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Diffstat (limited to 'lib/Transforms/Scalar/GVN.cpp')
| -rw-r--r-- | lib/Transforms/Scalar/GVN.cpp | 1738 |
1 files changed, 1738 insertions, 0 deletions
diff --git a/lib/Transforms/Scalar/GVN.cpp b/lib/Transforms/Scalar/GVN.cpp new file mode 100644 index 0000000000000..733dfa97a1547 --- /dev/null +++ b/lib/Transforms/Scalar/GVN.cpp @@ -0,0 +1,1738 @@ +//===- GVN.cpp - Eliminate redundant values and loads ---------------------===// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// 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. +// +//===----------------------------------------------------------------------===// + +#define DEBUG_TYPE "gvn" +#include "llvm/Transforms/Scalar.h" +#include "llvm/BasicBlock.h" +#include "llvm/Constants.h" +#include "llvm/DerivedTypes.h" +#include "llvm/Function.h" +#include "llvm/IntrinsicInst.h" +#include "llvm/Value.h" +#include "llvm/ADT/DenseMap.h" +#include "llvm/ADT/DepthFirstIterator.h" +#include "llvm/ADT/PostOrderIterator.h" +#include "llvm/ADT/SmallPtrSet.h" +#include "llvm/ADT/SmallVector.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/Analysis/Dominators.h" +#include "llvm/Analysis/AliasAnalysis.h" +#include "llvm/Analysis/MemoryDependenceAnalysis.h" +#include "llvm/Support/CFG.h" +#include "llvm/Support/CommandLine.h" +#include "llvm/Support/Compiler.h" +#include "llvm/Support/Debug.h" +#include "llvm/Transforms/Utils/BasicBlockUtils.h" +#include <cstdio> +using namespace llvm; + +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(NumPRELoad, "Number of loads PRE'd"); + +static cl::opt<bool> EnablePRE("enable-pre", + cl::init(true), cl::Hidden); +cl::opt<bool> EnableLoadPRE("enable-load-pre", cl::init(true)); + +//===----------------------------------------------------------------------===// +// ValueTable Class +//===----------------------------------------------------------------------===// + +/// This class holds the mapping between values and value numbers. It is used +/// as an efficient mechanism to determine the expression-wise equivalence of +/// two values. +namespace { + struct VISIBILITY_HIDDEN Expression { + enum ExpressionOpcode { ADD, SUB, MUL, UDIV, SDIV, FDIV, UREM, SREM, + FREM, SHL, LSHR, ASHR, AND, OR, XOR, ICMPEQ, + ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE, + ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ, + FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE, + FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE, + FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT, + SHUFFLE, SELECT, TRUNC, ZEXT, SEXT, FPTOUI, + FPTOSI, UITOFP, SITOFP, FPTRUNC, FPEXT, + PTRTOINT, INTTOPTR, BITCAST, GEP, CALL, CONSTANT, + EMPTY, TOMBSTONE }; + + ExpressionOpcode opcode; + const Type* type; + uint32_t firstVN; + uint32_t secondVN; + uint32_t thirdVN; + SmallVector<uint32_t, 4> varargs; + Value* function; + + Expression() { } + Expression(ExpressionOpcode o) : opcode(o) { } + + bool operator==(const Expression &other) const { + if (opcode != other.opcode) + return false; + else if (opcode == EMPTY || opcode == TOMBSTONE) + return true; + else if (type != other.type) + return false; + else if (function != other.function) + return false; + else if (firstVN != other.firstVN) + return false; + else if (secondVN != other.secondVN) + return false; + else if (thirdVN != other.thirdVN) + return false; + else { + if (varargs.size() != other.varargs.size()) + return false; + + for (size_t i = 0; i < varargs.size(); ++i) + if (varargs[i] != other.varargs[i]) + return false; + + return true; + } + } + + bool operator!=(const Expression &other) const { + return !(*this == other); + } + }; + + class VISIBILITY_HIDDEN ValueTable { + private: + DenseMap<Value*, uint32_t> valueNumbering; + DenseMap<Expression, uint32_t> expressionNumbering; + AliasAnalysis* AA; + MemoryDependenceAnalysis* MD; + DominatorTree* DT; + + uint32_t nextValueNumber; + + Expression::ExpressionOpcode getOpcode(BinaryOperator* BO); + Expression::ExpressionOpcode getOpcode(CmpInst* C); + Expression::ExpressionOpcode getOpcode(CastInst* C); + Expression create_expression(BinaryOperator* BO); + Expression create_expression(CmpInst* C); + Expression create_expression(ShuffleVectorInst* V); + Expression create_expression(ExtractElementInst* C); + Expression create_expression(InsertElementInst* V); + Expression create_expression(SelectInst* V); + Expression create_expression(CastInst* C); + Expression create_expression(GetElementPtrInst* G); + Expression create_expression(CallInst* C); + Expression create_expression(Constant* C); + public: + ValueTable() : nextValueNumber(1) { } + uint32_t lookup_or_add(Value* V); + uint32_t lookup(Value* V) const; + void add(Value* V, uint32_t num); + void clear(); + void erase(Value* v); + unsigned size(); + void setAliasAnalysis(AliasAnalysis* A) { AA = A; } + AliasAnalysis *getAliasAnalysis() const { return AA; } + void setMemDep(MemoryDependenceAnalysis* M) { MD = M; } + void setDomTree(DominatorTree* D) { DT = D; } + uint32_t getNextUnusedValueNumber() { return nextValueNumber; } + void verifyRemoved(const Value *) const; + }; +} + +namespace llvm { +template <> struct DenseMapInfo<Expression> { + static inline Expression getEmptyKey() { + return Expression(Expression::EMPTY); + } + + static inline Expression getTombstoneKey() { + return Expression(Expression::TOMBSTONE); + } + + static unsigned getHashValue(const Expression e) { + unsigned hash = e.opcode; + + hash = e.firstVN + hash * 37; + hash = e.secondVN + hash * 37; + hash = e.thirdVN + hash * 37; + + hash = ((unsigned)((uintptr_t)e.type >> 4) ^ + (unsigned)((uintptr_t)e.type >> 9)) + + hash * 37; + + for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(), + E = e.varargs.end(); I != E; ++I) + hash = *I + hash * 37; + + hash = ((unsigned)((uintptr_t)e.function >> 4) ^ + (unsigned)((uintptr_t)e.function >> 9)) + + hash * 37; + + return hash; + } + static bool isEqual(const Expression &LHS, const Expression &RHS) { + return LHS == RHS; + } + static bool isPod() { return true; } +}; +} + +//===----------------------------------------------------------------------===// +// ValueTable Internal Functions +//===----------------------------------------------------------------------===// +Expression::ExpressionOpcode ValueTable::getOpcode(BinaryOperator* BO) { + switch(BO->getOpcode()) { + default: // THIS SHOULD NEVER HAPPEN + assert(0 && "Binary operator with unknown opcode?"); + case Instruction::Add: return Expression::ADD; + case Instruction::Sub: return Expression::SUB; + case Instruction::Mul: return Expression::MUL; + case Instruction::UDiv: return Expression::UDIV; + case Instruction::SDiv: return Expression::SDIV; + case Instruction::FDiv: return Expression::FDIV; + case Instruction::URem: return Expression::UREM; + case Instruction::SRem: return Expression::SREM; + case Instruction::FRem: return Expression::FREM; + case Instruction::Shl: return Expression::SHL; + case Instruction::LShr: return Expression::LSHR; + case Instruction::AShr: return Expression::ASHR; + case Instruction::And: return Expression::AND; + case Instruction::Or: return Expression::OR; + case Instruction::Xor: return Expression::XOR; + } +} + +Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) { + if (isa<ICmpInst>(C) || isa<VICmpInst>(C)) { + switch (C->getPredicate()) { + default: // THIS SHOULD NEVER HAPPEN + assert(0 && "Comparison with unknown predicate?"); + case ICmpInst::ICMP_EQ: return Expression::ICMPEQ; + case ICmpInst::ICMP_NE: return Expression::ICMPNE; + case ICmpInst::ICMP_UGT: return Expression::ICMPUGT; + case ICmpInst::ICMP_UGE: return Expression::ICMPUGE; + case ICmpInst::ICMP_ULT: return Expression::ICMPULT; + case ICmpInst::ICMP_ULE: return Expression::ICMPULE; + case ICmpInst::ICMP_SGT: return Expression::ICMPSGT; + case ICmpInst::ICMP_SGE: return Expression::ICMPSGE; + case ICmpInst::ICMP_SLT: return Expression::ICMPSLT; + case ICmpInst::ICMP_SLE: return Expression::ICMPSLE; + } + } + assert((isa<FCmpInst>(C) || isa<VFCmpInst>(C)) && "Unknown compare"); + switch (C->getPredicate()) { + default: // THIS SHOULD NEVER HAPPEN + assert(0 && "Comparison with unknown predicate?"); + case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ; + case FCmpInst::FCMP_OGT: return Expression::FCMPOGT; + case FCmpInst::FCMP_OGE: return Expression::FCMPOGE; + case FCmpInst::FCMP_OLT: return Expression::FCMPOLT; + case FCmpInst::FCMP_OLE: return Expression::FCMPOLE; + case FCmpInst::FCMP_ONE: return Expression::FCMPONE; + case FCmpInst::FCMP_ORD: return Expression::FCMPORD; + case FCmpInst::FCMP_UNO: return Expression::FCMPUNO; + case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ; + case FCmpInst::FCMP_UGT: return Expression::FCMPUGT; + case FCmpInst::FCMP_UGE: return Expression::FCMPUGE; + case FCmpInst::FCMP_ULT: return Expression::FCMPULT; + case FCmpInst::FCMP_ULE: return Expression::FCMPULE; + case FCmpInst::FCMP_UNE: return Expression::FCMPUNE; + } +} + +Expression::ExpressionOpcode ValueTable::getOpcode(CastInst* C) { + switch(C->getOpcode()) { + default: // THIS SHOULD NEVER HAPPEN + assert(0 && "Cast operator with unknown opcode?"); + case Instruction::Trunc: return Expression::TRUNC; + case Instruction::ZExt: return Expression::ZEXT; + case Instruction::SExt: return Expression::SEXT; + case Instruction::FPToUI: return Expression::FPTOUI; + case Instruction::FPToSI: return Expression::FPTOSI; + case Instruction::UIToFP: return Expression::UITOFP; + case Instruction::SIToFP: return Expression::SITOFP; + case Instruction::FPTrunc: return Expression::FPTRUNC; + case Instruction::FPExt: return Expression::FPEXT; + case Instruction::PtrToInt: return Expression::PTRTOINT; + case Instruction::IntToPtr: return Expression::INTTOPTR; + case Instruction::BitCast: return Expression::BITCAST; + } +} + +Expression ValueTable::create_expression(CallInst* C) { + Expression e; + + e.type = C->getType(); + e.firstVN = 0; + e.secondVN = 0; + e.thirdVN = 0; + e.function = C->getCalledFunction(); + e.opcode = Expression::CALL; + + for (CallInst::op_iterator I = C->op_begin()+1, E = C->op_end(); + I != E; ++I) + e.varargs.push_back(lookup_or_add(*I)); + + return e; +} + +Expression ValueTable::create_expression(BinaryOperator* BO) { + Expression e; + + e.firstVN = lookup_or_add(BO->getOperand(0)); + e.secondVN = lookup_or_add(BO->getOperand(1)); + e.thirdVN = 0; + e.function = 0; + e.type = BO->getType(); + e.opcode = getOpcode(BO); + + return e; +} + +Expression ValueTable::create_expression(CmpInst* C) { + Expression e; + + e.firstVN = lookup_or_add(C->getOperand(0)); + e.secondVN = lookup_or_add(C->getOperand(1)); + e.thirdVN = 0; + e.function = 0; + e.type = C->getType(); + e.opcode = getOpcode(C); + + return e; +} + +Expression ValueTable::create_expression(CastInst* C) { + Expression e; + + e.firstVN = lookup_or_add(C->getOperand(0)); + e.secondVN = 0; + e.thirdVN = 0; + e.function = 0; + e.type = C->getType(); + e.opcode = getOpcode(C); + + return e; +} + +Expression ValueTable::create_expression(ShuffleVectorInst* S) { + Expression e; + + e.firstVN = lookup_or_add(S->getOperand(0)); + e.secondVN = lookup_or_add(S->getOperand(1)); + e.thirdVN = lookup_or_add(S->getOperand(2)); + e.function = 0; + e.type = S->getType(); + e.opcode = Expression::SHUFFLE; + + return e; +} + +Expression ValueTable::create_expression(ExtractElementInst* E) { + Expression e; + + e.firstVN = lookup_or_add(E->getOperand(0)); + e.secondVN = lookup_or_add(E->getOperand(1)); + e.thirdVN = 0; + e.function = 0; + e.type = E->getType(); + e.opcode = Expression::EXTRACT; + + return e; +} + +Expression ValueTable::create_expression(InsertElementInst* I) { + Expression e; + + e.firstVN = lookup_or_add(I->getOperand(0)); + e.secondVN = lookup_or_add(I->getOperand(1)); + e.thirdVN = lookup_or_add(I->getOperand(2)); + e.function = 0; + e.type = I->getType(); + e.opcode = Expression::INSERT; + + return e; +} + +Expression ValueTable::create_expression(SelectInst* I) { + Expression e; + + e.firstVN = lookup_or_add(I->getCondition()); + e.secondVN = lookup_or_add(I->getTrueValue()); + e.thirdVN = lookup_or_add(I->getFalseValue()); + e.function = 0; + e.type = I->getType(); + e.opcode = Expression::SELECT; + + return e; +} + +Expression ValueTable::create_expression(GetElementPtrInst* G) { + Expression e; + + e.firstVN = lookup_or_add(G->getPointerOperand()); + e.secondVN = 0; + e.thirdVN = 0; + e.function = 0; + e.type = G->getType(); + e.opcode = Expression::GEP; + + for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end(); + I != E; ++I) + e.varargs.push_back(lookup_or_add(*I)); + + return e; +} + +//===----------------------------------------------------------------------===// +// ValueTable External Functions +//===----------------------------------------------------------------------===// + +/// add - Insert a value into the table with a specified value number. +void ValueTable::add(Value* V, uint32_t num) { + valueNumbering.insert(std::make_pair(V, num)); +} + +/// 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 ValueTable::lookup_or_add(Value* V) { + DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); + if (VI != valueNumbering.end()) + return VI->second; + + if (CallInst* C = dyn_cast<CallInst>(V)) { + if (AA->doesNotAccessMemory(C)) { + Expression e = create_expression(C); + + DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); + if (EI != expressionNumbering.end()) { + valueNumbering.insert(std::make_pair(V, EI->second)); + return EI->second; + } else { + expressionNumbering.insert(std::make_pair(e, nextValueNumber)); + valueNumbering.insert(std::make_pair(V, nextValueNumber)); + + return nextValueNumber++; + } + } else if (AA->onlyReadsMemory(C)) { + Expression e = create_expression(C); + + if (expressionNumbering.find(e) == expressionNumbering.end()) { + expressionNumbering.insert(std::make_pair(e, nextValueNumber)); + valueNumbering.insert(std::make_pair(V, nextValueNumber)); + return nextValueNumber++; + } + + MemDepResult local_dep = MD->getDependency(C); + + if (!local_dep.isDef() && !local_dep.isNonLocal()) { + valueNumbering.insert(std::make_pair(V, nextValueNumber)); + return nextValueNumber++; + } + + if (local_dep.isDef()) { + CallInst* local_cdep = cast<CallInst>(local_dep.getInst()); + + if (local_cdep->getNumOperands() != C->getNumOperands()) { + valueNumbering.insert(std::make_pair(V, nextValueNumber)); + return nextValueNumber++; + } + + for (unsigned i = 1; i < C->getNumOperands(); ++i) { + uint32_t c_vn = lookup_or_add(C->getOperand(i)); + uint32_t cd_vn = lookup_or_add(local_cdep->getOperand(i)); + if (c_vn != cd_vn) { + valueNumbering.insert(std::make_pair(V, nextValueNumber)); + return nextValueNumber++; + } + } + + uint32_t v = lookup_or_add(local_cdep); + valueNumbering.insert(std::make_pair(V, v)); + return v; + } + + // Non-local case. + const MemoryDependenceAnalysis::NonLocalDepInfo &deps = + MD->getNonLocalCallDependency(CallSite(C)); + // FIXME: call/call dependencies for readonly calls should return def, not + // clobber! Move the checking logic to MemDep! + CallInst* cdep = 0; + + // 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 MemoryDependenceAnalysis::NonLocalDepEntry *I = &deps[i]; + // Ignore non-local dependencies. + if (I->second.isNonLocal()) + continue; + + // We don't handle non-depedencies. If we already have a call, reject + // instruction dependencies. + if (I->second.isClobber() || cdep != 0) { + cdep = 0; + break; + } + + CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->second.getInst()); + // FIXME: All duplicated with non-local case. + if (NonLocalDepCall && DT->properlyDominates(I->first, C->getParent())){ + cdep = NonLocalDepCall; + continue; + } + + cdep = 0; + break; + } + + if (!cdep) { + valueNumbering.insert(std::make_pair(V, nextValueNumber)); + return nextValueNumber++; + } + + if (cdep->getNumOperands() != C->getNumOperands()) { + valueNumbering.insert(std::make_pair(V, nextValueNumber)); + return nextValueNumber++; + } + for (unsigned i = 1; i < C->getNumOperands(); ++i) { + uint32_t c_vn = lookup_or_add(C->getOperand(i)); + uint32_t cd_vn = lookup_or_add(cdep->getOperand(i)); + if (c_vn != cd_vn) { + valueNumbering.insert(std::make_pair(V, nextValueNumber)); + return nextValueNumber++; + } + } + + uint32_t v = lookup_or_add(cdep); + valueNumbering.insert(std::make_pair(V, v)); + return v; + + } else { + valueNumbering.insert(std::make_pair(V, nextValueNumber)); + return nextValueNumber++; + } + } else if (BinaryOperator* BO = dyn_cast<BinaryOperator>(V)) { + Expression e = create_expression(BO); + + DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); + if (EI != expressionNumbering.end()) { + valueNumbering.insert(std::make_pair(V, EI->second)); + return EI->second; + } else { + expressionNumbering.insert(std::make_pair(e, nextValueNumber)); + valueNumbering.insert(std::make_pair(V, nextValueNumber)); + + return nextValueNumber++; + } + } else if (CmpInst* C = dyn_cast<CmpInst>(V)) { + Expression e = create_expression(C); + + DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); + if (EI != expressionNumbering.end()) { + valueNumbering.insert(std::make_pair(V, EI->second)); + return EI->second; + } else { + expressionNumbering.insert(std::make_pair(e, nextValueNumber)); + valueNumbering.insert(std::make_pair(V, nextValueNumber)); + + return nextValueNumber++; + } + } else if (ShuffleVectorInst* U = dyn_cast<ShuffleVectorInst>(V)) { + Expression e = create_expression(U); + + DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); + if (EI != expressionNumbering.end()) { + valueNumbering.insert(std::make_pair(V, EI->second)); + return EI->second; + } else { + expressionNumbering.insert(std::make_pair(e, nextValueNumber)); + valueNumbering.insert(std::make_pair(V, nextValueNumber)); + + return nextValueNumber++; + } + } else if (ExtractElementInst* U = dyn_cast<ExtractElementInst>(V)) { + Expression e = create_expression(U); + + DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); + if (EI != expressionNumbering.end()) { + valueNumbering.insert(std::make_pair(V, EI->second)); + return EI->second; + } else { + expressionNumbering.insert(std::make_pair(e, nextValueNumber)); + valueNumbering.insert(std::make_pair(V, nextValueNumber)); + + return nextValueNumber++; + } + } else if (InsertElementInst* U = dyn_cast<InsertElementInst>(V)) { + Expression e = create_expression(U); + + DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); + if (EI != expressionNumbering.end()) { + valueNumbering.insert(std::make_pair(V, EI->second)); + return EI->second; + } else { + expressionNumbering.insert(std::make_pair(e, nextValueNumber)); + valueNumbering.insert(std::make_pair(V, nextValueNumber)); + + return nextValueNumber++; + } + } else if (SelectInst* U = dyn_cast<SelectInst>(V)) { + Expression e = create_expression(U); + + DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); + if (EI != expressionNumbering.end()) { + valueNumbering.insert(std::make_pair(V, EI->second)); + return EI->second; + } else { + expressionNumbering.insert(std::make_pair(e, nextValueNumber)); + valueNumbering.insert(std::make_pair(V, nextValueNumber)); + + return nextValueNumber++; + } + } else if (CastInst* U = dyn_cast<CastInst>(V)) { + Expression e = create_expression(U); + + DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); + if (EI != expressionNumbering.end()) { + valueNumbering.insert(std::make_pair(V, EI->second)); + return EI->second; + } else { + expressionNumbering.insert(std::make_pair(e, nextValueNumber)); + valueNumbering.insert(std::make_pair(V, nextValueNumber)); + + return nextValueNumber++; + } + } else if (GetElementPtrInst* U = dyn_cast<GetElementPtrInst>(V)) { + Expression e = create_expression(U); + + DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); + if (EI != expressionNumbering.end()) { + valueNumbering.insert(std::make_pair(V, EI->second)); + return EI->second; + } else { + expressionNumbering.insert(std::make_pair(e, nextValueNumber)); + valueNumbering.insert(std::make_pair(V, nextValueNumber)); + + return nextValueNumber++; + } + } else { + valueNumbering.insert(std::make_pair(V, nextValueNumber)); + return nextValueNumber++; + } +} + +/// lookup - Returns the value number of the specified value. Fails if +/// the value has not yet been numbered. +uint32_t ValueTable::lookup(Value* V) const { + DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); + assert(VI != valueNumbering.end() && "Value not numbered?"); + return VI->second; +} + +/// clear - Remove all entries from the ValueTable +void ValueTable::clear() { + valueNumbering.clear(); + expressionNumbering.clear(); + nextValueNumber = 1; +} + +/// erase - Remove a value from the value numbering +void ValueTable::erase(Value* V) { + valueNumbering.erase(V); +} + +/// verifyRemoved - Verify that the value is removed from all internal data +/// structures. +void ValueTable::verifyRemoved(const Value *V) const { + for (DenseMap<Value*, uint32_t>::iterator + I = valueNumbering.begin(), E = valueNumbering.end(); I != E; ++I) { + assert(I->first != V && "Inst still occurs in value numbering map!"); + } +} + +//===----------------------------------------------------------------------===// +// GVN Pass +//===----------------------------------------------------------------------===// + +namespace { + struct VISIBILITY_HIDDEN ValueNumberScope { + ValueNumberScope* parent; + DenseMap<uint32_t, Value*> table; + + ValueNumberScope(ValueNumberScope* p) : parent(p) { } + }; +} + +namespace { + + class VISIBILITY_HIDDEN GVN : public FunctionPass { + bool runOnFunction(Function &F); + public: + static char ID; // Pass identification, replacement for typeid + GVN() : FunctionPass(&ID) { } + + private: + MemoryDependenceAnalysis *MD; + DominatorTree *DT; + + ValueTable VN; + DenseMap<BasicBlock*, ValueNumberScope*> localAvail; + + typedef DenseMap<Value*, SmallPtrSet<Instruction*, 4> > PhiMapType; + PhiMapType phiMap; + + + // This transformation requires dominator postdominator info + virtual void getAnalysisUsage(AnalysisUsage &AU) const { + AU.addRequired<DominatorTree>(); + AU.addRequired<MemoryDependenceAnalysis>(); + AU.addRequired<AliasAnalysis>(); + + AU.addPreserved<DominatorTree>(); + AU.addPreserved<AliasAnalysis>(); + } + + // Helper fuctions + // FIXME: eliminate or document these better + bool processLoad(LoadInst* L, + SmallVectorImpl<Instruction*> &toErase); + bool processInstruction(Instruction* I, + SmallVectorImpl<Instruction*> &toErase); + bool processNonLocalLoad(LoadInst* L, + SmallVectorImpl<Instruction*> &toErase); + bool processBlock(BasicBlock* BB); + Value *GetValueForBlock(BasicBlock *BB, Instruction* orig, + DenseMap<BasicBlock*, Value*> &Phis, + bool top_level = false); + void dump(DenseMap<uint32_t, Value*>& d); + bool iterateOnFunction(Function &F); + Value* CollapsePhi(PHINode* p); + bool isSafeReplacement(PHINode* p, Instruction* inst); + bool performPRE(Function& F); + Value* lookupNumber(BasicBlock* BB, uint32_t num); + bool mergeBlockIntoPredecessor(BasicBlock* BB); + Value* AttemptRedundancyElimination(Instruction* orig, unsigned valno); + void cleanupGlobalSets(); + void verifyRemoved(const Instruction *I) const; + }; + + char GVN::ID = 0; +} + +// createGVNPass - The public interface to this file... +FunctionPass *llvm::createGVNPass() { return new GVN(); } + +static RegisterPass<GVN> X("gvn", + "Global Value Numbering"); + +void GVN::dump(DenseMap<uint32_t, Value*>& d) { + printf("{\n"); + for (DenseMap<uint32_t, Value*>::iterator I = d.begin(), + E = d.end(); I != E; ++I) { + printf("%d\n", I->first); + I->second->dump(); + } + printf("}\n"); +} + +Value* GVN::CollapsePhi(PHINode* p) { + Value* constVal = p->hasConstantValue(); + if (!constVal) return 0; + + Instruction* inst = dyn_cast<Instruction>(constVal); + if (!inst) + return constVal; + + if (DT->dominates(inst, p)) + if (isSafeReplacement(p, inst)) + return inst; + return 0; +} + +bool GVN::isSafeReplacement(PHINode* p, Instruction* inst) { + if (!isa<PHINode>(inst)) + return true; + + for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end(); + UI != E; ++UI) + if (PHINode* use_phi = dyn_cast<PHINode>(UI)) + if (use_phi->getParent() == inst->getParent()) + return false; + + return true; +} + +/// GetValueForBlock - Get the value to use within the specified basic block. +/// available values are in Phis. +Value *GVN::GetValueForBlock(BasicBlock *BB, Instruction* orig, + DenseMap<BasicBlock*, Value*> &Phis, + bool top_level) { + + // If we have already computed this value, return the previously computed val. + DenseMap<BasicBlock*, Value*>::iterator V = Phis.find(BB); + if (V != Phis.end() && !top_level) return V->second; + + // If the block is unreachable, just return undef, since this path + // can't actually occur at runtime. + if (!DT->isReachableFromEntry(BB)) + return Phis[BB] = UndefValue::get(orig->getType()); + + if (BasicBlock *Pred = BB->getSinglePredecessor()) { + Value *ret = GetValueForBlock(Pred, orig, Phis); + Phis[BB] = ret; + return ret; + } + + // Get the number of predecessors of this block so we can reserve space later. + // If there is already a PHI in it, use the #preds from it, otherwise count. + // Getting it from the PHI is constant time. + unsigned NumPreds; + if (PHINode *ExistingPN = dyn_cast<PHINode>(BB->begin())) + NumPreds = ExistingPN->getNumIncomingValues(); + else + NumPreds = std::distance(pred_begin(BB), pred_end(BB)); + + // Otherwise, the idom is the loop, so we need to insert a PHI node. Do so + // now, then get values to fill in the incoming values for the PHI. + PHINode *PN = PHINode::Create(orig->getType(), orig->getName()+".rle", + BB->begin()); + PN->reserveOperandSpace(NumPreds); + + Phis.insert(std::make_pair(BB, PN)); + + // Fill in the incoming values for the block. + for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { + Value* val = GetValueForBlock(*PI, orig, Phis); + PN->addIncoming(val, *PI); + } + + VN.getAliasAnalysis()->copyValue(orig, PN); + + // Attempt to collapse PHI nodes that are trivially redundant + Value* v = CollapsePhi(PN); + if (!v) { + // Cache our phi construction results + if (LoadInst* L = dyn_cast<LoadInst>(orig)) + phiMap[L->getPointerOperand()].insert(PN); + else + phiMap[orig].insert(PN); + + return PN; + } + + PN->replaceAllUsesWith(v); + if (isa<PointerType>(v->getType())) + MD->invalidateCachedPointerInfo(v); + + for (DenseMap<BasicBlock*, Value*>::iterator I = Phis.begin(), + E = Phis.end(); I != E; ++I) + if (I->second == PN) + I->second = v; + + DEBUG(cerr << "GVN removed: " << *PN); + MD->removeInstruction(PN); + PN->eraseFromParent(); + DEBUG(verifyRemoved(PN)); + + Phis[BB] = v; + return v; +} + +/// IsValueFullyAvailableInBlock - 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. +/// 3) we are speculating for this block and have used that to speculate for +/// other blocks. +static bool IsValueFullyAvailableInBlock(BasicBlock *BB, + DenseMap<BasicBlock*, char> &FullyAvailableBlocks) { + // Optimistically assume that the block is fully available and check to see + // if we already know about this block in one lookup. + std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV = + FullyAvailableBlocks.insert(std::make_pair(BB, 2)); + + // If the entry already existed for this block, return the precomputed value. + if (!IV.second) { + // If this is a speculative "available" value, mark it as being used for + // speculation of other blocks. + if (IV.first->second == 2) + IV.first->second = 3; + return IV.first->second != 0; + } + + // Otherwise, see if it is fully available in all predecessors. + pred_iterator PI = pred_begin(BB), PE = pred_end(BB); + + // If this block has no predecessors, it isn't live-in here. + if (PI == PE) + goto SpeculationFailure; + + for (; PI != PE; ++PI) + // If the value isn't fully available in one of our predecessors, then it + // isn't fully available in this block either. Undo our previous + // optimistic assumption and bail out. + if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks)) + goto SpeculationFailure; + + return true; + +// SpeculationFailure - If we get here, we found out that this is not, after +// all, a fully-available block. We have a problem if we speculated on this and +// used the speculation to mark other blocks as available. +SpeculationFailure: + char &BBVal = FullyAvailableBlocks[BB]; + + // If we didn't speculate on this, just return with it set to false. + if (BBVal == 2) { + BBVal = 0; + return false; + } + + // If we did speculate on this value, we could have blocks set to 1 that are + // incorrect. Walk the (transitive) successors of this block and mark them as + // 0 if set to one. + SmallVector<BasicBlock*, 32> BBWorklist; + BBWorklist.push_back(BB); + + while (!BBWorklist.empty()) { + BasicBlock *Entry = BBWorklist.pop_back_val(); + // Note that this sets blocks to 0 (unavailable) if they happen to not + // already be in FullyAvailableBlocks. This is safe. + char &EntryVal = FullyAvailableBlocks[Entry]; + if (EntryVal == 0) continue; // Already unavailable. + + // Mark as unavailable. + EntryVal = 0; + + for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I) + BBWorklist.push_back(*I); + } + + return false; +} + +/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are +/// non-local by performing PHI construction. +bool GVN::processNonLocalLoad(LoadInst *LI, + SmallVectorImpl<Instruction*> &toErase) { + // Find the non-local dependencies of the load. + SmallVector<MemoryDependenceAnalysis::NonLocalDepEntry, 64> Deps; + MD->getNonLocalPointerDependency(LI->getOperand(0), true, LI->getParent(), + Deps); + //DEBUG(cerr << "INVESTIGATING NONLOCAL LOAD: " << Deps.size() << *LI); + + // 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. + if (Deps.size() > 100) + 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 (Deps.size() == 1 && Deps[0].second.isClobber()) + return false; + + // 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). + SmallVector<std::pair<BasicBlock*, Value*>, 16> ValuesPerBlock; + SmallVector<BasicBlock*, 16> UnavailableBlocks; + + for (unsigned i = 0, e = Deps.size(); i != e; ++i) { + BasicBlock *DepBB = Deps[i].first; + MemDepResult DepInfo = Deps[i].second; + + if (DepInfo.isClobber()) { + UnavailableBlocks.push_back(DepBB); + continue; + } + + Instruction *DepInst = DepInfo.getInst(); + + // Loading the allocation -> undef. + if (isa<AllocationInst>(DepInst)) { + ValuesPerBlock.push_back(std::make_pair(DepBB, + UndefValue::get(LI->getType()))); + continue; + } + + if (StoreInst* S = dyn_cast<StoreInst>(DepInst)) { + // Reject loads and stores that are to the same address but are of + // different types. + // NOTE: 403.gcc does have this case (e.g. in readonly_fields_p) because + // of bitfield access, it would be interesting to optimize for it at some + // point. + if (S->getOperand(0)->getType() != LI->getType()) { + UnavailableBlocks.push_back(DepBB); + continue; + } + + ValuesPerBlock.push_back(std::make_pair(DepBB, S->getOperand(0))); + + } else if (LoadInst* LD = dyn_cast<LoadInst>(DepInst)) { + if (LD->getType() != LI->getType()) { + UnavailableBlocks.push_back(DepBB); + continue; + } + ValuesPerBlock.push_back(std::make_pair(DepBB, LD)); + } else { + UnavailableBlocks.push_back(DepBB); + continue; + } + } + + // If we have no predecessors that produce a known value for this load, exit + // early. + if (ValuesPerBlock.empty()) return false; + + // 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()) { + // Use cached PHI construction information from previous runs + SmallPtrSet<Instruction*, 4> &p = phiMap[LI->getPointerOperand()]; + // FIXME: What does phiMap do? Are we positive it isn't getting invalidated? + for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end(); + I != E; ++I) { + if ((*I)->getParent() == LI->getParent()) { + DEBUG(cerr << "GVN REMOVING NONLOCAL LOAD #1: " << *LI); + LI->replaceAllUsesWith(*I); + if (isa<PointerType>((*I)->getType())) + MD->invalidateCachedPointerInfo(*I); + toErase.push_back(LI); + NumGVNLoad++; + return true; + } + + ValuesPerBlock.push_back(std::make_pair((*I)->getParent(), *I)); + } + + DEBUG(cerr << "GVN REMOVING NONLOCAL LOAD: " << *LI); + + DenseMap<BasicBlock*, Value*> BlockReplValues; + BlockReplValues.insert(ValuesPerBlock.begin(), ValuesPerBlock.end()); + // Perform PHI construction. + Value* v = GetValueForBlock(LI->getParent(), LI, BlockReplValues, true); + LI->replaceAllUsesWith(v); + + if (isa<PHINode>(v)) + v->takeName(LI); + if (isa<PointerType>(v->getType())) + MD->invalidateCachedPointerInfo(v); + toErase.push_back(LI); + NumGVNLoad++; + return true; + } + + if (!EnablePRE || !EnableLoadPRE) + return false; + + // 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; + for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i) + Blockers.insert(UnavailableBlocks[i]); + + // Lets find first basic block with more than one predecessor. Walk backwards + // through predecessors if needed. + BasicBlock *LoadBB = LI->getParent(); + BasicBlock *TmpBB = LoadBB; + + bool isSinglePred = false; + while (TmpBB->getSinglePredecessor()) { + isSinglePred = true; + TmpBB = TmpBB->getSinglePredecessor(); + if (!TmpBB) // If haven't found any, bail now. + return false; + if (TmpBB == LoadBB) // Infinite (unreachable) loop. + return false; + if (Blockers.count(TmpBB)) + return false; + } + + assert(TmpBB); + LoadBB = TmpBB; + + // If we have a repl set with LI itself in it, this means we have a loop where + // at least one of the values is LI. Since this means that we won't be able + // to eliminate LI even if we insert uses in the other predecessors, we will + // end up increasing code size. Reject this by scanning for LI. + for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) + if (ValuesPerBlock[i].second == LI) + return false; + + if (isSinglePred) { + bool isHot = false; + for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) + if (Instruction *I = dyn_cast<Instruction>(ValuesPerBlock[i].second)) + // "Hot" Instruction is in some loop (because it dominates its dep. + // instruction). + if (DT->dominates(LI, I)) { + isHot = true; + break; + } + + // We are interested only in "hot" instructions. We don't want to do any + // mis-optimizations here. + if (!isHot) + return false; + } + + // Okay, we have some hope :). Check to see if the loaded value is fully + // available in all but one predecessor. + // FIXME: If we could restructure the CFG, we could make a common pred with + // all the preds that don't have an available LI and insert a new load into + // that one block. + BasicBlock *UnavailablePred = 0; + + DenseMap<BasicBlock*, char> FullyAvailableBlocks; + for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) + FullyAvailableBlocks[ValuesPerBlock[i].first] = true; + for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i) + FullyAvailableBlocks[UnavailableBlocks[i]] = false; + + for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB); + PI != E; ++PI) { + if (IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks)) + continue; + + // If this load is not available in multiple predecessors, reject it. + if (UnavailablePred && UnavailablePred != *PI) + return false; + UnavailablePred = *PI; + } + + assert(UnavailablePred != 0 && + "Fully available value should be eliminated above!"); + + // If the loaded pointer is PHI node defined in this block, do PHI translation + // to get its value in the predecessor. + Value *LoadPtr = LI->getOperand(0)->DoPHITranslation(LoadBB, UnavailablePred); + + // Make sure the value is live in the predecessor. If it was defined by a + // non-PHI instruction in this block, we don't know how to recompute it above. + if (Instruction *LPInst = dyn_cast<Instruction>(LoadPtr)) + if (!DT->dominates(LPInst->getParent(), UnavailablePred)) { + DEBUG(cerr << "COULDN'T PRE LOAD BECAUSE PTR IS UNAVAILABLE IN PRED: " + << *LPInst << *LI << "\n"); + return false; + } + + // We don't currently handle critical edges :( + if (UnavailablePred->getTerminator()->getNumSuccessors() != 1) { + DEBUG(cerr << "COULD NOT PRE LOAD BECAUSE OF CRITICAL EDGE '" + << UnavailablePred->getName() << "': " << *LI); + return false; + } + + // 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. + DEBUG(cerr << "GVN REMOVING PRE LOAD: " << *LI); + + Value *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false, + LI->getAlignment(), + UnavailablePred->getTerminator()); + + SmallPtrSet<Instruction*, 4> &p = phiMap[LI->getPointerOperand()]; + for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end(); + I != E; ++I) + ValuesPerBlock.push_back(std::make_pair((*I)->getParent(), *I)); + + DenseMap<BasicBlock*, Value*> BlockReplValues; + BlockReplValues.insert(ValuesPerBlock.begin(), ValuesPerBlock.end()); + BlockReplValues[UnavailablePred] = NewLoad; + + // Perform PHI construction. + Value* v = GetValueForBlock(LI->getParent(), LI, BlockReplValues, true); + LI->replaceAllUsesWith(v); + if (isa<PHINode>(v)) + v->takeName(LI); + if (isa<PointerType>(v->getType())) + MD->invalidateCachedPointerInfo(v); + toErase.push_back(LI); + NumPRELoad++; + return true; +} + +/// processLoad - Attempt to eliminate a load, first by eliminating it +/// locally, and then attempting non-local elimination if that fails. +bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) { + if (L->isVolatile()) + return false; + + Value* pointer = L->getPointerOperand(); + + // ... to a pointer that has been loaded from before... + MemDepResult dep = MD->getDependency(L); + + // If the value isn't available, don't do anything! + if (dep.isClobber()) { + DEBUG( + // fast print dep, using operator<< on instruction would be too slow + DOUT << "GVN: load "; + WriteAsOperand(*DOUT.stream(), L); + Instruction *I = dep.getInst(); + DOUT << " is clobbered by " << *I; + ); + return false; + } + + // If it is defined in another block, try harder. + if (dep.isNonLocal()) + return processNonLocalLoad(L, toErase); + + Instruction *DepInst = dep.getInst(); + if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) { + // Only forward substitute stores to loads of the same type. + // FIXME: Could do better! + if (DepSI->getPointerOperand()->getType() != pointer->getType()) + return false; + + // Remove it! + L->replaceAllUsesWith(DepSI->getOperand(0)); + if (isa<PointerType>(DepSI->getOperand(0)->getType())) + MD->invalidateCachedPointerInfo(DepSI->getOperand(0)); + toErase.push_back(L); + NumGVNLoad++; + return true; + } + + if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) { + // Only forward substitute stores to loads of the same type. + // FIXME: Could do better! load i32 -> load i8 -> truncate on little endian. + if (DepLI->getType() != L->getType()) + return false; + + // Remove it! + L->replaceAllUsesWith(DepLI); + if (isa<PointerType>(DepLI->getType())) + MD->invalidateCachedPointerInfo(DepLI); + toErase.push_back(L); + NumGVNLoad++; + return true; + } + + // If this load really doesn't depend on anything, then we must be loading an + // undef value. This can happen when loading for a fresh allocation with no + // intervening stores, for example. + if (isa<AllocationInst>(DepInst)) { + L->replaceAllUsesWith(UndefValue::get(L->getType())); + toErase.push_back(L); + NumGVNLoad++; + return true; + } + + return false; +} + +Value* GVN::lookupNumber(BasicBlock* BB, uint32_t num) { + DenseMap<BasicBlock*, ValueNumberScope*>::iterator I = localAvail.find(BB); + if (I == localAvail.end()) + return 0; + + ValueNumberScope* locals = I->second; + + while (locals) { + DenseMap<uint32_t, Value*>::iterator I = locals->table.find(num); + if (I != locals->table.end()) + return I->second; + else + locals = locals->parent; + } + + return 0; +} + +/// AttemptRedundancyElimination - If the "fast path" of redundancy elimination +/// by inheritance from the dominator fails, see if we can perform phi +/// construction to eliminate the redundancy. +Value* GVN::AttemptRedundancyElimination(Instruction* orig, unsigned valno) { + BasicBlock* BaseBlock = orig->getParent(); + + SmallPtrSet<BasicBlock*, 4> Visited; + SmallVector<BasicBlock*, 8> Stack; + Stack.push_back(BaseBlock); + + DenseMap<BasicBlock*, Value*> Results; + + // Walk backwards through our predecessors, looking for instances of the + // value number we're looking for. Instances are recorded in the Results + // map, which is then used to perform phi construction. + while (!Stack.empty()) { + BasicBlock* Current = Stack.back(); + Stack.pop_back(); + + // If we've walked all the way to a proper dominator, then give up. Cases + // where the instance is in the dominator will have been caught by the fast + // path, and any cases that require phi construction further than this are + // probably not worth it anyways. Note that this is a SIGNIFICANT compile + // time improvement. + if (DT->properlyDominates(Current, orig->getParent())) return 0; + + DenseMap<BasicBlock*, ValueNumberScope*>::iterator LA = + localAvail.find(Current); + if (LA == localAvail.end()) return 0; + DenseMap<uint32_t, Value*>::iterator V = LA->second->table.find(valno); + + if (V != LA->second->table.end()) { + // Found an instance, record it. + Results.insert(std::make_pair(Current, V->second)); + continue; + } + + // If we reach the beginning of the function, then give up. + if (pred_begin(Current) == pred_end(Current)) + return 0; + + for (pred_iterator PI = pred_begin(Current), PE = pred_end(Current); + PI != PE; ++PI) + if (Visited.insert(*PI)) + Stack.push_back(*PI); + } + + // If we didn't find instances, give up. Otherwise, perform phi construction. + if (Results.size() == 0) + return 0; + else + return GetValueForBlock(BaseBlock, orig, Results, true); +} + +/// processInstruction - When calculating availability, handle an instruction +/// by inserting it into the appropriate sets +bool GVN::processInstruction(Instruction *I, + SmallVectorImpl<Instruction*> &toErase) { + if (LoadInst* L = dyn_cast<LoadInst>(I)) { + bool changed = processLoad(L, toErase); + + if (!changed) { + unsigned num = VN.lookup_or_add(L); + localAvail[I->getParent()]->table.insert(std::make_pair(num, L)); + } + + return changed; + } + + uint32_t nextNum = VN.getNextUnusedValueNumber(); + unsigned num = VN.lookup_or_add(I); + + if (BranchInst* BI = dyn_cast<BranchInst>(I)) { + localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); + + if (!BI->isConditional() || isa<Constant>(BI->getCondition())) + return false; + + Value* branchCond = BI->getCondition(); + uint32_t condVN = VN.lookup_or_add(branchCond); + + BasicBlock* trueSucc = BI->getSuccessor(0); + BasicBlock* falseSucc = BI->getSuccessor(1); + + if (trueSucc->getSinglePredecessor()) + localAvail[trueSucc]->table[condVN] = ConstantInt::getTrue(); + if (falseSucc->getSinglePredecessor()) + localAvail[falseSucc]->table[condVN] = ConstantInt::getFalse(); + + return false; + + // Allocations are always uniquely numbered, so we can save time and memory + // by fast failing them. + } else if (isa<AllocationInst>(I) || isa<TerminatorInst>(I)) { + localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); + return false; + } + + // Collapse PHI nodes + if (PHINode* p = dyn_cast<PHINode>(I)) { + Value* constVal = CollapsePhi(p); + + if (constVal) { + for (PhiMapType::iterator PI = phiMap.begin(), PE = phiMap.end(); + PI != PE; ++PI) + PI->second.erase(p); + + p->replaceAllUsesWith(constVal); + if (isa<PointerType>(constVal->getType())) + MD->invalidateCachedPointerInfo(constVal); + VN.erase(p); + + toErase.push_back(p); + } else { + localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); + } + + // 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! + } else if (num == nextNum) { + localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); + + // Perform fast-path value-number based elimination of values inherited from + // dominators. + } else if (Value* repl = lookupNumber(I->getParent(), num)) { + // Remove it! + VN.erase(I); + I->replaceAllUsesWith(repl); + if (isa<PointerType>(repl->getType())) + MD->invalidateCachedPointerInfo(repl); + toErase.push_back(I); + return true; + +#if 0 + // Perform slow-pathvalue-number based elimination with phi construction. + } else if (Value* repl = AttemptRedundancyElimination(I, num)) { + // Remove it! + VN.erase(I); + I->replaceAllUsesWith(repl); + if (isa<PointerType>(repl->getType())) + MD->invalidateCachedPointerInfo(repl); + toErase.push_back(I); + return true; +#endif + } else { + localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); + } + + return false; +} + +/// runOnFunction - This is the main transformation entry point for a function. +bool GVN::runOnFunction(Function& F) { + MD = &getAnalysis<MemoryDependenceAnalysis>(); + DT = &getAnalysis<DominatorTree>(); + VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>()); + VN.setMemDep(MD); + VN.setDomTree(DT); + + bool changed = false; + bool shouldContinue = true; + + // Merge unconditional branches, allowing PRE to catch more + // optimization opportunities. + for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) { + BasicBlock* BB = FI; + ++FI; + bool removedBlock = MergeBlockIntoPredecessor(BB, this); + if (removedBlock) NumGVNBlocks++; + + changed |= removedBlock; + } + + unsigned Iteration = 0; + + while (shouldContinue) { + DEBUG(cerr << "GVN iteration: " << Iteration << "\n"); + shouldContinue = iterateOnFunction(F); + changed |= shouldContinue; + ++Iteration; + } + + if (EnablePRE) { + 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(); + + return changed; +} + + +bool GVN::processBlock(BasicBlock* BB) { + // FIXME: Kill off toErase by doing erasing eagerly in a helper function (and + // incrementing BI before processing an instruction). + SmallVector<Instruction*, 8> toErase; + bool changed_function = false; + + for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); + BI != BE;) { + changed_function |= processInstruction(BI, toErase); + if (toErase.empty()) { + ++BI; + continue; + } + + // If we need some instructions deleted, do it now. + NumGVNInstr += toErase.size(); + + // Avoid iterator invalidation. + bool AtStart = BI == BB->begin(); + if (!AtStart) + --BI; + + for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(), + E = toErase.end(); I != E; ++I) { + DEBUG(cerr << "GVN removed: " << **I); + MD->removeInstruction(*I); + (*I)->eraseFromParent(); + DEBUG(verifyRemoved(*I)); + } + toErase.clear(); + + if (AtStart) + BI = BB->begin(); + else + ++BI; + } + + return changed_function; +} + +/// performPRE - Perform a purely local form of PRE that looks for diamond +/// control flow patterns and attempts to perform simple PRE at the join point. +bool GVN::performPRE(Function& F) { + bool Changed = false; + SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit; + DenseMap<BasicBlock*, Value*> predMap; + for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()), + DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) { + BasicBlock* CurrentBlock = *DI; + + // Nothing to PRE in the entry block. + if (CurrentBlock == &F.getEntryBlock()) continue; + + for (BasicBlock::iterator BI = CurrentBlock->begin(), + BE = CurrentBlock->end(); BI != BE; ) { + Instruction *CurInst = BI++; + + if (isa<AllocationInst>(CurInst) || isa<TerminatorInst>(CurInst) || + isa<PHINode>(CurInst) || (CurInst->getType() == Type::VoidTy) || + CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() || + isa<DbgInfoIntrinsic>(CurInst)) + continue; + + 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 = 0; + predMap.clear(); + + for (pred_iterator PI = pred_begin(CurrentBlock), + PE = pred_end(CurrentBlock); PI != PE; ++PI) { + // We're not interested in PRE where the block is its + // own predecessor, on in blocks with predecessors + // that are not reachable. + if (*PI == CurrentBlock) { + numWithout = 2; + break; + } else if (!localAvail.count(*PI)) { + numWithout = 2; + break; + } + + DenseMap<uint32_t, Value*>::iterator predV = + localAvail[*PI]->table.find(valno); + if (predV == localAvail[*PI]->table.end()) { + PREPred = *PI; + numWithout++; + } else if (predV->second == CurInst) { + numWithout = 2; + } else { + predMap[*PI] = predV->second; + numWith++; + } + } + + // Don't do PRE when it might increase code size, i.e. when + // we would need to insert instructions in more than one pred. + if (numWithout != 1 || numWith == 0) + continue; + + // We can't do PRE safely on a critical edge, so instead we schedule + // the edge to be split and perform the PRE the next time we iterate + // on the function. + unsigned succNum = 0; + for (unsigned i = 0, e = PREPred->getTerminator()->getNumSuccessors(); + i != e; ++i) + if (PREPred->getTerminator()->getSuccessor(i) == CurrentBlock) { + succNum = i; + break; + } + + if (isCriticalEdge(PREPred->getTerminator(), succNum)) { + toSplit.push_back(std::make_pair(PREPred->getTerminator(), succNum)); + continue; + } + + // Instantiate the expression the in predecessor that lacked it. + // 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 original present will have been instantiated earlier + // in this loop. + Instruction* PREInstr = CurInst->clone(); + bool success = true; + for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) { + Value *Op = PREInstr->getOperand(i); + if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op)) + continue; + + if (Value *V = lookupNumber(PREPred, VN.lookup(Op))) { + PREInstr->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) { + delete PREInstr; + DEBUG(verifyRemoved(PREInstr)); + continue; + } + + PREInstr->insertBefore(PREPred->getTerminator()); + PREInstr->setName(CurInst->getName() + ".pre"); + predMap[PREPred] = PREInstr; + VN.add(PREInstr, valno); + NumGVNPRE++; + + // Update the availability map to include the new instruction. + localAvail[PREPred]->table.insert(std::make_pair(valno, PREInstr)); + + // Create a PHI to make the value available in this block. + PHINode* Phi = PHINode::Create(CurInst->getType(), + CurInst->getName() + ".pre-phi", + CurrentBlock->begin()); + for (pred_iterator PI = pred_begin(CurrentBlock), + PE = pred_end(CurrentBlock); PI != PE; ++PI) + Phi->addIncoming(predMap[*PI], *PI); + + VN.add(Phi, valno); + localAvail[CurrentBlock]->table[valno] = Phi; + + CurInst->replaceAllUsesWith(Phi); + if (isa<PointerType>(Phi->getType())) + MD->invalidateCachedPointerInfo(Phi); + VN.erase(CurInst); + + DEBUG(cerr << "GVN PRE removed: " << *CurInst); + MD->removeInstruction(CurInst); + CurInst->eraseFromParent(); + DEBUG(verifyRemoved(CurInst)); + Changed = true; + } + } + + for (SmallVector<std::pair<TerminatorInst*, unsigned>, 4>::iterator + I = toSplit.begin(), E = toSplit.end(); I != E; ++I) + SplitCriticalEdge(I->first, I->second, this); + + return Changed || toSplit.size(); +} + +/// iterateOnFunction - Executes one iteration of GVN +bool GVN::iterateOnFunction(Function &F) { + cleanupGlobalSets(); + + for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()), + DE = df_end(DT->getRootNode()); DI != DE; ++DI) { + if (DI->getIDom()) + localAvail[DI->getBlock()] = + new ValueNumberScope(localAvail[DI->getIDom()->getBlock()]); + else + localAvail[DI->getBlock()] = new ValueNumberScope(0); + } + + // Top-down walk of the dominator tree + bool changed = false; +#if 0 + // Needed for value numbering with phi construction to work. + ReversePostOrderTraversal<Function*> RPOT(&F); + for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(), + RE = RPOT.end(); RI != RE; ++RI) + changed |= processBlock(*RI); +#else + for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()), + DE = df_end(DT->getRootNode()); DI != DE; ++DI) + changed |= processBlock(DI->getBlock()); +#endif + + return changed; +} + +void GVN::cleanupGlobalSets() { + VN.clear(); + phiMap.clear(); + + for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator + I = localAvail.begin(), E = localAvail.end(); I != E; ++I) + delete I->second; + localAvail.clear(); +} + +/// verifyRemoved - Verify that the specified instruction does not occur in our +/// internal data structures. +void GVN::verifyRemoved(const Instruction *Inst) const { + VN.verifyRemoved(Inst); + + // Walk through the PHI map to make sure the instruction isn't hiding in there + // somewhere. + for (PhiMapType::iterator + I = phiMap.begin(), E = phiMap.end(); I != E; ++I) { + assert(I->first != Inst && "Inst is still a key in PHI map!"); + + for (SmallPtrSet<Instruction*, 4>::iterator + II = I->second.begin(), IE = I->second.end(); II != IE; ++II) { + assert(*II != Inst && "Inst is still a value in PHI map!"); + } + } + + // Walk through the value number scope to make sure the instruction isn't + // ferreted away in it. + for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator + I = localAvail.begin(), E = localAvail.end(); I != E; ++I) { + const ValueNumberScope *VNS = I->second; + + while (VNS) { + for (DenseMap<uint32_t, Value*>::iterator + II = VNS->table.begin(), IE = VNS->table.end(); II != IE; ++II) { + assert(II->second != Inst && "Inst still in value numbering scope!"); + } + + VNS = VNS->parent; + } + } +} |