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//===- EHStreamer.h - Exception Handling Directive Streamer -----*- C++ -*-===//
// The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
// This file contains support for writing exception info into assembly files.
#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 {
/// 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;
/// 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. 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.
virtual void computeCallSiteTable(
SmallVectorImpl<CallSiteEntry> &CallSites,
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; }
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