llvm/clang/include/clang/AST/Expr.h

//===--- Expr.h - Classes for representing expressions ----------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
//  This file defines the Expr interface and subclasses.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_CLANG_AST_EXPR_H
#define LLVM_CLANG_AST_EXPR_H

#include "clang/AST/APNumericStorage.h"
#include "clang/AST/APValue.h"
#include "clang/AST/ASTVector.h"
#include "clang/AST/ComputeDependence.h"
#include "clang/AST/Decl.h"
#include "clang/AST/DeclAccessPair.h"
#include "clang/AST/DependenceFlags.h"
#include "clang/AST/OperationKinds.h"
#include "clang/AST/Stmt.h"
#include "clang/AST/TemplateBase.h"
#include "clang/AST/Type.h"
#include "clang/Basic/CharInfo.h"
#include "clang/Basic/LangOptions.h"
#include "clang/Basic/SyncScope.h"
#include "clang/Basic/TypeTraits.h"
#include "llvm/ADT/APFloat.h"
#include "llvm/ADT/APSInt.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/iterator.h"
#include "llvm/ADT/iterator_range.h"
#include "llvm/Support/AtomicOrdering.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/TrailingObjects.h"
#include <optional>

namespace clang {
  class APValue;
  class ASTContext;
  class BlockDecl;
  class CXXBaseSpecifier;
  class CXXMemberCallExpr;
  class CXXOperatorCallExpr;
  class CastExpr;
  class Decl;
  class IdentifierInfo;
  class MaterializeTemporaryExpr;
  class NamedDecl;
  class ObjCPropertyRefExpr;
  class OpaqueValueExpr;
  class ParmVarDecl;
  class StringLiteral;
  class TargetInfo;
  class ValueDecl;

/// A simple array of base specifiers.
CXXCastPath;

/// An adjustment to be made to the temporary created when emitting a
/// reference binding, which accesses a particular subobject of that temporary.
struct SubobjectAdjustment { … };

/// This represents one expression.  Note that Expr's are subclasses of Stmt.
/// This allows an expression to be transparently used any place a Stmt is
/// required.
class Expr : public ValueStmt { … };
// PointerLikeTypeTraits is specialized so it can be used with a forward-decl of
// Expr. Verify that we got it right.
static_assert …;

ConstantExprKind;

//===----------------------------------------------------------------------===//
// Wrapper Expressions.
//===----------------------------------------------------------------------===//

/// FullExpr - Represents a "full-expression" node.
class FullExpr : public Expr { … };

/// Describes the kind of result that can be tail-allocated.
enum class ConstantResultStorageKind { … };

/// ConstantExpr - An expression that occurs in a constant context and
/// optionally the result of evaluating the expression.
class ConstantExpr final
    : public FullExpr,
      private llvm::TrailingObjects<ConstantExpr, APValue, uint64_t> { … };

//===----------------------------------------------------------------------===//
// Primary Expressions.
//===----------------------------------------------------------------------===//

/// OpaqueValueExpr - An expression referring to an opaque object of a
/// fixed type and value class.  These don't correspond to concrete
/// syntax; instead they're used to express operations (usually copy
/// operations) on values whose source is generally obvious from
/// context.
class OpaqueValueExpr : public Expr { … };

/// A reference to a declared variable, function, enum, etc.
/// [C99 6.5.1p2]
///
/// This encodes all the information about how a declaration is referenced
/// within an expression.
///
/// There are several optional constructs attached to DeclRefExprs only when
/// they apply in order to conserve memory. These are laid out past the end of
/// the object, and flags in the DeclRefExprBitfield track whether they exist:
///
///   DeclRefExprBits.HasQualifier:
///       Specifies when this declaration reference expression has a C++
///       nested-name-specifier.
///   DeclRefExprBits.HasFoundDecl:
///       Specifies when this declaration reference expression has a record of
///       a NamedDecl (different from the referenced ValueDecl) which was found
///       during name lookup and/or overload resolution.
///   DeclRefExprBits.HasTemplateKWAndArgsInfo:
///       Specifies when this declaration reference expression has an explicit
///       C++ template keyword and/or template argument list.
///   DeclRefExprBits.RefersToEnclosingVariableOrCapture
///       Specifies when this declaration reference expression (validly)
///       refers to an enclosed local or a captured variable.
class DeclRefExpr final
    : public Expr,
      private llvm::TrailingObjects<DeclRefExpr, NestedNameSpecifierLoc,
                                    NamedDecl *, ASTTemplateKWAndArgsInfo,
                                    TemplateArgumentLoc> { … };

class IntegerLiteral : public Expr, public APIntStorage { … };

class FixedPointLiteral : public Expr, public APIntStorage { … };

enum class CharacterLiteralKind { … };

class CharacterLiteral : public Expr { … };

class FloatingLiteral : public Expr, private APFloatStorage { … };

/// ImaginaryLiteral - We support imaginary integer and floating point literals,
/// like "1.0i".  We represent these as a wrapper around FloatingLiteral and
/// IntegerLiteral classes.  Instances of this class always have a Complex type
/// whose element type matches the subexpression.
///
class ImaginaryLiteral : public Expr { … };

enum class StringLiteralKind { … };

/// StringLiteral - This represents a string literal expression, e.g. "foo"
/// or L"bar" (wide strings). The actual string data can be obtained with
/// getBytes() and is NOT null-terminated. The length of the string data is
/// determined by calling getByteLength().
///
/// The C type for a string is always a ConstantArrayType. In C++, the char
/// type is const qualified, in C it is not.
///
/// Note that strings in C can be formed by concatenation of multiple string
/// literal pptokens in translation phase #6. This keeps track of the locations
/// of each of these pieces.
///
/// Strings in C can also be truncated and extended by assigning into arrays,
/// e.g. with constructs like:
///   char X[2] = "foobar";
/// In this case, getByteLength() will return 6, but the string literal will
/// have type "char[2]".
class StringLiteral final
    : public Expr,
      private llvm::TrailingObjects<StringLiteral, unsigned, SourceLocation,
                                    char> { … };

enum class PredefinedIdentKind { … };

/// [C99 6.4.2.2] - A predefined identifier such as __func__.
class PredefinedExpr final
    : public Expr,
      private llvm::TrailingObjects<PredefinedExpr, Stmt *> { … };

/// This expression type represents an asterisk in an OpenACC Size-Expr, used in
/// the 'tile' and 'gang' clauses. It is of 'int' type, but should not be
/// evaluated.
class OpenACCAsteriskSizeExpr final : public Expr { … };

// This represents a use of the __builtin_sycl_unique_stable_name, which takes a
// type-id, and at CodeGen time emits a unique string representation of the
// type in a way that permits us to properly encode information about the SYCL
// kernels.
class SYCLUniqueStableNameExpr final : public Expr { … };

/// ParenExpr - This represents a parenthesized expression, e.g. "(1)".  This
/// AST node is only formed if full location information is requested.
class ParenExpr : public Expr { … };

/// UnaryOperator - This represents the unary-expression's (except sizeof and
/// alignof), the postinc/postdec operators from postfix-expression, and various
/// extensions.
///
/// Notes on various nodes:
///
/// Real/Imag - These return the real/imag part of a complex operand.  If
///   applied to a non-complex value, the former returns its operand and the
///   later returns zero in the type of the operand.
///
class UnaryOperator final
    : public Expr,
      private llvm::TrailingObjects<UnaryOperator, FPOptionsOverride> { … };

/// Helper class for OffsetOfExpr.

// __builtin_offsetof(type, identifier(.identifier|[expr])*)
class OffsetOfNode { … };

/// OffsetOfExpr - [C99 7.17] - This represents an expression of the form
/// offsetof(record-type, member-designator). For example, given:
/// @code
/// struct S {
///   float f;
///   double d;
/// };
/// struct T {
///   int i;
///   struct S s[10];
/// };
/// @endcode
/// we can represent and evaluate the expression @c offsetof(struct T, s[2].d).

class OffsetOfExpr final
    : public Expr,
      private llvm::TrailingObjects<OffsetOfExpr, OffsetOfNode, Expr *> { … };

/// UnaryExprOrTypeTraitExpr - expression with either a type or (unevaluated)
/// expression operand.  Used for sizeof/alignof (C99 6.5.3.4) and
/// vec_step (OpenCL 1.1 6.11.12).
class UnaryExprOrTypeTraitExpr : public Expr { … };

//===----------------------------------------------------------------------===//
// Postfix Operators.
//===----------------------------------------------------------------------===//

/// ArraySubscriptExpr - [C99 6.5.2.1] Array Subscripting.
class ArraySubscriptExpr : public Expr { … };

/// MatrixSubscriptExpr - Matrix subscript expression for the MatrixType
/// extension.
/// MatrixSubscriptExpr can be either incomplete (only Base and RowIdx are set
/// so far, the type is IncompleteMatrixIdx) or complete (Base, RowIdx and
/// ColumnIdx refer to valid expressions). Incomplete matrix expressions only
/// exist during the initial construction of the AST.
class MatrixSubscriptExpr : public Expr { … };

/// CallExpr - Represents a function call (C99 6.5.2.2, C++ [expr.call]).
/// CallExpr itself represents a normal function call, e.g., "f(x, 2)",
/// while its subclasses may represent alternative syntax that (semantically)
/// results in a function call. For example, CXXOperatorCallExpr is
/// a subclass for overloaded operator calls that use operator syntax, e.g.,
/// "str1 + str2" to resolve to a function call.
class CallExpr : public Expr { … };

/// MemberExpr - [C99 6.5.2.3] Structure and Union Members.  X->F and X.F.
///
class MemberExpr final
    : public Expr,
      private llvm::TrailingObjects<MemberExpr, NestedNameSpecifierLoc,
                                    DeclAccessPair, ASTTemplateKWAndArgsInfo,
                                    TemplateArgumentLoc> { … };

/// CompoundLiteralExpr - [C99 6.5.2.5]
///
class CompoundLiteralExpr : public Expr { … };

/// CastExpr - Base class for type casts, including both implicit
/// casts (ImplicitCastExpr) and explicit casts that have some
/// representation in the source code (ExplicitCastExpr's derived
/// classes).
class CastExpr : public Expr { … };

/// ImplicitCastExpr - Allows us to explicitly represent implicit type
/// conversions, which have no direct representation in the original
/// source code. For example: converting T[]->T*, void f()->void
/// (*f)(), float->double, short->int, etc.
///
/// In C, implicit casts always produce rvalues. However, in C++, an
/// implicit cast whose result is being bound to a reference will be
/// an lvalue or xvalue. For example:
///
/// @code
/// class Base { };
/// class Derived : public Base { };
/// Derived &&ref();
/// void f(Derived d) {
///   Base& b = d; // initializer is an ImplicitCastExpr
///                // to an lvalue of type Base
///   Base&& r = ref(); // initializer is an ImplicitCastExpr
///                     // to an xvalue of type Base
/// }
/// @endcode
class ImplicitCastExpr final
    : public CastExpr,
      private llvm::TrailingObjects<ImplicitCastExpr, CXXBaseSpecifier *,
                                    FPOptionsOverride> { … };

/// ExplicitCastExpr - An explicit cast written in the source
/// code.
///
/// This class is effectively an abstract class, because it provides
/// the basic representation of an explicitly-written cast without
/// specifying which kind of cast (C cast, functional cast, static
/// cast, etc.) was written; specific derived classes represent the
/// particular style of cast and its location information.
///
/// Unlike implicit casts, explicit cast nodes have two different
/// types: the type that was written into the source code, and the
/// actual type of the expression as determined by semantic
/// analysis. These types may differ slightly. For example, in C++ one
/// can cast to a reference type, which indicates that the resulting
/// expression will be an lvalue or xvalue. The reference type, however,
/// will not be used as the type of the expression.
class ExplicitCastExpr : public CastExpr { … };

/// CStyleCastExpr - An explicit cast in C (C99 6.5.4) or a C-style
/// cast in C++ (C++ [expr.cast]), which uses the syntax
/// (Type)expr. For example: @c (int)f.
class CStyleCastExpr final
    : public ExplicitCastExpr,
      private llvm::TrailingObjects<CStyleCastExpr, CXXBaseSpecifier *,
                                    FPOptionsOverride> { … };

/// A builtin binary operation expression such as "x + y" or "x <= y".
///
/// This expression node kind describes a builtin binary operation,
/// such as "x + y" for integer values "x" and "y". The operands will
/// already have been converted to appropriate types (e.g., by
/// performing promotions or conversions).
///
/// In C++, where operators may be overloaded, a different kind of
/// expression node (CXXOperatorCallExpr) is used to express the
/// invocation of an overloaded operator with operator syntax. Within
/// a C++ template, whether BinaryOperator or CXXOperatorCallExpr is
/// used to store an expression "x + y" depends on the subexpressions
/// for x and y. If neither x or y is type-dependent, and the "+"
/// operator resolves to a built-in operation, BinaryOperator will be
/// used to express the computation (x and y may still be
/// value-dependent). If either x or y is type-dependent, or if the
/// "+" resolves to an overloaded operator, CXXOperatorCallExpr will
/// be used to express the computation.
class BinaryOperator : public Expr { … };

/// CompoundAssignOperator - For compound assignments (e.g. +=), we keep
/// track of the type the operation is performed in.  Due to the semantics of
/// these operators, the operands are promoted, the arithmetic performed, an
/// implicit conversion back to the result type done, then the assignment takes
/// place.  This captures the intermediate type which the computation is done
/// in.
class CompoundAssignOperator : public BinaryOperator { … };

inline size_t BinaryOperator::offsetOfTrailingStorage() const { … }

/// AbstractConditionalOperator - An abstract base class for
/// ConditionalOperator and BinaryConditionalOperator.
class AbstractConditionalOperator : public Expr { … };

/// ConditionalOperator - The ?: ternary operator.  The GNU "missing
/// middle" extension is a BinaryConditionalOperator.
class ConditionalOperator : public AbstractConditionalOperator { … };

/// BinaryConditionalOperator - The GNU extension to the conditional
/// operator which allows the middle operand to be omitted.
///
/// This is a different expression kind on the assumption that almost
/// every client ends up needing to know that these are different.
class BinaryConditionalOperator : public AbstractConditionalOperator { … };

inline Expr *AbstractConditionalOperator::getCond() const { … }

inline Expr *AbstractConditionalOperator::getTrueExpr() const { … }

inline Expr *AbstractConditionalOperator::getFalseExpr() const { … }

/// AddrLabelExpr - The GNU address of label extension, representing &&label.
class AddrLabelExpr : public Expr { … };

/// StmtExpr - This is the GNU Statement Expression extension: ({int X=4; X;}).
/// The StmtExpr contains a single CompoundStmt node, which it evaluates and
/// takes the value of the last subexpression.
///
/// A StmtExpr is always an r-value; values "returned" out of a
/// StmtExpr will be copied.
class StmtExpr : public Expr { … };

/// ShuffleVectorExpr - clang-specific builtin-in function
/// __builtin_shufflevector.
/// This AST node represents a operator that does a constant
/// shuffle, similar to LLVM's shufflevector instruction. It takes
/// two vectors and a variable number of constant indices,
/// and returns the appropriately shuffled vector.
class ShuffleVectorExpr : public Expr { … };

/// ConvertVectorExpr - Clang builtin function __builtin_convertvector
/// This AST node provides support for converting a vector type to another
/// vector type of the same arity.
class ConvertVectorExpr : public Expr { … };

/// ChooseExpr - GNU builtin-in function __builtin_choose_expr.
/// This AST node is similar to the conditional operator (?:) in C, with
/// the following exceptions:
/// - the test expression must be a integer constant expression.
/// - the expression returned acts like the chosen subexpression in every
///   visible way: the type is the same as that of the chosen subexpression,
///   and all predicates (whether it's an l-value, whether it's an integer
///   constant expression, etc.) return the same result as for the chosen
///   sub-expression.
class ChooseExpr : public Expr { … };

/// GNUNullExpr - Implements the GNU __null extension, which is a name
/// for a null pointer constant that has integral type (e.g., int or
/// long) and is the same size and alignment as a pointer. The __null
/// extension is typically only used by system headers, which define
/// NULL as __null in C++ rather than using 0 (which is an integer
/// that may not match the size of a pointer).
class GNUNullExpr : public Expr { … };

/// Represents a call to the builtin function \c __builtin_va_arg.
class VAArgExpr : public Expr { … };

enum class SourceLocIdentKind { … };

/// Represents a function call to one of __builtin_LINE(), __builtin_COLUMN(),
/// __builtin_FUNCTION(), __builtin_FUNCSIG(), __builtin_FILE(),
/// __builtin_FILE_NAME() or __builtin_source_location().
class SourceLocExpr final : public Expr { … };

/// Stores data related to a single #embed directive.
struct EmbedDataStorage { … };

/// Represents a reference to #emded data. By default, this references the whole
/// range. Otherwise it represents a subrange of data imported by #embed
/// directive. Needed to handle nested initializer lists with #embed directives.
/// Example:
///  struct S {
///    int x, y;
///  };
///
///  struct T {
///    int x[2];
///    struct S s
///  };
///
///  struct T t[] = {
///  #embed "data" // data contains 10 elements;
///  };
///
/// The resulting semantic form of initializer list will contain (EE stands
/// for EmbedExpr):
///  { {EE(first two data elements), {EE(3rd element), EE(4th element) }},
///  { {EE(5th and 6th element), {EE(7th element), EE(8th element) }},
///  { {EE(9th and 10th element), { zeroinitializer }}}
///
/// EmbedExpr inside of a semantic initializer list and referencing more than
/// one element can only appear for arrays of scalars.
class EmbedExpr final : public Expr { … };

/// Describes an C or C++ initializer list.
///
/// InitListExpr describes an initializer list, which can be used to
/// initialize objects of different types, including
/// struct/class/union types, arrays, and vectors. For example:
///
/// @code
/// struct foo x = { 1, { 2, 3 } };
/// @endcode
///
/// Prior to semantic analysis, an initializer list will represent the
/// initializer list as written by the user, but will have the
/// placeholder type "void". This initializer list is called the
/// syntactic form of the initializer, and may contain C99 designated
/// initializers (represented as DesignatedInitExprs), initializations
/// of subobject members without explicit braces, and so on. Clients
/// interested in the original syntax of the initializer list should
/// use the syntactic form of the initializer list.
///
/// After semantic analysis, the initializer list will represent the
/// semantic form of the initializer, where the initializations of all
/// subobjects are made explicit with nested InitListExpr nodes and
/// C99 designators have been eliminated by placing the designated
/// initializations into the subobject they initialize. Additionally,
/// any "holes" in the initialization, where no initializer has been
/// specified for a particular subobject, will be replaced with
/// implicitly-generated ImplicitValueInitExpr expressions that
/// value-initialize the subobjects. Note, however, that the
/// initializer lists may still have fewer initializers than there are
/// elements to initialize within the object.
///
/// After semantic analysis has completed, given an initializer list,
/// method isSemanticForm() returns true if and only if this is the
/// semantic form of the initializer list (note: the same AST node
/// may at the same time be the syntactic form).
/// Given the semantic form of the initializer list, one can retrieve
/// the syntactic form of that initializer list (when different)
/// using method getSyntacticForm(); the method returns null if applied
/// to a initializer list which is already in syntactic form.
/// Similarly, given the syntactic form (i.e., an initializer list such
/// that isSemanticForm() returns false), one can retrieve the semantic
/// form using method getSemanticForm().
/// Since many initializer lists have the same syntactic and semantic forms,
/// getSyntacticForm() may return NULL, indicating that the current
/// semantic initializer list also serves as its syntactic form.
class InitListExpr : public Expr { … };

/// Represents a C99 designated initializer expression.
///
/// A designated initializer expression (C99 6.7.8) contains one or
/// more designators (which can be field designators, array
/// designators, or GNU array-range designators) followed by an
/// expression that initializes the field or element(s) that the
/// designators refer to. For example, given:
///
/// @code
/// struct point {
///   double x;
///   double y;
/// };
/// struct point ptarray[10] = { [2].y = 1.0, [2].x = 2.0, [0].x = 1.0 };
/// @endcode
///
/// The InitListExpr contains three DesignatedInitExprs, the first of
/// which covers @c [2].y=1.0. This DesignatedInitExpr will have two
/// designators, one array designator for @c [2] followed by one field
/// designator for @c .y. The initialization expression will be 1.0.
class DesignatedInitExpr final
    : public Expr,
      private llvm::TrailingObjects<DesignatedInitExpr, Stmt *> { … };

/// Represents a place-holder for an object not to be initialized by
/// anything.
///
/// This only makes sense when it appears as part of an updater of a
/// DesignatedInitUpdateExpr (see below). The base expression of a DIUE
/// initializes a big object, and the NoInitExpr's mark the spots within the
/// big object not to be overwritten by the updater.
///
/// \see DesignatedInitUpdateExpr
class NoInitExpr : public Expr { … };

// In cases like:
//   struct Q { int a, b, c; };
//   Q *getQ();
//   void foo() {
//     struct A { Q q; } a = { *getQ(), .q.b = 3 };
//   }
//
// We will have an InitListExpr for a, with type A, and then a
// DesignatedInitUpdateExpr for "a.q" with type Q. The "base" for this DIUE
// is the call expression *getQ(); the "updater" for the DIUE is ".q.b = 3"
//
class DesignatedInitUpdateExpr : public Expr { … };

/// Represents a loop initializing the elements of an array.
///
/// The need to initialize the elements of an array occurs in a number of
/// contexts:
///
///  * in the implicit copy/move constructor for a class with an array member
///  * when a lambda-expression captures an array by value
///  * when a decomposition declaration decomposes an array
///
/// There are two subexpressions: a common expression (the source array)
/// that is evaluated once up-front, and a per-element initializer that
/// runs once for each array element.
///
/// Within the per-element initializer, the common expression may be referenced
/// via an OpaqueValueExpr, and the current index may be obtained via an
/// ArrayInitIndexExpr.
class ArrayInitLoopExpr : public Expr { … };

/// Represents the index of the current element of an array being
/// initialized by an ArrayInitLoopExpr. This can only appear within the
/// subexpression of an ArrayInitLoopExpr.
class ArrayInitIndexExpr : public Expr { … };

/// Represents an implicitly-generated value initialization of
/// an object of a given type.
///
/// Implicit value initializations occur within semantic initializer
/// list expressions (InitListExpr) as placeholders for subobject
/// initializations not explicitly specified by the user.
///
/// \see InitListExpr
class ImplicitValueInitExpr : public Expr { … };

class ParenListExpr final
    : public Expr,
      private llvm::TrailingObjects<ParenListExpr, Stmt *> { … };

/// Represents a C11 generic selection.
///
/// A generic selection (C11 6.5.1.1) contains an unevaluated controlling
/// expression, followed by one or more generic associations.  Each generic
/// association specifies a type name and an expression, or "default" and an
/// expression (in which case it is known as a default generic association).
/// The type and value of the generic selection are identical to those of its
/// result expression, which is defined as the expression in the generic
/// association with a type name that is compatible with the type of the
/// controlling expression, or the expression in the default generic association
/// if no types are compatible.  For example:
///
/// @code
/// _Generic(X, double: 1, float: 2, default: 3)
/// @endcode
///
/// The above expression evaluates to 1 if 1.0 is substituted for X, 2 if 1.0f
/// or 3 if "hello".
///
/// As an extension, generic selections are allowed in C++, where the following
/// additional semantics apply:
///
/// Any generic selection whose controlling expression is type-dependent or
/// which names a dependent type in its association list is result-dependent,
/// which means that the choice of result expression is dependent.
/// Result-dependent generic associations are both type- and value-dependent.
///
/// We also allow an extended form in both C and C++ where the controlling
/// predicate for the selection expression is a type rather than an expression.
/// This type argument form does not perform any conversions for the
/// controlling type, which makes it suitable for use with qualified type
/// associations, which is not possible with the expression form.
class GenericSelectionExpr final
    : public Expr,
      private llvm::TrailingObjects<GenericSelectionExpr, Stmt *,
                                    TypeSourceInfo *> { … };

//===----------------------------------------------------------------------===//
// Clang Extensions
//===----------------------------------------------------------------------===//

/// ExtVectorElementExpr - This represents access to specific elements of a
/// vector, and may occur on the left hand side or right hand side.  For example
/// the following is legal:  "V.xy = V.zw" if V is a 4 element extended vector.
///
/// Note that the base may have either vector or pointer to vector type, just
/// like a struct field reference.
///
class ExtVectorElementExpr : public Expr { … };

/// BlockExpr - Adaptor class for mixing a BlockDecl with expressions.
/// ^{ statement-body }   or   ^(int arg1, float arg2){ statement-body }
class BlockExpr : public Expr { … };

/// Copy initialization expr of a __block variable and a boolean flag that
/// indicates whether the expression can throw.
struct BlockVarCopyInit { … };

/// AsTypeExpr - Clang builtin function __builtin_astype [OpenCL 6.2.4.2]
/// This AST node provides support for reinterpreting a type to another
/// type of the same size.
class AsTypeExpr : public Expr { … };

/// PseudoObjectExpr - An expression which accesses a pseudo-object
/// l-value.  A pseudo-object is an abstract object, accesses to which
/// are translated to calls.  The pseudo-object expression has a
/// syntactic form, which shows how the expression was actually
/// written in the source code, and a semantic form, which is a series
/// of expressions to be executed in order which detail how the
/// operation is actually evaluated.  Optionally, one of the semantic
/// forms may also provide a result value for the expression.
///
/// If any of the semantic-form expressions is an OpaqueValueExpr,
/// that OVE is required to have a source expression, and it is bound
/// to the result of that source expression.  Such OVEs may appear
/// only in subsequent semantic-form expressions and as
/// sub-expressions of the syntactic form.
///
/// PseudoObjectExpr should be used only when an operation can be
/// usefully described in terms of fairly simple rewrite rules on
/// objects and functions that are meant to be used by end-developers.
/// For example, under the Itanium ABI, dynamic casts are implemented
/// as a call to a runtime function called __dynamic_cast; using this
/// class to describe that would be inappropriate because that call is
/// not really part of the user-visible semantics, and instead the
/// cast is properly reflected in the AST and IR-generation has been
/// taught to generate the call as necessary.  In contrast, an
/// Objective-C property access is semantically defined to be
/// equivalent to a particular message send, and this is very much
/// part of the user model.  The name of this class encourages this
/// modelling design.
class PseudoObjectExpr final
    : public Expr,
      private llvm::TrailingObjects<PseudoObjectExpr, Expr *> { … };

/// AtomicExpr - Variadic atomic builtins: __atomic_exchange, __atomic_fetch_*,
/// __atomic_load, __atomic_store, and __atomic_compare_exchange_*, for the
/// similarly-named C++11 instructions, and __c11 variants for <stdatomic.h>,
/// and corresponding __opencl_atomic_* for OpenCL 2.0.
/// All of these instructions take one primary pointer, at least one memory
/// order. The instructions for which getScopeModel returns non-null value
/// take one synch scope.
class AtomicExpr : public Expr { … };

/// TypoExpr - Internal placeholder for expressions where typo correction
/// still needs to be performed and/or an error diagnostic emitted.
class TypoExpr : public Expr { … };

/// This class represents BOTH the OpenMP Array Section and OpenACC 'subarray',
/// with a boolean differentiator.
/// OpenMP 5.0 [2.1.5, Array Sections].
/// To specify an array section in an OpenMP construct, array subscript
/// expressions are extended with the following syntax:
/// \code
/// [ lower-bound : length : stride ]
/// [ lower-bound : length : ]
/// [ lower-bound : length ]
/// [ lower-bound : : stride ]
/// [ lower-bound : : ]
/// [ lower-bound : ]
/// [ : length : stride ]
/// [ : length : ]
/// [ : length ]
/// [ : : stride ]
/// [ : : ]
/// [ : ]
/// \endcode
/// The array section must be a subset of the original array.
/// Array sections are allowed on multidimensional arrays. Base language array
/// subscript expressions can be used to specify length-one dimensions of
/// multidimensional array sections.
/// Each of the lower-bound, length, and stride expressions if specified must be
/// an integral type expressions of the base language. When evaluated
/// they represent a set of integer values as follows:
/// \code
/// { lower-bound, lower-bound + stride, lower-bound + 2 * stride,... ,
/// lower-bound + ((length - 1) * stride) }
/// \endcode
/// The lower-bound and length must evaluate to non-negative integers.
/// The stride must evaluate to a positive integer.
/// When the size of the array dimension is not known, the length must be
/// specified explicitly.
/// When the stride is absent it defaults to 1.
/// When the length is absent it defaults to ⌈(size − lower-bound)/stride⌉,
/// where size is the size of the array dimension. When the lower-bound is
/// absent it defaults to 0.
///
///
/// OpenACC 3.3 [2.7.1 Data Specification in Data Clauses]
/// In C and C++, a subarray is an array name followed by an extended array
/// range specification in brackets, with start and length, such as
///
/// AA[2:n]
///
/// If the lower bound is missing, zero is used. If the length is missing and
/// the array has known size, the size of the array is used; otherwise the
/// length is required. The subarray AA[2:n] means elements AA[2], AA[3], . . .
/// , AA[2+n-1]. In C and C++, a two dimensional array may be declared in at
/// least four ways:
///
/// -Statically-sized array: float AA[100][200];
/// -Pointer to statically sized rows: typedef float row[200]; row* BB;
/// -Statically-sized array of pointers: float* CC[200];
/// -Pointer to pointers: float** DD;
///
/// Each dimension may be statically sized, or a pointer to dynamically
/// allocated memory. Each of these may be included in a data clause using
/// subarray notation to specify a rectangular array:
///
/// -AA[2:n][0:200]
/// -BB[2:n][0:m]
/// -CC[2:n][0:m]
/// -DD[2:n][0:m]
///
/// Multidimensional rectangular subarrays in C and C++ may be specified for any
/// array with any combination of statically-sized or dynamically-allocated
/// dimensions. For statically sized dimensions, all dimensions except the first
/// must specify the whole extent to preserve the contiguous data restriction,
/// discussed below. For dynamically allocated dimensions, the implementation
/// will allocate pointers in device memory corresponding to the pointers in
/// local memory and will fill in those pointers as appropriate.
///
/// In Fortran, a subarray is an array name followed by a comma-separated list
/// of range specifications in parentheses, with lower and upper bound
/// subscripts, such as
///
/// arr(1:high,low:100)
///
/// If either the lower or upper bounds are missing, the declared or allocated
/// bounds of the array, if known, are used. All dimensions except the last must
/// specify the whole extent, to preserve the contiguous data restriction,
/// discussed below.
///
/// Restrictions
///
/// -In Fortran, the upper bound for the last dimension of an assumed-size dummy
/// array must be specified.
///
/// -In C and C++, the length for dynamically allocated dimensions of an array
/// must be explicitly specified.
///
/// -In C and C++, modifying pointers in pointer arrays during the data
/// lifetime, either on the host or on the device, may result in undefined
/// behavior.
///
/// -If a subarray  appears in a data clause, the implementation may choose to
/// allocate memory for only that subarray on the accelerator.
///
/// -In Fortran, array pointers may appear, but pointer association is not
/// preserved in device memory.
///
/// -Any array or subarray in a data clause, including Fortran array pointers,
/// must be a contiguous section of memory, except for dynamic multidimensional
/// C arrays.
///
/// -In C and C++, if a variable or array of composite type appears, all the
/// data members of the struct or class are allocated and copied, as
/// appropriate. If a composite member is a pointer type, the data addressed by
/// that pointer are not implicitly copied.
///
/// -In Fortran, if a variable or array of composite type appears, all the
/// members of that derived type are allocated and copied, as appropriate. If
/// any member has the allocatable or pointer attribute, the data accessed
/// through that member are not copied.
///
/// -If an expression is used in a subscript or subarray expression in a clause
/// on a data construct, the same value is used when copying data at the end of
/// the data region, even if the values of variables in the expression change
/// during the data region.
class ArraySectionExpr : public Expr { … };

/// This class represents temporary values used to represent inout and out
/// arguments in HLSL. From the callee perspective these parameters are more or
/// less __restrict__ T&. They are guaranteed to not alias any memory. inout
/// parameters are initialized by the caller, and out parameters are references
/// to uninitialized memory.
///
/// In the caller, the argument expression creates a temporary in local memory
/// and the address of the temporary is passed into the callee. There may be
/// implicit conversion sequences to initialize the temporary, and on expiration
/// of the temporary an inverse conversion sequence is applied as a write-back
/// conversion to the source l-value.
///
/// This AST node has three sub-expressions:
///  - An OpaqueValueExpr with a source that is the argument lvalue expression.
///  - An OpaqueValueExpr with a source that is an implicit conversion
///    sequence from the source lvalue to the argument type.
///  - An expression that assigns the second expression into the first,
///    performing any necessary conversions.
class HLSLOutArgExpr : public Expr { … };

/// Frontend produces RecoveryExprs on semantic errors that prevent creating
/// other well-formed expressions. E.g. when type-checking of a binary operator
/// fails, we cannot produce a BinaryOperator expression. Instead, we can choose
/// to produce a recovery expression storing left and right operands.
///
/// RecoveryExpr does not have any semantic meaning in C++, it is only useful to
/// preserve expressions in AST that would otherwise be dropped. It captures
/// subexpressions of some expression that we could not construct and source
/// range covered by the expression.
///
/// By default, RecoveryExpr uses dependence-bits to take advantage of existing
/// machinery to deal with dependent code in C++, e.g. RecoveryExpr is preserved
/// in `decltype(<broken-expr>)` as part of the `DependentDecltypeType`. In
/// addition to that, clang does not report most errors on dependent
/// expressions, so we get rid of bogus errors for free. However, note that
/// unlike other dependent expressions, RecoveryExpr can be produced in
/// non-template contexts.
///
/// We will preserve the type in RecoveryExpr when the type is known, e.g.
/// preserving the return type for a broken non-overloaded function call, a
/// overloaded call where all candidates have the same return type. In this
/// case, the expression is not type-dependent (unless the known type is itself
/// dependent)
///
/// One can also reliably suppress all bogus errors on expressions containing
/// recovery expressions by examining results of Expr::containsErrors().
class RecoveryExpr final : public Expr,
                           private llvm::TrailingObjects<RecoveryExpr, Expr *> { … };

} // end namespace clang

#endif // LLVM_CLANG_AST_EXPR_H