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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.
//
//===----------------------------------------------------------------------===//
#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/Instructions.h"
#include "llvm/ParameterAttributes.h"
#include "llvm/Value.h"
#include "llvm/ADT/BitVector.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/Support/GetElementPtrTypeIterator.h"
#include "llvm/Target/TargetData.h"
#include <list>
using namespace llvm;
STATISTIC(NumGVNInstr, "Number of instructions deleted");
STATISTIC(NumGVNLoad, "Number of loads deleted");
STATISTIC(NumMemSetInfer, "Number of memsets inferred");
namespace {
cl::opt<bool>
FormMemSet("form-memset-from-stores",
cl::desc("Transform straight-line stores to memsets"),
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, 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;
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();
void setAliasAnalysis(AliasAnalysis* A) { AA = A; }
uint32_t hash_operand(Value* v);
};
}
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;
}
}
uint32_t ValueTable::hash_operand(Value* v) {
if (CallInst* CI = dyn_cast<CallInst>(v))
if (!AA->doesNotAccessMemory(CI))
return nextValueNumber++;
return lookup_or_add(v);
}
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(hash_operand(*I));
return e;
}
Expression ValueTable::create_expression(BinaryOperator* BO) {
Expression e;
e.firstVN = hash_operand(BO->getOperand(0));
e.secondVN = hash_operand(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 = hash_operand(C->getOperand(0));
e.secondVN = hash_operand(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 = hash_operand(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 = hash_operand(S->getOperand(0));
e.secondVN = hash_operand(S->getOperand(1));
e.thirdVN = hash_operand(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 = hash_operand(E->getOperand(0));
e.secondVN = hash_operand(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 = hash_operand(I->getOperand(0));
e.secondVN = hash_operand(I->getOperand(1));
e.thirdVN = hash_operand(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 = hash_operand(I->getCondition());
e.secondVN = hash_operand(I->getTrueValue());
e.thirdVN = hash_operand(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 = hash_operand(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(hash_operand(*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->onlyReadsMemory(C)) { // includes doesNotAccessMemory
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 {
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;
BitVector numbers;
public:
ValueNumberedSet() { numbers.resize(1); }
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) {
if (i >= numbers.size())
numbers.resize(i+1);
numbers.set(i);
}
void operator=(const ValueNumberedSet& other) {
contents = other.contents;
numbers = other.numbers;
}
void reset(unsigned i) {
if (i < numbers.size())
numbers.reset(i);
}
bool test(unsigned i) {
if (i >= numbers.size())
return false;
return numbers.test(i);
}
void clear() {
contents.clear();
numbers.clear();
}
};
}
//===----------------------------------------------------------------------===//
// 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.addRequired<TargetData>();
AU.addPreserved<AliasAnalysis>();
AU.addPreserved<MemoryDependenceAnalysis>();
AU.addPreserved<TargetData>();
}
// 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 processStore(StoreInst *SI, SmallVectorImpl<Instruction*> &toErase);
bool processInstruction(Instruction* I,
ValueNumberedSet& currAvail,
DenseMap<Value*, LoadInst*>& lastSeenLoad,
SmallVectorImpl<Instruction*> &toErase);
bool processNonLocalLoad(LoadInst* L,
SmallVectorImpl<Instruction*> &toErase);
bool processMemCpy(MemCpyInst* M, MemCpyInst* MDep,
SmallVectorImpl<Instruction*> &toErase);
bool performCallSlotOptzn(MemCpyInst* cpy, CallInst* C,
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) {
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;
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 = new PHINode(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);
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;
}
/// isBytewiseValue - If the specified value can be set by repeating the same
/// byte in memory, return the i8 value that it is represented with. This is
/// true for all i8 values obviously, but is also true for i32 0, i32 -1,
/// i16 0xF0F0, double 0.0 etc. If the value can't be handled with a repeated
/// byte store (e.g. i16 0x1234), return null.
static Value *isBytewiseValue(Value *V) {
// All byte-wide stores are splatable, even of arbitrary variables.
if (V->getType() == Type::Int8Ty) return V;
// Constant float and double values can be handled as integer values if the
// corresponding integer value is "byteable". An important case is 0.0.
if (ConstantFP *CFP = dyn_cast<ConstantFP>(V)) {
if (CFP->getType() == Type::FloatTy)
V = ConstantExpr::getBitCast(CFP, Type::Int32Ty);
if (CFP->getType() == Type::DoubleTy)
V = ConstantExpr::getBitCast(CFP, Type::Int64Ty);
// Don't handle long double formats, which have strange constraints.
}
// We can handle constant integers that are power of two in size and a
// multiple of 8 bits.
if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
unsigned Width = CI->getBitWidth();
if (isPowerOf2_32(Width) && Width > 8) {
// We can handle this value if the recursive binary decomposition is the
// same at all levels.
APInt Val = CI->getValue();
APInt Val2;
while (Val.getBitWidth() != 8) {
unsigned NextWidth = Val.getBitWidth()/2;
Val2 = Val.lshr(NextWidth);
Val2.trunc(Val.getBitWidth()/2);
Val.trunc(Val.getBitWidth()/2);
// If the top/bottom halves aren't the same, reject it.
if (Val != Val2)
return 0;
}
return ConstantInt::get(Val);
}
}
// Conceptually, we could handle things like:
// %a = zext i8 %X to i16
// %b = shl i16 %a, 8
// %c = or i16 %a, %b
// but until there is an example that actually needs this, it doesn't seem
// worth worrying about.
return 0;
}
static int64_t GetOffsetFromIndex(const GetElementPtrInst *GEP, unsigned Idx,
bool &VariableIdxFound, TargetData &TD) {
// Skip over the first indices.
gep_type_iterator GTI = gep_type_begin(GEP);
for (unsigned i = 1; i != Idx; ++i, ++GTI)
/*skip along*/;
// Compute the offset implied by the rest of the indices.
int64_t Offset = 0;
for (unsigned i = Idx, e = GEP->getNumOperands(); i != e; ++i, ++GTI) {
ConstantInt *OpC = dyn_cast<ConstantInt>(GEP->getOperand(i));
if (OpC == 0)
return VariableIdxFound = true;
if (OpC->isZero()) continue; // No offset.
// Handle struct indices, which add their field offset to the pointer.
if (const StructType *STy = dyn_cast<StructType>(*GTI)) {
Offset += TD.getStructLayout(STy)->getElementOffset(OpC->getZExtValue());
continue;
}
// Otherwise, we have a sequential type like an array or vector. Multiply
// the index by the ElementSize.
uint64_t Size = TD.getABITypeSize(GTI.getIndexedType());
Offset += Size*OpC->getSExtValue();
}
return Offset;
}
/// IsPointerOffset - Return true if Ptr1 is provably equal to Ptr2 plus a
/// constant offset, and return that constant offset. For example, Ptr1 might
/// be &A[42], and Ptr2 might be &A[40]. In this case offset would be -8.
static bool IsPointerOffset(Value *Ptr1, Value *Ptr2, int64_t &Offset,
TargetData &TD) {
// Right now we handle the case when Ptr1/Ptr2 are both GEPs with an identical
// base. After that base, they may have some number of common (and
// potentially variable) indices. After that they handle some constant
// offset, which determines their offset from each other. At this point, we
// handle no other case.
GetElementPtrInst *GEP1 = dyn_cast<GetElementPtrInst>(Ptr1);
GetElementPtrInst *GEP2 = dyn_cast<GetElementPtrInst>(Ptr2);
if (!GEP1 || !GEP2 || GEP1->getOperand(0) != GEP2->getOperand(0))
return false;
// Skip any common indices and track the GEP types.
unsigned Idx = 1;
for (; Idx != GEP1->getNumOperands() && Idx != GEP2->getNumOperands(); ++Idx)
if (GEP1->getOperand(Idx) != GEP2->getOperand(Idx))
break;
bool VariableIdxFound = false;
int64_t Offset1 = GetOffsetFromIndex(GEP1, Idx, VariableIdxFound, TD);
int64_t Offset2 = GetOffsetFromIndex(GEP2, Idx, VariableIdxFound, TD);
if (VariableIdxFound) return false;
Offset = Offset2-Offset1;
return true;
}
/// MemsetRange - Represents a range of memset'd bytes with the ByteVal value.
/// This allows us to analyze stores like:
/// store 0 -> P+1
/// store 0 -> P+0
/// store 0 -> P+3
/// store 0 -> P+2
/// which sometimes happens with stores to arrays of structs etc. When we see
/// the first store, we make a range [1, 2). The second store extends the range
/// to [0, 2). The third makes a new range [2, 3). The fourth store joins the
/// two ranges into [0, 3) which is memset'able.
namespace {
struct MemsetRange {
// Start/End - A semi range that describes the span that this range covers.
// The range is closed at the start and open at the end: [Start, End).
int64_t Start, End;
/// StartPtr - The getelementptr instruction that points to the start of the
/// range.
Value *StartPtr;
/// Alignment - The known alignment of the first store.
unsigned Alignment;
/// TheStores - The actual stores that make up this range.
SmallVector<StoreInst*, 16> TheStores;
bool isProfitableToUseMemset(const TargetData &TD) const;
};
} // end anon namespace
bool MemsetRange::isProfitableToUseMemset(const TargetData &TD) const {
// If we found more than 8 stores to merge or 64 bytes, use memset.
if (TheStores.size() >= 8 || End-Start >= 64) return true;
// Assume that the code generator is capable of merging pairs of stores
// together if it wants to.
if (TheStores.size() <= 2) return false;
// If we have fewer than 8 stores, it can still be worthwhile to do this.
// For example, merging 4 i8 stores into an i32 store is useful almost always.
// However, merging 2 32-bit stores isn't useful on a 32-bit architecture (the
// memset will be split into 2 32-bit stores anyway) and doing so can
// pessimize the llvm optimizer.
//
// Since we don't have perfect knowledge here, make some assumptions: assume
// the maximum GPR width is the same size as the pointer size and assume that
// this width can be stored. If so, check to see whether we will end up
// actually reducing the number of stores used.
unsigned Bytes = unsigned(End-Start);
unsigned NumPointerStores = Bytes/TD.getPointerSize();
// Assume the remaining bytes if any are done a byte at a time.
unsigned NumByteStores = Bytes - NumPointerStores*TD.getPointerSize();
// If we will reduce the # stores (according to this heuristic), do the
// transformation. This encourages merging 4 x i8 -> i32 and 2 x i16 -> i32
// etc.
return TheStores.size() > NumPointerStores+NumByteStores;
}
namespace {
class MemsetRanges {
/// Ranges - A sorted list of the memset ranges. We use std::list here
/// because each element is relatively large and expensive to copy.
std::list<MemsetRange> Ranges;
typedef std::list<MemsetRange>::iterator range_iterator;
TargetData &TD;
public:
MemsetRanges(TargetData &td) : TD(td) {}
typedef std::list<MemsetRange>::const_iterator const_iterator;
const_iterator begin() const { return Ranges.begin(); }
const_iterator end() const { return Ranges.end(); }
bool empty() const { return Ranges.empty(); }
void addStore(int64_t OffsetFromFirst, StoreInst *SI);
};
} // end anon namespace
/// addStore - Add a new store to the MemsetRanges data structure. This adds a
/// new range for the specified store at the specified offset, merging into
/// existing ranges as appropriate.
void MemsetRanges::addStore(int64_t Start, StoreInst *SI) {
int64_t End = Start+TD.getTypeStoreSize(SI->getOperand(0)->getType());
// Do a linear search of the ranges to see if this can be joined and/or to
// find the insertion point in the list. We keep the ranges sorted for
// simplicity here. This is a linear search of a linked list, which is ugly,
// however the number of ranges is limited, so this won't get crazy slow.
range_iterator I = Ranges.begin(), E = Ranges.end();
while (I != E && Start > I->End)
++I;
// We now know that I == E, in which case we didn't find anything to merge
// with, or that Start <= I->End. If End < I->Start or I == E, then we need
// to insert a new range. Handle this now.
if (I == E || End < I->Start) {
MemsetRange &R = *Ranges.insert(I, MemsetRange());
R.Start = Start;
R.End = End;
R.StartPtr = SI->getPointerOperand();
R.Alignment = SI->getAlignment();
R.TheStores.push_back(SI);
return;
}
// This store overlaps with I, add it.
I->TheStores.push_back(SI);
// At this point, we may have an interval that completely contains our store.
// If so, just add it to the interval and return.
if (I->Start <= Start && I->End >= End)
return;
// Now we know that Start <= I->End and End >= I->Start so the range overlaps
// but is not entirely contained within the range.
// See if the range extends the start of the range. In this case, it couldn't
// possibly cause it to join the prior range, because otherwise we would have
// stopped on *it*.
if (Start < I->Start) {
I->Start = Start;
I->StartPtr = SI->getPointerOperand();
}
// Now we know that Start <= I->End and Start >= I->Start (so the startpoint
// is in or right at the end of I), and that End >= I->Start. Extend I out to
// End.
if (End > I->End) {
I->End = End;
range_iterator NextI = I;;
while (++NextI != E && End >= NextI->Start) {
// Merge the range in.
I->TheStores.append(NextI->TheStores.begin(), NextI->TheStores.end());
if (NextI->End > I->End)
I->End = NextI->End;
Ranges.erase(NextI);
NextI = I;
}
}
}
/// processStore - When GVN is scanning forward over instructions, we look for
/// some other patterns to fold away. In particular, this looks for stores to
/// neighboring locations of memory. If it sees enough consequtive ones
/// (currently 4) it attempts to merge them together into a memcpy/memset.
bool GVN::processStore(StoreInst *SI, SmallVectorImpl<Instruction*> &toErase) {
if (!FormMemSet) return false;
if (SI->isVolatile()) return false;
// There are two cases that are interesting for this code to handle: memcpy
// and memset. Right now we only handle memset.
// Ensure that the value being stored is something that can be memset'able a
// byte at a time like "0" or "-1" or any width, as well as things like
// 0xA0A0A0A0 and 0.0.
Value *ByteVal = isBytewiseValue(SI->getOperand(0));
if (!ByteVal)
return false;
TargetData &TD = getAnalysis<TargetData>();
AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
// Okay, so we now have a single store that can be splatable. Scan to find
// all subsequent stores of the same value to offset from the same pointer.
// Join these together into ranges, so we can decide whether contiguous blocks
// are stored.
MemsetRanges Ranges(TD);
Value *StartPtr = SI->getPointerOperand();
BasicBlock::iterator BI = SI;
for (++BI; !isa<TerminatorInst>(BI); ++BI) {
if (isa<CallInst>(BI) || isa<InvokeInst>(BI)) {
// If the call is readnone, ignore it, otherwise bail out. We don't even
// allow readonly here because we don't want something like:
// A[1] = 2; strlen(A); A[2] = 2; -> memcpy(A, ...); strlen(A).
if (AA.getModRefBehavior(CallSite::get(BI)) ==
AliasAnalysis::DoesNotAccessMemory)
continue;
// TODO: If this is a memset, try to join it in.
break;
} else if (isa<VAArgInst>(BI) || isa<LoadInst>(BI))
break;
// If this is a non-store instruction it is fine, ignore it.
StoreInst *NextStore = dyn_cast<StoreInst>(BI);
if (NextStore == 0) continue;
// If this is a store, see if we can merge it in.
if (NextStore->isVolatile()) break;
// Check to see if this stored value is of the same byte-splattable value.
if (ByteVal != isBytewiseValue(NextStore->getOperand(0)))
break;
// Check to see if this store is to a constant offset from the start ptr.
int64_t Offset;
if (!IsPointerOffset(StartPtr, NextStore->getPointerOperand(), Offset, TD))
break;
Ranges.addStore(Offset, NextStore);
}
// If we have no ranges, then we just had a single store with nothing that
// could be merged in. This is a very common case of course.
if (Ranges.empty())
return false;
// If we had at least one store that could be merged in, add the starting
// store as well. We try to avoid this unless there is at least something
// interesting as a small compile-time optimization.
Ranges.addStore(0, SI);
Function *MemSetF = 0;
// Now that we have full information about ranges, loop over the ranges and
// emit memset's for anything big enough to be worthwhile.
bool MadeChange = false;
for (MemsetRanges::const_iterator I = Ranges.begin(), E = Ranges.end();
I != E; ++I) {
const MemsetRange &Range = *I;
if (Range.TheStores.size() == 1) continue;
// If it is profitable to lower this range to memset, do so now.
if (!Range.isProfitableToUseMemset(TD))
continue;
// Otherwise, we do want to transform this! Create a new memset. We put
// the memset right before the first instruction that isn't part of this
// memset block. This ensure that the memset is dominated by any addressing
// instruction needed by the start of the block.
BasicBlock::iterator InsertPt = BI;
if (MemSetF == 0)
MemSetF = Intrinsic::getDeclaration(SI->getParent()->getParent()
->getParent(), Intrinsic::memset_i64);
// Get the starting pointer of the block.
StartPtr = Range.StartPtr;
// Cast the start ptr to be i8* as memset requires.
const Type *i8Ptr = PointerType::getUnqual(Type::Int8Ty);
if (StartPtr->getType() != i8Ptr)
StartPtr = new BitCastInst(StartPtr, i8Ptr, StartPtr->getNameStart(),
InsertPt);
Value *Ops[] = {
StartPtr, ByteVal, // Start, value
ConstantInt::get(Type::Int64Ty, Range.End-Range.Start), // size
ConstantInt::get(Type::Int32Ty, Range.Alignment) // align
};
Value *C = new CallInst(MemSetF, Ops, Ops+4, "", InsertPt);
DEBUG(cerr << "Replace stores:\n";
for (unsigned i = 0, e = Range.TheStores.size(); i != e; ++i)
cerr << *Range.TheStores[i];
cerr << "With: " << *C); C=C;
// Zap all the stores.
toErase.append(Range.TheStores.begin(), Range.TheStores.end());
++NumMemSetInfer;
MadeChange = true;
}
return MadeChange;
}
/// performCallSlotOptzn - takes a memcpy and a call that it depends on,
/// and checks for the possibility of a call slot optimization by having
/// the call write its result directly into the destination of the memcpy.
bool GVN::performCallSlotOptzn(MemCpyInst *cpy, CallInst *C,
SmallVectorImpl<Instruction*> &toErase) {
// The general transformation to keep in mind is
//
// call @func(..., src, ...)
// memcpy(dest, src, ...)
//
// ->
//
// memcpy(dest, src, ...)
// call @func(..., dest, ...)
//
// Since moving the memcpy is technically awkward, we additionally check that
// src only holds uninitialized values at the moment of the call, meaning that
// the memcpy can be discarded rather than moved.
// Deliberately get the source and destination with bitcasts stripped away,
// because we'll need to do type comparisons based on the underlying type.
Value* cpyDest = cpy->getDest();
Value* cpySrc = cpy->getSource();
CallSite CS = CallSite::get(C);
// We need to be able to reason about the size of the memcpy, so we require
// that it be a constant.
ConstantInt* cpyLength = dyn_cast<ConstantInt>(cpy->getLength());
if (!cpyLength)
return false;
// Require that src be an alloca. This simplifies the reasoning considerably.
AllocaInst* srcAlloca = dyn_cast<AllocaInst>(cpySrc);
if (!srcAlloca)
return false;
// Check that all of src is copied to dest.
TargetData& TD = getAnalysis<TargetData>();
ConstantInt* srcArraySize = dyn_cast<ConstantInt>(srcAlloca->getArraySize());
if (!srcArraySize)
return false;
uint64_t srcSize = TD.getABITypeSize(srcAlloca->getAllocatedType()) *
srcArraySize->getZExtValue();
if (cpyLength->getZExtValue() < srcSize)
return false;
// Check that accessing the first srcSize bytes of dest will not cause a
// trap. Otherwise the transform is invalid since it might cause a trap
// to occur earlier than it otherwise would.
if (AllocaInst* A = dyn_cast<AllocaInst>(cpyDest)) {
// The destination is an alloca. Check it is larger than srcSize.
ConstantInt* destArraySize = dyn_cast<ConstantInt>(A->getArraySize());
if (!destArraySize)
return false;
uint64_t destSize = TD.getABITypeSize(A->getAllocatedType()) *
destArraySize->getZExtValue();
if (destSize < srcSize)
return false;
} else if (Argument* A = dyn_cast<Argument>(cpyDest)) {
// If the destination is an sret parameter then only accesses that are
// outside of the returned struct type can trap.
if (!A->hasStructRetAttr())
return false;
const Type* StructTy = cast<PointerType>(A->getType())->getElementType();
uint64_t destSize = TD.getABITypeSize(StructTy);
if (destSize < srcSize)
return false;
} else {
return false;
}
// Check that src is not accessed except via the call and the memcpy. This
// guarantees that it holds only undefined values when passed in (so the final
// memcpy can be dropped), that it is not read or written between the call and
// the memcpy, and that writing beyond the end of it is undefined.
SmallVector<User*, 8> srcUseList(srcAlloca->use_begin(),
srcAlloca->use_end());
while (!srcUseList.empty()) {
User* UI = srcUseList.back();
srcUseList.pop_back();
if (isa<GetElementPtrInst>(UI) || isa<BitCastInst>(UI)) {
for (User::use_iterator I = UI->use_begin(), E = UI->use_end();
I != E; ++I)
srcUseList.push_back(*I);
} else if (UI != C && UI != cpy) {
return false;
}
}
// Since we're changing the parameter to the callsite, we need to make sure
// that what would be the new parameter dominates the callsite.
DominatorTree& DT = getAnalysis<DominatorTree>();
if (Instruction* cpyDestInst = dyn_cast<Instruction>(cpyDest))
if (!DT.dominates(cpyDestInst, C))
return false;
// In addition to knowing that the call does not access src in some
// unexpected manner, for example via a global, which we deduce from
// the use analysis, we also need to know that it does not sneakily
// access dest. We rely on AA to figure this out for us.
AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
if (AA.getModRefInfo(C, cpy->getRawDest(), srcSize) !=
AliasAnalysis::NoModRef)
return false;
// All the checks have passed, so do the transformation.
for (unsigned i = 0; i < CS.arg_size(); ++i)
if (CS.getArgument(i) == cpySrc) {
if (cpySrc->getType() != cpyDest->getType())
cpyDest = CastInst::createPointerCast(cpyDest, cpySrc->getType(),
cpyDest->getName(), C);
CS.setArgument(i, cpyDest);
}
// Drop any cached information about the call, because we may have changed
// its dependence information by changing its parameter.
MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
MD.dropInstruction(C);
// Remove the memcpy
MD.removeInstruction(cpy);
toErase.push_back(cpy);
return true;
}
/// processMemCpy - perform simplication of memcpy's. If we have memcpy A which
/// copies X to Y, and memcpy B which copies Y to Z, then we can rewrite B to be
/// a memcpy from X to Z (or potentially a memmove, depending on circumstances).
/// This allows later passes to remove the first memcpy altogether.
bool GVN::processMemCpy(MemCpyInst* M, MemCpyInst* MDep,
SmallVectorImpl<Instruction*> &toErase) {
// We can only transforms memcpy's where the dest of one is the source of the
// other
if (M->getSource() != MDep->getDest())
return false;
// Second, the length of the memcpy's must be the same, or the preceeding one
// must be larger than the following one.
ConstantInt* C1 = dyn_cast<ConstantInt>(MDep->getLength());
ConstantInt* C2 = dyn_cast<ConstantInt>(M->getLength());
if (!C1 || !C2)
return false;
uint64_t DepSize = C1->getValue().getZExtValue();
uint64_t CpySize = C2->getValue().getZExtValue();
if (DepSize < CpySize)
return false;
// Finally, we have to make sure that the dest of the second does not
// alias the source of the first
AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
if (AA.alias(M->getRawDest(), CpySize, MDep->getRawSource(), DepSize) !=
AliasAnalysis::NoAlias)
return false;
else if (AA.alias(M->getRawDest(), CpySize, M->getRawSource(), CpySize) !=
AliasAnalysis::NoAlias)
return false;
else if (AA.alias(MDep->getRawDest(), DepSize, MDep->getRawSource(), DepSize)
!= AliasAnalysis::NoAlias)
return false;
// If all checks passed, then we can transform these memcpy's
Function* MemCpyFun = Intrinsic::getDeclaration(
M->getParent()->getParent()->getParent(),
M->getIntrinsicID());
std::vector<Value*> args;
args.push_back(M->getRawDest());
args.push_back(MDep->getRawSource());
args.push_back(M->getLength());
args.push_back(M->getAlignment());
CallInst* C = new CallInst(MemCpyFun, args.begin(), args.end(), "", M);
MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
if (MD.getDependency(C) == MDep) {
MD.dropInstruction(M);
toErase.push_back(M);
return true;
}
MD.removeInstruction(C);
toErase.push_back(C);
return false;
}
/// 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);
if (StoreInst *SI = dyn_cast<StoreInst>(I))
return processStore(SI, toErase);
if (MemCpyInst* M = dyn_cast<MemCpyInst>(I)) {
MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
// The are two possible optimizations we can do for memcpy:
// a) memcpy-memcpy xform which exposes redundance for DSE
// b) call-memcpy xform for return slot optimization
Instruction* dep = MD.getDependency(M);
if (dep == MemoryDependenceAnalysis::None ||
dep == MemoryDependenceAnalysis::NonLocal)
return false;
if (MemCpyInst *MemCpy = dyn_cast<MemCpyInst>(dep))
return processMemCpy(M, MemCpy, toErase);
if (CallInst* C = dyn_cast<CallInst>(dep))
return performCallSlotOptzn(M, C, toErase);
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);
if (CallInst* CI = dyn_cast<CallInst>(I)) {
AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
if (!AA.doesNotAccessMemory(CI)) {
MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
if (cast<Instruction>(repl)->getParent() != CI->getParent() ||
MD.getDependency(CI) != MD.getDependency(cast<CallInst>(repl))) {
// There must be an intervening may-alias store, so nothing from
// this point on will be able to be replaced with the preceding call
currAvail.erase(repl);
currAvail.insert(I);
return false;
}
}
}
// Remove it!
MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
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) {
VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>());
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;
DominatorTree &DT = getAnalysis<DominatorTree>();
SmallVector<Instruction*, 8> toErase;
DenseMap<Value*, LoadInst*> lastSeenLoad;
// 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()];
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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