definition of the constexpr function FUN.
   Check that its BODY fulfills the propriate requirements and
   enter it in the constexpr function definition table.
   For constructor BODY is actually the TREE_LIST of the
   member-initializer list.  */

tree
register_constexpr_fundef (tree fun, tree body)
{
  constexpr_fundef entry;
  constexpr_fundef **slot;

  if (!is_valid_constexpr_fn (fun, !DECL_GENERATED_P (fun)))
    return NULL;

  tree massaged = massage_constexpr_body (fun, body);
  if (massaged == NULL_TREE || massaged == error_mark_node)
    {
      if (!DECL_CONSTRUCTOR_P (fun))
	error ("body of %<constexpr%> function %qD not a return-statement",
	       fun);
      return NULL;
    }

  if (!potential_rvalue_constant_expression (massaged))
    {
      if (!DECL_GENERATED_P (fun))
	require_potential_rvalue_constant_expression (massaged);
      return NULL;
    }

  if (DECL_CONSTRUCTOR_P (fun) && !DECL_DEFAULTED_FN (fun)
      && cx_check_missing_mem_inits (DECL_CONTEXT (fun),
				     massaged, !DECL_GENERATED_P (fun)))
    return NULL;

  /* Create the constexpr function table if necessary.  */
  if (constexpr_fundef_table == NULL)
    constexpr_fundef_table
      = hash_table<constexpr_fundef_hasher>::create_ggc (101);

  entry.decl = fun;
  tree saved_fn = current_function_decl;
  bool clear_ctx = false;
  current_function_decl = fun;
  if (DECL_RESULT (fun) && DECL_CONTEXT (DECL_RESULT (fun)) == NULL_TREE)
    {
      clear_ctx = true;
      DECL_CONTEXT (DECL_RESULT (fun)) = fun;
    }
  entry.body = copy_fn (fun, entry.parms, entry.result);
  current_function_decl = saved_fn;
  slot = constexpr_fundef_table->find_slot (&entry, INSERT);
  if (clear_ctx)
    DECL_CONTEXT (DECL_RESULT (fun)) = NULL_TREE;

  gcc_assert (*slot == NULL);
  *slot = ggc_alloc<constexpr_fundef> ();
  **slot = entry;

  return fun;
}

/* FUN is a non-constexpr function called in a context that requires a
   constant expression.  If it comes from a constexpr template, explain why
   the instantiation isn't constexpr.  */

void
explain_invalid_constexpr_fn (tree fun)
{
  static hash_set<tree> *diagnosed;
  tree body;
  location_t save_loc;
  /* Only diagnose defaulted functions, lambdas, or instantiations.  */
  if (!DECL_DEFAULTED_FN (fun)
      && !LAMBDA_TYPE_P (CP_DECL_CONTEXT (fun))
      && !is_instantiation_of_constexpr (fun))
    return;
  if (diagnosed == NULL)
    diagnosed = new hash_set<tree>;
  if (diagnosed->add (fun))
    /* Already explained.  */
    return;

  save_loc = input_location;
  if (!lambda_static_thunk_p (fun))
    {
      /* Diagnostics should completely ignore the static thunk, so leave
	 input_location set to our caller's location.  */
      input_location = DECL_SOURCE_LOCATION (fun);
      inform (input_location,
	      "%qD is not usable as a %<constexpr%> function because:", fun);
    }
  /* First check the declaration.  */
  if (is_valid_constexpr_fn (fun, true))
    {
      /* Then if it's OK, the body.  */
      if (!DECL_DECLARED_CONSTEXPR_P (fun)
	  && !LAMBDA_TYPE_P (CP_DECL_CONTEXT (fun)))
	explain_implicit_non_constexpr (fun);
      else
	{
	  body = massage_constexpr_body (fun, DECL_SAVED_TREE (fun));
	  require_potential_rvalue_constant_expression (body);
	  if (DECL_CONSTRUCTOR_P (fun))
	    cx_check_missing_mem_inits (DECL_CONTEXT (fun), body, true);
	}
    }
  input_location = save_loc;
}

/* Objects of this type represent calls to constexpr functions
   along with the bindings of parameters to their arguments, for
   the purpose of compile time evaluation.  */

struct GTY((for_user)) constexpr_call {
  /* Description of the constexpr function definition.  */
  constexpr_fundef *fundef;
  /* Parameter bindings environment.  A TREE_LIST where each TREE_PURPOSE
     is a parameter _DECL and the TREE_VALUE is the value of the parameter.
     Note: This arrangement is made to accommodate the use of
     iterative_hash_template_arg (see pt.c).  If you change this
     representation, also change the hash calculation in
     cxx_eval_call_expression.  */
  tree bindings;
  /* Result of the call.
       NULL means the call is being evaluated.
       error_mark_node means that the evaluation was erroneous;
       otherwise, the actuall value of the call.  */
  tree result;
  /* The hash of this call; we remember it here to avoid having to
     recalculate it when expanding the hash table.  */
  hashval_t hash;
  /* Whether __builtin_is_constant_evaluated() should evaluate to true.  */
  bool manifestly_const_eval;
};

struct constexpr_call_hasher : ggc_ptr_hash<constexpr_call>
{
  static hashval_t hash (constexpr_call *);
  static bool equal (constexpr_call *, constexpr_call *);
};

enum constexpr_switch_state {
  /* Used when processing a switch for the first time by cxx_eval_switch_expr
     and default: label for that switch has not been seen yet.  */
  css_default_not_seen,
  /* Used when processing a switch for the first time by cxx_eval_switch_expr
     and default: label for that switch has been seen already.  */
  css_default_seen,
  /* Used when processing a switch for the second time by
     cxx_eval_switch_expr, where default: label should match.  */
  css_default_processing
};

/* The constexpr expansion context.  CALL is the current function
   expansion, CTOR is the current aggregate initializer, OBJECT is the
   object being initialized by CTOR, either a VAR_DECL or a _REF.  VALUES
   is a map of values of variables initialized within the expression.  */

struct constexpr_ctx {
  /* The innermost call we're evaluating.  */
  constexpr_call *call;
  /* Values for any temporaries or local variables within the
     constant-expression. */
  hash_map<tree,tree> *values;
  /* SAVE_EXPRs that we've seen within the current LOOP_EXPR.  NULL if we
     aren't inside a loop.  */
  vec<tree> *save_exprs;
  /* The CONSTRUCTOR we're currently building up for an aggregate
     initializer.  */
  tree ctor;
  /* The object we're building the CONSTRUCTOR for.  */
  tree object;
  /* If inside SWITCH_EXPR.  */
  constexpr_switch_state *css_state;
  /* Number of cxx_eval_constant_expression calls (except skipped ones,
     on simple constants or location wrappers) encountered during current
     cxx_eval_outermost_constant_expr call.  */
  HOST_WIDE_INT *constexpr_ops_count;

  /* Whether we should error on a non-constant expression or fail quietly.  */
  bool quiet;
  /* Whether we are strictly conforming to constant expression rules or
     trying harder to get a constant value.  */
  bool strict;
  /* Whether __builtin_is_constant_evaluated () should be true.  */
  bool manifestly_const_eval;
};

/* A table of all constexpr calls that have been evaluated by the
   compiler in this translation unit.  */

static GTY (()) hash_table<constexpr_call_hasher> *constexpr_call_table;

static tree cxx_eval_constant_expression (const constexpr_ctx *, tree,
					  bool, bool *, bool *, tree * = NULL);

/* Compute a hash value for a constexpr call representation.  */

inline hashval_t
constexpr_call_hasher::hash (constexpr_call *info)
{
  return info->hash;
}

/* Return true if the objects pointed to by P and Q represent calls
   to the same constexpr function with the same arguments.
   Otherwise, return false.  */

bool
constexpr_call_hasher::equal (constexpr_call *lhs, constexpr_call *rhs)
{
  tree lhs_bindings;
  tree rhs_bindings;
  if (lhs == rhs)
    return true;
  if (lhs->hash != rhs->hash)
    return false;
  if (lhs->manifestly_const_eval != rhs->manifestly_const_eval)
    return false;
  if (!constexpr_fundef_hasher::equal (lhs->fundef, rhs->fundef))
    return false;
  lhs_bindings = lhs->bindings;
  rhs_bindings = rhs->bindings;
  while (lhs_bindings != NULL && rhs_bindings != NULL)
    {
      tree lhs_arg = TREE_VALUE (lhs_bindings);
      tree rhs_arg = TREE_VALUE (rhs_bindings);
      gcc_assert (same_type_ignoring_top_level_qualifiers_p
		  (TREE_TYPE (lhs_arg), TREE_TYPE (rhs_arg)));
      if (!cp_tree_equal (lhs_arg, rhs_arg))
        return false;
      lhs_bindings = TREE_CHAIN (lhs_bindings);
      rhs_bindings = TREE_CHAIN (rhs_bindings);
    }
  return lhs_bindings == rhs_bindings;
}

/* Initialize the constexpr call table, if needed.  */

static void
maybe_initialize_constexpr_call_table (void)
{
  if (constexpr_call_table == NULL)
    constexpr_call_table = hash_table<constexpr_call_hasher>::create_ggc (101);
}

/* During constexpr CALL_EXPR evaluation, to avoid issues with sharing when
   a function happens to get called recursively, we unshare the callee
   function's body and evaluate this unshared copy instead of evaluating the
   original body.

   FUNDEF_COPIES_TABLE is a per-function freelist of these unshared function
   copies.  The underlying data structure of FUNDEF_COPIES_TABLE is a hash_map
   that's keyed off of the original FUNCTION_DECL and whose value is a
   TREE_LIST of this function's unused copies awaiting reuse.

   This is not GC-deletable to avoid GC affecting UID generation.  */

static GTY(()) hash_map<tree, tree> *fundef_copies_table;

/* Initialize FUNDEF_COPIES_TABLE if it's not initialized.  */

static void
maybe_initialize_fundef_copies_table ()
{
  if (fundef_copies_table == NULL)
    fundef_copies_table = hash_map<tree,tree>::create_ggc (101);
}

/* Reuse a copy or create a new unshared copy of the function FUN.
   Return this copy.  We use a TREE_LIST whose PURPOSE is body, VALUE
   is parms, TYPE is result.  */

static tree
get_fundef_copy (constexpr_fundef *fundef)
{
  maybe_initialize_fundef_copies_table ();

  tree copy;
  bool existed;
  tree *slot = &fundef_copies_table->get_or_insert (fundef->decl, &existed);

  if (!existed)
    {
      /* There is no cached function available, or in use.  We can use
	 the function directly.  That the slot is now created records
	 that this function is now in use.  */
      copy = build_tree_list (fundef->body, fundef->parms);
      TREE_TYPE (copy) = fundef->result;
    }
  else if (*slot == NULL_TREE)
    {
      /* We've already used the function itself, so make a copy.  */
      copy = build_tree_list (NULL, NULL);
      tree saved_body = DECL_SAVED_TREE (fundef->decl);
      tree saved_parms = DECL_ARGUMENTS (fundef->decl);
      tree saved_result = DECL_RESULT (fundef->decl);
      tree saved_fn = current_function_decl;
      DECL_SAVED_TREE (fundef->decl) = fundef->body;
      DECL_ARGUMENTS (fundef->decl) = fundef->parms;
      DECL_RESULT (fundef->decl) = fundef->result;
      current_function_decl = fundef->decl;
      TREE_PURPOSE (copy) = copy_fn (fundef->decl, TREE_VALUE (copy),
				     TREE_TYPE (copy));
      current_function_decl = saved_fn;
      DECL_RESULT (fundef->decl) = saved_result;
      DECL_ARGUMENTS (fundef->decl) = saved_parms;
      DECL_SAVED_TREE (fundef->decl) = saved_body;
    }
  else
    {
      /* We have a cached function available.  */
      copy = *slot;
      *slot = TREE_CHAIN (copy);
    }

  return copy;
}

/* Save the copy COPY of function FUN for later reuse by
   get_fundef_copy().  By construction, there will always be an entry
   to find.  */

static void
save_fundef_copy (tree fun, tree copy)
{
  tree *slot = fundef_copies_table->get (fun);
  TREE_CHAIN (copy) = *slot;
  *slot = copy;
}

/* We have an expression tree T that represents a call, either CALL_EXPR
   or AGGR_INIT_EXPR.  Return the Nth argument.  */

static inline tree
get_nth_callarg (tree t, int n)
{
  switch (TREE_CODE (t))
    {
    case CALL_EXPR:
      return CALL_EXPR_ARG (t, n);

    case AGGR_INIT_EXPR:
      return AGGR_INIT_EXPR_ARG (t, n);

    default:
      gcc_unreachable ();
      return NULL;
    }
}

/* Attempt to evaluate T which represents a call to a builtin function.
   We assume here that all builtin functions evaluate to scalar types
   represented by _CST nodes.  */

static tree
cxx_eval_builtin_function_call (const constexpr_ctx *ctx, tree t, tree fun,
				bool lval,
				bool *non_constant_p, bool *overflow_p)
{
  const int nargs = call_expr_nargs (t);
  tree *args = (tree *) alloca (nargs * sizeof (tree));
  tree new_call;
  int i;

  /* Don't fold __builtin_constant_p within a constexpr function.  */
  bool bi_const_p = DECL_IS_BUILTIN_CONSTANT_P (fun);

  /* If we aren't requiring a constant expression, defer __builtin_constant_p
     in a constexpr function until we have values for the parameters.  */
  if (bi_const_p
      && !ctx->manifestly_const_eval
      && current_function_decl
      && DECL_DECLARED_CONSTEXPR_P (current_function_decl))
    {
      *non_constant_p = true;
      return t;
    }

  /* For __builtin_is_constant_evaluated, defer it if not
     ctx->manifestly_const_eval, otherwise fold it to true.  */
  if (fndecl_built_in_p (fun, CP_BUILT_IN_IS_CONSTANT_EVALUATED,
			 BUILT_IN_FRONTEND))
    {
      if (!ctx->manifestly_const_eval)
	{
	  *non_constant_p = true;
	  return t;
	}
      return boolean_true_node;
    }

  /* Be permissive for arguments to built-ins; __builtin_constant_p should
     return constant false for a non-constant argument.  */
  constexpr_ctx new_ctx = *ctx;
  new_ctx.quiet = true;
  for (i = 0; i < nargs; ++i)
    {
      args[i] = CALL_EXPR_ARG (t, i);
      /* If builtin_valid_in_constant_expr_p is true,
	 potential_constant_expression_1 has not recursed into the arguments
	 of the builtin, verify it here.  */
      if (!builtin_valid_in_constant_expr_p (fun)
	  || potential_constant_expression (args[i]))
	{
	  bool dummy1 = false, dummy2 = false;
	  args[i] = cxx_eval_constant_expression (&new_ctx, args[i], false,
						  &dummy1, &dummy2);
	}

      if (bi_const_p)
	/* For __builtin_constant_p, fold all expressions with constant values
	   even if they aren't C++ constant-expressions.  */
	args[i] = cp_fold_rvalue (args[i]);
    }

  bool save_ffbcp = force_folding_builtin_constant_p;
  force_folding_builtin_constant_p = true;
  tree save_cur_fn = current_function_decl;
  /* Return name of ctx->call->fundef->decl for __builtin_FUNCTION ().  */
  if (fndecl_built_in_p (fun, BUILT_IN_FUNCTION)
      && ctx->call
      && ctx->call->fundef)
    current_function_decl = ctx->call->fundef->decl;
  new_call = fold_builtin_call_array (EXPR_LOCATION (t), TREE_TYPE (t),
				      CALL_EXPR_FN (t), nargs, args);
  current_function_decl = save_cur_fn;
  force_folding_builtin_constant_p = save_ffbcp;
  if (new_call == NULL)
    {
      if (!*non_constant_p && !ctx->quiet)
	{
	  /* Do not allow__builtin_unreachable in constexpr function.
	     The __builtin_unreachable call with BUILTINS_LOCATION
	     comes from cp_maybe_instrument_return.  */
	  if (fndecl_built_in_p (fun, BUILT_IN_UNREACHABLE)
	      && EXPR_LOCATION (t) == BUILTINS_LOCATION)
	    error ("%<constexpr%> call flows off the end of the function");
	  else
	    {
	      new_call = build_call_array_loc (EXPR_LOCATION (t), TREE_TYPE (t),
					       CALL_EXPR_FN (t), nargs, args);
	      error ("%q+E is not a constant expression", new_call);
	    }
	}
      *non_constant_p = true;
      return t;
    }

  if (!potential_constant_expression (new_call))
    {
      if (!*non_constant_p && !ctx->quiet)
	error ("%q+E is not a constant expression", new_call);
      *non_constant_p = true;
      return t;
    }

  return cxx_eval_constant_expression (&new_ctx, new_call, lval,
				       non_constant_p, overflow_p);
}

/* TEMP is the constant value of a temporary object of type TYPE.  Adjust
   the type of the value to match.  */

static tree
adjust_temp_type (tree type, tree temp)
{
  if (same_type_p (TREE_TYPE (temp), type))
    return temp;
  /* Avoid wrapping an aggregate value in a NOP_EXPR.  */
  if (TREE_CODE (temp) == CONSTRUCTOR)
    {
      /* build_constructor wouldn't retain various CONSTRUCTOR flags.  */
      tree t = copy_node (temp);
      TREE_TYPE (t) = type;
      return t;
    }
  if (TREE_CODE (temp) == EMPTY_CLASS_EXPR)
    return build0 (EMPTY_CLASS_EXPR, type);
  gcc_assert (scalarish_type_p (type));
  /* Now we know we're dealing with a scalar, and a prvalue of non-class
     type is cv-unqualified.  */
  return cp_fold_convert (cv_unqualified (type), temp);
}

/* Callback for walk_tree used by unshare_constructor.  */

static tree
find_constructor (tree *tp, int *walk_subtrees, void *)
{
  if (TYPE_P (*tp))
    *walk_subtrees = 0;
  if (TREE_CODE (*tp) == CONSTRUCTOR)
    return *tp;
  return NULL_TREE;
}

/* If T is a CONSTRUCTOR or an expression that has a CONSTRUCTOR node as a
   subexpression, return an unshared copy of T.  Otherwise return T.  */

tree
unshare_constructor (tree t)
{
  tree ctor = walk_tree (&t, find_constructor, NULL, NULL);
  if (ctor != NULL_TREE)
    return unshare_expr (t);
  return t;
}

/* Subroutine of cxx_eval_call_expression.
   We are processing a call expression (either CALL_EXPR or
   AGGR_INIT_EXPR) in the context of CTX.  Evaluate
   all arguments and bind their values to correspondings
   parameters, making up the NEW_CALL context.  */

static void
cxx_bind_parameters_in_call (const constexpr_ctx *ctx, tree t,
                             constexpr_call *new_call,
			     bool *non_constant_p, bool *overflow_p,
			     bool *non_constant_args)
{
  const int nargs = call_expr_nargs (t);
  tree fun = new_call->fundef->decl;
  tree parms = new_call->fundef->parms;
  int i;
  tree *p = &new_call->bindings;
  for (i = 0; i < nargs; ++i)
    {
      tree x, arg;
      tree type = parms ? TREE_TYPE (parms) : void_type_node;
      x = get_nth_callarg (t, i);
      /* For member function, the first argument is a pointer to the implied
         object.  For a constructor, it might still be a dummy object, in
         which case we get the real argument from ctx. */
      if (i == 0 && DECL_CONSTRUCTOR_P (fun)
	  && is_dummy_object (x))
	{
	  x = ctx->object;
	  x = build_address (x);
	}
      if (TREE_ADDRESSABLE (type))
	/* Undo convert_for_arg_passing work here.  */
	x = convert_from_reference (x);
      arg = cxx_eval_constant_expression (ctx, x, /*lval=*/false,
					  non_constant_p, overflow_p);
      /* Don't VERIFY_CONSTANT here.  */
      if (*non_constant_p && ctx->quiet)
	return;
      /* Just discard ellipsis args after checking their constantitude.  */
      if (!parms)
	continue;

      if (!*non_constant_p)
	{
	  /* Don't share a CONSTRUCTOR that might be changed.  */
	  arg = unshare_constructor (arg);
	  /* Make sure the binding has the same type as the parm.  But
	     only for constant args.  */
	  if (!TYPE_REF_P (type))
	    arg = adjust_temp_type (type, arg);
	  if (!TREE_CONSTANT (arg))
	    *non_constant_args = true;

	  /* For virtual calls, adjust the this argument, so that it is
	     the object on which the method is called, rather than
	     one of its bases.  */
	  if (i == 0 && DECL_VIRTUAL_P (fun))
	    {
	      tree addr = arg;
	      STRIP_NOPS (addr);
	      if (TREE_CODE (addr) == ADDR_EXPR)
		{
		  tree obj = TREE_OPERAND (addr, 0);
		  while (TREE_CODE (obj) == COMPONENT_REF
			 && DECL_FIELD_IS_BASE (TREE_OPERAND (obj, 1))
			 && !same_type_ignoring_top_level_qualifiers_p
					(TREE_TYPE (obj), DECL_CONTEXT (fun)))
		    obj = TREE_OPERAND (obj, 0);
		  if (obj != TREE_OPERAND (addr, 0))
		    arg = build_fold_addr_expr_with_type (obj,
							  TREE_TYPE (arg));
		}
	    }

	  *p = build_tree_list (parms, arg);
	  p = &TREE_CHAIN (*p);
	}
      parms = TREE_CHAIN (parms);
    }
}

/* Variables and functions to manage constexpr call expansion context.
   These do not need to be marked for PCH or GC.  */

/* FIXME remember and print actual constant arguments.  */
static vec<tree> call_stack;
static int call_stack_tick;
static int last_cx_error_tick;

static bool
push_cx_call_context (tree call)
{
  ++call_stack_tick;
  if (!EXPR_HAS_LOCATION (call))
    SET_EXPR_LOCATION (call, input_location);
  call_stack.safe_push (call);
  if (call_stack.length () > (unsigned) max_constexpr_depth)
    return false;
  return true;
}

static void
pop_cx_call_context (void)
{
  ++call_stack_tick;
  call_stack.pop ();
}

vec<tree> 
cx_error_context (void)
{
  vec<tree> r = vNULL;
  if (call_stack_tick != last_cx_error_tick
      && !call_stack.is_empty ())
    r = call_stack;
  last_cx_error_tick = call_stack_tick;
  return r;
}

/* Evaluate a call T to a GCC internal function when possible and return
   the evaluated result or, under the control of CTX, give an error, set
   NON_CONSTANT_P, and return the unevaluated call T otherwise.  */

static tree
cxx_eval_internal_function (const constexpr_ctx *ctx, tree t,
			    bool lval,
			    bool *non_constant_p, bool *overflow_p)
{
  enum tree_code opcode = ERROR_MARK;

  switch (CALL_EXPR_IFN (t))
    {
    case IFN_UBSAN_NULL:
    case IFN_UBSAN_BOUNDS:
    case IFN_UBSAN_VPTR:
    case IFN_FALLTHROUGH:
      return void_node;

    case IFN_ADD_OVERFLOW:
      opcode = PLUS_EXPR;
      break;
    case IFN_SUB_OVERFLOW:
      opcode = MINUS_EXPR;
      break;
    case IFN_MUL_OVERFLOW:
      opcode = MULT_EXPR;
      break;

    case IFN_LAUNDER:
      return cxx_eval_constant_expression (ctx, CALL_EXPR_ARG (t, 0),
					   false, non_constant_p, overflow_p);

    case IFN_VEC_CONVERT:
      {
	tree arg = cxx_eval_constant_expression (ctx, CALL_EXPR_ARG (t, 0),
						 false, non_constant_p,
						 overflow_p);
	if (TREE_CODE (arg) == VECTOR_CST)
	  if (tree r = fold_const_call (CFN_VEC_CONVERT, TREE_TYPE (t), arg))
	    return r;
      }
      /* FALLTHRU */

    default:
      if (!ctx->quiet)
	error_at (cp_expr_loc_or_loc (t, input_location),
		  "call to internal function %qE", t);
      *non_constant_p = true;
      return t;
    }

  /* Evaluate constant arguments using OPCODE and return a complex
     number containing the result and the overflow bit.  */
  tree arg0 = cxx_eval_constant_expression (ctx, CALL_EXPR_ARG (t, 0), lval,
					    non_constant_p, overflow_p);
  tree arg1 = cxx_eval_constant_expression (ctx, CALL_EXPR_ARG (t, 1), lval,
					    non_constant_p, overflow_p);

  if (TREE_CODE (arg0) == INTEGER_CST && TREE_CODE (arg1) == INTEGER_CST)
    {
      location_t loc = cp_expr_loc_or_loc (t, input_location);
      tree type = TREE_TYPE (TREE_TYPE (t));
      tree result = fold_binary_loc (loc, opcode, type,
				     fold_convert_loc (loc, type, arg0),
				     fold_convert_loc (loc, type, arg1));
      tree ovf
	= build_int_cst (type, arith_overflowed_p (opcode, type, arg0, arg1));
      /* Reset TREE_OVERFLOW to avoid warnings for the overflow.  */
      if (TREE_OVERFLOW (result))
	TREE_OVERFLOW (result) = 0;

      return build_complex (TREE_TYPE (t), result, ovf);
    }

  *non_constant_p = true;
  return t;
}

/* Clean CONSTRUCTOR_NO_CLEARING from CTOR and its sub-aggregates.  */

static void
clear_no_implicit_zero (tree ctor)
{
  if (CONSTRUCTOR_NO_CLEARING (ctor))
    {
      CONSTRUCTOR_NO_CLEARING (ctor) = false;
      tree elt; unsigned HOST_WIDE_INT idx;
      FOR_EACH_CONSTRUCTOR_VALUE (CONSTRUCTOR_ELTS (ctor), idx, elt)
	if (TREE_CODE (elt) == CONSTRUCTOR)
	  clear_no_implicit_zero (elt);
    }
}

/* Subroutine of cxx_eval_constant_expression.
   Evaluate the call expression tree T in the context of OLD_CALL expression
   evaluation.  */

static tree
cxx_eval_call_expression (const constexpr_ctx *ctx, tree t,
			  bool lval,
			  bool *non_constant_p, bool *overflow_p)
{
  location_t loc = cp_expr_loc_or_loc (t, input_location);
  tree fun = get_function_named_in_call (t);
  constexpr_call new_call
    = { NULL, NULL, NULL, 0, ctx->manifestly_const_eval };
  bool depth_ok;

  if (fun == NULL_TREE)
    return cxx_eval_internal_function (ctx, t, lval,
				       non_constant_p, overflow_p);

  if (TREE_CODE (fun) != FUNCTION_DECL)
    {
      /* Might be a constexpr function pointer.  */
      fun = cxx_eval_constant_expression (ctx, fun,
					  /*lval*/false, non_constant_p,
					  overflow_p);
      STRIP_NOPS (fun);
      if (TREE_CODE (fun) == ADDR_EXPR)
	fun = TREE_OPERAND (fun, 0);
      /* For TARGET_VTABLE_USES_DESCRIPTORS targets, there is no
	 indirection, the called expression is a pointer into the
	 virtual table which should contain FDESC_EXPR.  Extract the
	 FUNCTION_DECL from there.  */
      else if (TARGET_VTABLE_USES_DESCRIPTORS
	       && TREE_CODE (fun) == POINTER_PLUS_EXPR
	       && TREE_CODE (TREE_OPERAND (fun, 0)) == ADDR_EXPR
	       && TREE_CODE (TREE_OPERAND (fun, 1)) == INTEGER_CST)
	{
	  tree d = TREE_OPERAND (TREE_OPERAND (fun, 0), 0);
	  if (VAR_P (d)
	      && DECL_VTABLE_OR_VTT_P (d)
	      && TREE_CODE (TREE_TYPE (d)) == ARRAY_TYPE
	      && TREE_TYPE (TREE_TYPE (d)) == vtable_entry_type
	      && DECL_INITIAL (d)
	      && TREE_CODE (DECL_INITIAL (d)) == CONSTRUCTOR)
	    {
	      tree i = int_const_binop (TRUNC_DIV_EXPR, TREE_OPERAND (fun, 1),
					TYPE_SIZE_UNIT (vtable_entry_type));
	      HOST_WIDE_INT idx = find_array_ctor_elt (DECL_INITIAL (d), i);
	      if (idx >= 0)
		{
		  tree fdesc
		    = (*CONSTRUCTOR_ELTS (DECL_INITIAL (d)))[idx].value;
		  if (TREE_CODE (fdesc) == FDESC_EXPR
		      && integer_zerop (TREE_OPERAND (fdesc, 1)))
		    fun = TREE_OPERAND (fdesc, 0);
		}
	    }
	}
    }
  if (TREE_CODE (fun) != FUNCTION_DECL)
    {
      if (!ctx->quiet && !*non_constant_p)
	error_at (loc, "expression %qE does not designate a %<constexpr%> "
		  "function", fun);
      *non_constant_p = true;
      return t;
    }
  if (DECL_CLONED_FUNCTION_P (fun))
    fun = DECL_CLONED_FUNCTION (fun);

  if (is_ubsan_builtin_p (fun))
    return void_node;

  if (fndecl_built_in_p (fun))
    return cxx_eval_builtin_function_call (ctx, t, fun,
					   lval, non_constant_p, overflow_p);
  if (!DECL_DECLARED_CONSTEXPR_P (fun))
    {
      if (!ctx->quiet)
	{
	  if (!lambda_static_thunk_p (fun))
	    error_at (loc, "call to non-%<constexpr%> function %qD", fun);
	  explain_invalid_constexpr_fn (fun);
	}
      *non_constant_p = true;
      return t;
    }

  constexpr_ctx new_ctx = *ctx;
  if (DECL_CONSTRUCTOR_P (fun) && !ctx->object
      && TREE_CODE (t) == AGGR_INIT_EXPR)
    {
      /* We want to have an initialization target for an AGGR_INIT_EXPR.
	 If we don't already have one in CTX, use the AGGR_INIT_EXPR_SLOT.  */
      new_ctx.object = AGGR_INIT_EXPR_SLOT (t);
      tree ctor = new_ctx.ctor = build_constructor (DECL_CONTEXT (fun), NULL);
      CONSTRUCTOR_NO_CLEARING (ctor) = true;
      ctx->values->put (new_ctx.object, ctor);
      ctx = &new_ctx;
    }

  /* Shortcut trivial constructor/op=.  */
  if (trivial_fn_p (fun))
    {
      tree init = NULL_TREE;
      if (call_expr_nargs (t) == 2)
	init = convert_from_reference (get_nth_callarg (t, 1));
      else if (TREE_CODE (t) == AGGR_INIT_EXPR
	       && AGGR_INIT_ZERO_FIRST (t))
	init = build_zero_init (DECL_CONTEXT (fun), NULL_TREE, false);
      if (init)
	{
	  tree op = get_nth_callarg (t, 0);
	  if (is_dummy_object (op))
	    op = ctx->object;
	  else
	    op = build1 (INDIRECT_REF, TREE_TYPE (TREE_TYPE (op)), op);
	  tree set = build2 (MODIFY_EXPR, TREE_TYPE (op), op, init);
	  new_ctx.call = &new_call;
	  return cxx_eval_constant_expression (&new_ctx, set, lval,
					       non_constant_p, overflow_p);
	}
    }

  /* We can't defer instantiating the function any longer.  */
  if (!DECL_INITIAL (fun)
      && DECL_TEMPLOID_INSTANTIATION (fun))
    {
      location_t save_loc = input_location;
      input_location = loc;
      ++function_depth;
      instantiate_decl (fun, /*defer_ok*/false, /*expl_inst*/false);
      --function_depth;
      input_location = save_loc;
    }

  /* If in direct recursive call, optimize definition search.  */
  if (ctx && ctx->call && ctx->call->fundef && ctx->call->fundef->decl == fun)
    new_call.fundef = ctx->call->fundef;
  else
    {
      new_call.fundef = retrieve_constexpr_fundef (fun);
      if (new_call.fundef == NULL || new_call.fundef->body == NULL
	  || fun == current_function_decl)
        {
	  if (!ctx->quiet)
	    {
	      /* We need to check for current_function_decl here in case we're
		 being called during cp_fold_function, because at that point
		 DECL_INITIAL is set properly and we have a fundef but we
		 haven't lowered invisirefs yet (c++/70344).  */
	      if (DECL_INITIAL (fun) == error_mark_node
		  || fun == current_function_decl)
		error_at (loc, "%qD called in a constant expression before its "
			  "definition is complete", fun);
	      else if (DECL_INITIAL (fun))
		{
		  /* The definition of fun was somehow unsuitable.  But pretend
		     that lambda static thunks don't exist.  */
		  if (!lambda_static_thunk_p (fun))
		    error_at (loc, "%qD called in a constant expression", fun);
		  explain_invalid_constexpr_fn (fun);
		}
	      else
		error_at (loc, "%qD used before its definition", fun);
	    }
	  *non_constant_p = true;
          return t;
        }
    }

  bool non_constant_args = false;
  cxx_bind_parameters_in_call (ctx, t, &new_call,
			       non_constant_p, overflow_p, &non_constant_args);
  if (*non_constant_p)
    return t;

  depth_ok = push_cx_call_context (t);

  tree result = NULL_TREE;

  constexpr_call *entry = NULL;
  if (depth_ok && !non_constant_args && ctx->strict)
    {
      new_call.hash = constexpr_fundef_hasher::hash (new_call.fundef);
      new_call.hash
	= iterative_hash_template_arg (new_call.bindings, new_call.hash);
      new_call.hash
	= iterative_hash_object (ctx->manifestly_const_eval, new_call.hash);

      /* If we have seen this call before, we are done.  */
      maybe_initialize_constexpr_call_table ();
      constexpr_call **slot
	= constexpr_call_table->find_slot (&new_call, INSERT);
      entry = *slot;
      if (entry == NULL)
	{
	  /* We need to keep a pointer to the entry, not just the slot, as the
	     slot can move in the call to cxx_eval_builtin_function_call.  */
	  *slot = entry = ggc_alloc<constexpr_call> ();
	  *entry = new_call;
	}
      /* Calls that are in progress have their result set to NULL,
	 so that we can detect circular dependencies.  */
      else if (entry->result == NULL)
	{
	  if (!ctx->quiet)
	    error ("call has circular dependency");
	  *non_constant_p = true;
	  entry->result = result = error_mark_node;
	}
      else
	result = entry->result;
    }

  if (!depth_ok)
    {
      if (!ctx->quiet)
	error ("%<constexpr%> evaluation depth exceeds maximum of %d (use "
	       "%<-fconstexpr-depth=%> to increase the maximum)",
	       max_constexpr_depth);
      *non_constant_p = true;
      result = error_mark_node;
    }
  else
    {
      if (result && result != error_mark_node)
	/* OK */;
      else if (!DECL_SAVED_TREE (fun))
	{
	  /* When at_eof >= 2, cgraph has started throwing away
	     DECL_SAVED_TREE, so fail quietly.  FIXME we get here because of
	     late code generation for VEC_INIT_EXPR, which needs to be
	     completely reconsidered.  */
	  gcc_assert (at_eof >= 2 && ctx->quiet);
	  *non_constant_p = true;
	}
      else
	{
	  tree body, parms, res;

	  /* Reuse or create a new unshared copy of this function's body.  */
	  tree copy = get_fundef_copy (new_call.fundef);
	  body = TREE_PURPOSE (copy);
	  parms = TREE_VALUE (copy);
	  res = TREE_TYPE (copy);

	  /* Associate the bindings with the remapped parms.  */
	  tree bound = new_call.bindings;
	  tree remapped = parms;
	  while (bound)
	    {
	      tree oparm = TREE_PURPOSE (bound);
	      tree arg = TREE_VALUE (bound);
	      gcc_assert (DECL_NAME (remapped) == DECL_NAME (oparm));
	      /* Don't share a CONSTRUCTOR that might be changed.  */
	      arg = unshare_constructor (arg);
	      ctx->values->put (remapped, arg);
	      bound = TREE_CHAIN (bound);
	      remapped = DECL_CHAIN (remapped);
	    }
	  /* Add the RESULT_DECL to the values map, too.  */
	  tree slot = NULL_TREE;
	  if (DECL_BY_REFERENCE (res))
	    {
	      slot = AGGR_INIT_EXPR_SLOT (t);
	      tree addr = build_address (slot);
	      addr = build_nop (TREE_TYPE (res), addr);
	      ctx->values->put (res, addr);
	      ctx->values->put (slot, NULL_TREE);
	    }
	  else
	    ctx->values->put (res, NULL_TREE);

	  /* Track the callee's evaluated SAVE_EXPRs so that we can forget
	     their values after the call.  */
	  constexpr_ctx ctx_with_save_exprs = *ctx;
	  auto_vec<tree, 10> save_exprs;
	  ctx_with_save_exprs.save_exprs = &save_exprs;
	  ctx_with_save_exprs.call = &new_call;

	  tree jump_target = NULL_TREE;
	  cxx_eval_constant_expression (&ctx_with_save_exprs, body,
					lval, non_constant_p, overflow_p,
					&jump_target);

	  if (DECL_CONSTRUCTOR_P (fun))
	    /* This can be null for a subobject constructor call, in
	       which case what we care about is the initialization
	       side-effects rather than the value.  We could get at the
	       value by evaluating *this, but we don't bother; there's
	       no need to put such a call in the hash table.  */
	    result = lval ? ctx->object : ctx->ctor;
	  else if (VOID_TYPE_P (TREE_TYPE (res)))
	    result = void_node;
	  else
	    {
	      result = *ctx->values->get (slot ? slot : res);
	      if (result == NULL_TREE && !*non_constant_p)
		{
		  if (!ctx->quiet)
		    error ("%<constexpr%> call flows off the end "
			   "of the function");
		  *non_constant_p = true;
		}
	    }

	  /* Forget the saved values of the callee's SAVE_EXPRs.  */
	  unsigned int i;
	  tree save_expr;
	  FOR_EACH_VEC_ELT (save_exprs, i, save_expr)
	    ctx_with_save_exprs.values->remove (save_expr);

	  /* Remove the parms/result from the values map.  Is it worth
	     bothering to do this when the map itself is only live for
	     one constexpr evaluation?  If so, maybe also clear out
	     other vars from call, maybe in BIND_EXPR handling?  */
	  ctx->values->remove (res);
	  if (slot)
	    ctx->values->remove (slot);
	  for (tree parm = parms; parm; parm = TREE_CHAIN (parm))
	    ctx->values->remove (parm);

	  /* Make the unshared function copy we used available for re-use.  */
	  save_fundef_copy (fun, copy);
	}

      if (result == error_mark_node)
	*non_constant_p = true;
      if (*non_constant_p || *overflow_p)
	result = error_mark_node;
      else if (!result)
	result = void_node;
      if (entry)
	entry->result = result;
    }

  /* The result of a constexpr function must be completely initialized.  */
  if (TREE_CODE (result) == CONSTRUCTOR)
    clear_no_implicit_zero (result);

  pop_cx_call_context ();
  return unshare_constructor (result);
}

/* FIXME speed this up, it's taking 16% of compile time on sieve testcase.  */

bool
reduced_constant_expression_p (tree t)
{
  if (t == NULL_TREE)
    return false;

  switch (TREE_CODE (t))
    {
    case PTRMEM_CST:
      /* Even if we can't lower this yet, it's constant.  */
      return true;

    case CONSTRUCTOR:
      /* And we need to handle PTRMEM_CST wrapped in a CONSTRUCTOR.  */
      tree idx, val, field; unsigned HOST_WIDE_INT i;
      if (CONSTRUCTOR_NO_CLEARING (t))
	{
	  if (TREE_CODE (TREE_TYPE (t)) == VECTOR_TYPE)
	    /* An initialized vector would have a VECTOR_CST.  */
	    return false;
	  else
	    field = next_initializable_field (TYPE_FIELDS (TREE_TYPE (t)));
	}
      else
	field = NULL_TREE;
      FOR_EACH_CONSTRUCTOR_ELT (CONSTRUCTOR_ELTS (t), i, idx, val)
	{
	  /* If VAL is null, we're in the middle of initializing this
	     element.  */
	  if (!reduced_constant_expression_p (val))
	    return false;
	  if (field)
	    {
	      if (idx != field)
		return false;
	      field = next_initializable_field (DECL_CHAIN (field));
	    }
	}
      if (field)
	return false;
      else if (CONSTRUCTOR_NO_CLEARING (t))
	/* All the fields are initialized.  */
	CONSTRUCTOR_NO_CLEARING (t) = false;
      return true;

    default:
      /* FIXME are we calling this too much?  */
      return initializer_constant_valid_p (t, TREE_TYPE (t)) != NULL_TREE;
    }
}

/* Some expressions may have constant operands but are not constant
   themselves, such as 1/0.  Call this function to check for that
   condition.

   We only call this in places that require an arithmetic constant, not in
   places where we might have a non-constant expression that can be a
   component of a constant expression, such as the address of a constexpr
   variable that might be dereferenced later.  */

static bool
verify_constant (tree t, bool allow_non_constant, bool *non_constant_p,
		 bool *overflow_p)
{
  if (!*non_constant_p && !reduced_constant_expression_p (t))
    {
      if (!allow_non_constant)
	error ("%q+E is not a constant expression", t);
      *non_constant_p = true;
    }
  if (TREE_OVERFLOW_P (t))
    {
      if (!allow_non_constant)
	{
	  permerror (input_location, "overflow in constant expression");
	  /* If we're being permissive (and are in an enforcing
	     context), ignore the overflow.  */
	  if (flag_permissive)
	    return *non_constant_p;
	}
      *overflow_p = true;
    }
  return *non_constant_p;
}

/* Check whether the shift operation with code CODE and type TYPE on LHS
   and RHS is undefined.  If it is, give an error with an explanation,
   and return true; return false otherwise.  */

static bool
cxx_eval_check_shift_p (location_t loc, const constexpr_ctx *ctx,
			enum tree_code code, tree type, tree lhs, tree rhs)
{
  if ((code != LSHIFT_EXPR && code != RSHIFT_EXPR)
      || TREE_CODE (lhs) != INTEGER_CST
      || TREE_CODE (rhs) != INTEGER_CST)
    return false;

  tree lhstype = TREE_TYPE (lhs);
  unsigned HOST_WIDE_INT uprec = TYPE_PRECISION (TREE_TYPE (lhs));

  /* [expr.shift] The behavior is undefined if the right operand
     is negative, or greater than or equal to the length in bits
     of the promoted left operand.  */
  if (tree_int_cst_sgn (rhs) == -1)
    {
      if (!ctx->quiet)
	permerror (loc, "right operand of shift expression %q+E is negative",
		   build2_loc (loc, code, type, lhs, rhs));
      return (!flag_permissive || ctx->quiet);
    }
  if (compare_tree_int (rhs, uprec) >= 0)
    {
      if (!ctx->quiet)
	permerror (loc, "right operand of shift expression %q+E is >= than "
		   "the precision of the left operand",
		   build2_loc (loc, code, type, lhs, rhs));
      return (!flag_permissive || ctx->quiet);
    }

  /* The value of E1 << E2 is E1 left-shifted E2 bit positions; [...]
     if E1 has a signed type and non-negative value, and E1x2^E2 is
     representable in the corresponding unsigned type of the result type,
     then that value, converted to the result type, is the resulting value;
     otherwise, the behavior is undefined.
     For C++2a:
     The value of E1 << E2 is the unique value congruent to E1 x 2^E2 modulo
     2^N, where N is the range exponent of the type of the result.  */
  if (code == LSHIFT_EXPR
      && !TYPE_OVERFLOW_WRAPS (lhstype)
      && cxx_dialect >= cxx11
      && cxx_dialect < cxx2a)
    {
      if (tree_int_cst_sgn (lhs) == -1)
	{
	  if (!ctx->quiet)
	    permerror (loc,
		       "left operand of shift expression %q+E is negative",
		       build2_loc (loc, code, type, lhs, rhs));
	  return (!flag_permissive || ctx->quiet);
	}
      /* For signed x << y the following:
	 (unsigned) x >> ((prec (lhs) - 1) - y)
	 if > 1, is undefined.  The right-hand side of this formula
	 is the highest bit of the LHS that can be set (starting from 0),
	 so that the shift doesn't overflow.  We then right-shift the LHS
	 to see whether any other bit is set making the original shift
	 undefined -- the result is not representable in the corresponding
	 unsigned type.  */
      tree t = build_int_cst (unsigned_type_node, uprec - 1);
      t = fold_build2 (MINUS_EXPR, unsigned_type_node, t, rhs);
      tree ulhs = fold_convert (unsigned_type_for (lhstype), lhs);
      t = fold_build2 (RSHIFT_EXPR, TREE_TYPE (ulhs), ulhs, t);
      if (tree_int_cst_lt (integer_one_node, t))
	{
	  if (!ctx->quiet)
	    permerror (loc, "shift expression %q+E overflows",
		       build2_loc (loc, code, type, lhs, rhs));
	  return (!flag_permissive || ctx->quiet);
	}
    }
  return false;
}

/* Subroutine of cxx_eval_constant_expression.
   Attempt to reduce the unary expression tree T to a compile time value.
   If successful, return the value.  Otherwise issue a diagnostic
   and return error_mark_node.  */

static tree
cxx_eval_unary_expression (const constexpr_ctx *ctx, tree t,
			   bool /*lval*/,
			   bool *non_constant_p, bool *overflow_p)
{
  tree r;
  tree orig_arg = TREE_OPERAND (t, 0);
  tree arg = cxx_eval_constant_expression (ctx, orig_arg, /*lval*/false,
					   non_constant_p, overflow_p);
  VERIFY_CONSTANT (arg);
  location_t loc = EXPR_LOCATION (t);
  enum tree_code code = TREE_CODE (t);
  tree type = TREE_TYPE (t);
  r = fold_unary_loc (loc, code, type, arg);
  if (r == NULL_TREE)
    {
      if (arg == orig_arg)
	r = t;
      else
	r = build1_loc (loc, code, type, arg);
    }
  VERIFY_CONSTANT (r);
  return r;
}

/* Helper function for cxx_eval_binary_expression.  Try to optimize
   original POINTER_PLUS_EXPR T, LHS p+ RHS, return NULL_TREE if the
   generic folding should be used.  */

static tree
cxx_fold_pointer_plus_expression (const constexpr_ctx *ctx, tree t,
				  tree lhs, tree rhs, bool *non_constant_p,
				  bool *overflow_p)
{
  STRIP_NOPS (lhs);
  if (TREE_CODE (lhs) != ADDR_EXPR)
    return NULL_TREE;

  lhs = TREE_OPERAND (lhs, 0);

  /* &A[i] p+ j => &A[i + j] */
  if (TREE_CODE (lhs) == ARRAY_REF
      && TREE_CODE (TREE_OPERAND (lhs, 1)) == INTEGER_CST
      && TREE_CODE (rhs) == INTEGER_CST
      && TYPE_SIZE_UNIT (TREE_TYPE (lhs))
      && TREE_CODE (TYPE_SIZE_UNIT (TREE_TYPE (lhs))) == INTEGER_CST)
    {
      tree orig_type = TREE_TYPE (t);
      location_t loc = EXPR_LOCATION (t);
      tree type = TREE_TYPE (lhs);

      t = fold_convert_loc (loc, ssizetype, TREE_OPERAND (lhs, 1));
      tree nelts = array_type_nelts_top (TREE_TYPE (TREE_OPERAND (lhs, 0)));
      nelts = cxx_eval_constant_expression (ctx, nelts, false, non_constant_p,
					    overflow_p);
      if (*non_constant_p)
	return NULL_TREE;
      /* Don't fold an out-of-bound access.  */
      if (!tree_int_cst_le (t, nelts))
	return NULL_TREE;
      rhs = cp_fold_convert (ssizetype, rhs);
      /* Don't fold if rhs can't be divided exactly by TYPE_SIZE_UNIT.
	 constexpr int A[1]; ... (char *)&A[0] + 1 */
      if (!integer_zerop (fold_build2_loc (loc, TRUNC_MOD_EXPR, sizetype,
					   rhs, TYPE_SIZE_UNIT (type))))
	return NULL_TREE;
      /* Make sure to treat the second operand of POINTER_PLUS_EXPR
	 as signed.  */
      rhs = fold_build2_loc (loc, EXACT_DIV_EXPR, ssizetype, rhs,
			     TYPE_SIZE_UNIT (type));
      t = size_binop_loc (loc, PLUS_EXPR, rhs, t);
      t = build4_loc (loc, ARRAY_REF, type, TREE_OPERAND (lhs, 0),
		      t, NULL_TREE, NULL_TREE);
      t = cp_build_addr_expr (t, tf_warning_or_error);
      t = cp_fold_convert (orig_type, t);
      return cxx_eval_constant_expression (ctx, t, /*lval*/false,
					   non_constant_p, overflow_p);
    }

  return NULL_TREE;
}

/* Subroutine of cxx_eval_constant_expression.
   Like cxx_eval_unary_expression, except for binary expressions.  */

static tree
cxx_eval_binary_expression (const constexpr_ctx *ctx, tree t,
			    bool /*lval*/,
			    bool *non_constant_p, bool *overflow_p)
{
  tree r = NULL_TREE;
  tree orig_lhs = TREE_OPERAND (t, 0);
  tree orig_rhs = TREE_OPERAND (t, 1);
  tree lhs, rhs;
  lhs = cxx_eval_constant_expression (ctx, orig_lhs, /*lval*/false,
				      non_constant_p, overflow_p);
  /* Don't VERIFY_CONSTANT here, it's unnecessary and will break pointer
     subtraction.  */
  if (*non_constant_p)
    return t;
  rhs = cxx_eval_constant_expression (ctx, orig_rhs, /*lval*/false,
				      non_constant_p, overflow_p);
  if (*non_constant_p)
    return t;

  location_t loc = EXPR_LOCATION (t);
  enum tree_code code = TREE_CODE (t);
  tree type = TREE_TYPE (t);

  if (code == EQ_EXPR || code == NE_EXPR)
    {
      bool is_code_eq = (code == EQ_EXPR);

      if (TREE_CODE (lhs) == PTRMEM_CST
	  && TREE_CODE (rhs) == PTRMEM_CST)
	{
	  tree lmem = PTRMEM_CST_MEMBER (lhs);
	  tree rmem = PTRMEM_CST_MEMBER (rhs);
	  bool eq;
	  if (TREE_CODE (lmem) == TREE_CODE (rmem)
	      && TREE_CODE (lmem) == FIELD_DECL
	      && TREE_CODE (DECL_CONTEXT (lmem)) == UNION_TYPE
	      && same_type_p (DECL_CONTEXT (lmem),
			      DECL_CONTEXT (rmem)))
	    /* If both refer to (possibly different) members of the same union
	       (12.3), they compare equal. */
	    eq = true;
	  else
	    eq = cp_tree_equal (lhs, rhs);
	  r = constant_boolean_node (eq == is_code_eq, type);
	}
      else if ((TREE_CODE (lhs) == PTRMEM_CST
		|| TREE_CODE (rhs) == PTRMEM_CST)
	       && (null_member_pointer_value_p (lhs)
		   || null_member_pointer_value_p (rhs)))
	r = constant_boolean_node (!is_code_eq, type);
      else if (TREE_CODE (lhs) == PTRMEM_CST)
	lhs = cplus_expand_constant (lhs);
      else if (TREE_CODE (rhs) == PTRMEM_CST)
	rhs = cplus_expand_constant (rhs);
    }
  if (code == POINTER_PLUS_EXPR && !*non_constant_p
      && integer_zerop (lhs) && !integer_zerop (rhs))
    {
      if (!ctx->quiet)
	error ("arithmetic involving a null pointer in %qE", lhs);
      *non_constant_p = true;
      return t;
    }
  else if (code == POINTER_PLUS_EXPR)
    r = cxx_fold_pointer_plus_expression (ctx, t, lhs, rhs, non_constant_p,
					  overflow_p);

  if (r == NULL_TREE)
    r = fold_binary_loc (loc, code, type, lhs, rhs);

  if (r == NULL_TREE)
    {
      if (lhs == orig_lhs && rhs == orig_rhs)
	r = t;
      else
	r = build2_loc (loc, code, type, lhs, rhs);
    }
  else if (cxx_eval_check_shift_p (loc, ctx, code, type, lhs, rhs))
    *non_constant_p = true;
  /* Don't VERIFY_CONSTANT if this might be dealing with a pointer to
     a local array in a constexpr function.  */
  bool ptr = INDIRECT_TYPE_P (TREE_TYPE (lhs));
  if (!ptr)
    VERIFY_CONSTANT (r);
  return r;
}

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

static tree
cxx_eval_conditional_expression (const constexpr_ctx *ctx, tree t,
				 bool lval,
				 bool *non_constant_p, bool *overflow_p,
				 tree *jump_target)
{
  tree val = cxx_eval_constant_expression (ctx, TREE_OPERAND (t, 0),
					   /*lval*/false,
					   non_constant_p, overflow_p);
  VERIFY_CONSTANT (val);
  /* Don't VERIFY_CONSTANT the other operands.  */
  if (integer_zerop (val))
    val = TREE_OPERAND (t, 2);
  else
    val = TREE_OPERAND (t, 1);
  if (TREE_CODE (t) == IF_STMT && !val)
    val = void_node;
  return cxx_eval_constant_expression (ctx, val, lval, non_constant_p,
				       overflow_p, jump_target);
}

/* Subroutine of cxx_eval_constant_expression.
   Attempt to evaluate vector condition expressions.  Unlike
   cxx_eval_conditional_expression, VEC_COND_EXPR acts like a normal
   ternary arithmetics operation, where all 3 arguments have to be
   evaluated as constants and then folding computes the result from
   them.  */

static tree
cxx_eval_vector_conditional_expression (const constexpr_ctx *ctx, tree t,
					bool *non_constant_p, bool *overflow_p)
{
  tree arg1 = cxx_eval_constant_expression (ctx, TREE_OPERAND (t, 0),
					    /*lval*/false,
					    non_constant_p, overflow_p);
  VERIFY_CONSTANT (arg1);
  tree arg2 = cxx_eval_constant_expression (ctx, TREE_OPERAND (t, 1),
					    /*lval*/false,
					    non_constant_p, overflow_p);
  VERIFY_CONSTANT (arg2);
  tree arg3 = cxx_eval_constant_expression (ctx, TREE_OPERAND (t, 2),
					    /*lval*/false,
					    non_constant_p, overflow_p);
  VERIFY_CONSTANT (arg3);
  location_t loc = EXPR_LOCATION (t);
  tree type = TREE_TYPE (t);
  tree r = fold_ternary_loc (loc, VEC_COND_EXPR, type, arg1, arg2, arg3);
  if (r == NULL_TREE)
    {
      if (arg1 == TREE_OPERAND (t, 0)
	  && arg2 == TREE_OPERAND (t, 1)
	  && arg3 == TREE_OPERAND (t, 2))
	r = t;
      else
	r = build3_loc (loc, VEC_COND_EXPR, type, arg1, arg2, arg3);
    }
  VERIFY_CONSTANT (r);
  return r;
}

/* Returns less than, equal to, or greater than zero if KEY is found to be
   less than, to match, or to be greater than the constructor_elt's INDEX.  */

static int
array_index_cmp (tree key, tree index)
{
  gcc_assert (TREE_CODE (key) == INTEGER_CST);

  switch (TREE_CODE (index))
    {
    case INTEGER_CST:
      return tree_int_cst_compare (key, index);
    case RANGE_EXPR:
      {
	tree lo = TREE_OPERAND (index, 0);
	tree hi = TREE_OPERAND (index, 1);
	if (tree_int_cst_lt (key, lo))
	  return -1;
	else if (tree_int_cst_lt (hi, key))
	  return 1;
	else
	  return 0;
      }
    default:
      gcc_unreachable ();
    }
}

/* Returns the index of the constructor_elt of ARY which matches DINDEX, or -1
   if none.  If INSERT is true, insert a matching element rather than fail.  */

static HOST_WIDE_INT
find_array_ctor_elt (tree ary, tree dindex, bool insert)
{
  if (tree_int_cst_sgn (dindex) < 0)
    return -1;

  unsigned HOST_WIDE_INT i = tree_to_uhwi (dindex);
  vec<constructor_elt, va_gc> *elts = CONSTRUCTOR_ELTS (ary);
  unsigned HOST_WIDE_INT len = vec_safe_length (elts);

  unsigned HOST_WIDE_INT end = len;
  unsigned HOST_WIDE_INT begin = 0;

  /* If the last element of the CONSTRUCTOR has its own index, we can assume
     that the same is true of the other elements and index directly.  */
  if (end > 0)
    {
      tree cindex = (*elts)[end - 1].index;
      if (TREE_CODE (cindex) == INTEGER_CST
	  && compare_tree_int (cindex, end - 1) == 0)
	{
	  if (i < end)
	    return i;
	  else
	    begin = end;
	}
    }

  /* Otherwise, find a matching index by means of a binary search.  */
  while (begin != end)
    {
      unsigned HOST_WIDE_INT middle = (begin + end) / 2;
      constructor_elt &elt = (*elts)[middle];
      tree idx = elt.index;

      int cmp = array_index_cmp (dindex, idx);
      if (cmp < 0)
	end = middle;
      else if (cmp > 0)
	begin = middle + 1;
      else
	{
	  if (insert && TREE_CODE (idx) == RANGE_EXPR)
	    {
	      /* We need to split the range.  */
	      constructor_elt e;
	      tree lo = TREE_OPERAND (idx, 0);
	      tree hi = TREE_OPERAND (idx, 1);
	      tree value = elt.value;
	      dindex = fold_convert (sizetype, dindex);
	      if (tree_int_cst_lt (lo, dindex))
		{
		  /* There are still some lower elts; shorten the range.  */
		  tree new_hi = int_const_binop (MINUS_EXPR, dindex,
						 size_one_node);
		  if (tree_int_cst_equal (lo, new_hi))
		    /* Only one element left, no longer a range.  */
		    elt.index = lo;
		  else
		    TREE_OPERAND (idx, 1) = new_hi;
		  /* Append the element we want to insert.  */
		  ++middle;
		  e.index = dindex;
		  e.value = unshare_constructor (value);
		  vec_safe_insert (CONSTRUCTOR_ELTS (ary), middle, e);
		}
	      else
		/* No lower elts, the range elt is now ours.  */
		elt.index = dindex;

	      if (tree_int_cst_lt (dindex, hi))
		{
		  /* There are still some higher elts; append a range.  */
		  tree new_lo = int_const_binop (PLUS_EXPR, dindex,
						 size_one_node);
		  if (tree_int_cst_equal (new_lo, hi))
		    e.index = hi;
		  else
		    e.index = build2 (RANGE_EXPR, sizetype, new_lo, hi);
		  e.value = unshare_constructor (value);
		  vec_safe_insert (CONSTRUCTOR_ELTS (ary), middle + 1, e);
		}
	    }
	  return middle;
	}
    }

  if (insert)
    {
      constructor_elt e = { dindex, NULL_TREE };
      vec_safe_insert (CONSTRUCTOR_ELTS (ary), end, e);
      return end;
    }

  return -1;
}

/* Under the control of CTX, issue a detailed diagnostic for
   an out-of-bounds subscript INDEX into the expression ARRAY.  */

static void
diag_array_subscript (const constexpr_ctx *ctx, tree array, tree index)
{
  if (!ctx->quiet)
    {
      tree arraytype = TREE_TYPE (array);

      /* Convert the unsigned array subscript to a signed integer to avoid
	 printing huge numbers for small negative values.  */
      tree sidx = fold_convert (ssizetype, index);
      if (DECL_P (array))
	{
	  if (TYPE_DOMAIN (arraytype))
	    error ("array subscript value %qE is outside the bounds "
	           "of array %qD of type %qT", sidx, array, arraytype);
	  else
	    error ("non-zero array subscript %qE is used with array %qD of "
		   "type %qT with unknown bounds", sidx, array, arraytype);
	  inform (DECL_SOURCE_LOCATION (array), "declared here");
	}
      else if (TYPE_DOMAIN (arraytype))
	error ("array subscript value %qE is outside the bounds "
	       "of array type %qT", sidx, arraytype);
      else
	error ("non-zero array subscript %qE is used with array of type %qT "
	       "with unknown bounds", sidx, arraytype);
    }
}

/* Return the number of elements for TYPE (which is an ARRAY_TYPE or
   a VECTOR_TYPE).  */

static tree
get_array_or_vector_nelts (const constexpr_ctx *ctx, tree type,
			   bool *non_constant_p, bool *overflow_p)
{
  tree nelts;
  if (TREE_CODE (type) == ARRAY_TYPE)
    {
      if (TYPE_DOMAIN (type))
	nelts = array_type_nelts_top (type);
      else
	nelts = size_zero_node;
    }
  else if (VECTOR_TYPE_P (type))
    nelts = size_int (TYPE_VECTOR_SUBPARTS (type));
  else
    gcc_unreachable ();

  /* For VLAs, the number of elements won't be an integer constant.  */
  nelts = cxx_eval_constant_expression (ctx, nelts, false,
					non_constant_p, overflow_p);
  return nelts;
}

/* Extract element INDEX consisting of CHARS_PER_ELT chars from
   STRING_CST STRING.  */

static tree
extract_string_elt (tree string, unsigned chars_per_elt, unsigned index)
{
  tree type = cv_unqualified (TREE_TYPE (TREE_TYPE (string)));
  tree r;

  if (chars_per_elt == 1)
    r = build_int_cst (type, TREE_STRING_POINTER (string)[index]);
  else
    {
      const unsigned char *ptr
	= ((const unsigned char *)TREE_STRING_POINTER (string)
	   + index * chars_per_elt);
      r = native_interpret_expr (type, ptr, chars_per_elt);
    }
  return r;
}

/* Subroutine of cxx_eval_constant_expression.
   Attempt to reduce a reference to an array slot.  */

static tree
cxx_eval_array_reference (const constexpr_ctx *ctx, tree t,
			  bool lval,
			  bool *non_constant_p, bool *overflow_p)
{
  tree oldary = TREE_OPERAND (t, 0);
  tree ary = cxx_eval_constant_expression (ctx, oldary,
					   lval,
					   non_constant_p, overflow_p);
  tree index, oldidx;
  HOST_WIDE_INT i = 0;
  tree elem_type = NULL_TREE;
  unsigned len = 0, elem_nchars = 1;
  if (*non_constant_p)
    return t;
  oldidx = TREE_OPERAND (t, 1);
  index = cxx_eval_constant_expression (ctx, oldidx,
					false,
					non_constant_p, overflow_p);
  VERIFY_CONSTANT (index);
  if (!lval)
    {
      elem_type = TREE_TYPE (TREE_TYPE (ary));
      if (TREE_CODE (ary) == VIEW_CONVERT_EXPR
	  && VECTOR_TYPE_P (TREE_TYPE (TREE_OPERAND (ary, 0)))
	  && TREE_TYPE (t) == TREE_TYPE (TREE_TYPE (TREE_OPERAND (ary, 0))))
	ary = TREE_OPERAND (ary, 0);
      if (TREE_CODE (ary) == CONSTRUCTOR)
	len = CONSTRUCTOR_NELTS (ary);
      else if (TREE_CODE (ary) == STRING_CST)
	{
	  elem_nchars = (TYPE_PRECISION (elem_type)
			 / TYPE_PRECISION (char_type_node));
	  len = (unsigned) TREE_STRING_LENGTH (ary) / elem_nchars;
	}
      else if (TREE_CODE (ary) == VECTOR_CST)
	/* We don't create variable-length VECTOR_CSTs.  */
	len = VECTOR_CST_NELTS (ary).to_constant ();
      else
	{
	  /* We can't do anything with other tree codes, so use
	     VERIFY_CONSTANT to complain and fail.  */
	  VERIFY_CONSTANT (ary);
	  gcc_unreachable ();
	}

      if (!tree_fits_shwi_p (index)
	  || (i = tree_to_shwi (index)) < 0)
	{
	  diag_array_subscript (ctx, ary, index);
	  *non_constant_p = true;
	  return t;
	}
    }

  tree nelts = get_array_or_vector_nelts (ctx, TREE_TYPE (ary), non_constant_p,
					  overflow_p);
  VERIFY_CONSTANT (nelts);
  if ((lval
       ? !tree_int_cst_le (index, nelts)
       : !tree_int_cst_lt (index, nelts))
      || tree_int_cst_sgn (index) < 0)
    {
      diag_array_subscript (ctx, ary, index);
      *non_constant_p = true;
      return t;
    }

  if (lval && ary == oldary && index == oldidx)
    return t;
  else if (lval)
    return build4 (ARRAY_REF, TREE_TYPE (t), ary, index, NULL, NULL);

  bool found;
  if (TREE_CODE (ary) == CONSTRUCTOR)
    {
      HOST_WIDE_INT ix = find_array_ctor_elt (ary, index);
      found = (ix >= 0);
      if (found)
	i = ix;
    }
  else
    found = (i < len);

  if (found)
    {
      tree r;
      if (TREE_CODE (ary) == CONSTRUCTOR)
	r = (*CONSTRUCTOR_ELTS (ary))[i].value;
      else if (TREE_CODE (ary) == VECTOR_CST)
	r = VECTOR_CST_ELT (ary, i);
      else
	r = extract_string_elt (ary, elem_nchars, i);

      if (r)
	/* Don't VERIFY_CONSTANT here.  */
	return r;

      /* Otherwise the element doesn't have a value yet.  */
    }

  /* Not found.  */

  if (TREE_CODE (ary) == CONSTRUCTOR
      && CONSTRUCTOR_NO_CLEARING (ary))
    {
      /* 'ary' is part of the aggregate initializer we're currently
	 building; if there's no initializer for this element yet,
	 that's an error.  */
      if (!ctx->quiet)
	error ("accessing uninitialized array element");
      *non_constant_p = true;
      return t;
    }

  /* If it's within the array bounds but doesn't have an explicit
     initializer, it's initialized from {}.  But use build_value_init
     directly for non-aggregates to avoid creating a garbage CONSTRUCTOR.  */
  tree val;
  if (CP_AGGREGATE_TYPE_P (elem_type))
    {
      tree empty_ctor = build_constructor (init_list_type_node, NULL);
      val = digest_init (elem_type, empty_ctor, tf_warning_or_error);
    }
  else
    val = build_value_init (elem_type, tf_warning_or_error);
  return cxx_eval_constant_expression (ctx, val, lval, non_constant_p,
				       overflow_p);
}

/* Subroutine of cxx_eval_constant_expression.
   Attempt to reduce a field access of a value of class type.  */

static tree
cxx_eval_component_reference (const constexpr_ctx *ctx, tree t,
			      bool lval,
			      bool *non_constant_p, bool *overflow_p)
{
  unsigned HOST_WIDE_INT i;
  tree field;
  tree value;
  tree part = TREE_OPERAND (t, 1);
  tree orig_whole = TREE_OPERAND (t, 0);
  tree whole = cxx_eval_constant_expression (ctx, orig_whole,
					     lval,
					     non_constant_p, overflow_p);
  if (INDIRECT_REF_P (whole)
      && integer_zerop (TREE_OPERAND (whole, 0)))
    {
      if (!ctx->quiet)
	error ("dereferencing a null pointer in %qE", orig_whole);
      *non_constant_p = true;
      return t;
    }

  if (TREE_CODE (whole) == PTRMEM_CST)
    whole = cplus_expand_constant (whole);
  if (whole == orig_whole)
    return t;
  if (lval)
    return fold_build3 (COMPONENT_REF, TREE_TYPE (t),
			whole, part, NULL_TREE);
  /* Don't VERIFY_CONSTANT here; we only want to check that we got a
     CONSTRUCTOR.  */
  if (!*non_constant_p && TREE_CODE (whole) != CONSTRUCTOR)
    {
      if (!ctx->quiet)
	error ("%qE is not a constant expression", orig_whole);
      *non_constant_p = true;
    }
  if (DECL_MUTABLE_P (part))
    {
      if (!ctx->quiet)
	error ("mutable %qD is not usable in a constant expression", part);
      *non_constant_p = true;
    }
  if (*non_constant_p)
    return t;
  bool pmf = TYPE_PTRMEMFUNC_P (TREE_TYPE (whole));
  FOR_EACH_CONSTRUCTOR_ELT (CONSTRUCTOR_ELTS (whole), i, field, value)
    {
      /* Use name match for PMF fields, as a variant will have a
	 different FIELD_DECL with a different type.  */
      if (pmf ? DECL_NAME (field) == DECL_NAME (part)
	  : field == part)
	{
	  if (value)
	    {
	      STRIP_ANY_LOCATION_WRAPPER (value);
	      return value;
	    }
	  else
	    /* We're in the middle of initializing it.  */
	    break;
	}
    }
  if (TREE_CODE (TREE_TYPE (whole)) == UNION_TYPE
      && CONSTRUCTOR_NELTS (whole) > 0)
    {
      /* DR 1188 says we don't have to deal with this.  */
      if (!ctx->quiet)
	error ("accessing %qD member instead of initialized %qD member in "
	       "constant expression", part, CONSTRUCTOR_ELT (whole, 0)->index);
      *non_constant_p = true;
      return t;
    }

  /* We only create a CONSTRUCTOR for a subobject when we modify it, so empty
     classes never get represented; throw together a value now.  */
  if (is_really_empty_class (TREE_TYPE (t), /*ignore_vptr*/false))
    return build_constructor (TREE_TYPE (t), NULL);

  gcc_assert (DECL_CONTEXT (part) == TYPE_MAIN_VARIANT (TREE_TYPE (whole)));

  if (CONSTRUCTOR_NO_CLEARING (whole))
    {
      /* 'whole' is part of the aggregate initializer we're currently
	 building; if there's no initializer for this member yet, that's an
	 error.  */
      if (!ctx->quiet)
	error ("accessing uninitialized member %qD", part);
      *non_constant_p = true;
      return t;
    }

  /* If there's no explicit init for this field, it's value-initialized.  */
  value = build_value_init (TREE_TYPE (t), tf_warning_or_error);
  return cxx_eval_constant_expression (ctx, value,
				       lval,
				       non_constant_p, overflow_p);
}

/* Subroutine of cxx_eval_constant_expression.
   Attempt to reduce a field access of a value of class type that is
   expressed as a BIT_FIELD_REF.  */

static tree
cxx_eval_bit_field_ref (const constexpr_ctx *ctx, tree t,
			bool lval,
			bool *non_constant_p, bool *overflow_p)
{
  tree orig_whole = TREE_OPERAND (t, 0);
  tree retval, fldval, utype, mask;
  bool fld_seen = false;
  HOST_WIDE_INT istart, isize;
  tree whole = cxx_eval_constant_expression (ctx, orig_whole,
					     lval,
					     non_constant_p, overflow_p);
  tree start, field, value;
  unsigned HOST_WIDE_INT i;

  if (whole == orig_whole)
    return t;
  /* Don't VERIFY_CONSTANT here; we only want to check that we got a
     CONSTRUCTOR.  */
  if (!*non_constant_p
      && TREE_CODE (whole) != VECTOR_CST
      && TREE_CODE (whole) != CONSTRUCTOR)
    {
      if (!ctx->quiet)
	error ("%qE is not a constant expression", orig_whole);
      *non_constant_p = true;
    }
  if (*non_constant_p)
    return t;

  if (TREE_CODE (whole) == VECTOR_CST)
    return fold_ternary (BIT_FIELD_REF, TREE_TYPE (t), whole,
			 TREE_OPERAND (t, 1), TREE_OPERAND (t, 2));

  start = TREE_OPERAND (t, 2);
  istart = tree_to_shwi (start);
  isize = tree_to_shwi (TREE_OPERAND (t, 1));
  utype = TREE_TYPE (t);
  if (!TYPE_UNSIGNED (utype))
    utype = build_nonstandard_integer_type (TYPE_PRECISION (utype), 1);
  retval = build_int_cst (utype, 0);
  FOR_EACH_CONSTRUCTOR_ELT (CONSTRUCTOR_ELTS (whole), i, field, value)
    {
      tree bitpos = bit_position (field);
      STRIP_ANY_LOCATION_WRAPPER (value);
      if (bitpos == start && DECL_SIZE (field) == TREE_OPERAND (t, 1))
	return value;
      if (TREE_CODE (TREE_TYPE (field)) == INTEGER_TYPE
	  && TREE_CODE (value) == INTEGER_CST
	  && tree_fits_shwi_p (bitpos)
	  && tree_fits_shwi_p (DECL_SIZE (field)))
	{
	  HOST_WIDE_INT bit = tree_to_shwi (bitpos);
	  HOST_WIDE_INT sz = tree_to_shwi (DECL_SIZE (field));
	  HOST_WIDE_INT shift;
	  if (bit >= istart && bit + sz <= istart + isize)
	    {
	      fldval = fold_convert (utype, value);
	      mask = build_int_cst_type (utype, -1);
	      mask = fold_build2 (LSHIFT_EXPR, utype, mask,
				  size_int (TYPE_PRECISION (utype) - sz));
	      mask = fold_build2 (RSHIFT_EXPR, utype, mask,
				  size_int (TYPE_PRECISION (utype) - sz));
	      fldval = fold_build2 (BIT_AND_EXPR, utype, fldval, mask);
	      shift = bit - istart;
	      if (BYTES_BIG_ENDIAN)
		shift = TYPE_PRECISION (utype) - shift - sz;
	      fldval = fold_build2 (LSHIFT_EXPR, utype, fldval,
				    size_int (shift));
	      retval = fold_build2 (BIT_IOR_EXPR, utype, retval, fldval);
	      fld_seen = true;
	    }
	}
    }
  if (fld_seen)
    return fold_convert (TREE_TYPE (t), retval);
  gcc_unreachable ();
  return error_mark_node;
}

/* Subroutine of cxx_eval_constant_expression.
   Evaluate a short-circuited logical expression T in the context
   of a given constexpr CALL.  BAILOUT_VALUE is the value for
   early return.  CONTINUE_VALUE is used here purely for
   sanity check purposes.  */

static tree
cxx_eval_logical_expression (const constexpr_ctx *ctx, tree t,
                             tree bailout_value, tree continue_value,
			     bool lval,
			     bool *non_constant_p, bool *overflow_p)
{
  tree r;
  tree lhs = cxx_eval_constant_expression (ctx, TREE_OPERAND (t, 0),
					   lval,
					   non_constant_p, overflow_p);
  VERIFY_CONSTANT (lhs);
  if (tree_int_cst_equal (lhs, bailout_value))
    return lhs;
  gcc_assert (tree_int_cst_equal (lhs, continue_value));
  r = cxx_eval_constant_expression (ctx, TREE_OPERAND (t, 1),
				    lval, non_constant_p,
				    overflow_p);
  VERIFY_CONSTANT (r);
  return r;
}

/* REF is a COMPONENT_REF designating a particular field.  V is a vector of
   CONSTRUCTOR elements to initialize (part of) an object containing that
   field.  Return a pointer to the constructor_elt corresponding to the
   initialization of the field.  */

static constructor_elt *
base_field_constructor_elt (vec<constructor_elt, va_gc> *v, tree ref)
{
  tree aggr = TREE_OPERAND (ref, 0);
  tree field = TREE_OPERAND (ref, 1);
  HOST_WIDE_INT i;
  constructor_elt *ce;

  gcc_assert (TREE_CODE (ref) == COMPONENT_REF);

  if (TREE_CODE (aggr) == COMPONENT_REF)
    {
      constructor_elt *base_ce
	= base_field_constructor_elt (v, aggr);
      v = CONSTRUCTOR_ELTS (base_ce->value);
    }

  for (i = 0; vec_safe_iterate (v, i, &ce); ++i)
    if (ce->index == field)
      return ce;

  gcc_unreachable ();
  return NULL;
}

/* Some of the expressions fed to the constexpr mechanism are calls to
   constructors, which have type void.  In that case, return the type being
   initialized by the constructor.  */

static tree
initialized_type (tree t)
{
  if (TYPE_P (t))
    return t;
  tree type = TREE_TYPE (t);
  if (TREE_CODE (t) == CALL_EXPR)
    {
      /* A constructor call has void type, so we need to look deeper.  */
      tree fn = get_function_named_in_call (t);
      if (fn && TREE_CODE (fn) == FUNCTION_DECL
	  && DECL_CXX_CONSTRUCTOR_P (fn))
	type = DECL_CONTEXT (fn);
    }
  else if (TREE_CODE (t) == COMPOUND_EXPR)
    return initialized_type (TREE_OPERAND (t, 1));
  else if (TREE_CODE (t) == AGGR_INIT_EXPR)
    type = TREE_TYPE (AGGR_INIT_EXPR_SLOT (t));
  return cv_unqualified (type);
}

/* We're about to initialize element INDEX of an array or class from VALUE.
   Set up NEW_CTX appropriately by adjusting .object to refer to the
   subobject and creating a new CONSTRUCTOR if the element is itself
   a class or array.  */

static void
init_subob_ctx (const constexpr_ctx *ctx, constexpr_ctx &new_ctx,
	       tree index, tree &value)
{
  new_ctx = *ctx;

  if (index && TREE_CODE (index) != INTEGER_CST
      && TREE_CODE (index) != FIELD_DECL)
    /* This won't have an element in the new CONSTRUCTOR.  */
    return;

  tree type = initialized_type (value);
  if (!AGGREGATE_TYPE_P (type) && !VECTOR_TYPE_P (type))
    /* A non-aggregate member doesn't get its own CONSTRUCTOR.  */
    return;

  /* The sub-aggregate initializer might contain a placeholder;
     update object to refer to the subobject and ctor to refer to
     the (newly created) sub-initializer.  */
  if (ctx->object)
    new_ctx.object = build_ctor_subob_ref (index, type, ctx->object);
  tree elt = build_constructor (type, NULL);
  CONSTRUCTOR_NO_CLEARING (elt) = true;
  new_ctx.ctor = elt;

  if (TREE_CODE (value) == TARGET_EXPR)
    /* Avoid creating another CONSTRUCTOR when we expand the TARGET_EXPR.  */
    value = TARGET_EXPR_INITIAL (value);
}

/* We're about to process an initializer for a class or array TYPE.  Make
   sure that CTX is set up appropriately.  */

static void
verify_ctor_sanity (const constexpr_ctx *ctx, tree type)
{
  /* We don't bother building a ctor for an empty base subobject.  */
  if (is_empty_class (type))
    return;

  /* We're in the middle of an initializer that might involve placeholders;
     our caller should have created a CONSTRUCTOR for us to put the
     initializer into.  We will either return that constructor or T.  */
  gcc_assert (ctx->ctor);
  gcc_assert (same_type_ignoring_top_level_qualifiers_p
	      (type, TREE_TYPE (ctx->ctor)));
  /* We used to check that ctx->ctor was empty, but that isn't the case when
     the object is zero-initialized before calling the constructor.  */
  if (ctx->object)
    {
      tree otype = TREE_TYPE (ctx->object);
      gcc_assert (same_type_ignoring_top_level_qualifiers_p (type, otype)
		  /* Handle flexible array members.  */
		  || (TREE_CODE (otype) == ARRAY_TYPE
		      && TYPE_DOMAIN (otype) == NULL_TREE
		      && TREE_CODE (type) == ARRAY_TYPE
		      && (same_type_ignoring_top_level_qualifiers_p
			  (TREE_TYPE (type), TREE_TYPE (otype)))));
    }
  gcc_assert (!ctx->object || !DECL_P (ctx->object)
	      || *(ctx->values->get (ctx->object)) == ctx->ctor);
}

/* Subroutine of cxx_eval_constant_expression.
   The expression tree T denotes a C-style array or a C-style
   aggregate.  Reduce it to a constant expression.  */

static tree
cxx_eval_bare_aggregate (const constexpr_ctx *ctx, tree t,
			 bool lval,
			 bool *non_constant_p, bool *overflow_p)
{
  vec<constructor_elt, va_gc> *v = CONSTRUCTOR_ELTS (t);
  bool changed = false;
  gcc_assert (!BRACE_ENCLOSED_INITIALIZER_P (t));
  tree type = TREE_TYPE (t);

  constexpr_ctx new_ctx;
  if (TYPE_PTRMEMFUNC_P (type) || VECTOR_TYPE_P (type))
    {
      /* We don't really need the ctx->ctor business for a PMF or
	 vector, but it's simpler to use the same code.  */
      new_ctx = *ctx;
      new_ctx.ctor = build_constructor (type, NULL);
      new_ctx.object = NULL_TREE;
      ctx = &new_ctx;
    };
  verify_ctor_sanity (ctx, type);
  vec<constructor_elt, va_gc> **p = &CONSTRUCTOR_ELTS (ctx->ctor);
  vec_alloc (*p, vec_safe_length (v));

  unsigned i;
  tree index, value;
  bool constant_p = true;
  bool side_effects_p = false;
  FOR_EACH_CONSTRUCTOR_ELT (v, i, index, value)
    {
      tree orig_value = value;
      init_subob_ctx (ctx, new_ctx, index, value);
      if (new_ctx.ctor != ctx->ctor)
	/* If we built a new CONSTRUCTOR, attach it now so that other
	   initializers can refer to it.  */
	CONSTRUCTOR_APPEND_ELT (*p, index, new_ctx.ctor);
      tree elt = cxx_eval_constant_expression (&new_ctx, value,
					       lval,
					       non_constant_p, overflow_p);
      /* Don't VERIFY_CONSTANT here.  */
      if (ctx->quiet && *non_constant_p)
	break;
      if (elt != orig_value)
	changed = true;

      if (!TREE_CONSTANT (elt))
	constant_p = false;
      if (TREE_SIDE_EFFECTS (elt))
	side_effects_p = true;
      if (index && TREE_CODE (index) == COMPONENT_REF)
	{
	  /* This is an initialization of a vfield inside a base
	     subaggregate that we already initialized; push this
	     initialization into the previous initialization.  */
	  constructor_elt *inner = base_field_constructor_elt (*p, index);
	  inner->value = elt;
	  changed = true;
	}
      else if (index
	       && (TREE_CODE (index) == NOP_EXPR
		   || TREE_CODE (index) == POINTER_PLUS_EXPR))
	{
	  /* This is an initializer for an empty base; now that we've
	     checked that it's constant, we can ignore it.  */
	  gcc_assert (is_empty_class (TREE_TYPE (TREE_TYPE (index))));
	  changed = true;
	}
      else
	{
	  if (new_ctx.ctor != ctx->ctor)
	    {
	      /* We appended this element above; update the value.  */
	      gcc_assert ((*p)->last().index == index);
	      (*p)->last().value = elt;
	    }
<