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978796eaad
llvm-6502/lib/Transforms/Scalar/GVN.cpp
Chris Lattner 978796eaad Make GVN be more intelligent about redundant load 
elimination: when finding dependent load/stores, realize that
they are the same if aliasing claims must alias instead of relying
on the pointers to be exactly equal.  This makes load elimination
more aggressive.  For example, on 403.gcc, we had:

<     68 gvn    - Number of instructions PRE'd
< 152718 gvn    - Number of instructions deleted
<  49699 gvn    - Number of loads deleted
<   6153 memdep - Number of dirty cached non-local responses
< 169336 memdep - Number of fully cached non-local responses
< 162428 memdep - Number of uncached non-local responses

now we have:

>     64 gvn    - Number of instructions PRE'd
> 153623 gvn    - Number of instructions deleted
>  49856 gvn    - Number of loads deleted
>   5022 memdep - Number of dirty cached non-local responses
> 159030 memdep - Number of fully cached non-local responses
> 162443 memdep - Number of uncached non-local responses

That's an extra 157 loads deleted and extra 905 other instructions nuked.

This slows down GVN very slightly, from 3.91 to 3.96s.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@60314 91177308-0d34-0410-b5e6-96231b3b80d8
2008-12-01 01:31:36 +00:00

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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"
#include <cstdio>
using namespace llvm;
STATISTIC(NumGVNInstr, "Number of instructions deleted");
STATISTIC(NumGVNLoad, "Number of loads deleted");
STATISTIC(NumGVNPRE, "Number of instructions PRE'd");
STATISTIC(NumGVNBlocks, "Number of blocks merged");
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; }
AliasAnalysis *getAliasAnalysis() const { return AA; }
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++;
}
MemDepResult local_dep = MD->getDependency(C);
if (local_dep.isNone()) {
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
if (Instruction *LocalDepInst = local_dep.getInst()) {
if (!isa<CallInst>(LocalDepInst)) {
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
CallInst* local_cdep = cast<CallInst>(LocalDepInst);
if (local_cdep->getCalledFunction() != C->getCalledFunction() ||
local_cdep->getNumOperands() != C->getNumOperands()) {
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
if (!C->getCalledFunction()) {
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
for (unsigned i = 1; i < C->getNumOperands(); ++i) {
uint32_t c_vn = lookup_or_add(C->getOperand(i));
uint32_t cd_vn = lookup_or_add(local_cdep->getOperand(i));
if (c_vn != cd_vn) {
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
}
uint32_t v = lookup_or_add(local_cdep);
valueNumbering.insert(std::make_pair(V, v));
return v;
}
const MemoryDependenceAnalysis::NonLocalDepInfo &deps =
MD->getNonLocalDependency(C);
CallInst* cdep = 0;
// Check to see if we have a single dominating call instruction that is
// identical to C.
for (unsigned i = 0, e = deps.size(); i != e; ++i) {
const MemoryDependenceAnalysis::NonLocalDepEntry *I = &deps[i];
// Ignore non-local dependencies.
if (I->second.isNonLocal())
continue;
// We don't handle non-depedencies. If we already have a call, reject
// instruction dependencies.
if (I->second.isNone() || cdep != 0) {
cdep = 0;
break;
}
CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->second.getInst());
// FIXME: All duplicated with non-local case.
if (NonLocalDepCall && DT->properlyDominates(I->first, C->getParent())){
cdep = NonLocalDepCall;
continue;
}
cdep = 0;
break;
}
if (!cdep) {
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
if (cdep->getCalledFunction() != C->getCalledFunction() ||
cdep->getNumOperands() != C->getNumOperands()) {
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
if (!C->getCalledFunction()) {
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
for (unsigned i = 1; i < C->getNumOperands(); ++i) {
uint32_t c_vn = lookup_or_add(C->getOperand(i));
uint32_t cd_vn = lookup_or_add(cdep->getOperand(i));
if (c_vn != cd_vn) {
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
}
uint32_t v = lookup_or_add(cdep);
valueNumbering.insert(std::make_pair(V, v));
return v;
} else {
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
} else if (BinaryOperator* BO = dyn_cast<BinaryOperator>(V)) {
Expression e = create_expression(BO);
DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
if (EI != expressionNumbering.end()) {
valueNumbering.insert(std::make_pair(V, EI->second));
return EI->second;
} else {
expressionNumbering.insert(std::make_pair(e, nextValueNumber));
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
} else if (CmpInst* C = dyn_cast<CmpInst>(V)) {
Expression e = create_expression(C);
DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
if (EI != expressionNumbering.end()) {
valueNumbering.insert(std::make_pair(V, EI->second));
return EI->second;
} else {
expressionNumbering.insert(std::make_pair(e, nextValueNumber));
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
} else if (ShuffleVectorInst* U = dyn_cast<ShuffleVectorInst>(V)) {
Expression e = create_expression(U);
DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
if (EI != expressionNumbering.end()) {
valueNumbering.insert(std::make_pair(V, EI->second));
return EI->second;
} else {
expressionNumbering.insert(std::make_pair(e, nextValueNumber));
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
} else if (ExtractElementInst* U = dyn_cast<ExtractElementInst>(V)) {
Expression e = create_expression(U);
DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
if (EI != expressionNumbering.end()) {
valueNumbering.insert(std::make_pair(V, EI->second));
return EI->second;
} else {
expressionNumbering.insert(std::make_pair(e, nextValueNumber));
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
} else if (InsertElementInst* U = dyn_cast<InsertElementInst>(V)) {
Expression e = create_expression(U);
DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
if (EI != expressionNumbering.end()) {
valueNumbering.insert(std::make_pair(V, EI->second));
return EI->second;
} else {
expressionNumbering.insert(std::make_pair(e, nextValueNumber));
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
} else if (SelectInst* U = dyn_cast<SelectInst>(V)) {
Expression e = create_expression(U);
DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
if (EI != expressionNumbering.end()) {
valueNumbering.insert(std::make_pair(V, EI->second));
return EI->second;
} else {
expressionNumbering.insert(std::make_pair(e, nextValueNumber));
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
} else if (CastInst* U = dyn_cast<CastInst>(V)) {
Expression e = create_expression(U);
DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
if (EI != expressionNumbering.end()) {
valueNumbering.insert(std::make_pair(V, EI->second));
return EI->second;
} else {
expressionNumbering.insert(std::make_pair(e, nextValueNumber));
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
} else if (GetElementPtrInst* U = dyn_cast<GetElementPtrInst>(V)) {
Expression e = create_expression(U);
DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
if (EI != expressionNumbering.end()) {
valueNumbering.insert(std::make_pair(V, EI->second));
return EI->second;
} else {
expressionNumbering.insert(std::make_pair(e, nextValueNumber));
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
} else {
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
}
}
/// lookup - Returns the value number of the specified value. Fails if
/// the value has not yet been numbered.
uint32_t ValueTable::lookup(Value* V) const {
DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
assert(VI != valueNumbering.end() && "Value not numbered?");
return VI->second;
}
/// clear - Remove all entries from the ValueTable
void ValueTable::clear() {
valueNumbering.clear();
expressionNumbering.clear();
nextValueNumber = 1;
}
/// erase - Remove a value from the value numbering
void ValueTable::erase(Value* V) {
valueNumbering.erase(V);
}
//===----------------------------------------------------------------------===//
// GVN Pass
//===----------------------------------------------------------------------===//
namespace {
struct VISIBILITY_HIDDEN ValueNumberScope {
ValueNumberScope* parent;
DenseMap<uint32_t, Value*> table;
ValueNumberScope(ValueNumberScope* p) : parent(p) { }
};
}
namespace {
class VISIBILITY_HIDDEN GVN : public FunctionPass {
bool runOnFunction(Function &F);
public:
static char ID; // Pass identification, replacement for typeid
GVN() : FunctionPass(&ID) { }
private:
MemoryDependenceAnalysis *MD;
DominatorTree *DT;
ValueTable VN;
DenseMap<BasicBlock*, ValueNumberScope*> localAvail;
typedef DenseMap<Value*, SmallPtrSet<Instruction*, 4> > PhiMapType;
PhiMapType phiMap;
// This transformation requires dominator postdominator info
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<DominatorTree>();
AU.addRequired<MemoryDependenceAnalysis>();
AU.addRequired<AliasAnalysis>();
AU.addPreserved<DominatorTree>();
AU.addPreserved<AliasAnalysis>();
}
// Helper fuctions
// FIXME: eliminate or document these better
bool processLoad(LoadInst* L,
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);
void cleanupGlobalSets();
};
char GVN::ID = 0;
}
// createGVNPass - The public interface to this file...
FunctionPass *llvm::createGVNPass() { return new GVN(); }
static RegisterPass<GVN> X("gvn",
"Global Value Numbering");
void GVN::dump(DenseMap<uint32_t, Value*>& d) {
printf("{\n");
for (DenseMap<uint32_t, Value*>::iterator I = d.begin(),
E = d.end(); I != E; ++I) {
printf("%d\n", I->first);
I->second->dump();
}
printf("}\n");
}
Value* GVN::CollapsePhi(PHINode* p) {
Value* constVal = p->hasConstantValue();
if (!constVal) return 0;
Instruction* inst = dyn_cast<Instruction>(constVal);
if (!inst)
return constVal;
if (DT->dominates(inst, p))
if (isSafeReplacement(p, inst))
return inst;
return 0;
}
bool GVN::isSafeReplacement(PHINode* p, Instruction* inst) {
if (!isa<PHINode>(inst))
return true;
for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end();
UI != E; ++UI)
if (PHINode* use_phi = dyn_cast<PHINode>(UI))
if (use_phi->getParent() == inst->getParent())
return false;
return true;
}
/// GetValueForBlock - Get the value to use within the specified basic block.
/// available values are in Phis.
Value *GVN::GetValueForBlock(BasicBlock *BB, 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 (!DT->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);
}
VN.getAliasAnalysis()->copyValue(orig, PN);
// Attempt to collapse PHI nodes that are trivially redundant
Value* v = CollapsePhi(PN);
if (!v) {
// Cache our phi construction results
phiMap[orig->getPointerOperand()].insert(PN);
return 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;
DEBUG(cerr << "GVN removed: " << *PN);
MD->removeInstruction(PN);
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
const MemoryDependenceAnalysis::NonLocalDepInfo &deps =
MD->getNonLocalDependency(L);
DEBUG(cerr << "INVESTIGATING NONLOCAL LOAD: " << deps.size() << *L);
#if 0
DEBUG(for (unsigned i = 0, e = deps.size(); i != e; ++i) {
cerr << " " << deps[i].first->getName();
if (Instruction *I = deps[i].second.getInst())
cerr << *I;
else
cerr << "\n";
});
#endif
// 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;
BasicBlock *EntryBlock = &L->getParent()->getParent()->getEntryBlock();
DenseMap<BasicBlock*, Value*> repl;
// Filter out useless results (non-locals, etc)
for (unsigned i = 0, e = deps.size(); i != e; ++i) {
BasicBlock *DepBB = deps[i].first;
MemDepResult DepInfo = deps[i].second;
if (DepInfo.isNonLocal()) {
// If this is a non-local dependency in the entry block, then we depend on
// the value live-in at the start of the function. We could insert a load
// in the entry block to get this, but for now we'll just bail out.
//
// FIXME: Consider emitting a load in the entry block to catch this case!
// Tricky part is to sink so that it doesn't execute in places where it
// isn't needed.
if (DepBB == EntryBlock)
return false;
continue;
}
if (DepInfo.isNone()) {
repl[DepBB] = UndefValue::get(L->getType());
continue;
}
if (StoreInst* S = dyn_cast<StoreInst>(DepInfo.getInst())) {
// Reject loads and stores that are to the same address but are of
// different types.
// NOTE: 403.gcc does have this case (e.g. in readonly_fields_p) because
// of bitfield access, it would be interesting to optimize for it at some
// point.
if (S->getOperand(0)->getType() != L->getType())
return false;
if (S->getPointerOperand() != L->getPointerOperand() &&
VN.getAliasAnalysis()->alias(S->getPointerOperand(), 1,
L->getPointerOperand(), 1)
!= AliasAnalysis::MustAlias)
return false;
repl[DepBB] = S->getOperand(0);
} else if (LoadInst* LD = dyn_cast<LoadInst>(DepInfo.getInst())) {
if (LD->getType() != L->getType())
return false;
if (LD->getPointerOperand() != L->getPointerOperand() &&
VN.getAliasAnalysis()->alias(LD->getPointerOperand(), 1,
L->getPointerOperand(), 1)
!= AliasAnalysis::MustAlias)
return false;
repl[DepBB] = 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()) {
L->replaceAllUsesWith(*I);
toErase.push_back(L);
NumGVNLoad++;
return true;
}
repl.insert(std::make_pair((*I)->getParent(), *I));
}
DEBUG(cerr << "GVN REMOVING NONLOCAL LOAD: " << *L);
// Perform PHI construction
SmallPtrSet<BasicBlock*, 4> visited;
Value* v = GetValueForBlock(L->getParent(), L, repl, true);
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;
MemDepResult dep = MD->getDependency(L);
if (dep.isNonLocal() &&
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 (Instruction *DepInst = dep.getInst()) {
// ... that depends on a store ...
if (StoreInst* S = dyn_cast<StoreInst>(DepInst)) {
if (S->getPointerOperand() == pointer) {
// Remove it!
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 (!isa<LoadInst>(DepInst)) {
// Only want to handle loads below.
break;
} else if (!last) {
// If we don't depend on a store, and we haven't
// been loaded before, bail.
break;
} else if (DepInst == last) {
// Remove it!
L->replaceAllUsesWith(last);
toErase.push_back(L);
deletedLoad = true;
NumGVNLoad++;
break;
} else {
dep = MD->getDependencyFrom(L, DepInst, DepInst->getParent());
}
}
// If this load really doesn't depend on anything, then we must be loading an
// undef value. This can happen when loading for a fresh allocation with no
// intervening stores, for example.
if (dep.isNone()) {
// If this load depends directly on an allocation, there isn't
// anything stored there; therefore, we can optimize this load
// to undef.
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!
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) {
MD = &getAnalysis<MemoryDependenceAnalysis>();
DT = &getAnalysis<DominatorTree>();
VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>());
VN.setMemDep(MD);
VN.setDomTree(DT);
bool changed = false;
bool shouldContinue = true;
// Merge unconditional branches, allowing PRE to catch more
// optimization opportunities.
for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) {
BasicBlock* BB = FI;
++FI;
bool removedBlock = MergeBlockIntoPredecessor(BB, this);
if (removedBlock) NumGVNBlocks++;
changed |= removedBlock;
}
while (shouldContinue) {
shouldContinue = iterateOnFunction(F);
changed |= shouldContinue;
}
if (EnablePRE) {
bool PREChanged = true;
while (PREChanged) {
PREChanged = performPRE(F);
changed |= PREChanged;
}
}
cleanupGlobalSets();
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) {
DEBUG(cerr << "GVN removed: " << **I);
MD->removeInstruction(*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++;
DEBUG(cerr << "GVN removed: " << *erase);
MD->removeInstruction(erase);
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) {
cleanupGlobalSets();
// 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;
}
void GVN::cleanupGlobalSets() {
VN.clear();
phiMap.clear();
for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator
I = localAvail.begin(), E = localAvail.end(); I != E; ++I)
delete I->second;
localAvail.clear();
}
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