Verifier.cpp

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//===-- Verifier.cpp - Implement the Module Verifier -------------*- C++ -*-==//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines the function verifier interface, that can be used for some
// sanity checking of input to the system.
//
// Note that this does not provide full `Java style' security and verifications,
// instead it just tries to ensure that code is well-formed.
//
//  * Both of a binary operator's parameters are of the same type
//  * Verify that the indices of mem access instructions match other operands
//  * Verify that arithmetic and other things are only performed on first-class
//    types.  Verify that shifts & logicals only happen on integrals f.e.
//  * All of the constants in a switch statement are of the correct type
//  * The code is in valid SSA form
//  * It should be illegal to put a label into any other type (like a structure)
//    or to return one. [except constant arrays!]
//  * Only phi nodes can be self referential: 'add i32 %0, %0 ; <int>:0' is bad
//  * PHI nodes must have an entry for each predecessor, with no extras.
//  * PHI nodes must be the first thing in a basic block, all grouped together
//  * PHI nodes must have at least one entry
//  * All basic blocks should only end with terminator insts, not contain them
//  * The entry node to a function must not have predecessors
//  * All Instructions must be embedded into a basic block
//  * Functions cannot take a void-typed parameter
//  * Verify that a function's argument list agrees with it's declared type.
//  * It is illegal to specify a name for a void value.
//  * It is illegal to have a internal global value with no initializer
//  * It is illegal to have a ret instruction that returns a value that does not
//    agree with the function return value type.
//  * Function call argument types match the function prototype
//  * All other things that are tested by asserts spread about the code...
//
//===----------------------------------------------------------------------===//

#include "llvm/Analysis/Verifier.h"
#include "llvm/CallingConv.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/InlineAsm.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/Module.h"
#include "llvm/ModuleProvider.h"
#include "llvm/Pass.h"
#include "llvm/PassManager.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Assembly/Writer.h"
#include "llvm/CodeGen/ValueTypes.h"
#include "llvm/Support/CallSite.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/InstVisitor.h"
#include "llvm/Support/Streams.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Support/Compiler.h"
#include <algorithm>
#include <sstream>
#include <cstdarg>
using namespace llvm;

namespace {  // Anonymous namespace for class
  struct VISIBILITY_HIDDEN PreVerifier : public FunctionPass {
    static char ID; // Pass ID, replacement for typeid

    PreVerifier() : FunctionPass(&ID) { }

    // Check that the prerequisites for successful DominatorTree construction
    // are satisfied.
    bool runOnFunction(Function &F) {
      bool Broken = false;

      for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) {
        if (I->empty() || !I->back().isTerminator()) {
          cerr << "Basic Block does not have terminator!\n";
          WriteAsOperand(*cerr, I, true);
          cerr << "\n";
          Broken = true;
        }
      }

      if (Broken)
        abort();

      return false;
    }
  };
}

char PreVerifier::ID = 0;
static RegisterPass<PreVerifier>
PreVer("preverify", "Preliminary module verification");
static const PassInfo *const PreVerifyID = &PreVer;

namespace {
  struct VISIBILITY_HIDDEN
     Verifier : public FunctionPass, InstVisitor<Verifier> {
    static char ID; // Pass ID, replacement for typeid
    bool Broken;          // Is this module found to be broken?
    bool RealPass;        // Are we not being run by a PassManager?
    VerifierFailureAction action;
                          // What to do if verification fails.
    Module *Mod;          // Module we are verifying right now
    DominatorTree *DT; // Dominator Tree, caution can be null!
    std::stringstream msgs;  // A stringstream to collect messages

    /// InstInThisBlock - when verifying a basic block, keep track of all of the
    /// instructions we have seen so far.  This allows us to do efficient
    /// dominance checks for the case when an instruction has an operand that is
    /// an instruction in the same block.
    SmallPtrSet<Instruction*, 16> InstsInThisBlock;

    Verifier()
      : FunctionPass(&ID), 
      Broken(false), RealPass(true), action(AbortProcessAction),
      DT(0), msgs( std::ios::app | std::ios::out ) {}
    explicit Verifier(VerifierFailureAction ctn)
      : FunctionPass(&ID), 
      Broken(false), RealPass(true), action(ctn), DT(0),
      msgs( std::ios::app | std::ios::out ) {}
    explicit Verifier(bool AB)
      : FunctionPass(&ID), 
      Broken(false), RealPass(true),
      action( AB ? AbortProcessAction : PrintMessageAction), DT(0),
      msgs( std::ios::app | std::ios::out ) {}
    explicit Verifier(DominatorTree &dt)
      : FunctionPass(&ID), 
      Broken(false), RealPass(false), action(PrintMessageAction),
      DT(&dt), msgs( std::ios::app | std::ios::out ) {}


    bool doInitialization(Module &M) {
      Mod = &M;
      verifyTypeSymbolTable(M.getTypeSymbolTable());

      // If this is a real pass, in a pass manager, we must abort before
      // returning back to the pass manager, or else the pass manager may try to
      // run other passes on the broken module.
      if (RealPass)
        return abortIfBroken();
      return false;
    }

    bool runOnFunction(Function &F) {
      // Get dominator information if we are being run by PassManager
      if (RealPass) DT = &getAnalysis<DominatorTree>();

      Mod = F.getParent();

      visit(F);
      InstsInThisBlock.clear();

      // If this is a real pass, in a pass manager, we must abort before
      // returning back to the pass manager, or else the pass manager may try to
      // run other passes on the broken module.
      if (RealPass)
        return abortIfBroken();

      return false;
    }

    bool doFinalization(Module &M) {
      // Scan through, checking all of the external function's linkage now...
      for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
        visitGlobalValue(*I);

        // Check to make sure function prototypes are okay.
        if (I->isDeclaration()) visitFunction(*I);
      }

      for (Module::global_iterator I = M.global_begin(), E = M.global_end(); 
           I != E; ++I)
        visitGlobalVariable(*I);

      for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end(); 
           I != E; ++I)
        visitGlobalAlias(*I);

      // If the module is broken, abort at this time.
      return abortIfBroken();
    }

    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
      AU.setPreservesAll();
      AU.addRequiredID(PreVerifyID);
      if (RealPass)
        AU.addRequired<DominatorTree>();
    }

    /// abortIfBroken - If the module is broken and we are supposed to abort on
    /// this condition, do so.
    ///
    bool abortIfBroken() {
      if (!Broken) return false;
      msgs << "Broken module found, ";
      switch (action) {
      default: assert(0 && "Unknown action");
      case AbortProcessAction:
        msgs << "compilation aborted!\n";
        cerr << msgs.str();
        abort();
      case PrintMessageAction:
        msgs << "verification continues.\n";
        cerr << msgs.str();
        return false;
      case ReturnStatusAction:
        msgs << "compilation terminated.\n";
        return Broken;
      }
    }


    // Verification methods...
    void verifyTypeSymbolTable(TypeSymbolTable &ST);
    void visitGlobalValue(GlobalValue &GV);
    void visitGlobalVariable(GlobalVariable &GV);
    void visitGlobalAlias(GlobalAlias &GA);
    void visitFunction(Function &F);
    void visitBasicBlock(BasicBlock &BB);
    using InstVisitor<Verifier>::visit;
       
    void visit(Instruction &I);
       
    void visitTruncInst(TruncInst &I);
    void visitZExtInst(ZExtInst &I);
    void visitSExtInst(SExtInst &I);
    void visitFPTruncInst(FPTruncInst &I);
    void visitFPExtInst(FPExtInst &I);
    void visitFPToUIInst(FPToUIInst &I);
    void visitFPToSIInst(FPToSIInst &I);
    void visitUIToFPInst(UIToFPInst &I);
    void visitSIToFPInst(SIToFPInst &I);
    void visitIntToPtrInst(IntToPtrInst &I);
    void visitPtrToIntInst(PtrToIntInst &I);
    void visitBitCastInst(BitCastInst &I);
    void visitPHINode(PHINode &PN);
    void visitBinaryOperator(BinaryOperator &B);
    void visitICmpInst(ICmpInst &IC);
    void visitFCmpInst(FCmpInst &FC);
    void visitExtractElementInst(ExtractElementInst &EI);
    void visitInsertElementInst(InsertElementInst &EI);
    void visitShuffleVectorInst(ShuffleVectorInst &EI);
    void visitVAArgInst(VAArgInst &VAA) { visitInstruction(VAA); }
    void visitCallInst(CallInst &CI);
    void visitInvokeInst(InvokeInst &II);
    void visitGetElementPtrInst(GetElementPtrInst &GEP);
    void visitLoadInst(LoadInst &LI);
    void visitStoreInst(StoreInst &SI);
    void visitInstruction(Instruction &I);
    void visitTerminatorInst(TerminatorInst &I);
    void visitReturnInst(ReturnInst &RI);
    void visitSwitchInst(SwitchInst &SI);
    void visitSelectInst(SelectInst &SI);
    void visitUserOp1(Instruction &I);
    void visitUserOp2(Instruction &I) { visitUserOp1(I); }
    void visitIntrinsicFunctionCall(Intrinsic::ID ID, CallInst &CI);
    void visitAllocationInst(AllocationInst &AI);
    void visitExtractValueInst(ExtractValueInst &EVI);
    void visitInsertValueInst(InsertValueInst &IVI);

    void VerifyCallSite(CallSite CS);
    void VerifyIntrinsicPrototype(Intrinsic::ID ID, Function *F,
                                  unsigned Count, ...);
    void VerifyAttrs(Attributes Attrs, const Type *Ty,
                     bool isReturnValue, const Value *V);
    void VerifyFunctionAttrs(const FunctionType *FT, const AttrListPtr &Attrs,
                             const Value *V);

    void WriteValue(const Value *V) {
      if (!V) return;
      if (isa<Instruction>(V)) {
        msgs << *V;
      } else {
        WriteAsOperand(msgs, V, true, Mod);
        msgs << "\n";
      }
    }

    void WriteType(const Type *T) {
      if ( !T ) return;
      WriteTypeSymbolic(msgs, T, Mod );
    }


    // CheckFailed - A check failed, so print out the condition and the message
    // that failed.  This provides a nice place to put a breakpoint if you want
    // to see why something is not correct.
    void CheckFailed(const std::string &Message,
                     const Value *V1 = 0, const Value *V2 = 0,
                     const Value *V3 = 0, const Value *V4 = 0) {
      msgs << Message << "\n";
      WriteValue(V1);
      WriteValue(V2);
      WriteValue(V3);
      WriteValue(V4);
      Broken = true;
    }

    void CheckFailed( const std::string& Message, const Value* V1,
                      const Type* T2, const Value* V3 = 0 ) {
      msgs << Message << "\n";
      WriteValue(V1);
      WriteType(T2);
      WriteValue(V3);
      Broken = true;
    }
  };
} // End anonymous namespace

char Verifier::ID = 0;
static RegisterPass<Verifier> X("verify", "Module Verifier");

// Assert - We know that cond should be true, if not print an error message.
#define Assert(C, M) \
  do { if (!(C)) { CheckFailed(M); return; } } while (0)
#define Assert1(C, M, V1) \
  do { if (!(C)) { CheckFailed(M, V1); return; } } while (0)
#define Assert2(C, M, V1, V2) \
  do { if (!(C)) { CheckFailed(M, V1, V2); return; } } while (0)
#define Assert3(C, M, V1, V2, V3) \
  do { if (!(C)) { CheckFailed(M, V1, V2, V3); return; } } while (0)
#define Assert4(C, M, V1, V2, V3, V4) \
  do { if (!(C)) { CheckFailed(M, V1, V2, V3, V4); return; } } while (0)


void Verifier::visit(Instruction &I) {
  for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i)
    Assert1(I.getOperand(i) != 0, "Operand is null", &I);
  InstVisitor<Verifier>::visit(I);
}


void Verifier::visitGlobalValue(GlobalValue &GV) {
  Assert1(!GV.isDeclaration() ||
          GV.hasExternalLinkage() ||
          GV.hasDLLImportLinkage() ||
          GV.hasExternalWeakLinkage() ||
          GV.hasGhostLinkage() ||
          (isa<GlobalAlias>(GV) &&
           (GV.hasInternalLinkage() || GV.hasWeakLinkage())),
  "Global is external, but doesn't have external or dllimport or weak linkage!",
          &GV);

  Assert1(!GV.hasDLLImportLinkage() || GV.isDeclaration(),
          "Global is marked as dllimport, but not external", &GV);
  
  Assert1(!GV.hasAppendingLinkage() || isa<GlobalVariable>(GV),
          "Only global variables can have appending linkage!", &GV);

  if (GV.hasAppendingLinkage()) {
    GlobalVariable &GVar = cast<GlobalVariable>(GV);
    Assert1(isa<ArrayType>(GVar.getType()->getElementType()),
            "Only global arrays can have appending linkage!", &GV);
  }
}

void Verifier::visitGlobalVariable(GlobalVariable &GV) {
  if (GV.hasInitializer()) {
    Assert1(GV.getInitializer()->getType() == GV.getType()->getElementType(),
            "Global variable initializer type does not match global "
            "variable type!", &GV);
  } else {
    Assert1(GV.hasExternalLinkage() || GV.hasDLLImportLinkage() ||
            GV.hasExternalWeakLinkage(),
            "invalid linkage type for global declaration", &GV);
  }

  visitGlobalValue(GV);
}

void Verifier::visitGlobalAlias(GlobalAlias &GA) {
  Assert1(!GA.getName().empty(),
          "Alias name cannot be empty!", &GA);
  Assert1(GA.hasExternalLinkage() || GA.hasInternalLinkage() ||
          GA.hasWeakLinkage(),
          "Alias should have external or external weak linkage!", &GA);
  Assert1(GA.getAliasee(),
          "Aliasee cannot be NULL!", &GA);
  Assert1(GA.getType() == GA.getAliasee()->getType(),
          "Alias and aliasee types should match!", &GA);

  if (!isa<GlobalValue>(GA.getAliasee())) {
    const ConstantExpr *CE = dyn_cast<ConstantExpr>(GA.getAliasee());
    Assert1(CE && CE->getOpcode() == Instruction::BitCast &&
            isa<GlobalValue>(CE->getOperand(0)),
            "Aliasee should be either GlobalValue or bitcast of GlobalValue",
            &GA);
  }

  const GlobalValue* Aliasee = GA.resolveAliasedGlobal(/*stopOnWeak*/ false);
  Assert1(Aliasee,
          "Aliasing chain should end with function or global variable", &GA);

  visitGlobalValue(GA);
}

void Verifier::verifyTypeSymbolTable(TypeSymbolTable &ST) {
}

// VerifyAttrs - Check the given parameter attributes for an argument or return
// value of the specified type.  The value V is printed in error messages.
void Verifier::VerifyAttrs(Attributes Attrs, const Type *Ty, 
                           bool isReturnValue, const Value *V) {
  if (Attrs == Attribute::None)
    return;

  if (isReturnValue) {
    Attributes RetI = Attrs & Attribute::ParameterOnly;
    Assert1(!RetI, "Attribute " + Attribute::getAsString(RetI) +
            " does not apply to return values!", V);
  }
  Attributes FnCheckAttr = Attrs & Attribute::FunctionOnly;
  Assert1(!FnCheckAttr, "Attribute " + Attribute::getAsString(FnCheckAttr) +
          " only applies to functions!", V);
  
  for (unsigned i = 0;
       i < array_lengthof(Attribute::MutuallyIncompatible); ++i) {
    Attributes MutI = Attrs & Attribute::MutuallyIncompatible[i];
    Assert1(!(MutI & (MutI - 1)), "Attributes " +
            Attribute::getAsString(MutI) + " are incompatible!", V);
  }

  Attributes TypeI = Attrs & Attribute::typeIncompatible(Ty);
  Assert1(!TypeI, "Wrong type for attribute " +
          Attribute::getAsString(TypeI), V);

  Attributes ByValI = Attrs & Attribute::ByVal;
  if (const PointerType *PTy = dyn_cast<PointerType>(Ty)) {
    Assert1(!ByValI || PTy->getElementType()->isSized(),
            "Attribute " + Attribute::getAsString(ByValI) +
            " does not support unsized types!", V);
  } else {
    Assert1(!ByValI,
            "Attribute " + Attribute::getAsString(ByValI) +
            " only applies to parameters with pointer type!", V);
  }
}

// VerifyFunctionAttrs - Check parameter attributes against a function type.
// The value V is printed in error messages.
void Verifier::VerifyFunctionAttrs(const FunctionType *FT,
                                   const AttrListPtr &Attrs,
                                   const Value *V) {
  if (Attrs.isEmpty())
    return;

  bool SawNest = false;

  for (unsigned i = 0, e = Attrs.getNumSlots(); i != e; ++i) {
    const AttributeWithIndex &Attr = Attrs.getSlot(i);

    const Type *Ty;
    if (Attr.Index == 0)
      Ty = FT->getReturnType();
    else if (Attr.Index-1 < FT->getNumParams())
      Ty = FT->getParamType(Attr.Index-1);
    else
      break;  // VarArgs attributes, don't verify.
    
    VerifyAttrs(Attr.Attrs, Ty, Attr.Index == 0, V);

    if (Attr.Attrs & Attribute::Nest) {
      Assert1(!SawNest, "More than one parameter has attribute nest!", V);
      SawNest = true;
    }

    if (Attr.Attrs & Attribute::StructRet)
      Assert1(Attr.Index == 1, "Attribute sret not on first parameter!", V);
  }

  Attributes FAttrs = Attrs.getFnAttributes();
  Assert1(!(FAttrs & (~Attribute::FunctionOnly)),
          "Attribute " + Attribute::getAsString(FAttrs) +
          " does not apply to function!", V);
      
  for (unsigned i = 0;
       i < array_lengthof(Attribute::MutuallyIncompatible); ++i) {
    Attributes MutI = FAttrs & Attribute::MutuallyIncompatible[i];
    Assert1(!(MutI & (MutI - 1)), "Attributes " +
            Attribute::getAsString(MutI) + " are incompatible!", V);
  }
}

static bool VerifyAttributeCount(const AttrListPtr &Attrs, unsigned Params) {
  if (Attrs.isEmpty())
    return true;
    
  unsigned LastSlot = Attrs.getNumSlots() - 1;
  unsigned LastIndex = Attrs.getSlot(LastSlot).Index;
  if (LastIndex <= Params
      || (LastIndex == (unsigned)~0
          && (LastSlot == 0 || Attrs.getSlot(LastSlot - 1).Index <= Params)))  
    return true;
    
  return false;
}
// visitFunction - Verify that a function is ok.
//
void Verifier::visitFunction(Function &F) {
  // Check function arguments.
  const FunctionType *FT = F.getFunctionType();
  unsigned NumArgs = F.arg_size();

  Assert2(FT->getNumParams() == NumArgs,
          "# formal arguments must match # of arguments for function type!",
          &F, FT);
  Assert1(F.getReturnType()->isFirstClassType() ||
          F.getReturnType() == Type::VoidTy || 
          isa<StructType>(F.getReturnType()),
          "Functions cannot return aggregate values!", &F);

  Assert1(!F.hasStructRetAttr() || F.getReturnType() == Type::VoidTy,
          "Invalid struct return type!", &F);

  const AttrListPtr &Attrs = F.getAttributes();

  Assert1(VerifyAttributeCount(Attrs, FT->getNumParams()),
          "Attributes after last parameter!", &F);

  // Check function attributes.
  VerifyFunctionAttrs(FT, Attrs, &F);

  // Check that this function meets the restrictions on this calling convention.
  switch (F.getCallingConv()) {
  default:
    break;
  case CallingConv::C:
    break;
  case CallingConv::Fast:
  case CallingConv::Cold:
  case CallingConv::X86_FastCall:
    Assert1(!F.isVarArg(),
            "Varargs functions must have C calling conventions!", &F);
    break;
  }
  
  // Check that the argument values match the function type for this function...
  unsigned i = 0;
  for (Function::arg_iterator I = F.arg_begin(), E = F.arg_end();
       I != E; ++I, ++i) {
    Assert2(I->getType() == FT->getParamType(i),
            "Argument value does not match function argument type!",
            I, FT->getParamType(i));
    Assert1(I->getType()->isFirstClassType(),
            "Function arguments must have first-class types!", I);
  }

  if (F.isDeclaration()) {
    Assert1(F.hasExternalLinkage() || F.hasDLLImportLinkage() ||
            F.hasExternalWeakLinkage() || F.hasGhostLinkage(),
            "invalid linkage type for function declaration", &F);
  } else {
    // Verify that this function (which has a body) is not named "llvm.*".  It
    // is not legal to define intrinsics.
    if (F.getName().size() >= 5)
      Assert1(F.getName().substr(0, 5) != "llvm.",
              "llvm intrinsics cannot be defined!", &F);
    
    // Check the entry node
    BasicBlock *Entry = &F.getEntryBlock();
    Assert1(pred_begin(Entry) == pred_end(Entry),
            "Entry block to function must not have predecessors!", Entry);
  }
}


// verifyBasicBlock - Verify that a basic block is well formed...
//
void Verifier::visitBasicBlock(BasicBlock &BB) {
  InstsInThisBlock.clear();

  // Ensure that basic blocks have terminators!
  Assert1(BB.getTerminator(), "Basic Block does not have terminator!", &BB);

  // Check constraints that this basic block imposes on all of the PHI nodes in
  // it.
  if (isa<PHINode>(BB.front())) {
    SmallVector<BasicBlock*, 8> Preds(pred_begin(&BB), pred_end(&BB));
    SmallVector<std::pair<BasicBlock*, Value*>, 8> Values;
    std::sort(Preds.begin(), Preds.end());
    PHINode *PN;
    for (BasicBlock::iterator I = BB.begin(); (PN = dyn_cast<PHINode>(I));++I) {

      // Ensure that PHI nodes have at least one entry!
      Assert1(PN->getNumIncomingValues() != 0,
              "PHI nodes must have at least one entry.  If the block is dead, "
              "the PHI should be removed!", PN);
      Assert1(PN->getNumIncomingValues() == Preds.size(),
              "PHINode should have one entry for each predecessor of its "
              "parent basic block!", PN);

      // Get and sort all incoming values in the PHI node...
      Values.clear();
      Values.reserve(PN->getNumIncomingValues());
      for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
        Values.push_back(std::make_pair(PN->getIncomingBlock(i),
                                        PN->getIncomingValue(i)));
      std::sort(Values.begin(), Values.end());

      for (unsigned i = 0, e = Values.size(); i != e; ++i) {
        // Check to make sure that if there is more than one entry for a
        // particular basic block in this PHI node, that the incoming values are
        // all identical.
        //
        Assert4(i == 0 || Values[i].first  != Values[i-1].first ||
                Values[i].second == Values[i-1].second,
                "PHI node has multiple entries for the same basic block with "
                "different incoming values!", PN, Values[i].first,
                Values[i].second, Values[i-1].second);

        // Check to make sure that the predecessors and PHI node entries are
        // matched up.
        Assert3(Values[i].first == Preds[i],
                "PHI node entries do not match predecessors!", PN,
                Values[i].first, Preds[i]);
      }
    }
  }
}

void Verifier::visitTerminatorInst(TerminatorInst &I) {
  // Ensure that terminators only exist at the end of the basic block.
  Assert1(&I == I.getParent()->getTerminator(),
          "Terminator found in the middle of a basic block!", I.getParent());
  visitInstruction(I);
}

void Verifier::visitReturnInst(ReturnInst &RI) {
  Function *F = RI.getParent()->getParent();
  unsigned N = RI.getNumOperands();
  if (F->getReturnType() == Type::VoidTy) 
    Assert2(N == 0,
            "Found return instr that returns void in Function of non-void "
            "return type!", &RI, F->getReturnType());
  else if (N == 1 && F->getReturnType() == RI.getOperand(0)->getType()) {
    // Exactly one return value and it matches the return type. Good.
  } else if (const StructType *STy = dyn_cast<StructType>(F->getReturnType())) {
    // The return type is a struct; check for multiple return values.
    Assert2(STy->getNumElements() == N,
            "Incorrect number of return values in ret instruction!",
            &RI, F->getReturnType());
    for (unsigned i = 0; i != N; ++i)
      Assert2(STy->getElementType(i) == RI.getOperand(i)->getType(),
              "Function return type does not match operand "
              "type of return inst!", &RI, F->getReturnType());
  } else if (const ArrayType *ATy = dyn_cast<ArrayType>(F->getReturnType())) {
    // The return type is an array; check for multiple return values.
    Assert2(ATy->getNumElements() == N,
            "Incorrect number of return values in ret instruction!",
            &RI, F->getReturnType());
    for (unsigned i = 0; i != N; ++i)
      Assert2(ATy->getElementType() == RI.getOperand(i)->getType(),
              "Function return type does not match operand "
              "type of return inst!", &RI, F->getReturnType());
  } else {
    CheckFailed("Function return type does not match operand "
                "type of return inst!", &RI, F->getReturnType());
  }
  
  // Check to make sure that the return value has necessary properties for
  // terminators...
  visitTerminatorInst(RI);
}

void Verifier::visitSwitchInst(SwitchInst &SI) {
  // Check to make sure that all of the constants in the switch instruction
  // have the same type as the switched-on value.
  const Type *SwitchTy = SI.getCondition()->getType();
  for (unsigned i = 1, e = SI.getNumCases(); i != e; ++i)
    Assert1(SI.getCaseValue(i)->getType() == SwitchTy,
            "Switch constants must all be same type as switch value!", &SI);

  visitTerminatorInst(SI);
}

void Verifier::visitSelectInst(SelectInst &SI) {
  if (const VectorType* vt
             = dyn_cast<VectorType>(SI.getCondition()->getType())) {
    Assert1( vt->getElementType() == Type::Int1Ty,
            "Select condition type must be vector of bool!", &SI);
    if (const VectorType* val_vt
             = dyn_cast<VectorType>(SI.getTrueValue()->getType())) {
      Assert1( vt->getNumElements() == val_vt->getNumElements(),
               "Select vector size != value vector size", &SI);
    } else {
      Assert1(0, "Vector select values must have vector types", &SI);
    }
  } else {
    Assert1(SI.getCondition()->getType() == Type::Int1Ty,
            "Select condition type must be bool!", &SI);
  }
  Assert1(SI.getTrueValue()->getType() == SI.getFalseValue()->getType(),
          "Select values must have identical types!", &SI);
  Assert1(SI.getTrueValue()->getType() == SI.getType(),
          "Select values must have same type as select instruction!", &SI);
  visitInstruction(SI);
}


/// visitUserOp1 - User defined operators shouldn't live beyond the lifetime of
/// a pass, if any exist, it's an error.
///
void Verifier::visitUserOp1(Instruction &I) {
  Assert1(0, "User-defined operators should not live outside of a pass!", &I);
}

void Verifier::visitTruncInst(TruncInst &I) {
  // Get the source and destination types
  const Type *SrcTy = I.getOperand(0)->getType();
  const Type *DestTy = I.getType();

  // Get the size of the types in bits, we'll need this later
  unsigned SrcBitSize = SrcTy->getPrimitiveSizeInBits();
  unsigned DestBitSize = DestTy->getPrimitiveSizeInBits();

  Assert1(SrcTy->isIntOrIntVector(), "Trunc only operates on integer", &I);
  Assert1(DestTy->isIntOrIntVector(), "Trunc only produces integer", &I);
  Assert1(SrcBitSize > DestBitSize,"DestTy too big for Trunc", &I);

  visitInstruction(I);
}

void Verifier::visitZExtInst(ZExtInst &I) {
  // Get the source and destination types
  const Type *SrcTy = I.getOperand(0)->getType();
  const Type *DestTy = I.getType();

  // Get the size of the types in bits, we'll need this later
  Assert1(SrcTy->isIntOrIntVector(), "ZExt only operates on integer", &I);
  Assert1(DestTy->isIntOrIntVector(), "ZExt only produces an integer", &I);
  unsigned SrcBitSize = SrcTy->getPrimitiveSizeInBits();
  unsigned DestBitSize = DestTy->getPrimitiveSizeInBits();

  Assert1(SrcBitSize < DestBitSize,"Type too small for ZExt", &I);

  visitInstruction(I);
}

void Verifier::visitSExtInst(SExtInst &I) {
  // Get the source and destination types
  const Type *SrcTy = I.getOperand(0)->getType();
  const Type *DestTy = I.getType();

  // Get the size of the types in bits, we'll need this later
  unsigned SrcBitSize = SrcTy->getPrimitiveSizeInBits();
  unsigned DestBitSize = DestTy->getPrimitiveSizeInBits();

  Assert1(SrcTy->isIntOrIntVector(), "SExt only operates on integer", &I);
  Assert1(DestTy->isIntOrIntVector(), "SExt only produces an integer", &I);
  Assert1(SrcBitSize < DestBitSize,"Type too small for SExt", &I);

  visitInstruction(I);
}

void Verifier::visitFPTruncInst(FPTruncInst &I) {
  // Get the source and destination types
  const Type *SrcTy = I.getOperand(0)->getType();
  const Type *DestTy = I.getType();
  // Get the size of the types in bits, we'll need this later
  unsigned SrcBitSize = SrcTy->getPrimitiveSizeInBits();
  unsigned DestBitSize = DestTy->getPrimitiveSizeInBits();

  Assert1(SrcTy->isFPOrFPVector(),"FPTrunc only operates on FP", &I);
  Assert1(DestTy->isFPOrFPVector(),"FPTrunc only produces an FP", &I);
  Assert1(SrcBitSize > DestBitSize,"DestTy too big for FPTrunc", &I);

  visitInstruction(I);
}

void Verifier::visitFPExtInst(FPExtInst &I) {
  // Get the source and destination types
  const Type *SrcTy = I.getOperand(0)->getType();
  const Type *DestTy = I.getType();

  // Get the size of the types in bits, we'll need this later
  unsigned SrcBitSize = SrcTy->getPrimitiveSizeInBits();
  unsigned DestBitSize = DestTy->getPrimitiveSizeInBits();

  Assert1(SrcTy->isFPOrFPVector(),"FPExt only operates on FP", &I);
  Assert1(DestTy->isFPOrFPVector(),"FPExt only produces an FP", &I);
  Assert1(SrcBitSize < DestBitSize,"DestTy too small for FPExt", &I);

  visitInstruction(I);
}

void Verifier::visitUIToFPInst(UIToFPInst &I) {
  // Get the source and destination types
  const Type *SrcTy = I.getOperand(0)->getType();
  const Type *DestTy = I.getType();

  bool SrcVec = isa<VectorType>(SrcTy);
  bool DstVec = isa<VectorType>(DestTy);

  Assert1(SrcVec == DstVec,
          "UIToFP source and dest must both be vector or scalar", &I);
  Assert1(SrcTy->isIntOrIntVector(),
          "UIToFP source must be integer or integer vector", &I);
  Assert1(DestTy->isFPOrFPVector(),
          "UIToFP result must be FP or FP vector", &I);

  if (SrcVec && DstVec)
    Assert1(cast<VectorType>(SrcTy)->getNumElements() ==
            cast<VectorType>(DestTy)->getNumElements(),
            "UIToFP source and dest vector length mismatch", &I);

  visitInstruction(I);
}

void Verifier::visitSIToFPInst(SIToFPInst &I) {
  // Get the source and destination types