//===- InstCombineCompares.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 visitICmp and visitFCmp functions. // //===----------------------------------------------------------------------===// #include "InstCombine.h" #include "llvm/IntrinsicInst.h" #include "llvm/Analysis/InstructionSimplify.h" #include "llvm/Analysis/MemoryBuiltins.h" #include "llvm/Target/TargetData.h" #include "llvm/Support/ConstantRange.h" #include "llvm/Support/GetElementPtrTypeIterator.h" #include "llvm/Support/PatternMatch.h" using namespace llvm; using namespace PatternMatch; static ConstantInt *getOne(Constant *C) { return ConstantInt::get(cast(C->getType()), 1); } /// AddOne - Add one to a ConstantInt static Constant *AddOne(Constant *C) { return ConstantExpr::getAdd(C, ConstantInt::get(C->getType(), 1)); } /// SubOne - Subtract one from a ConstantInt static Constant *SubOne(Constant *C) { return ConstantExpr::getSub(C, ConstantInt::get(C->getType(), 1)); } static ConstantInt *ExtractElement(Constant *V, Constant *Idx) { return cast(ConstantExpr::getExtractElement(V, Idx)); } static bool HasAddOverflow(ConstantInt *Result, ConstantInt *In1, ConstantInt *In2, bool IsSigned) { if (IsSigned) if (In2->getValue().isNegative()) return Result->getValue().sgt(In1->getValue()); else return Result->getValue().slt(In1->getValue()); else return Result->getValue().ult(In1->getValue()); } /// AddWithOverflow - Compute Result = In1+In2, returning true if the result /// overflowed for this type. static bool AddWithOverflow(Constant *&Result, Constant *In1, Constant *In2, bool IsSigned = false) { Result = ConstantExpr::getAdd(In1, In2); if (const VectorType *VTy = dyn_cast(In1->getType())) { for (unsigned i = 0, e = VTy->getNumElements(); i != e; ++i) { Constant *Idx = ConstantInt::get(Type::getInt32Ty(In1->getContext()), i); if (HasAddOverflow(ExtractElement(Result, Idx), ExtractElement(In1, Idx), ExtractElement(In2, Idx), IsSigned)) return true; } return false; } return HasAddOverflow(cast(Result), cast(In1), cast(In2), IsSigned); } static bool HasSubOverflow(ConstantInt *Result, ConstantInt *In1, ConstantInt *In2, bool IsSigned) { if (IsSigned) if (In2->getValue().isNegative()) return Result->getValue().slt(In1->getValue()); else return Result->getValue().sgt(In1->getValue()); else return Result->getValue().ugt(In1->getValue()); } /// SubWithOverflow - Compute Result = In1-In2, returning true if the result /// overflowed for this type. static bool SubWithOverflow(Constant *&Result, Constant *In1, Constant *In2, bool IsSigned = false) { Result = ConstantExpr::getSub(In1, In2); if (const VectorType *VTy = dyn_cast(In1->getType())) { for (unsigned i = 0, e = VTy->getNumElements(); i != e; ++i) { Constant *Idx = ConstantInt::get(Type::getInt32Ty(In1->getContext()), i); if (HasSubOverflow(ExtractElement(Result, Idx), ExtractElement(In1, Idx), ExtractElement(In2, Idx), IsSigned)) return true; } return false; } return HasSubOverflow(cast(Result), cast(In1), cast(In2), IsSigned); } /// isSignBitCheck - Given an exploded icmp instruction, return true if the /// comparison only checks the sign bit. If it only checks the sign bit, set /// TrueIfSigned if the result of the comparison is true when the input value is /// signed. static bool isSignBitCheck(ICmpInst::Predicate pred, ConstantInt *RHS, bool &TrueIfSigned) { switch (pred) { case ICmpInst::ICMP_SLT: // True if LHS s< 0 TrueIfSigned = true; return RHS->isZero(); case ICmpInst::ICMP_SLE: // True if LHS s<= RHS and RHS == -1 TrueIfSigned = true; return RHS->isAllOnesValue(); case ICmpInst::ICMP_SGT: // True if LHS s> -1 TrueIfSigned = false; return RHS->isAllOnesValue(); case ICmpInst::ICMP_UGT: // True if LHS u> RHS and RHS == high-bit-mask - 1 TrueIfSigned = true; return RHS->getValue() == APInt::getSignedMaxValue(RHS->getType()->getPrimitiveSizeInBits()); case ICmpInst::ICMP_UGE: // True if LHS u>= RHS and RHS == high-bit-mask (2^7, 2^15, 2^31, etc) TrueIfSigned = true; return RHS->getValue().isSignBit(); default: return false; } } // isHighOnes - Return true if the constant is of the form 1+0+. // This is the same as lowones(~X). static bool isHighOnes(const ConstantInt *CI) { return (~CI->getValue() + 1).isPowerOf2(); } /// ComputeSignedMinMaxValuesFromKnownBits - Given a signed integer type and a /// set of known zero and one bits, compute the maximum and minimum values that /// could have the specified known zero and known one bits, returning them in /// min/max. static void ComputeSignedMinMaxValuesFromKnownBits(const APInt& KnownZero, const APInt& KnownOne, APInt& Min, APInt& Max) { assert(KnownZero.getBitWidth() == KnownOne.getBitWidth() && KnownZero.getBitWidth() == Min.getBitWidth() && KnownZero.getBitWidth() == Max.getBitWidth() && "KnownZero, KnownOne and Min, Max must have equal bitwidth."); APInt UnknownBits = ~(KnownZero|KnownOne); // The minimum value is when all unknown bits are zeros, EXCEPT for the sign // bit if it is unknown. Min = KnownOne; Max = KnownOne|UnknownBits; if (UnknownBits.isNegative()) { // Sign bit is unknown Min.setBit(Min.getBitWidth()-1); Max.clearBit(Max.getBitWidth()-1); } } // ComputeUnsignedMinMaxValuesFromKnownBits - Given an unsigned integer type and // a set of known zero and one bits, compute the maximum and minimum values that // could have the specified known zero and known one bits, returning them in // min/max. static void ComputeUnsignedMinMaxValuesFromKnownBits(const APInt &KnownZero, const APInt &KnownOne, APInt &Min, APInt &Max) { assert(KnownZero.getBitWidth() == KnownOne.getBitWidth() && KnownZero.getBitWidth() == Min.getBitWidth() && KnownZero.getBitWidth() == Max.getBitWidth() && "Ty, KnownZero, KnownOne and Min, Max must have equal bitwidth."); APInt UnknownBits = ~(KnownZero|KnownOne); // The minimum value is when the unknown bits are all zeros. Min = KnownOne; // The maximum value is when the unknown bits are all ones. Max = KnownOne|UnknownBits; } /// FoldCmpLoadFromIndexedGlobal - Called we see this pattern: /// cmp pred (load (gep GV, ...)), cmpcst /// where GV is a global variable with a constant initializer. Try to simplify /// this into some simple computation that does not need the load. For example /// we can optimize "icmp eq (load (gep "foo", 0, i)), 0" into "icmp eq i, 3". /// /// If AndCst is non-null, then the loaded value is masked with that constant /// before doing the comparison. This handles cases like "A[i]&4 == 0". Instruction *InstCombiner:: FoldCmpLoadFromIndexedGlobal(GetElementPtrInst *GEP, GlobalVariable *GV, CmpInst &ICI, ConstantInt *AndCst) { // We need TD information to know the pointer size unless this is inbounds. if (!GEP->isInBounds() && TD == 0) return 0; ConstantArray *Init = dyn_cast(GV->getInitializer()); if (Init == 0 || Init->getNumOperands() > 1024) return 0; // There are many forms of this optimization we can handle, for now, just do // the simple index into a single-dimensional array. // // Require: GEP GV, 0, i {{, constant indices}} if (GEP->getNumOperands() < 3 || !isa(GEP->getOperand(1)) || !cast(GEP->getOperand(1))->isZero() || isa(GEP->getOperand(2))) return 0; // Check that indices after the variable are constants and in-range for the // type they index. Collect the indices. This is typically for arrays of // structs. SmallVector LaterIndices; const Type *EltTy = cast(Init->getType())->getElementType(); for (unsigned i = 3, e = GEP->getNumOperands(); i != e; ++i) { ConstantInt *Idx = dyn_cast(GEP->getOperand(i)); if (Idx == 0) return 0; // Variable index. uint64_t IdxVal = Idx->getZExtValue(); if ((unsigned)IdxVal != IdxVal) return 0; // Too large array index. if (const StructType *STy = dyn_cast(EltTy)) EltTy = STy->getElementType(IdxVal); else if (const ArrayType *ATy = dyn_cast(EltTy)) { if (IdxVal >= ATy->getNumElements()) return 0; EltTy = ATy->getElementType(); } else { return 0; // Unknown type. } LaterIndices.push_back(IdxVal); } enum { Overdefined = -3, Undefined = -2 }; // Variables for our state machines. // FirstTrueElement/SecondTrueElement - Used to emit a comparison of the form // "i == 47 | i == 87", where 47 is the first index the condition is true for, // and 87 is the second (and last) index. FirstTrueElement is -2 when // undefined, otherwise set to the first true element. SecondTrueElement is // -2 when undefined, -3 when overdefined and >= 0 when that index is true. int FirstTrueElement = Undefined, SecondTrueElement = Undefined; // FirstFalseElement/SecondFalseElement - Used to emit a comparison of the // form "i != 47 & i != 87". Same state transitions as for true elements. int FirstFalseElement = Undefined, SecondFalseElement = Undefined; /// TrueRangeEnd/FalseRangeEnd - In conjunction with First*Element, these /// define a state machine that triggers for ranges of values that the index /// is true or false for. This triggers on things like "abbbbc"[i] == 'b'. /// This is -2 when undefined, -3 when overdefined, and otherwise the last /// index in the range (inclusive). We use -2 for undefined here because we /// use relative comparisons and don't want 0-1 to match -1. int TrueRangeEnd = Undefined, FalseRangeEnd = Undefined; // MagicBitvector - This is a magic bitvector where we set a bit if the // comparison is true for element 'i'. If there are 64 elements or less in // the array, this will fully represent all the comparison results. uint64_t MagicBitvector = 0; // Scan the array and see if one of our patterns matches. Constant *CompareRHS = cast(ICI.getOperand(1)); for (unsigned i = 0, e = Init->getNumOperands(); i != e; ++i) { Constant *Elt = Init->getOperand(i); // If this is indexing an array of structures, get the structure element. if (!LaterIndices.empty()) Elt = ConstantExpr::getExtractValue(Elt, LaterIndices.data(), LaterIndices.size()); // If the element is masked, handle it. if (AndCst) Elt = ConstantExpr::getAnd(Elt, AndCst); // Find out if the comparison would be true or false for the i'th element. Constant *C = ConstantFoldCompareInstOperands(ICI.getPredicate(), Elt, CompareRHS, TD); // If the result is undef for this element, ignore it. if (isa(C)) { // Extend range state machines to cover this element in case there is an // undef in the middle of the range. if (TrueRangeEnd == (int)i-1) TrueRangeEnd = i; if (FalseRangeEnd == (int)i-1) FalseRangeEnd = i; continue; } // If we can't compute the result for any of the elements, we have to give // up evaluating the entire conditional. if (!isa(C)) return 0; // Otherwise, we know if the comparison is true or false for this element, // update our state machines. bool IsTrueForElt = !cast(C)->isZero(); // State machine for single/double/range index comparison. if (IsTrueForElt) { // Update the TrueElement state machine. if (FirstTrueElement == Undefined) FirstTrueElement = TrueRangeEnd = i; // First true element. else { // Update double-compare state machine. if (SecondTrueElement == Undefined) SecondTrueElement = i; else SecondTrueElement = Overdefined; // Update range state machine. if (TrueRangeEnd == (int)i-1) TrueRangeEnd = i; else TrueRangeEnd = Overdefined; } } else { // Update the FalseElement state machine. if (FirstFalseElement == Undefined) FirstFalseElement = FalseRangeEnd = i; // First false element. else { // Update double-compare state machine. if (SecondFalseElement == Undefined) SecondFalseElement = i; else SecondFalseElement = Overdefined; // Update range state machine. if (FalseRangeEnd == (int)i-1) FalseRangeEnd = i; else FalseRangeEnd = Overdefined; } } // If this element is in range, update our magic bitvector. if (i < 64 && IsTrueForElt) MagicBitvector |= 1ULL << i; // If all of our states become overdefined, bail out early. Since the // predicate is expensive, only check it every 8 elements. This is only // really useful for really huge arrays. if ((i & 8) == 0 && i >= 64 && SecondTrueElement == Overdefined && SecondFalseElement == Overdefined && TrueRangeEnd == Overdefined && FalseRangeEnd == Overdefined) return 0; } // Now that we've scanned the entire array, emit our new comparison(s). We // order the state machines in complexity of the generated code. Value *Idx = GEP->getOperand(2); // If the index is larger than the pointer size of the target, truncate the // index down like the GEP would do implicitly. We don't have to do this for // an inbounds GEP because the index can't be out of range. if (!GEP->isInBounds() && Idx->getType()->getPrimitiveSizeInBits() > TD->getPointerSizeInBits()) Idx = Builder->CreateTrunc(Idx, TD->getIntPtrType(Idx->getContext())); // If the comparison is only true for one or two elements, emit direct // comparisons. if (SecondTrueElement != Overdefined) { // None true -> false. if (FirstTrueElement == Undefined) return ReplaceInstUsesWith(ICI, ConstantInt::getFalse(GEP->getContext())); Value *FirstTrueIdx = ConstantInt::get(Idx->getType(), FirstTrueElement); // True for one element -> 'i == 47'. if (SecondTrueElement == Undefined) return new ICmpInst(ICmpInst::ICMP_EQ, Idx, FirstTrueIdx); // True for two elements -> 'i == 47 | i == 72'. Value *C1 = Builder->CreateICmpEQ(Idx, FirstTrueIdx); Value *SecondTrueIdx = ConstantInt::get(Idx->getType(), SecondTrueElement); Value *C2 = Builder->CreateICmpEQ(Idx, SecondTrueIdx); return BinaryOperator::CreateOr(C1, C2); } // If the comparison is only false for one or two elements, emit direct // comparisons. if (SecondFalseElement != Overdefined) { // None false -> true. if (FirstFalseElement == Undefined) return ReplaceInstUsesWith(ICI, ConstantInt::getTrue(GEP->getContext())); Value *FirstFalseIdx = ConstantInt::get(Idx->getType(), FirstFalseElement); // False for one element -> 'i != 47'. if (SecondFalseElement == Undefined) return new ICmpInst(ICmpInst::ICMP_NE, Idx, FirstFalseIdx); // False for two elements -> 'i != 47 & i != 72'. Value *C1 = Builder->CreateICmpNE(Idx, FirstFalseIdx); Value *SecondFalseIdx = ConstantInt::get(Idx->getType(),SecondFalseElement); Value *C2 = Builder->CreateICmpNE(Idx, SecondFalseIdx); return BinaryOperator::CreateAnd(C1, C2); } // If the comparison can be replaced with a range comparison for the elements // where it is true, emit the range check. if (TrueRangeEnd != Overdefined) { assert(TrueRangeEnd != FirstTrueElement && "Should emit single compare"); // Generate (i-FirstTrue) getType(), -FirstTrueElement); Idx = Builder->CreateAdd(Idx, Offs); } Value *End = ConstantInt::get(Idx->getType(), TrueRangeEnd-FirstTrueElement+1); return new ICmpInst(ICmpInst::ICMP_ULT, Idx, End); } // False range check. if (FalseRangeEnd != Overdefined) { assert(FalseRangeEnd != FirstFalseElement && "Should emit single compare"); // Generate (i-FirstFalse) >u (FalseRangeEnd-FirstFalse). if (FirstFalseElement) { Value *Offs = ConstantInt::get(Idx->getType(), -FirstFalseElement); Idx = Builder->CreateAdd(Idx, Offs); } Value *End = ConstantInt::get(Idx->getType(), FalseRangeEnd-FirstFalseElement); return new ICmpInst(ICmpInst::ICMP_UGT, Idx, End); } // If a 32-bit or 64-bit magic bitvector captures the entire comparison state // of this load, replace it with computation that does: // ((magic_cst >> i) & 1) != 0 if (Init->getNumOperands() <= 32 || (TD && Init->getNumOperands() <= 64 && TD->isLegalInteger(64))) { const Type *Ty; if (Init->getNumOperands() <= 32) Ty = Type::getInt32Ty(Init->getContext()); else Ty = Type::getInt64Ty(Init->getContext()); Value *V = Builder->CreateIntCast(Idx, Ty, false); V = Builder->CreateLShr(ConstantInt::get(Ty, MagicBitvector), V); V = Builder->CreateAnd(ConstantInt::get(Ty, 1), V); return new ICmpInst(ICmpInst::ICMP_NE, V, ConstantInt::get(Ty, 0)); } return 0; } /// EvaluateGEPOffsetExpression - Return a value that can be used to compare /// the *offset* implied by a GEP to zero. For example, if we have &A[i], we /// want to return 'i' for "icmp ne i, 0". Note that, in general, indices can /// be complex, and scales are involved. The above expression would also be /// legal to codegen as "icmp ne (i*4), 0" (assuming A is a pointer to i32). /// This later form is less amenable to optimization though, and we are allowed /// to generate the first by knowing that pointer arithmetic doesn't overflow. /// /// If we can't emit an optimized form for this expression, this returns null. /// static Value *EvaluateGEPOffsetExpression(User *GEP, Instruction &I, InstCombiner &IC) { TargetData &TD = *IC.getTargetData(); gep_type_iterator GTI = gep_type_begin(GEP); // Check to see if this gep only has a single variable index. If so, and if // any constant indices are a multiple of its scale, then we can compute this // in terms of the scale of the variable index. For example, if the GEP // implies an offset of "12 + i*4", then we can codegen this as "3 + i", // because the expression will cross zero at the same point. unsigned i, e = GEP->getNumOperands(); int64_t Offset = 0; for (i = 1; i != e; ++i, ++GTI) { if (ConstantInt *CI = dyn_cast(GEP->getOperand(i))) { // Compute the aggregate offset of constant indices. if (CI->isZero()) continue; // Handle a struct index, which adds its field offset to the pointer. if (const StructType *STy = dyn_cast(*GTI)) { Offset += TD.getStructLayout(STy)->getElementOffset(CI->getZExtValue()); } else { uint64_t Size = TD.getTypeAllocSize(GTI.getIndexedType()); Offset += Size*CI->getSExtValue(); } } else { // Found our variable index. break; } } // If there are no variable indices, we must have a constant offset, just // evaluate it the general way. if (i == e) return 0; Value *VariableIdx = GEP->getOperand(i); // Determine the scale factor of the variable element. For example, this is // 4 if the variable index is into an array of i32. uint64_t VariableScale = TD.getTypeAllocSize(GTI.getIndexedType()); // Verify that there are no other variable indices. If so, emit the hard way. for (++i, ++GTI; i != e; ++i, ++GTI) { ConstantInt *CI = dyn_cast(GEP->getOperand(i)); if (!CI) return 0; // Compute the aggregate offset of constant indices. if (CI->isZero()) continue; // Handle a struct index, which adds its field offset to the pointer. if (const StructType *STy = dyn_cast(*GTI)) { Offset += TD.getStructLayout(STy)->getElementOffset(CI->getZExtValue()); } else { uint64_t Size = TD.getTypeAllocSize(GTI.getIndexedType()); Offset += Size*CI->getSExtValue(); } } // Okay, we know we have a single variable index, which must be a // pointer/array/vector index. If there is no offset, life is simple, return // the index. unsigned IntPtrWidth = TD.getPointerSizeInBits(); if (Offset == 0) { // Cast to intptrty in case a truncation occurs. If an extension is needed, // we don't need to bother extending: the extension won't affect where the // computation crosses zero. if (VariableIdx->getType()->getPrimitiveSizeInBits() > IntPtrWidth) VariableIdx = new TruncInst(VariableIdx, TD.getIntPtrType(VariableIdx->getContext()), VariableIdx->getName(), &I); return VariableIdx; } // Otherwise, there is an index. The computation we will do will be modulo // the pointer size, so get it. uint64_t PtrSizeMask = ~0ULL >> (64-IntPtrWidth); Offset &= PtrSizeMask; VariableScale &= PtrSizeMask; // To do this transformation, any constant index must be a multiple of the // variable scale factor. For example, we can evaluate "12 + 4*i" as "3 + i", // but we can't evaluate "10 + 3*i" in terms of i. Check that the offset is a // multiple of the variable scale. int64_t NewOffs = Offset / (int64_t)VariableScale; if (Offset != NewOffs*(int64_t)VariableScale) return 0; // Okay, we can do this evaluation. Start by converting the index to intptr. const Type *IntPtrTy = TD.getIntPtrType(VariableIdx->getContext()); if (VariableIdx->getType() != IntPtrTy) VariableIdx = CastInst::CreateIntegerCast(VariableIdx, IntPtrTy, true /*SExt*/, VariableIdx->getName(), &I); Constant *OffsetVal = ConstantInt::get(IntPtrTy, NewOffs); return BinaryOperator::CreateAdd(VariableIdx, OffsetVal, "offset", &I); } /// FoldGEPICmp - Fold comparisons between a GEP instruction and something /// else. At this point we know that the GEP is on the LHS of the comparison. Instruction *InstCombiner::FoldGEPICmp(GEPOperator *GEPLHS, Value *RHS, ICmpInst::Predicate Cond, Instruction &I) { // Look through bitcasts. if (BitCastInst *BCI = dyn_cast(RHS)) RHS = BCI->getOperand(0); Value *PtrBase = GEPLHS->getOperand(0); if (TD && PtrBase == RHS && GEPLHS->isInBounds()) { // ((gep Ptr, OFFSET) cmp Ptr) ---> (OFFSET cmp 0). // This transformation (ignoring the base and scales) is valid because we // know pointers can't overflow since the gep is inbounds. See if we can // output an optimized form. Value *Offset = EvaluateGEPOffsetExpression(GEPLHS, I, *this); // If not, synthesize the offset the hard way. if (Offset == 0) Offset = EmitGEPOffset(GEPLHS); return new ICmpInst(ICmpInst::getSignedPredicate(Cond), Offset, Constant::getNullValue(Offset->getType())); } else if (GEPOperator *GEPRHS = dyn_cast(RHS)) { // If the base pointers are different, but the indices are the same, just // compare the base pointer. if (PtrBase != GEPRHS->getOperand(0)) { bool IndicesTheSame = GEPLHS->getNumOperands()==GEPRHS->getNumOperands(); IndicesTheSame &= GEPLHS->getOperand(0)->getType() == GEPRHS->getOperand(0)->getType(); if (IndicesTheSame) for (unsigned i = 1, e = GEPLHS->getNumOperands(); i != e; ++i) if (GEPLHS->getOperand(i) != GEPRHS->getOperand(i)) { IndicesTheSame = false; break; } // If all indices are the same, just compare the base pointers. if (IndicesTheSame) return new ICmpInst(ICmpInst::getSignedPredicate(Cond), GEPLHS->getOperand(0), GEPRHS->getOperand(0)); // Otherwise, the base pointers are different and the indices are // different, bail out. return 0; } // If one of the GEPs has all zero indices, recurse. bool AllZeros = true; for (unsigned i = 1, e = GEPLHS->getNumOperands(); i != e; ++i) if (!isa(GEPLHS->getOperand(i)) || !cast(GEPLHS->getOperand(i))->isNullValue()) { AllZeros = false; break; } if (AllZeros) return FoldGEPICmp(GEPRHS, GEPLHS->getOperand(0), ICmpInst::getSwappedPredicate(Cond), I); // If the other GEP has all zero indices, recurse. AllZeros = true; for (unsigned i = 1, e = GEPRHS->getNumOperands(); i != e; ++i) if (!isa(GEPRHS->getOperand(i)) || !cast(GEPRHS->getOperand(i))->isNullValue()) { AllZeros = false; break; } if (AllZeros) return FoldGEPICmp(GEPLHS, GEPRHS->getOperand(0), Cond, I); if (GEPLHS->getNumOperands() == GEPRHS->getNumOperands()) { // If the GEPs only differ by one index, compare it. unsigned NumDifferences = 0; // Keep track of # differences. unsigned DiffOperand = 0; // The operand that differs. for (unsigned i = 1, e = GEPRHS->getNumOperands(); i != e; ++i) if (GEPLHS->getOperand(i) != GEPRHS->getOperand(i)) { if (GEPLHS->getOperand(i)->getType()->getPrimitiveSizeInBits() != GEPRHS->getOperand(i)->getType()->getPrimitiveSizeInBits()) { // Irreconcilable differences. NumDifferences = 2; break; } else { if (NumDifferences++) break; DiffOperand = i; } } if (NumDifferences == 0) // SAME GEP? return ReplaceInstUsesWith(I, // No comparison is needed here. ConstantInt::get(Type::getInt1Ty(I.getContext()), ICmpInst::isTrueWhenEqual(Cond))); else if (NumDifferences == 1) { Value *LHSV = GEPLHS->getOperand(DiffOperand); Value *RHSV = GEPRHS->getOperand(DiffOperand); // Make sure we do a signed comparison here. return new ICmpInst(ICmpInst::getSignedPredicate(Cond), LHSV, RHSV); } } // Only lower this if the icmp is the only user of the GEP or if we expect // the result to fold to a constant! if (TD && (isa(GEPLHS) || GEPLHS->hasOneUse()) && (isa(GEPRHS) || GEPRHS->hasOneUse())) { // ((gep Ptr, OFFSET1) cmp (gep Ptr, OFFSET2) ---> (OFFSET1 cmp OFFSET2) Value *L = EmitGEPOffset(GEPLHS); Value *R = EmitGEPOffset(GEPRHS); return new ICmpInst(ICmpInst::getSignedPredicate(Cond), L, R); } } return 0; } /// FoldICmpAddOpCst - Fold "icmp pred (X+CI), X". Instruction *InstCombiner::FoldICmpAddOpCst(ICmpInst &ICI, Value *X, ConstantInt *CI, ICmpInst::Predicate Pred, Value *TheAdd) { // If we have X+0, exit early (simplifying logic below) and let it get folded // elsewhere. icmp X+0, X -> icmp X, X if (CI->isZero()) { bool isTrue = ICmpInst::isTrueWhenEqual(Pred); return ReplaceInstUsesWith(ICI, ConstantInt::get(ICI.getType(), isTrue)); } // (X+4) == X -> false. if (Pred == ICmpInst::ICMP_EQ) return ReplaceInstUsesWith(ICI, ConstantInt::getFalse(X->getContext())); // (X+4) != X -> true. if (Pred == ICmpInst::ICMP_NE) return ReplaceInstUsesWith(ICI, ConstantInt::getTrue(X->getContext())); // From this point on, we know that (X+C <= X) --> (X+C < X) because C != 0, // so the values can never be equal. Similiarly for all other "or equals" // operators. // (X+1) X >u (MAXUINT-1) --> X == 255 // (X+2) X >u (MAXUINT-2) --> X > 253 // (X+MAXUINT) X >u (MAXUINT-MAXUINT) --> X != 0 if (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_ULE) { Value *R = ConstantExpr::getSub(ConstantInt::getAllOnesValue(CI->getType()), CI); return new ICmpInst(ICmpInst::ICMP_UGT, X, R); } // (X+1) >u X --> X X != 255 // (X+2) >u X --> X X u X --> X X X == 0 if (Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_UGE) return new ICmpInst(ICmpInst::ICMP_ULT, X, ConstantExpr::getNeg(CI)); unsigned BitWidth = CI->getType()->getPrimitiveSizeInBits(); ConstantInt *SMax = ConstantInt::get(X->getContext(), APInt::getSignedMaxValue(BitWidth)); // (X+ 1) X >s (MAXSINT-1) --> X == 127 // (X+ 2) X >s (MAXSINT-2) --> X >s 125 // (X+MAXSINT) X >s (MAXSINT-MAXSINT) --> X >s 0 // (X+MINSINT) X >s (MAXSINT-MINSINT) --> X >s -1 // (X+ -2) X >s (MAXSINT- -2) --> X >s 126 // (X+ -1) X >s (MAXSINT- -1) --> X != 127 if (Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_SLE) return new ICmpInst(ICmpInst::ICMP_SGT, X, ConstantExpr::getSub(SMax, CI)); // (X+ 1) >s X --> X X != 127 // (X+ 2) >s X --> X X s X --> X X s X --> X X s X --> X X s X --> X X == -128 assert(Pred == ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_SGE); Constant *C = ConstantInt::get(X->getContext(), CI->getValue()-1); return new ICmpInst(ICmpInst::ICMP_SLT, X, ConstantExpr::getSub(SMax, C)); } /// FoldICmpDivCst - Fold "icmp pred, ([su]div X, DivRHS), CmpRHS" where DivRHS /// and CmpRHS are both known to be integer constants. Instruction *InstCombiner::FoldICmpDivCst(ICmpInst &ICI, BinaryOperator *DivI, ConstantInt *DivRHS) { ConstantInt *CmpRHS = cast(ICI.getOperand(1)); const APInt &CmpRHSV = CmpRHS->getValue(); // FIXME: If the operand types don't match the type of the divide // then don't attempt this transform. The code below doesn't have the // logic to deal with a signed divide and an unsigned compare (and // vice versa). This is because (x /s C1) getOpcode() == Instruction::SDiv; if (!ICI.isEquality() && DivIsSigned != ICI.isSigned()) return 0; if (DivRHS->isZero()) return 0; // The ProdOV computation fails on divide by zero. if (DivIsSigned && DivRHS->isAllOnesValue()) return 0; // The overflow computation also screws up here if (DivRHS->isOne()) { // This eliminates some funny cases with INT_MIN. ICI.setOperand(0, DivI->getOperand(0)); // X/1 == X. return &ICI; } // Compute Prod = CI * DivRHS. We are essentially solving an equation // of form X/C1=C2. We solve for X by multiplying C1 (DivRHS) and // C2 (CI). By solving for X we can turn this into a range check // instead of computing a divide. Constant *Prod = ConstantExpr::getMul(CmpRHS, DivRHS); // Determine if the product overflows by seeing if the product is // not equal to the divide. Make sure we do the same kind of divide // as in the LHS instruction that we're folding. bool ProdOV = (DivIsSigned ? ConstantExpr::getSDiv(Prod, DivRHS) : ConstantExpr::getUDiv(Prod, DivRHS)) != CmpRHS; // Get the ICmp opcode ICmpInst::Predicate Pred = ICI.getPredicate(); /// If the division is known to be exact, then there is no remainder from the /// divide, so the covered range size is unit, otherwise it is the divisor. ConstantInt *RangeSize = DivI->isExact() ? getOne(Prod) : DivRHS; // Figure out the interval that is being checked. For example, a comparison // like "X /u 5 == 0" is really checking that X is in the interval [0, 5). // Compute this interval based on the constants involved and the signedness of // the compare/divide. This computes a half-open interval, keeping track of // whether either value in the interval overflows. After analysis each // overflow variable is set to 0 if it's corresponding bound variable is valid // -1 if overflowed off the bottom end, or +1 if overflowed off the top end. int LoOverflow = 0, HiOverflow = 0; Constant *LoBound = 0, *HiBound = 0; if (!DivIsSigned) { // udiv // e.g. X/5 op 3 --> [15, 20) LoBound = Prod; HiOverflow = LoOverflow = ProdOV; if (!HiOverflow) { // If this is not an exact divide, then many values in the range collapse // to the same result value. HiOverflow = AddWithOverflow(HiBound, LoBound, RangeSize, false); } } else if (DivRHS->getValue().isStrictlyPositive()) { // Divisor is > 0. if (CmpRHSV == 0) { // (X / pos) op 0 // Can't overflow. e.g. X/2 op 0 --> [-1, 2) LoBound = ConstantExpr::getNeg(SubOne(RangeSize)); HiBound = RangeSize; } else if (CmpRHSV.isStrictlyPositive()) { // (X / pos) op pos LoBound = Prod; // e.g. X/5 op 3 --> [15, 20) HiOverflow = LoOverflow = ProdOV; if (!HiOverflow) HiOverflow = AddWithOverflow(HiBound, Prod, RangeSize, true); } else { // (X / pos) op neg // e.g. X/5 op -3 --> [-15-4, -15+1) --> [-19, -14) HiBound = AddOne(Prod); LoOverflow = HiOverflow = ProdOV ? -1 : 0; if (!LoOverflow) { ConstantInt *DivNeg =cast(ConstantExpr::getNeg(RangeSize)); LoOverflow = AddWithOverflow(LoBound, HiBound, DivNeg, true) ? -1 : 0; } } } else if (DivRHS->getValue().isNegative()) { // Divisor is < 0. if (DivI->isExact()) RangeSize = cast(ConstantExpr::getNeg(RangeSize)); if (CmpRHSV == 0) { // (X / neg) op 0 // e.g. X/-5 op 0 --> [-4, 5) LoBound = AddOne(RangeSize); HiBound = cast(ConstantExpr::getNeg(RangeSize)); if (HiBound == DivRHS) { // -INTMIN = INTMIN HiOverflow = 1; // [INTMIN+1, overflow) HiBound = 0; // e.g. X/INTMIN = 0 --> X > INTMIN } } else if (CmpRHSV.isStrictlyPositive()) { // (X / neg) op pos // e.g. X/-5 op 3 --> [-19, -14) HiBound = AddOne(Prod); HiOverflow = LoOverflow = ProdOV ? -1 : 0; if (!LoOverflow) LoOverflow = AddWithOverflow(LoBound, HiBound, RangeSize, true) ? -1:0; } else { // (X / neg) op neg LoBound = Prod; // e.g. X/-5 op -3 --> [15, 20) LoOverflow = HiOverflow = ProdOV; if (!HiOverflow) HiOverflow = SubWithOverflow(HiBound, Prod, RangeSize, true); } // Dividing by a negative swaps the condition. LT <-> GT Pred = ICmpInst::getSwappedPredicate(Pred); } Value *X = DivI->getOperand(0); switch (Pred) { default: llvm_unreachable("Unhandled icmp opcode!"); case ICmpInst::ICMP_EQ: if (LoOverflow && HiOverflow) return ReplaceInstUsesWith(ICI, ConstantInt::getFalse(ICI.getContext())); if (HiOverflow) return new ICmpInst(DivIsSigned ? ICmpInst::ICMP_SGE : ICmpInst::ICMP_UGE, X, LoBound); if (LoOverflow) return new ICmpInst(DivIsSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT, X, HiBound); return ReplaceInstUsesWith(ICI, InsertRangeTest(X, LoBound, HiBound, DivIsSigned, true)); case ICmpInst::ICMP_NE: if (LoOverflow && HiOverflow) return ReplaceInstUsesWith(ICI, ConstantInt::getTrue(ICI.getContext())); if (HiOverflow) return new ICmpInst(DivIsSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT, X, LoBound); if (LoOverflow) return new ICmpInst(DivIsSigned ? ICmpInst::ICMP_SGE : ICmpInst::ICMP_UGE, X, HiBound); return ReplaceInstUsesWith(ICI, InsertRangeTest(X, LoBound, HiBound, DivIsSigned, false)); case ICmpInst::ICMP_ULT: case ICmpInst::ICMP_SLT: if (LoOverflow == +1) // Low bound is greater than input range. return ReplaceInstUsesWith(ICI, ConstantInt::getTrue(ICI.getContext())); if (LoOverflow == -1) // Low bound is less than input range. return ReplaceInstUsesWith(ICI, ConstantInt::getFalse(ICI.getContext())); return new ICmpInst(Pred, X, LoBound); case ICmpInst::ICMP_UGT: case ICmpInst::ICMP_SGT: if (HiOverflow == +1) // High bound greater than input range. return ReplaceInstUsesWith(ICI, ConstantInt::getFalse(ICI.getContext())); if (HiOverflow == -1) // High bound less than input range. return ReplaceInstUsesWith(ICI, ConstantInt::getTrue(ICI.getContext())); if (Pred == ICmpInst::ICMP_UGT) return new ICmpInst(ICmpInst::ICMP_UGE, X, HiBound); return new ICmpInst(ICmpInst::ICMP_SGE, X, HiBound); } } /// FoldICmpShrCst - Handle "icmp(([al]shr X, cst1), cst2)". Instruction *InstCombiner::FoldICmpShrCst(ICmpInst &ICI, BinaryOperator *Shr, ConstantInt *ShAmt) { const APInt &CmpRHSV = cast(ICI.getOperand(1))->getValue(); // Check that the shift amount is in range. If not, don't perform // undefined shifts. When the shift is visited it will be // simplified. uint32_t TypeBits = CmpRHSV.getBitWidth(); uint32_t ShAmtVal = (uint32_t)ShAmt->getLimitedValue(TypeBits); if (ShAmtVal >= TypeBits || ShAmtVal == 0) return 0; if (!ICI.isEquality()) { // If we have an unsigned comparison and an ashr, we can't simplify this. // Similarly for signed comparisons with lshr. if (ICI.isSigned() != (Shr->getOpcode() == Instruction::AShr)) return 0; // Otherwise, all lshr and all exact ashr's are equivalent to a udiv/sdiv by // a power of 2. Since we already have logic to simplify these, transform // to div and then simplify the resultant comparison. if (Shr->getOpcode() == Instruction::AShr && !Shr->isExact()) return 0; // Revisit the shift (to delete it). Worklist.Add(Shr); Constant *DivCst = ConstantInt::get(Shr->getType(), APInt::getOneBitSet(TypeBits, ShAmtVal)); Value *Tmp = Shr->getOpcode() == Instruction::AShr ? Builder->CreateSDiv(Shr->getOperand(0), DivCst, "", Shr->isExact()) : Builder->CreateUDiv(Shr->getOperand(0), DivCst, "", Shr->isExact()); ICI.setOperand(0, Tmp); // If the builder folded the binop, just return it. BinaryOperator *TheDiv = dyn_cast(Tmp); if (TheDiv == 0) return &ICI; // Otherwise, fold this div/compare. assert(TheDiv->getOpcode() == Instruction::SDiv || TheDiv->getOpcode() == Instruction::UDiv); Instruction *Res = FoldICmpDivCst(ICI, TheDiv, cast(DivCst)); assert(Res && "This div/cst should have folded!"); return Res; } // If we are comparing against bits always shifted out, the // comparison cannot succeed. APInt Comp = CmpRHSV << ShAmtVal; ConstantInt *ShiftedCmpRHS = ConstantInt::get(ICI.getContext(), Comp); if (Shr->getOpcode() == Instruction::LShr) Comp = Comp.lshr(ShAmtVal); else Comp = Comp.ashr(ShAmtVal); if (Comp != CmpRHSV) { // Comparing against a bit that we know is zero. bool IsICMP_NE = ICI.getPredicate() == ICmpInst::ICMP_NE; Constant *Cst = ConstantInt::get(Type::getInt1Ty(ICI.getContext()), IsICMP_NE); return ReplaceInstUsesWith(ICI, Cst); } // Otherwise, check to see if the bits shifted out are known to be zero. // If so, we can compare against the unshifted value: // (X & 4) >> 1 == 2 --> (X & 4) == 4. if (Shr->hasOneUse() && Shr->isExact()) return new ICmpInst(ICI.getPredicate(), Shr->getOperand(0), ShiftedCmpRHS); if (Shr->hasOneUse()) { // Otherwise strength reduce the shift into an and. APInt Val(APInt::getHighBitsSet(TypeBits, TypeBits - ShAmtVal)); Constant *Mask = ConstantInt::get(ICI.getContext(), Val); Value *And = Builder->CreateAnd(Shr->getOperand(0), Mask, Shr->getName()+".mask"); return new ICmpInst(ICI.getPredicate(), And, ShiftedCmpRHS); } return 0; } /// visitICmpInstWithInstAndIntCst - Handle "icmp (instr, intcst)". /// Instruction *InstCombiner::visitICmpInstWithInstAndIntCst(ICmpInst &ICI, Instruction *LHSI, ConstantInt *RHS) { const APInt &RHSV = RHS->getValue(); switch (LHSI->getOpcode()) { case Instruction::Trunc: if (ICI.isEquality() && LHSI->hasOneUse()) { // Simplify icmp eq (trunc x to i8), 42 -> icmp eq x, 42|highbits if all // of the high bits truncated out of x are known. unsigned DstBits = LHSI->getType()->getPrimitiveSizeInBits(), SrcBits = LHSI->getOperand(0)->getType()->getPrimitiveSizeInBits(); APInt Mask(APInt::getHighBitsSet(SrcBits, SrcBits-DstBits)); APInt KnownZero(SrcBits, 0), KnownOne(SrcBits, 0); ComputeMaskedBits(LHSI->getOperand(0), Mask, KnownZero, KnownOne); // If all the high bits are known, we can do this xform. if ((KnownZero|KnownOne).countLeadingOnes() >= SrcBits-DstBits) { // Pull in the high bits from known-ones set. APInt NewRHS = RHS->getValue().zext(SrcBits); NewRHS |= KnownOne; return new ICmpInst(ICI.getPredicate(), LHSI->getOperand(0), ConstantInt::get(ICI.getContext(), NewRHS)); } } break; case Instruction::Xor: // (icmp pred (xor X, XorCST), CI) if (ConstantInt *XorCST = dyn_cast(LHSI->getOperand(1))) { // If this is a comparison that tests the signbit (X < 0) or (x > -1), // fold the xor. if ((ICI.getPredicate() == ICmpInst::ICMP_SLT && RHSV == 0) || (ICI.getPredicate() == ICmpInst::ICMP_SGT && RHSV.isAllOnesValue())) { Value *CompareVal = LHSI->getOperand(0); // If the sign bit of the XorCST is not set, there is no change to // the operation, just stop using the Xor. if (!XorCST->getValue().isNegative()) { ICI.setOperand(0, CompareVal); Worklist.Add(LHSI); return &ICI; } // Was the old condition true if the operand is positive? bool isTrueIfPositive = ICI.getPredicate() == ICmpInst::ICMP_SGT; // If so, the new one isn't. isTrueIfPositive ^= true; if (isTrueIfPositive) return new ICmpInst(ICmpInst::ICMP_SGT, CompareVal, SubOne(RHS)); else return new ICmpInst(ICmpInst::ICMP_SLT, CompareVal, AddOne(RHS)); } if (LHSI->hasOneUse()) { // (icmp u/s (xor A SignBit), C) -> (icmp s/u A, (xor C SignBit)) if (!ICI.isEquality() && XorCST->getValue().isSignBit()) { const APInt &SignBit = XorCST->getValue(); ICmpInst::Predicate Pred = ICI.isSigned() ? ICI.getUnsignedPredicate() : ICI.getSignedPredicate(); return new ICmpInst(Pred, LHSI->getOperand(0), ConstantInt::get(ICI.getContext(), RHSV ^ SignBit)); } // (icmp u/s (xor A ~SignBit), C) -> (icmp s/u (xor C ~SignBit), A) if (!ICI.isEquality() && XorCST->getValue().isMaxSignedValue()) { const APInt &NotSignBit = XorCST->getValue(); ICmpInst::Predicate Pred = ICI.isSigned() ? ICI.getUnsignedPredicate() : ICI.getSignedPredicate(); Pred = ICI.getSwappedPredicate(Pred); return new ICmpInst(Pred, LHSI->getOperand(0), ConstantInt::get(ICI.getContext(), RHSV ^ NotSignBit)); } } } break; case Instruction::And: // (icmp pred (and X, AndCST), RHS) if (LHSI->hasOneUse() && isa(LHSI->getOperand(1)) && LHSI->getOperand(0)->hasOneUse()) { ConstantInt *AndCST = cast(LHSI->getOperand(1)); // If the LHS is an AND of a truncating cast, we can widen the // and/compare to be the input width without changing the value // produced, eliminating a cast. if (TruncInst *Cast = dyn_cast(LHSI->getOperand(0))) { // We can do this transformation if either the AND constant does not // have its sign bit set or if it is an equality comparison. // Extending a relational comparison when we're checking the sign // bit would not work. if (Cast->hasOneUse() && (ICI.isEquality() || (AndCST->getValue().isNonNegative() && RHSV.isNonNegative()))) { uint32_t BitWidth = cast(Cast->getOperand(0)->getType())->getBitWidth(); APInt NewCST = AndCST->getValue().zext(BitWidth); APInt NewCI = RHSV.zext(BitWidth); Value *NewAnd = Builder->CreateAnd(Cast->getOperand(0), ConstantInt::get(ICI.getContext(), NewCST), LHSI->getName()); return new ICmpInst(ICI.getPredicate(), NewAnd, ConstantInt::get(ICI.getContext(), NewCI)); } } // If this is: (X >> C1) & C2 != C3 (where any shift and any compare // could exist), turn it into (X & (C2 << C1)) != (C3 << C1). This // happens a LOT in code produced by the C front-end, for bitfield // access. BinaryOperator *Shift = dyn_cast(LHSI->getOperand(0)); if (Shift && !Shift->isShift()) Shift = 0; ConstantInt *ShAmt; ShAmt = Shift ? dyn_cast(Shift->getOperand(1)) : 0; const Type *Ty = Shift ? Shift->getType() : 0; // Type of the shift. const Type *AndTy = AndCST->getType(); // Type of the and. // We can fold this as long as we can't shift unknown bits // into the mask. This can only happen with signed shift // rights, as they sign-extend. if (ShAmt) { bool CanFold = Shift->isLogicalShift(); if (!CanFold) { // To test for the bad case of the signed shr, see if any // of the bits shifted in could be tested after the mask. uint32_t TyBits = Ty->getPrimitiveSizeInBits(); int ShAmtVal = TyBits - ShAmt->getLimitedValue(TyBits); uint32_t BitWidth = AndTy->getPrimitiveSizeInBits(); if ((APInt::getHighBitsSet(BitWidth, BitWidth-ShAmtVal) & AndCST->getValue()) == 0) CanFold = true; } if (CanFold) { Constant *NewCst; if (Shift->getOpcode() == Instruction::Shl) NewCst = ConstantExpr::getLShr(RHS, ShAmt); else NewCst = ConstantExpr::getShl(RHS, ShAmt); // Check to see if we are shifting out any of the bits being // compared. if (ConstantExpr::get(Shift->getOpcode(), NewCst, ShAmt) != RHS) { // If we shifted bits out, the fold is not going to work out. // As a special case, check to see if this means that the // result is always true or false now. if (ICI.getPredicate() == ICmpInst::ICMP_EQ) return ReplaceInstUsesWith(ICI, ConstantInt::getFalse(ICI.getContext())); if (ICI.getPredicate() == ICmpInst::ICMP_NE) return ReplaceInstUsesWith(ICI, ConstantInt::getTrue(ICI.getContext())); } else { ICI.setOperand(1, NewCst); Constant *NewAndCST; if (Shift->getOpcode() == Instruction::Shl) NewAndCST = ConstantExpr::getLShr(AndCST, ShAmt); else NewAndCST = ConstantExpr::getShl(AndCST, ShAmt); LHSI->setOperand(1, NewAndCST); LHSI->setOperand(0, Shift->getOperand(0)); Worklist.Add(Shift); // Shift is dead. return &ICI; } } } // Turn ((X >> Y) & C) == 0 into (X & (C << Y)) == 0. The later is // preferable because it allows the C<hasOneUse() && RHSV == 0 && ICI.isEquality() && !Shift->isArithmeticShift() && !isa(Shift->getOperand(0))) { // Compute C << Y. Value *NS; if (Shift->getOpcode() == Instruction::LShr) { NS = Builder->CreateShl(AndCST, Shift->getOperand(1), "tmp"); } else { // Insert a logical shift. NS = Builder->CreateLShr(AndCST, Shift->getOperand(1), "tmp"); } // Compute X & (C << Y). Value *NewAnd = Builder->CreateAnd(Shift->getOperand(0), NS, LHSI->getName()); ICI.setOperand(0, NewAnd); return &ICI; } } // Try to optimize things like "A[i]&42 == 0" to index computations. if (LoadInst *LI = dyn_cast(LHSI->getOperand(0))) { if (GetElementPtrInst *GEP = dyn_cast(LI->getOperand(0))) if (GlobalVariable *GV = dyn_cast(GEP->getOperand(0))) if (GV->isConstant() && GV->hasDefinitiveInitializer() && !LI->isVolatile() && isa(LHSI->getOperand(1))) { ConstantInt *C = cast(LHSI->getOperand(1)); if (Instruction *Res = FoldCmpLoadFromIndexedGlobal(GEP, GV,ICI, C)) return Res; } } break; case Instruction::Or: { if (!ICI.isEquality() || !RHS->isNullValue() || !LHSI->hasOneUse()) break; Value *P, *Q; if (match(LHSI, m_Or(m_PtrToInt(m_Value(P)), m_PtrToInt(m_Value(Q))))) { // Simplify icmp eq (or (ptrtoint P), (ptrtoint Q)), 0 // -> and (icmp eq P, null), (icmp eq Q, null). Value *ICIP = Builder->CreateICmp(ICI.getPredicate(), P, Constant::getNullValue(P->getType())); Value *ICIQ = Builder->CreateICmp(ICI.getPredicate(), Q, Constant::getNullValue(Q->getType())); Instruction *Op; if (ICI.getPredicate() == ICmpInst::ICMP_EQ) Op = BinaryOperator::CreateAnd(ICIP, ICIQ); else Op = BinaryOperator::CreateOr(ICIP, ICIQ); return Op; } break; } case Instruction::Shl: { // (icmp pred (shl X, ShAmt), CI) ConstantInt *ShAmt = dyn_cast(LHSI->getOperand(1)); if (!ShAmt) break; uint32_t TypeBits = RHSV.getBitWidth(); // Check that the shift amount is in range. If not, don't perform // undefined shifts. When the shift is visited it will be // simplified. if (ShAmt->uge(TypeBits)) break; if (ICI.isEquality()) { // If we are comparing against bits always shifted out, the // comparison cannot succeed. Constant *Comp = ConstantExpr::getShl(ConstantExpr::getLShr(RHS, ShAmt), ShAmt); if (Comp != RHS) {// Comparing against a bit that we know is zero. bool IsICMP_NE = ICI.getPredicate() == ICmpInst::ICMP_NE; Constant *Cst = ConstantInt::get(Type::getInt1Ty(ICI.getContext()), IsICMP_NE); return ReplaceInstUsesWith(ICI, Cst); } // If the shift is NUW, then it is just shifting out zeros, no need for an // AND. if (cast(LHSI)->hasNoUnsignedWrap()) return new ICmpInst(ICI.getPredicate(), LHSI->getOperand(0), ConstantExpr::getLShr(RHS, ShAmt)); if (LHSI->hasOneUse()) { // Otherwise strength reduce the shift into an and. uint32_t ShAmtVal = (uint32_t)ShAmt->getLimitedValue(TypeBits); Constant *Mask = ConstantInt::get(ICI.getContext(), APInt::getLowBitsSet(TypeBits, TypeBits-ShAmtVal)); Value *And = Builder->CreateAnd(LHSI->getOperand(0),Mask, LHSI->getName()+".mask"); return new ICmpInst(ICI.getPredicate(), And, ConstantExpr::getLShr(RHS, ShAmt)); } } // Otherwise, if this is a comparison of the sign bit, simplify to and/test. bool TrueIfSigned = false; if (LHSI->hasOneUse() && isSignBitCheck(ICI.getPredicate(), RHS, TrueIfSigned)) { // (X << 31) (X&1) != 0 Constant *Mask = ConstantInt::get(LHSI->getOperand(0)->getType(), APInt::getOneBitSet(TypeBits, TypeBits-ShAmt->getZExtValue()-1)); Value *And = Builder->CreateAnd(LHSI->getOperand(0), Mask, LHSI->getName()+".mask"); return new ICmpInst(TrueIfSigned ? ICmpInst::ICMP_NE : ICmpInst::ICMP_EQ, And, Constant::getNullValue(And->getType())); } break; } case Instruction::LShr: // (icmp pred (shr X, ShAmt), CI) case Instruction::AShr: { // Handle equality comparisons of shift-by-constant. BinaryOperator *BO = cast(LHSI); if (ConstantInt *ShAmt = dyn_cast(LHSI->getOperand(1))) { if (Instruction *Res = FoldICmpShrCst(ICI, BO, ShAmt)) return Res; } // Handle exact shr's. if (ICI.isEquality() && BO->isExact() && BO->hasOneUse()) { if (RHSV.isMinValue()) return new ICmpInst(ICI.getPredicate(), BO->getOperand(0), RHS); } break; } case Instruction::SDiv: case Instruction::UDiv: // Fold: icmp pred ([us]div X, C1), C2 -> range test // Fold this div into the comparison, producing a range check. // Determine, based on the divide type, what the range is being // checked. If there is an overflow on the low or high side, remember // it, otherwise compute the range [low, hi) bounding the new value. // See: InsertRangeTest above for the kinds of replacements possible. if (ConstantInt *DivRHS = dyn_cast(LHSI->getOperand(1))) if (Instruction *R = FoldICmpDivCst(ICI, cast(LHSI), DivRHS)) return R; break; case Instruction::Add: // Fold: icmp pred (add X, C1), C2 if (!ICI.isEquality()) { ConstantInt *LHSC = dyn_cast(LHSI->getOperand(1)); if (!LHSC) break; const APInt &LHSV = LHSC->getValue(); ConstantRange CR = ICI.makeConstantRange(ICI.getPredicate(), RHSV) .subtract(LHSV); if (ICI.isSigned()) { if (CR.getLower().isSignBit()) { return new ICmpInst(ICmpInst::ICMP_SLT, LHSI->getOperand(0), ConstantInt::get(ICI.getContext(),CR.getUpper())); } else if (CR.getUpper().isSignBit()) { return new ICmpInst(ICmpInst::ICMP_SGE, LHSI->getOperand(0), ConstantInt::get(ICI.getContext(),CR.getLower())); } } else { if (CR.getLower().isMinValue()) { return new ICmpInst(ICmpInst::ICMP_ULT, LHSI->getOperand(0), ConstantInt::get(ICI.getContext(),CR.getUpper())); } else if (CR.getUpper().isMinValue()) { return new ICmpInst(ICmpInst::ICMP_UGE, LHSI->getOperand(0), ConstantInt::get(ICI.getContext(),CR.getLower())); } } } break; } // Simplify icmp_eq and icmp_ne instructions with integer constant RHS. if (ICI.isEquality()) { bool isICMP_NE = ICI.getPredicate() == ICmpInst::ICMP_NE; // If the first operand is (add|sub|and|or|xor|rem) with a constant, and // the second operand is a constant, simplify a bit. if (BinaryOperator *BO = dyn_cast(LHSI)) { switch (BO->getOpcode()) { case Instruction::SRem: // If we have a signed (X % (2^c)) == 0, turn it into an unsigned one. if (RHSV == 0 && isa(BO->getOperand(1)) &&BO->hasOneUse()){ const APInt &V = cast(BO->getOperand(1))->getValue(); if (V.sgt(1) && V.isPowerOf2()) { Value *NewRem = Builder->CreateURem(BO->getOperand(0), BO->getOperand(1), BO->getName()); return new ICmpInst(ICI.getPredicate(), NewRem, Constant::getNullValue(BO->getType())); } } break; case Instruction::Add: // Replace ((add A, B) != C) with (A != C-B) if B & C are constants. if (ConstantInt *BOp1C = dyn_cast(BO->getOperand(1))) { if (BO->hasOneUse()) return new ICmpInst(ICI.getPredicate(), BO->getOperand(0), ConstantExpr::getSub(RHS, BOp1C)); } else if (RHSV == 0) { // Replace ((add A, B) != 0) with (A != -B) if A or B is // efficiently invertible, or if the add has just this one use. Value *BOp0 = BO->getOperand(0), *BOp1 = BO->getOperand(1); if (Value *NegVal = dyn_castNegVal(BOp1)) return new ICmpInst(ICI.getPredicate(), BOp0, NegVal); else if (Value *NegVal = dyn_castNegVal(BOp0)) return new ICmpInst(ICI.getPredicate(), NegVal, BOp1); else if (BO->hasOneUse()) { Value *Neg = Builder->CreateNeg(BOp1); Neg->takeName(BO); return new ICmpInst(ICI.getPredicate(), BOp0, Neg); } } break; case Instruction::Xor: // For the xor case, we can xor two constants together, eliminating // the explicit xor. if (Constant *BOC = dyn_cast(BO->getOperand(1))) return new ICmpInst(ICI.getPredicate(), BO->getOperand(0), ConstantExpr::getXor(RHS, BOC)); // FALLTHROUGH case Instruction::Sub: // Replace (([sub|xor] A, B) != 0) with (A != B) if (RHSV == 0) return new ICmpInst(ICI.getPredicate(), BO->getOperand(0), BO->getOperand(1)); break; case Instruction::Or: // If bits are being or'd in that are not present in the constant we // are comparing against, then the comparison could never succeed! if (ConstantInt *BOC = dyn_cast(BO->getOperand(1))) { Constant *NotCI = ConstantExpr::getNot(RHS); if (!ConstantExpr::getAnd(BOC, NotCI)->isNullValue()) return ReplaceInstUsesWith(ICI, ConstantInt::get(Type::getInt1Ty(ICI.getContext()), isICMP_NE)); } break; case Instruction::And: if (ConstantInt *BOC = dyn_cast(BO->getOperand(1))) { // If bits are being compared against that are and'd out, then the // comparison can never succeed! if ((RHSV & ~BOC->getValue()) != 0) return ReplaceInstUsesWith(ICI, ConstantInt::get(Type::getInt1Ty(ICI.getContext()), isICMP_NE)); // If we have ((X & C) == C), turn it into ((X & C) != 0). if (RHS == BOC && RHSV.isPowerOf2()) return new ICmpInst(isICMP_NE ? ICmpInst::ICMP_EQ : ICmpInst::ICMP_NE, LHSI, Constant::getNullValue(RHS->getType())); // Replace (and X, (1 << size(X)-1) != 0) with x s< 0 if (BOC->getValue().isSignBit()) { Value *X = BO->getOperand(0); Constant *Zero = Constant::getNullValue(X->getType()); ICmpInst::Predicate pred = isICMP_NE ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_SGE; return new ICmpInst(pred, X, Zero); } // ((X & ~7) == 0) --> X < 8 if (RHSV == 0 && isHighOnes(BOC)) { Value *X = BO->getOperand(0); Constant *NegX = ConstantExpr::getNeg(BOC); ICmpInst::Predicate pred = isICMP_NE ? ICmpInst::ICMP_UGE : ICmpInst::ICMP_ULT; return new ICmpInst(pred, X, NegX); } } default: break; } } else if (IntrinsicInst *II = dyn_cast(LHSI)) { // Handle icmp {eq|ne} , intcst. switch (II->getIntrinsicID()) { case Intrinsic::bswap: Worklist.Add(II); ICI.setOperand(0, II->getArgOperand(0)); ICI.setOperand(1, ConstantInt::get(II->getContext(), RHSV.byteSwap())); return &ICI; case Intrinsic::ctlz: case Intrinsic::cttz: // ctz(A) == bitwidth(a) -> A == 0 and likewise for != if (RHSV == RHS->getType()->getBitWidth()) { Worklist.Add(II); ICI.setOperand(0, II->getArgOperand(0)); ICI.setOperand(1, ConstantInt::get(RHS->getType(), 0)); return &ICI; } break; case Intrinsic::ctpop: // popcount(A) == 0 -> A == 0 and likewise for != if (RHS->isZero()) { Worklist.Add(II); ICI.setOperand(0, II->getArgOperand(0)); ICI.setOperand(1, RHS); return &ICI; } break; default: break; } } } return 0; } /// visitICmpInstWithCastAndCast - Handle icmp (cast x to y), (cast/cst). /// We only handle extending casts so far. /// Instruction *InstCombiner::visitICmpInstWithCastAndCast(ICmpInst &ICI) { const CastInst *LHSCI = cast(ICI.getOperand(0)); Value *LHSCIOp = LHSCI->getOperand(0); const Type *SrcTy = LHSCIOp->getType(); const Type *DestTy = LHSCI->getType(); Value *RHSCIOp; // Turn icmp (ptrtoint x), (ptrtoint/c) into a compare of the input if the // integer type is the same size as the pointer type. if (TD && LHSCI->getOpcode() == Instruction::PtrToInt && TD->getPointerSizeInBits() == cast(DestTy)->getBitWidth()) { Value *RHSOp = 0; if (Constant *RHSC = dyn_cast(ICI.getOperand(1))) { RHSOp = ConstantExpr::getIntToPtr(RHSC, SrcTy); } else if (PtrToIntInst *RHSC = dyn_cast(ICI.getOperand(1))) { RHSOp = RHSC->getOperand(0); // If the pointer types don't match, insert a bitcast. if (LHSCIOp->getType() != RHSOp->getType()) RHSOp = Builder->CreateBitCast(RHSOp, LHSCIOp->getType()); } if (RHSOp) return new ICmpInst(ICI.getPredicate(), LHSCIOp, RHSOp); } // The code below only handles extension cast instructions, so far. // Enforce this. if (LHSCI->getOpcode() != Instruction::ZExt && LHSCI->getOpcode() != Instruction::SExt) return 0; bool isSignedExt = LHSCI->getOpcode() == Instruction::SExt; bool isSignedCmp = ICI.isSigned(); if (CastInst *CI = dyn_cast(ICI.getOperand(1))) { // Not an extension from the same type? RHSCIOp = CI->getOperand(0); if (RHSCIOp->getType() != LHSCIOp->getType()) return 0; // If the signedness of the two casts doesn't agree (i.e. one is a sext // and the other is a zext), then we can't handle this. if (CI->getOpcode() != LHSCI->getOpcode()) return 0; // Deal with equality cases early. if (ICI.isEquality()) return new ICmpInst(ICI.getPredicate(), LHSCIOp, RHSCIOp); // A signed comparison of sign extended values simplifies into a // signed comparison. if (isSignedCmp && isSignedExt) return new ICmpInst(ICI.getPredicate(), LHSCIOp, RHSCIOp); // The other three cases all fold into an unsigned comparison. return new ICmpInst(ICI.getUnsignedPredicate(), LHSCIOp, RHSCIOp); } // If we aren't dealing with a constant on the RHS, exit early ConstantInt *CI = dyn_cast(ICI.getOperand(1)); if (!CI) return 0; // Compute the constant that would happen if we truncated to SrcTy then // reextended to DestTy. Constant *Res1 = ConstantExpr::getTrunc(CI, SrcTy); Constant *Res2 = ConstantExpr::getCast(LHSCI->getOpcode(), Res1, DestTy); // If the re-extended constant didn't change... if (Res2 == CI) { // Deal with equality cases early. if (ICI.isEquality()) return new ICmpInst(ICI.getPredicate(), LHSCIOp, Res1); // A signed comparison of sign extended values simplifies into a // signed comparison. if (isSignedExt && isSignedCmp) return new ICmpInst(ICI.getPredicate(), LHSCIOp, Res1); // The other three cases all fold into an unsigned comparison. return new ICmpInst(ICI.getUnsignedPredicate(), LHSCIOp, Res1); } // The re-extended constant changed so the constant cannot be represented // in the shorter type. Consequently, we cannot emit a simple comparison. // All the cases that fold to true or false will have already been handled // by SimplifyICmpInst, so only deal with the tricky case. if (isSignedCmp || !isSignedExt) return 0; // Evaluate the comparison for LT (we invert for GT below). LE and GE cases // should have been folded away previously and not enter in here. // We're performing an unsigned comp with a sign extended value. // This is true if the input is >= 0. [aka >s -1] Constant *NegOne = Constant::getAllOnesValue(SrcTy); Value *Result = Builder->CreateICmpSGT(LHSCIOp, NegOne, ICI.getName()); // Finally, return the value computed. if (ICI.getPredicate() == ICmpInst::ICMP_ULT) return ReplaceInstUsesWith(ICI, Result); assert(ICI.getPredicate() == ICmpInst::ICMP_UGT && "ICmp should be folded!"); return BinaryOperator::CreateNot(Result); } /// ProcessUGT_ADDCST_ADD - The caller has matched a pattern of the form: /// I = icmp ugt (add (add A, B), CI2), CI1 /// If this is of the form: /// sum = a + b /// if (sum+128 >u 255) /// Then replace it with llvm.sadd.with.overflow.i8. /// static Instruction *ProcessUGT_ADDCST_ADD(ICmpInst &I, Value *A, Value *B, ConstantInt *CI2, ConstantInt *CI1, InstCombiner &IC) { // The transformation we're trying to do here is to transform this into an // llvm.sadd.with.overflow. To do this, we have to replace the original add // with a narrower add, and discard the add-with-constant that is part of the // range check (if we can't eliminate it, this isn't profitable). // In order to eliminate the add-with-constant, the compare can be its only // use. Instruction *AddWithCst = cast(I.getOperand(0)); if (!AddWithCst->hasOneUse()) return 0; // If CI2 is 2^7, 2^15, 2^31, then it might be an sadd.with.overflow. if (!CI2->getValue().isPowerOf2()) return 0; unsigned NewWidth = CI2->getValue().countTrailingZeros(); if (NewWidth != 7 && NewWidth != 15 && NewWidth != 31) return 0; // The width of the new add formed is 1 more than the bias. ++NewWidth; // Check to see that CI1 is an all-ones value with NewWidth bits. if (CI1->getBitWidth() == NewWidth || CI1->getValue() != APInt::getLowBitsSet(CI1->getBitWidth(), NewWidth)) return 0; // In order to replace the original add with a narrower // llvm.sadd.with.overflow, the only uses allowed are the add-with-constant // and truncates that discard the high bits of the add. Verify that this is // the case. Instruction *OrigAdd = cast(AddWithCst->getOperand(0)); for (Value::use_iterator UI = OrigAdd->use_begin(), E = OrigAdd->use_end(); UI != E; ++UI) { if (*UI == AddWithCst) continue; // Only accept truncates for now. We would really like a nice recursive // predicate like SimplifyDemandedBits, but which goes downwards the use-def // chain to see which bits of a value are actually demanded. If the // original add had another add which was then immediately truncated, we // could still do the transformation. TruncInst *TI = dyn_cast(*UI); if (TI == 0 || TI->getType()->getPrimitiveSizeInBits() > NewWidth) return 0; } // If the pattern matches, truncate the inputs to the narrower type and // use the sadd_with_overflow intrinsic to efficiently compute both the // result and the overflow bit. Module *M = I.getParent()->getParent()->getParent(); const Type *NewType = IntegerType::get(OrigAdd->getContext(), NewWidth); Value *F = Intrinsic::getDeclaration(M, Intrinsic::sadd_with_overflow, &NewType, 1); InstCombiner::BuilderTy *Builder = IC.Builder; // Put the new code above the original add, in case there are any uses of the // add between the add and the compare. Builder->SetInsertPoint(OrigAdd); Value *TruncA = Builder->CreateTrunc(A, NewType, A->getName()+".trunc"); Value *TruncB = Builder->CreateTrunc(B, NewType, B->getName()+".trunc"); CallInst *Call = Builder->CreateCall2(F, TruncA, TruncB, "sadd"); Value *Add = Builder->CreateExtractValue(Call, 0, "sadd.result"); Value *ZExt = Builder->CreateZExt(Add, OrigAdd->getType()); // The inner add was the result of the narrow add, zero extended to the // wider type. Replace it with the result computed by the intrinsic. IC.ReplaceInstUsesWith(*OrigAdd, ZExt); // The original icmp gets replaced with the overflow value. return ExtractValueInst::Create(Call, 1, "sadd.overflow"); } static Instruction *ProcessUAddIdiom(Instruction &I, Value *OrigAddV, InstCombiner &IC) { // Don't bother doing this transformation for pointers, don't do it for // vectors. if (!isa(OrigAddV->getType())) return 0; // If the add is a constant expr, then we don't bother transforming it. Instruction *OrigAdd = dyn_cast(OrigAddV); if (OrigAdd == 0) return 0; Value *LHS = OrigAdd->getOperand(0), *RHS = OrigAdd->getOperand(1); // Put the new code above the original add, in case there are any uses of the // add between the add and the compare. InstCombiner::BuilderTy *Builder = IC.Builder; Builder->SetInsertPoint(OrigAdd); Module *M = I.getParent()->getParent()->getParent(); const Type *Ty = LHS->getType(); Value *F = Intrinsic::getDeclaration(M, Intrinsic::uadd_with_overflow, &Ty,1); CallInst *Call = Builder->CreateCall2(F, LHS, RHS, "uadd"); Value *Add = Builder->CreateExtractValue(Call, 0); IC.ReplaceInstUsesWith(*OrigAdd, Add); // The original icmp gets replaced with the overflow value. return ExtractValueInst::Create(Call, 1, "uadd.overflow"); } // DemandedBitsLHSMask - When performing a comparison against a constant, // it is possible that not all the bits in the LHS are demanded. This helper // method computes the mask that IS demanded. static APInt DemandedBitsLHSMask(ICmpInst &I, unsigned BitWidth, bool isSignCheck) { if (isSignCheck) return APInt::getSignBit(BitWidth); ConstantInt *CI = dyn_cast(I.getOperand(1)); if (!CI) return APInt::getAllOnesValue(BitWidth); const APInt &RHS = CI->getValue(); switch (I.getPredicate()) { // For a UGT comparison, we don't care about any bits that // correspond to the trailing ones of the comparand. The value of these // bits doesn't impact the outcome of the comparison, because any value // greater than the RHS must differ in a bit higher than these due to carry. case ICmpInst::ICMP_UGT: { unsigned trailingOnes = RHS.countTrailingOnes(); APInt lowBitsSet = APInt::getLowBitsSet(BitWidth, trailingOnes); return ~lowBitsSet; } // Similarly, for a ULT comparison, we don't care about the trailing zeros. // Any value less than the RHS must differ in a higher bit because of carries. case ICmpInst::ICMP_ULT: { unsigned trailingZeros = RHS.countTrailingZeros(); APInt lowBitsSet = APInt::getLowBitsSet(BitWidth, trailingZeros); return ~lowBitsSet; } default: return APInt::getAllOnesValue(BitWidth); } } Instruction *InstCombiner::visitICmpInst(ICmpInst &I) { bool Changed = false; Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1); /// Orders the operands of the compare so that they are listed from most /// complex to least complex. This puts constants before unary operators, /// before binary operators. if (getComplexity(Op0) < getComplexity(Op1)) { I.swapOperands(); std::swap(Op0, Op1); Changed = true; } if (Value *V = SimplifyICmpInst(I.getPredicate(), Op0, Op1, TD)) return ReplaceInstUsesWith(I, V); const Type *Ty = Op0->getType(); // icmp's with boolean values can always be turned into bitwise operations if (Ty->isIntegerTy(1)) { switch (I.getPredicate()) { default: llvm_unreachable("Invalid icmp instruction!"); case ICmpInst::ICMP_EQ: { // icmp eq i1 A, B -> ~(A^B) Value *Xor = Builder->CreateXor(Op0, Op1, I.getName()+"tmp"); return BinaryOperator::CreateNot(Xor); } case ICmpInst::ICMP_NE: // icmp eq i1 A, B -> A^B return BinaryOperator::CreateXor(Op0, Op1); case ICmpInst::ICMP_UGT: std::swap(Op0, Op1); // Change icmp ugt -> icmp ult // FALL THROUGH case ICmpInst::ICMP_ULT:{ // icmp ult i1 A, B -> ~A & B Value *Not = Builder->CreateNot(Op0, I.getName()+"tmp"); return BinaryOperator::CreateAnd(Not, Op1); } case ICmpInst::ICMP_SGT: std::swap(Op0, Op1); // Change icmp sgt -> icmp slt // FALL THROUGH case ICmpInst::ICMP_SLT: { // icmp slt i1 A, B -> A & ~B Value *Not = Builder->CreateNot(Op1, I.getName()+"tmp"); return BinaryOperator::CreateAnd(Not, Op0); } case ICmpInst::ICMP_UGE: std::swap(Op0, Op1); // Change icmp uge -> icmp ule // FALL THROUGH case ICmpInst::ICMP_ULE: { // icmp ule i1 A, B -> ~A | B Value *Not = Builder->CreateNot(Op0, I.getName()+"tmp"); return BinaryOperator::CreateOr(Not, Op1); } case ICmpInst::ICMP_SGE: std::swap(Op0, Op1); // Change icmp sge -> icmp sle // FALL THROUGH case ICmpInst::ICMP_SLE: { // icmp sle i1 A, B -> A | ~B Value *Not = Builder->CreateNot(Op1, I.getName()+"tmp"); return BinaryOperator::CreateOr(Not, Op0); } } } unsigned BitWidth = 0; if (Ty->isIntOrIntVectorTy()) BitWidth = Ty->getScalarSizeInBits(); else if (TD) // Pointers require TD info to get their size. BitWidth = TD->getTypeSizeInBits(Ty->getScalarType()); bool isSignBit = false; // See if we are doing a comparison with a constant. if (ConstantInt *CI = dyn_cast(Op1)) { Value *A = 0, *B = 0; // Match the following pattern, which is a common idiom when writing // overflow-safe integer arithmetic function. The source performs an // addition in wider type, and explicitly checks for overflow using // comparisons against INT_MIN and INT_MAX. Simplify this by using the // sadd_with_overflow intrinsic. // // TODO: This could probably be generalized to handle other overflow-safe // operations if we worked out the formulas to compute the appropriate // magic constants. // // sum = a + b // if (sum+128 >u 255) ... -> llvm.sadd.with.overflow.i8 { ConstantInt *CI2; // I = icmp ugt (add (add A, B), CI2), CI if (I.getPredicate() == ICmpInst::ICMP_UGT && match(Op0, m_Add(m_Add(m_Value(A), m_Value(B)), m_ConstantInt(CI2)))) if (Instruction *Res = ProcessUGT_ADDCST_ADD(I, A, B, CI2, CI, *this)) return Res; } // (icmp ne/eq (sub A B) 0) -> (icmp ne/eq A, B) if (I.isEquality() && CI->isZero() && match(Op0, m_Sub(m_Value(A), m_Value(B)))) { // (icmp cond A B) if cond is equality return new ICmpInst(I.getPredicate(), A, B); } // If we have an icmp le or icmp ge instruction, turn it into the // appropriate icmp lt or icmp gt instruction. This allows us to rely on // them being folded in the code below. The SimplifyICmpInst code has // already handled the edge cases for us, so we just assert on them. switch (I.getPredicate()) { default: break; case ICmpInst::ICMP_ULE: assert(!CI->isMaxValue(false)); // A <=u MAX -> TRUE return new ICmpInst(ICmpInst::ICMP_ULT, Op0, ConstantInt::get(CI->getContext(), CI->getValue()+1)); case ICmpInst::ICMP_SLE: assert(!CI->isMaxValue(true)); // A <=s MAX -> TRUE return new ICmpInst(ICmpInst::ICMP_SLT, Op0, ConstantInt::get(CI->getContext(), CI->getValue()+1)); case ICmpInst::ICMP_UGE: assert(!CI->isMinValue(false)); // A >=u MIN -> TRUE return new ICmpInst(ICmpInst::ICMP_UGT, Op0, ConstantInt::get(CI->getContext(), CI->getValue()-1)); case ICmpInst::ICMP_SGE: assert(!CI->isMinValue(true)); // A >=s MIN -> TRUE return new ICmpInst(ICmpInst::ICMP_SGT, Op0, ConstantInt::get(CI->getContext(), CI->getValue()-1)); } // If this comparison is a normal comparison, it demands all // bits, if it is a sign bit comparison, it only demands the sign bit. bool UnusedBit; isSignBit = isSignBitCheck(I.getPredicate(), CI, UnusedBit); } // See if we can fold the comparison based on range information we can get // by checking whether bits are known to be zero or one in the input. if (BitWidth != 0) { APInt Op0KnownZero(BitWidth, 0), Op0KnownOne(BitWidth, 0); APInt Op1KnownZero(BitWidth, 0), Op1KnownOne(BitWidth, 0); if (SimplifyDemandedBits(I.getOperandUse(0), DemandedBitsLHSMask(I, BitWidth, isSignBit), Op0KnownZero, Op0KnownOne, 0)) return &I; if (SimplifyDemandedBits(I.getOperandUse(1), APInt::getAllOnesValue(BitWidth), Op1KnownZero, Op1KnownOne, 0)) return &I; // Given the known and unknown bits, compute a range that the LHS could be // in. Compute the Min, Max and RHS values based on the known bits. For the // EQ and NE we use unsigned values. APInt Op0Min(BitWidth, 0), Op0Max(BitWidth, 0); APInt Op1Min(BitWidth, 0), Op1Max(BitWidth, 0); if (I.isSigned()) { ComputeSignedMinMaxValuesFromKnownBits(Op0KnownZero, Op0KnownOne, Op0Min, Op0Max); ComputeSignedMinMaxValuesFromKnownBits(Op1KnownZero, Op1KnownOne, Op1Min, Op1Max); } else { ComputeUnsignedMinMaxValuesFromKnownBits(Op0KnownZero, Op0KnownOne, Op0Min, Op0Max); ComputeUnsignedMinMaxValuesFromKnownBits(Op1KnownZero, Op1KnownOne, Op1Min, Op1Max); } // If Min and Max are known to be the same, then SimplifyDemandedBits // figured out that the LHS is a constant. Just constant fold this now so // that code below can assume that Min != Max. if (!isa(Op0) && Op0Min == Op0Max) return new ICmpInst(I.getPredicate(), ConstantInt::get(Op0->getType(), Op0Min), Op1); if (!isa(Op1) && Op1Min == Op1Max) return new ICmpInst(I.getPredicate(), Op0, ConstantInt::get(Op1->getType(), Op1Min)); // Based on the range information we know about the LHS, see if we can // simplify this comparison. For example, (x&4) < 8 is always true. switch (I.getPredicate()) { default: llvm_unreachable("Unknown icmp opcode!"); case ICmpInst::ICMP_EQ: { if (Op0Max.ult(Op1Min) || Op0Min.ugt(Op1Max)) return ReplaceInstUsesWith(I, ConstantInt::getFalse(I.getType())); // If all bits are known zero except for one, then we know at most one // bit is set. If the comparison is against zero, then this is a check // to see if *that* bit is set. APInt Op0KnownZeroInverted = ~Op0KnownZero; if (~Op1KnownZero == 0 && Op0KnownZeroInverted.isPowerOf2()) { // If the LHS is an AND with the same constant, look through it. Value *LHS = 0; ConstantInt *LHSC = 0; if (!match(Op0, m_And(m_Value(LHS), m_ConstantInt(LHSC))) || LHSC->getValue() != Op0KnownZeroInverted) LHS = Op0; // If the LHS is 1 << x, and we know the result is a power of 2 like 8, // then turn "((1 << x)&8) == 0" into "x != 3". Value *X = 0; if (match(LHS, m_Shl(m_One(), m_Value(X)))) { unsigned CmpVal = Op0KnownZeroInverted.countTrailingZeros(); return new ICmpInst(ICmpInst::ICMP_NE, X, ConstantInt::get(X->getType(), CmpVal)); } // If the LHS is 8 >>u x, and we know the result is a power of 2 like 1, // then turn "((8 >>u x)&1) == 0" into "x != 3". const APInt *CI; if (Op0KnownZeroInverted == 1 && match(LHS, m_LShr(m_Power2(CI), m_Value(X)))) return new ICmpInst(ICmpInst::ICMP_NE, X, ConstantInt::get(X->getType(), CI->countTrailingZeros())); } break; } case ICmpInst::ICMP_NE: { if (Op0Max.ult(Op1Min) || Op0Min.ugt(Op1Max)) return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getType())); // If all bits are known zero except for one, then we know at most one // bit is set. If the comparison is against zero, then this is a check // to see if *that* bit is set. APInt Op0KnownZeroInverted = ~Op0KnownZero; if (~Op1KnownZero == 0 && Op0KnownZeroInverted.isPowerOf2()) { // If the LHS is an AND with the same constant, look through it. Value *LHS = 0; ConstantInt *LHSC = 0; if (!match(Op0, m_And(m_Value(LHS), m_ConstantInt(LHSC))) || LHSC->getValue() != Op0KnownZeroInverted) LHS = Op0; // If the LHS is 1 << x, and we know the result is a power of 2 like 8, // then turn "((1 << x)&8) != 0" into "x == 3". Value *X = 0; if (match(LHS, m_Shl(m_One(), m_Value(X)))) { unsigned CmpVal = Op0KnownZeroInverted.countTrailingZeros(); return new ICmpInst(ICmpInst::ICMP_EQ, X, ConstantInt::get(X->getType(), CmpVal)); } // If the LHS is 8 >>u x, and we know the result is a power of 2 like 1, // then turn "((8 >>u x)&1) != 0" into "x == 3". const APInt *CI; if (Op0KnownZeroInverted == 1 && match(LHS, m_LShr(m_Power2(CI), m_Value(X)))) return new ICmpInst(ICmpInst::ICMP_EQ, X, ConstantInt::get(X->getType(), CI->countTrailingZeros())); } break; } case ICmpInst::ICMP_ULT: if (Op0Max.ult(Op1Min)) // A true if max(A) < min(B) return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getType())); if (Op0Min.uge(Op1Max)) // A false if min(A) >= max(B) return ReplaceInstUsesWith(I, ConstantInt::getFalse(I.getType())); if (Op1Min == Op0Max) // A A != B if max(A) == min(B) return new ICmpInst(ICmpInst::ICMP_NE, Op0, Op1); if (ConstantInt *CI = dyn_cast(Op1)) { if (Op1Max == Op0Min+1) // A A == C-1 if min(A)+1 == C return new ICmpInst(ICmpInst::ICMP_EQ, Op0, ConstantInt::get(CI->getContext(), CI->getValue()-1)); // (x (x >s -1) -> true if sign bit clear if (CI->isMinValue(true)) return new ICmpInst(ICmpInst::ICMP_SGT, Op0, Constant::getAllOnesValue(Op0->getType())); } break; case ICmpInst::ICMP_UGT: if (Op0Min.ugt(Op1Max)) // A >u B -> true if min(A) > max(B) return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getType())); if (Op0Max.ule(Op1Min)) // A >u B -> false if max(A) <= max(B) return ReplaceInstUsesWith(I, ConstantInt::getFalse(I.getType())); if (Op1Max == Op0Min) // A >u B -> A != B if min(A) == max(B) return new ICmpInst(ICmpInst::ICMP_NE, Op0, Op1); if (ConstantInt *CI = dyn_cast(Op1)) { if (Op1Min == Op0Max-1) // A >u C -> A == C+1 if max(a)-1 == C return new ICmpInst(ICmpInst::ICMP_EQ, Op0, ConstantInt::get(CI->getContext(), CI->getValue()+1)); // (x >u 2147483647) -> (x true if sign bit set if (CI->isMaxValue(true)) return new ICmpInst(ICmpInst::ICMP_SLT, Op0, Constant::getNullValue(Op0->getType())); } break; case ICmpInst::ICMP_SLT: if (Op0Max.slt(Op1Min)) // A true if max(A) < min(C) return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getType())); if (Op0Min.sge(Op1Max)) // A false if min(A) >= max(C) return ReplaceInstUsesWith(I, ConstantInt::getFalse(I.getType())); if (Op1Min == Op0Max) // A A != B if max(A) == min(B) return new ICmpInst(ICmpInst::ICMP_NE, Op0, Op1); if (ConstantInt *CI = dyn_cast(Op1)) { if (Op1Max == Op0Min+1) // A A == C-1 if min(A)+1 == C return new ICmpInst(ICmpInst::ICMP_EQ, Op0, ConstantInt::get(CI->getContext(), CI->getValue()-1)); } break; case ICmpInst::ICMP_SGT: if (Op0Min.sgt(Op1Max)) // A >s B -> true if min(A) > max(B) return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getType())); if (Op0Max.sle(Op1Min)) // A >s B -> false if max(A) <= min(B) return ReplaceInstUsesWith(I, ConstantInt::getFalse(I.getType())); if (Op1Max == Op0Min) // A >s B -> A != B if min(A) == max(B) return new ICmpInst(ICmpInst::ICMP_NE, Op0, Op1); if (ConstantInt *CI = dyn_cast(Op1)) { if (Op1Min == Op0Max-1) // A >s C -> A == C+1 if max(A)-1 == C return new ICmpInst(ICmpInst::ICMP_EQ, Op0, ConstantInt::get(CI->getContext(), CI->getValue()+1)); } break; case ICmpInst::ICMP_SGE: assert(!isa(Op1) && "ICMP_SGE with ConstantInt not folded!"); if (Op0Min.sge(Op1Max)) // A >=s B -> true if min(A) >= max(B) return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getType())); if (Op0Max.slt(Op1Min)) // A >=s B -> false if max(A) < min(B) return ReplaceInstUsesWith(I, ConstantInt::getFalse(I.getType())); break; case ICmpInst::ICMP_SLE: assert(!isa(Op1) && "ICMP_SLE with ConstantInt not folded!"); if (Op0Max.sle(Op1Min)) // A <=s B -> true if max(A) <= min(B) return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getType())); if (Op0Min.sgt(Op1Max)) // A <=s B -> false if min(A) > max(B) return ReplaceInstUsesWith(I, ConstantInt::getFalse(I.getType())); break; case ICmpInst::ICMP_UGE: assert(!isa(Op1) && "ICMP_UGE with ConstantInt not folded!"); if (Op0Min.uge(Op1Max)) // A >=u B -> true if min(A) >= max(B) return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getType())); if (Op0Max.ult(Op1Min)) // A >=u B -> false if max(A) < min(B) return ReplaceInstUsesWith(I, ConstantInt::getFalse(I.getType())); break; case ICmpInst::ICMP_ULE: assert(!isa(Op1) && "ICMP_ULE with ConstantInt not folded!"); if (Op0Max.ule(Op1Min)) // A <=u B -> true if max(A) <= min(B) return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getType())); if (Op0Min.ugt(Op1Max)) // A <=u B -> false if min(A) > max(B) return ReplaceInstUsesWith(I, ConstantInt::getFalse(I.getType())); break; } // Turn a signed comparison into an unsigned one if both operands // are known to have the same sign. if (I.isSigned() && ((Op0KnownZero.isNegative() && Op1KnownZero.isNegative()) || (Op0KnownOne.isNegative() && Op1KnownOne.isNegative()))) return new ICmpInst(I.getUnsignedPredicate(), Op0, Op1); } // Test if the ICmpInst instruction is used exclusively by a select as // part of a minimum or maximum operation. If so, refrain from doing // any other folding. This helps out other analyses which understand // non-obfuscated minimum and maximum idioms, such as ScalarEvolution // and CodeGen. And in this case, at least one of the comparison // operands has at least one user besides the compare (the select), // which would often largely negate the benefit of folding anyway. if (I.hasOneUse()) if (SelectInst *SI = dyn_cast(*I.use_begin())) if ((SI->getOperand(1) == Op0 && SI->getOperand(2) == Op1) || (SI->getOperand(2) == Op0 && SI->getOperand(1) == Op1)) return 0; // See if we are doing a comparison between a constant and an instruction that // can be folded into the comparison. if (ConstantInt *CI = dyn_cast(Op1)) { // Since the RHS is a ConstantInt (CI), if the left hand side is an // instruction, see if that instruction also has constants so that the // instruction can be folded into the icmp if (Instruction *LHSI = dyn_cast(Op0)) if (Instruction *Res = visitICmpInstWithInstAndIntCst(I, LHSI, CI)) return Res; } // Handle icmp with constant (but not simple integer constant) RHS if (Constant *RHSC = dyn_cast(Op1)) { if (Instruction *LHSI = dyn_cast(Op0)) switch (LHSI->getOpcode()) { case Instruction::GetElementPtr: // icmp pred GEP (P, int 0, int 0, int 0), null -> icmp pred P, null if (RHSC->isNullValue() && cast(LHSI)->hasAllZeroIndices()) return new ICmpInst(I.getPredicate(), LHSI->getOperand(0), Constant::getNullValue(LHSI->getOperand(0)->getType())); break; case Instruction::PHI: // Only fold icmp into the PHI if the phi and icmp are in the same // block. If in the same block, we're encouraging jump threading. If // not, we are just pessimizing the code by making an i1 phi. if (LHSI->getParent() == I.getParent()) if (Instruction *NV = FoldOpIntoPhi(I)) return NV; break; case Instruction::Select: { // If either operand of the select is a constant, we can fold the // comparison into the select arms, which will cause one to be // constant folded and the select turned into a bitwise or. Value *Op1 = 0, *Op2 = 0; if (Constant *C = dyn_cast(LHSI->getOperand(1))) Op1 = ConstantExpr::getICmp(I.getPredicate(), C, RHSC); if (Constant *C = dyn_cast(LHSI->getOperand(2))) Op2 = ConstantExpr::getICmp(I.getPredicate(), C, RHSC); // We only want to perform this transformation if it will not lead to // additional code. This is true if either both sides of the select // fold to a constant (in which case the icmp is replaced with a select // which will usually simplify) or this is the only user of the // select (in which case we are trading a select+icmp for a simpler // select+icmp). if ((Op1 && Op2) || (LHSI->hasOneUse() && (Op1 || Op2))) { if (!Op1) Op1 = Builder->CreateICmp(I.getPredicate(), LHSI->getOperand(1), RHSC, I.getName()); if (!Op2) Op2 = Builder->CreateICmp(I.getPredicate(), LHSI->getOperand(2), RHSC, I.getName()); return SelectInst::Create(LHSI->getOperand(0), Op1, Op2); } break; } case Instruction::IntToPtr: // icmp pred inttoptr(X), null -> icmp pred X, 0 if (RHSC->isNullValue() && TD && TD->getIntPtrType(RHSC->getContext()) == LHSI->getOperand(0)->getType()) return new ICmpInst(I.getPredicate(), LHSI->getOperand(0), Constant::getNullValue(LHSI->getOperand(0)->getType())); break; case Instruction::Load: // Try to optimize things like "A[i] > 4" to index computations. if (GetElementPtrInst *GEP = dyn_cast(LHSI->getOperand(0))) { if (GlobalVariable *GV = dyn_cast(GEP->getOperand(0))) if (GV->isConstant() && GV->hasDefinitiveInitializer() && !cast(LHSI)->isVolatile()) if (Instruction *Res = FoldCmpLoadFromIndexedGlobal(GEP, GV, I)) return Res; } break; } } // If we can optimize a 'icmp GEP, P' or 'icmp P, GEP', do so now. if (GEPOperator *GEP = dyn_cast(Op0)) if (Instruction *NI = FoldGEPICmp(GEP, Op1, I.getPredicate(), I)) return NI; if (GEPOperator *GEP = dyn_cast(Op1)) if (Instruction *NI = FoldGEPICmp(GEP, Op0, ICmpInst::getSwappedPredicate(I.getPredicate()), I)) return NI; // Test to see if the operands of the icmp are casted versions of other // values. If the ptr->ptr cast can be stripped off both arguments, we do so // now. if (BitCastInst *CI = dyn_cast(Op0)) { if (Op0->getType()->isPointerTy() && (isa(Op1) || isa(Op1))) { // We keep moving the cast from the left operand over to the right // operand, where it can often be eliminated completely. Op0 = CI->getOperand(0); // If operand #1 is a bitcast instruction, it must also be a ptr->ptr cast // so eliminate it as well. if (BitCastInst *CI2 = dyn_cast(Op1)) Op1 = CI2->getOperand(0); // If Op1 is a constant, we can fold the cast into the constant. if (Op0->getType() != Op1->getType()) { if (Constant *Op1C = dyn_cast(Op1)) { Op1 = ConstantExpr::getBitCast(Op1C, Op0->getType()); } else { // Otherwise, cast the RHS right before the icmp Op1 = Builder->CreateBitCast(Op1, Op0->getType()); } } return new ICmpInst(I.getPredicate(), Op0, Op1); } } if (isa(Op0)) { // Handle the special case of: icmp (cast bool to X), // This comes up when you have code like // int X = A < B; // if (X) ... // For generality, we handle any zero-extension of any operand comparison // with a constant or another cast from the same type. if (isa(Op1) || isa(Op1)) if (Instruction *R = visitICmpInstWithCastAndCast(I)) return R; } // Special logic for binary operators. BinaryOperator *BO0 = dyn_cast(Op0); BinaryOperator *BO1 = dyn_cast(Op1); if (BO0 || BO1) { CmpInst::Predicate Pred = I.getPredicate(); bool NoOp0WrapProblem = false, NoOp1WrapProblem = false; if (BO0 && isa(BO0)) NoOp0WrapProblem = ICmpInst::isEquality(Pred) || (CmpInst::isUnsigned(Pred) && BO0->hasNoUnsignedWrap()) || (CmpInst::isSigned(Pred) && BO0->hasNoSignedWrap()); if (BO1 && isa(BO1)) NoOp1WrapProblem = ICmpInst::isEquality(Pred) || (CmpInst::isUnsigned(Pred) && BO1->hasNoUnsignedWrap()) || (CmpInst::isSigned(Pred) && BO1->hasNoSignedWrap()); // Analyze the case when either Op0 or Op1 is an add instruction. // Op0 = A + B (or A and B are null); Op1 = C + D (or C and D are null). Value *A = 0, *B = 0, *C = 0, *D = 0; if (BO0 && BO0->getOpcode() == Instruction::Add) A = BO0->getOperand(0), B = BO0->getOperand(1); if (BO1 && BO1->getOpcode() == Instruction::Add) C = BO1->getOperand(0), D = BO1->getOperand(1); // icmp (X+Y), X -> icmp Y, 0 for equalities or if there is no overflow. if ((A == Op1 || B == Op1) && NoOp0WrapProblem) return new ICmpInst(Pred, A == Op1 ? B : A, Constant::getNullValue(Op1->getType())); // icmp X, (X+Y) -> icmp 0, Y for equalities or if there is no overflow. if ((C == Op0 || D == Op0) && NoOp1WrapProblem) return new ICmpInst(Pred, Constant::getNullValue(Op0->getType()), C == Op0 ? D : C); // icmp (X+Y), (X+Z) -> icmp Y, Z for equalities or if there is no overflow. if (A && C && (A == C || A == D || B == C || B == D) && NoOp0WrapProblem && NoOp1WrapProblem && // Try not to increase register pressure. BO0->hasOneUse() && BO1->hasOneUse()) { // Determine Y and Z in the form icmp (X+Y), (X+Z). Value *Y = (A == C || A == D) ? B : A; Value *Z = (C == A || C == B) ? D : C; return new ICmpInst(Pred, Y, Z); } // Analyze the case when either Op0 or Op1 is a sub instruction. // Op0 = A - B (or A and B are null); Op1 = C - D (or C and D are null). A = 0; B = 0; C = 0; D = 0; if (BO0 && BO0->getOpcode() == Instruction::Sub) A = BO0->getOperand(0), B = BO0->getOperand(1); if (BO1 && BO1->getOpcode() == Instruction::Sub) C = BO1->getOperand(0), D = BO1->getOperand(1); // icmp (X-Y), X -> icmp 0, Y for equalities or if there is no overflow. if (A == Op1 && NoOp0WrapProblem) return new ICmpInst(Pred, Constant::getNullValue(Op1->getType()), B); // icmp X, (X-Y) -> icmp Y, 0 for equalities or if there is no overflow. if (C == Op0 && NoOp1WrapProblem) return new ICmpInst(Pred, D, Constant::getNullValue(Op0->getType())); // icmp (Y-X), (Z-X) -> icmp Y, Z for equalities or if there is no overflow. if (B && D && B == D && NoOp0WrapProblem && NoOp1WrapProblem && // Try not to increase register pressure. BO0->hasOneUse() && BO1->hasOneUse()) return new ICmpInst(Pred, A, C); // icmp (X-Y), (X-Z) -> icmp Z, Y for equalities or if there is no overflow. if (A && C && A == C && NoOp0WrapProblem && NoOp1WrapProblem && // Try not to increase register pressure. BO0->hasOneUse() && BO1->hasOneUse()) return new ICmpInst(Pred, D, B); BinaryOperator *SRem = NULL; // icmp (srem X, Y), Y if (BO0 && BO0->getOpcode() == Instruction::SRem && Op1 == BO0->getOperand(1)) SRem = BO0; // icmp Y, (srem X, Y) else if (BO1 && BO1->getOpcode() == Instruction::SRem && Op0 == BO1->getOperand(1)) SRem = BO1; if (SRem) { // We don't check hasOneUse to avoid increasing register pressure because // the value we use is the same value this instruction was already using. switch (SRem == BO0 ? ICmpInst::getSwappedPredicate(Pred) : Pred) { default: break; case ICmpInst::ICMP_EQ: return ReplaceInstUsesWith(I, ConstantInt::getFalse(I.getType())); case ICmpInst::ICMP_NE: return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getType())); case ICmpInst::ICMP_SGT: case ICmpInst::ICMP_SGE: return new ICmpInst(ICmpInst::ICMP_SGT, SRem->getOperand(1), Constant::getAllOnesValue(SRem->getType())); case ICmpInst::ICMP_SLT: case ICmpInst::ICMP_SLE: return new ICmpInst(ICmpInst::ICMP_SLT, SRem->getOperand(1), Constant::getNullValue(SRem->getType())); } } if (BO0 && BO1 && BO0->getOpcode() == BO1->getOpcode() && BO0->hasOneUse() && BO1->hasOneUse() && BO0->getOperand(1) == BO1->getOperand(1)) { switch (BO0->getOpcode()) { default: break; case Instruction::Add: case Instruction::Sub: case Instruction::Xor: if (I.isEquality()) // a+x icmp eq/ne b+x --> a icmp b return new ICmpInst(I.getPredicate(), BO0->getOperand(0), BO1->getOperand(0)); // icmp u/s (a ^ signbit), (b ^ signbit) --> icmp s/u a, b if (ConstantInt *CI = dyn_cast(BO0->getOperand(1))) { if (CI->getValue().isSignBit()) { ICmpInst::Predicate Pred = I.isSigned() ? I.getUnsignedPredicate() : I.getSignedPredicate(); return new ICmpInst(Pred, BO0->getOperand(0), BO1->getOperand(0)); } if (CI->getValue().isMaxSignedValue()) { ICmpInst::Predicate Pred = I.isSigned() ? I.getUnsignedPredicate() : I.getSignedPredicate(); Pred = I.getSwappedPredicate(Pred); return new ICmpInst(Pred, BO0->getOperand(0), BO1->getOperand(0)); } } break; case Instruction::Mul: if (!I.isEquality()) break; if (ConstantInt *CI = dyn_cast(BO0->getOperand(1))) { // a * Cst icmp eq/ne b * Cst --> a & Mask icmp b & Mask // Mask = -1 >> count-trailing-zeros(Cst). if (!CI->isZero() && !CI->isOne()) { const APInt &AP = CI->getValue(); ConstantInt *Mask = ConstantInt::get(I.getContext(), APInt::getLowBitsSet(AP.getBitWidth(), AP.getBitWidth() - AP.countTrailingZeros())); Value *And1 = Builder->CreateAnd(BO0->getOperand(0), Mask); Value *And2 = Builder->CreateAnd(BO1->getOperand(0), Mask); return new ICmpInst(I.getPredicate(), And1, And2); } } break; case Instruction::UDiv: case Instruction::LShr: if (I.isSigned()) break; // fall-through case Instruction::SDiv: case Instruction::AShr: if (!BO0->isExact() && !BO1->isExact()) break; return new ICmpInst(I.getPredicate(), BO0->getOperand(0), BO1->getOperand(0)); case Instruction::Shl: { bool NUW = BO0->hasNoUnsignedWrap() && BO1->hasNoUnsignedWrap(); bool NSW = BO0->hasNoSignedWrap() && BO1->hasNoSignedWrap(); if (!NUW && !NSW) break; if (!NSW && I.isSigned()) break; return new ICmpInst(I.getPredicate(), BO0->getOperand(0), BO1->getOperand(0)); } } } } { Value *A, *B; // ~x < ~y --> y < x // ~x < cst --> ~cst < x if (match(Op0, m_Not(m_Value(A)))) { if (match(Op1, m_Not(m_Value(B)))) return new ICmpInst(I.getPredicate(), B, A); if (ConstantInt *RHSC = dyn_cast(Op1)) return new ICmpInst(I.getPredicate(), ConstantExpr::getNot(RHSC), A); } // (a+b) llvm.uadd.with.overflow. // (a+b) llvm.uadd.with.overflow. if (I.getPredicate() == ICmpInst::ICMP_ULT && match(Op0, m_Add(m_Value(A), m_Value(B))) && (Op1 == A || Op1 == B)) if (Instruction *R = ProcessUAddIdiom(I, Op0, *this)) return R; // a >u (a+b) --> llvm.uadd.with.overflow. // b >u (a+b) --> llvm.uadd.with.overflow. if (I.getPredicate() == ICmpInst::ICMP_UGT && match(Op1, m_Add(m_Value(A), m_Value(B))) && (Op0 == A || Op0 == B)) if (Instruction *R = ProcessUAddIdiom(I, Op1, *this)) return R; } if (I.isEquality()) { Value *A, *B, *C, *D; if (match(Op0, m_Xor(m_Value(A), m_Value(B)))) { if (A == Op1 || B == Op1) { // (A^B) == A -> B == 0 Value *OtherVal = A == Op1 ? B : A; return new ICmpInst(I.getPredicate(), OtherVal, Constant::getNullValue(A->getType())); } if (match(Op1, m_Xor(m_Value(C), m_Value(D)))) { // A^c1 == C^c2 --> A == C^(c1^c2) ConstantInt *C1, *C2; if (match(B, m_ConstantInt(C1)) && match(D, m_ConstantInt(C2)) && Op1->hasOneUse()) { Constant *NC = ConstantInt::get(I.getContext(), C1->getValue() ^ C2->getValue()); Value *Xor = Builder->CreateXor(C, NC, "tmp"); return new ICmpInst(I.getPredicate(), A, Xor); } // A^B == A^D -> B == D if (A == C) return new ICmpInst(I.getPredicate(), B, D); if (A == D) return new ICmpInst(I.getPredicate(), B, C); if (B == C) return new ICmpInst(I.getPredicate(), A, D); if (B == D) return new ICmpInst(I.getPredicate(), A, C); } } if (match(Op1, m_Xor(m_Value(A), m_Value(B))) && (A == Op0 || B == Op0)) { // A == (A^B) -> B == 0 Value *OtherVal = A == Op0 ? B : A; return new ICmpInst(I.getPredicate(), OtherVal, Constant::getNullValue(A->getType())); } // (X&Z) == (Y&Z) -> (X^Y) & Z == 0 if (Op0->hasOneUse() && Op1->hasOneUse() && match(Op0, m_And(m_Value(A), m_Value(B))) && match(Op1, m_And(m_Value(C), m_Value(D)))) { Value *X = 0, *Y = 0, *Z = 0; if (A == C) { X = B; Y = D; Z = A; } else if (A == D) { X = B; Y = C; Z = A; } else if (B == C) { X = A; Y = D; Z = B; } else if (B == D) { X = A; Y = C; Z = B; } if (X) { // Build (X^Y) & Z Op1 = Builder->CreateXor(X, Y, "tmp"); Op1 = Builder->CreateAnd(Op1, Z, "tmp"); I.setOperand(0, Op1); I.setOperand(1, Constant::getNullValue(Op1->getType())); return &I; } } } { Value *X; ConstantInt *Cst; // icmp X+Cst, X if (match(Op0, m_Add(m_Value(X), m_ConstantInt(Cst))) && Op1 == X) return FoldICmpAddOpCst(I, X, Cst, I.getPredicate(), Op0); // icmp X, X+Cst if (match(Op1, m_Add(m_Value(X), m_ConstantInt(Cst))) && Op0 == X) return FoldICmpAddOpCst(I, X, Cst, I.getSwappedPredicate(), Op1); } return Changed ? &I : 0; } /// FoldFCmp_IntToFP_Cst - Fold fcmp ([us]itofp x, cst) if possible. /// Instruction *InstCombiner::FoldFCmp_IntToFP_Cst(FCmpInst &I, Instruction *LHSI, Constant *RHSC) { if (!isa(RHSC)) return 0; const APFloat &RHS = cast(RHSC)->getValueAPF(); // Get the width of the mantissa. We don't want to hack on conversions that // might lose information from the integer, e.g. "i64 -> float" int MantissaWidth = LHSI->getType()->getFPMantissaWidth(); if (MantissaWidth == -1) return 0; // Unknown. // Check to see that the input is converted from an integer type that is small // enough that preserves all bits. TODO: check here for "known" sign bits. // This would allow us to handle (fptosi (x >>s 62) to float) if x is i64 f.e. unsigned InputSize = LHSI->getOperand(0)->getType()->getScalarSizeInBits(); // If this is a uitofp instruction, we need an extra bit to hold the sign. bool LHSUnsigned = isa(LHSI); if (LHSUnsigned) ++InputSize; // If the conversion would lose info, don't hack on this. if ((int)InputSize > MantissaWidth) return 0; // Otherwise, we can potentially simplify the comparison. We know that it // will always come through as an integer value and we know the constant is // not a NAN (it would have been previously simplified). assert(!RHS.isNaN() && "NaN comparison not already folded!"); ICmpInst::Predicate Pred; switch (I.getPredicate()) { default: llvm_unreachable("Unexpected predicate!"); case FCmpInst::FCMP_UEQ: case FCmpInst::FCMP_OEQ: Pred = ICmpInst::ICMP_EQ; break; case FCmpInst::FCMP_UGT: case FCmpInst::FCMP_OGT: Pred = LHSUnsigned ? ICmpInst::ICMP_UGT : ICmpInst::ICMP_SGT; break; case FCmpInst::FCMP_UGE: case FCmpInst::FCMP_OGE: Pred = LHSUnsigned ? ICmpInst::ICMP_UGE : ICmpInst::ICMP_SGE; break; case FCmpInst::FCMP_ULT: case FCmpInst::FCMP_OLT: Pred = LHSUnsigned ? ICmpInst::ICMP_ULT : ICmpInst::ICMP_SLT; break; case FCmpInst::FCMP_ULE: case FCmpInst::FCMP_OLE: Pred = LHSUnsigned ? ICmpInst::ICMP_ULE : ICmpInst::ICMP_SLE; break; case FCmpInst::FCMP_UNE: case FCmpInst::FCMP_ONE: Pred = ICmpInst::ICMP_NE; break; case FCmpInst::FCMP_ORD: return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getContext())); case FCmpInst::FCMP_UNO: return ReplaceInstUsesWith(I, ConstantInt::getFalse(I.getContext())); } const IntegerType *IntTy = cast(LHSI->getOperand(0)->getType()); // Now we know that the APFloat is a normal number, zero or inf. // See if the FP constant is too large for the integer. For example, // comparing an i8 to 300.0. unsigned IntWidth = IntTy->getScalarSizeInBits(); if (!LHSUnsigned) { // If the RHS value is > SignedMax, fold the comparison. This handles +INF // and large values. APFloat SMax(RHS.getSemantics(), APFloat::fcZero, false); SMax.convertFromAPInt(APInt::getSignedMaxValue(IntWidth), true, APFloat::rmNearestTiesToEven); if (SMax.compare(RHS) == APFloat::cmpLessThan) { // smax < 13123.0 if (Pred == ICmpInst::ICMP_NE || Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_SLE) return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getContext())); return ReplaceInstUsesWith(I, ConstantInt::getFalse(I.getContext())); } } else { // If the RHS value is > UnsignedMax, fold the comparison. This handles // +INF and large values. APFloat UMax(RHS.getSemantics(), APFloat::fcZero, false); UMax.convertFromAPInt(APInt::getMaxValue(IntWidth), false, APFloat::rmNearestTiesToEven); if (UMax.compare(RHS) == APFloat::cmpLessThan) { // umax < 13123.0 if (Pred == ICmpInst::ICMP_NE || Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_ULE) return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getContext())); return ReplaceInstUsesWith(I, ConstantInt::getFalse(I.getContext())); } } if (!LHSUnsigned) { // See if the RHS value is < SignedMin. APFloat SMin(RHS.getSemantics(), APFloat::fcZero, false); SMin.convertFromAPInt(APInt::getSignedMinValue(IntWidth), true, APFloat::rmNearestTiesToEven); if (SMin.compare(RHS) == APFloat::cmpGreaterThan) { // smin > 12312.0 if (Pred == ICmpInst::ICMP_NE || Pred == ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_SGE) return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getContext())); return ReplaceInstUsesWith(I, ConstantInt::getFalse(I.getContext())); } } // Okay, now we know that the FP constant fits in the range [SMIN, SMAX] or // [0, UMAX], but it may still be fractional. See if it is fractional by // casting the FP value to the integer value and back, checking for equality. // Don't do this for zero, because -0.0 is not fractional. Constant *RHSInt = LHSUnsigned ? ConstantExpr::getFPToUI(RHSC, IntTy) : ConstantExpr::getFPToSI(RHSC, IntTy); if (!RHS.isZero()) { bool Equal = LHSUnsigned ? ConstantExpr::getUIToFP(RHSInt, RHSC->getType()) == RHSC : ConstantExpr::getSIToFP(RHSInt, RHSC->getType()) == RHSC; if (!Equal) { // If we had a comparison against a fractional value, we have to adjust // the compare predicate and sometimes the value. RHSC is rounded towards // zero at this point. switch (Pred) { default: llvm_unreachable("Unexpected integer comparison!"); case ICmpInst::ICMP_NE: // (float)int != 4.4 --> true return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getContext())); case ICmpInst::ICMP_EQ: // (float)int == 4.4 --> false return ReplaceInstUsesWith(I, ConstantInt::getFalse(I.getContext())); case ICmpInst::ICMP_ULE: // (float)int <= 4.4 --> int <= 4 // (float)int <= -4.4 --> false if (RHS.isNegative()) return ReplaceInstUsesWith(I, ConstantInt::getFalse(I.getContext())); break; case ICmpInst::ICMP_SLE: // (float)int <= 4.4 --> int <= 4 // (float)int <= -4.4 --> int < -4 if (RHS.isNegative()) Pred = ICmpInst::ICMP_SLT; break; case ICmpInst::ICMP_ULT: // (float)int < -4.4 --> false // (float)int < 4.4 --> int <= 4 if (RHS.isNegative()) return ReplaceInstUsesWith(I, ConstantInt::getFalse(I.getContext())); Pred = ICmpInst::ICMP_ULE; break; case ICmpInst::ICMP_SLT: // (float)int < -4.4 --> int < -4 // (float)int < 4.4 --> int <= 4 if (!RHS.isNegative()) Pred = ICmpInst::ICMP_SLE; break; case ICmpInst::ICMP_UGT: // (float)int > 4.4 --> int > 4 // (float)int > -4.4 --> true if (RHS.isNegative()) return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getContext())); break; case ICmpInst::ICMP_SGT: // (float)int > 4.4 --> int > 4 // (float)int > -4.4 --> int >= -4 if (RHS.isNegative()) Pred = ICmpInst::ICMP_SGE; break; case ICmpInst::ICMP_UGE: // (float)int >= -4.4 --> true // (float)int >= 4.4 --> int > 4 if (!RHS.isNegative()) return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getContext())); Pred = ICmpInst::ICMP_UGT; break; case ICmpInst::ICMP_SGE: // (float)int >= -4.4 --> int >= -4 // (float)int >= 4.4 --> int > 4 if (!RHS.isNegative()) Pred = ICmpInst::ICMP_SGT; break; } } } // Lower this FP comparison into an appropriate integer version of the // comparison. return new ICmpInst(Pred, LHSI->getOperand(0), RHSInt); } Instruction *InstCombiner::visitFCmpInst(FCmpInst &I) { bool Changed = false; /// Orders the operands of the compare so that they are listed from most /// complex to least complex. This puts constants before unary operators, /// before binary operators. if (getComplexity(I.getOperand(0)) < getComplexity(I.getOperand(1))) { I.swapOperands(); Changed = true; } Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1); if (Value *V = SimplifyFCmpInst(I.getPredicate(), Op0, Op1, TD)) return ReplaceInstUsesWith(I, V); // Simplify 'fcmp pred X, X' if (Op0 == Op1) { switch (I.getPredicate()) { default: llvm_unreachable("Unknown predicate!"); case FCmpInst::FCMP_UNO: // True if unordered: isnan(X) | isnan(Y) case FCmpInst::FCMP_ULT: // True if unordered or less than case FCmpInst::FCMP_UGT: // True if unordered or greater than case FCmpInst::FCMP_UNE: // True if unordered or not equal // Canonicalize these to be 'fcmp uno %X, 0.0'. I.setPredicate(FCmpInst::FCMP_UNO); I.setOperand(1, Constant::getNullValue(Op0->getType())); return &I; case FCmpInst::FCMP_ORD: // True if ordered (no nans) case FCmpInst::FCMP_OEQ: // True if ordered and equal case FCmpInst::FCMP_OGE: // True if ordered and greater than or equal case FCmpInst::FCMP_OLE: // True if ordered and less than or equal // Canonicalize these to be 'fcmp ord %X, 0.0'. I.setPredicate(FCmpInst::FCMP_ORD); I.setOperand(1, Constant::getNullValue(Op0->getType())); return &I; } } // Handle fcmp with constant RHS if (Constant *RHSC = dyn_cast(Op1)) { if (Instruction *LHSI = dyn_cast(Op0)) switch (LHSI->getOpcode()) { case Instruction::PHI: // Only fold fcmp into the PHI if the phi and fcmp are in the same // block. If in the same block, we're encouraging jump threading. If // not, we are just pessimizing the code by making an i1 phi. if (LHSI->getParent() == I.getParent()) if (Instruction *NV = FoldOpIntoPhi(I)) return NV; break; case Instruction::SIToFP: case Instruction::UIToFP: if (Instruction *NV = FoldFCmp_IntToFP_Cst(I, LHSI, RHSC)) return NV; break; case Instruction::Select: { // If either operand of the select is a constant, we can fold the // comparison into the select arms, which will cause one to be // constant folded and the select turned into a bitwise or. Value *Op1 = 0, *Op2 = 0; if (LHSI->hasOneUse()) { if (Constant *C = dyn_cast(LHSI->getOperand(1))) { // Fold the known value into the constant operand. Op1 = ConstantExpr::getCompare(I.getPredicate(), C, RHSC); // Insert a new FCmp of the other select operand. Op2 = Builder->CreateFCmp(I.getPredicate(), LHSI->getOperand(2), RHSC, I.getName()); } else if (Constant *C = dyn_cast(LHSI->getOperand(2))) { // Fold the known value into the constant operand. Op2 = ConstantExpr::getCompare(I.getPredicate(), C, RHSC); // Insert a new FCmp of the other select operand. Op1 = Builder->CreateFCmp(I.getPredicate(), LHSI->getOperand(1), RHSC, I.getName()); } } if (Op1) return SelectInst::Create(LHSI->getOperand(0), Op1, Op2); break; } case Instruction::Load: if (GetElementPtrInst *GEP = dyn_cast(LHSI->getOperand(0))) { if (GlobalVariable *GV = dyn_cast(GEP->getOperand(0))) if (GV->isConstant() && GV->hasDefinitiveInitializer() && !cast(LHSI)->isVolatile()) if (Instruction *Res = FoldCmpLoadFromIndexedGlobal(GEP, GV, I)) return Res; } break; } } return Changed ? &I : 0; }