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//===-- JumpInstrTables.h: Jump-Instruction Tables --------------*- C++ -*-===//
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
///
/// \file
/// \brief An implementation of tables consisting of jump instructions
///
//===----------------------------------------------------------------------===//
#ifndef LLVM_CODEGEN_JUMPINSTRTABLES_H
#define LLVM_CODEGEN_JUMPINSTRTABLES_H
#include "llvm/ADT/DenseMap.h"
#include "llvm/Pass.h"
#include "llvm/Target/TargetOptions.h"
namespace llvm {
class Constant;
class Function;
class FunctionType;
class JumpInstrTableInfo;
class Module;
/// A class to manage a set of jump tables indexed on function type. It looks at
/// each function in the module to find all the functions that have the
/// jumptable attribute set. For each such function, it creates a new
/// jump-instruction-table function and stores the mapping in the ImmutablePass
/// JumpInstrTableInfo.
///
/// These special functions get lowered in AsmPrinter to assembly of the form:
/// \verbatim
/// .globl f
/// .type f,@function
/// .align 8,0x90
/// f:
/// jmp f_orig@PLT
/// \endverbatim
///
/// Support for an architecture depends on three functions in TargetInstrInfo:
/// getUnconditionalBranch, getTrap, and getJumpInstrTableEntryBound. AsmPrinter
/// uses these to generate the appropriate instructions for the jump statement
/// (an unconditional branch) and for padding to make the table have a size that
/// is a power of two. This padding uses a trap instruction to ensure that calls
/// to this area halt the program. The default implementations of these
/// functions call llvm_unreachable, except for getJumpInstrTableEntryBound,
/// which returns 0 by default.
class JumpInstrTables : public ModulePass {
public:
static char ID;
JumpInstrTables();
JumpInstrTables(JumpTable::JumpTableType JTT);
virtual ~JumpInstrTables();
bool runOnModule(Module &M) override;
const char *getPassName() const override { return "Jump-Instruction Tables"; }
void getAnalysisUsage(AnalysisUsage &AU) const override;
/// Creates a jump-instruction table function for the Target and adds it to
/// the tables.
Function *insertEntry(Module &M, Function *Target);
/// Checks to see if there is already a table for the given FunctionType.
bool hasTable(FunctionType *FunTy);
/// Maps the function into a subset of function types, depending on the
/// jump-instruction table style selected from JumpTableTypes in
/// JumpInstrTables.cpp. The choice of mapping determines the number of
/// jump-instruction tables generated by this pass. E.g., the simplest mapping
/// converts every function type into void f(); so, all functions end up in a
/// single table.
static FunctionType *transformType(JumpTable::JumpTableType JTT,
FunctionType *FunTy);
private:
/// The metadata used while a jump table is being built
struct TableMeta {
/// The number of this table
unsigned TableNum;
/// The current number of jump entries in the table.
unsigned Count;
};
typedef DenseMap<FunctionType *, struct TableMeta> JumpMap;
/// The current state of functions and jump entries in the table(s).
JumpMap Metadata;
/// The ImmutablePass that stores information about the generated tables.
JumpInstrTableInfo *JITI;
/// The total number of tables.
unsigned TableCount;
/// The type of tables to build.
JumpTable::JumpTableType JTType;
};
/// Creates a JumpInstrTables pass for the given type of jump table.
ModulePass *createJumpInstrTablesPass(JumpTable::JumpTableType JTT);
}
#endif /* LLVM_CODEGEN_JUMPINSTRTABLES_H */
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