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      1 //===-- Instruction.cpp - Implement the Instruction class -----------------===//
      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 // This file implements the Instruction class for the IR library.
     11 //
     12 //===----------------------------------------------------------------------===//
     13 
     14 #include "llvm/IR/Instruction.h"
     15 #include "llvm/IR/Constants.h"
     16 #include "llvm/IR/Instructions.h"
     17 #include "llvm/IR/Module.h"
     18 #include "llvm/IR/Operator.h"
     19 #include "llvm/IR/Type.h"
     20 #include "llvm/Support/CallSite.h"
     21 #include "llvm/Support/LeakDetector.h"
     22 using namespace llvm;
     23 
     24 Instruction::Instruction(Type *ty, unsigned it, Use *Ops, unsigned NumOps,
     25                          Instruction *InsertBefore)
     26   : User(ty, Value::InstructionVal + it, Ops, NumOps), Parent(0) {
     27   // Make sure that we get added to a basicblock
     28   LeakDetector::addGarbageObject(this);
     29 
     30   // If requested, insert this instruction into a basic block...
     31   if (InsertBefore) {
     32     assert(InsertBefore->getParent() &&
     33            "Instruction to insert before is not in a basic block!");
     34     InsertBefore->getParent()->getInstList().insert(InsertBefore, this);
     35   }
     36 }
     37 
     38 Instruction::Instruction(Type *ty, unsigned it, Use *Ops, unsigned NumOps,
     39                          BasicBlock *InsertAtEnd)
     40   : User(ty, Value::InstructionVal + it, Ops, NumOps), Parent(0) {
     41   // Make sure that we get added to a basicblock
     42   LeakDetector::addGarbageObject(this);
     43 
     44   // append this instruction into the basic block
     45   assert(InsertAtEnd && "Basic block to append to may not be NULL!");
     46   InsertAtEnd->getInstList().push_back(this);
     47 }
     48 
     49 
     50 // Out of line virtual method, so the vtable, etc has a home.
     51 Instruction::~Instruction() {
     52   assert(Parent == 0 && "Instruction still linked in the program!");
     53   if (hasMetadataHashEntry())
     54     clearMetadataHashEntries();
     55 }
     56 
     57 
     58 void Instruction::setParent(BasicBlock *P) {
     59   if (getParent()) {
     60     if (!P) LeakDetector::addGarbageObject(this);
     61   } else {
     62     if (P) LeakDetector::removeGarbageObject(this);
     63   }
     64 
     65   Parent = P;
     66 }
     67 
     68 void Instruction::removeFromParent() {
     69   getParent()->getInstList().remove(this);
     70 }
     71 
     72 void Instruction::eraseFromParent() {
     73   getParent()->getInstList().erase(this);
     74 }
     75 
     76 /// insertBefore - Insert an unlinked instructions into a basic block
     77 /// immediately before the specified instruction.
     78 void Instruction::insertBefore(Instruction *InsertPos) {
     79   InsertPos->getParent()->getInstList().insert(InsertPos, this);
     80 }
     81 
     82 /// insertAfter - Insert an unlinked instructions into a basic block
     83 /// immediately after the specified instruction.
     84 void Instruction::insertAfter(Instruction *InsertPos) {
     85   InsertPos->getParent()->getInstList().insertAfter(InsertPos, this);
     86 }
     87 
     88 /// moveBefore - Unlink this instruction from its current basic block and
     89 /// insert it into the basic block that MovePos lives in, right before
     90 /// MovePos.
     91 void Instruction::moveBefore(Instruction *MovePos) {
     92   MovePos->getParent()->getInstList().splice(MovePos,getParent()->getInstList(),
     93                                              this);
     94 }
     95 
     96 /// Set or clear the unsafe-algebra flag on this instruction, which must be an
     97 /// operator which supports this flag. See LangRef.html for the meaning of this
     98 /// flag.
     99 void Instruction::setHasUnsafeAlgebra(bool B) {
    100   assert(isa<FPMathOperator>(this) && "setting fast-math flag on invalid op");
    101   cast<FPMathOperator>(this)->setHasUnsafeAlgebra(B);
    102 }
    103 
    104 /// Set or clear the NoNaNs flag on this instruction, which must be an operator
    105 /// which supports this flag. See LangRef.html for the meaning of this flag.
    106 void Instruction::setHasNoNaNs(bool B) {
    107   assert(isa<FPMathOperator>(this) && "setting fast-math flag on invalid op");
    108   cast<FPMathOperator>(this)->setHasNoNaNs(B);
    109 }
    110 
    111 /// Set or clear the no-infs flag on this instruction, which must be an operator
    112 /// which supports this flag. See LangRef.html for the meaning of this flag.
    113 void Instruction::setHasNoInfs(bool B) {
    114   assert(isa<FPMathOperator>(this) && "setting fast-math flag on invalid op");
    115   cast<FPMathOperator>(this)->setHasNoInfs(B);
    116 }
    117 
    118 /// Set or clear the no-signed-zeros flag on this instruction, which must be an
    119 /// operator which supports this flag. See LangRef.html for the meaning of this
    120 /// flag.
    121 void Instruction::setHasNoSignedZeros(bool B) {
    122   assert(isa<FPMathOperator>(this) && "setting fast-math flag on invalid op");
    123   cast<FPMathOperator>(this)->setHasNoSignedZeros(B);
    124 }
    125 
    126 /// Set or clear the allow-reciprocal flag on this instruction, which must be an
    127 /// operator which supports this flag. See LangRef.html for the meaning of this
    128 /// flag.
    129 void Instruction::setHasAllowReciprocal(bool B) {
    130   assert(isa<FPMathOperator>(this) && "setting fast-math flag on invalid op");
    131   cast<FPMathOperator>(this)->setHasAllowReciprocal(B);
    132 }
    133 
    134 /// Convenience function for setting all the fast-math flags on this
    135 /// instruction, which must be an operator which supports these flags. See
    136 /// LangRef.html for the meaning of these flats.
    137 void Instruction::setFastMathFlags(FastMathFlags FMF) {
    138   assert(isa<FPMathOperator>(this) && "setting fast-math flag on invalid op");
    139   cast<FPMathOperator>(this)->setFastMathFlags(FMF);
    140 }
    141 
    142 /// Determine whether the unsafe-algebra flag is set.
    143 bool Instruction::hasUnsafeAlgebra() const {
    144   assert(isa<FPMathOperator>(this) && "setting fast-math flag on invalid op");
    145   return cast<FPMathOperator>(this)->hasUnsafeAlgebra();
    146 }
    147 
    148 /// Determine whether the no-NaNs flag is set.
    149 bool Instruction::hasNoNaNs() const {
    150   assert(isa<FPMathOperator>(this) && "setting fast-math flag on invalid op");
    151   return cast<FPMathOperator>(this)->hasNoNaNs();
    152 }
    153 
    154 /// Determine whether the no-infs flag is set.
    155 bool Instruction::hasNoInfs() const {
    156   assert(isa<FPMathOperator>(this) && "setting fast-math flag on invalid op");
    157   return cast<FPMathOperator>(this)->hasNoInfs();
    158 }
    159 
    160 /// Determine whether the no-signed-zeros flag is set.
    161 bool Instruction::hasNoSignedZeros() const {
    162   assert(isa<FPMathOperator>(this) && "setting fast-math flag on invalid op");
    163   return cast<FPMathOperator>(this)->hasNoSignedZeros();
    164 }
    165 
    166 /// Determine whether the allow-reciprocal flag is set.
    167 bool Instruction::hasAllowReciprocal() const {
    168   assert(isa<FPMathOperator>(this) && "setting fast-math flag on invalid op");
    169   return cast<FPMathOperator>(this)->hasAllowReciprocal();
    170 }
    171 
    172 /// Convenience function for getting all the fast-math flags, which must be an
    173 /// operator which supports these flags. See LangRef.html for the meaning of
    174 /// these flats.
    175 FastMathFlags Instruction::getFastMathFlags() const {
    176   assert(isa<FPMathOperator>(this) && "setting fast-math flag on invalid op");
    177   return cast<FPMathOperator>(this)->getFastMathFlags();
    178 }
    179 
    180 /// Copy I's fast-math flags
    181 void Instruction::copyFastMathFlags(const Instruction *I) {
    182   setFastMathFlags(I->getFastMathFlags());
    183 }
    184 
    185 
    186 const char *Instruction::getOpcodeName(unsigned OpCode) {
    187   switch (OpCode) {
    188   // Terminators
    189   case Ret:    return "ret";
    190   case Br:     return "br";
    191   case Switch: return "switch";
    192   case IndirectBr: return "indirectbr";
    193   case Invoke: return "invoke";
    194   case Resume: return "resume";
    195   case Unreachable: return "unreachable";
    196 
    197   // Standard binary operators...
    198   case Add: return "add";
    199   case FAdd: return "fadd";
    200   case Sub: return "sub";
    201   case FSub: return "fsub";
    202   case Mul: return "mul";
    203   case FMul: return "fmul";
    204   case UDiv: return "udiv";
    205   case SDiv: return "sdiv";
    206   case FDiv: return "fdiv";
    207   case URem: return "urem";
    208   case SRem: return "srem";
    209   case FRem: return "frem";
    210 
    211   // Logical operators...
    212   case And: return "and";
    213   case Or : return "or";
    214   case Xor: return "xor";
    215 
    216   // Memory instructions...
    217   case Alloca:        return "alloca";
    218   case Load:          return "load";
    219   case Store:         return "store";
    220   case AtomicCmpXchg: return "cmpxchg";
    221   case AtomicRMW:     return "atomicrmw";
    222   case Fence:         return "fence";
    223   case GetElementPtr: return "getelementptr";
    224 
    225   // Convert instructions...
    226   case Trunc:     return "trunc";
    227   case ZExt:      return "zext";
    228   case SExt:      return "sext";
    229   case FPTrunc:   return "fptrunc";
    230   case FPExt:     return "fpext";
    231   case FPToUI:    return "fptoui";
    232   case FPToSI:    return "fptosi";
    233   case UIToFP:    return "uitofp";
    234   case SIToFP:    return "sitofp";
    235   case IntToPtr:  return "inttoptr";
    236   case PtrToInt:  return "ptrtoint";
    237   case BitCast:   return "bitcast";
    238 
    239   // Other instructions...
    240   case ICmp:           return "icmp";
    241   case FCmp:           return "fcmp";
    242   case PHI:            return "phi";
    243   case Select:         return "select";
    244   case Call:           return "call";
    245   case Shl:            return "shl";
    246   case LShr:           return "lshr";
    247   case AShr:           return "ashr";
    248   case VAArg:          return "va_arg";
    249   case ExtractElement: return "extractelement";
    250   case InsertElement:  return "insertelement";
    251   case ShuffleVector:  return "shufflevector";
    252   case ExtractValue:   return "extractvalue";
    253   case InsertValue:    return "insertvalue";
    254   case LandingPad:     return "landingpad";
    255 
    256   default: return "<Invalid operator> ";
    257   }
    258 }
    259 
    260 /// isIdenticalTo - Return true if the specified instruction is exactly
    261 /// identical to the current one.  This means that all operands match and any
    262 /// extra information (e.g. load is volatile) agree.
    263 bool Instruction::isIdenticalTo(const Instruction *I) const {
    264   return isIdenticalToWhenDefined(I) &&
    265          SubclassOptionalData == I->SubclassOptionalData;
    266 }
    267 
    268 /// isIdenticalToWhenDefined - This is like isIdenticalTo, except that it
    269 /// ignores the SubclassOptionalData flags, which specify conditions
    270 /// under which the instruction's result is undefined.
    271 bool Instruction::isIdenticalToWhenDefined(const Instruction *I) const {
    272   if (getOpcode() != I->getOpcode() ||
    273       getNumOperands() != I->getNumOperands() ||
    274       getType() != I->getType())
    275     return false;
    276 
    277   // We have two instructions of identical opcode and #operands.  Check to see
    278   // if all operands are the same.
    279   for (unsigned i = 0, e = getNumOperands(); i != e; ++i)
    280     if (getOperand(i) != I->getOperand(i))
    281       return false;
    282 
    283   // Check special state that is a part of some instructions.
    284   if (const LoadInst *LI = dyn_cast<LoadInst>(this))
    285     return LI->isVolatile() == cast<LoadInst>(I)->isVolatile() &&
    286            LI->getAlignment() == cast<LoadInst>(I)->getAlignment() &&
    287            LI->getOrdering() == cast<LoadInst>(I)->getOrdering() &&
    288            LI->getSynchScope() == cast<LoadInst>(I)->getSynchScope();
    289   if (const StoreInst *SI = dyn_cast<StoreInst>(this))
    290     return SI->isVolatile() == cast<StoreInst>(I)->isVolatile() &&
    291            SI->getAlignment() == cast<StoreInst>(I)->getAlignment() &&
    292            SI->getOrdering() == cast<StoreInst>(I)->getOrdering() &&
    293            SI->getSynchScope() == cast<StoreInst>(I)->getSynchScope();
    294   if (const CmpInst *CI = dyn_cast<CmpInst>(this))
    295     return CI->getPredicate() == cast<CmpInst>(I)->getPredicate();
    296   if (const CallInst *CI = dyn_cast<CallInst>(this))
    297     return CI->isTailCall() == cast<CallInst>(I)->isTailCall() &&
    298            CI->getCallingConv() == cast<CallInst>(I)->getCallingConv() &&
    299            CI->getAttributes() == cast<CallInst>(I)->getAttributes();
    300   if (const InvokeInst *CI = dyn_cast<InvokeInst>(this))
    301     return CI->getCallingConv() == cast<InvokeInst>(I)->getCallingConv() &&
    302            CI->getAttributes() == cast<InvokeInst>(I)->getAttributes();
    303   if (const InsertValueInst *IVI = dyn_cast<InsertValueInst>(this))
    304     return IVI->getIndices() == cast<InsertValueInst>(I)->getIndices();
    305   if (const ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(this))
    306     return EVI->getIndices() == cast<ExtractValueInst>(I)->getIndices();
    307   if (const FenceInst *FI = dyn_cast<FenceInst>(this))
    308     return FI->getOrdering() == cast<FenceInst>(FI)->getOrdering() &&
    309            FI->getSynchScope() == cast<FenceInst>(FI)->getSynchScope();
    310   if (const AtomicCmpXchgInst *CXI = dyn_cast<AtomicCmpXchgInst>(this))
    311     return CXI->isVolatile() == cast<AtomicCmpXchgInst>(I)->isVolatile() &&
    312            CXI->getOrdering() == cast<AtomicCmpXchgInst>(I)->getOrdering() &&
    313            CXI->getSynchScope() == cast<AtomicCmpXchgInst>(I)->getSynchScope();
    314   if (const AtomicRMWInst *RMWI = dyn_cast<AtomicRMWInst>(this))
    315     return RMWI->getOperation() == cast<AtomicRMWInst>(I)->getOperation() &&
    316            RMWI->isVolatile() == cast<AtomicRMWInst>(I)->isVolatile() &&
    317            RMWI->getOrdering() == cast<AtomicRMWInst>(I)->getOrdering() &&
    318            RMWI->getSynchScope() == cast<AtomicRMWInst>(I)->getSynchScope();
    319   if (const PHINode *thisPHI = dyn_cast<PHINode>(this)) {
    320     const PHINode *otherPHI = cast<PHINode>(I);
    321     for (unsigned i = 0, e = thisPHI->getNumOperands(); i != e; ++i) {
    322       if (thisPHI->getIncomingBlock(i) != otherPHI->getIncomingBlock(i))
    323         return false;
    324     }
    325     return true;
    326   }
    327   return true;
    328 }
    329 
    330 // isSameOperationAs
    331 // This should be kept in sync with isEquivalentOperation in
    332 // lib/Transforms/IPO/MergeFunctions.cpp.
    333 bool Instruction::isSameOperationAs(const Instruction *I,
    334                                     unsigned flags) const {
    335   bool IgnoreAlignment = flags & CompareIgnoringAlignment;
    336   bool UseScalarTypes  = flags & CompareUsingScalarTypes;
    337 
    338   if (getOpcode() != I->getOpcode() ||
    339       getNumOperands() != I->getNumOperands() ||
    340       (UseScalarTypes ?
    341        getType()->getScalarType() != I->getType()->getScalarType() :
    342        getType() != I->getType()))
    343     return false;
    344 
    345   // We have two instructions of identical opcode and #operands.  Check to see
    346   // if all operands are the same type
    347   for (unsigned i = 0, e = getNumOperands(); i != e; ++i)
    348     if (UseScalarTypes ?
    349         getOperand(i)->getType()->getScalarType() !=
    350           I->getOperand(i)->getType()->getScalarType() :
    351         getOperand(i)->getType() != I->getOperand(i)->getType())
    352       return false;
    353 
    354   // Check special state that is a part of some instructions.
    355   if (const LoadInst *LI = dyn_cast<LoadInst>(this))
    356     return LI->isVolatile() == cast<LoadInst>(I)->isVolatile() &&
    357            (LI->getAlignment() == cast<LoadInst>(I)->getAlignment() ||
    358             IgnoreAlignment) &&
    359            LI->getOrdering() == cast<LoadInst>(I)->getOrdering() &&
    360            LI->getSynchScope() == cast<LoadInst>(I)->getSynchScope();
    361   if (const StoreInst *SI = dyn_cast<StoreInst>(this))
    362     return SI->isVolatile() == cast<StoreInst>(I)->isVolatile() &&
    363            (SI->getAlignment() == cast<StoreInst>(I)->getAlignment() ||
    364             IgnoreAlignment) &&
    365            SI->getOrdering() == cast<StoreInst>(I)->getOrdering() &&
    366            SI->getSynchScope() == cast<StoreInst>(I)->getSynchScope();
    367   if (const CmpInst *CI = dyn_cast<CmpInst>(this))
    368     return CI->getPredicate() == cast<CmpInst>(I)->getPredicate();
    369   if (const CallInst *CI = dyn_cast<CallInst>(this))
    370     return CI->isTailCall() == cast<CallInst>(I)->isTailCall() &&
    371            CI->getCallingConv() == cast<CallInst>(I)->getCallingConv() &&
    372            CI->getAttributes() == cast<CallInst>(I)->getAttributes();
    373   if (const InvokeInst *CI = dyn_cast<InvokeInst>(this))
    374     return CI->getCallingConv() == cast<InvokeInst>(I)->getCallingConv() &&
    375            CI->getAttributes() ==
    376              cast<InvokeInst>(I)->getAttributes();
    377   if (const InsertValueInst *IVI = dyn_cast<InsertValueInst>(this))
    378     return IVI->getIndices() == cast<InsertValueInst>(I)->getIndices();
    379   if (const ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(this))
    380     return EVI->getIndices() == cast<ExtractValueInst>(I)->getIndices();
    381   if (const FenceInst *FI = dyn_cast<FenceInst>(this))
    382     return FI->getOrdering() == cast<FenceInst>(I)->getOrdering() &&
    383            FI->getSynchScope() == cast<FenceInst>(I)->getSynchScope();
    384   if (const AtomicCmpXchgInst *CXI = dyn_cast<AtomicCmpXchgInst>(this))
    385     return CXI->isVolatile() == cast<AtomicCmpXchgInst>(I)->isVolatile() &&
    386            CXI->getOrdering() == cast<AtomicCmpXchgInst>(I)->getOrdering() &&
    387            CXI->getSynchScope() == cast<AtomicCmpXchgInst>(I)->getSynchScope();
    388   if (const AtomicRMWInst *RMWI = dyn_cast<AtomicRMWInst>(this))
    389     return RMWI->getOperation() == cast<AtomicRMWInst>(I)->getOperation() &&
    390            RMWI->isVolatile() == cast<AtomicRMWInst>(I)->isVolatile() &&
    391            RMWI->getOrdering() == cast<AtomicRMWInst>(I)->getOrdering() &&
    392            RMWI->getSynchScope() == cast<AtomicRMWInst>(I)->getSynchScope();
    393 
    394   return true;
    395 }
    396 
    397 /// isUsedOutsideOfBlock - Return true if there are any uses of I outside of the
    398 /// specified block.  Note that PHI nodes are considered to evaluate their
    399 /// operands in the corresponding predecessor block.
    400 bool Instruction::isUsedOutsideOfBlock(const BasicBlock *BB) const {
    401   for (const_use_iterator UI = use_begin(), E = use_end(); UI != E; ++UI) {
    402     // PHI nodes uses values in the corresponding predecessor block.  For other
    403     // instructions, just check to see whether the parent of the use matches up.
    404     const User *U = *UI;
    405     const PHINode *PN = dyn_cast<PHINode>(U);
    406     if (PN == 0) {
    407       if (cast<Instruction>(U)->getParent() != BB)
    408         return true;
    409       continue;
    410     }
    411 
    412     if (PN->getIncomingBlock(UI) != BB)
    413       return true;
    414   }
    415   return false;
    416 }
    417 
    418 /// mayReadFromMemory - Return true if this instruction may read memory.
    419 ///
    420 bool Instruction::mayReadFromMemory() const {
    421   switch (getOpcode()) {
    422   default: return false;
    423   case Instruction::VAArg:
    424   case Instruction::Load:
    425   case Instruction::Fence: // FIXME: refine definition of mayReadFromMemory
    426   case Instruction::AtomicCmpXchg:
    427   case Instruction::AtomicRMW:
    428     return true;
    429   case Instruction::Call:
    430     return !cast<CallInst>(this)->doesNotAccessMemory();
    431   case Instruction::Invoke:
    432     return !cast<InvokeInst>(this)->doesNotAccessMemory();
    433   case Instruction::Store:
    434     return !cast<StoreInst>(this)->isUnordered();
    435   }
    436 }
    437 
    438 /// mayWriteToMemory - Return true if this instruction may modify memory.
    439 ///
    440 bool Instruction::mayWriteToMemory() const {
    441   switch (getOpcode()) {
    442   default: return false;
    443   case Instruction::Fence: // FIXME: refine definition of mayWriteToMemory
    444   case Instruction::Store:
    445   case Instruction::VAArg:
    446   case Instruction::AtomicCmpXchg:
    447   case Instruction::AtomicRMW:
    448     return true;
    449   case Instruction::Call:
    450     return !cast<CallInst>(this)->onlyReadsMemory();
    451   case Instruction::Invoke:
    452     return !cast<InvokeInst>(this)->onlyReadsMemory();
    453   case Instruction::Load:
    454     return !cast<LoadInst>(this)->isUnordered();
    455   }
    456 }
    457 
    458 bool Instruction::mayThrow() const {
    459   if (const CallInst *CI = dyn_cast<CallInst>(this))
    460     return !CI->doesNotThrow();
    461   return isa<ResumeInst>(this);
    462 }
    463 
    464 bool Instruction::mayReturn() const {
    465   if (const CallInst *CI = dyn_cast<CallInst>(this))
    466     return !CI->doesNotReturn();
    467   return true;
    468 }
    469 
    470 /// isAssociative - Return true if the instruction is associative:
    471 ///
    472 ///   Associative operators satisfy:  x op (y op z) === (x op y) op z
    473 ///
    474 /// In LLVM, the Add, Mul, And, Or, and Xor operators are associative.
    475 ///
    476 bool Instruction::isAssociative(unsigned Opcode) {
    477   return Opcode == And || Opcode == Or || Opcode == Xor ||
    478          Opcode == Add || Opcode == Mul;
    479 }
    480 
    481 bool Instruction::isAssociative() const {
    482   unsigned Opcode = getOpcode();
    483   if (isAssociative(Opcode))
    484     return true;
    485 
    486   switch (Opcode) {
    487   case FMul:
    488   case FAdd:
    489     return cast<FPMathOperator>(this)->hasUnsafeAlgebra();
    490   default:
    491     return false;
    492   }
    493 }
    494 
    495 /// isCommutative - Return true if the instruction is commutative:
    496 ///
    497 ///   Commutative operators satisfy: (x op y) === (y op x)
    498 ///
    499 /// In LLVM, these are the associative operators, plus SetEQ and SetNE, when
    500 /// applied to any type.
    501 ///
    502 bool Instruction::isCommutative(unsigned op) {
    503   switch (op) {
    504   case Add:
    505   case FAdd:
    506   case Mul:
    507   case FMul:
    508   case And:
    509   case Or:
    510   case Xor:
    511     return true;
    512   default:
    513     return false;
    514   }
    515 }
    516 
    517 /// isIdempotent - Return true if the instruction is idempotent:
    518 ///
    519 ///   Idempotent operators satisfy:  x op x === x
    520 ///
    521 /// In LLVM, the And and Or operators are idempotent.
    522 ///
    523 bool Instruction::isIdempotent(unsigned Opcode) {
    524   return Opcode == And || Opcode == Or;
    525 }
    526 
    527 /// isNilpotent - Return true if the instruction is nilpotent:
    528 ///
    529 ///   Nilpotent operators satisfy:  x op x === Id,
    530 ///
    531 ///   where Id is the identity for the operator, i.e. a constant such that
    532 ///     x op Id === x and Id op x === x for all x.
    533 ///
    534 /// In LLVM, the Xor operator is nilpotent.
    535 ///
    536 bool Instruction::isNilpotent(unsigned Opcode) {
    537   return Opcode == Xor;
    538 }
    539 
    540 Instruction *Instruction::clone() const {
    541   Instruction *New = clone_impl();
    542   New->SubclassOptionalData = SubclassOptionalData;
    543   if (!hasMetadata())
    544     return New;
    545 
    546   // Otherwise, enumerate and copy over metadata from the old instruction to the
    547   // new one.
    548   SmallVector<std::pair<unsigned, MDNode*>, 4> TheMDs;
    549   getAllMetadataOtherThanDebugLoc(TheMDs);
    550   for (unsigned i = 0, e = TheMDs.size(); i != e; ++i)
    551     New->setMetadata(TheMDs[i].first, TheMDs[i].second);
    552 
    553   New->setDebugLoc(getDebugLoc());
    554   return New;
    555 }
    556