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llvm-project/llvm/lib/Transforms/Scalar/GVN.cpp

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//===- 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/Instructions.h"
#include "llvm/Value.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DepthFirstIterator.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"
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");
static cl::opt<bool> EnablePRE("enable-pre",
cl::init(true), cl::Hidden);
//===----------------------------------------------------------------------===//
// 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 {
if (opcode != other.opcode)
return true;
else if (opcode == EMPTY || opcode == TOMBSTONE)
return false;
else if (type != other.type)
return true;
else if (function != other.function)
return true;
else if (firstVN != other.firstVN)
return true;
else if (secondVN != other.secondVN)
return true;
else if (thirdVN != other.thirdVN)
return true;
else {
if (varargs.size() != other.varargs.size())
return true;
for (size_t i = 0; i < varargs.size(); ++i)
if (varargs[i] != other.varargs[i])
return true;
return false;
}
}
};
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; }
void setMemDep(MemoryDependenceAnalysis* M) { MD = M; }
void setDomTree(DominatorTree* D) { DT = D; }
uint32_t getNextUnusedValueNumber() { return nextValueNumber; }
};
}
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++;
}
Instruction* local_dep = MD->getDependency(C);
if (local_dep == MemoryDependenceAnalysis::None) {
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
} else if (local_dep != MemoryDependenceAnalysis::NonLocal) {
if (!isa<CallInst>(local_dep)) {
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
CallInst* local_cdep = cast<CallInst>(local_dep);
if (local_cdep->getCalledFunction() != C->getCalledFunction() ||
local_cdep->getNumOperands() != C->getNumOperands()) {
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
} else if (!C->getCalledFunction()) {
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
} else {
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;
}
}
DenseMap<BasicBlock*, Value*> deps;
MD->getNonLocalDependency(C, deps);
CallInst* cdep = 0;
for (DenseMap<BasicBlock*, Value*>::iterator I = deps.begin(),
E = deps.end(); I != E; ++I) {
if (I->second == MemoryDependenceAnalysis::None) {
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
} else if (I->second != MemoryDependenceAnalysis::NonLocal) {
if (DT->properlyDominates(I->first, C->getParent())) {
if (CallInst* CD = dyn_cast<CallInst>(I->second))
cdep = CD;
else {
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
} else {
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
}
}
if (!cdep) {
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
if (cdep->getCalledFunction() != C->getCalledFunction() ||
cdep->getNumOperands() != C->getNumOperands()) {
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
} else if (!C->getCalledFunction()) {
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
} else {
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);
}
//===----------------------------------------------------------------------===//
// 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:
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,
DenseMap<Value*, LoadInst*> &lastLoad,
SmallVectorImpl<Instruction*> &toErase);
bool processInstruction(Instruction* I,
DenseMap<Value*, LoadInst*>& lastSeenLoad,
SmallVectorImpl<Instruction*> &toErase);
bool processNonLocalLoad(LoadInst* L,
SmallVectorImpl<Instruction*> &toErase);
bool processBlock(DomTreeNode* DTN);
Value *GetValueForBlock(BasicBlock *BB, LoadInst* 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);
};
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) {
DominatorTree &DT = getAnalysis<DominatorTree>();
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, LoadInst* 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 (!getAnalysis<DominatorTree>().isReachableFromEntry(BB))
return Phis[BB] = UndefValue::get(orig->getType());
BasicBlock* singlePred = BB->getSinglePredecessor();
if (singlePred) {
Value *ret = GetValueForBlock(singlePred, orig, Phis);
Phis[BB] = ret;
return ret;
}
// 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(std::distance(pred_begin(BB), pred_end(BB)));
if (Phis.count(BB) == 0)
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);
}
AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
AA.copyValue(orig, PN);
// Attempt to collapse PHI nodes that are trivially redundant
Value* v = CollapsePhi(PN);
if (!v) {
// Cache our phi construction results
phiMap[orig->getPointerOperand()].insert(PN);
return PN;
}
MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
MD.removeInstruction(PN);
PN->replaceAllUsesWith(v);
for (DenseMap<BasicBlock*, Value*>::iterator I = Phis.begin(),
E = Phis.end(); I != E; ++I)
if (I->second == PN)
I->second = v;
PN->eraseFromParent();
Phis[BB] = v;
return v;
}
/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are
/// non-local by performing PHI construction.
bool GVN::processNonLocalLoad(LoadInst* L,
SmallVectorImpl<Instruction*> &toErase) {
MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
// Find the non-local dependencies of the load
DenseMap<BasicBlock*, Value*> deps;
MD.getNonLocalDependency(L, 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.
if (deps.size() > 100)
return false;
DenseMap<BasicBlock*, Value*> repl;
// Filter out useless results (non-locals, etc)
for (DenseMap<BasicBlock*, Value*>::iterator I = deps.begin(), E = deps.end();
I != E; ++I) {
if (I->second == MemoryDependenceAnalysis::None)
return false;
if (I->second == MemoryDependenceAnalysis::NonLocal)
continue;
if (StoreInst* S = dyn_cast<StoreInst>(I->second)) {
if (S->getPointerOperand() != L->getPointerOperand())
return false;
repl[I->first] = S->getOperand(0);
} else if (LoadInst* LD = dyn_cast<LoadInst>(I->second)) {
if (LD->getPointerOperand() != L->getPointerOperand())
return false;
repl[I->first] = LD;
} else {
return false;
}
}
// Use cached PHI construction information from previous runs
SmallPtrSet<Instruction*, 4>& p = phiMap[L->getPointerOperand()];
for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end();
I != E; ++I) {
if ((*I)->getParent() == L->getParent()) {
MD.removeInstruction(L);
L->replaceAllUsesWith(*I);
toErase.push_back(L);
NumGVNLoad++;
return true;
}
repl.insert(std::make_pair((*I)->getParent(), *I));
}
// Perform PHI construction
SmallPtrSet<BasicBlock*, 4> visited;
Value* v = GetValueForBlock(L->getParent(), L, repl, true);
MD.removeInstruction(L);
L->replaceAllUsesWith(v);
toErase.push_back(L);
NumGVNLoad++;
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, DenseMap<Value*, LoadInst*> &lastLoad,
SmallVectorImpl<Instruction*> &toErase) {
if (L->isVolatile()) {
lastLoad[L->getPointerOperand()] = L;
return false;
}
Value* pointer = L->getPointerOperand();
LoadInst*& last = lastLoad[pointer];
// ... to a pointer that has been loaded from before...
MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
bool removedNonLocal = false;
Instruction* dep = MD.getDependency(L);
if (dep == MemoryDependenceAnalysis::NonLocal &&
L->getParent() != &L->getParent()->getParent()->getEntryBlock()) {
removedNonLocal = processNonLocalLoad(L, toErase);
if (!removedNonLocal)
last = L;
return removedNonLocal;
}
bool deletedLoad = false;
// Walk up the dependency chain until we either find
// a dependency we can use, or we can't walk any further
while (dep != MemoryDependenceAnalysis::None &&
dep != MemoryDependenceAnalysis::NonLocal &&
(isa<LoadInst>(dep) || isa<StoreInst>(dep))) {
// ... that depends on a store ...
if (StoreInst* S = dyn_cast<StoreInst>(dep)) {
if (S->getPointerOperand() == pointer) {
// Remove it!
MD.removeInstruction(L);
L->replaceAllUsesWith(S->getOperand(0));
toErase.push_back(L);
deletedLoad = true;
NumGVNLoad++;
}
// Whether we removed it or not, we can't
// go any further
break;
} else if (!last) {
// If we don't depend on a store, and we haven't
// been loaded before, bail.
break;
} else if (dep == last) {
// Remove it!
MD.removeInstruction(L);
L->replaceAllUsesWith(last);
toErase.push_back(L);
deletedLoad = true;
NumGVNLoad++;
break;
} else {
dep = MD.getDependency(L, dep);
}
}
if (dep != MemoryDependenceAnalysis::None &&
dep != MemoryDependenceAnalysis::NonLocal &&
isa<AllocationInst>(dep)) {
// Check that this load is actually from the
// allocation we found
Value* v = L->getOperand(0);
while (true) {
if (BitCastInst *BC = dyn_cast<BitCastInst>(v))
v = BC->getOperand(0);
else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(v))
v = GEP->getOperand(0);
else
break;
}
if (v == dep) {
// If this load depends directly on an allocation, there isn't
// anything stored there; therefore, we can optimize this load
// to undef.
MD.removeInstruction(L);
L->replaceAllUsesWith(UndefValue::get(L->getType()));
toErase.push_back(L);
deletedLoad = true;
NumGVNLoad++;
}
}
if (!deletedLoad)
last = L;
return deletedLoad;
}
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;
}
/// processInstruction - When calculating availability, handle an instruction
/// by inserting it into the appropriate sets
bool GVN::processInstruction(Instruction *I,
DenseMap<Value*, LoadInst*> &lastSeenLoad,
SmallVectorImpl<Instruction*> &toErase) {
if (LoadInst* L = dyn_cast<LoadInst>(I)) {
bool changed = processLoad(L, lastSeenLoad, 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);
// Allocations are always uniquely numbered, so we can save time and memory
// by fast failing them.
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)
if (PI->second.count(p))
PI->second.erase(p);
p->replaceAllUsesWith(constVal);
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 value-number based elimination
} else if (Value* repl = lookupNumber(I->getParent(), num)) {
// Remove it!
MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
MD.removeInstruction(I);
VN.erase(I);
I->replaceAllUsesWith(repl);
toErase.push_back(I);
return true;
} else {
localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
}
return false;
}
// GVN::runOnFunction - This is the main transformation entry point for a
// function.
//
bool GVN::runOnFunction(Function& F) {
VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>());
VN.setMemDep(&getAnalysis<MemoryDependenceAnalysis>());
VN.setDomTree(&getAnalysis<DominatorTree>());
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;
}
while (shouldContinue) {
shouldContinue = iterateOnFunction(F);
changed |= shouldContinue;
}
if (EnablePRE) {
bool PREChanged = true;
while (PREChanged) {
PREChanged = performPRE(F);
changed |= PREChanged;
}
}
return changed;
}
bool GVN::processBlock(DomTreeNode* DTN) {
BasicBlock* BB = DTN->getBlock();
SmallVector<Instruction*, 8> toErase;
DenseMap<Value*, LoadInst*> lastSeenLoad;
bool changed_function = false;
if (DTN->getIDom())
localAvail[BB] =
new ValueNumberScope(localAvail[DTN->getIDom()->getBlock()]);
else
localAvail[BB] = new ValueNumberScope(0);
for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
BI != BE;) {
changed_function |= processInstruction(BI, lastSeenLoad, 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)
(*I)->eraseFromParent();
if (AtStart)
BI = BB->begin();
else
++BI;
toErase.clear();
}
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;
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; ) {
if (isa<AllocationInst>(BI) || isa<TerminatorInst>(BI) ||
isa<PHINode>(BI) || BI->mayReadFromMemory() ||
BI->mayWriteToMemory()) {
BI++;
continue;
}
uint32_t valno = VN.lookup(BI);
// 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;
DenseMap<BasicBlock*, Value*> predMap;
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 == BI) {
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) {
BI++;
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));
changed = true;
BI++;
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 = BI->clone();
bool success = true;
for (unsigned i = 0; i < BI->getNumOperands(); ++i) {
Value* op = BI->getOperand(i);
if (isa<Argument>(op) || isa<Constant>(op) || isa<GlobalValue>(op))
PREInstr->setOperand(i, op);
else {
Value* V = lookupNumber(PREPred, VN.lookup(op));
if (!V) {
success = false;
break;
} else
PREInstr->setOperand(i, V);
}
}
// 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;
BI++;
continue;
}
PREInstr->insertBefore(PREPred->getTerminator());
PREInstr->setName(BI->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(BI->getType(),
BI->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;
BI->replaceAllUsesWith(Phi);
VN.erase(BI);
Instruction* erase = BI;
BI++;
erase->eraseFromParent();
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) {
// Clean out global sets from any previous functions
VN.clear();
phiMap.clear();
for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator
I = localAvail.begin(), E = localAvail.end(); I != E; ++I)
delete I->second;
localAvail.clear();
DominatorTree &DT = getAnalysis<DominatorTree>();
// Top-down walk of the dominator tree
bool changed = false;
for (df_iterator<DomTreeNode*> DI = df_begin(DT.getRootNode()),
DE = df_end(DT.getRootNode()); DI != DE; ++DI)
changed |= processBlock(*DI);
return changed;
}
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