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llvm/include/llvm/MC/MCExpr.h
Peter Collingbourne 7da5357aca ARM/ELF: Better codegen for global variable addresses. 
In PIC mode we were previously computing global variable addresses (or GOT
entry addresses) by adding the PC, the PC-relative GOT displacement and
the GOT-relative symbol/GOT entry displacement. Because the latter two
displacements are fixed, we ended up performing one more addition than
necessary.

This change causes us to compute addresses using a single PC-relative
displacement, resulting in a shorter code sequence. This reduces code size
by about 4% in a recent build of Chromium for Android.

As a result of this change we no longer need to compute the GOT base address
in the ARM backend, which allows us to remove the Global Base Reg pass and
SDAG lowering for the GOT.

We also now no longer use the GOT when addressing a symbol which is known
to be defined in the same linkage unit. Specifically, the symbol must have
either hidden visibility or a strong definition in the current module in
order to not use the the GOT.

This is a change from the previous behaviour where we would use the GOT to
address externally visible symbols defined in the same module. I think the
only cases where this could matter are cases involving symbol interposition,
but we don't really support that well anyway.

Differential Revision: http://reviews.llvm.org/D13650

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@251322 91177308-0d34-0410-b5e6-96231b3b80d8
2015-10-26 18:23:16 +00:00

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//===- MCExpr.h - Assembly Level Expressions --------------------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_MC_MCEXPR_H
#define LLVM_MC_MCEXPR_H
#include "llvm/ADT/DenseMap.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/DataTypes.h"
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;
typedef DenseMap<const MCSection *, uint64_t> SectionAddrMap;
/// \brief 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;
MCExpr(const MCExpr&) = delete;
void operator=(const MCExpr&) = delete;
bool evaluateAsAbsolute(int64_t &Res, const MCAssembler *Asm,
const MCAsmLayout *Layout,
const SectionAddrMap *Addrs) const;
bool evaluateAsAbsolute(int64_t &Res, const MCAssembler *Asm,
const MCAsmLayout *Layout,
const SectionAddrMap *Addrs, bool InSet) const;
protected:
explicit MCExpr(ExprKind Kind) : Kind(Kind) {}
bool evaluateAsRelocatableImpl(MCValue &Res, const MCAssembler *Asm,
const MCAsmLayout *Layout,
const MCFixup *Fixup,
const SectionAddrMap *Addrs, bool InSet) const;
public:
/// \name Accessors
/// @{
ExprKind getKind() const { return Kind; }
/// @}
/// \name Utility Methods
/// @{
void print(raw_ostream &OS, const MCAsmInfo *MAI) const;
void dump() const;
/// @}
/// \name Expression Evaluation
/// @{
/// \brief 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 MCAsmLayout &Layout) const;
bool evaluateKnownAbsolute(int64_t &Res, const MCAsmLayout &Layout) const;
/// \brief 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;
/// \brief 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;
/// \brief 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;
}
//// \brief Represent a constant integer expression.
class MCConstantExpr : public MCExpr {
int64_t Value;
explicit MCConstantExpr(int64_t Value)
: MCExpr(MCExpr::Constant), Value(Value) {}
public:
/// \name Construction
/// @{
static const MCConstantExpr *create(int64_t Value, MCContext &Ctx);
/// @}
/// \name Accessors
/// @{
int64_t getValue() const { return Value; }
/// @}
static bool classof(const MCExpr *E) {
return E->getKind() == MCExpr::Constant;
}
};
/// \brief 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_GOTPCREL,
VK_GOTTPOFF,
VK_INDNTPOFF,
VK_NTPOFF,
VK_GOTNTPOFF,
VK_PLT,
VK_TLSGD,
VK_TLSLD,
VK_TLSLDM,
VK_TPOFF,
VK_DTPOFF,
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_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_TLSCALL, // symbol(tlscall)
VK_ARM_TLSDESC, // symbol(tlsdesc)
VK_ARM_TLSDESCSEQ,
VK_PPC_LO, // symbol@l
VK_PPC_HI, // symbol@h
VK_PPC_HA, // symbol@ha
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_DTPMOD, // symbol@dtpmod
VK_PPC_TPREL, // symbol@tprel
VK_PPC_TPREL_LO, // symbol@tprel@l
VK_PPC_TPREL_HI, // symbol@tprel@h
VK_PPC_TPREL_HA, // symbol@tprel@ha
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, // symbol@dtprel
VK_PPC_DTPREL_LO, // symbol@dtprel@l
VK_PPC_DTPREL_HI, // symbol@dtprel@h
VK_PPC_DTPREL_HA, // symbol@dtprel@ha
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_Mips_GPREL,
VK_Mips_GOT_CALL,
VK_Mips_GOT16,
VK_Mips_GOT,
VK_Mips_ABS_HI,
VK_Mips_ABS_LO,
VK_Mips_TLSGD,
VK_Mips_TLSLDM,
VK_Mips_DTPREL_HI,
VK_Mips_DTPREL_LO,
VK_Mips_GOTTPREL,
VK_Mips_TPREL_HI,
VK_Mips_TPREL_LO,
VK_Mips_GPOFF_HI,
VK_Mips_GPOFF_LO,
VK_Mips_GOT_DISP,
VK_Mips_GOT_PAGE,
VK_Mips_GOT_OFST,
VK_Mips_HIGHER,
VK_Mips_HIGHEST,
VK_Mips_GOT_HI16,
VK_Mips_GOT_LO16,
VK_Mips_CALL_HI16,
VK_Mips_CALL_LO16,
VK_Mips_PCREL_HI16,
VK_Mips_PCREL_LO16,
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_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);
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);
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;
}
};
/// \brief 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)
: MCExpr(MCExpr::Unary), Op(Op), Expr(Expr) {}
public:
/// \name Construction
/// @{
static const MCUnaryExpr *create(Opcode Op, const MCExpr *Expr,
MCContext &Ctx);
static const MCUnaryExpr *createLNot(const MCExpr *Expr, MCContext &Ctx) {
return create(LNot, Expr, Ctx);
}
static const MCUnaryExpr *createMinus(const MCExpr *Expr, MCContext &Ctx) {
return create(Minus, Expr, Ctx);
}
static const MCUnaryExpr *createNot(const MCExpr *Expr, MCContext &Ctx) {
return create(Not, Expr, Ctx);
}
static const MCUnaryExpr *createPlus(const MCExpr *Expr, MCContext &Ctx) {
return create(Plus, Expr, Ctx);
}
/// @}
/// \name Accessors
/// @{
/// \brief Get the kind of this unary expression.
Opcode getOpcode() const { return Op; }
/// \brief Get the child of this unary expression.
const MCExpr *getSubExpr() const { return Expr; }
/// @}
static bool classof(const MCExpr *E) {
return E->getKind() == MCExpr::Unary;
}
};
/// \brief 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)
: MCExpr(MCExpr::Binary), Op(Op), LHS(LHS), RHS(RHS) {}
public:
/// \name Construction
/// @{
static const MCBinaryExpr *create(Opcode Op, const MCExpr *LHS,
const MCExpr *RHS, MCContext &Ctx);
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
/// @{
/// \brief Get the kind of this binary expression.
Opcode getOpcode() const { return Op; }
/// \brief Get the left-hand side expression of the binary operator.
const MCExpr *getLHS() const { return LHS; }
/// \brief 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;
}
};
/// \brief 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) {}
virtual ~MCTargetExpr() {}
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;
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
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