| //===- GVN.cpp - Eliminate redundant values and loads ---------------------===// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This pass performs global value numbering to eliminate fully redundant |
| // instructions. It also performs simple dead load elimination. |
| // |
| // Note that this pass does the value numbering itself; it does not use the |
| // ValueNumbering analysis passes. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Transforms/Scalar/GVN.h" |
| #include "llvm/ADT/DenseMap.h" |
| #include "llvm/ADT/DepthFirstIterator.h" |
| #include "llvm/ADT/Hashing.h" |
| #include "llvm/ADT/MapVector.h" |
| #include "llvm/ADT/PointerIntPair.h" |
| #include "llvm/ADT/PostOrderIterator.h" |
| #include "llvm/ADT/STLExtras.h" |
| #include "llvm/ADT/SetVector.h" |
| #include "llvm/ADT/SmallPtrSet.h" |
| #include "llvm/ADT/SmallVector.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/Analysis/AliasAnalysis.h" |
| #include "llvm/Analysis/AssumeBundleQueries.h" |
| #include "llvm/Analysis/AssumptionCache.h" |
| #include "llvm/Analysis/CFG.h" |
| #include "llvm/Analysis/DomTreeUpdater.h" |
| #include "llvm/Analysis/GlobalsModRef.h" |
| #include "llvm/Analysis/InstructionSimplify.h" |
| #include "llvm/Analysis/LoopInfo.h" |
| #include "llvm/Analysis/MemoryBuiltins.h" |
| #include "llvm/Analysis/MemoryDependenceAnalysis.h" |
| #include "llvm/Analysis/MemorySSA.h" |
| #include "llvm/Analysis/MemorySSAUpdater.h" |
| #include "llvm/Analysis/OptimizationRemarkEmitter.h" |
| #include "llvm/Analysis/PHITransAddr.h" |
| #include "llvm/Analysis/TargetLibraryInfo.h" |
| #include "llvm/Analysis/ValueTracking.h" |
| #include "llvm/Config/llvm-config.h" |
| #include "llvm/IR/Attributes.h" |
| #include "llvm/IR/BasicBlock.h" |
| #include "llvm/IR/Constant.h" |
| #include "llvm/IR/Constants.h" |
| #include "llvm/IR/DataLayout.h" |
| #include "llvm/IR/DebugLoc.h" |
| #include "llvm/IR/Dominators.h" |
| #include "llvm/IR/Function.h" |
| #include "llvm/IR/InstrTypes.h" |
| #include "llvm/IR/Instruction.h" |
| #include "llvm/IR/Instructions.h" |
| #include "llvm/IR/IntrinsicInst.h" |
| #include "llvm/IR/Intrinsics.h" |
| #include "llvm/IR/LLVMContext.h" |
| #include "llvm/IR/Metadata.h" |
| #include "llvm/IR/Module.h" |
| #include "llvm/IR/Operator.h" |
| #include "llvm/IR/PassManager.h" |
| #include "llvm/IR/PatternMatch.h" |
| #include "llvm/IR/Type.h" |
| #include "llvm/IR/Use.h" |
| #include "llvm/IR/Value.h" |
| #include "llvm/InitializePasses.h" |
| #include "llvm/Pass.h" |
| #include "llvm/Support/Casting.h" |
| #include "llvm/Support/CommandLine.h" |
| #include "llvm/Support/Compiler.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/Support/raw_ostream.h" |
| #include "llvm/Transforms/Utils.h" |
| #include "llvm/Transforms/Utils/AssumeBundleBuilder.h" |
| #include "llvm/Transforms/Utils/BasicBlockUtils.h" |
| #include "llvm/Transforms/Utils/Local.h" |
| #include "llvm/Transforms/Utils/SSAUpdater.h" |
| #include "llvm/Transforms/Utils/VNCoercion.h" |
| #include <algorithm> |
| #include <cassert> |
| #include <cstdint> |
| #include <utility> |
| |
| using namespace llvm; |
| using namespace llvm::gvn; |
| using namespace llvm::VNCoercion; |
| using namespace PatternMatch; |
| |
| #define DEBUG_TYPE "gvn" |
| |
| STATISTIC(NumGVNInstr, "Number of instructions deleted"); |
| STATISTIC(NumGVNLoad, "Number of loads deleted"); |
| STATISTIC(NumGVNPRE, "Number of instructions PRE'd"); |
| STATISTIC(NumGVNBlocks, "Number of blocks merged"); |
| STATISTIC(NumGVNSimpl, "Number of instructions simplified"); |
| STATISTIC(NumGVNEqProp, "Number of equalities propagated"); |
| STATISTIC(NumPRELoad, "Number of loads PRE'd"); |
| STATISTIC(NumPRELoopLoad, "Number of loop loads PRE'd"); |
| |
| STATISTIC(IsValueFullyAvailableInBlockNumSpeculationsMax, |
| "Number of blocks speculated as available in " |
| "IsValueFullyAvailableInBlock(), max"); |
| STATISTIC(MaxBBSpeculationCutoffReachedTimes, |
| "Number of times we we reached gvn-max-block-speculations cut-off " |
| "preventing further exploration"); |
| |
| static cl::opt<bool> GVNEnablePRE("enable-pre", cl::init(true), cl::Hidden); |
| static cl::opt<bool> GVNEnableLoadPRE("enable-load-pre", cl::init(true)); |
| static cl::opt<bool> GVNEnableLoadInLoopPRE("enable-load-in-loop-pre", |
| cl::init(true)); |
| static cl::opt<bool> |
| GVNEnableSplitBackedgeInLoadPRE("enable-split-backedge-in-load-pre", |
| cl::init(true)); |
| static cl::opt<bool> GVNEnableMemDep("enable-gvn-memdep", cl::init(true)); |
| |
| static cl::opt<uint32_t> MaxNumDeps( |
| "gvn-max-num-deps", cl::Hidden, cl::init(100), cl::ZeroOrMore, |
| cl::desc("Max number of dependences to attempt Load PRE (default = 100)")); |
| |
| // This is based on IsValueFullyAvailableInBlockNumSpeculationsMax stat. |
| static cl::opt<uint32_t> MaxBBSpeculations( |
| "gvn-max-block-speculations", cl::Hidden, cl::init(600), cl::ZeroOrMore, |
| cl::desc("Max number of blocks we're willing to speculate on (and recurse " |
| "into) when deducing if a value is fully available or not in GVN " |
| "(default = 600)")); |
| |
| struct llvm::GVNPass::Expression { |
| uint32_t opcode; |
| bool commutative = false; |
| Type *type = nullptr; |
| SmallVector<uint32_t, 4> varargs; |
| |
| Expression(uint32_t o = ~2U) : opcode(o) {} |
| |
| bool operator==(const Expression &other) const { |
| if (opcode != other.opcode) |
| return false; |
| if (opcode == ~0U || opcode == ~1U) |
| return true; |
| if (type != other.type) |
| return false; |
| if (varargs != other.varargs) |
| return false; |
| return true; |
| } |
| |
| friend hash_code hash_value(const Expression &Value) { |
| return hash_combine( |
| Value.opcode, Value.type, |
| hash_combine_range(Value.varargs.begin(), Value.varargs.end())); |
| } |
| }; |
| |
| namespace llvm { |
| |
| template <> struct DenseMapInfo<GVNPass::Expression> { |
| static inline GVNPass::Expression getEmptyKey() { return ~0U; } |
| static inline GVNPass::Expression getTombstoneKey() { return ~1U; } |
| |
| static unsigned getHashValue(const GVNPass::Expression &e) { |
| using llvm::hash_value; |
| |
| return static_cast<unsigned>(hash_value(e)); |
| } |
| |
| static bool isEqual(const GVNPass::Expression &LHS, |
| const GVNPass::Expression &RHS) { |
| return LHS == RHS; |
| } |
| }; |
| |
| } // end namespace llvm |
| |
| /// Represents a particular available value that we know how to materialize. |
| /// Materialization of an AvailableValue never fails. An AvailableValue is |
| /// implicitly associated with a rematerialization point which is the |
| /// location of the instruction from which it was formed. |
| struct llvm::gvn::AvailableValue { |
| enum ValType { |
| SimpleVal, // A simple offsetted value that is accessed. |
| LoadVal, // A value produced by a load. |
| MemIntrin, // A memory intrinsic which is loaded from. |
| UndefVal // A UndefValue representing a value from dead block (which |
| // is not yet physically removed from the CFG). |
| }; |
| |
| /// V - The value that is live out of the block. |
| PointerIntPair<Value *, 2, ValType> Val; |
| |
| /// Offset - The byte offset in Val that is interesting for the load query. |
| unsigned Offset = 0; |
| |
| static AvailableValue get(Value *V, unsigned Offset = 0) { |
| AvailableValue Res; |
| Res.Val.setPointer(V); |
| Res.Val.setInt(SimpleVal); |
| Res.Offset = Offset; |
| return Res; |
| } |
| |
| static AvailableValue getMI(MemIntrinsic *MI, unsigned Offset = 0) { |
| AvailableValue Res; |
| Res.Val.setPointer(MI); |
| Res.Val.setInt(MemIntrin); |
| Res.Offset = Offset; |
| return Res; |
| } |
| |
| static AvailableValue getLoad(LoadInst *Load, unsigned Offset = 0) { |
| AvailableValue Res; |
| Res.Val.setPointer(Load); |
| Res.Val.setInt(LoadVal); |
| Res.Offset = Offset; |
| return Res; |
| } |
| |
| static AvailableValue getUndef() { |
| AvailableValue Res; |
| Res.Val.setPointer(nullptr); |
| Res.Val.setInt(UndefVal); |
| Res.Offset = 0; |
| return Res; |
| } |
| |
| bool isSimpleValue() const { return Val.getInt() == SimpleVal; } |
| bool isCoercedLoadValue() const { return Val.getInt() == LoadVal; } |
| bool isMemIntrinValue() const { return Val.getInt() == MemIntrin; } |
| bool isUndefValue() const { return Val.getInt() == UndefVal; } |
| |
| Value *getSimpleValue() const { |
| assert(isSimpleValue() && "Wrong accessor"); |
| return Val.getPointer(); |
| } |
| |
| LoadInst *getCoercedLoadValue() const { |
| assert(isCoercedLoadValue() && "Wrong accessor"); |
| return cast<LoadInst>(Val.getPointer()); |
| } |
| |
| MemIntrinsic *getMemIntrinValue() const { |
| assert(isMemIntrinValue() && "Wrong accessor"); |
| return cast<MemIntrinsic>(Val.getPointer()); |
| } |
| |
| /// Emit code at the specified insertion point to adjust the value defined |
| /// here to the specified type. This handles various coercion cases. |
| Value *MaterializeAdjustedValue(LoadInst *Load, Instruction *InsertPt, |
| GVNPass &gvn) const; |
| }; |
| |
| /// Represents an AvailableValue which can be rematerialized at the end of |
| /// the associated BasicBlock. |
| struct llvm::gvn::AvailableValueInBlock { |
| /// BB - The basic block in question. |
| BasicBlock *BB = nullptr; |
| |
| /// AV - The actual available value |
| AvailableValue AV; |
| |
| static AvailableValueInBlock get(BasicBlock *BB, AvailableValue &&AV) { |
| AvailableValueInBlock Res; |
| Res.BB = BB; |
| Res.AV = std::move(AV); |
| return Res; |
| } |
| |
| static AvailableValueInBlock get(BasicBlock *BB, Value *V, |
| unsigned Offset = 0) { |
| return get(BB, AvailableValue::get(V, Offset)); |
| } |
| |
| static AvailableValueInBlock getUndef(BasicBlock *BB) { |
| return get(BB, AvailableValue::getUndef()); |
| } |
| |
| /// Emit code at the end of this block to adjust the value defined here to |
| /// the specified type. This handles various coercion cases. |
| Value *MaterializeAdjustedValue(LoadInst *Load, GVNPass &gvn) const { |
| return AV.MaterializeAdjustedValue(Load, BB->getTerminator(), gvn); |
| } |
| }; |
| |
| //===----------------------------------------------------------------------===// |
| // ValueTable Internal Functions |
| //===----------------------------------------------------------------------===// |
| |
| GVNPass::Expression GVNPass::ValueTable::createExpr(Instruction *I) { |
| Expression e; |
| e.type = I->getType(); |
| e.opcode = I->getOpcode(); |
| if (const GCRelocateInst *GCR = dyn_cast<GCRelocateInst>(I)) { |
| // gc.relocate is 'special' call: its second and third operands are |
| // not real values, but indices into statepoint's argument list. |
| // Use the refered to values for purposes of identity. |
| e.varargs.push_back(lookupOrAdd(GCR->getOperand(0))); |
| e.varargs.push_back(lookupOrAdd(GCR->getBasePtr())); |
| e.varargs.push_back(lookupOrAdd(GCR->getDerivedPtr())); |
| } else { |
| for (Use &Op : I->operands()) |
| e.varargs.push_back(lookupOrAdd(Op)); |
| } |
| if (I->isCommutative()) { |
| // Ensure that commutative instructions that only differ by a permutation |
| // of their operands get the same value number by sorting the operand value |
| // numbers. Since commutative operands are the 1st two operands it is more |
| // efficient to sort by hand rather than using, say, std::sort. |
| assert(I->getNumOperands() >= 2 && "Unsupported commutative instruction!"); |
| if (e.varargs[0] > e.varargs[1]) |
| std::swap(e.varargs[0], e.varargs[1]); |
| e.commutative = true; |
| } |
| |
| if (auto *C = dyn_cast<CmpInst>(I)) { |
| // Sort the operand value numbers so x<y and y>x get the same value number. |
| CmpInst::Predicate Predicate = C->getPredicate(); |
| if (e.varargs[0] > e.varargs[1]) { |
| std::swap(e.varargs[0], e.varargs[1]); |
| Predicate = CmpInst::getSwappedPredicate(Predicate); |
| } |
| e.opcode = (C->getOpcode() << 8) | Predicate; |
| e.commutative = true; |
| } else if (auto *E = dyn_cast<InsertValueInst>(I)) { |
| e.varargs.append(E->idx_begin(), E->idx_end()); |
| } else if (auto *SVI = dyn_cast<ShuffleVectorInst>(I)) { |
| ArrayRef<int> ShuffleMask = SVI->getShuffleMask(); |
| e.varargs.append(ShuffleMask.begin(), ShuffleMask.end()); |
| } |
| |
| return e; |
| } |
| |
| GVNPass::Expression GVNPass::ValueTable::createCmpExpr( |
| unsigned Opcode, CmpInst::Predicate Predicate, Value *LHS, Value *RHS) { |
| assert((Opcode == Instruction::ICmp || Opcode == Instruction::FCmp) && |
| "Not a comparison!"); |
| Expression e; |
| e.type = CmpInst::makeCmpResultType(LHS->getType()); |
| e.varargs.push_back(lookupOrAdd(LHS)); |
| e.varargs.push_back(lookupOrAdd(RHS)); |
| |
| // Sort the operand value numbers so x<y and y>x get the same value number. |
| if (e.varargs[0] > e.varargs[1]) { |
| std::swap(e.varargs[0], e.varargs[1]); |
| Predicate = CmpInst::getSwappedPredicate(Predicate); |
| } |
| e.opcode = (Opcode << 8) | Predicate; |
| e.commutative = true; |
| return e; |
| } |
| |
| GVNPass::Expression |
| GVNPass::ValueTable::createExtractvalueExpr(ExtractValueInst *EI) { |
| assert(EI && "Not an ExtractValueInst?"); |
| Expression e; |
| e.type = EI->getType(); |
| e.opcode = 0; |
| |
| WithOverflowInst *WO = dyn_cast<WithOverflowInst>(EI->getAggregateOperand()); |
| if (WO != nullptr && EI->getNumIndices() == 1 && *EI->idx_begin() == 0) { |
| // EI is an extract from one of our with.overflow intrinsics. Synthesize |
| // a semantically equivalent expression instead of an extract value |
| // expression. |
| e.opcode = WO->getBinaryOp(); |
| e.varargs.push_back(lookupOrAdd(WO->getLHS())); |
| e.varargs.push_back(lookupOrAdd(WO->getRHS())); |
| return e; |
| } |
| |
| // Not a recognised intrinsic. Fall back to producing an extract value |
| // expression. |
| e.opcode = EI->getOpcode(); |
| for (Use &Op : EI->operands()) |
| e.varargs.push_back(lookupOrAdd(Op)); |
| |
| append_range(e.varargs, EI->indices()); |
| |
| return e; |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // ValueTable External Functions |
| //===----------------------------------------------------------------------===// |
| |
| GVNPass::ValueTable::ValueTable() = default; |
| GVNPass::ValueTable::ValueTable(const ValueTable &) = default; |
| GVNPass::ValueTable::ValueTable(ValueTable &&) = default; |
| GVNPass::ValueTable::~ValueTable() = default; |
| GVNPass::ValueTable & |
| GVNPass::ValueTable::operator=(const GVNPass::ValueTable &Arg) = default; |
| |
| /// add - Insert a value into the table with a specified value number. |
| void GVNPass::ValueTable::add(Value *V, uint32_t num) { |
| valueNumbering.insert(std::make_pair(V, num)); |
| if (PHINode *PN = dyn_cast<PHINode>(V)) |
| NumberingPhi[num] = PN; |
| } |
| |
| uint32_t GVNPass::ValueTable::lookupOrAddCall(CallInst *C) { |
| if (AA->doesNotAccessMemory(C)) { |
| Expression exp = createExpr(C); |
| uint32_t e = assignExpNewValueNum(exp).first; |
| valueNumbering[C] = e; |
| return e; |
| } else if (MD && AA->onlyReadsMemory(C)) { |
| Expression exp = createExpr(C); |
| auto ValNum = assignExpNewValueNum(exp); |
| if (ValNum.second) { |
| valueNumbering[C] = ValNum.first; |
| return ValNum.first; |
| } |
| |
| MemDepResult local_dep = MD->getDependency(C); |
| |
| if (!local_dep.isDef() && !local_dep.isNonLocal()) { |
| valueNumbering[C] = nextValueNumber; |
| return nextValueNumber++; |
| } |
| |
| if (local_dep.isDef()) { |
| // For masked load/store intrinsics, the local_dep may actully be |
| // a normal load or store instruction. |
| CallInst *local_cdep = dyn_cast<CallInst>(local_dep.getInst()); |
| |
| if (!local_cdep || local_cdep->arg_size() != C->arg_size()) { |
| valueNumbering[C] = nextValueNumber; |
| return nextValueNumber++; |
| } |
| |
| for (unsigned i = 0, e = C->arg_size(); i < e; ++i) { |
| uint32_t c_vn = lookupOrAdd(C->getArgOperand(i)); |
| uint32_t cd_vn = lookupOrAdd(local_cdep->getArgOperand(i)); |
| if (c_vn != cd_vn) { |
| valueNumbering[C] = nextValueNumber; |
| return nextValueNumber++; |
| } |
| } |
| |
| uint32_t v = lookupOrAdd(local_cdep); |
| valueNumbering[C] = v; |
| return v; |
| } |
| |
| // Non-local case. |
| const MemoryDependenceResults::NonLocalDepInfo &deps = |
| MD->getNonLocalCallDependency(C); |
| // FIXME: Move the checking logic to MemDep! |
| CallInst* cdep = nullptr; |
| |
| // Check to see if we have a single dominating call instruction that is |
| // identical to C. |
| for (unsigned i = 0, e = deps.size(); i != e; ++i) { |
| const NonLocalDepEntry *I = &deps[i]; |
| if (I->getResult().isNonLocal()) |
| continue; |
| |
| // We don't handle non-definitions. If we already have a call, reject |
| // instruction dependencies. |
| if (!I->getResult().isDef() || cdep != nullptr) { |
| cdep = nullptr; |
| break; |
| } |
| |
| CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->getResult().getInst()); |
| // FIXME: All duplicated with non-local case. |
| if (NonLocalDepCall && DT->properlyDominates(I->getBB(), C->getParent())){ |
| cdep = NonLocalDepCall; |
| continue; |
| } |
| |
| cdep = nullptr; |
| break; |
| } |
| |
| if (!cdep) { |
| valueNumbering[C] = nextValueNumber; |
| return nextValueNumber++; |
| } |
| |
| if (cdep->arg_size() != C->arg_size()) { |
| valueNumbering[C] = nextValueNumber; |
| return nextValueNumber++; |
| } |
| for (unsigned i = 0, e = C->arg_size(); i < e; ++i) { |
| uint32_t c_vn = lookupOrAdd(C->getArgOperand(i)); |
| uint32_t cd_vn = lookupOrAdd(cdep->getArgOperand(i)); |
| if (c_vn != cd_vn) { |
| valueNumbering[C] = nextValueNumber; |
| return nextValueNumber++; |
| } |
| } |
| |
| uint32_t v = lookupOrAdd(cdep); |
| valueNumbering[C] = v; |
| return v; |
| } else { |
| valueNumbering[C] = nextValueNumber; |
| return nextValueNumber++; |
| } |
| } |
| |
| /// Returns true if a value number exists for the specified value. |
| bool GVNPass::ValueTable::exists(Value *V) const { |
| return valueNumbering.count(V) != 0; |
| } |
| |
| /// lookup_or_add - Returns the value number for the specified value, assigning |
| /// it a new number if it did not have one before. |
| uint32_t GVNPass::ValueTable::lookupOrAdd(Value *V) { |
| DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); |
| if (VI != valueNumbering.end()) |
| return VI->second; |
| |
| if (!isa<Instruction>(V)) { |
| valueNumbering[V] = nextValueNumber; |
| return nextValueNumber++; |
| } |
| |
| Instruction* I = cast<Instruction>(V); |
| Expression exp; |
| switch (I->getOpcode()) { |
| case Instruction::Call: |
| return lookupOrAddCall(cast<CallInst>(I)); |
| case Instruction::FNeg: |
| case Instruction::Add: |
| case Instruction::FAdd: |
| case Instruction::Sub: |
| case Instruction::FSub: |
| case Instruction::Mul: |
| case Instruction::FMul: |
| case Instruction::UDiv: |
| case Instruction::SDiv: |
| case Instruction::FDiv: |
| case Instruction::URem: |
| case Instruction::SRem: |
| case Instruction::FRem: |
| case Instruction::Shl: |
| case Instruction::LShr: |
| case Instruction::AShr: |
| case Instruction::And: |
| case Instruction::Or: |
| case Instruction::Xor: |
| case Instruction::ICmp: |
| case Instruction::FCmp: |
| case Instruction::Trunc: |
| case Instruction::ZExt: |
| case Instruction::SExt: |
| case Instruction::FPToUI: |
| case Instruction::FPToSI: |
| case Instruction::UIToFP: |
| case Instruction::SIToFP: |
| case Instruction::FPTrunc: |
| case Instruction::FPExt: |
| case Instruction::PtrToInt: |
| case Instruction::IntToPtr: |
| case Instruction::AddrSpaceCast: |
| case Instruction::BitCast: |
| case Instruction::Select: |
| case Instruction::Freeze: |
| case Instruction::ExtractElement: |
| case Instruction::InsertElement: |
| case Instruction::ShuffleVector: |
| case Instruction::InsertValue: |
| case Instruction::GetElementPtr: |
| exp = createExpr(I); |
| break; |
| case Instruction::ExtractValue: |
| exp = createExtractvalueExpr(cast<ExtractValueInst>(I)); |
| break; |
| case Instruction::PHI: |
| valueNumbering[V] = nextValueNumber; |
| NumberingPhi[nextValueNumber] = cast<PHINode>(V); |
| return nextValueNumber++; |
| default: |
| valueNumbering[V] = nextValueNumber; |
| return nextValueNumber++; |
| } |
| |
| uint32_t e = assignExpNewValueNum(exp).first; |
| valueNumbering[V] = e; |
| return e; |
| } |
| |
| /// Returns the value number of the specified value. Fails if |
| /// the value has not yet been numbered. |
| uint32_t GVNPass::ValueTable::lookup(Value *V, bool Verify) const { |
| DenseMap<Value*, uint32_t>::const_iterator VI = valueNumbering.find(V); |
| if (Verify) { |
| assert(VI != valueNumbering.end() && "Value not numbered?"); |
| return VI->second; |
| } |
| return (VI != valueNumbering.end()) ? VI->second : 0; |
| } |
| |
| /// Returns the value number of the given comparison, |
| /// assigning it a new number if it did not have one before. Useful when |
| /// we deduced the result of a comparison, but don't immediately have an |
| /// instruction realizing that comparison to hand. |
| uint32_t GVNPass::ValueTable::lookupOrAddCmp(unsigned Opcode, |
| CmpInst::Predicate Predicate, |
| Value *LHS, Value *RHS) { |
| Expression exp = createCmpExpr(Opcode, Predicate, LHS, RHS); |
| return assignExpNewValueNum(exp).first; |
| } |
| |
| /// Remove all entries from the ValueTable. |
| void GVNPass::ValueTable::clear() { |
| valueNumbering.clear(); |
| expressionNumbering.clear(); |
| NumberingPhi.clear(); |
| PhiTranslateTable.clear(); |
| nextValueNumber = 1; |
| Expressions.clear(); |
| ExprIdx.clear(); |
| nextExprNumber = 0; |
| } |
| |
| /// Remove a value from the value numbering. |
| void GVNPass::ValueTable::erase(Value *V) { |
| uint32_t Num = valueNumbering.lookup(V); |
| valueNumbering.erase(V); |
| // If V is PHINode, V <--> value number is an one-to-one mapping. |
| if (isa<PHINode>(V)) |
| NumberingPhi.erase(Num); |
| } |
| |
| /// verifyRemoved - Verify that the value is removed from all internal data |
| /// structures. |
| void GVNPass::ValueTable::verifyRemoved(const Value *V) const { |
| for (DenseMap<Value*, uint32_t>::const_iterator |
| I = valueNumbering.begin(), E = valueNumbering.end(); I != E; ++I) { |
| assert(I->first != V && "Inst still occurs in value numbering map!"); |
| } |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // GVN Pass |
| //===----------------------------------------------------------------------===// |
| |
| bool GVNPass::isPREEnabled() const { |
| return Options.AllowPRE.getValueOr(GVNEnablePRE); |
| } |
| |
| bool GVNPass::isLoadPREEnabled() const { |
| return Options.AllowLoadPRE.getValueOr(GVNEnableLoadPRE); |
| } |
| |
| bool GVNPass::isLoadInLoopPREEnabled() const { |
| return Options.AllowLoadInLoopPRE.getValueOr(GVNEnableLoadInLoopPRE); |
| } |
| |
| bool GVNPass::isLoadPRESplitBackedgeEnabled() const { |
| return Options.AllowLoadPRESplitBackedge.getValueOr( |
| GVNEnableSplitBackedgeInLoadPRE); |
| } |
| |
| bool GVNPass::isMemDepEnabled() const { |
| return Options.AllowMemDep.getValueOr(GVNEnableMemDep); |
| } |
| |
| PreservedAnalyses GVNPass::run(Function &F, FunctionAnalysisManager &AM) { |
| // FIXME: The order of evaluation of these 'getResult' calls is very |
| // significant! Re-ordering these variables will cause GVN when run alone to |
| // be less effective! We should fix memdep and basic-aa to not exhibit this |
| // behavior, but until then don't change the order here. |
| auto &AC = AM.getResult<AssumptionAnalysis>(F); |
| auto &DT = AM.getResult<DominatorTreeAnalysis>(F); |
| auto &TLI = AM.getResult<TargetLibraryAnalysis>(F); |
| auto &AA = AM.getResult<AAManager>(F); |
| auto *MemDep = |
| isMemDepEnabled() ? &AM.getResult<MemoryDependenceAnalysis>(F) : nullptr; |
| auto *LI = AM.getCachedResult<LoopAnalysis>(F); |
| auto *MSSA = AM.getCachedResult<MemorySSAAnalysis>(F); |
| auto &ORE = AM.getResult<OptimizationRemarkEmitterAnalysis>(F); |
| bool Changed = runImpl(F, AC, DT, TLI, AA, MemDep, LI, &ORE, |
| MSSA ? &MSSA->getMSSA() : nullptr); |
| if (!Changed) |
| return PreservedAnalyses::all(); |
| PreservedAnalyses PA; |
| PA.preserve<DominatorTreeAnalysis>(); |
| PA.preserve<TargetLibraryAnalysis>(); |
| if (MSSA) |
| PA.preserve<MemorySSAAnalysis>(); |
| if (LI) |
| PA.preserve<LoopAnalysis>(); |
| return PA; |
| } |
| |
| void GVNPass::printPipeline( |
| raw_ostream &OS, function_ref<StringRef(StringRef)> MapClassName2PassName) { |
| static_cast<PassInfoMixin<GVNPass> *>(this)->printPipeline( |
| OS, MapClassName2PassName); |
| |
| OS << "<"; |
| if (Options.AllowPRE != None) |
| OS << (Options.AllowPRE.getValue() ? "" : "no-") << "pre;"; |
| if (Options.AllowLoadPRE != None) |
| OS << (Options.AllowLoadPRE.getValue() ? "" : "no-") << "load-pre;"; |
| if (Options.AllowLoadPRESplitBackedge != None) |
| OS << (Options.AllowLoadPRESplitBackedge.getValue() ? "" : "no-") |
| << "split-backedge-load-pre;"; |
| if (Options.AllowMemDep != None) |
| OS << (Options.AllowMemDep.getValue() ? "" : "no-") << "memdep"; |
| OS << ">"; |
| } |
| |
| #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP) |
| LLVM_DUMP_METHOD void GVNPass::dump(DenseMap<uint32_t, Value *> &d) const { |
| errs() << "{\n"; |
| for (auto &I : d) { |
| errs() << I.first << "\n"; |
| I.second->dump(); |
| } |
| errs() << "}\n"; |
| } |
| #endif |
| |
| enum class AvailabilityState : char { |
| /// We know the block *is not* fully available. This is a fixpoint. |
| Unavailable = 0, |
| /// We know the block *is* fully available. This is a fixpoint. |
| Available = 1, |
| /// We do not know whether the block is fully available or not, |
| /// but we are currently speculating that it will be. |
| /// If it would have turned out that the block was, in fact, not fully |
| /// available, this would have been cleaned up into an Unavailable. |
| SpeculativelyAvailable = 2, |
| }; |
| |
| /// Return true if we can prove that the value |
| /// we're analyzing is fully available in the specified block. As we go, keep |
| /// track of which blocks we know are fully alive in FullyAvailableBlocks. This |
| /// map is actually a tri-state map with the following values: |
| /// 0) we know the block *is not* fully available. |
| /// 1) we know the block *is* fully available. |
| /// 2) we do not know whether the block is fully available or not, but we are |
| /// currently speculating that it will be. |
| static bool IsValueFullyAvailableInBlock( |
| BasicBlock *BB, |
| DenseMap<BasicBlock *, AvailabilityState> &FullyAvailableBlocks) { |
| SmallVector<BasicBlock *, 32> Worklist; |
| Optional<BasicBlock *> UnavailableBB; |
| |
| // The number of times we didn't find an entry for a block in a map and |
| // optimistically inserted an entry marking block as speculatively available. |
| unsigned NumNewNewSpeculativelyAvailableBBs = 0; |
| |
| #ifndef NDEBUG |
| SmallSet<BasicBlock *, 32> NewSpeculativelyAvailableBBs; |
| SmallVector<BasicBlock *, 32> AvailableBBs; |
| #endif |
| |
| Worklist.emplace_back(BB); |
| while (!Worklist.empty()) { |
| BasicBlock *CurrBB = Worklist.pop_back_val(); // LoadFO - depth-first! |
| // Optimistically assume that the block is Speculatively Available and check |
| // to see if we already know about this block in one lookup. |
| std::pair<DenseMap<BasicBlock *, AvailabilityState>::iterator, bool> IV = |
| FullyAvailableBlocks.try_emplace( |
| CurrBB, AvailabilityState::SpeculativelyAvailable); |
| AvailabilityState &State = IV.first->second; |
| |
| // Did the entry already exist for this block? |
| if (!IV.second) { |
| if (State == AvailabilityState::Unavailable) { |
| UnavailableBB = CurrBB; |
| break; // Backpropagate unavailability info. |
| } |
| |
| #ifndef NDEBUG |
| AvailableBBs.emplace_back(CurrBB); |
| #endif |
| continue; // Don't recurse further, but continue processing worklist. |
| } |
| |
| // No entry found for block. |
| ++NumNewNewSpeculativelyAvailableBBs; |
| bool OutOfBudget = NumNewNewSpeculativelyAvailableBBs > MaxBBSpeculations; |
| |
| // If we have exhausted our budget, mark this block as unavailable. |
| // Also, if this block has no predecessors, the value isn't live-in here. |
| if (OutOfBudget || pred_empty(CurrBB)) { |
| MaxBBSpeculationCutoffReachedTimes += (int)OutOfBudget; |
| State = AvailabilityState::Unavailable; |
| UnavailableBB = CurrBB; |
| break; // Backpropagate unavailability info. |
| } |
| |
| // Tentatively consider this block as speculatively available. |
| #ifndef NDEBUG |
| NewSpeculativelyAvailableBBs.insert(CurrBB); |
| #endif |
| // And further recurse into block's predecessors, in depth-first order! |
| Worklist.append(pred_begin(CurrBB), pred_end(CurrBB)); |
| } |
| |
| #if LLVM_ENABLE_STATS |
| IsValueFullyAvailableInBlockNumSpeculationsMax.updateMax( |
| NumNewNewSpeculativelyAvailableBBs); |
| #endif |
| |
| // If the block isn't marked as fixpoint yet |
| // (the Unavailable and Available states are fixpoints) |
| auto MarkAsFixpointAndEnqueueSuccessors = |
| [&](BasicBlock *BB, AvailabilityState FixpointState) { |
| auto It = FullyAvailableBlocks.find(BB); |
| if (It == FullyAvailableBlocks.end()) |
| return; // Never queried this block, leave as-is. |
| switch (AvailabilityState &State = It->second) { |
| case AvailabilityState::Unavailable: |
| case AvailabilityState::Available: |
| return; // Don't backpropagate further, continue processing worklist. |
| case AvailabilityState::SpeculativelyAvailable: // Fix it! |
| State = FixpointState; |
| #ifndef NDEBUG |
| assert(NewSpeculativelyAvailableBBs.erase(BB) && |
| "Found a speculatively available successor leftover?"); |
| #endif |
| // Queue successors for further processing. |
| Worklist.append(succ_begin(BB), succ_end(BB)); |
| return; |
| } |
| }; |
| |
| if (UnavailableBB) { |
| // Okay, we have encountered an unavailable block. |
| // Mark speculatively available blocks reachable from UnavailableBB as |
| // unavailable as well. Paths are terminated when they reach blocks not in |
| // FullyAvailableBlocks or they are not marked as speculatively available. |
| Worklist.clear(); |
| Worklist.append(succ_begin(*UnavailableBB), succ_end(*UnavailableBB)); |
| while (!Worklist.empty()) |
| MarkAsFixpointAndEnqueueSuccessors(Worklist.pop_back_val(), |
| AvailabilityState::Unavailable); |
| } |
| |
| #ifndef NDEBUG |
| Worklist.clear(); |
| for (BasicBlock *AvailableBB : AvailableBBs) |
| Worklist.append(succ_begin(AvailableBB), succ_end(AvailableBB)); |
| while (!Worklist.empty()) |
| MarkAsFixpointAndEnqueueSuccessors(Worklist.pop_back_val(), |
| AvailabilityState::Available); |
| |
| assert(NewSpeculativelyAvailableBBs.empty() && |
| "Must have fixed all the new speculatively available blocks."); |
| #endif |
| |
| return !UnavailableBB; |
| } |
| |
| /// Given a set of loads specified by ValuesPerBlock, |
| /// construct SSA form, allowing us to eliminate Load. This returns the value |
| /// that should be used at Load's definition site. |
| static Value * |
| ConstructSSAForLoadSet(LoadInst *Load, |
| SmallVectorImpl<AvailableValueInBlock> &ValuesPerBlock, |
| GVNPass &gvn) { |
| // Check for the fully redundant, dominating load case. In this case, we can |
| // just use the dominating value directly. |
| if (ValuesPerBlock.size() == 1 && |
| gvn.getDominatorTree().properlyDominates(ValuesPerBlock[0].BB, |
| Load->getParent())) { |
| assert(!ValuesPerBlock[0].AV.isUndefValue() && |
| "Dead BB dominate this block"); |
| return ValuesPerBlock[0].MaterializeAdjustedValue(Load, gvn); |
| } |
| |
| // Otherwise, we have to construct SSA form. |
| SmallVector<PHINode*, 8> NewPHIs; |
| SSAUpdater SSAUpdate(&NewPHIs); |
| SSAUpdate.Initialize(Load->getType(), Load->getName()); |
| |
| for (const AvailableValueInBlock &AV : ValuesPerBlock) { |
| BasicBlock *BB = AV.BB; |
| |
| if (AV.AV.isUndefValue()) |
| continue; |
| |
| if (SSAUpdate.HasValueForBlock(BB)) |
| continue; |
| |
| // If the value is the load that we will be eliminating, and the block it's |
| // available in is the block that the load is in, then don't add it as |
| // SSAUpdater will resolve the value to the relevant phi which may let it |
| // avoid phi construction entirely if there's actually only one value. |
| if (BB == Load->getParent() && |
| ((AV.AV.isSimpleValue() && AV.AV.getSimpleValue() == Load) || |
| (AV.AV.isCoercedLoadValue() && AV.AV.getCoercedLoadValue() == Load))) |
| continue; |
| |
| SSAUpdate.AddAvailableValue(BB, AV.MaterializeAdjustedValue(Load, gvn)); |
| } |
| |
| // Perform PHI construction. |
| return SSAUpdate.GetValueInMiddleOfBlock(Load->getParent()); |
| } |
| |
| Value *AvailableValue::MaterializeAdjustedValue(LoadInst *Load, |
| Instruction *InsertPt, |
| GVNPass &gvn) const { |
| Value *Res; |
| Type *LoadTy = Load->getType(); |
| const DataLayout &DL = Load->getModule()->getDataLayout(); |
| if (isSimpleValue()) { |
| Res = getSimpleValue(); |
| if (Res->getType() != LoadTy) { |
| Res = getStoreValueForLoad(Res, Offset, LoadTy, InsertPt, DL); |
| |
| LLVM_DEBUG(dbgs() << "GVN COERCED NONLOCAL VAL:\nOffset: " << Offset |
| << " " << *getSimpleValue() << '\n' |
| << *Res << '\n' |
| << "\n\n\n"); |
| } |
| } else if (isCoercedLoadValue()) { |
| LoadInst *CoercedLoad = getCoercedLoadValue(); |
| if (CoercedLoad->getType() == LoadTy && Offset == 0) { |
| Res = CoercedLoad; |
| } else { |
| Res = getLoadValueForLoad(CoercedLoad, Offset, LoadTy, InsertPt, DL); |
| // We would like to use gvn.markInstructionForDeletion here, but we can't |
| // because the load is already memoized into the leader map table that GVN |
| // tracks. It is potentially possible to remove the load from the table, |
| // but then there all of the operations based on it would need to be |
| // rehashed. Just leave the dead load around. |
| gvn.getMemDep().removeInstruction(CoercedLoad); |
| LLVM_DEBUG(dbgs() << "GVN COERCED NONLOCAL LOAD:\nOffset: " << Offset |
| << " " << *getCoercedLoadValue() << '\n' |
| << *Res << '\n' |
| << "\n\n\n"); |
| } |
| } else if (isMemIntrinValue()) { |
| Res = getMemInstValueForLoad(getMemIntrinValue(), Offset, LoadTy, |
| InsertPt, DL); |
| LLVM_DEBUG(dbgs() << "GVN COERCED NONLOCAL MEM INTRIN:\nOffset: " << Offset |
| << " " << *getMemIntrinValue() << '\n' |
| << *Res << '\n' |
| << "\n\n\n"); |
| } else { |
| llvm_unreachable("Should not materialize value from dead block"); |
| } |
| assert(Res && "failed to materialize?"); |
| return Res; |
| } |
| |
| static bool isLifetimeStart(const Instruction *Inst) { |
| if (const IntrinsicInst* II = dyn_cast<IntrinsicInst>(Inst)) |
| return II->getIntrinsicID() == Intrinsic::lifetime_start; |
| return false; |
| } |
| |
| /// Assuming To can be reached from both From and Between, does Between lie on |
| /// every path from From to To? |
| static bool liesBetween(const Instruction *From, Instruction *Between, |
| const Instruction *To, DominatorTree *DT) { |
| if (From->getParent() == Between->getParent()) |
| return DT->dominates(From, Between); |
| SmallSet<BasicBlock *, 1> Exclusion; |
| Exclusion.insert(Between->getParent()); |
| return !isPotentiallyReachable(From, To, &Exclusion, DT); |
| } |
| |
| /// Try to locate the three instruction involved in a missed |
| /// load-elimination case that is due to an intervening store. |
| static void reportMayClobberedLoad(LoadInst *Load, MemDepResult DepInfo, |
| DominatorTree *DT, |
| OptimizationRemarkEmitter *ORE) { |
| using namespace ore; |
| |
| User *OtherAccess = nullptr; |
| |
| OptimizationRemarkMissed R(DEBUG_TYPE, "LoadClobbered", Load); |
| R << "load of type " << NV("Type", Load->getType()) << " not eliminated" |
| << setExtraArgs(); |
| |
| for (auto *U : Load->getPointerOperand()->users()) { |
| if (U != Load && (isa<LoadInst>(U) || isa<StoreInst>(U)) && |
| cast<Instruction>(U)->getFunction() == Load->getFunction() && |
| DT->dominates(cast<Instruction>(U), Load)) { |
| // Use the most immediately dominating value |
| if (OtherAccess) { |
| if (DT->dominates(cast<Instruction>(OtherAccess), cast<Instruction>(U))) |
| OtherAccess = U; |
| else |
| assert(DT->dominates(cast<Instruction>(U), |
| cast<Instruction>(OtherAccess))); |
| } else |
| OtherAccess = U; |
| } |
| } |
| |
| if (!OtherAccess) { |
| // There is no dominating use, check if we can find a closest non-dominating |
| // use that lies between any other potentially available use and Load. |
| for (auto *U : Load->getPointerOperand()->users()) { |
| if (U != Load && (isa<LoadInst>(U) || isa<StoreInst>(U)) && |
| cast<Instruction>(U)->getFunction() == Load->getFunction() && |
| isPotentiallyReachable(cast<Instruction>(U), Load, nullptr, DT)) { |
| if (OtherAccess) { |
| if (liesBetween(cast<Instruction>(OtherAccess), cast<Instruction>(U), |
| Load, DT)) { |
| OtherAccess = U; |
| } else if (!liesBetween(cast<Instruction>(U), |
| cast<Instruction>(OtherAccess), Load, DT)) { |
| // These uses are both partially available at Load were it not for |
| // the clobber, but neither lies strictly after the other. |
| OtherAccess = nullptr; |
| break; |
| } // else: keep current OtherAccess since it lies between U and Load |
| } else { |
| OtherAccess = U; |
| } |
| } |
| } |
| } |
| |
| if (OtherAccess) |
| R << " in favor of " << NV("OtherAccess", OtherAccess); |
| |
| R << " because it is clobbered by " << NV("ClobberedBy", DepInfo.getInst()); |
| |
| ORE->emit(R); |
| } |
| |
| bool GVNPass::AnalyzeLoadAvailability(LoadInst *Load, MemDepResult DepInfo, |
| Value *Address, AvailableValue &Res) { |
| assert((DepInfo.isDef() || DepInfo.isClobber()) && |
| "expected a local dependence"); |
| assert(Load->isUnordered() && "rules below are incorrect for ordered access"); |
| |
| const DataLayout &DL = Load->getModule()->getDataLayout(); |
| |
| Instruction *DepInst = DepInfo.getInst(); |
| if (DepInfo.isClobber()) { |
| // If the dependence is to a store that writes to a superset of the bits |
| // read by the load, we can extract the bits we need for the load from the |
| // stored value. |
| if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) { |
| // Can't forward from non-atomic to atomic without violating memory model. |
| if (Address && Load->isAtomic() <= DepSI->isAtomic()) { |
| int Offset = |
| analyzeLoadFromClobberingStore(Load->getType(), Address, DepSI, DL); |
| if (Offset != -1) { |
| Res = AvailableValue::get(DepSI->getValueOperand(), Offset); |
| return true; |
| } |
| } |
| } |
| |
| // Check to see if we have something like this: |
| // load i32* P |
| // load i8* (P+1) |
| // if we have this, replace the later with an extraction from the former. |
| if (LoadInst *DepLoad = dyn_cast<LoadInst>(DepInst)) { |
| // If this is a clobber and L is the first instruction in its block, then |
| // we have the first instruction in the entry block. |
| // Can't forward from non-atomic to atomic without violating memory model. |
| if (DepLoad != Load && Address && |
| Load->isAtomic() <= DepLoad->isAtomic()) { |
| Type *LoadType = Load->getType(); |
| int Offset = -1; |
| |
| // If MD reported clobber, check it was nested. |
| if (DepInfo.isClobber() && |
| canCoerceMustAliasedValueToLoad(DepLoad, LoadType, DL)) { |
| const auto ClobberOff = MD->getClobberOffset(DepLoad); |
| // GVN has no deal with a negative offset. |
| Offset = (ClobberOff == None || ClobberOff.getValue() < 0) |
| ? -1 |
| : ClobberOff.getValue(); |
| } |
| if (Offset == -1) |
| Offset = |
| analyzeLoadFromClobberingLoad(LoadType, Address, DepLoad, DL); |
| if (Offset != -1) { |
| Res = AvailableValue::getLoad(DepLoad, Offset); |
| return true; |
| } |
| } |
| } |
| |
| // If the clobbering value is a memset/memcpy/memmove, see if we can |
| // forward a value on from it. |
| if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(DepInst)) { |
| if (Address && !Load->isAtomic()) { |
| int Offset = analyzeLoadFromClobberingMemInst(Load->getType(), Address, |
| DepMI, DL); |
| if (Offset != -1) { |
| Res = AvailableValue::getMI(DepMI, Offset); |
| return true; |
| } |
| } |
| } |
| // Nothing known about this clobber, have to be conservative |
| LLVM_DEBUG( |
| // fast print dep, using operator<< on instruction is too slow. |
| dbgs() << "GVN: load "; Load->printAsOperand(dbgs()); |
| dbgs() << " is clobbered by " << *DepInst << '\n';); |
| if (ORE->allowExtraAnalysis(DEBUG_TYPE)) |
| reportMayClobberedLoad(Load, DepInfo, DT, ORE); |
| |
| return false; |
| } |
| assert(DepInfo.isDef() && "follows from above"); |
| |
| // Loading the allocation -> undef. |
| if (isa<AllocaInst>(DepInst) || isMallocLikeFn(DepInst, TLI) || |
| isAlignedAllocLikeFn(DepInst, TLI) || |
| // Loading immediately after lifetime begin -> undef. |
| isLifetimeStart(DepInst)) { |
| Res = AvailableValue::get(UndefValue::get(Load->getType())); |
| return true; |
| } |
| |
| // Loading from calloc (which zero initializes memory) -> zero |
| if (isCallocLikeFn(DepInst, TLI)) { |
| Res = AvailableValue::get(Constant::getNullValue(Load->getType())); |
| return true; |
| } |
| |
| if (StoreInst *S = dyn_cast<StoreInst>(DepInst)) { |
| // Reject loads and stores that are to the same address but are of |
| // different types if we have to. If the stored value is convertable to |
| // the loaded value, we can reuse it. |
| if (!canCoerceMustAliasedValueToLoad(S->getValueOperand(), Load->getType(), |
| DL)) |
| return false; |
| |
| // Can't forward from non-atomic to atomic without violating memory model. |
| if (S->isAtomic() < Load->isAtomic()) |
| return false; |
| |
| Res = AvailableValue::get(S->getValueOperand()); |
| return true; |
| } |
| |
| if (LoadInst *LD = dyn_cast<LoadInst>(DepInst)) { |
| // If the types mismatch and we can't handle it, reject reuse of the load. |
| // If the stored value is larger or equal to the loaded value, we can reuse |
| // it. |
| if (!canCoerceMustAliasedValueToLoad(LD, Load->getType(), DL)) |
| return false; |
| |
| // Can't forward from non-atomic to atomic without violating memory model. |
| if (LD->isAtomic() < Load->isAtomic()) |
| return false; |
| |
| Res = AvailableValue::getLoad(LD); |
| return true; |
| } |
| |
| // Unknown def - must be conservative |
| LLVM_DEBUG( |
| // fast print dep, using operator<< on instruction is too slow. |
| dbgs() << "GVN: load "; Load->printAsOperand(dbgs()); |
| dbgs() << " has unknown def " << *DepInst << '\n';); |
| return false; |
| } |
| |
| void GVNPass::AnalyzeLoadAvailability(LoadInst *Load, LoadDepVect &Deps, |
| AvailValInBlkVect &ValuesPerBlock, |
| UnavailBlkVect &UnavailableBlocks) { |
| // Filter out useless results (non-locals, etc). Keep track of the blocks |
| // where we have a value available in repl, also keep track of whether we see |
| // dependencies that produce an unknown value for the load (such as a call |
| // that could potentially clobber the load). |
| unsigned NumDeps = Deps.size(); |
| for (unsigned i = 0, e = NumDeps; i != e; ++i) { |
| BasicBlock *DepBB = Deps[i].getBB(); |
| MemDepResult DepInfo = Deps[i].getResult(); |
| |
| if (DeadBlocks.count(DepBB)) { |
| // Dead dependent mem-op disguise as a load evaluating the same value |
| // as the load in question. |
| ValuesPerBlock.push_back(AvailableValueInBlock::getUndef(DepBB)); |
| continue; |
| } |
| |
| if (!DepInfo.isDef() && !DepInfo.isClobber()) { |
| UnavailableBlocks.push_back(DepBB); |
| continue; |
| } |
| |
| // The address being loaded in this non-local block may not be the same as |
| // the pointer operand of the load if PHI translation occurs. Make sure |
| // to consider the right address. |
| Value *Address = Deps[i].getAddress(); |
| |
| AvailableValue AV; |
| if (AnalyzeLoadAvailability(Load, DepInfo, Address, AV)) { |
| // subtlety: because we know this was a non-local dependency, we know |
| // it's safe to materialize anywhere between the instruction within |
| // DepInfo and the end of it's block. |
| ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, |
| std::move(AV))); |
| } else { |
| UnavailableBlocks.push_back(DepBB); |
| } |
| } |
| |
| assert(NumDeps == ValuesPerBlock.size() + UnavailableBlocks.size() && |
| "post condition violation"); |
| } |
| |
| void GVNPass::eliminatePartiallyRedundantLoad( |
| LoadInst *Load, AvailValInBlkVect &ValuesPerBlock, |
| MapVector<BasicBlock *, Value *> &AvailableLoads) { |
| for (const auto &AvailableLoad : AvailableLoads) { |
| BasicBlock *UnavailableBlock = AvailableLoad.first; |
| Value *LoadPtr = AvailableLoad.second; |
| |
| auto *NewLoad = |
| new LoadInst(Load->getType(), LoadPtr, Load->getName() + ".pre", |
| Load->isVolatile(), Load->getAlign(), Load->getOrdering(), |
| Load->getSyncScopeID(), UnavailableBlock->getTerminator()); |
| NewLoad->setDebugLoc(Load->getDebugLoc()); |
| if (MSSAU) { |
| auto *MSSA = MSSAU->getMemorySSA(); |
| // Get the defining access of the original load or use the load if it is a |
| // MemoryDef (e.g. because it is volatile). The inserted loads are |
| // guaranteed to load from the same definition. |
| auto *LoadAcc = MSSA->getMemoryAccess(Load); |
| auto *DefiningAcc = |
| isa<MemoryDef>(LoadAcc) ? LoadAcc : LoadAcc->getDefiningAccess(); |
| auto *NewAccess = MSSAU->createMemoryAccessInBB( |
| NewLoad, DefiningAcc, NewLoad->getParent(), |
| MemorySSA::BeforeTerminator); |
| if (auto *NewDef = dyn_cast<MemoryDef>(NewAccess)) |
| MSSAU->insertDef(NewDef, /*RenameUses=*/true); |
| else |
| MSSAU->insertUse(cast<MemoryUse>(NewAccess), /*RenameUses=*/true); |
| } |
| |
| // Transfer the old load's AA tags to the new load. |
| AAMDNodes Tags = Load->getAAMetadata(); |
| if (Tags) |
| NewLoad->setAAMetadata(Tags); |
| |
| if (auto *MD = Load->getMetadata(LLVMContext::MD_invariant_load)) |
| NewLoad->setMetadata(LLVMContext::MD_invariant_load, MD); |
| if (auto *InvGroupMD = Load->getMetadata(LLVMContext::MD_invariant_group)) |
| NewLoad->setMetadata(LLVMContext::MD_invariant_group, InvGroupMD); |
| if (auto *RangeMD = Load->getMetadata(LLVMContext::MD_range)) |
| NewLoad->setMetadata(LLVMContext::MD_range, RangeMD); |
| if (auto *AccessMD = Load->getMetadata(LLVMContext::MD_access_group)) |
| if (LI && |
| LI->getLoopFor(Load->getParent()) == LI->getLoopFor(UnavailableBlock)) |
| NewLoad->setMetadata(LLVMContext::MD_access_group, AccessMD); |
| |
| // We do not propagate the old load's debug location, because the new |
| // load now lives in a different BB, and we want to avoid a jumpy line |
| // table. |
| // FIXME: How do we retain source locations without causing poor debugging |
| // behavior? |
| |
| // Add the newly created load. |
| ValuesPerBlock.push_back( |
| AvailableValueInBlock::get(UnavailableBlock, NewLoad)); |
| MD->invalidateCachedPointerInfo(LoadPtr); |
| LLVM_DEBUG(dbgs() << "GVN INSERTED " << *NewLoad << '\n'); |
| } |
| |
| // Perform PHI construction. |
| Value *V = ConstructSSAForLoadSet(Load, ValuesPerBlock, *this); |
| Load->replaceAllUsesWith(V); |
| if (isa<PHINode>(V)) |
| V->takeName(Load); |
| if (Instruction *I = dyn_cast<Instruction>(V)) |
| I->setDebugLoc(Load->getDebugLoc()); |
| if (V->getType()->isPtrOrPtrVectorTy()) |
| MD->invalidateCachedPointerInfo(V); |
| markInstructionForDeletion(Load); |
| ORE->emit([&]() { |
| return OptimizationRemark(DEBUG_TYPE, "LoadPRE", Load) |
| << "load eliminated by PRE"; |
| }); |
| } |
| |
| bool GVNPass::PerformLoadPRE(LoadInst *Load, AvailValInBlkVect &ValuesPerBlock, |
| UnavailBlkVect &UnavailableBlocks) { |
| // Okay, we have *some* definitions of the value. This means that the value |
| // is available in some of our (transitive) predecessors. Lets think about |
| // doing PRE of this load. This will involve inserting a new load into the |
| // predecessor when it's not available. We could do this in general, but |
| // prefer to not increase code size. As such, we only do this when we know |
| // that we only have to insert *one* load (which means we're basically moving |
| // the load, not inserting a new one). |
| |
| SmallPtrSet<BasicBlock *, 4> Blockers(UnavailableBlocks.begin(), |
| UnavailableBlocks.end()); |
| |
| // Let's find the first basic block with more than one predecessor. Walk |
| // backwards through predecessors if needed. |
| BasicBlock *LoadBB = Load->getParent(); |
| BasicBlock *TmpBB = LoadBB; |
| |
| // Check that there is no implicit control flow instructions above our load in |
| // its block. If there is an instruction that doesn't always pass the |
| // execution to the following instruction, then moving through it may become |
| // invalid. For example: |
| // |
| // int arr[LEN]; |
| // int index = ???; |
| // ... |
| // guard(0 <= index && index < LEN); |
| // use(arr[index]); |
| // |
| // It is illegal to move the array access to any point above the guard, |
| // because if the index is out of bounds we should deoptimize rather than |
| // access the array. |
| // Check that there is no guard in this block above our instruction. |
| bool MustEnsureSafetyOfSpeculativeExecution = |
| ICF->isDominatedByICFIFromSameBlock(Load); |
| |
| while (TmpBB->getSinglePredecessor()) { |
| TmpBB = TmpBB->getSinglePredecessor(); |
| if (TmpBB == LoadBB) // Infinite (unreachable) loop. |
| return false; |
| if (Blockers.count(TmpBB)) |
| return false; |
| |
| // If any of these blocks has more than one successor (i.e. if the edge we |
| // just traversed was critical), then there are other paths through this |
| // block along which the load may not be anticipated. Hoisting the load |
| // above this block would be adding the load to execution paths along |
| // which it was not previously executed. |
| if (TmpBB->getTerminator()->getNumSuccessors() != 1) |
| return false; |
| |
| // Check that there is no implicit control flow in a block above. |
| MustEnsureSafetyOfSpeculativeExecution = |
| MustEnsureSafetyOfSpeculativeExecution || ICF->hasICF(TmpBB); |
| } |
| |
| assert(TmpBB); |
| LoadBB = TmpBB; |
| |
| // Check to see how many predecessors have the loaded value fully |
| // available. |
| MapVector<BasicBlock *, Value *> PredLoads; |
| DenseMap<BasicBlock *, AvailabilityState> FullyAvailableBlocks; |
| for (const AvailableValueInBlock &AV : ValuesPerBlock) |
| FullyAvailableBlocks[AV.BB] = AvailabilityState::Available; |
| for (BasicBlock *UnavailableBB : UnavailableBlocks) |
| FullyAvailableBlocks[UnavailableBB] = AvailabilityState::Unavailable; |
| |
| SmallVector<BasicBlock *, 4> CriticalEdgePred; |
| for (BasicBlock *Pred : predecessors(LoadBB)) { |
| // If any predecessor block is an EH pad that does not allow non-PHI |
| // instructions before the terminator, we can't PRE the load. |
| if (Pred->getTerminator()->isEHPad()) { |
| LLVM_DEBUG( |
| dbgs() << "COULD NOT PRE LOAD BECAUSE OF AN EH PAD PREDECESSOR '" |
| << Pred->getName() << "': " << *Load << '\n'); |
| return false; |
| } |
| |
| if (IsValueFullyAvailableInBlock(Pred, FullyAvailableBlocks)) { |
| continue; |
| } |
| |
| if (Pred->getTerminator()->getNumSuccessors() != 1) { |
| if (isa<IndirectBrInst>(Pred->getTerminator())) { |
| LLVM_DEBUG( |
| dbgs() << "COULD NOT PRE LOAD BECAUSE OF INDBR CRITICAL EDGE '" |
| << Pred->getName() << "': " << *Load << '\n'); |
| return false; |
| } |
| |
| // FIXME: Can we support the fallthrough edge? |
| if (isa<CallBrInst>(Pred->getTerminator())) { |
| LLVM_DEBUG( |
| dbgs() << "COULD NOT PRE LOAD BECAUSE OF CALLBR CRITICAL EDGE '" |
| << Pred->getName() << "': " << *Load << '\n'); |
| return false; |
| } |
| |
| if (LoadBB->isEHPad()) { |
| LLVM_DEBUG( |
| dbgs() << "COULD NOT PRE LOAD BECAUSE OF AN EH PAD CRITICAL EDGE '" |
| << Pred->getName() << "': " << *Load << '\n'); |
| return false; |
| } |
| |
| // Do not split backedge as it will break the canonical loop form. |
| if (!isLoadPRESplitBackedgeEnabled()) |
| if (DT->dominates(LoadBB, Pred)) { |
| LLVM_DEBUG( |
| dbgs() |
| << "COULD NOT PRE LOAD BECAUSE OF A BACKEDGE CRITICAL EDGE '" |
| << Pred->getName() << "': " << *Load << '\n'); |
| return false; |
| } |
| |
| CriticalEdgePred.push_back(Pred); |
| } else { |
| // Only add the predecessors that will not be split for now. |
| PredLoads[Pred] = nullptr; |
| } |
| } |
| |
| // Decide whether PRE is profitable for this load. |
| unsigned NumUnavailablePreds = PredLoads.size() + CriticalEdgePred.size(); |
| assert(NumUnavailablePreds != 0 && |
| "Fully available value should already be eliminated!"); |
| |
| // If this load is unavailable in multiple predecessors, reject it. |
| // FIXME: If we could restructure the CFG, we could make a common pred with |
| // all the preds that don't have an available Load and insert a new load into |
| // that one block. |
| if (NumUnavailablePreds != 1) |
| return false; |
| |
| // Now we know where we will insert load. We must ensure that it is safe |
| // to speculatively execute the load at that points. |
| if (MustEnsureSafetyOfSpeculativeExecution) { |
| if (CriticalEdgePred.size()) |
| if (!isSafeToSpeculativelyExecute(Load, LoadBB->getFirstNonPHI(), DT)) |
| return false; |
| for (auto &PL : PredLoads) |
| if (!isSafeToSpeculativelyExecute(Load, PL.first->getTerminator(), DT)) |
| return false; |
| } |
| |
| // Split critical edges, and update the unavailable predecessors accordingly. |
| for (BasicBlock *OrigPred : CriticalEdgePred) { |
| BasicBlock *NewPred = splitCriticalEdges(OrigPred, LoadBB); |
| assert(!PredLoads.count(OrigPred) && "Split edges shouldn't be in map!"); |
| PredLoads[NewPred] = nullptr; |
| LLVM_DEBUG(dbgs() << "Split critical edge " << OrigPred->getName() << "->" |
| << LoadBB->getName() << '\n'); |
| } |
| |
| // Check if the load can safely be moved to all the unavailable predecessors. |
| bool CanDoPRE = true; |
| const DataLayout &DL = Load->getModule()->getDataLayout(); |
| SmallVector<Instruction*, 8> NewInsts; |
| for (auto &PredLoad : PredLoads) { |
| BasicBlock *UnavailablePred = PredLoad.first; |
| |
| // Do PHI translation to get its value in the predecessor if necessary. The |
| // returned pointer (if non-null) is guaranteed to dominate UnavailablePred. |
| // We do the translation for each edge we skipped by going from Load's block |
| // to LoadBB, otherwise we might miss pieces needing translation. |
| |
| // If all preds have a single successor, then we know it is safe to insert |
| // the load on the pred (?!?), so we can insert code to materialize the |
| // pointer if it is not available. |
| Value *LoadPtr = Load->getPointerOperand(); |
| BasicBlock *Cur = Load->getParent(); |
| while (Cur != LoadBB) { |
| PHITransAddr Address(LoadPtr, DL, AC); |
| LoadPtr = Address.PHITranslateWithInsertion( |
| Cur, Cur->getSinglePredecessor(), *DT, NewInsts); |
| if (!LoadPtr) { |
| CanDoPRE = false; |
| break; |
| } |
| Cur = Cur->getSinglePredecessor(); |
| } |
| |
| if (LoadPtr) { |
| PHITransAddr Address(LoadPtr, DL, AC); |
| LoadPtr = Address.PHITranslateWithInsertion(LoadBB, UnavailablePred, *DT, |
| NewInsts); |
| } |
| // If we couldn't find or insert a computation of this phi translated value, |
| // we fail PRE. |
| if (!LoadPtr) { |
| LLVM_DEBUG(dbgs() << "COULDN'T INSERT PHI TRANSLATED VALUE OF: " |
| << *Load->getPointerOperand() << "\n"); |
| CanDoPRE = false; |
| break; |
| } |
| |
| PredLoad.second = LoadPtr; |
| } |
| |
| if (!CanDoPRE) { |
| while (!NewInsts.empty()) { |
| // Erase instructions generated by the failed PHI translation before |
| // trying to number them. PHI translation might insert instructions |
| // in basic blocks other than the current one, and we delete them |
| // directly, as markInstructionForDeletion only allows removing from the |
| // current basic block. |
| NewInsts.pop_back_val()->eraseFromParent(); |
| } |
| // HINT: Don't revert the edge-splitting as following transformation may |
| // also need to split these critical edges. |
| return !CriticalEdgePred.empty(); |
| } |
| |
| // Okay, we can eliminate this load by inserting a reload in the predecessor |
| // and using PHI construction to get the value in the other predecessors, do |
| // it. |
| LLVM_DEBUG(dbgs() << "GVN REMOVING PRE LOAD: " << *Load << '\n'); |
| LLVM_DEBUG(if (!NewInsts.empty()) dbgs() << "INSERTED " << NewInsts.size() |
| << " INSTS: " << *NewInsts.back() |
| << '\n'); |
| |
| // Assign value numbers to the new instructions. |
| for (Instruction *I : NewInsts) { |
| // Instructions that have been inserted in predecessor(s) to materialize |
| // the load address do not retain their original debug locations. Doing |
| // so could lead to confusing (but correct) source attributions. |
| I->updateLocationAfterHoist(); |
| |
| // FIXME: We really _ought_ to insert these value numbers into their |
| // parent's availability map. However, in doing so, we risk getting into |
| // ordering issues. If a block hasn't been processed yet, we would be |
| // marking a value as AVAIL-IN, which isn't what we intend. |
| VN.lookupOrAdd(I); |
| } |
| |
| eliminatePartiallyRedundantLoad(Load, ValuesPerBlock, PredLoads); |
| ++NumPRELoad; |
| return true; |
| } |
| |
| bool GVNPass::performLoopLoadPRE(LoadInst *Load, |
| AvailValInBlkVect &ValuesPerBlock, |
| UnavailBlkVect &UnavailableBlocks) { |
| if (!LI) |
| return false; |
| |
| const Loop *L = LI->getLoopFor(Load->getParent()); |
| // TODO: Generalize to other loop blocks that dominate the latch. |
| if (!L || L->getHeader() != Load->getParent()) |
| return false; |
| |
| BasicBlock *Preheader = L->getLoopPreheader(); |
| BasicBlock *Latch = L->getLoopLatch(); |
| if (!Preheader || !Latch) |
| return false; |
| |
| Value *LoadPtr = Load->getPointerOperand(); |
| // Must be available in preheader. |
| if (!L->isLoopInvariant(LoadPtr)) |
| return false; |
| |
| // We plan to hoist the load to preheader without introducing a new fault. |
| // In order to do it, we need to prove that we cannot side-exit the loop |
| // once loop header is first entered before execution of the load. |
| if (ICF->isDominatedByICFIFromSameBlock(Load)) |
| return false; |
| |
| BasicBlock *LoopBlock = nullptr; |
| for (auto *Blocker : UnavailableBlocks) { |
| // Blockers from outside the loop are handled in preheader. |
| if (!L->contains(Blocker)) |
| continue; |
| |
| // Only allow one loop block. Loop header is not less frequently executed |
| // than each loop block, and likely it is much more frequently executed. But |
| // in case of multiple loop blocks, we need extra information (such as block |
| // frequency info) to understand whether it is profitable to PRE into |
| // multiple loop blocks. |
| if (LoopBlock) |
| return false; |
| |
| // Do not sink into inner loops. This may be non-profitable. |
| if (L != LI->getLoopFor(Blocker)) |
| return false; |
| |
| // Blocks that dominate the latch execute on every single iteration, maybe |
| // except the last one. So PREing into these blocks doesn't make much sense |
| // in most cases. But the blocks that do not necessarily execute on each |
| // iteration are sometimes much colder than the header, and this is when |
| // PRE is potentially profitable. |
| if (DT->dominates(Blocker, Latch)) |
| return false; |
| |
| // Make sure that the terminator itself doesn't clobber. |
| if (Blocker->getTerminator()->mayWriteToMemory()) |
| return false; |
| |
| LoopBlock = Blocker; |
| } |
| |
| if (!LoopBlock) |
| return false; |
| |
| // Make sure the memory at this pointer cannot be freed, therefore we can |
| // safely reload from it after clobber. |
| if (LoadPtr->canBeFreed()) |
| return false; |
| |
| // TODO: Support critical edge splitting if blocker has more than 1 successor. |
| MapVector<BasicBlock *, Value *> AvailableLoads; |
| AvailableLoads[LoopBlock] = LoadPtr; |
| AvailableLoads[Preheader] = LoadPtr; |
| |
| LLVM_DEBUG(dbgs() << "GVN REMOVING PRE LOOP LOAD: " << *Load << '\n'); |
| eliminatePartiallyRedundantLoad(Load, ValuesPerBlock, AvailableLoads); |
| ++NumPRELoopLoad; |
| return true; |
| } |
| |
| static void reportLoadElim(LoadInst *Load, Value *AvailableValue, |
| OptimizationRemarkEmitter *ORE) { |
| using namespace ore; |
| |
| ORE->emit([&]() { |
| return OptimizationRemark(DEBUG_TYPE, "LoadElim", Load) |
| << "load of type " << NV("Type", Load->getType()) << " eliminated" |
| << setExtraArgs() << " in favor of " |
| << NV("InfavorOfValue", AvailableValue); |
| }); |
| } |
| |
| /// Attempt to eliminate a load whose dependencies are |
| /// non-local by performing PHI construction. |
| bool GVNPass::processNonLocalLoad(LoadInst *Load) { |
| // non-local speculations are not allowed under asan. |
| if (Load->getParent()->getParent()->hasFnAttribute( |
| Attribute::SanitizeAddress) || |
| Load->getParent()->getParent()->hasFnAttribute( |
| Attribute::SanitizeHWAddress)) |
| return false; |
| |
| // Step 1: Find the non-local dependencies of the load. |
| LoadDepVect Deps; |
| MD->getNonLocalPointerDependency(Load, Deps); |
| |
| // If we had to process more than one hundred blocks to find the |
| // dependencies, this load isn't worth worrying about. Optimizing |
| // it will be too expensive. |
| unsigned NumDeps = Deps.size(); |
| if (NumDeps > MaxNumDeps) |
| return false; |
| |
| // If we had a phi translation failure, we'll have a single entry which is a |
| // clobber in the current block. Reject this early. |
| if (NumDeps == 1 && |
| !Deps[0].getResult().isDef() && !Deps[0].getResult().isClobber()) { |
| LLVM_DEBUG(dbgs() << "GVN: non-local load "; Load->printAsOperand(dbgs()); |
| dbgs() << " has unknown dependencies\n";); |
| return false; |
| } |
| |
| bool Changed = false; |
| // If this load follows a GEP, see if we can PRE the indices before analyzing. |
| if (GetElementPtrInst *GEP = |
| dyn_cast<GetElementPtrInst>(Load->getOperand(0))) { |
| for (Use &U : GEP->indices()) |
| if (Instruction *I = dyn_cast<Instruction>(U.get())) |
| Changed |= performScalarPRE(I); |
| } |
| |
| // Step 2: Analyze the availability of the load |
| AvailValInBlkVect ValuesPerBlock; |
| UnavailBlkVect UnavailableBlocks; |
| AnalyzeLoadAvailability(Load, Deps, ValuesPerBlock, UnavailableBlocks); |
| |
| // If we have no predecessors that produce a known value for this load, exit |
| // early. |
| if (ValuesPerBlock.empty()) |
| return Changed; |
| |
| // Step 3: Eliminate fully redundancy. |
| // |
| // If all of the instructions we depend on produce a known value for this |
| // load, then it is fully redundant and we can use PHI insertion to compute |
| // its value. Insert PHIs and remove the fully redundant value now. |
| if (UnavailableBlocks.empty()) { |
| LLVM_DEBUG(dbgs() << "GVN REMOVING NONLOCAL LOAD: " << *Load << '\n'); |
| |
| // Perform PHI construction. |
| Value *V = ConstructSSAForLoadSet(Load, ValuesPerBlock, *this); |
| Load->replaceAllUsesWith(V); |
| |
| if (isa<PHINode>(V)) |
| V->takeName(Load); |
| if (Instruction *I = dyn_cast<Instruction>(V)) |
| // If instruction I has debug info, then we should not update it. |
| // Also, if I has a null DebugLoc, then it is still potentially incorrect |
| // to propagate Load's DebugLoc because Load may not post-dominate I. |
| if (Load->getDebugLoc() && Load->getParent() == I->getParent()) |
| I->setDebugLoc(Load->getDebugLoc()); |
| if (V->getType()->isPtrOrPtrVectorTy()) |
| MD->invalidateCachedPointerInfo(V); |
| markInstructionForDeletion(Load); |
| ++NumGVNLoad; |
| reportLoadElim(Load, V, ORE); |
| return true; |
| } |
| |
| // Step 4: Eliminate partial redundancy. |
| if (!isPREEnabled() || !isLoadPREEnabled()) |
| return Changed; |
| if (!isLoadInLoopPREEnabled() && LI && LI->getLoopFor(Load->getParent())) |
| return Changed; |
| |
| if (performLoopLoadPRE(Load, ValuesPerBlock, UnavailableBlocks) || |
| PerformLoadPRE(Load, ValuesPerBlock, UnavailableBlocks)) |
| return true; |
| |
| return Changed; |
| } |
| |
| static bool impliesEquivalanceIfTrue(CmpInst* Cmp) { |
| if (Cmp->getPredicate() == CmpInst::Predicate::ICMP_EQ) |
| return true; |
| |
| // Floating point comparisons can be equal, but not equivalent. Cases: |
| // NaNs for unordered operators |
| // +0.0 vs 0.0 for all operators |
| if (Cmp->getPredicate() == CmpInst::Predicate::FCMP_OEQ || |
| (Cmp->getPredicate() == CmpInst::Predicate::FCMP_UEQ && |
| Cmp->getFastMathFlags().noNaNs())) { |
| Value *LHS = Cmp->getOperand(0); |
| Value *RHS = Cmp->getOperand(1); |
| // If we can prove either side non-zero, then equality must imply |
| // equivalence. |
| // FIXME: We should do this optimization if 'no signed zeros' is |
| // applicable via an instruction-level fast-math-flag or some other |
| // indicator that relaxed FP semantics are being used. |
| if (isa<ConstantFP>(LHS) && !cast<ConstantFP>(LHS)->isZero()) |
| return true; |
| if (isa<ConstantFP>(RHS) && !cast<ConstantFP>(RHS)->isZero()) |
| return true;; |
| // TODO: Handle vector floating point constants |
| } |
| return false; |
| } |
| |
| static bool impliesEquivalanceIfFalse(CmpInst* Cmp) { |
| if (Cmp->getPredicate() == CmpInst::Predicate::ICMP_NE) |
| return true; |
| |
| // Floating point comparisons can be equal, but not equivelent. Cases: |
| // NaNs for unordered operators |
| // +0.0 vs 0.0 for all operators |
| if ((Cmp->getPredicate() == CmpInst::Predicate::FCMP_ONE && |
| Cmp->getFastMathFlags().noNaNs()) || |
| Cmp->getPredicate() == CmpInst::Predicate::FCMP_UNE) { |
| Value *LHS = Cmp->getOperand(0); |
| Value *RHS = Cmp->getOperand(1); |
| // If we can prove either side non-zero, then equality must imply |
| // equivalence. |
| // FIXME: We should do this optimization if 'no signed zeros' is |
| // applicable via an instruction-level fast-math-flag or some other |
| // indicator that relaxed FP semantics are being used. |
| if (isa<ConstantFP>(LHS) && !cast<ConstantFP>(LHS)->isZero()) |
| return true; |
| if (isa<ConstantFP>(RHS) && !cast<ConstantFP>(RHS)->isZero()) |
| return true;; |
| // TODO: Handle vector floating point constants |
| } |
| return false; |
| } |
| |
| |
| static bool hasUsersIn(Value *V, BasicBlock *BB) { |
| for (User *U : V->users()) |
| if (isa<Instruction>(U) && |
| cast<Instruction>(U)->getParent() == BB) |
| return true; |
| return false; |
| } |
| |
| bool GVNPass::processAssumeIntrinsic(AssumeInst *IntrinsicI) { |
| Value *V = IntrinsicI->getArgOperand(0); |
| |
| if (ConstantInt *Cond = dyn_cast<ConstantInt>(V)) { |
| if (Cond->isZero()) { |
| Type *Int8Ty = Type::getInt8Ty(V->getContext()); |
| // Insert a new store to null instruction before the load to indicate that |
| // this code is not reachable. FIXME: We could insert unreachable |
| // instruction directly because we can modify the CFG. |
| auto *NewS = new StoreInst(UndefValue::get(Int8Ty), |
| Constant::getNullValue(Int8Ty->getPointerTo()), |
| IntrinsicI); |
| if (MSSAU) { |
| const MemoryUseOrDef *FirstNonDom = nullptr; |
| const auto *AL = |
| MSSAU->getMemorySSA()->getBlockAccesses(IntrinsicI->getParent()); |
| |
| // If there are accesses in the current basic block, find the first one |
| // that does not come before NewS. The new memory access is inserted |
| // after the found access or before the terminator if no such access is |
| // found. |
| if (AL) { |
| for (auto &Acc : *AL) { |
| if (auto *Current = dyn_cast<MemoryUseOrDef>(&Acc)) |
| if (!Current->getMemoryInst()->comesBefore(NewS)) { |
| FirstNonDom = Current; |
| break; |
| } |
| } |
| } |
| |
| // This added store is to null, so it will never executed and we can |
| // just use the LiveOnEntry def as defining access. |
| auto *NewDef = |
| FirstNonDom ? MSSAU->createMemoryAccessBefore( |
| NewS, MSSAU->getMemorySSA()->getLiveOnEntryDef(), |
| const_cast<MemoryUseOrDef *>(FirstNonDom)) |
| : MSSAU->createMemoryAccessInBB( |
| NewS, MSSAU->getMemorySSA()->getLiveOnEntryDef(), |
| NewS->getParent(), MemorySSA::BeforeTerminator); |
| |
| MSSAU->insertDef(cast<MemoryDef>(NewDef), /*RenameUses=*/false); |
| } |
| } |
| if (isAssumeWithEmptyBundle(*IntrinsicI)) |
| markInstructionForDeletion(IntrinsicI); |
| return false; |
| } else if (isa<Constant>(V)) { |
| // If it's not false, and constant, it must evaluate to true. This means our |
| // assume is assume(true), and thus, pointless, and we don't want to do |
| // anything more here. |
| return false; |
| } |
| |
| Constant *True = ConstantInt::getTrue(V->getContext()); |
| bool Changed = false; |
| |
| for (BasicBlock *Successor : successors(IntrinsicI->getParent())) { |
| BasicBlockEdge Edge(IntrinsicI->getParent(), Successor); |
| |
| // This property is only true in dominated successors, propagateEquality |
| // will check dominance for us. |
| Changed |= propagateEquality(V, True, Edge, false); |
| } |
| |
| // We can replace assume value with true, which covers cases like this: |
| // call void @llvm.assume(i1 %cmp) |
| // br i1 %cmp, label %bb1, label %bb2 ; will change %cmp to true |
| ReplaceOperandsWithMap[V] = True; |
| |
| // Similarly, after assume(!NotV) we know that NotV == false. |
| Value *NotV; |
| if (match(V, m_Not(m_Value(NotV)))) |
| ReplaceOperandsWithMap[NotV] = ConstantInt::getFalse(V->getContext()); |
| |
| // If we find an equality fact, canonicalize all dominated uses in this block |
| // to one of the two values. We heuristically choice the "oldest" of the |
| // two where age is determined by value number. (Note that propagateEquality |
| // above handles the cross block case.) |
| // |
| // Key case to cover are: |
| // 1) |
| // %cmp = fcmp oeq float 3.000000e+00, %0 ; const on lhs could happen |
| // call void @llvm.assume(i1 %cmp) |
| // ret float %0 ; will change it to ret float 3.000000e+00 |
| // 2) |
| // %load = load float, float* %addr |
| // %cmp = fcmp oeq float %load, %0 |
| // call void @llvm.assume(i1 %cmp) |
| // ret float %load ; will change it to ret float %0 |
| if (auto *CmpI = dyn_cast<CmpInst>(V)) { |
| if (impliesEquivalanceIfTrue(CmpI)) { |
| Value *CmpLHS = CmpI->getOperand(0); |
| Value *CmpRHS = CmpI->getOperand(1); |
| // Heuristically pick the better replacement -- the choice of heuristic |
| // isn't terribly important here, but the fact we canonicalize on some |
| // replacement is for exposing other simplifications. |
| // TODO: pull this out as a helper function and reuse w/existing |
| // (slightly different) logic. |
| if (isa<Constant>(CmpLHS) && !isa<Constant>(CmpRHS)) |
| std::swap(CmpLHS, CmpRHS); |
| if (!isa<Instruction>(CmpLHS) && isa<Instruction>(CmpRHS)) |
| std::swap(CmpLHS, CmpRHS); |
| if ((isa<Argument>(CmpLHS) && isa<Argument>(CmpRHS)) || |
| (isa<Instruction>(CmpLHS) && isa<Instruction>(CmpRHS))) { |
| // Move the 'oldest' value to the right-hand side, using the value |
| // number as a proxy for age. |
| uint32_t LVN = VN.lookupOrAdd(CmpLHS); |
| uint32_t RVN = VN.lookupOrAdd(CmpRHS); |
| if (LVN < RVN) |
| std::swap(CmpLHS, CmpRHS); |
| } |
| |
| // Handle degenerate case where we either haven't pruned a dead path or a |
| // removed a trivial assume yet. |
| if (isa<Constant>(CmpLHS) && isa<Constant>(CmpRHS)) |
| return Changed; |
| |
| LLVM_DEBUG(dbgs() << "Replacing dominated uses of " |
| << *CmpLHS << " with " |
| << *CmpRHS << " in block " |
| << IntrinsicI->getParent()->getName() << "\n"); |
| |
| |
| // Setup the replacement map - this handles uses within the same block |
| if (hasUsersIn(CmpLHS, IntrinsicI->getParent())) |
| ReplaceOperandsWithMap[CmpLHS] = CmpRHS; |
| |
| // NOTE: The non-block local cases are handled by the call to |
| // propagateEquality above; this block is just about handling the block |
| // local cases. TODO: There's a bunch of logic in propagateEqualiy which |
| // isn't duplicated for the block local case, can we share it somehow? |
| } |
| } |
| return Changed; |
| } |
| |
| static void patchAndReplaceAllUsesWith(Instruction *I, Value *Repl) { |
| patchReplacementInstruction(I, Repl); |
| I->replaceAllUsesWith(Repl); |
| } |
| |
| /// Attempt to eliminate a load, first by eliminating it |
| /// locally, and then attempting non-local elimination if that fails. |
| bool GVNPass::processLoad(LoadInst *L) { |
| if (!MD) |
| return false; |
| |
| // This code hasn't been audited for ordered or volatile memory access |
| if (!L->isUnordered()) |
| return false; |
| |
| if (L->use_empty()) { |
| markInstructionForDeletion(L); |
| return true; |
| } |
| |
| // ... to a pointer that has been loaded from before... |
| MemDepResult Dep = MD->getDependency(L); |
| |
| // If it is defined in another block, try harder. |
| if (Dep.isNonLocal()) |
| return processNonLocalLoad(L); |
| |
| // Only handle the local case below |
| if (!Dep.isDef() && !Dep.isClobber()) { |
| // This might be a NonFuncLocal or an Unknown |
| LLVM_DEBUG( |
| // fast print dep, using operator<< on instruction is too slow. |
| dbgs() << "GVN: load "; L->printAsOperand(dbgs()); |
| dbgs() << " has unknown dependence\n";); |
| return false; |
| } |
| |
| AvailableValue AV; |
| if (AnalyzeLoadAvailability(L, Dep, L->getPointerOperand(), AV)) { |
| Value *AvailableValue = AV.MaterializeAdjustedValue(L, L, *this); |
| |
| // Replace the load! |
| patchAndReplaceAllUsesWith(L, AvailableValue); |
| markInstructionForDeletion(L); |
| if (MSSAU) |
| MSSAU->removeMemoryAccess(L); |
| ++NumGVNLoad; |
| reportLoadElim(L, AvailableValue, ORE); |
| // Tell MDA to reexamine the reused pointer since we might have more |
| // information after forwarding it. |
| if (MD && AvailableValue->getType()->isPtrOrPtrVectorTy()) |
| MD->invalidateCachedPointerInfo(AvailableValue); |
| return true; |
| } |
| |
| return false; |
| } |
| |
| /// Return a pair the first field showing the value number of \p Exp and the |
| /// second field showing whether it is a value number newly created. |
| std::pair<uint32_t, bool> |
| GVNPass::ValueTable::assignExpNewValueNum(Expression &Exp) { |
| uint32_t &e = expressionNumbering[Exp]; |
| bool CreateNewValNum = !e; |
| if (CreateNewValNum) { |
| Expressions.push_back(Exp); |
| if (ExprIdx.size() < nextValueNumber + 1) |
| ExprIdx.resize(nextValueNumber * 2); |
| e = nextValueNumber; |
| ExprIdx[nextValueNumber++] = nextExprNumber++; |
| } |
| return {e, CreateNewValNum}; |
| } |
| |
| /// Return whether all the values related with the same \p num are |
| /// defined in \p BB. |
| bool GVNPass::ValueTable::areAllValsInBB(uint32_t Num, const BasicBlock *BB, |
| GVNPass &Gvn) { |
| LeaderTableEntry *Vals = &Gvn.LeaderTable[Num]; |
| while (Vals && Vals->BB == BB) |
| Vals = Vals->Next; |
| return !Vals; |
| } |
| |
| /// Wrap phiTranslateImpl to provide caching functionality. |
| uint32_t GVNPass::ValueTable::phiTranslate(const BasicBlock *Pred, |
| const BasicBlock *PhiBlock, |
| uint32_t Num, GVNPass &Gvn) { |
| auto FindRes = PhiTranslateTable.find({Num, Pred}); |
| if (FindRes != PhiTranslateTable.end()) |
| return FindRes->second; |
| uint32_t NewNum = phiTranslateImpl(Pred, PhiBlock, Num, Gvn); |
| PhiTranslateTable.insert({{Num, Pred}, NewNum}); |
| return NewNum; |
| } |
| |
| // Return true if the value number \p Num and NewNum have equal value. |
| // Return false if the result is unknown. |
| bool GVNPass::ValueTable::areCallValsEqual(uint32_t Num, uint32_t NewNum, |
| const BasicBlock *Pred, |
| const BasicBlock *PhiBlock, |
| GVNPass &Gvn) { |
| CallInst *Call = nullptr; |
| LeaderTableEntry *Vals = &Gvn.LeaderTable[Num]; |
| while (Vals) { |
| Call = dyn_cast<CallInst>(Vals->Val); |
| if (Call && Call->getParent() == PhiBlock) |
| break; |
| Vals = Vals->Next; |
| } |
| |
| if (AA->doesNotAccessMemory(Call)) |
| return true; |
| |
| if (!MD || !AA->onlyReadsMemory(Call)) |
| return false; |
| |
| MemDepResult local_dep = MD->getDependency(Call); |
| if (!local_dep.isNonLocal()) |
| return false; |
| |
| const MemoryDependenceResults::NonLocalDepInfo &deps = |
| MD->getNonLocalCallDependency(Call); |
| |
| // Check to see if the Call has no function local clobber. |
| for (const NonLocalDepEntry &D : deps) { |
| if (D.getResult().isNonFuncLocal()) |
| return true; |
| } |
| return false; |
| } |
| |
| /// Translate value number \p Num using phis, so that it has the values of |
| /// the phis in BB. |
| uint32_t GVNPass::ValueTable::phiTranslateImpl(const BasicBlock *Pred, |
| const BasicBlock *PhiBlock, |
| uint32_t Num, GVNPass &Gvn) { |
| if (PHINode *PN = NumberingPhi[Num]) { |
| for (unsigned i = 0; i != PN->getNumIncomingValues(); ++i) { |
| if (PN->getParent() == PhiBlock && PN->getIncomingBlock(i) == Pred) |
| if (uint32_t TransVal = lookup(PN->getIncomingValue(i), false)) |
| return TransVal; |
| } |
| return Num; |
| } |
| |
| // If there is any value related with Num is defined in a BB other than |
| // PhiBlock, it cannot depend on a phi in PhiBlock without going through |
| // a backedge. We can do an early exit in that case to save compile time. |
| if (!areAllValsInBB(Num, PhiBlock, Gvn)) |
| return Num; |
| |
| if (Num >= ExprIdx.size() || ExprIdx[Num] == 0) |
| return Num; |
| Expression Exp = Expressions[ExprIdx[Num]]; |
| |
| for (unsigned i = 0; i < Exp.varargs.size(); i++) { |
| // For InsertValue and ExtractValue, some varargs are index numbers |
| // instead of value numbers. Those index numbers should not be |
| // translated. |
| if ((i > 1 && Exp.opcode == Instruction::InsertValue) || |
| (i > 0 && Exp.opcode == Instruction::ExtractValue) || |
| (i > 1 && Exp.opcode == Instruction::ShuffleVector)) |
| continue; |
| Exp.varargs[i] = phiTranslate(Pred, PhiBlock, Exp.varargs[i], Gvn); |
| } |
| |
| if (Exp.commutative) { |
| assert(Exp.varargs.size() >= 2 && "Unsupported commutative instruction!"); |
| if (Exp.varargs[0] > Exp.varargs[1]) { |
| std::swap(Exp.varargs[0], Exp.varargs[1]); |
| uint32_t Opcode = Exp.opcode >> 8; |
| if (Opcode == Instruction::ICmp || Opcode == Instruction::FCmp) |
| Exp.opcode = (Opcode << 8) | |
| CmpInst::getSwappedPredicate( |
| static_cast<CmpInst::Predicate>(Exp.opcode & 255)); |
| } |
| } |
| |
| if (uint32_t NewNum = expressionNumbering[Exp]) { |
| if (Exp.opcode == Instruction::Call && NewNum != Num) |
| return areCallValsEqual(Num, NewNum, Pred, PhiBlock, Gvn) ? NewNum : Num; |
| return NewNum; |
| } |
| return Num; |
| } |
| |
| /// Erase stale entry from phiTranslate cache so phiTranslate can be computed |
| /// again. |
| void GVNPass::ValueTable::eraseTranslateCacheEntry( |
| uint32_t Num, const BasicBlock &CurrBlock) { |
| for (const BasicBlock *Pred : predecessors(&CurrBlock)) |
| PhiTranslateTable.erase({Num, Pred}); |
| } |
| |
| // In order to find a leader for a given value number at a |
| // specific basic block, we first obtain the list of all Values for that number, |
| // and then scan the list to find one whose block dominates the block in |
| // question. This is fast because dominator tree queries consist of only |
| // a few comparisons of DFS numbers. |
| Value *GVNPass::findLeader(const BasicBlock *BB, uint32_t num) { |
| LeaderTableEntry Vals = LeaderTable[num]; |
| if (!Vals.Val) return nullptr; |
| |
| Value *Val = nullptr; |
| if (DT->dominates(Vals.BB, BB)) { |
| Val = Vals.Val; |
| if (isa<Constant>(Val)) return Val; |
| } |
| |
| LeaderTableEntry* Next = Vals.Next; |
| while (Next) { |
| if (DT->dominates(Next->BB, BB)) { |
| if (isa<Constant>(Next->Val)) return Next->Val; |
| if (!Val) Val = Next->Val; |
| } |
| |
| Next = Next->Next; |
| } |
| |
| return Val; |
| } |
| |
| /// There is an edge from 'Src' to 'Dst'. Return |
| /// true if every path from the entry block to 'Dst' passes via this edge. In |
| /// particular 'Dst' must not be reachable via another edge from 'Src'. |
| static bool isOnlyReachableViaThisEdge(const BasicBlockEdge &E, |
| DominatorTree *DT) { |
| // While in theory it is interesting to consider the case in which Dst has |
| // more than one predecessor, because Dst might be part of a loop which is |
| // only reachable from Src, in practice it is pointless since at the time |
| // GVN runs all such loops have preheaders, which means that Dst will have |
| // been changed to have only one predecessor, namely Src. |
| const BasicBlock *Pred = E.getEnd()->getSinglePredecessor(); |
| assert((!Pred || Pred == E.getStart()) && |
| "No edge between these basic blocks!"); |
| return Pred != nullptr; |
| } |
| |
| void GVNPass::assignBlockRPONumber(Function &F) { |
| BlockRPONumber.clear(); |
| uint32_t NextBlockNumber = 1; |
| ReversePostOrderTraversal<Function *> RPOT(&F); |
| for (BasicBlock *BB : RPOT) |
| BlockRPONumber[BB] = NextBlockNumber++; |
| InvalidBlockRPONumbers = false; |
| } |
| |
| bool GVNPass::replaceOperandsForInBlockEquality(Instruction *Instr) const { |
| bool Changed = false; |
| for (unsigned OpNum = 0; OpNum < Instr->getNumOperands(); ++OpNum) { |
| Value *Operand = Instr->getOperand(OpNum); |
| auto it = ReplaceOperandsWithMap.find(Operand); |
| if (it != ReplaceOperandsWithMap.end()) { |
| LLVM_DEBUG(dbgs() << "GVN replacing: " << *Operand << " with " |
| << *it->second << " in instruction " << *Instr << '\n'); |
| Instr->setOperand(OpNum, it->second); |
| Changed = true; |
| } |
| } |
| return Changed; |
| } |
| |
| /// The given values are known to be equal in every block |
| /// dominated by 'Root'. Exploit this, for example by replacing 'LHS' with |
| /// 'RHS' everywhere in the scope. Returns whether a change was made. |
| /// If DominatesByEdge is false, then it means that we will propagate the RHS |
| /// value starting from the end of Root.Start. |
| bool GVNPass::propagateEquality(Value *LHS, Value *RHS, |
| const BasicBlockEdge &Root, |
| bool DominatesByEdge) { |
| SmallVector<std::pair<Value*, Value*>, 4> Worklist; |
| Worklist.push_back(std::make_pair(LHS, RHS)); |
| bool Changed = false; |
| // For speed, compute a conservative fast approximation to |
| // DT->dominates(Root, Root.getEnd()); |
| const bool RootDominatesEnd = isOnlyReachableViaThisEdge(Root, DT); |
| |
| while (!Worklist.empty()) { |
| std::pair<Value*, Value*> Item = Worklist.pop_back_val(); |
| LHS = Item.first; RHS = Item.second; |
| |
| if (LHS == RHS) |
| continue; |
| assert(LHS->getType() == RHS->getType() && "Equality but unequal types!"); |
| |
| // Don't try to propagate equalities between constants. |
| if (isa<Constant>(LHS) && isa<Constant>(RHS)) |
| continue; |
| |
| // Prefer a constant on the right-hand side, or an Argument if no constants. |
| if (isa<Constant>(LHS) || (isa<Argument>(LHS) && !isa<Constant>(RHS))) |
| std::swap(LHS, RHS); |
| assert((isa<Argument>(LHS) || isa<Instruction>(LHS)) && "Unexpected value!"); |
| |
| // If there is no obvious reason to prefer the left-hand side over the |
| // right-hand side, ensure the longest lived term is on the right-hand side, |
| // so the shortest lived term will be replaced by the longest lived. |
| // This tends to expose more simplifications. |
| uint32_t LVN = VN.lookupOrAdd(LHS); |
| if ((isa<Argument>(LHS) && isa<Argument>(RHS)) || |
| (isa<Instruction>(LHS) && isa<Instruction>(RHS))) { |
| // Move the 'oldest' value to the right-hand side, using the value number |
| // as a proxy for age. |
| uint32_t RVN = VN.lookupOrAdd(RHS); |
| if (LVN < RVN) { |
| std::swap(LHS, RHS); |
| LVN = RVN; |
| } |
| } |
| |
| // If value numbering later sees that an instruction in the scope is equal |
| // to 'LHS' then ensure it will be turned into 'RHS'. In order to preserve |
| // the invariant that instructions only occur in the leader table for their |
| // own value number (this is used by removeFromLeaderTable), do not do this |
| // if RHS is an instruction (if an instruction in the scope is morphed into |
| // LHS then it will be turned into RHS by the next GVN iteration anyway, so |
| // using the leader table is about compiling faster, not optimizing better). |
| // The leader table only tracks basic blocks, not edges. Only add to if we |
| // have the simple case where the edge dominates the end. |
| if (RootDominatesEnd && !isa<Instruction>(RHS)) |
| addToLeaderTable(LVN, RHS, Root.getEnd()); |
| |
| // Replace all occurrences of 'LHS' with 'RHS' everywhere in the scope. As |
| // LHS always has at least one use that is not dominated by Root, this will |
| // never do anything if LHS has only one use. |
| if (!LHS->hasOneUse()) { |
| unsigned NumReplacements = |
| DominatesByEdge |
| ? replaceDominatedUsesWith(LHS, RHS, *DT, Root) |
| : replaceDominatedUsesWith(LHS, RHS, *DT, Root.getStart()); |
| |
| Changed |= NumReplacements > 0; |
| NumGVNEqProp += NumReplacements; |
| // Cached information for anything that uses LHS will be invalid. |
| if (MD) |
| MD->invalidateCachedPointerInfo(LHS); |
| } |
| |
| // Now try to deduce additional equalities from this one. For example, if |
| // the known equality was "(A != B)" == "false" then it follows that A and B |
| // are equal in the scope. Only boolean equalities with an explicit true or |
| // false RHS are currently supported. |
| if (!RHS->getType()->isIntegerTy(1)) |
| // Not a boolean equality - bail out. |
| continue; |
| ConstantInt *CI = dyn_cast<ConstantInt>(RHS); |
| if (!CI) |
| // RHS neither 'true' nor 'false' - bail out. |
| continue; |
| // Whether RHS equals 'true'. Otherwise it equals 'false'. |
| bool isKnownTrue = CI->isMinusOne(); |
| bool isKnownFalse = !isKnownTrue; |
| |
| // If "A && B" is known true then both A and B are known true. If "A || B" |
| // is known false then both A and B are known false. |
| Value *A, *B; |
| if ((isKnownTrue && match(LHS, m_LogicalAnd(m_Value(A), m_Value(B)))) || |
| (isKnownFalse && match(LHS, m_LogicalOr(m_Value(A), m_Value(B))))) { |
| Worklist.push_back(std::make_pair(A, RHS)); |
| Worklist.push_back(std::make_pair(B, RHS)); |
| continue; |
| } |
| |
| // If we are propagating an equality like "(A == B)" == "true" then also |
| // propagate the equality A == B. When propagating a comparison such as |
| // "(A >= B)" == "true", replace all instances of "A < B" with "false". |
| if (CmpInst *Cmp = dyn_cast<CmpInst>(LHS)) { |
| Value *Op0 = Cmp->getOperand(0), *Op1 = Cmp->getOperand(1); |
| |
| // If "A == B" is known true, or "A != B" is known false, then replace |
| // A with B everywhere in the scope. For floating point operations, we |
| // have to be careful since equality does not always imply equivalance. |
| if ((isKnownTrue && impliesEquivalanceIfTrue(Cmp)) || |
| (isKnownFalse && impliesEquivalanceIfFalse(Cmp))) |
| Worklist.push_back(std::make_pair(Op0, Op1)); |
| |
| // If "A >= B" is known true, replace "A < B" with false everywhere. |
| CmpInst::Predicate NotPred = Cmp->getInversePredicate(); |
| Constant *NotVal = ConstantInt::get(Cmp->getType(), isKnownFalse); |
| // Since we don't have the instruction "A < B" immediately to hand, work |
| // out the value number that it would have and use that to find an |
| // appropriate instruction (if any). |
| uint32_t NextNum = VN.getNextUnusedValueNumber(); |
| uint32_t Num = VN.lookupOrAddCmp(Cmp->getOpcode(), NotPred, Op0, Op1); |
| // If the number we were assigned was brand new then there is no point in |
| // looking for an instruction realizing it: there cannot be one! |
| if (Num < NextNum) { |
| Value *NotCmp = findLeader(Root.getEnd(), Num); |
| if (NotCmp && isa<Instruction>(NotCmp)) { |
| unsigned NumReplacements = |
| DominatesByEdge |
| ? replaceDominatedUsesWith(NotCmp, NotVal, *DT, Root) |
| : replaceDominatedUsesWith(NotCmp, NotVal, *DT, |
| Root.getStart()); |
| Changed |= NumReplacements > 0; |
| NumGVNEqProp += NumReplacements; |
| // Cached information for anything that uses NotCmp will be invalid. |
| if (MD) |
| MD->invalidateCachedPointerInfo(NotCmp); |
| } |
| } |
| // Ensure that any instruction in scope that gets the "A < B" value number |
| // is replaced with false. |
| // The leader table only tracks basic blocks, not edges. Only add to if we |
| // have the simple case where the edge dominates the end. |
| if (RootDominatesEnd) |
| addToLeaderTable(Num, NotVal, Root.getEnd()); |
| |
| continue; |
| } |
| } |
| |
| return Changed; |
| } |
| |
| /// When calculating availability, handle an instruction |
| /// by inserting it into the appropriate sets |
| bool GVNPass::processInstruction(Instruction *I) { |
| // Ignore dbg info intrinsics. |
| if (isa<DbgInfoIntrinsic>(I)) |
| return false; |
| |
| // If the instruction can be easily simplified then do so now in preference |
| // to value numbering it. Value numbering often exposes redundancies, for |
| // example if it determines that %y is equal to %x then the instruction |
| // "%z = and i32 %x, %y" becomes "%z = and i32 %x, %x" which we now simplify. |
| const DataLayout &DL = I->getModule()->getDataLayout(); |
| if (Value *V = SimplifyInstruction(I, {DL, TLI, DT, AC})) { |
| bool Changed = false; |
| if (!I->use_empty()) { |
| // Simplification can cause a special instruction to become not special. |
| // For example, devirtualization to a willreturn function. |
| ICF->removeUsersOf(I); |
| I->replaceAllUsesWith(V); |
| Changed = true; |
| } |
| if (isInstructionTriviallyDead(I, TLI)) { |
| markInstructionForDeletion(I); |
| Changed = true; |
| } |
| if (Changed) { |
| if (MD && V->getType()->isPtrOrPtrVectorTy()) |
| MD->invalidateCachedPointerInfo(V); |
| ++NumGVNSimpl; |
| return true; |
| } |
| } |
| |
| if (auto *Assume = dyn_cast<AssumeInst>(I)) |
| return processAssumeIntrinsic(Assume); |
| |
| if (LoadInst *Load = dyn_cast<LoadInst>(I)) { |
| if (processLoad(Load)) |
| return true; |
| |
| unsigned Num = VN.lookupOrAdd(Load); |
| addToLeaderTable(Num, Load, Load->getParent()); |
| return false; |
| } |
| |
| // For conditional branches, we can perform simple conditional propagation on |
| // the condition value itself. |
| if (BranchInst *BI = dyn_cast<BranchInst>(I)) { |
| if (!BI->isConditional()) |
| return false; |
| |
| if (isa<Constant>(BI->getCondition())) |
| return processFoldableCondBr(BI); |
| |
| Value *BranchCond = BI->getCondition(); |
| BasicBlock *TrueSucc = BI->getSuccessor(0); |
| BasicBlock *FalseSucc = BI->getSuccessor(1); |
| // Avoid multiple edges early. |
| if (TrueSucc == FalseSucc) |
| return false; |
| |
| BasicBlock *Parent = BI->getParent(); |
| bool Changed = false; |
| |
| Value *TrueVal = ConstantInt::getTrue(TrueSucc->getContext()); |
| BasicBlockEdge TrueE(Parent, TrueSucc); |
| Changed |= propagateEquality(BranchCond, TrueVal, TrueE, true); |
| |
| Value *FalseVal = ConstantInt::getFalse(FalseSucc->getContext()); |
| BasicBlockEdge FalseE(Parent, FalseSucc); |
| Changed |= propagateEquality(BranchCond, FalseVal, FalseE, true); |
| |
| return Changed; |
| } |
| |
| // For switches, propagate the case values into the case destinations. |
| if (SwitchInst *SI = dyn_cast<SwitchInst>(I)) { |
| Value *SwitchCond = SI->getCondition(); |
| BasicBlock *Parent = SI->getParent(); |
| bool Changed = false; |
| |
| // Remember how many outgoing edges there are to every successor. |
| SmallDenseMap<BasicBlock *, unsigned, 16> SwitchEdges; |
| for (unsigned i = 0, n = SI->getNumSuccessors(); i != n; ++i) |
| ++SwitchEdges[SI->getSuccessor(i)]; |
| |
| for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); |
| i != e; ++i) { |
| BasicBlock *Dst = i->getCaseSuccessor(); |
| // If there is only a single edge, propagate the case value into it. |
| if (SwitchEdges.lookup(Dst) == 1) { |
| BasicBlockEdge E(Parent, Dst); |
| Changed |= propagateEquality(SwitchCond, i->getCaseValue(), E, true); |
| } |
| } |
| return Changed; |
| } |
| |
| // Instructions with void type don't return a value, so there's |
| // no point in trying to find redundancies in them. |
| if (I->getType()->isVoidTy()) |
| return false; |
| |
| uint32_t NextNum = VN.getNextUnusedValueNumber(); |
| unsigned Num = VN.lookupOrAdd(I); |
| |
| // Allocations are always uniquely numbered, so we can save time and memory |
| // by fast failing them. |
| if (isa<AllocaInst>(I) || I->isTerminator() || isa<PHINode>(I)) { |
| addToLeaderTable(Num, I, I->getParent()); |
| return false; |
| } |
| |
| // If the number we were assigned was a brand new VN, then we don't |
| // need to do a lookup to see if the number already exists |
| // somewhere in the domtree: it can't! |
| if (Num >= NextNum) { |
| addToLeaderTable(Num, I, I->getParent()); |
| return false; |
| } |
| |
| // Perform fast-path value-number based elimination of values inherited from |
| // dominators. |
| Value *Repl = findLeader(I->getParent(), Num); |
| if (!Repl) { |
| // Failure, just remember this instance for future use. |
| addToLeaderTable(Num, I, I->getParent()); |
| return false; |
| } else if (Repl == I) { |
| // If I was the result of a shortcut PRE, it might already be in the table |
| // and the best replacement for itself. Nothing to do. |
| return false; |
| } |
| |
| // Remove it! |
| patchAndReplaceAllUsesWith(I, Repl); |
| if (MD && Repl->getType()->isPtrOrPtrVectorTy()) |
| MD->invalidateCachedPointerInfo(Repl); |
| markInstructionForDeletion(I); |
| return true; |
| } |
| |
| /// runOnFunction - This is the main transformation entry point for a function. |
| bool GVNPass::runImpl(Function &F, AssumptionCache &RunAC, DominatorTree &RunDT, |
| const TargetLibraryInfo &RunTLI, AAResults &RunAA, |
| MemoryDependenceResults *RunMD, LoopInfo *LI, |
| OptimizationRemarkEmitter *RunORE, MemorySSA *MSSA) { |
| AC = &RunAC; |
| DT = &RunDT; |
| VN.setDomTree(DT); |
| TLI = &RunTLI; |
| VN.setAliasAnalysis(&RunAA); |
| MD = RunMD; |
| ImplicitControlFlowTracking ImplicitCFT; |
| ICF = &ImplicitCFT; |
| this->LI = LI; |
| VN.setMemDep(MD); |
| ORE = RunORE; |
| InvalidBlockRPONumbers = true; |
| MemorySSAUpdater Updater(MSSA); |
| MSSAU = MSSA ? &Updater : nullptr; |
| |
| bool Changed = false; |
| bool ShouldContinue = true; |
| |
| DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Eager); |
| // Merge unconditional branches, allowing PRE to catch more |
| // optimization opportunities. |
| for (BasicBlock &BB : llvm::make_early_inc_range(F)) { |
| bool removedBlock = MergeBlockIntoPredecessor(&BB, &DTU, LI, MSSAU, MD); |
| if (removedBlock) |
| ++NumGVNBlocks; |
| |
| Changed |= removedBlock; |
| } |
| |
| unsigned Iteration = 0; |
| while (ShouldContinue) { |
| LLVM_DEBUG(dbgs() << "GVN iteration: " << Iteration << "\n"); |
| ShouldContinue = iterateOnFunction(F); |
| Changed |= ShouldContinue; |
| ++Iteration; |
| } |
| |
| if (isPREEnabled()) { |
| // Fabricate val-num for dead-code in order to suppress assertion in |
| // performPRE(). |
| assignValNumForDeadCode(); |
| bool PREChanged = true; |
| while (PREChanged) { |
| PREChanged = performPRE(F); |
| Changed |= PREChanged; |
| } |
| } |
| |
| // FIXME: Should perform GVN again after PRE does something. PRE can move |
| // computations into blocks where they become fully redundant. Note that |
| // we can't do this until PRE's critical edge splitting updates memdep. |
| // Actually, when this happens, we should just fully integrate PRE into GVN. |
| |
| cleanupGlobalSets(); |
| // Do not cleanup DeadBlocks in cleanupGlobalSets() as it's called for each |
| // iteration. |
| DeadBlocks.clear(); |
| |
| if (MSSA && VerifyMemorySSA) |
| MSSA->verifyMemorySSA(); |
| |
| return Changed; |
| } |
| |
| bool GVNPass::processBlock(BasicBlock *BB) { |
| // FIXME: Kill off InstrsToErase by doing erasing eagerly in a helper function |
| // (and incrementing BI before processing an instruction). |
| assert(InstrsToErase.empty() && |
| "We expect InstrsToErase to be empty across iterations"); |
| if (DeadBlocks.count(BB)) |
| return false; |
| |
| // Clearing map before every BB because it can be used only for single BB. |
| ReplaceOperandsWithMap.clear(); |
| bool ChangedFunction = false; |
| |
| // Since we may not have visited the input blocks of the phis, we can't |
| // use our normal hash approach for phis. Instead, simply look for |
| // obvious duplicates. The first pass of GVN will tend to create |
| // identical phis, and the second or later passes can eliminate them. |
| ChangedFunction |= EliminateDuplicatePHINodes(BB); |
| |
| for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); |
| BI != BE;) { |
| if (!ReplaceOperandsWithMap.empty()) |
| ChangedFunction |= replaceOperandsForInBlockEquality(&*BI); |
| ChangedFunction |= processInstruction(&*BI); |
| |
| if (InstrsToErase.empty()) { |
| ++BI; |
| continue; |
| } |
| |
| // If we need some instructions deleted, do it now. |
| NumGVNInstr += InstrsToErase.size(); |
| |
| // Avoid iterator invalidation. |
| bool AtStart = BI == BB->begin(); |
| if (!AtStart) |
| --BI; |
| |
| for (auto *I : InstrsToErase) { |
| assert(I->getParent() == BB && "Removing instruction from wrong block?"); |
| LLVM_DEBUG(dbgs() << "GVN removed: " << *I << '\n'); |
| salvageKnowledge(I, AC); |
| salvageDebugInfo(*I); |
| if (MD) MD->removeInstruction(I); |
| if (MSSAU) |
| MSSAU->removeMemoryAccess(I); |
| LLVM_DEBUG(verifyRemoved(I)); |
| ICF->removeInstruction(I); |
| I->eraseFromParent(); |
| } |
| InstrsToErase.clear(); |
| |
| if (AtStart) |
| BI = BB->begin(); |
| else |
| ++BI; |
| } |
| |
| return ChangedFunction; |
| } |
| |
| // Instantiate an expression in a predecessor that lacked it. |
| bool GVNPass::performScalarPREInsertion(Instruction *Instr, BasicBlock *Pred, |
| BasicBlock *Curr, unsigned int ValNo) { |
| // Because we are going top-down through the block, all value numbers |
| // will be available in the predecessor by the time we need them. Any |
| // that weren't originally present will have been instantiated earlier |
| // in this loop. |
| bool success = true; |
| for (unsigned i = 0, e = Instr->getNumOperands(); i != e; ++i) { |
| Value *Op = Instr->getOperand(i); |
| if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op)) |
| continue; |
| // This could be a newly inserted instruction, in which case, we won't |
| // find a value number, and should give up before we hurt ourselves. |
| // FIXME: Rewrite the infrastructure to let it easier to value number |
| // and process newly inserted instructions. |
| if (!VN.exists(Op)) { |
| success = false; |
| break; |
| } |
| uint32_t TValNo = |
| VN.phiTranslate(Pred, Curr, VN.lookup(Op), *this); |
| if (Value *V = findLeader(Pred, TValNo)) { |
| Instr->setOperand(i, V); |
| } else { |
| success = false; |
| break; |
| } |
| } |
| |
| // Fail out if we encounter an operand that is not available in |
| // the PRE predecessor. This is typically because of loads which |
| // are not value numbered precisely. |
| if (!success) |
| return false; |
| |
| Instr->insertBefore(Pred->getTerminator()); |
| Instr->setName(Instr->getName() + ".pre"); |
| Instr->setDebugLoc(Instr->getDebugLoc()); |
| |
| ICF->insertInstructionTo(Instr, Pred); |
| |
| unsigned Num = VN.lookupOrAdd(Instr); |
| VN.add(Instr, Num); |
| |
| // Update the availability map to include the new instruction. |
| addToLeaderTable(Num, Instr, Pred); |
| return true; |
| } |
| |
| bool GVNPass::performScalarPRE(Instruction *CurInst) { |
| if (isa<AllocaInst>(CurInst) || CurInst->isTerminator() || |
| isa<PHINode>(CurInst) || CurInst->getType()->isVoidTy() || |
| CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() || |
| isa<DbgInfoIntrinsic>(CurInst)) |
| return false; |
| |
| // Don't do PRE on compares. The PHI would prevent CodeGenPrepare from |
| // sinking the compare again, and it would force the code generator to |
| // move the i1 from processor flags or predicate registers into a general |
| // purpose register. |
| if (isa<CmpInst>(CurInst)) |
| return false; |
| |
| // Don't do PRE on GEPs. The inserted PHI would prevent CodeGenPrepare from |
| // sinking the addressing mode computation back to its uses. Extending the |
| // GEP's live range increases the register pressure, and therefore it can |
| // introduce unnecessary spills. |
| // |
| // This doesn't prevent Load PRE. PHI translation will make the GEP available |
| // to the load by moving it to the predecessor block if necessary. |
| if (isa<GetElementPtrInst>(CurInst)) |
| return false; |
| |
| if (auto *CallB = dyn_cast<CallBase>(CurInst)) { |
| // We don't currently value number ANY inline asm calls. |
| if (CallB->isInlineAsm()) |
| return false; |
| // Don't do PRE on convergent calls. |
| if (CallB->isConvergent()) |
| return false; |
| } |
| |
| uint32_t ValNo = VN.lookup(CurInst); |
| |
| // Look for the predecessors for PRE opportunities. We're |
| // only trying to solve the basic diamond case, where |
| // a value is computed in the successor and one predecessor, |
| // but not the other. We also explicitly disallow cases |
| // where the successor is its own predecessor, because they're |
| // more complicated to get right. |
| unsigned NumWith = 0; |
| unsigned NumWithout = 0; |
| BasicBlock *PREPred = nullptr; |
| BasicBlock *CurrentBlock = CurInst->getParent(); |
| |
| // Update the RPO numbers for this function. |
| if (InvalidBlockRPONumbers) |
| assignBlockRPONumber(*CurrentBlock->getParent()); |
| |
| SmallVector<std::pair<Value *, BasicBlock *>, 8> predMap; |
| for (BasicBlock *P : predecessors(CurrentBlock)) { |
| // We're not interested in PRE where blocks with predecessors that are |
| // not reachable. |
| if (!DT->isReachableFromEntry(P)) { |
| NumWithout = 2; |
| break; |
| } |
| // It is not safe to do PRE when P->CurrentBlock is a loop backedge, and |
| // when CurInst has operand defined in CurrentBlock (so it may be defined |
| // by phi in the loop header). |
| assert(BlockRPONumber.count(P) && BlockRPONumber.count(CurrentBlock) && |
| "Invalid BlockRPONumber map."); |
| if (BlockRPONumber[P] >= BlockRPONumber[CurrentBlock] && |
| llvm::any_of(CurInst->operands(), [&](const Use &U) { |
| if (auto *Inst = dyn_cast<Instruction>(U.get())) |
| return Inst->getParent() == CurrentBlock; |
| return false; |
| })) { |
| NumWithout = 2; |
| break; |
| } |
| |
| uint32_t TValNo = VN.phiTranslate(P, CurrentBlock, ValNo, *this); |
| Value *predV = findLeader(P, TValNo); |
| |