DWARF parsing and writing support using LLVM (#2520)

This imports LLVM code for DWARF handling. That code has the
Apache 2 license like us. It's also the same code used to
emit DWARF in the common toolchain, so it seems like a safe choice.

This adds two passes: --dwarfdump which runs the same code LLVM
runs for llvm-dwarfdump. This shows we can parse it ok, and will
be useful for debugging. And --dwarfupdate writes out the DWARF
sections (unchanged from what we read, so it just roundtrips - for
updating we need #2515).

This puts LLVM in thirdparty which is added here.

All the LLVM code is behind USE_LLVM_DWARF, which is on
by default, but off in JS for now, as it increases code size by 20%.

This current approach imports the LLVM files directly. This is not
how they are intended to be used, so it required a bunch of
local changes - more than I expected actually, for the platform-specific
stuff. For now this seems to work, so it may be good enough, but
in the long term we may want to switch to linking against libllvm.
A downside to doing that is that binaryen users would need to
have an LLVM build, and even in the waterfall builds we'd have a
problem - while we ship LLVM there anyhow, we constantly update
it, which means that binaryen would need to be on latest llvm all
the time too (which otherwise, given DWARF is quite stable, we
might not need to constantly update).

An even larger issue is that as I did this work I learned about how
DWARF works in LLVM, and while the reading code is easy to
reuse, the writing code is trickier. The main code path is heavily
integrated with the MC layer, which we don't have - we might want
to create a "fake MC layer" for that, but it sounds hard. Instead,
there is the YAML path which is used mostly for testing, and which
can convert DWARF to and from YAML and from binary. Using
the non-YAML parts there, we can convert binary DWARF to
the YAML layer's nice Info data, then convert that to binary. This
works, however, this is not the path LLVM uses normally, and it
supports only some basic DWARF sections - I had to add ranges
support, in fact. So if we need more complex things, we may end
up needing to use the MC layer approach, or consider some other
DWARF library. However, hopefully that should not affect the core
binaryen code which just calls a library for DWARF stuff.

Helps #2400

1 files changed, 616 insertions, 0 deletions

diff --git a/third_party/llvm-project/include/llvm/MC/MCExpr.h b/third_party/llvm-project/include/llvm/MC/MCExpr.h
new file mode 100644
index 000000000..eb2786501
--- /dev/null
+++ b/third_party/llvm-project/include/llvm/MC/MCExpr.h
@@ -0,0 +1,616 @@
+//===- MCExpr.h - Assembly Level 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_MC_MCEXPR_H
+#define LLVM_MC_MCEXPR_H
+
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/Support/SMLoc.h"
+#include <cstdint>
+
+namespace llvm {
+
+class MCAsmInfo;
+class MCAsmLayout;
+class MCAssembler;
+class MCContext;
+class MCFixup;
+class MCFragment;
+class MCSection;
+class MCStreamer;
+class MCSymbol;
+class MCValue;
+class raw_ostream;
+class StringRef;
+
+using SectionAddrMap = DenseMap<const MCSection *, uint64_t>;
+
+/// Base class for the full range of assembler expressions which are
+/// needed for parsing.
+class MCExpr {
+public:
+  enum ExprKind {
+    Binary,    ///< Binary expressions.
+    Constant,  ///< Constant expressions.
+    SymbolRef, ///< References to labels and assigned expressions.
+    Unary,     ///< Unary expressions.
+    Target     ///< Target specific expression.
+  };
+
+private:
+  ExprKind Kind;
+  SMLoc Loc;
+
+  bool evaluateAsAbsolute(int64_t &Res, const MCAssembler *Asm,
+                          const MCAsmLayout *Layout,
+                          const SectionAddrMap *Addrs, bool InSet) const;
+
+protected:
+  explicit MCExpr(ExprKind Kind, SMLoc Loc) : Kind(Kind), Loc(Loc) {}
+
+  bool evaluateAsRelocatableImpl(MCValue &Res, const MCAssembler *Asm,
+                                 const MCAsmLayout *Layout,
+                                 const MCFixup *Fixup,
+                                 const SectionAddrMap *Addrs, bool InSet) const;
+
+public:
+  MCExpr(const MCExpr &) = delete;
+  MCExpr &operator=(const MCExpr &) = delete;
+
+  /// \name Accessors
+  /// @{
+
+  ExprKind getKind() const { return Kind; }
+  SMLoc getLoc() const { return Loc; }
+
+  /// @}
+  /// \name Utility Methods
+  /// @{
+
+  void print(raw_ostream &OS, const MCAsmInfo *MAI,
+             bool InParens = false) const;
+  void dump() const;
+
+  /// @}
+  /// \name Expression Evaluation
+  /// @{
+
+  /// Try to evaluate the expression to an absolute value.
+  ///
+  /// \param Res - The absolute value, if evaluation succeeds.
+  /// \param Layout - The assembler layout object to use for evaluating symbol
+  /// values. If not given, then only non-symbolic expressions will be
+  /// evaluated.
+  /// \return - True on success.
+  bool evaluateAsAbsolute(int64_t &Res, const MCAsmLayout &Layout,
+                          const SectionAddrMap &Addrs) const;
+  bool evaluateAsAbsolute(int64_t &Res) const;
+  bool evaluateAsAbsolute(int64_t &Res, const MCAssembler &Asm) const;
+  bool evaluateAsAbsolute(int64_t &Res, const MCAssembler *Asm) const;
+  bool evaluateAsAbsolute(int64_t &Res, const MCAsmLayout &Layout) const;
+
+  bool evaluateKnownAbsolute(int64_t &Res, const MCAsmLayout &Layout) const;
+
+  /// Try to evaluate the expression to a relocatable value, i.e. an
+  /// expression of the fixed form (a - b + constant).
+  ///
+  /// \param Res - The relocatable value, if evaluation succeeds.
+  /// \param Layout - The assembler layout object to use for evaluating values.
+  /// \param Fixup - The Fixup object if available.
+  /// \return - True on success.
+  bool evaluateAsRelocatable(MCValue &Res, const MCAsmLayout *Layout,
+                             const MCFixup *Fixup) const;
+
+  /// Try to evaluate the expression to the form (a - b + constant) where
+  /// neither a nor b are variables.
+  ///
+  /// This is a more aggressive variant of evaluateAsRelocatable. The intended
+  /// use is for when relocations are not available, like the .size directive.
+  bool evaluateAsValue(MCValue &Res, const MCAsmLayout &Layout) const;
+
+  /// Find the "associated section" for this expression, which is
+  /// currently defined as the absolute section for constants, or
+  /// otherwise the section associated with the first defined symbol in the
+  /// expression.
+  MCFragment *findAssociatedFragment() const;
+
+  /// @}
+};
+
+inline raw_ostream &operator<<(raw_ostream &OS, const MCExpr &E) {
+  E.print(OS, nullptr);
+  return OS;
+}
+
+////  Represent a constant integer expression.
+class MCConstantExpr : public MCExpr {
+  int64_t Value;
+  bool PrintInHex = false;
+
+  explicit MCConstantExpr(int64_t Value)
+      : MCExpr(MCExpr::Constant, SMLoc()), Value(Value) {}
+
+  MCConstantExpr(int64_t Value, bool PrintInHex)
+      : MCExpr(MCExpr::Constant, SMLoc()), Value(Value),
+        PrintInHex(PrintInHex) {}
+
+public:
+  /// \name Construction
+  /// @{
+
+  static const MCConstantExpr *create(int64_t Value, MCContext &Ctx,
+                                      bool PrintInHex = false);
+
+  /// @}
+  /// \name Accessors
+  /// @{
+
+  int64_t getValue() const { return Value; }
+
+  bool useHexFormat() const { return PrintInHex; }
+
+  /// @}
+
+  static bool classof(const MCExpr *E) {
+    return E->getKind() == MCExpr::Constant;
+  }
+};
+
+///  Represent a reference to a symbol from inside an expression.
+///
+/// A symbol reference in an expression may be a use of a label, a use of an
+/// assembler variable (defined constant), or constitute an implicit definition
+/// of the symbol as external.
+class MCSymbolRefExpr : public MCExpr {
+public:
+  enum VariantKind : uint16_t {
+    VK_None,
+    VK_Invalid,
+
+    VK_GOT,
+    VK_GOTOFF,
+    VK_GOTREL,
+    VK_GOTPCREL,
+    VK_GOTTPOFF,
+    VK_INDNTPOFF,
+    VK_NTPOFF,
+    VK_GOTNTPOFF,
+    VK_PLT,
+    VK_TLSGD,
+    VK_TLSLD,
+    VK_TLSLDM,
+    VK_TPOFF,
+    VK_DTPOFF,
+    VK_TLSCALL,   // symbol(tlscall)
+    VK_TLSDESC,   // symbol(tlsdesc)
+    VK_TLVP,      // Mach-O thread local variable relocations
+    VK_TLVPPAGE,
+    VK_TLVPPAGEOFF,
+    VK_PAGE,
+    VK_PAGEOFF,
+    VK_GOTPAGE,
+    VK_GOTPAGEOFF,
+    VK_SECREL,
+    VK_SIZE,      // symbol@SIZE
+    VK_WEAKREF,   // The link between the symbols in .weakref foo, bar
+
+    VK_X86_ABS8,
+
+    VK_ARM_NONE,
+    VK_ARM_GOT_PREL,
+    VK_ARM_TARGET1,
+    VK_ARM_TARGET2,
+    VK_ARM_PREL31,
+    VK_ARM_SBREL,          // symbol(sbrel)
+    VK_ARM_TLSLDO,         // symbol(tlsldo)
+    VK_ARM_TLSDESCSEQ,
+
+    VK_AVR_NONE,
+    VK_AVR_LO8,
+    VK_AVR_HI8,
+    VK_AVR_HLO8,
+    VK_AVR_DIFF8,
+    VK_AVR_DIFF16,
+    VK_AVR_DIFF32,
+
+    VK_PPC_LO,             // symbol@l
+    VK_PPC_HI,             // symbol@h
+    VK_PPC_HA,             // symbol@ha
+    VK_PPC_HIGH,           // symbol@high
+    VK_PPC_HIGHA,          // symbol@higha
+    VK_PPC_HIGHER,         // symbol@higher
+    VK_PPC_HIGHERA,        // symbol@highera
+    VK_PPC_HIGHEST,        // symbol@highest
+    VK_PPC_HIGHESTA,       // symbol@highesta
+    VK_PPC_GOT_LO,         // symbol@got@l
+    VK_PPC_GOT_HI,         // symbol@got@h
+    VK_PPC_GOT_HA,         // symbol@got@ha
+    VK_PPC_TOCBASE,        // symbol@tocbase
+    VK_PPC_TOC,            // symbol@toc
+    VK_PPC_TOC_LO,         // symbol@toc@l
+    VK_PPC_TOC_HI,         // symbol@toc@h
+    VK_PPC_TOC_HA,         // symbol@toc@ha
+    VK_PPC_U,              // symbol@u
+    VK_PPC_L,              // symbol@l
+    VK_PPC_DTPMOD,         // symbol@dtpmod
+    VK_PPC_TPREL_LO,       // symbol@tprel@l
+    VK_PPC_TPREL_HI,       // symbol@tprel@h
+    VK_PPC_TPREL_HA,       // symbol@tprel@ha
+    VK_PPC_TPREL_HIGH,     // symbol@tprel@high
+    VK_PPC_TPREL_HIGHA,    // symbol@tprel@higha
+    VK_PPC_TPREL_HIGHER,   // symbol@tprel@higher
+    VK_PPC_TPREL_HIGHERA,  // symbol@tprel@highera
+    VK_PPC_TPREL_HIGHEST,  // symbol@tprel@highest
+    VK_PPC_TPREL_HIGHESTA, // symbol@tprel@highesta
+    VK_PPC_DTPREL_LO,      // symbol@dtprel@l
+    VK_PPC_DTPREL_HI,      // symbol@dtprel@h
+    VK_PPC_DTPREL_HA,      // symbol@dtprel@ha
+    VK_PPC_DTPREL_HIGH,    // symbol@dtprel@high
+    VK_PPC_DTPREL_HIGHA,   // symbol@dtprel@higha
+    VK_PPC_DTPREL_HIGHER,  // symbol@dtprel@higher
+    VK_PPC_DTPREL_HIGHERA, // symbol@dtprel@highera
+    VK_PPC_DTPREL_HIGHEST, // symbol@dtprel@highest
+    VK_PPC_DTPREL_HIGHESTA,// symbol@dtprel@highesta
+    VK_PPC_GOT_TPREL,      // symbol@got@tprel
+    VK_PPC_GOT_TPREL_LO,   // symbol@got@tprel@l
+    VK_PPC_GOT_TPREL_HI,   // symbol@got@tprel@h
+    VK_PPC_GOT_TPREL_HA,   // symbol@got@tprel@ha
+    VK_PPC_GOT_DTPREL,     // symbol@got@dtprel
+    VK_PPC_GOT_DTPREL_LO,  // symbol@got@dtprel@l
+    VK_PPC_GOT_DTPREL_HI,  // symbol@got@dtprel@h
+    VK_PPC_GOT_DTPREL_HA,  // symbol@got@dtprel@ha
+    VK_PPC_TLS,            // symbol@tls
+    VK_PPC_GOT_TLSGD,      // symbol@got@tlsgd
+    VK_PPC_GOT_TLSGD_LO,   // symbol@got@tlsgd@l
+    VK_PPC_GOT_TLSGD_HI,   // symbol@got@tlsgd@h
+    VK_PPC_GOT_TLSGD_HA,   // symbol@got@tlsgd@ha
+    VK_PPC_TLSGD,          // symbol@tlsgd
+    VK_PPC_GOT_TLSLD,      // symbol@got@tlsld
+    VK_PPC_GOT_TLSLD_LO,   // symbol@got@tlsld@l
+    VK_PPC_GOT_TLSLD_HI,   // symbol@got@tlsld@h
+    VK_PPC_GOT_TLSLD_HA,   // symbol@got@tlsld@ha
+    VK_PPC_TLSLD,          // symbol@tlsld
+    VK_PPC_LOCAL,          // symbol@local
+
+    VK_COFF_IMGREL32, // symbol@imgrel (image-relative)
+
+    VK_Hexagon_PCREL,
+    VK_Hexagon_LO16,
+    VK_Hexagon_HI16,
+    VK_Hexagon_GPREL,
+    VK_Hexagon_GD_GOT,
+    VK_Hexagon_LD_GOT,
+    VK_Hexagon_GD_PLT,
+    VK_Hexagon_LD_PLT,
+    VK_Hexagon_IE,
+    VK_Hexagon_IE_GOT,
+
+    VK_WASM_TYPEINDEX, // Reference to a symbol's type (signature)
+    VK_WASM_MBREL,     // Memory address relative to memory base
+    VK_WASM_TBREL,     // Table index relative to table bare
+
+    VK_AMDGPU_GOTPCREL32_LO, // symbol@gotpcrel32@lo
+    VK_AMDGPU_GOTPCREL32_HI, // symbol@gotpcrel32@hi
+    VK_AMDGPU_REL32_LO,      // symbol@rel32@lo
+    VK_AMDGPU_REL32_HI,      // symbol@rel32@hi
+    VK_AMDGPU_REL64,         // symbol@rel64
+    VK_AMDGPU_ABS32_LO,      // symbol@abs32@lo
+    VK_AMDGPU_ABS32_HI,      // symbol@abs32@hi
+
+    VK_TPREL,
+    VK_DTPREL
+  };
+
+private:
+  /// The symbol reference modifier.
+  const VariantKind Kind;
+
+  /// Specifies how the variant kind should be printed.
+  const unsigned UseParensForSymbolVariant : 1;
+
+  // FIXME: Remove this bit.
+  const unsigned HasSubsectionsViaSymbols : 1;
+
+  /// The symbol being referenced.
+  const MCSymbol *Symbol;
+
+  explicit MCSymbolRefExpr(const MCSymbol *Symbol, VariantKind Kind,
+                           const MCAsmInfo *MAI, SMLoc Loc = SMLoc());
+
+public:
+  /// \name Construction
+  /// @{
+
+  static const MCSymbolRefExpr *create(const MCSymbol *Symbol, MCContext &Ctx) {
+    return MCSymbolRefExpr::create(Symbol, VK_None, Ctx);
+  }
+
+  static const MCSymbolRefExpr *create(const MCSymbol *Symbol, VariantKind Kind,
+                                       MCContext &Ctx, SMLoc Loc = SMLoc());
+  static const MCSymbolRefExpr *create(StringRef Name, VariantKind Kind,
+                                       MCContext &Ctx);
+
+  /// @}
+  /// \name Accessors
+  /// @{
+
+  const MCSymbol &getSymbol() const { return *Symbol; }
+
+  VariantKind getKind() const { return Kind; }
+
+  void printVariantKind(raw_ostream &OS) const;
+
+  bool hasSubsectionsViaSymbols() const { return HasSubsectionsViaSymbols; }
+
+  /// @}
+  /// \name Static Utility Functions
+  /// @{
+
+  static StringRef getVariantKindName(VariantKind Kind);
+
+  static VariantKind getVariantKindForName(StringRef Name);
+
+  /// @}
+
+  static bool classof(const MCExpr *E) {
+    return E->getKind() == MCExpr::SymbolRef;
+  }
+};
+
+/// Unary assembler expressions.
+class MCUnaryExpr : public MCExpr {
+public:
+  enum Opcode {
+    LNot,  ///< Logical negation.
+    Minus, ///< Unary minus.
+    Not,   ///< Bitwise negation.
+    Plus   ///< Unary plus.
+  };
+
+private:
+  Opcode Op;
+  const MCExpr *Expr;
+
+  MCUnaryExpr(Opcode Op, const MCExpr *Expr, SMLoc Loc)
+      : MCExpr(MCExpr::Unary, Loc), Op(Op), Expr(Expr) {}
+
+public:
+  /// \name Construction
+  /// @{
+
+  static const MCUnaryExpr *create(Opcode Op, const MCExpr *Expr,
+                                   MCContext &Ctx, SMLoc Loc = SMLoc());
+
+  static const MCUnaryExpr *createLNot(const MCExpr *Expr, MCContext &Ctx, SMLoc Loc = SMLoc()) {
+    return create(LNot, Expr, Ctx, Loc);
+  }
+
+  static const MCUnaryExpr *createMinus(const MCExpr *Expr, MCContext &Ctx, SMLoc Loc = SMLoc()) {
+    return create(Minus, Expr, Ctx, Loc);
+  }
+
+  static const MCUnaryExpr *createNot(const MCExpr *Expr, MCContext &Ctx, SMLoc Loc = SMLoc()) {
+    return create(Not, Expr, Ctx, Loc);
+  }
+
+  static const MCUnaryExpr *createPlus(const MCExpr *Expr, MCContext &Ctx, SMLoc Loc = SMLoc()) {
+    return create(Plus, Expr, Ctx, Loc);
+  }
+
+  /// @}
+  /// \name Accessors
+  /// @{
+
+  /// Get the kind of this unary expression.
+  Opcode getOpcode() const { return Op; }
+
+  /// Get the child of this unary expression.
+  const MCExpr *getSubExpr() const { return Expr; }
+
+  /// @}
+
+  static bool classof(const MCExpr *E) {
+    return E->getKind() == MCExpr::Unary;
+  }
+};
+
+/// Binary assembler expressions.
+class MCBinaryExpr : public MCExpr {
+public:
+  enum Opcode {
+    Add,  ///< Addition.
+    And,  ///< Bitwise and.
+    Div,  ///< Signed division.
+    EQ,   ///< Equality comparison.
+    GT,   ///< Signed greater than comparison (result is either 0 or some
+          ///< target-specific non-zero value)
+    GTE,  ///< Signed greater than or equal comparison (result is either 0 or
+          ///< some target-specific non-zero value).
+    LAnd, ///< Logical and.
+    LOr,  ///< Logical or.
+    LT,   ///< Signed less than comparison (result is either 0 or
+          ///< some target-specific non-zero value).
+    LTE,  ///< Signed less than or equal comparison (result is either 0 or
+          ///< some target-specific non-zero value).
+    Mod,  ///< Signed remainder.
+    Mul,  ///< Multiplication.
+    NE,   ///< Inequality comparison.
+    Or,   ///< Bitwise or.
+    Shl,  ///< Shift left.
+    AShr, ///< Arithmetic shift right.
+    LShr, ///< Logical shift right.
+    Sub,  ///< Subtraction.
+    Xor   ///< Bitwise exclusive or.
+  };
+
+private:
+  Opcode Op;
+  const MCExpr *LHS, *RHS;
+
+  MCBinaryExpr(Opcode Op, const MCExpr *LHS, const MCExpr *RHS,
+               SMLoc Loc = SMLoc())
+      : MCExpr(MCExpr::Binary, Loc), Op(Op), LHS(LHS), RHS(RHS) {}
+
+public:
+  /// \name Construction
+  /// @{
+
+  static const MCBinaryExpr *create(Opcode Op, const MCExpr *LHS,
+                                    const MCExpr *RHS, MCContext &Ctx,
+                                    SMLoc Loc = SMLoc());
+
+  static const MCBinaryExpr *createAdd(const MCExpr *LHS, const MCExpr *RHS,
+                                       MCContext &Ctx) {
+    return create(Add, LHS, RHS, Ctx);
+  }
+
+  static const MCBinaryExpr *createAnd(const MCExpr *LHS, const MCExpr *RHS,
+                                       MCContext &Ctx) {
+    return create(And, LHS, RHS, Ctx);
+  }
+
+  static const MCBinaryExpr *createDiv(const MCExpr *LHS, const MCExpr *RHS,
+                                       MCContext &Ctx) {
+    return create(Div, LHS, RHS, Ctx);
+  }
+
+  static const MCBinaryExpr *createEQ(const MCExpr *LHS, const MCExpr *RHS,
+                                      MCContext &Ctx) {
+    return create(EQ, LHS, RHS, Ctx);
+  }
+
+  static const MCBinaryExpr *createGT(const MCExpr *LHS, const MCExpr *RHS,
+                                      MCContext &Ctx) {
+    return create(GT, LHS, RHS, Ctx);
+  }
+
+  static const MCBinaryExpr *createGTE(const MCExpr *LHS, const MCExpr *RHS,
+                                       MCContext &Ctx) {
+    return create(GTE, LHS, RHS, Ctx);
+  }
+
+  static const MCBinaryExpr *createLAnd(const MCExpr *LHS, const MCExpr *RHS,
+                                        MCContext &Ctx) {
+    return create(LAnd, LHS, RHS, Ctx);
+  }
+
+  static const MCBinaryExpr *createLOr(const MCExpr *LHS, const MCExpr *RHS,
+                                       MCContext &Ctx) {
+    return create(LOr, LHS, RHS, Ctx);
+  }
+
+  static const MCBinaryExpr *createLT(const MCExpr *LHS, const MCExpr *RHS,
+                                      MCContext &Ctx) {
+    return create(LT, LHS, RHS, Ctx);
+  }
+
+  static const MCBinaryExpr *createLTE(const MCExpr *LHS, const MCExpr *RHS,
+                                       MCContext &Ctx) {
+    return create(LTE, LHS, RHS, Ctx);
+  }
+
+  static const MCBinaryExpr *createMod(const MCExpr *LHS, const MCExpr *RHS,
+                                       MCContext &Ctx) {
+    return create(Mod, LHS, RHS, Ctx);
+  }
+
+  static const MCBinaryExpr *createMul(const MCExpr *LHS, const MCExpr *RHS,
+                                       MCContext &Ctx) {
+    return create(Mul, LHS, RHS, Ctx);
+  }
+
+  static const MCBinaryExpr *createNE(const MCExpr *LHS, const MCExpr *RHS,
+                                      MCContext &Ctx) {
+    return create(NE, LHS, RHS, Ctx);
+  }
+
+  static const MCBinaryExpr *createOr(const MCExpr *LHS, const MCExpr *RHS,
+                                      MCContext &Ctx) {
+    return create(Or, LHS, RHS, Ctx);
+  }
+
+  static const MCBinaryExpr *createShl(const MCExpr *LHS, const MCExpr *RHS,
+                                       MCContext &Ctx) {
+    return create(Shl, LHS, RHS, Ctx);
+  }
+
+  static const MCBinaryExpr *createAShr(const MCExpr *LHS, const MCExpr *RHS,
+                                       MCContext &Ctx) {
+    return create(AShr, LHS, RHS, Ctx);
+  }
+
+  static const MCBinaryExpr *createLShr(const MCExpr *LHS, const MCExpr *RHS,
+                                       MCContext &Ctx) {
+    return create(LShr, LHS, RHS, Ctx);
+  }
+
+  static const MCBinaryExpr *createSub(const MCExpr *LHS, const MCExpr *RHS,
+                                       MCContext &Ctx) {
+    return create(Sub, LHS, RHS, Ctx);
+  }
+
+  static const MCBinaryExpr *createXor(const MCExpr *LHS, const MCExpr *RHS,
+                                       MCContext &Ctx) {
+    return create(Xor, LHS, RHS, Ctx);
+  }
+
+  /// @}
+  /// \name Accessors
+  /// @{
+
+  /// Get the kind of this binary expression.
+  Opcode getOpcode() const { return Op; }
+
+  /// Get the left-hand side expression of the binary operator.
+  const MCExpr *getLHS() const { return LHS; }
+
+  /// Get the right-hand side expression of the binary operator.
+  const MCExpr *getRHS() const { return RHS; }
+
+  /// @}
+
+  static bool classof(const MCExpr *E) {
+    return E->getKind() == MCExpr::Binary;
+  }
+};
+
+/// This is an extension point for target-specific MCExpr subclasses to
+/// implement.
+///
+/// NOTE: All subclasses are required to have trivial destructors because
+/// MCExprs are bump pointer allocated and not destructed.
+class MCTargetExpr : public MCExpr {
+  virtual void anchor();
+
+protected:
+  MCTargetExpr() : MCExpr(Target, SMLoc()) {}
+  virtual ~MCTargetExpr() = default;
+
+public:
+  virtual void printImpl(raw_ostream &OS, const MCAsmInfo *MAI) const = 0;
+  virtual bool evaluateAsRelocatableImpl(MCValue &Res,
+                                         const MCAsmLayout *Layout,
+                                         const MCFixup *Fixup) const = 0;
+  // allow Target Expressions to be checked for equality
+  virtual bool isEqualTo(const MCExpr *x) const { return false; }
+  // This should be set when assigned expressions are not valid ".set"
+  // expressions, e.g. registers, and must be inlined.
+  virtual bool inlineAssignedExpr() const { return false; }
+  virtual void visitUsedExpr(MCStreamer& Streamer) const = 0;
+  virtual MCFragment *findAssociatedFragment() const = 0;
+
+  virtual void fixELFSymbolsInTLSFixups(MCAssembler &) const = 0;
+
+  static bool classof(const MCExpr *E) {
+    return E->getKind() == MCExpr::Target;
+  }
+};
+
+} // end namespace llvm
+
+#endif // LLVM_MC_MCEXPR_H