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Diffstat (limited to 'lib/Transforms/Scalar/Float2Int.cpp')
| -rw-r--r-- | lib/Transforms/Scalar/Float2Int.cpp | 540 |
1 files changed, 540 insertions, 0 deletions
diff --git a/lib/Transforms/Scalar/Float2Int.cpp b/lib/Transforms/Scalar/Float2Int.cpp new file mode 100644 index 0000000..c931422 --- /dev/null +++ b/lib/Transforms/Scalar/Float2Int.cpp @@ -0,0 +1,540 @@ +//===- Float2Int.cpp - Demote floating point ops to work on integers ------===// +// +// 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 Float2Int pass, which aims to demote floating +// point operations to work on integers, where that is losslessly possible. +// +//===----------------------------------------------------------------------===// + +#define DEBUG_TYPE "float2int" +#include "llvm/ADT/APInt.h" +#include "llvm/ADT/APSInt.h" +#include "llvm/ADT/DenseMap.h" +#include "llvm/ADT/EquivalenceClasses.h" +#include "llvm/ADT/MapVector.h" +#include "llvm/ADT/SmallVector.h" +#include "llvm/IR/ConstantRange.h" +#include "llvm/IR/Constants.h" +#include "llvm/IR/IRBuilder.h" +#include "llvm/IR/InstIterator.h" +#include "llvm/IR/Instructions.h" +#include "llvm/IR/Module.h" +#include "llvm/Pass.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/raw_ostream.h" +#include "llvm/Transforms/Scalar.h" +#include <deque> +#include <functional> // For std::function +using namespace llvm; + +// The algorithm is simple. Start at instructions that convert from the +// float to the int domain: fptoui, fptosi and fcmp. Walk up the def-use +// graph, using an equivalence datastructure to unify graphs that interfere. +// +// Mappable instructions are those with an integer corrollary that, given +// integer domain inputs, produce an integer output; fadd, for example. +// +// If a non-mappable instruction is seen, this entire def-use graph is marked +// as non-transformable. If we see an instruction that converts from the +// integer domain to FP domain (uitofp,sitofp), we terminate our walk. + +/// The largest integer type worth dealing with. +static cl::opt<unsigned> +MaxIntegerBW("float2int-max-integer-bw", cl::init(64), cl::Hidden, + cl::desc("Max integer bitwidth to consider in float2int" + "(default=64)")); + +namespace { + struct Float2Int : public FunctionPass { + static char ID; // Pass identification, replacement for typeid + Float2Int() : FunctionPass(ID) { + initializeFloat2IntPass(*PassRegistry::getPassRegistry()); + } + + bool runOnFunction(Function &F) override; + void getAnalysisUsage(AnalysisUsage &AU) const override { + AU.setPreservesCFG(); + } + + void findRoots(Function &F, SmallPtrSet<Instruction*,8> &Roots); + ConstantRange seen(Instruction *I, ConstantRange R); + ConstantRange badRange(); + ConstantRange unknownRange(); + ConstantRange validateRange(ConstantRange R); + void walkBackwards(const SmallPtrSetImpl<Instruction*> &Roots); + void walkForwards(); + bool validateAndTransform(); + Value *convert(Instruction *I, Type *ToTy); + void cleanup(); + + MapVector<Instruction*, ConstantRange > SeenInsts; + SmallPtrSet<Instruction*,8> Roots; + EquivalenceClasses<Instruction*> ECs; + MapVector<Instruction*, Value*> ConvertedInsts; + LLVMContext *Ctx; + }; +} + +char Float2Int::ID = 0; +INITIALIZE_PASS(Float2Int, "float2int", "Float to int", false, false) + +// Given a FCmp predicate, return a matching ICmp predicate if one +// exists, otherwise return BAD_ICMP_PREDICATE. +static CmpInst::Predicate mapFCmpPred(CmpInst::Predicate P) { + switch (P) { + case CmpInst::FCMP_OEQ: + case CmpInst::FCMP_UEQ: + return CmpInst::ICMP_EQ; + case CmpInst::FCMP_OGT: + case CmpInst::FCMP_UGT: + return CmpInst::ICMP_SGT; + case CmpInst::FCMP_OGE: + case CmpInst::FCMP_UGE: + return CmpInst::ICMP_SGE; + case CmpInst::FCMP_OLT: + case CmpInst::FCMP_ULT: + return CmpInst::ICMP_SLT; + case CmpInst::FCMP_OLE: + case CmpInst::FCMP_ULE: + return CmpInst::ICMP_SLE; + case CmpInst::FCMP_ONE: + case CmpInst::FCMP_UNE: + return CmpInst::ICMP_NE; + default: + return CmpInst::BAD_ICMP_PREDICATE; + } +} + +// Given a floating point binary operator, return the matching +// integer version. +static Instruction::BinaryOps mapBinOpcode(unsigned Opcode) { + switch (Opcode) { + default: llvm_unreachable("Unhandled opcode!"); + case Instruction::FAdd: return Instruction::Add; + case Instruction::FSub: return Instruction::Sub; + case Instruction::FMul: return Instruction::Mul; + } +} + +// Find the roots - instructions that convert from the FP domain to +// integer domain. +void Float2Int::findRoots(Function &F, SmallPtrSet<Instruction*,8> &Roots) { + for (auto &I : inst_range(F)) { + switch (I.getOpcode()) { + default: break; + case Instruction::FPToUI: + case Instruction::FPToSI: + Roots.insert(&I); + break; + case Instruction::FCmp: + if (mapFCmpPred(cast<CmpInst>(&I)->getPredicate()) != + CmpInst::BAD_ICMP_PREDICATE) + Roots.insert(&I); + break; + } + } +} + +// Helper - mark I as having been traversed, having range R. +ConstantRange Float2Int::seen(Instruction *I, ConstantRange R) { + DEBUG(dbgs() << "F2I: " << *I << ":" << R << "\n"); + if (SeenInsts.find(I) != SeenInsts.end()) + SeenInsts.find(I)->second = R; + else + SeenInsts.insert(std::make_pair(I, R)); + return R; +} + +// Helper - get a range representing a poison value. +ConstantRange Float2Int::badRange() { + return ConstantRange(MaxIntegerBW + 1, true); +} +ConstantRange Float2Int::unknownRange() { + return ConstantRange(MaxIntegerBW + 1, false); +} +ConstantRange Float2Int::validateRange(ConstantRange R) { + if (R.getBitWidth() > MaxIntegerBW + 1) + return badRange(); + return R; +} + +// The most obvious way to structure the search is a depth-first, eager +// search from each root. However, that require direct recursion and so +// can only handle small instruction sequences. Instead, we split the search +// up into two phases: +// - walkBackwards: A breadth-first walk of the use-def graph starting from +// the roots. Populate "SeenInsts" with interesting +// instructions and poison values if they're obvious and +// cheap to compute. Calculate the equivalance set structure +// while we're here too. +// - walkForwards: Iterate over SeenInsts in reverse order, so we visit +// defs before their uses. Calculate the real range info. + +// Breadth-first walk of the use-def graph; determine the set of nodes +// we care about and eagerly determine if some of them are poisonous. +void Float2Int::walkBackwards(const SmallPtrSetImpl<Instruction*> &Roots) { + std::deque<Instruction*> Worklist(Roots.begin(), Roots.end()); + while (!Worklist.empty()) { + Instruction *I = Worklist.back(); + Worklist.pop_back(); + + if (SeenInsts.find(I) != SeenInsts.end()) + // Seen already. + continue; + + switch (I->getOpcode()) { + // FIXME: Handle select and phi nodes. + default: + // Path terminated uncleanly. + seen(I, badRange()); + break; + + case Instruction::UIToFP: { + // Path terminated cleanly. + unsigned BW = I->getOperand(0)->getType()->getPrimitiveSizeInBits(); + APInt Min = APInt::getMinValue(BW).zextOrSelf(MaxIntegerBW+1); + APInt Max = APInt::getMaxValue(BW).zextOrSelf(MaxIntegerBW+1); + seen(I, validateRange(ConstantRange(Min, Max))); + continue; + } + + case Instruction::SIToFP: { + // Path terminated cleanly. + unsigned BW = I->getOperand(0)->getType()->getPrimitiveSizeInBits(); + APInt SMin = APInt::getSignedMinValue(BW).sextOrSelf(MaxIntegerBW+1); + APInt SMax = APInt::getSignedMaxValue(BW).sextOrSelf(MaxIntegerBW+1); + seen(I, validateRange(ConstantRange(SMin, SMax))); + continue; + } + + case Instruction::FAdd: + case Instruction::FSub: + case Instruction::FMul: + case Instruction::FPToUI: + case Instruction::FPToSI: + case Instruction::FCmp: + seen(I, unknownRange()); + break; + } + + for (Value *O : I->operands()) { + if (Instruction *OI = dyn_cast<Instruction>(O)) { + // Unify def-use chains if they interfere. + ECs.unionSets(I, OI); + if (SeenInsts.find(I)->second != badRange()) + Worklist.push_back(OI); + } else if (!isa<ConstantFP>(O)) { + // Not an instruction or ConstantFP? we can't do anything. + seen(I, badRange()); + } + } + } +} + +// Walk forwards down the list of seen instructions, so we visit defs before +// uses. +void Float2Int::walkForwards() { + for (auto It = SeenInsts.rbegin(), E = SeenInsts.rend(); It != E; ++It) { + if (It->second != unknownRange()) + continue; + + Instruction *I = It->first; + std::function<ConstantRange(ArrayRef<ConstantRange>)> Op; + switch (I->getOpcode()) { + // FIXME: Handle select and phi nodes. + default: + case Instruction::UIToFP: + case Instruction::SIToFP: + llvm_unreachable("Should have been handled in walkForwards!"); + + case Instruction::FAdd: + Op = [](ArrayRef<ConstantRange> Ops) { + assert(Ops.size() == 2 && "FAdd is a binary operator!"); + return Ops[0].add(Ops[1]); + }; + break; + + case Instruction::FSub: + Op = [](ArrayRef<ConstantRange> Ops) { + assert(Ops.size() == 2 && "FSub is a binary operator!"); + return Ops[0].sub(Ops[1]); + }; + break; + + case Instruction::FMul: + Op = [](ArrayRef<ConstantRange> Ops) { + assert(Ops.size() == 2 && "FMul is a binary operator!"); + return Ops[0].multiply(Ops[1]); + }; + break; + + // + // Root-only instructions - we'll only see these if they're the + // first node in a walk. + // + case Instruction::FPToUI: + case Instruction::FPToSI: + Op = [](ArrayRef<ConstantRange> Ops) { + assert(Ops.size() == 1 && "FPTo[US]I is a unary operator!"); + return Ops[0]; + }; + break; + + case Instruction::FCmp: + Op = [](ArrayRef<ConstantRange> Ops) { + assert(Ops.size() == 2 && "FCmp is a binary operator!"); + return Ops[0].unionWith(Ops[1]); + }; + break; + } + + bool Abort = false; + SmallVector<ConstantRange,4> OpRanges; + for (Value *O : I->operands()) { + if (Instruction *OI = dyn_cast<Instruction>(O)) { + assert(SeenInsts.find(OI) != SeenInsts.end() && + "def not seen before use!"); + OpRanges.push_back(SeenInsts.find(OI)->second); + } else if (ConstantFP *CF = dyn_cast<ConstantFP>(O)) { + // Work out if the floating point number can be losslessly represented + // as an integer. + // APFloat::convertToInteger(&Exact) purports to do what we want, but + // the exactness can be too precise. For example, negative zero can + // never be exactly converted to an integer. + // + // Instead, we ask APFloat to round itself to an integral value - this + // preserves sign-of-zero - then compare the result with the original. + // + APFloat F = CF->getValueAPF(); + + // First, weed out obviously incorrect values. Non-finite numbers + // can't be represented and neither can negative zero, unless + // we're in fast math mode. + if (!F.isFinite() || + (F.isZero() && F.isNegative() && isa<FPMathOperator>(I) && + !I->hasNoSignedZeros())) { + seen(I, badRange()); + Abort = true; + break; + } + + APFloat NewF = F; + auto Res = NewF.roundToIntegral(APFloat::rmNearestTiesToEven); + if (Res != APFloat::opOK || NewF.compare(F) != APFloat::cmpEqual) { + seen(I, badRange()); + Abort = true; + break; + } + // OK, it's representable. Now get it. + APSInt Int(MaxIntegerBW+1, false); + bool Exact; + CF->getValueAPF().convertToInteger(Int, + APFloat::rmNearestTiesToEven, + &Exact); + OpRanges.push_back(ConstantRange(Int)); + } else { + llvm_unreachable("Should have already marked this as badRange!"); + } + } + + // Reduce the operands' ranges to a single range and return. + if (!Abort) + seen(I, Op(OpRanges)); + } +} + +// If there is a valid transform to be done, do it. +bool Float2Int::validateAndTransform() { + bool MadeChange = false; + + // Iterate over every disjoint partition of the def-use graph. + for (auto It = ECs.begin(), E = ECs.end(); It != E; ++It) { + ConstantRange R(MaxIntegerBW + 1, false); + bool Fail = false; + Type *ConvertedToTy = nullptr; + + // For every member of the partition, union all the ranges together. + for (auto MI = ECs.member_begin(It), ME = ECs.member_end(); + MI != ME; ++MI) { + Instruction *I = *MI; + auto SeenI = SeenInsts.find(I); + if (SeenI == SeenInsts.end()) + continue; + + R = R.unionWith(SeenI->second); + // We need to ensure I has no users that have not been seen. + // If it does, transformation would be illegal. + // + // Don't count the roots, as they terminate the graphs. + if (Roots.count(I) == 0) { + // Set the type of the conversion while we're here. + if (!ConvertedToTy) + ConvertedToTy = I->getType(); + for (User *U : I->users()) { + Instruction *UI = dyn_cast<Instruction>(U); + if (!UI || SeenInsts.find(UI) == SeenInsts.end()) { + DEBUG(dbgs() << "F2I: Failing because of " << *U << "\n"); + Fail = true; + break; + } + } + } + if (Fail) + break; + } + + // If the set was empty, or we failed, or the range is poisonous, + // bail out. + if (ECs.member_begin(It) == ECs.member_end() || Fail || + R.isFullSet() || R.isSignWrappedSet()) + continue; + assert(ConvertedToTy && "Must have set the convertedtoty by this point!"); + + // The number of bits required is the maximum of the upper and + // lower limits, plus one so it can be signed. + unsigned MinBW = std::max(R.getLower().getMinSignedBits(), + R.getUpper().getMinSignedBits()) + 1; + DEBUG(dbgs() << "F2I: MinBitwidth=" << MinBW << ", R: " << R << "\n"); + + // If we've run off the realms of the exactly representable integers, + // the floating point result will differ from an integer approximation. + + // Do we need more bits than are in the mantissa of the type we converted + // to? semanticsPrecision returns the number of mantissa bits plus one + // for the sign bit. + unsigned MaxRepresentableBits + = APFloat::semanticsPrecision(ConvertedToTy->getFltSemantics()) - 1; + if (MinBW > MaxRepresentableBits) { + DEBUG(dbgs() << "F2I: Value not guaranteed to be representable!\n"); + continue; + } + if (MinBW > 64) { + DEBUG(dbgs() << "F2I: Value requires more than 64 bits to represent!\n"); + continue; + } + + // OK, R is known to be representable. Now pick a type for it. + // FIXME: Pick the smallest legal type that will fit. + Type *Ty = (MinBW > 32) ? Type::getInt64Ty(*Ctx) : Type::getInt32Ty(*Ctx); + + for (auto MI = ECs.member_begin(It), ME = ECs.member_end(); + MI != ME; ++MI) + convert(*MI, Ty); + MadeChange = true; + } + + return MadeChange; +} + +Value *Float2Int::convert(Instruction *I, Type *ToTy) { + if (ConvertedInsts.find(I) != ConvertedInsts.end()) + // Already converted this instruction. + return ConvertedInsts[I]; + + SmallVector<Value*,4> NewOperands; + for (Value *V : I->operands()) { + // Don't recurse if we're an instruction that terminates the path. + if (I->getOpcode() == Instruction::UIToFP || + I->getOpcode() == Instruction::SIToFP) { + NewOperands.push_back(V); + } else if (Instruction *VI = dyn_cast<Instruction>(V)) { + NewOperands.push_back(convert(VI, ToTy)); + } else if (ConstantFP *CF = dyn_cast<ConstantFP>(V)) { + APSInt Val(ToTy->getPrimitiveSizeInBits(), /*IsUnsigned=*/false); + bool Exact; + CF->getValueAPF().convertToInteger(Val, + APFloat::rmNearestTiesToEven, + &Exact); + NewOperands.push_back(ConstantInt::get(ToTy, Val)); + } else { + llvm_unreachable("Unhandled operand type?"); + } + } + + // Now create a new instruction. + IRBuilder<> IRB(I); + Value *NewV = nullptr; + switch (I->getOpcode()) { + default: llvm_unreachable("Unhandled instruction!"); + + case Instruction::FPToUI: + NewV = IRB.CreateZExtOrTrunc(NewOperands[0], I->getType()); + break; + + case Instruction::FPToSI: + NewV = IRB.CreateSExtOrTrunc(NewOperands[0], I->getType()); + break; + + case Instruction::FCmp: { + CmpInst::Predicate P = mapFCmpPred(cast<CmpInst>(I)->getPredicate()); + assert(P != CmpInst::BAD_ICMP_PREDICATE && "Unhandled predicate!"); + NewV = IRB.CreateICmp(P, NewOperands[0], NewOperands[1], I->getName()); + break; + } + + case Instruction::UIToFP: + NewV = IRB.CreateZExtOrTrunc(NewOperands[0], ToTy); + break; + + case Instruction::SIToFP: + NewV = IRB.CreateSExtOrTrunc(NewOperands[0], ToTy); + break; + + case Instruction::FAdd: + case Instruction::FSub: + case Instruction::FMul: + NewV = IRB.CreateBinOp(mapBinOpcode(I->getOpcode()), + NewOperands[0], NewOperands[1], + I->getName()); + break; + } + + // If we're a root instruction, RAUW. + if (Roots.count(I)) + I->replaceAllUsesWith(NewV); + + ConvertedInsts[I] = NewV; + return NewV; +} + +// Perform dead code elimination on the instructions we just modified. +void Float2Int::cleanup() { + for (auto I = ConvertedInsts.rbegin(), E = ConvertedInsts.rend(); + I != E; ++I) + I->first->eraseFromParent(); +} + +bool Float2Int::runOnFunction(Function &F) { + if (skipOptnoneFunction(F)) + return false; + + DEBUG(dbgs() << "F2I: Looking at function " << F.getName() << "\n"); + // Clear out all state. + ECs = EquivalenceClasses<Instruction*>(); + SeenInsts.clear(); + ConvertedInsts.clear(); + Roots.clear(); + + Ctx = &F.getParent()->getContext(); + + findRoots(F, Roots); + + walkBackwards(Roots); + walkForwards(); + + bool Modified = validateAndTransform(); + if (Modified) + cleanup(); + return Modified; +} + +FunctionPass *llvm::createFloat2IntPass() { + return new Float2Int(); +} + |