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llvm-6502/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.
//
//===----------------------------------------------------------------------===//
#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/SparseBitVector.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/Compiler.h"
#include "llvm/Support/Debug.h"
#include <list>
using namespace llvm;
STATISTIC(NumGVNInstr, "Number of instructions deleted");
STATISTIC(NumGVNLoad, "Number of loads deleted");
//===----------------------------------------------------------------------===//
// ValueTable Class
//===----------------------------------------------------------------------===//
static DominatorTree* DT;
static AliasAnalysis* AA;
static MemoryDependenceAnalysis* MD;
/// 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, 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;
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);
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();
};
}
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)) {
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) && "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
//===----------------------------------------------------------------------===//
/// 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);
Instruction* dep = MD->getDependency(C);
if (dep == MemoryDependenceAnalysis::NonLocal ||
!isa<CallInst>(dep)) {
expressionNumbering.insert(std::make_pair(e, nextValueNumber));
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
CallInst* cdep = cast<CallInst>(dep);
Expression d_exp = create_expression(cdep);
if (e != d_exp) {
expressionNumbering.insert(std::make_pair(e, nextValueNumber));
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
} else {
uint32_t v = expressionNumbering[d_exp];
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);
}
//===----------------------------------------------------------------------===//
// ValueNumberedSet Class
//===----------------------------------------------------------------------===//
namespace {
class VISIBILITY_HIDDEN ValueNumberedSet {
private:
SmallPtrSet<Value*, 8> contents;
SparseBitVector<64> numbers;
public:
ValueNumberedSet() { }
ValueNumberedSet(const ValueNumberedSet& other) {
numbers = other.numbers;
contents = other.contents;
}
typedef SmallPtrSet<Value*, 8>::iterator iterator;
iterator begin() { return contents.begin(); }
iterator end() { return contents.end(); }
bool insert(Value* v) { return contents.insert(v); }
void insert(iterator I, iterator E) { contents.insert(I, E); }
void erase(Value* v) { contents.erase(v); }
unsigned count(Value* v) { return contents.count(v); }
size_t size() { return contents.size(); }
void set(unsigned i) {
numbers.set(i);
}
void operator=(const ValueNumberedSet& other) {
contents = other.contents;
numbers = other.numbers;
}
void reset(unsigned i) {
numbers.reset(i);
}
bool test(unsigned i) {
return numbers.test(i);
}
};
}
//===----------------------------------------------------------------------===//
// GVN Pass
//===----------------------------------------------------------------------===//
namespace {
class VISIBILITY_HIDDEN GVN : public FunctionPass {
bool runOnFunction(Function &F);
public:
static char ID; // Pass identification, replacement for typeid
GVN() : FunctionPass((intptr_t)&ID) { }
private:
ValueTable VN;
DenseMap<BasicBlock*, ValueNumberedSet> availableOut;
typedef DenseMap<Value*, SmallPtrSet<Instruction*, 4> > PhiMapType;
PhiMapType phiMap;
// This transformation requires dominator postdominator info
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
AU.addRequired<DominatorTree>();
AU.addRequired<MemoryDependenceAnalysis>();
AU.addRequired<AliasAnalysis>();
AU.addPreserved<AliasAnalysis>();
AU.addPreserved<MemoryDependenceAnalysis>();
}
// Helper fuctions
// FIXME: eliminate or document these better
Value* find_leader(ValueNumberedSet& vals, uint32_t v) ;
void val_insert(ValueNumberedSet& s, Value* v);
bool processLoad(LoadInst* L,
DenseMap<Value*, LoadInst*> &lastLoad,
SmallVectorImpl<Instruction*> &toErase);
bool processInstruction(Instruction* I,
ValueNumberedSet& currAvail,
DenseMap<Value*, LoadInst*>& lastSeenLoad,
SmallVectorImpl<Instruction*> &toErase);
bool processNonLocalLoad(LoadInst* L,
SmallVectorImpl<Instruction*> &toErase);
Value *GetValueForBlock(BasicBlock *BB, LoadInst* orig,
DenseMap<BasicBlock*, Value*> &Phis,
bool top_level = false);
void dump(DenseMap<BasicBlock*, Value*>& d);
bool iterateOnFunction(Function &F);
Value* CollapsePhi(PHINode* p);
bool isSafeReplacement(PHINode* p, Instruction* inst);
};
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");
/// find_leader - Given a set and a value number, return the first
/// element of the set with that value number, or 0 if no such element
/// is present
Value* GVN::find_leader(ValueNumberedSet& vals, uint32_t v) {
if (!vals.test(v))
return 0;
for (ValueNumberedSet::iterator I = vals.begin(), E = vals.end();
I != E; ++I)
if (v == VN.lookup(*I))
return *I;
assert(0 && "No leader found, but present bit is set?");
return 0;
}
/// val_insert - Insert a value into a set only if there is not a value
/// with the same value number already in the set
void GVN::val_insert(ValueNumberedSet& s, Value* v) {
uint32_t num = VN.lookup(v);
if (!s.test(num))
s.insert(v);
}
void GVN::dump(DenseMap<BasicBlock*, Value*>& d) {
printf("{\n");
for (DenseMap<BasicBlock*, Value*>::iterator I = d.begin(),
E = d.end(); I != E; ++I) {
if (I->second == MemoryDependenceAnalysis::None)
printf("None\n");
else
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, 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;
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);
}
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;
}
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) {
// Find the non-local dependencies of the load
DenseMap<BasicBlock*, Value*> deps;
MD->getNonLocalDependency(L, deps);
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...
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;
}
/// processInstruction - When calculating availability, handle an instruction
/// by inserting it into the appropriate sets
bool GVN::processInstruction(Instruction *I, ValueNumberedSet &currAvail,
DenseMap<Value*, LoadInst*> &lastSeenLoad,
SmallVectorImpl<Instruction*> &toErase) {
if (LoadInst* L = dyn_cast<LoadInst>(I))
return processLoad(L, lastSeenLoad, toErase);
// Allocations are always uniquely numbered, so we can save time and memory
// by fast failing them.
if (isa<AllocationInst>(I))
return false;
unsigned num = VN.lookup_or_add(I);
// 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);
}
// Perform value-number based elimination
} else if (currAvail.test(num)) {
Value* repl = find_leader(currAvail, num);
// Remove it!
MD->removeInstruction(I);
VN.erase(I);
I->replaceAllUsesWith(repl);
toErase.push_back(I);
return true;
} else if (!I->isTerminator()) {
currAvail.set(num);
currAvail.insert(I);
}
return false;
}
// GVN::runOnFunction - This is the main transformation entry point for a
// function.
//
bool GVN::runOnFunction(Function& F) {
DT = &getAnalysis<DominatorTree>();
AA = &getAnalysis<AliasAnalysis>();
MD = &getAnalysis<MemoryDependenceAnalysis>();
bool changed = false;
bool shouldContinue = true;
while (shouldContinue) {
shouldContinue = iterateOnFunction(F);
changed |= shouldContinue;
}
return changed;
}
// GVN::iterateOnFunction - Executes one iteration of GVN
bool GVN::iterateOnFunction(Function &F) {
// Clean out global sets from any previous functions
VN.clear();
availableOut.clear();
phiMap.clear();
bool changed_function = false;
SmallVector<Instruction*, 8> toErase;
DenseMap<Value*, LoadInst*> lastSeenLoad;
DenseMap<DomTreeNode*, size_t> numChildrenVisited;
// Top-down walk of the dominator tree
for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
E = df_end(DT->getRootNode()); DI != E; ++DI) {
// Get the set to update for this block
ValueNumberedSet& currAvail = availableOut[DI->getBlock()];
lastSeenLoad.clear();
BasicBlock* BB = DI->getBlock();
// A block inherits AVAIL_OUT from its dominator
if (DI->getIDom() != 0) {
currAvail = availableOut[DI->getIDom()->getBlock()];
numChildrenVisited[DI->getIDom()]++;
if (numChildrenVisited[DI->getIDom()] == DI->getIDom()->getNumChildren()) {
availableOut.erase(DI->getIDom()->getBlock());
numChildrenVisited.erase(DI->getIDom());
}
}
for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
BI != BE;) {
changed_function |= processInstruction(BI, currAvail,
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;
}
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