path: root/lib/Transforms/Utils/LowerInvoke.cpp

//===- LowerInvoke.cpp - Eliminate Invoke & Unwind instructions -----------===//
// 
//                     The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
// 
//===----------------------------------------------------------------------===//
//
// This transformation is designed for use by code generators which do not yet
// support stack unwinding.  This pass supports two models of exception handling
// lowering, the 'cheap' support and the 'expensive' support.
//
// 'Cheap' exception handling support gives the program the ability to execute
// any program which does not "throw an exception", by turning 'invoke'
// instructions into calls and by turning 'unwind' instructions into calls to
// abort().  If the program does dynamically use the unwind instruction, the
// program will print a message then abort.
//
// 'Expensive' exception handling support gives the full exception handling
// support to the program at making the 'invoke' instruction really expensive.
// It basically inserts setjmp/longjmp calls to emulate the exception handling
// as necessary.
//
// Because the 'expensive' support slows down programs a lot, and EH is only
// used for a subset of the programs, it must be specifically enabled by an
// option.
//
//===----------------------------------------------------------------------===//

#include "llvm/Transforms/Scalar.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Instructions.h"
#include "llvm/Module.h"
#include "llvm/Pass.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "Support/Statistic.h"
#include "Support/CommandLine.h"
#include <csetjmp>
using namespace llvm;

namespace {
  Statistic<> NumLowered("lowerinvoke", "Number of invoke & unwinds replaced");
  cl::opt<bool> ExpensiveEHSupport("enable-correct-eh-support", 
 cl::desc("Make the -lowerinvoke pass insert expensive, but correct, EH code"));

  class LowerInvoke : public FunctionPass {
    // Used for both models.
    Function *WriteFn;
    Function *AbortFn;
    Value *AbortMessage;
    unsigned AbortMessageLength;

    // Used for expensive EH support.
    const Type *JBLinkTy;
    GlobalVariable *JBListHead;
    Function *SetJmpFn, *LongJmpFn;
  public:
    bool doInitialization(Module &M);
    bool runOnFunction(Function &F);
  private:
    bool insertCheapEHSupport(Function &F);
    bool insertExpensiveEHSupport(Function &F);
  };

  RegisterOpt<LowerInvoke>
  X("lowerinvoke", "Lower invoke and unwind, for unwindless code generators");
}

// Public Interface To the LowerInvoke pass.
FunctionPass *llvm::createLowerInvokePass() { return new LowerInvoke(); }

// doInitialization - Make sure that there is a prototype for abort in the
// current module.
bool LowerInvoke::doInitialization(Module &M) {
  const Type *VoidPtrTy = PointerType::get(Type::SByteTy);
  if (ExpensiveEHSupport) {
    // Insert a type for the linked list of jump buffers.  Unfortunately, we
    // don't know the size of the target's setjmp buffer, so we make a guess.
    // If this guess turns out to be too small, bad stuff could happen.
    unsigned JmpBufSize = 200;  // PPC has 192 words
    assert(sizeof(jmp_buf) <= JmpBufSize*sizeof(void*) &&
       "LowerInvoke doesn't know about targets with jmp_buf size > 200 words!");
    const Type *JmpBufTy = ArrayType::get(VoidPtrTy, JmpBufSize);

    { // The type is recursive, so use a type holder.
      std::vector<const Type*> Elements;
      OpaqueType *OT = OpaqueType::get();
      Elements.push_back(PointerType::get(OT));
      Elements.push_back(JmpBufTy);
      PATypeHolder JBLType(StructType::get(Elements));
      OT->refineAbstractTypeTo(JBLType.get());  // Complete the cycle.
      JBLinkTy = JBLType.get();
    }

    const Type *PtrJBList = PointerType::get(JBLinkTy);

    // Now that we've done that, insert the jmpbuf list head global, unless it
    // already exists.
    if (!(JBListHead = M.getGlobalVariable("llvm.sjljeh.jblist", PtrJBList)))
      JBListHead = new GlobalVariable(PtrJBList, false,
                                      GlobalValue::LinkOnceLinkage,
                                      Constant::getNullValue(PtrJBList),
                                      "llvm.sjljeh.jblist", &M);
    SetJmpFn = M.getOrInsertFunction("setjmp", Type::IntTy,
                                     PointerType::get(JmpBufTy), 0);
    LongJmpFn = M.getOrInsertFunction("longjmp", Type::VoidTy,
                                      PointerType::get(JmpBufTy),
                                      Type::IntTy, 0);
    
    // The abort message for expensive EH support tells the user that the
    // program 'unwound' without an 'invoke' instruction.
    Constant *Msg =
      ConstantArray::get("ERROR: Exception thrown, but not caught!\n");
    AbortMessageLength = Msg->getNumOperands()-1;  // don't include \0
  
    GlobalVariable *MsgGV = M.getGlobalVariable("abort.msg", Msg->getType());
    if (MsgGV && (!MsgGV->hasInitializer() || MsgGV->getInitializer() != Msg))
      MsgGV = 0;
    if (!MsgGV)
      MsgGV = new GlobalVariable(Msg->getType(), true,
                                 GlobalValue::InternalLinkage,
                                 Msg, "abort.msg", &M);
    std::vector<Constant*> GEPIdx(2, Constant::getNullValue(Type::LongTy));
    AbortMessage =
      ConstantExpr::getGetElementPtr(ConstantPointerRef::get(MsgGV), GEPIdx);

  } else {
    // The abort message for cheap EH support tells the user that EH is not
    // enabled.
    Constant *Msg =
      ConstantArray::get("Exception handler needed, but not enabled.  Recompile"
                         " program with -enable-correct-eh-support.\n");
    AbortMessageLength = Msg->getNumOperands()-1;  // don't include \0
  
    GlobalVariable *MsgGV = M.getGlobalVariable("abort.msg", Msg->getType());
    if (MsgGV && (!MsgGV->hasInitializer() || MsgGV->getInitializer() != Msg))
      MsgGV = 0;

    if (!MsgGV)
      MsgGV = new GlobalVariable(Msg->getType(), true,
                                 GlobalValue::InternalLinkage,
                                 Msg, "abort.msg", &M);
    std::vector<Constant*> GEPIdx(2, Constant::getNullValue(Type::LongTy));
    AbortMessage =
      ConstantExpr::getGetElementPtr(ConstantPointerRef::get(MsgGV), GEPIdx);
  }

  // We need the 'write' and 'abort' functions for both models.
  WriteFn = M.getOrInsertFunction("write", Type::VoidTy, Type::IntTy,
                                  VoidPtrTy, Type::IntTy, 0);
  AbortFn = M.getOrInsertFunction("abort", Type::VoidTy, 0);
  return true;
}

bool LowerInvoke::insertCheapEHSupport(Function &F) {
  bool Changed = false;
  for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
    if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) {
      // Insert a normal call instruction...
      std::string Name = II->getName(); II->setName("");
      Value *NewCall = new CallInst(II->getCalledValue(),
                                    std::vector<Value*>(II->op_begin()+3,
                                                        II->op_end()), Name,II);
      II->replaceAllUsesWith(NewCall);
      
      // Insert an unconditional branch to the normal destination.
      new BranchInst(II->getNormalDest(), II);

      // Remove any PHI node entries from the exception destination.
      II->getExceptionalDest()->removePredecessor(BB);

      // Remove the invoke instruction now.
      BB->getInstList().erase(II);

      ++NumLowered; Changed = true;
    } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->getTerminator())) {
      // Insert a new call to write(2, AbortMessage, AbortMessageLength);
      std::vector<Value*> Args;
      Args.push_back(ConstantInt::get(Type::IntTy, 2));
      Args.push_back(AbortMessage);
      Args.push_back(ConstantInt::get(Type::IntTy, AbortMessageLength));
      new CallInst(WriteFn, Args, "", UI);

      // Insert a call to abort()
      new CallInst(AbortFn, std::vector<Value*>(), "", UI);

      // Insert a return instruction.  This really should be a "barrier", as it
      // is unreachable.
      new ReturnInst(F.getReturnType() == Type::VoidTy ? 0 :
                            Constant::getNullValue(F.getReturnType()), UI);

      // Remove the unwind instruction now.
      BB->getInstList().erase(UI);

      ++NumLowered; Changed = true;
    }
  return Changed;
}

bool LowerInvoke::insertExpensiveEHSupport(Function &F) {
  bool Changed = false;

  // If a function uses invoke, we have an alloca for the jump buffer.
  AllocaInst *JmpBuf = 0;

  // If this function contains an unwind instruction, two blocks get added: one
  // to actually perform the longjmp, and one to terminate the program if there
  // is no handler.
  BasicBlock *UnwindBlock = 0, *TermBlock = 0;
  std::vector<LoadInst*> JBPtrs;

  for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
    if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) {
      if (JmpBuf == 0)
        JmpBuf <