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      1 //===-- X86AsmPrinter.h - X86 implementation of AsmPrinter ------*- C++ -*-===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 
     10 #ifndef LLVM_LIB_TARGET_X86_X86ASMPRINTER_H
     11 #define LLVM_LIB_TARGET_X86_X86ASMPRINTER_H
     12 
     13 #include "X86Subtarget.h"
     14 #include "llvm/CodeGen/AsmPrinter.h"
     15 #include "llvm/CodeGen/StackMaps.h"
     16 #include "llvm/Target/TargetMachine.h"
     17 
     18 // Implemented in X86MCInstLower.cpp
     19 namespace {
     20   class X86MCInstLower;
     21 }
     22 
     23 namespace llvm {
     24 class MCStreamer;
     25 class MCSymbol;
     26 
     27 class LLVM_LIBRARY_VISIBILITY X86AsmPrinter : public AsmPrinter {
     28   const X86Subtarget *Subtarget;
     29   StackMaps SM;
     30 
     31   void GenerateExportDirective(const MCSymbol *Sym, bool IsData);
     32 
     33   // This utility class tracks the length of a stackmap instruction's 'shadow'.
     34   // It is used by the X86AsmPrinter to ensure that the stackmap shadow
     35   // invariants (i.e. no other stackmaps, patchpoints, or control flow within
     36   // the shadow) are met, while outputting a minimal number of NOPs for padding.
     37   //
     38   // To minimise the number of NOPs used, the shadow tracker counts the number
     39   // of instruction bytes output since the last stackmap. Only if there are too
     40   // few instruction bytes to cover the shadow are NOPs used for padding.
     41   class StackMapShadowTracker {
     42   public:
     43     StackMapShadowTracker(TargetMachine &TM);
     44     ~StackMapShadowTracker();
     45     void startFunction(MachineFunction &MF);
     46     void count(MCInst &Inst, const MCSubtargetInfo &STI);
     47 
     48     // Called to signal the start of a shadow of RequiredSize bytes.
     49     void reset(unsigned RequiredSize) {
     50       RequiredShadowSize = RequiredSize;
     51       CurrentShadowSize = 0;
     52       InShadow = true;
     53     }
     54 
     55     // Called before every stackmap/patchpoint, and at the end of basic blocks,
     56     // to emit any necessary padding-NOPs.
     57     void emitShadowPadding(MCStreamer &OutStreamer, const MCSubtargetInfo &STI);
     58   private:
     59     TargetMachine &TM;
     60     const MachineFunction *MF;
     61     std::unique_ptr<MCCodeEmitter> CodeEmitter;
     62     bool InShadow;
     63 
     64     // RequiredShadowSize holds the length of the shadow specified in the most
     65     // recently encountered STACKMAP instruction.
     66     // CurrentShadowSize counts the number of bytes encoded since the most
     67     // recently encountered STACKMAP, stopping when that number is greater than
     68     // or equal to RequiredShadowSize.
     69     unsigned RequiredShadowSize, CurrentShadowSize;
     70   };
     71 
     72   StackMapShadowTracker SMShadowTracker;
     73 
     74   // All instructions emitted by the X86AsmPrinter should use this helper
     75   // method.
     76   //
     77   // This helper function invokes the SMShadowTracker on each instruction before
     78   // outputting it to the OutStream. This allows the shadow tracker to minimise
     79   // the number of NOPs used for stackmap padding.
     80   void EmitAndCountInstruction(MCInst &Inst);
     81 
     82   void InsertStackMapShadows(MachineFunction &MF);
     83   void LowerSTACKMAP(const MachineInstr &MI);
     84   void LowerPATCHPOINT(const MachineInstr &MI);
     85 
     86   void LowerTlsAddr(X86MCInstLower &MCInstLowering, const MachineInstr &MI);
     87 
     88  public:
     89    explicit X86AsmPrinter(TargetMachine &TM,
     90                           std::unique_ptr<MCStreamer> Streamer)
     91        : AsmPrinter(TM, std::move(Streamer)), SM(*this), SMShadowTracker(TM) {}
     92 
     93   const char *getPassName() const override {
     94     return "X86 Assembly / Object Emitter";
     95   }
     96 
     97   const X86Subtarget &getSubtarget() const { return *Subtarget; }
     98 
     99   void EmitStartOfAsmFile(Module &M) override;
    100 
    101   void EmitEndOfAsmFile(Module &M) override;
    102 
    103   void EmitInstruction(const MachineInstr *MI) override;
    104 
    105   void EmitBasicBlockEnd(const MachineBasicBlock &MBB) override {
    106     SMShadowTracker.emitShadowPadding(OutStreamer, getSubtargetInfo());
    107   }
    108 
    109   bool PrintAsmOperand(const MachineInstr *MI, unsigned OpNo,
    110                        unsigned AsmVariant, const char *ExtraCode,
    111                        raw_ostream &OS) override;
    112   bool PrintAsmMemoryOperand(const MachineInstr *MI, unsigned OpNo,
    113                              unsigned AsmVariant, const char *ExtraCode,
    114                              raw_ostream &OS) override;
    115 
    116   /// \brief Return the symbol for the specified constant pool entry.
    117   MCSymbol *GetCPISymbol(unsigned CPID) const override;
    118 
    119   bool doInitialization(Module &M) override {
    120     SMShadowTracker.reset(0);
    121     SM.reset();
    122     return AsmPrinter::doInitialization(M);
    123   }
    124 
    125   bool runOnMachineFunction(MachineFunction &F) override;
    126 };
    127 
    128 } // end namespace llvm
    129 
    130 #endif
    131