1 //===-- llvm/Target/TargetAsmBackend.h - Target Asm Backend -----*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 #ifndef LLVM_TARGET_TARGETASMBACKEND_H
11 #define LLVM_TARGET_TARGETASMBACKEND_H
13 #include "llvm/System/DataTypes.h"
22 class SmallVectorImpl;
26 /// TargetAsmBackend - Generic interface to target specific assembler backends.
27 class TargetAsmBackend {
28 TargetAsmBackend(const TargetAsmBackend &); // DO NOT IMPLEMENT
29 void operator=(const TargetAsmBackend &); // DO NOT IMPLEMENT
30 protected: // Can only create subclasses.
31 TargetAsmBackend(const Target &);
33 /// TheTarget - The Target that this machine was created for.
34 const Target &TheTarget;
36 unsigned HasAbsolutizedSet : 1;
37 unsigned HasReliableSymbolDifference : 1;
38 unsigned HasScatteredSymbols : 1;
41 virtual ~TargetAsmBackend();
43 const Target &getTarget() const { return TheTarget; }
45 /// createObjectWriter - Create a new MCObjectWriter instance for use by the
46 /// assembler backend to emit the final object file.
47 virtual MCObjectWriter *createObjectWriter(raw_ostream &OS) const = 0;
49 /// hasAbsolutizedSet - Check whether this target "absolutizes"
50 /// assignments. That is, given code like:
56 /// will the value of 'tmp' be a relocatable expression, or the assembly time
57 /// value of L0 - L1. This distinction is only relevant for platforms that
58 /// support scattered symbols, since in the absence of scattered symbols (a -
59 /// b) cannot change after assembly.
60 bool hasAbsolutizedSet() const { return HasAbsolutizedSet; }
62 /// hasReliableSymbolDifference - Check whether this target implements
63 /// accurate relocations for differences between symbols. If not, differences
64 /// between symbols will always be relocatable expressions and any references
65 /// to temporary symbols will be assumed to be in the same atom, unless they
66 /// reside in a different section.
68 /// This should always be true (since it results in fewer relocations with no
69 /// loss of functionality), but is currently supported as a way to maintain
70 /// exact object compatibility with Darwin 'as' (on non-x86_64). It should
71 /// eventually should be eliminated. See also \see hasAbsolutizedSet.
72 bool hasReliableSymbolDifference() const {
73 return HasReliableSymbolDifference;
76 /// hasScatteredSymbols - Check whether this target supports scattered
77 /// symbols. If so, the assembler should assume that atoms can be scattered by
78 /// the linker. In particular, this means that the offsets between symbols
79 /// which are in distinct atoms is not known at link time, and the assembler
80 /// must generate fixups and relocations appropriately.
82 /// Note that the assembler currently does not reason about atoms, instead it
83 /// assumes all temporary symbols reside in the "current atom".
84 bool hasScatteredSymbols() const { return HasScatteredSymbols; }
86 /// doesSectionRequireSymbols - Check whether the given section requires that
87 /// all symbols (even temporaries) have symbol table entries.
88 virtual bool doesSectionRequireSymbols(const MCSection &Section) const {
92 /// isSectionAtomizable - Check whether the given section can be split into
95 /// \see MCAssembler::isSymbolLinkerVisible().
96 virtual bool isSectionAtomizable(const MCSection &Section) const {
100 /// isVirtualSection - Check whether the given section is "virtual", that is
101 /// has no actual object file contents.
102 virtual bool isVirtualSection(const MCSection &Section) const = 0;
104 /// ApplyFixup - Apply the \arg Value for given \arg Fixup into the provided
105 /// data fragment, at the offset specified by the fixup and following the
106 /// fixup kind as appropriate.
107 virtual void ApplyFixup(const MCFixup &Fixup, MCDataFragment &Fragment,
108 uint64_t Value) const = 0;
110 /// MayNeedRelaxation - Check whether the given instruction may need
113 /// \param Inst - The instruction to test.
114 virtual bool MayNeedRelaxation(const MCInst &Inst) const = 0;
116 /// RelaxInstruction - Relax the instruction in the given fragment to the next
117 /// wider instruction.
119 /// \param Inst - The instruction to relax, which may be the same as the
121 /// \parm Res [output] - On return, the relaxed instruction.
122 virtual void RelaxInstruction(const MCInst &Inst, MCInst &Res) const = 0;
124 /// WriteNopData - Write an (optimal) nop sequence of Count bytes to the given
125 /// output. If the target cannot generate such a sequence, it should return an
128 /// \return - True on success.
129 virtual bool WriteNopData(uint64_t Count, MCObjectWriter *OW) const = 0;
132 } // End llvm namespace