text: //===- EHStreamer.h - Exception Handling Directive Streamer -----*- 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
  //
  //===----------------------------------------------------------------------===//
  //
  // This file contains support for writing exception info into assembly files.
  //
  //===----------------------------------------------------------------------===//
  
  #ifndef LLVM_LIB_CODEGEN_ASMPRINTER_EHSTREAMER_H
  #define LLVM_LIB_CODEGEN_ASMPRINTER_EHSTREAMER_H
  
  #include "llvm/ADT/DenseMap.h"
  #include "llvm/CodeGen/AsmPrinterHandler.h"
  #include "llvm/Support/Compiler.h"
  
  namespace llvm {
  
  class AsmPrinter;
  struct LandingPadInfo;
  class MachineInstr;
  class MachineModuleInfo;
  class MCSymbol;
  template <typename T> class SmallVectorImpl;
  
  /// Emits exception handling directives.
  class LLVM_LIBRARY_VISIBILITY EHStreamer : public AsmPrinterHandler {
  protected:
    /// Target of directive emission.
    AsmPrinter *Asm;
  
    /// Collected machine module information.
    MachineModuleInfo *MMI;
  
    /// How many leading type ids two landing pads have in common.
    static unsigned sharedTypeIDs(const LandingPadInfo *L,
                                  const LandingPadInfo *R);
  
    /// Structure holding a try-range and the associated landing pad.
    struct PadRange {
      // The index of the landing pad.
      unsigned PadIndex;
  
      // The index of the begin and end labels in the landing pad's label lists.
      unsigned RangeIndex;
    };
  
    using RangeMapType = DenseMap<MCSymbol *, PadRange>;
  
    /// Structure describing an entry in the actions table.
    struct ActionEntry {
      int ValueForTypeID; // The value to write - may not be equal to the type id.
      int NextAction;
      unsigned Previous;
    };
  
    /// Structure describing an entry in the call-site table.
    struct CallSiteEntry {
      // The 'try-range' is BeginLabel .. EndLabel.
      MCSymbol *BeginLabel; // Null indicates the start of the function.
      MCSymbol *EndLabel;   // Null indicates the end of the function.
  
      // LPad contains the landing pad start labels.
      const LandingPadInfo *LPad; // Null indicates that there is no landing pad.
  
      unsigned Action;
    };
  
    /// Structure describing a contiguous range of call-sites which reside
    /// in the same procedure fragment. With -fbasic-block-sections, there will
    /// be one call site range per basic block section. Otherwise, we will have
    /// one call site range containing all the call sites in the function.
    struct CallSiteRange {
      // Symbol marking the beginning of the precedure fragment.
      MCSymbol *FragmentBeginLabel = nullptr;
      // Symbol marking the end of the procedure fragmnt.
      MCSymbol *FragmentEndLabel = nullptr;
      // LSDA symbol for this call-site range.
      MCSymbol *ExceptionLabel = nullptr;
      // Index of the first call-site entry in the call-site table which
      // belongs to this range.
      size_t CallSiteBeginIdx = 0;
      // Index just after the last call-site entry in the call-site table which
      // belongs to this range.
      size_t CallSiteEndIdx = 0;
      // Whether this is the call-site range containing all the landing pads.
      bool IsLPRange = false;
    };
  
    /// Compute the actions table and gather the first action index for each
    /// landing pad site.
    void computeActionsTable(
        const SmallVectorImpl<const LandingPadInfo *> &LandingPads,
        SmallVectorImpl<ActionEntry> &Actions,
        SmallVectorImpl<unsigned> &FirstActions);
  
    void computePadMap(const SmallVectorImpl<const LandingPadInfo *> &LandingPads,
                       RangeMapType &PadMap);
  
    /// Compute the call-site table and the call-site ranges. The entry for an
    /// invoke has a try-range containing the call, a non-zero landing pad and an
    /// appropriate action. The entry for an ordinary call has a try-range
    /// containing the call and zero for the landing pad and the action.  Calls
    /// marked 'nounwind' have no entry and must not be contained in the try-range
    /// of any entry - they form gaps in the table.  Entries must be ordered by
    /// try-range address. CallSiteRanges vector is only populated for Itanium
    /// exception handling.
    virtual void computeCallSiteTable(
        SmallVectorImpl<CallSiteEntry> &CallSites,
        SmallVectorImpl<CallSiteRange> &CallSiteRanges,
        const SmallVectorImpl<const LandingPadInfo *> &LandingPads,
        const SmallVectorImpl<unsigned> &FirstActions);
  
    /// Emit landing pads and actions.
    ///
    /// The general organization of the table is complex, but the basic concepts
    /// are easy.  First there is a header which describes the location and
    /// organization of the three components that follow.
    ///  1. The landing pad site information describes the range of code covered
    ///     by the try.  In our case it's an accumulation of the ranges covered
    ///     by the invokes in the try.  There is also a reference to the landing
    ///     pad that handles the exception once processed.  Finally an index into
    ///     the actions table.
    ///  2. The action table, in our case, is composed of pairs of type ids
    ///     and next action offset.  Starting with the action index from the
    ///     landing pad site, each type Id is checked for a match to the current
    ///     exception.  If it matches then the exception and type id are passed
    ///     on to the landing pad.  Otherwise the next action is looked up.  This
    ///     chain is terminated with a next action of zero.  If no type id is
    ///     found the frame is unwound and handling continues.
    ///  3. Type id table contains references to all the C++ typeinfo for all
    ///     catches in the function.  This tables is reversed indexed base 1.
    ///
    /// Returns the starting symbol of an exception table.
    MCSymbol *emitExceptionTable();
  
    virtual void emitTypeInfos(unsigned TTypeEncoding, MCSymbol *TTBaseLabel);
  
    // Helpers for identifying what kind of clause an EH typeid or selector
    // corresponds to. Negative selectors are for filter clauses, the zero
    // selector is for cleanups, and positive selectors are for catch clauses.
    static bool isFilterEHSelector(int Selector) { return Selector < 0; }
    static bool isCleanupEHSelector(int Selector) { return Selector == 0; }
    static bool isCatchEHSelector(int Selector) { return Selector > 0; }
  
  public:
    EHStreamer(AsmPrinter *A);
    ~EHStreamer() override;
  
    // Unused.
    void setSymbolSize(const MCSymbol *Sym, uint64_t Size) override {}
    void beginInstruction(const MachineInstr *MI) override {}
    void endInstruction() override {}
  
    /// Return `true' if this is a call to a function marked `nounwind'. Return
    /// `false' otherwise.
    static bool callToNoUnwindFunction(const MachineInstr *MI);
  };
  
  } // end namespace llvm
  
  #endif // LLVM_LIB_CODEGEN_ASMPRINTER_EHSTREAMER_H
  