//===- InstCombineCasts.cpp -----------------------------------------------===// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // This file implements the visit functions for cast operations. // //===----------------------------------------------------------------------===// #include "InstCombine.h" #include "llvm/Analysis/ConstantFolding.h" #include "llvm/Target/TargetData.h" #include "llvm/Support/PatternMatch.h" using namespace llvm; using namespace PatternMatch; /// DecomposeSimpleLinearExpr - Analyze 'Val', seeing if it is a simple linear /// expression. If so, decompose it, returning some value X, such that Val is /// X*Scale+Offset. /// static Value *DecomposeSimpleLinearExpr(Value *Val, unsigned &Scale, uint64_t &Offset) { if (ConstantInt *CI = dyn_cast(Val)) { Offset = CI->getZExtValue(); Scale = 0; return ConstantInt::get(Val->getType(), 0); } if (BinaryOperator *I = dyn_cast(Val)) { // Cannot look past anything that might overflow. OverflowingBinaryOperator *OBI = dyn_cast(Val); if (OBI && !OBI->hasNoUnsignedWrap()) { Scale = 1; Offset = 0; return Val; } if (ConstantInt *RHS = dyn_cast(I->getOperand(1))) { if (I->getOpcode() == Instruction::Shl) { // This is a value scaled by '1 << the shift amt'. Scale = UINT64_C(1) << RHS->getZExtValue(); Offset = 0; return I->getOperand(0); } if (I->getOpcode() == Instruction::Mul) { // This value is scaled by 'RHS'. Scale = RHS->getZExtValue(); Offset = 0; return I->getOperand(0); } if (I->getOpcode() == Instruction::Add) { // We have X+C. Check to see if we really have (X*C2)+C1, // where C1 is divisible by C2. unsigned SubScale; Value *SubVal = DecomposeSimpleLinearExpr(I->getOperand(0), SubScale, Offset); Offset += RHS->getZExtValue(); Scale = SubScale; return SubVal; } } } // Otherwise, we can't look past this. Scale = 1; Offset = 0; return Val; } /// PromoteCastOfAllocation - If we find a cast of an allocation instruction, /// try to eliminate the cast by moving the type information into the alloc. Instruction *InstCombiner::PromoteCastOfAllocation(BitCastInst &CI, AllocaInst &AI) { // This requires TargetData to get the alloca alignment and size information. if (!TD) return 0; PointerType *PTy = cast(CI.getType()); BuilderTy AllocaBuilder(*Builder); AllocaBuilder.SetInsertPoint(AI.getParent(), &AI); // Get the type really allocated and the type casted to. Type *AllocElTy = AI.getAllocatedType(); Type *CastElTy = PTy->getElementType(); if (!AllocElTy->isSized() || !CastElTy->isSized()) return 0; unsigned AllocElTyAlign = TD->getABITypeAlignment(AllocElTy); unsigned CastElTyAlign = TD->getABITypeAlignment(CastElTy); if (CastElTyAlign < AllocElTyAlign) return 0; // If the allocation has multiple uses, only promote it if we are strictly // increasing the alignment of the resultant allocation. If we keep it the // same, we open the door to infinite loops of various kinds. if (!AI.hasOneUse() && CastElTyAlign == AllocElTyAlign) return 0; uint64_t AllocElTySize = TD->getTypeAllocSize(AllocElTy); uint64_t CastElTySize = TD->getTypeAllocSize(CastElTy); if (CastElTySize == 0 || AllocElTySize == 0) return 0; // See if we can satisfy the modulus by pulling a scale out of the array // size argument. unsigned ArraySizeScale; uint64_t ArrayOffset; Value *NumElements = // See if the array size is a decomposable linear expr. DecomposeSimpleLinearExpr(AI.getOperand(0), ArraySizeScale, ArrayOffset); // If we can now satisfy the modulus, by using a non-1 scale, we really can // do the xform. if ((AllocElTySize*ArraySizeScale) % CastElTySize != 0 || (AllocElTySize*ArrayOffset ) % CastElTySize != 0) return 0; unsigned Scale = (AllocElTySize*ArraySizeScale)/CastElTySize; Value *Amt = 0; if (Scale == 1) { Amt = NumElements; } else { Amt = ConstantInt::get(AI.getArraySize()->getType(), Scale); // Insert before the alloca, not before the cast. Amt = AllocaBuilder.CreateMul(Amt, NumElements, "tmp"); } if (uint64_t Offset = (AllocElTySize*ArrayOffset)/CastElTySize) { Value *Off = ConstantInt::get(AI.getArraySize()->getType(), Offset, true); Amt = AllocaBuilder.CreateAdd(Amt, Off, "tmp"); } AllocaInst *New = AllocaBuilder.CreateAlloca(CastElTy, Amt); New->setAlignment(AI.getAlignment()); New->takeName(&AI); // If the allocation has multiple real uses, insert a cast and change all // things that used it to use the new cast. This will also hack on CI, but it // will die soon. if (!AI.hasOneUse()) { // New is the allocation instruction, pointer typed. AI is the original // allocation instruction, also pointer typed. Thus, cast to use is BitCast. Value *NewCast = AllocaBuilder.CreateBitCast(New, AI.getType(), "tmpcast"); ReplaceInstUsesWith(AI, NewCast); } return ReplaceInstUsesWith(CI, New); } /// EvaluateInDifferentType - Given an expression that /// CanEvaluateTruncated or CanEvaluateSExtd returns true for, actually /// insert the code to evaluate the expression. Value *InstCombiner::EvaluateInDifferentType(Value *V, Type *Ty, bool isSigned) { if (Constant *C = dyn_cast(V)) { C = ConstantExpr::getIntegerCast(C, Ty, isSigned /*Sext or ZExt*/); // If we got a constantexpr back, try to simplify it with TD info. if (ConstantExpr *CE = dyn_cast(C)) C = ConstantFoldConstantExpression(CE, TD); return C; } // Otherwise, it must be an instruction. Instruction *I = cast(V); Instruction *Res = 0; unsigned Opc = I->getOpcode(); switch (Opc) { case Instruction::Add: case Instruction::Sub: case Instruction::Mul: case Instruction::And: case Instruction::Or: case Instruction::Xor: case Instruction::AShr: case Instruction::LShr: case Instruction::Shl: case Instruction::UDiv: case Instruction::URem: { Value *LHS = EvaluateInDifferentType(I->getOperand(0), Ty, isSigned); Value *RHS = EvaluateInDifferentType(I->getOperand(1), Ty, isSigned); Res = BinaryOperator::Create((Instruction::BinaryOps)Opc, LHS, RHS); break; } case Instruction::Trunc: case Instruction::ZExt: case Instruction::SExt: // If the source type of the cast is the type we're trying for then we can // just return the source. There's no need to insert it because it is not // new. if (I->getOperand(0)->getType() == Ty) return I->getOperand(0); // Otherwise, must be the same type of cast, so just reinsert a new one. // This also handles the case of zext(trunc(x)) -> zext(x). Res = CastInst::CreateIntegerCast(I->getOperand(0), Ty, Opc == Instruction::SExt); break; case Instruction::Select: { Value *True = EvaluateInDifferentType(I->getOperand(1), Ty, isSigned); Value *False = EvaluateInDifferentType(I->getOperand(2), Ty, isSigned); Res = SelectInst::Create(I->getOperand(0), True, False); break; } case Instruction::PHI: { PHINode *OPN = cast(I); PHINode *NPN = PHINode::Create(Ty, OPN->getNumIncomingValues()); for (unsigned i = 0, e = OPN->getNumIncomingValues(); i != e; ++i) { Value *V =EvaluateInDifferentType(OPN->getIncomingValue(i), Ty, isSigned); NPN->addIncoming(V, OPN->getIncomingBlock(i)); } Res = NPN; break; } default: // TODO: Can handle more cases here. llvm_unreachable("Unreachable!"); break; } Res->takeName(I); return InsertNewInstWith(Res, *I); } /// This function is a wrapper around CastInst::isEliminableCastPair. It /// simply extracts arguments and returns what that function returns. static Instruction::CastOps isEliminableCastPair( const CastInst *CI, ///< The first cast instruction unsigned opcode, ///< The opcode of the second cast instruction Type *DstTy, ///< The target type for the second cast instruction TargetData *TD ///< The target data for pointer size ) { Type *SrcTy = CI->getOperand(0)->getType(); // A from above Type *MidTy = CI->getType(); // B from above // Get the opcodes of the two Cast instructions Instruction::CastOps firstOp = Instruction::CastOps(CI->getOpcode()); Instruction::CastOps secondOp = Instruction::CastOps(opcode); unsigned Res = CastInst::isEliminableCastPair(firstOp, secondOp, SrcTy, MidTy, DstTy, TD ? TD->getIntPtrType(CI->getContext()) : 0); // We don't want to form an inttoptr or ptrtoint that converts to an integer // type that differs from the pointer size. if ((Res == Instruction::IntToPtr && (!TD || SrcTy != TD->getIntPtrType(CI->getContext()))) || (Res == Instruction::PtrToInt && (!TD || DstTy != TD->getIntPtrType(CI->getContext())))) Res = 0; return Instruction::CastOps(Res); } /// ShouldOptimizeCast - Return true if the cast from "V to Ty" actually /// results in any code being generated and is interesting to optimize out. If /// the cast can be eliminated by some other simple transformation, we prefer /// to do the simplification first. bool InstCombiner::ShouldOptimizeCast(Instruction::CastOps opc, const Value *V, Type *Ty) { // Noop casts and casts of constants should be eliminated trivially. if (V->getType() == Ty || isa(V)) return false; // If this is another cast that can be eliminated, we prefer to have it // eliminated. if (const CastInst *CI = dyn_cast(V)) if (isEliminableCastPair(CI, opc, Ty, TD)) return false; // If this is a vector sext from a compare, then we don't want to break the // idiom where each element of the extended vector is either zero or all ones. if (opc == Instruction::SExt && isa(V) && Ty->isVectorTy()) return false; return true; } /// @brief Implement the transforms common to all CastInst visitors. Instruction *InstCombiner::commonCastTransforms(CastInst &CI) { Value *Src = CI.getOperand(0); // Many cases of "cast of a cast" are eliminable. If it's eliminable we just // eliminate it now. if (CastInst *CSrc = dyn_cast(Src)) { // A->B->C cast if (Instruction::CastOps opc = isEliminableCastPair(CSrc, CI.getOpcode(), CI.getType(), TD)) { // The first cast (CSrc) is eliminable so we need to fix up or replace // the second cast (CI). CSrc will then have a good chance of being dead. return CastInst::Create(opc, CSrc->getOperand(0), CI.getType()); } } // If we are casting a select then fold the cast into the select if (SelectInst *SI = dyn_cast(Src)) if (Instruction *NV = FoldOpIntoSelect(CI, SI)) return NV; // If we are casting a PHI then fold the cast into the PHI if (isa(Src)) { // We don't do this if this would create a PHI node with an illegal type if // it is currently legal. if (!Src->getType()->isIntegerTy() || !CI.getType()->isIntegerTy() || ShouldChangeType(CI.getType(), Src->getType())) if (Instruction *NV = FoldOpIntoPhi(CI)) return NV; } return 0; } /// CanEvaluateTruncated - Return true if we can evaluate the specified /// expression tree as type Ty instead of its larger type, and arrive with the /// same value. This is used by code that tries to eliminate truncates. /// /// Ty will always be a type smaller than V. We should return true if trunc(V) /// can be computed by computing V in the smaller type. If V is an instruction, /// then trunc(inst(x,y)) can be computed as inst(trunc(x),trunc(y)), which only /// makes sense if x and y can be efficiently truncated. /// /// This function works on both vectors and scalars. /// static bool CanEvaluateTruncated(Value *V, Type *Ty) { // We can always evaluate constants in another type. if (isa(V)) return true; Instruction *I = dyn_cast(V); if (!I) return false; Type *OrigTy = V->getType(); // If this is an extension from the dest type, we can eliminate it, even if it // has multiple uses. if ((isa(I) || isa(I)) && I->getOperand(0)->getType() == Ty) return true; // We can't extend or shrink something that has multiple uses: doing so would // require duplicating the instruction in general, which isn't profitable. if (!I->hasOneUse()) return false; unsigned Opc = I->getOpcode(); switch (Opc) { case Instruction::Add: case Instruction::Sub: case Instruction::Mul: case Instruction::And: case Instruction::Or: case Instruction::Xor: // These operators can all arbitrarily be extended or truncated. return CanEvaluateTruncated(I->getOperand(0), Ty) && CanEvaluateTruncated(I->getOperand(1), Ty); case Instruction::UDiv: case Instruction::URem: { // UDiv and URem can be truncated if all the truncated bits are zero. uint32_t OrigBitWidth = OrigTy->getScalarSizeInBits(); uint32_t BitWidth = Ty->getScalarSizeInBits(); if (BitWidth < OrigBitWidth) { APInt Mask = APInt::getHighBitsSet(OrigBitWidth, OrigBitWidth-BitWidth); if (MaskedValueIsZero(I->getOperand(0), Mask) && MaskedValueIsZero(I->getOperand(1), Mask)) { return CanEvaluateTruncated(I->getOperand(0), Ty) && CanEvaluateTruncated(I->getOperand(1), Ty); } } break; } case Instruction::Shl: // If we are truncating the result of this SHL, and if it's a shift of a // constant amount, we can always perform a SHL in a smaller type. if (ConstantInt *CI = dyn_cast(I->getOperand(1))) { uint32_t BitWidth = Ty->getScalarSizeInBits(); if (CI->getLimitedValue(BitWidth) < BitWidth) return CanEvaluateTruncated(I->getOperand(0), Ty); } break; case Instruction::LShr: // If this is a truncate of a logical shr, we can truncate it to a smaller // lshr iff we know that the bits we would otherwise be shifting in are // already zeros. if (ConstantInt *CI = dyn_cast(I->getOperand(1))) { uint32_t OrigBitWidth = OrigTy->getScalarSizeInBits(); uint32_t BitWidth = Ty->getScalarSizeInBits(); if (MaskedValueIsZero(I->getOperand(0), APInt::getHighBitsSet(OrigBitWidth, OrigBitWidth-BitWidth)) && CI->getLimitedValue(BitWidth) < BitWidth) { return CanEvaluateTruncated(I->getOperand(0), Ty); } } break; case Instruction::Trunc: // trunc(trunc(x)) -> trunc(x) return true; case Instruction::ZExt: case Instruction::SExt: // trunc(ext(x)) -> ext(x) if the source type is smaller than the new dest // trunc(ext(x)) -> trunc(x) if the source type is larger than the new dest return true; case Instruction::Select: { SelectInst *SI = cast(I); return CanEvaluateTruncated(SI->getTrueValue(), Ty) && CanEvaluateTruncated(SI->getFalseValue(), Ty); } case Instruction::PHI: { // We can change a phi if we can change all operands. Note that we never // get into trouble with cyclic PHIs here because we only consider // instructions with a single use. PHINode *PN = cast(I); for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) if (!CanEvaluateTruncated(PN->getIncomingValue(i), Ty)) return false; return true; } default: // TODO: Can handle more cases here. break; } return false; } Instruction *InstCombiner::visitTrunc(TruncInst &CI) { if (Instruction *Result = commonCastTransforms(CI)) return Result; // See if we can simplify any instructions used by the input whose sole // purpose is to compute bits we don't care about. if (SimplifyDemandedInstructionBits(CI)) return &CI; Value *Src = CI.getOperand(0); Type *DestTy = CI.getType(), *SrcTy = Src->getType(); // Attempt to truncate the entire input expression tree to the destination // type. Only do this if the dest type is a simple type, don't convert the // expression tree to something weird like i93 unless the source is also // strange. if ((DestTy->isVectorTy() || ShouldChangeType(SrcTy, DestTy)) && CanEvaluateTruncated(Src, DestTy)) { // If this cast is a truncate, evaluting in a different type always // eliminates the cast, so it is always a win. DEBUG(dbgs() << "ICE: EvaluateInDifferentType converting expression type" " to avoid cast: " << CI << '\n'); Value *Res = EvaluateInDifferentType(Src, DestTy, false); assert(Res->getType() == DestTy); return ReplaceInstUsesWith(CI, Res); } // Canonicalize trunc x to i1 -> (icmp ne (and x, 1), 0), likewise for vector. if (DestTy->getScalarSizeInBits() == 1) { Constant *One = ConstantInt::get(Src->getType(), 1); Src = Builder->CreateAnd(Src, One, "tmp"); Value *Zero = Constant::getNullValue(Src->getType()); return new ICmpInst(ICmpInst::ICMP_NE, Src, Zero); } // Transform trunc(lshr (zext A), Cst) to eliminate one type conversion. Value *A = 0; ConstantInt *Cst = 0; if (Src->hasOneUse() && match(Src, m_LShr(m_ZExt(m_Value(A)), m_ConstantInt(Cst)))) { // We have three types to worry about here, the type of A, the source of // the truncate (MidSize), and the destination of the truncate. We know that // ASize < MidSize and MidSize > ResultSize, but don't know the relation // between ASize and ResultSize. unsigned ASize = A->getType()->getPrimitiveSizeInBits(); // If the shift amount is larger than the size of A, then the result is // known to be zero because all the input bits got shifted out. if (Cst->getZExtValue() >= ASize) return ReplaceInstUsesWith(CI, Constant::getNullValue(CI.getType())); // Since we're doing an lshr and a zero extend, and know that the shift // amount is smaller than ASize, it is always safe to do the shift in A's // type, then zero extend or truncate to the result. Value *Shift = Builder->CreateLShr(A, Cst->getZExtValue()); Shift->takeName(Src); return CastInst::CreateIntegerCast(Shift, CI.getType(), false); } // Transform "trunc (and X, cst)" -> "and (trunc X), cst" so long as the dest // type isn't non-native. if (Src->hasOneUse() && isa(Src->getType()) && ShouldChangeType(Src->getType(), CI.getType()) && match(Src, m_And(m_Value(A), m_ConstantInt(Cst)))) { Value *NewTrunc = Builder->CreateTrunc(A, CI.getType(), A->getName()+".tr"); return BinaryOperator::CreateAnd(NewTrunc, ConstantExpr::getTrunc(Cst, CI.getType())); } return 0; } /// transformZExtICmp - Transform (zext icmp) to bitwise / integer operations /// in order to eliminate the icmp. Instruction *InstCombiner::transformZExtICmp(ICmpInst *ICI, Instruction &CI, bool DoXform) { // If we are just checking for a icmp eq of a single bit and zext'ing it // to an integer, then shift the bit to the appropriate place and then // cast to integer to avoid the comparison. if (ConstantInt *Op1C = dyn_cast(ICI->getOperand(1))) { const APInt &Op1CV = Op1C->getValue(); // zext (x x>>u31 true if signbit set. // zext (x >s -1) to i32 --> (x>>u31)^1 true if signbit clear. if ((ICI->getPredicate() == ICmpInst::ICMP_SLT && Op1CV == 0) || (ICI->getPredicate() == ICmpInst::ICMP_SGT &&Op1CV.isAllOnesValue())) { if (!DoXform) return ICI; Value *In = ICI->getOperand(0); Value *Sh = ConstantInt::get(In->getType(), In->getType()->getScalarSizeInBits()-1); In = Builder->CreateLShr(In, Sh, In->getName()+".lobit"); if (In->getType() != CI.getType()) In = Builder->CreateIntCast(In, CI.getType(), false/*ZExt*/, "tmp"); if (ICI->getPredicate() == ICmpInst::ICMP_SGT) { Constant *One = ConstantInt::get(In->getType(), 1); In = Builder->CreateXor(In, One, In->getName()+".not"); } return ReplaceInstUsesWith(CI, In); } // zext (X == 0) to i32 --> X^1 iff X has only the low bit set. // zext (X == 0) to i32 --> (X>>1)^1 iff X has only the 2nd bit set. // zext (X == 1) to i32 --> X iff X has only the low bit set. // zext (X == 2) to i32 --> X>>1 iff X has only the 2nd bit set. // zext (X != 0) to i32 --> X iff X has only the low bit set. // zext (X != 0) to i32 --> X>>1 iff X has only the 2nd bit set. // zext (X != 1) to i32 --> X^1 iff X has only the low bit set. // zext (X != 2) to i32 --> (X>>1)^1 iff X has only the 2nd bit set. if ((Op1CV == 0 || Op1CV.isPowerOf2()) && // This only works for EQ and NE ICI->isEquality()) { // If Op1C some other power of two, convert: uint32_t BitWidth = Op1C->getType()->getBitWidth(); APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0); APInt TypeMask(APInt::getAllOnesValue(BitWidth)); ComputeMaskedBits(ICI->getOperand(0), TypeMask, KnownZero, KnownOne); APInt KnownZeroMask(~KnownZero); if (KnownZeroMask.isPowerOf2()) { // Exactly 1 possible 1? if (!DoXform) return ICI; bool isNE = ICI->getPredicate() == ICmpInst::ICMP_NE; if (Op1CV != 0 && (Op1CV != KnownZeroMask)) { // (X&4) == 2 --> false // (X&4) != 2 --> true Constant *Res = ConstantInt::get(Type::getInt1Ty(CI.getContext()), isNE); Res = ConstantExpr::getZExt(Res, CI.getType()); return ReplaceInstUsesWith(CI, Res); } uint32_t ShiftAmt = KnownZeroMask.logBase2(); Value *In = ICI->getOperand(0); if (ShiftAmt) { // Perform a logical shr by shiftamt. // Insert the shift to put the result in the low bit. In = Builder->CreateLShr(In, ConstantInt::get(In->getType(),ShiftAmt), In->getName()+".lobit"); } if ((Op1CV != 0) == isNE) { // Toggle the low bit. Constant *One = ConstantInt::get(In->getType(), 1); In = Builder->CreateXor(In, One, "tmp"); } if (CI.getType() == In->getType()) return ReplaceInstUsesWith(CI, In); return CastInst::CreateIntegerCast(In, CI.getType(), false/*ZExt*/); } } } // icmp ne A, B is equal to xor A, B when A and B only really have one bit. // It is also profitable to transform icmp eq into not(xor(A, B)) because that // may lead to additional simplifications. if (ICI->isEquality() && CI.getType() == ICI->getOperand(0)->getType()) { if (IntegerType *ITy = dyn_cast(CI.getType())) { uint32_t BitWidth = ITy->getBitWidth(); Value *LHS = ICI->getOperand(0); Value *RHS = ICI->getOperand(1); APInt KnownZeroLHS(BitWidth, 0), KnownOneLHS(BitWidth, 0); APInt KnownZeroRHS(BitWidth, 0), KnownOneRHS(BitWidth, 0); APInt TypeMask(APInt::getAllOnesValue(BitWidth)); ComputeMaskedBits(LHS, TypeMask, KnownZeroLHS, KnownOneLHS); ComputeMaskedBits(RHS, TypeMask, KnownZeroRHS, KnownOneRHS); if (KnownZeroLHS == KnownZeroRHS && KnownOneLHS == KnownOneRHS) { APInt KnownBits = KnownZeroLHS | KnownOneLHS; APInt UnknownBit = ~KnownBits; if (UnknownBit.countPopulation() == 1) { if (!DoXform) return ICI; Value *Result = Builder->CreateXor(LHS, RHS); // Mask off any bits that are set and won't be shifted away. if (KnownOneLHS.uge(UnknownBit)) Result = Builder->CreateAnd(Result, ConstantInt::get(ITy, UnknownBit)); // Shift the bit we're testing down to the lsb. Result = Builder->CreateLShr( Result, ConstantInt::get(ITy, UnknownBit.countTrailingZeros())); if (ICI->getPredicate() == ICmpInst::ICMP_EQ) Result = Builder->CreateXor(Result, ConstantInt::get(ITy, 1)); Result->takeName(ICI); return ReplaceInstUsesWith(CI, Result); } } } } return 0; } /// CanEvaluateZExtd - Determine if the specified value can be computed in the /// specified wider type and produce the same low bits. If not, return false. /// /// If this function returns true, it can also return a non-zero number of bits /// (in BitsToClear) which indicates that the value it computes is correct for /// the zero extend, but that the additional BitsToClear bits need to be zero'd /// out. For example, to promote something like: /// /// %B = trunc i64 %A to i32 /// %C = lshr i32 %B, 8 /// %E = zext i32 %C to i64 /// /// CanEvaluateZExtd for the 'lshr' will return true, and BitsToClear will be /// set to 8 to indicate that the promoted value needs to have bits 24-31 /// cleared in addition to bits 32-63. Since an 'and' will be generated to /// clear the top bits anyway, doing this has no extra cost. /// /// This function works on both vectors and scalars. static bool CanEvaluateZExtd(Value *V, Type *Ty, unsigned &BitsToClear) { BitsToClear = 0; if (isa(V)) return true; Instruction *I = dyn_cast(V); if (!I) return false; // If the input is a truncate from the destination type, we can trivially // eliminate it, even if it has multiple uses. // FIXME: This is currently disabled until codegen can handle this without // pessimizing code, PR5997. if (0 && isa(I) && I->getOperand(0)->getType() == Ty) return true; // We can't extend or shrink something that has multiple uses: doing so would // require duplicating the instruction in general, which isn't profitable. if (!I->hasOneUse()) return false; unsigned Opc = I->getOpcode(), Tmp; switch (Opc) { case Instruction::ZExt: // zext(zext(x)) -> zext(x). case Instruction::SExt: // zext(sext(x)) -> sext(x). case Instruction::Trunc: // zext(trunc(x)) -> trunc(x) or zext(x) return true; case Instruction::And: case Instruction::Or: case Instruction::Xor: case Instruction::Add: case Instruction::Sub: case Instruction::Mul: case Instruction::Shl: if (!CanEvaluateZExtd(I->getOperand(0), Ty, BitsToClear) || !CanEvaluateZExtd(I->getOperand(1), Ty, Tmp)) return false; // These can all be promoted if neither operand has 'bits to clear'. if (BitsToClear == 0 && Tmp == 0) return true; // If the operation is an AND/OR/XOR and the bits to clear are zero in the // other side, BitsToClear is ok. if (Tmp == 0 && (Opc == Instruction::And || Opc == Instruction::Or || Opc == Instruction::Xor)) { // We use MaskedValueIsZero here for generality, but the case we care // about the most is constant RHS. unsigned VSize = V->getType()->getScalarSizeInBits(); if (MaskedValueIsZero(I->getOperand(1), APInt::getHighBitsSet(VSize, BitsToClear))) return true; } // Otherwise, we don't know how to analyze this BitsToClear case yet. return false; case Instruction::LShr: // We can promote lshr(x, cst) if we can promote x. This requires the // ultimate 'and' to clear out the high zero bits we're clearing out though. if (ConstantInt *Amt = dyn_cast(I->getOperand(1))) { if (!CanEvaluateZExtd(I->getOperand(0), Ty, BitsToClear)) return false; BitsToClear += Amt->getZExtValue(); if (BitsToClear > V->getType()->getScalarSizeInBits()) BitsToClear = V->getType()->getScalarSizeInBits(); return true; } // Cannot promote variable LSHR. return false; case Instruction::Select: if (!CanEvaluateZExtd(I->getOperand(1), Ty, Tmp) || !CanEvaluateZExtd(I->getOperand(2), Ty, BitsToClear) || // TODO: If important, we could handle the case when the BitsToClear are // known zero in the disagreeing side. Tmp != BitsToClear) return false; return true; case Instruction::PHI: { // We can change a phi if we can change all operands. Note that we never // get into trouble with cyclic PHIs here because we only consider // instructions with a single use. PHINode *PN = cast(I); if (!CanEvaluateZExtd(PN->getIncomingValue(0), Ty, BitsToClear)) return false; for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i) if (!CanEvaluateZExtd(PN->getIncomingValue(i), Ty, Tmp) || // TODO: If important, we could handle the case when the BitsToClear // are known zero in the disagreeing input. Tmp != BitsToClear) return false; return true; } default: // TODO: Can handle more cases here. return false; } } Instruction *InstCombiner::visitZExt(ZExtInst &CI) { // If this zero extend is only used by a truncate, let the truncate by // eliminated before we try to optimize this zext. if (CI.hasOneUse() && isa(CI.use_back())) return 0; // If one of the common conversion will work, do it. if (Instruction *Result = commonCastTransforms(CI)) return Result; // See if we can simplify any instructions used by the input whose sole // purpose is to compute bits we don't care about. if (SimplifyDemandedInstructionBits(CI)) return &CI; Value *Src = CI.getOperand(0); Type *SrcTy = Src->getType(), *DestTy = CI.getType(); // Attempt to extend the entire input expression tree to the destination // type. Only do this if the dest type is a simple type, don't convert the // expression tree to something weird like i93 unless the source is also // strange. unsigned BitsToClear; if ((DestTy->isVectorTy() || ShouldChangeType(SrcTy, DestTy)) && CanEvaluateZExtd(Src, DestTy, BitsToClear)) { assert(BitsToClear < SrcTy->getScalarSizeInBits() && "Unreasonable BitsToClear"); // Okay, we can transform this! Insert the new expression now. DEBUG(dbgs() << "ICE: EvaluateInDifferentType converting expression type" " to avoid zero extend: " << CI); Value *Res = EvaluateInDifferentType(Src, DestTy, false); assert(Res->getType() == DestTy); uint32_t SrcBitsKept = SrcTy->getScalarSizeInBits()-BitsToClear; uint32_t DestBitSize = DestTy->getScalarSizeInBits(); // If the high bits are already filled with zeros, just replace this // cast with the result. if (MaskedValueIsZero(Res, APInt::getHighBitsSet(DestBitSize, DestBitSize-SrcBitsKept))) return ReplaceInstUsesWith(CI, Res); // We need to emit an AND to clear the high bits. Constant *C = ConstantInt::get(Res->getType(), APInt::getLowBitsSet(DestBitSize, SrcBitsKept)); return BinaryOperator::CreateAnd(Res, C); } // If this is a TRUNC followed by a ZEXT then we are dealing with integral // types and if the sizes are just right we can convert this into a logical // 'and' which will be much cheaper than the pair of casts. if (TruncInst *CSrc = dyn_cast(Src)) { // A->B->C cast // TODO: Subsume this into EvaluateInDifferentType. // Get the sizes of the types involved. We know that the intermediate type // will be smaller than A or C, but don't know the relation between A and C. Value *A = CSrc->getOperand(0); unsigned SrcSize = A->getType()->getScalarSizeInBits(); unsigned MidSize = CSrc->getType()->getScalarSizeInBits(); unsigned DstSize = CI.getType()->getScalarSizeInBits(); // If we're actually extending zero bits, then if // SrcSize < DstSize: zext(a & mask) // SrcSize == DstSize: a & mask // SrcSize > DstSize: trunc(a) & mask if (SrcSize < DstSize) { APInt AndValue(APInt::getLowBitsSet(SrcSize, MidSize)); Constant *AndConst = ConstantInt::get(A->getType(), AndValue); Value *And = Builder->CreateAnd(A, AndConst, CSrc->getName()+".mask"); return new ZExtInst(And, CI.getType()); } if (SrcSize == DstSize) { APInt AndValue(APInt::getLowBitsSet(SrcSize, MidSize)); return BinaryOperator::CreateAnd(A, ConstantInt::get(A->getType(), AndValue)); } if (SrcSize > DstSize) { Value *Trunc = Builder->CreateTrunc(A, CI.getType(), "tmp"); APInt AndValue(APInt::getLowBitsSet(DstSize, MidSize)); return BinaryOperator::CreateAnd(Trunc, ConstantInt::get(Trunc->getType(), AndValue)); } } if (ICmpInst *ICI = dyn_cast(Src)) return transformZExtICmp(ICI, CI); BinaryOperator *SrcI = dyn_cast(Src); if (SrcI && SrcI->getOpcode() == Instruction::Or) { // zext (or icmp, icmp) --> or (zext icmp), (zext icmp) if at least one // of the (zext icmp) will be transformed. ICmpInst *LHS = dyn_cast(SrcI->getOperand(0)); ICmpInst *RHS = dyn_cast(SrcI->getOperand(1)); if (LHS && RHS && LHS->hasOneUse() && RHS->hasOneUse() && (transformZExtICmp(LHS, CI, false) || transformZExtICmp(RHS, CI, false))) { Value *LCast = Builder->CreateZExt(LHS, CI.getType(), LHS->getName()); Value *RCast = Builder->CreateZExt(RHS, CI.getType(), RHS->getName()); return BinaryOperator::Create(Instruction::Or, LCast, RCast); } } // zext(trunc(t) & C) -> (t & zext(C)). if (SrcI && SrcI->getOpcode() == Instruction::And && SrcI->hasOneUse()) if (ConstantInt *C = dyn_cast(SrcI->getOperand(1))) if (TruncInst *TI = dyn_cast(SrcI->getOperand(0))) { Value *TI0 = TI->getOperand(0); if (TI0->getType() == CI.getType()) return BinaryOperator::CreateAnd(TI0, ConstantExpr::getZExt(C, CI.getType())); } // zext((trunc(t) & C) ^ C) -> ((t & zext(C)) ^ zext(C)). if (SrcI && SrcI->getOpcode() == Instruction::Xor && SrcI->hasOneUse()) if (ConstantInt *C = dyn_cast(SrcI->getOperand(1))) if (BinaryOperator *And = dyn_cast(SrcI->getOperand(0))) if (And->getOpcode() == Instruction::And && And->hasOneUse() && And->getOperand(1) == C) if (TruncInst *TI = dyn_cast(And->getOperand(0))) { Value *TI0 = TI->getOperand(0); if (TI0->getType() == CI.getType()) { Constant *ZC = ConstantExpr::getZExt(C, CI.getType()); Value *NewAnd = Builder->CreateAnd(TI0, ZC, "tmp"); return BinaryOperator::CreateXor(NewAnd, ZC); } } // zext (xor i1 X, true) to i32 --> xor (zext i1 X to i32), 1 Value *X; if (SrcI && SrcI->hasOneUse() && SrcI->getType()->isIntegerTy(1) && match(SrcI, m_Not(m_Value(X))) && (!X->hasOneUse() || !isa(X))) { Value *New = Builder->CreateZExt(X, CI.getType()); return BinaryOperator::CreateXor(New, ConstantInt::get(CI.getType(), 1)); } return 0; } /// transformSExtICmp - Transform (sext icmp) to bitwise / integer operations /// in order to eliminate the icmp. Instruction *InstCombiner::transformSExtICmp(ICmpInst *ICI, Instruction &CI) { Value *Op0 = ICI->getOperand(0), *Op1 = ICI->getOperand(1); ICmpInst::Predicate Pred = ICI->getPredicate(); if (ConstantInt *Op1C = dyn_cast(Op1)) { // (x ashr x, 31 -> all ones if negative // (x >s -1) ? -1 : 0 -> not (ashr x, 31) -> all ones if positive if ((Pred == ICmpInst::ICMP_SLT && Op1C->isZero()) || (Pred == ICmpInst::ICMP_SGT && Op1C->isAllOnesValue())) { Value *Sh = ConstantInt::get(Op0->getType(), Op0->getType()->getScalarSizeInBits()-1); Value *In = Builder->CreateAShr(Op0, Sh, Op0->getName()+".lobit"); if (In->getType() != CI.getType()) In = Builder->CreateIntCast(In, CI.getType(), true/*SExt*/, "tmp"); if (Pred == ICmpInst::ICMP_SGT) In = Builder->CreateNot(In, In->getName()+".not"); return ReplaceInstUsesWith(CI, In); } // If we know that only one bit of the LHS of the icmp can be set and we // have an equality comparison with zero or a power of 2, we can transform // the icmp and sext into bitwise/integer operations. if (ICI->hasOneUse() && ICI->isEquality() && (Op1C->isZero() || Op1C->getValue().isPowerOf2())){ unsigned BitWidth = Op1C->getType()->getBitWidth(); APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0); APInt TypeMask(APInt::getAllOnesValue(BitWidth)); ComputeMaskedBits(Op0, TypeMask, KnownZero, KnownOne); APInt KnownZeroMask(~KnownZero); if (KnownZeroMask.isPowerOf2()) { Value *In = ICI->getOperand(0); // If the icmp tests for a known zero bit we can constant fold it. if (!Op1C->isZero() && Op1C->getValue() != KnownZeroMask) { Value *V = Pred == ICmpInst::ICMP_NE ? ConstantInt::getAllOnesValue(CI.getType()) : ConstantInt::getNullValue(CI.getType()); return ReplaceInstUsesWith(CI, V); } if (!Op1C->isZero() == (Pred == ICmpInst::ICMP_NE)) { // sext ((x & 2^n) == 0) -> (x >> n) - 1 // sext ((x & 2^n) != 2^n) -> (x >> n) - 1 unsigned ShiftAmt = KnownZeroMask.countTrailingZeros(); // Perform a right shift to place the desired bit in the LSB. if (ShiftAmt) In = Builder->CreateLShr(In, ConstantInt::get(In->getType(), ShiftAmt)); // At this point "In" is either 1 or 0. Subtract 1 to turn // {1, 0} -> {0, -1}. In = Builder->CreateAdd(In, ConstantInt::getAllOnesValue(In->getType()), "sext"); } else { // sext ((x & 2^n) != 0) -> (x << bitwidth-n) a>> bitwidth-1 // sext ((x & 2^n) == 2^n) -> (x << bitwidth-n) a>> bitwidth-1 unsigned ShiftAmt = KnownZeroMask.countLeadingZeros(); // Perform a left shift to place the desired bit in the MSB. if (ShiftAmt) In = Builder->CreateShl(In, ConstantInt::get(In->getType(), ShiftAmt)); // Distribute the bit over the whole bit width. In = Builder->CreateAShr(In, ConstantInt::get(In->getType(), BitWidth - 1), "sext"); } if (CI.getType() == In->getType()) return ReplaceInstUsesWith(CI, In); return CastInst::CreateIntegerCast(In, CI.getType(), true/*SExt*/); } } } // vector (x ashr x, 31 -> all ones if signed. if (VectorType *VTy = dyn_cast(CI.getType())) { if (Pred == ICmpInst::ICMP_SLT && match(Op1, m_Zero()) && Op0->getType() == CI.getType()) { Type *EltTy = VTy->getElementType(); // splat the shift constant to a constant vector. Constant *VSh = ConstantInt::get(VTy, EltTy->getScalarSizeInBits()-1); Value *In = Builder->CreateAShr(Op0, VSh, Op0->getName()+".lobit"); return ReplaceInstUsesWith(CI, In); } } return 0; } /// CanEvaluateSExtd - Return true if we can take the specified value /// and return it as type Ty without inserting any new casts and without /// changing the value of the common low bits. This is used by code that tries /// to promote integer operations to a wider types will allow us to eliminate /// the extension. /// /// This function works on both vectors and scalars. /// static bool CanEvaluateSExtd(Value *V, Type *Ty) { assert(V->getType()->getScalarSizeInBits() < Ty->getScalarSizeInBits() && "Can't sign extend type to a smaller type"); // If this is a constant, it can be trivially promoted. if (isa(V)) return true; Instruction *I = dyn_cast(V); if (!I) return false; // If this is a truncate from the dest type, we can trivially eliminate it, // even if it has multiple uses. // FIXME: This is currently disabled until codegen can handle this without // pessimizing code, PR5997. if (0 && isa(I) && I->getOperand(0)->getType() == Ty) return true; // We can't extend or shrink something that has multiple uses: doing so would // require duplicating the instruction in general, which isn't profitable. if (!I->hasOneUse()) return false; switch (I->getOpcode()) { case Instruction::SExt: // sext(sext(x)) -> sext(x) case Instruction::ZExt: // sext(zext(x)) -> zext(x) case Instruction::Trunc: // sext(trunc(x)) -> trunc(x) or sext(x) return true; case Instruction::And: case Instruction::Or: case Instruction::Xor: case Instruction::Add: case Instruction::Sub: case Instruction::Mul: // These operators can all arbitrarily be extended if their inputs can. return CanEvaluateSExtd(I->getOperand(0), Ty) && CanEvaluateSExtd(I->getOperand(1), Ty); //case Instruction::Shl: TODO //case Instruction::LShr: TODO case Instruction::Select: return CanEvaluateSExtd(I->getOperand(1), Ty) && CanEvaluateSExtd(I->getOperand(2), Ty); case Instruction::PHI: { // We can change a phi if we can change all operands. Note that we never // get into trouble with cyclic PHIs here because we only consider // instructions with a single use. PHINode *PN = cast(I); for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) if (!CanEvaluateSExtd(PN->getIncomingValue(i), Ty)) return false; return true; } default: // TODO: Can handle more cases here. break; } return false; } Instruction *InstCombiner::visitSExt(SExtInst &CI) { // If this sign extend is only used by a truncate, let the truncate by // eliminated before we try to optimize this zext. if (CI.hasOneUse() && isa(CI.use_back())) return 0; if (Instruction *I = commonCastTransforms(CI)) return I; // See if we can simplify any instructions used by the input whose sole // purpose is to compute bits we don't care about. if (SimplifyDemandedInstructionBits(CI)) return &CI; Value *Src = CI.getOperand(0); Type *SrcTy = Src->getType(), *DestTy = CI.getType(); // Attempt to extend the entire input expression tree to the destination // type. Only do this if the dest type is a simple type, don't convert the // expression tree to something weird like i93 unless the source is also // strange. if ((DestTy->isVectorTy() || ShouldChangeType(SrcTy, DestTy)) && CanEvaluateSExtd(Src, DestTy)) { // Okay, we can transform this! Insert the new expression now. DEBUG(dbgs() << "ICE: EvaluateInDifferentType converting expression type" " to avoid sign extend: " << CI); Value *Res = EvaluateInDifferentType(Src, DestTy, true); assert(Res->getType() == DestTy); uint32_t SrcBitSize = SrcTy->getScalarSizeInBits(); uint32_t DestBitSize = DestTy->getScalarSizeInBits(); // If the high bits are already filled with sign bit, just replace this // cast with the result. if (ComputeNumSignBits(Res) > DestBitSize - SrcBitSize) return ReplaceInstUsesWith(CI, Res); // We need to emit a shl + ashr to do the sign extend. Value *ShAmt = ConstantInt::get(DestTy, DestBitSize-SrcBitSize); return BinaryOperator::CreateAShr(Builder->CreateShl(Res, ShAmt, "sext"), ShAmt); } // If this input is a trunc from our destination, then turn sext(trunc(x)) // into shifts. if (TruncInst *TI = dyn_cast(Src)) if (TI->hasOneUse() && TI->getOperand(0)->getType() == DestTy) { uint32_t SrcBitSize = SrcTy->getScalarSizeInBits(); uint32_t DestBitSize = DestTy->getScalarSizeInBits(); // We need to emit a shl + ashr to do the sign extend. Value *ShAmt = ConstantInt::get(DestTy, DestBitSize-SrcBitSize); Value *Res = Builder->CreateShl(TI->getOperand(0), ShAmt, "sext"); return BinaryOperator::CreateAShr(Res, ShAmt); } if (ICmpInst *ICI = dyn_cast(Src)) return transformSExtICmp(ICI, CI); // If the input is a shl/ashr pair of a same constant, then this is a sign // extension from a smaller value. If we could trust arbitrary bitwidth // integers, we could turn this into a truncate to the smaller bit and then // use a sext for the whole extension. Since we don't, look deeper and check // for a truncate. If the source and dest are the same type, eliminate the // trunc and extend and just do shifts. For example, turn: // %a = trunc i32 %i to i8 // %b = shl i8 %a, 6 // %c = ashr i8 %b, 6 // %d = sext i8 %c to i32 // into: // %a = shl i32 %i, 30 // %d = ashr i32 %a, 30 Value *A = 0; // TODO: Eventually this could be subsumed by EvaluateInDifferentType. ConstantInt *BA = 0, *CA = 0; if (match(Src, m_AShr(m_Shl(m_Trunc(m_Value(A)), m_ConstantInt(BA)), m_ConstantInt(CA))) && BA == CA && A->getType() == CI.getType()) { unsigned MidSize = Src->getType()->getScalarSizeInBits(); unsigned SrcDstSize = CI.getType()->getScalarSizeInBits(); unsigned ShAmt = CA->getZExtValue()+SrcDstSize-MidSize; Constant *ShAmtV = ConstantInt::get(CI.getType(), ShAmt); A = Builder->CreateShl(A, ShAmtV, CI.getName()); return BinaryOperator::CreateAShr(A, ShAmtV); } return 0; } /// FitsInFPType - Return a Constant* for the specified FP constant if it fits /// in the specified FP type without changing its value. static Constant *FitsInFPType(ConstantFP *CFP, const fltSemantics &Sem) { bool losesInfo; APFloat F = CFP->getValueAPF(); (void)F.convert(Sem, APFloat::rmNearestTiesToEven, &losesInfo); if (!losesInfo) return ConstantFP::get(CFP->getContext(), F); return 0; } /// LookThroughFPExtensions - If this is an fp extension instruction, look /// through it until we get the source value. static Value *LookThroughFPExtensions(Value *V) { if (Instruction *I = dyn_cast(V)) if (I->getOpcode() == Instruction::FPExt) return LookThroughFPExtensions(I->getOperand(0)); // If this value is a constant, return the constant in the smallest FP type // that can accurately represent it. This allows us to turn // (float)((double)X+2.0) into x+2.0f. if (ConstantFP *CFP = dyn_cast(V)) { if (CFP->getType() == Type::getPPC_FP128Ty(V->getContext())) return V; // No constant folding of this. // See if the value can be truncated to float and then reextended. if (Value *V = FitsInFPType(CFP, APFloat::IEEEsingle)) return V; if (CFP->getType()->isDoubleTy()) return V; // Won't shrink. if (Value *V = FitsInFPType(CFP, APFloat::IEEEdouble)) return V; // Don't try to shrink to various long double types. } return V; } Instruction *InstCombiner::visitFPTrunc(FPTruncInst &CI) { if (Instruction *I = commonCastTransforms(CI)) return I; // If we have fptrunc(fadd (fpextend x), (fpextend y)), where x and y are // smaller than the destination type, we can eliminate the truncate by doing // the add as the smaller type. This applies to fadd/fsub/fmul/fdiv as well // as many builtins (sqrt, etc). BinaryOperator *OpI = dyn_cast(CI.getOperand(0)); if (OpI && OpI->hasOneUse()) { switch (OpI->getOpcode()) { default: break; case Instruction::FAdd: case Instruction::FSub: case Instruction::FMul: case Instruction::FDiv: case Instruction::FRem: Type *SrcTy = OpI->getType(); Value *LHSTrunc = LookThroughFPExtensions(OpI->getOperand(0)); Value *RHSTrunc = LookThroughFPExtensions(OpI->getOperand(1)); if (LHSTrunc->getType() != SrcTy && RHSTrunc->getType() != SrcTy) { unsigned DstSize = CI.getType()->getScalarSizeInBits(); // If the source types were both smaller than the destination type of // the cast, do this xform. if (LHSTrunc->getType()->getScalarSizeInBits() <= DstSize && RHSTrunc->getType()->getScalarSizeInBits() <= DstSize) { LHSTrunc = Builder->CreateFPExt(LHSTrunc, CI.getType()); RHSTrunc = Builder->CreateFPExt(RHSTrunc, CI.getType()); return BinaryOperator::Create(OpI->getOpcode(), LHSTrunc, RHSTrunc); } } break; } } // Fold (fptrunc (sqrt (fpext x))) -> (sqrtf x) // NOTE: This should be disabled by -fno-builtin-sqrt if we ever support it. CallInst *Call = dyn_cast(CI.getOperand(0)); if (Call && Call->getCalledFunction() && Call->getCalledFunction()->getName() == "sqrt" && Call->getNumArgOperands() == 1 && Call->hasOneUse()) { CastInst *Arg = dyn_cast(Call->getArgOperand(0)); if (Arg && Arg->getOpcode() == Instruction::FPExt && CI.getType()->isFloatTy() && Call->getType()->isDoubleTy() && Arg->getType()->isDoubleTy() && Arg->getOperand(0)->getType()->isFloatTy()) { Function *Callee = Call->getCalledFunction(); Module *M = CI.getParent()->getParent()->getParent(); Constant *SqrtfFunc = M->getOrInsertFunction("sqrtf", Callee->getAttributes(), Builder->getFloatTy(), Builder->getFloatTy(), NULL); CallInst *ret = CallInst::Create(SqrtfFunc, Arg->getOperand(0), "sqrtfcall"); ret->setAttributes(Callee->getAttributes()); // Remove the old Call. With -fmath-errno, it won't get marked readnone. ReplaceInstUsesWith(*Call, UndefValue::get(Call->getType())); EraseInstFromFunction(*Call); return ret; } } return 0; } Instruction *InstCombiner::visitFPExt(CastInst &CI) { return commonCastTransforms(CI); } Instruction *InstCombiner::visitFPToUI(FPToUIInst &FI) { Instruction *OpI = dyn_cast(FI.getOperand(0)); if (OpI == 0) return commonCastTransforms(FI); // fptoui(uitofp(X)) --> X // fptoui(sitofp(X)) --> X // This is safe if the intermediate type has enough bits in its mantissa to // accurately represent all values of X. For example, do not do this with // i64->float->i64. This is also safe for sitofp case, because any negative // 'X' value would cause an undefined result for the fptoui. if ((isa(OpI) || isa(OpI)) && OpI->getOperand(0)->getType() == FI.getType() && (int)FI.getType()->getScalarSizeInBits() < /*extra bit for sign */ OpI->getType()->getFPMantissaWidth()) return ReplaceInstUsesWith(FI, OpI->getOperand(0)); return commonCastTransforms(FI); } Instruction *InstCombiner::visitFPToSI(FPToSIInst &FI) { Instruction *OpI = dyn_cast(FI.getOperand(0)); if (OpI == 0) return commonCastTransforms(FI); // fptosi(sitofp(X)) --> X // fptosi(uitofp(X)) --> X // This is safe if the intermediate type has enough bits in its mantissa to // accurately represent all values of X. For example, do not do this with // i64->float->i64. This is also safe for sitofp case, because any negative // 'X' value would cause an undefined result for the fptoui. if ((isa(OpI) || isa(OpI)) && OpI->getOperand(0)->getType() == FI.getType() && (int)FI.getType()->getScalarSizeInBits() <= OpI->getType()->getFPMantissaWidth()) return ReplaceInstUsesWith(FI, OpI->getOperand(0)); return commonCastTransforms(FI); } Instruction *InstCombiner::visitUIToFP(CastInst &CI) { return commonCastTransforms(CI); } Instruction *InstCombiner::visitSIToFP(CastInst &CI) { return commonCastTransforms(CI); } Instruction *InstCombiner::visitIntToPtr(IntToPtrInst &CI) { // If the source integer type is not the intptr_t type for this target, do a // trunc or zext to the intptr_t type, then inttoptr of it. This allows the // cast to be exposed to other transforms. if (TD) { if (CI.getOperand(0)->getType()->getScalarSizeInBits() > TD->getPointerSizeInBits()) { Value *P = Builder->CreateTrunc(CI.getOperand(0), TD->getIntPtrType(CI.getContext()), "tmp"); return new IntToPtrInst(P, CI.getType()); } if (CI.getOperand(0)->getType()->getScalarSizeInBits() < TD->getPointerSizeInBits()) { Value *P = Builder->CreateZExt(CI.getOperand(0), TD->getIntPtrType(CI.getContext()), "tmp"); return new IntToPtrInst(P, CI.getType()); } } if (Instruction *I = commonCastTransforms(CI)) return I; return 0; } /// @brief Implement the transforms for cast of pointer (bitcast/ptrtoint) Instruction *InstCombiner::commonPointerCastTransforms(CastInst &CI) { Value *Src = CI.getOperand(0); if (GetElementPtrInst *GEP = dyn_cast(Src)) { // If casting the result of a getelementptr instruction with no offset, turn // this into a cast of the original pointer! if (GEP->hasAllZeroIndices()) { // Changing the cast operand is usually not a good idea but it is safe // here because the pointer operand is being replaced with another // pointer operand so the opcode doesn't need to change. Worklist.Add(GEP); CI.setOperand(0, GEP->getOperand(0)); return &CI; } // If the GEP has a single use, and the base pointer is a bitcast, and the // GEP computes a constant offset, see if we can convert these three // instructions into fewer. This typically happens with unions and other // non-type-safe code. if (TD && GEP->hasOneUse() && isa(GEP->getOperand(0)) && GEP->hasAllConstantIndices()) { // We are guaranteed to get a constant from EmitGEPOffset. ConstantInt *OffsetV = cast(EmitGEPOffset(GEP)); int64_t Offset = OffsetV->getSExtValue(); // Get the base pointer input of the bitcast, and the type it points to. Value *OrigBase = cast(GEP->getOperand(0))->getOperand(0); Type *GEPIdxTy = cast(OrigBase->getType())->getElementType(); SmallVector NewIndices; if (FindElementAtOffset(GEPIdxTy, Offset, NewIndices)) { // If we were able to index down into an element, create the GEP // and bitcast the result. This eliminates one bitcast, potentially // two. Value *NGEP = cast(GEP)->isInBounds() ? Builder->CreateInBoundsGEP(OrigBase, NewIndices) : Builder->CreateGEP(OrigBase, NewIndices); NGEP->takeName(GEP); if (isa(CI)) return new BitCastInst(NGEP, CI.getType()); assert(isa(CI)); return new PtrToIntInst(NGEP, CI.getType()); } } } return commonCastTransforms(CI); } Instruction *InstCombiner::visitPtrToInt(PtrToIntInst &CI) { // If the destination integer type is not the intptr_t type for this target, // do a ptrtoint to intptr_t then do a trunc or zext. This allows the cast // to be exposed to other transforms. if (TD) { if (CI.getType()->getScalarSizeInBits() < TD->getPointerSizeInBits()) { Value *P = Builder->CreatePtrToInt(CI.getOperand(0), TD->getIntPtrType(CI.getContext()), "tmp"); return new TruncInst(P, CI.getType()); } if (CI.getType()->getScalarSizeInBits() > TD->getPointerSizeInBits()) { Value *P = Builder->CreatePtrToInt(CI.getOperand(0), TD->getIntPtrType(CI.getContext()), "tmp"); return new ZExtInst(P, CI.getType()); } } return commonPointerCastTransforms(CI); } /// OptimizeVectorResize - This input value (which is known to have vector type) /// is being zero extended or truncated to the specified vector type. Try to /// replace it with a shuffle (and vector/vector bitcast) if possible. /// /// The source and destination vector types may have different element types. static Instruction *OptimizeVectorResize(Value *InVal, VectorType *DestTy, InstCombiner &IC) { // We can only do this optimization if the output is a multiple of the input // element size, or the input is a multiple of the output element size. // Convert the input type to have the same element type as the output. VectorType *SrcTy = cast(InVal->getType()); if (SrcTy->getElementType() != DestTy->getElementType()) { // The input types don't need to be identical, but for now they must be the // same size. There is no specific reason we couldn't handle things like // <4 x i16> -> <4 x i32> by bitcasting to <2 x i32> but haven't gotten // there yet. if (SrcTy->getElementType()->getPrimitiveSizeInBits() != DestTy->getElementType()->getPrimitiveSizeInBits()) return 0; SrcTy = VectorType::get(DestTy->getElementType(), SrcTy->getNumElements()); InVal = IC.Builder->CreateBitCast(InVal, SrcTy); } // Now that the element types match, get the shuffle mask and RHS of the // shuffle to use, which depends on whether we're increasing or decreasing the // size of the input. SmallVector ShuffleMask; Value *V2; IntegerType *Int32Ty = Type::getInt32Ty(SrcTy->getContext()); if (SrcTy->getNumElements() > DestTy->getNumElements()) { // If we're shrinking the number of elements, just shuffle in the low // elements from the input and use undef as the second shuffle input. V2 = UndefValue::get(SrcTy); for (unsigned i = 0, e = DestTy->getNumElements(); i != e; ++i) ShuffleMask.push_back(ConstantInt::get(Int32Ty, i)); } else { // If we're increasing the number of elements, shuffle in all of the // elements from InVal and fill the rest of the result elements with zeros // from a constant zero. V2 = Constant::getNullValue(SrcTy); unsigned SrcElts = SrcTy->getNumElements(); for (unsigned i = 0, e = SrcElts; i != e; ++i) ShuffleMask.push_back(ConstantInt::get(Int32Ty, i)); // The excess elements reference the first element of the zero input. ShuffleMask.append(DestTy->getNumElements()-SrcElts, ConstantInt::get(Int32Ty, SrcElts)); } return new ShuffleVectorInst(InVal, V2, ConstantVector::get(ShuffleMask)); } static bool isMultipleOfTypeSize(unsigned Value, Type *Ty) { return Value % Ty->getPrimitiveSizeInBits() == 0; } static unsigned getTypeSizeIndex(unsigned Value, Type *Ty) { return Value / Ty->getPrimitiveSizeInBits(); } /// CollectInsertionElements - V is a value which is inserted into a vector of /// VecEltTy. Look through the value to see if we can decompose it into /// insertions into the vector. See the example in the comment for /// OptimizeIntegerToVectorInsertions for the pattern this handles. /// The type of V is always a non-zero multiple of VecEltTy's size. /// /// This returns false if the pattern can't be matched or true if it can, /// filling in Elements with the elements found here. static bool CollectInsertionElements(Value *V, unsigned ElementIndex, SmallVectorImpl &Elements, Type *VecEltTy) { // Undef values never contribute useful bits to the result. if (isa(V)) return true; // If we got down to a value of the right type, we win, try inserting into the // right element. if (V->getType() == VecEltTy) { // Inserting null doesn't actually insert any elements. if (Constant *C = dyn_cast(V)) if (C->isNullValue()) return true; // Fail if multiple elements are inserted into this slot. if (ElementIndex >= Elements.size() || Elements[ElementIndex] != 0) return false; Elements[ElementIndex] = V; return true; } if (Constant *C = dyn_cast(V)) { // Figure out the # elements this provides, and bitcast it or slice it up // as required. unsigned NumElts = getTypeSizeIndex(C->getType()->getPrimitiveSizeInBits(), VecEltTy); // If the constant is the size of a vector element, we just need to bitcast // it to the right type so it gets properly inserted. if (NumElts == 1) return CollectInsertionElements(ConstantExpr::getBitCast(C, VecEltTy), ElementIndex, Elements, VecEltTy); // Okay, this is a constant that covers multiple elements. Slice it up into // pieces and insert each element-sized piece into the vector. if (!isa(C->getType())) C = ConstantExpr::getBitCast(C, IntegerType::get(V->getContext(), C->getType()->getPrimitiveSizeInBits())); unsigned ElementSize = VecEltTy->getPrimitiveSizeInBits(); Type *ElementIntTy = IntegerType::get(C->getContext(), ElementSize); for (unsigned i = 0; i != NumElts; ++i) { Constant *Piece = ConstantExpr::getLShr(C, ConstantInt::get(C->getType(), i*ElementSize)); Piece = ConstantExpr::getTrunc(Piece, ElementIntTy); if (!CollectInsertionElements(Piece, ElementIndex+i, Elements, VecEltTy)) return false; } return true; } if (!V->hasOneUse()) return false; Instruction *I = dyn_cast(V); if (I == 0) return false; switch (I->getOpcode()) { default: return false; // Unhandled case. case Instruction::BitCast: return CollectInsertionElements(I->getOperand(0), ElementIndex, Elements, VecEltTy); case Instruction::ZExt: if (!isMultipleOfTypeSize( I->getOperand(0)->getType()->getPrimitiveSizeInBits(), VecEltTy)) return false; return CollectInsertionElements(I->getOperand(0), ElementIndex, Elements, VecEltTy); case Instruction::Or: return CollectInsertionElements(I->getOperand(0), ElementIndex, Elements, VecEltTy) && CollectInsertionElements(I->getOperand(1), ElementIndex, Elements, VecEltTy); case Instruction::Shl: { // Must be shifting by a constant that is a multiple of the element size. ConstantInt *CI = dyn_cast(I->getOperand(1)); if (CI == 0) return false; if (!isMultipleOfTypeSize(CI->getZExtValue(), VecEltTy)) return false; unsigned IndexShift = getTypeSizeIndex(CI->getZExtValue(), VecEltTy); return CollectInsertionElements(I->getOperand(0), ElementIndex+IndexShift, Elements, VecEltTy); } } } /// OptimizeIntegerToVectorInsertions - If the input is an 'or' instruction, we /// may be doing shifts and ors to assemble the elements of the vector manually. /// Try to rip the code out and replace it with insertelements. This is to /// optimize code like this: /// /// %tmp37 = bitcast float %inc to i32 /// %tmp38 = zext i32 %tmp37 to i64 /// %tmp31 = bitcast float %inc5 to i32 /// %tmp32 = zext i32 %tmp31 to i64 /// %tmp33 = shl i64 %tmp32, 32 /// %ins35 = or i64 %tmp33, %tmp38 /// %tmp43 = bitcast i64 %ins35 to <2 x float> /// /// Into two insertelements that do "buildvector{%inc, %inc5}". static Value *OptimizeIntegerToVectorInsertions(BitCastInst &CI, InstCombiner &IC) { VectorType *DestVecTy = cast(CI.getType()); Value *IntInput = CI.getOperand(0); SmallVector Elements(DestVecTy->getNumElements()); if (!CollectInsertionElements(IntInput, 0, Elements, DestVecTy->getElementType())) return 0; // If we succeeded, we know that all of the element are specified by Elements // or are zero if Elements has a null entry. Recast this as a set of // insertions. Value *Result = Constant::getNullValue(CI.getType()); for (unsigned i = 0, e = Elements.size(); i != e; ++i) { if (Elements[i] == 0) continue; // Unset element. Result = IC.Builder->CreateInsertElement(Result, Elements[i], IC.Builder->getInt32(i)); } return Result; } /// OptimizeIntToFloatBitCast - See if we can optimize an integer->float/double /// bitcast. The various long double bitcasts can't get in here. static Instruction *OptimizeIntToFloatBitCast(BitCastInst &CI,InstCombiner &IC){ Value *Src = CI.getOperand(0); Type *DestTy = CI.getType(); // If this is a bitcast from int to float, check to see if the int is an // extraction from a vector. Value *VecInput = 0; // bitcast(trunc(bitcast(somevector))) if (match(Src, m_Trunc(m_BitCast(m_Value(VecInput)))) && isa(VecInput->getType())) { VectorType *VecTy = cast(VecInput->getType()); unsigned DestWidth = DestTy->getPrimitiveSizeInBits(); if (VecTy->getPrimitiveSizeInBits() % DestWidth == 0) { // If the element type of the vector doesn't match the result type, // bitcast it to be a vector type we can extract from. if (VecTy->getElementType() != DestTy) { VecTy = VectorType::get(DestTy, VecTy->getPrimitiveSizeInBits() / DestWidth); VecInput = IC.Builder->CreateBitCast(VecInput, VecTy); } return ExtractElementInst::Create(VecInput, IC.Builder->getInt32(0)); } } // bitcast(trunc(lshr(bitcast(somevector), cst)) ConstantInt *ShAmt = 0; if (match(Src, m_Trunc(m_LShr(m_BitCast(m_Value(VecInput)), m_ConstantInt(ShAmt)))) && isa(VecInput->getType())) { VectorType *VecTy = cast(VecInput->getType()); unsigned DestWidth = DestTy->getPrimitiveSizeInBits(); if (VecTy->getPrimitiveSizeInBits() % DestWidth == 0 && ShAmt->getZExtValue() % DestWidth == 0) { // If the element type of the vector doesn't match the result type, // bitcast it to be a vector type we can extract from. if (VecTy->getElementType() != DestTy) { VecTy = VectorType::get(DestTy, VecTy->getPrimitiveSizeInBits() / DestWidth); VecInput = IC.Builder->CreateBitCast(VecInput, VecTy); } unsigned Elt = ShAmt->getZExtValue() / DestWidth; return ExtractElementInst::Create(VecInput, IC.Builder->getInt32(Elt)); } } return 0; } Instruction *InstCombiner::visitBitCast(BitCastInst &CI) { // If the operands are integer typed then apply the integer transforms, // otherwise just apply the common ones. Value *Src = CI.getOperand(0); Type *SrcTy = Src->getType(); Type *DestTy = CI.getType(); // Get rid of casts from one type to the same type. These are useless and can // be replaced by the operand. if (DestTy == Src->getType()) return ReplaceInstUsesWith(CI, Src); if (PointerType *DstPTy = dyn_cast(DestTy)) { PointerType *SrcPTy = cast(SrcTy); Type *DstElTy = DstPTy->getElementType(); Type *SrcElTy = SrcPTy->getElementType(); // If the address spaces don't match, don't eliminate the bitcast, which is // required for changing types. if (SrcPTy->getAddressSpace() != DstPTy->getAddressSpace()) return 0; // If we are casting a alloca to a pointer to a type of the same // size, rewrite the allocation instruction to allocate the "right" type. // There is no need to modify malloc calls because it is their bitcast that // needs to be cleaned up. if (AllocaInst *AI = dyn_cast(Src)) if (Instruction *V = PromoteCastOfAllocation(CI, *AI)) return V; // If the source and destination are pointers, and this cast is equivalent // to a getelementptr X, 0, 0, 0... turn it into the appropriate gep. // This can enhance SROA and other transforms that want type-safe pointers. Constant *ZeroUInt = Constant::getNullValue(Type::getInt32Ty(CI.getContext())); unsigned NumZeros = 0; while (SrcElTy != DstElTy && isa(SrcElTy) && !SrcElTy->isPointerTy() && SrcElTy->getNumContainedTypes() /* not "{}" */) { SrcElTy = cast(SrcElTy)->getTypeAtIndex(ZeroUInt); ++NumZeros; } // If we found a path from the src to dest, create the getelementptr now. if (SrcElTy == DstElTy) { SmallVector Idxs(NumZeros+1, ZeroUInt); return GetElementPtrInst::CreateInBounds(Src, Idxs); } } // Try to optimize int -> float bitcasts. if ((DestTy->isFloatTy() || DestTy->isDoubleTy()) && isa(SrcTy)) if (Instruction *I = OptimizeIntToFloatBitCast(CI, *this)) return I; if (VectorType *DestVTy = dyn_cast(DestTy)) { if (DestVTy->getNumElements() == 1 && !SrcTy->isVectorTy()) { Value *Elem = Builder->CreateBitCast(Src, DestVTy->getElementType()); return InsertElementInst::Create(UndefValue::get(DestTy), Elem, Constant::getNullValue(Type::getInt32Ty(CI.getContext()))); // FIXME: Canonicalize bitcast(insertelement) -> insertelement(bitcast) } if (isa(SrcTy)) { // If this is a cast from an integer to vector, check to see if the input // is a trunc or zext of a bitcast from vector. If so, we can replace all // the casts with a shuffle and (potentially) a bitcast. if (isa(Src) || isa(Src)) { CastInst *SrcCast = cast(Src); if (BitCastInst *BCIn = dyn_cast(SrcCast->getOperand(0))) if (isa(BCIn->getOperand(0)->getType())) if (Instruction *I = OptimizeVectorResize(BCIn->getOperand(0), cast(DestTy), *this)) return I; } // If the input is an 'or' instruction, we may be doing shifts and ors to // assemble the elements of the vector manually. Try to rip the code out // and replace it with insertelements. if (Value *V = OptimizeIntegerToVectorInsertions(CI, *this)) return ReplaceInstUsesWith(CI, V); } } if (VectorType *SrcVTy = dyn_cast(SrcTy)) { if (SrcVTy->getNumElements() == 1 && !DestTy->isVectorTy()) { Value *Elem = Builder->CreateExtractElement(Src, Constant::getNullValue(Type::getInt32Ty(CI.getContext()))); return CastInst::Create(Instruction::BitCast, Elem, DestTy); } } if (ShuffleVectorInst *SVI = dyn_cast(Src)) { // Okay, we have (bitcast (shuffle ..)). Check to see if this is // a bitcast to a vector with the same # elts. if (SVI->hasOneUse() && DestTy->isVectorTy() && cast(DestTy)->getNumElements() == SVI->getType()->getNumElements() && SVI->getType()->getNumElements() == cast(SVI->getOperand(0)->getType())->getNumElements()) { BitCastInst *Tmp; // If either of the operands is a cast from CI.getType(), then // evaluating the shuffle in the casted destination's type will allow // us to eliminate at least one cast. if (((Tmp = dyn_cast(SVI->getOperand(0))) && Tmp->getOperand(0)->getType() == DestTy) || ((Tmp = dyn_cast(SVI->getOperand(1))) && Tmp->getOperand(0)->getType() == DestTy)) { Value *LHS = Builder->CreateBitCast(SVI->getOperand(0), DestTy); Value *RHS = Builder->CreateBitCast(SVI->getOperand(1), DestTy); // Return a new shuffle vector. Use the same element ID's, as we // know the vector types match #elts. return new ShuffleVectorInst(LHS, RHS, SVI->getOperand(2)); } } } if (SrcTy->isPointerTy()) return commonPointerCastTransforms(CI); return commonCastTransforms(CI); }