//===- EarlyCSE.cpp - Simple and fast CSE pass ----------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass performs a simple dominator tree walk that eliminates trivially
// redundant instructions.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "early-cse"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Instructions.h"
#include "llvm/Pass.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Target/TargetLibraryInfo.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/RecyclingAllocator.h"
#include "llvm/ADT/ScopedHashTable.h"
#include "llvm/ADT/Statistic.h"
#include <deque>
using namespace llvm;
STATISTIC(NumSimplify, "Number of instructions simplified or DCE'd");
STATISTIC(NumCSE, "Number of instructions CSE'd");
STATISTIC(NumCSELoad, "Number of load instructions CSE'd");
STATISTIC(NumCSECall, "Number of call instructions CSE'd");
STATISTIC(NumDSE, "Number of trivial dead stores removed");
static unsigned getHash(const void *V) {
return DenseMapInfo<const void*>::getHashValue(V);
}
//===----------------------------------------------------------------------===//
// SimpleValue
//===----------------------------------------------------------------------===//
namespace {
/// SimpleValue - Instances of this struct represent available values in the
/// scoped hash table.
struct SimpleValue {
Instruction *Inst;
SimpleValue(Instruction *I) : Inst(I) {
assert((isSentinel() || canHandle(I)) && "Inst can't be handled!");
}
bool isSentinel() const {
return Inst == DenseMapInfo<Instruction*>::getEmptyKey() ||
Inst == DenseMapInfo<Instruction*>::getTombstoneKey();
}
static bool canHandle(Instruction *Inst) {
// This can only handle non-void readnone functions.
if (CallInst *CI = dyn_cast<CallInst>(Inst))
return CI->doesNotAccessMemory() && !CI->getType()->isVoidTy();
return isa<CastInst>(Inst) || isa<BinaryOperator>(Inst) ||
isa<GetElementPtrInst>(Inst) || isa<CmpInst>(Inst) ||
isa<SelectInst>(Inst) || isa<ExtractElementInst>(Inst) ||
isa<InsertElementInst>(Inst) || isa<ShuffleVectorInst>(Inst) ||
isa<ExtractValueInst>(Inst) || isa<InsertValueInst>(Inst);
}
};
}
namespace llvm {
// SimpleValue is POD.
template<> struct isPodLike<SimpleValue> {
static const bool value = true;
};
template<> struct DenseMapInfo<SimpleValue> {
static inline SimpleValue getEmptyKey() {
return DenseMapInfo<Instruction*>::getEmptyKey();
}
static inline SimpleValue getTombstoneKey() {
return DenseMapInfo<Instruction*>::getTombstoneKey();
}
static unsigned getHashValue(SimpleValue Val);
static bool isEqual(SimpleValue LHS, SimpleValue RHS);
};
}
unsigned DenseMapInfo<SimpleValue>::getHashValue(SimpleValue Val) {
Instruction *Inst = Val.Inst;
// Hash in all of the operands as pointers.
unsigned Res = 0;
for (unsigned i = 0, e = Inst->getNumOperands(); i != e; ++i)
Res ^= getHash(Inst->getOperand(i)) << (i & 0xF);
if (CastInst *CI = dyn_cast<CastInst>(Inst))
Res ^= getHash(CI->getType());
else if (CmpInst *CI = dyn_cast<CmpInst>(Inst))
Res ^= CI->getPredicate();
else if (const ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(Inst)) {
for (ExtractValueInst::idx_iterator I = EVI->idx_begin(),
E = EVI->idx_end(); I != E; ++I)
Res ^= *I;
} else if (const InsertValueInst *IVI = dyn_cast<InsertValueInst>(Inst)) {
for (InsertValueInst::idx_iterator I = IVI->idx_begin(),
E = IVI->idx_end(); I != E; ++I)
Res ^= *I;
} else {
// nothing extra to hash in.
assert((isa<CallInst>(Inst) ||
isa<BinaryOperator>(Inst) || isa<GetElementPtrInst>(Inst) ||
isa<SelectInst>(Inst) || isa<ExtractElementInst>(Inst) ||
isa<InsertElementInst>(Inst) || isa<ShuffleVectorInst>(Inst)) &&
"Invalid/unknown instruction");
}
// Mix in the opcode.
return (Res << 1) ^ Inst->getOpcode();
}
bool DenseMapInfo<SimpleValue>::isEqual(SimpleValue LHS, SimpleValue RHS) {
Instruction *LHSI = LHS.Inst, *RHSI = RHS.Inst;
if (LHS.isSentinel() || RHS.isSentinel())
return LHSI == RHSI;
if (LHSI->getOpcode() != RHSI->getOpcode()) return false;
return LHSI->isIdenticalTo(RHSI);
}
//===----------------------------------------------------------------------===//
// CallValue
//===----------------------------------------------------------------------===//
namespace {
/// CallValue - Instances of this struct represent available call values in
/// the scoped hash table.
struct CallValue {
Instruction *Inst;
CallValue(Instruction *I) : Inst(I) {
assert((isSentinel() || canHandle(I)) && "Inst can't be handled!");
}
bool isSentinel() const {
return Inst == DenseMapInfo<Instruction*>::getEmptyKey() ||
Inst == DenseMapInfo<Instruction*>::getTombstoneKey();
}
static bool canHandle(Instruction *Inst) {
// Don't value number anything that returns void.
if (Inst->getType()->isVoidTy())
return false;
CallInst *CI = dyn_cast<CallInst>(Inst);
if (CI == 0 || !CI->onlyReadsMemory())
return false;
return true;
}
};
}
namespace llvm {
// CallValue is POD.
template<> struct isPodLike<CallValue> {
static const bool value = true;
};
template<> struct DenseMapInfo<CallValue> {
static inline CallValue getEmptyKey() {
return DenseMapInfo<Instruction*>::getEmptyKey();
}
static inline CallValue getTombstoneKey() {
return DenseMapInfo<Instruction*>::getTombstoneKey();
}
static unsigned getHashValue(CallValue Val);
static bool isEqual(CallValue LHS, CallValue RHS);
};
}
unsigned DenseMapInfo<CallValue>::getHashValue(CallValue Val) {
Instruction *Inst = Val.Inst;
// Hash in all of the operands as pointers.
unsigned Res = 0;
for (unsigned i = 0, e = Inst->getNumOperands(); i != e; ++i) {
assert(!Inst->getOperand(i)->getType()->isMetadataTy() &&
"Cannot value number calls with metadata operands");
Res ^= getHash(Inst->getOperand(i)) << (i & 0xF);
}
// Mix in the opcode.
return (Res << 1) ^ Inst->getOpcode();
}
bool DenseMapInfo<CallValue>::isEqual(CallValue LHS, CallValue RHS) {
Instruction *LHSI = LHS.Inst, *RHSI = RHS.Inst;
if (LHS.isSentinel() || RHS.isSentinel())
return LHSI == RHSI;
return LHSI->isIdenticalTo(RHSI);
}
//===----------------------------------------------------------------------===//
// EarlyCSE pass.
//===----------------------------------------------------------------------===//
namespace {
/// EarlyCSE - This pass does a simple depth-first walk over the dominator
/// tree, eliminating trivially redundant instructions and using instsimplify
/// to canonicalize things as it goes. It is intended to be fast and catch
/// obvious cases so that instcombine and other passes are more effective. It
/// is expected that a later pass of GVN will catch the interesting/hard
/// cases.
class EarlyCSE : public FunctionPass {
public:
const TargetData *TD;
const TargetLibraryInfo *TLI;
DominatorTree *DT;
typedef RecyclingAllocator<BumpPtrAllocator,
ScopedHashTableVal<SimpleValue, Value*> > AllocatorTy;
typedef ScopedHashTable<SimpleValue, Value*, DenseMapInfo<SimpleValue>,
AllocatorTy> ScopedHTType;
/// AvailableValues - This scoped hash table contains the current values of
/// all of our simple scalar expressions. As we walk down the domtree, we
/// look to see if instructions are in this: if so, we replace them with what
/// we find, otherwise we insert them so that dominated values can succeed in
/// their lookup.
ScopedHTType *AvailableValues;
/// AvailableLoads - This scoped hash table contains the current values
/// of loads. This allows us to get efficient access to dominating loads when
/// we have a fully redundant load. In addition to the most recent load, we
/// keep track of a generation count of the read, which is compared against
/// the current generation count. The current generation count is
/// incremented after every possibly writing memory operation, which ensures
/// that we only CSE loads with other loads that have no intervening store.
typedef RecyclingAllocator<BumpPtrAllocator,
ScopedHashTableVal<Value*, std::pair<Value*, unsigned> > > LoadMapAllocator;
typedef ScopedHashTable<Value*, std::pair<Value*, unsigned>,
DenseMapInfo<Value*>, LoadMapAllocator> LoadHTType;
LoadHTType *AvailableLoads;
/// AvailableCalls - This scoped hash table contains the current values
/// of read-only call values. It uses the same generation count as loads.
typedef ScopedHashTable<CallValue, std::pair<Value*, unsigned> > CallHTType;
CallHTType *AvailableCalls;
/// CurrentGeneration - This is the current generation of the memory value.
unsigned CurrentGeneration;
static char ID;
explicit EarlyCSE() : FunctionPass(ID) {
initializeEarlyCSEPass(*PassRegistry::getPassRegistry());
}
bool runOnFunction(Function &F);
private:
// NodeScope - almost a POD, but needs to call the constructors for the
// scoped hash tables so that a new scope gets pushed on. These are RAII so
// that the scope gets popped when the NodeScope is destroyed.
class NodeScope {
public:
NodeScope(ScopedHTType *availableValues,
LoadHTType *availableLoads,
CallHTType *availableCalls) :
Scope(*availableValues),
LoadScope(*availableLoads),
CallScope(*availableCalls) {}
private:
NodeScope(const NodeScope&); // DO NOT IMPLEMENT
ScopedHTType::ScopeTy Scope;
LoadHTType::ScopeTy LoadScope;
CallHTType::ScopeTy CallScope;
};
// StackNode - contains all the needed information to create a stack for
// doing a depth first tranversal of the tree. This includes scopes for
// values, loads, and calls as well as the generation. There is a child
// iterator so that the children do not need to be store spearately.
class StackNode {
public:
StackNode(ScopedHTType *availableValues,
LoadHTType *availableLoads,
CallHTType *availableCalls,
unsigned cg, DomTreeNode *n,
DomTreeNode::iterator child, DomTreeNode::iterator end) :
CurrentGeneration(cg), ChildGeneration(cg), Node(n),
ChildIter(child), EndIter(end),
Scopes(availableValues, availableLoads, availableCalls),
Processed(false) {}
// Accessors.
unsigned currentGeneration() { return CurrentGeneration; }
unsigned childGeneration() { return ChildGeneration; }
void childGeneration(unsigned generation) { ChildGeneration = generation; }
DomTreeNode *node() { return Node; }
DomTreeNode::iterator childIter() { return ChildIter; }
DomTreeNode *nextChild() {
DomTreeNode *child = *ChildIter;
++ChildIter;
return child;
}
DomTreeNode::iterator end() { return EndIter; }
bool isProcessed() { return Processed; }
void process() { Processed = true; }
private:
StackNode(const StackNode&); // DO NOT IMPLEMENT
// Members.
unsigned CurrentGeneration;
unsigned ChildGeneration;
DomTreeNode *Node;
DomTreeNode::iterator ChildIter;
DomTreeNode::iterator EndIter;
NodeScope Scopes;
bool Processed;
};
bool processNode(DomTreeNode *Node);
// This transformation requires dominator postdominator info
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<DominatorTree>();
AU.addRequired<TargetLibraryInfo>();
AU.setPreservesCFG();
}
};
}
char EarlyCSE::ID = 0;
// createEarlyCSEPass - The public interface to this file.
FunctionPass *llvm::createEarlyCSEPass() {
return new EarlyCSE();
}
INITIALIZE_PASS_BEGIN(EarlyCSE, "early-cse", "Early CSE", false, false)
INITIALIZE_PASS_DEPENDENCY(DominatorTree)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
INITIALIZE_PASS_END(EarlyCSE, "early-cse", "Early CSE", false, false)
bool EarlyCSE::processNode(DomTreeNode *Node) {
BasicBlock *BB = Node->getBlock();
// If this block has a single predecessor, then the predecessor is the parent
// of the domtree node and all of the live out memory values are still current
// in this block. If this block has multiple predecessors, then they could
// have invalidated the live-out memory values of our parent value. For now,
// just be conservative and invalidate memory if this block has multiple
// predecessors.
if (BB->getSinglePredecessor() == 0)
++CurrentGeneration;
/// LastStore - Keep track of the last non-volatile store that we saw... for
/// as long as there in no instruction that reads memory. If we see a store
/// to the same location, we delete the dead store. This zaps trivial dead
/// stores which can occur in bitfield code among other things.
StoreInst *LastStore = 0;
bool Changed = false;
// See if any instructions in the block can be eliminated. If so, do it. If
// not, add them to AvailableValues.
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
Instruction *Inst = I++;
// Dead instructions should just be removed.
if (isInstructionTriviallyDead(Inst)) {
DEBUG(dbgs() << "EarlyCSE DCE: " << *Inst << '\n');
Inst->eraseFromParent();
Changed = true;
++NumSimplify;
continue;
}
// If the instruction can be simplified (e.g. X+0 = X) then replace it with
// its simpler value.
if (Value *V = SimplifyInstruction(Inst, TD, TLI, DT)) {
DEBUG(dbgs() << "EarlyCSE Simplify: " << *Inst << " to: " << *V << '\n');
Inst->replaceAllUsesWith(V);
Inst->eraseFromParent();
Changed = true;
++NumSimplify;
continue;
}
// If this is a simple instruction that we can value number, process it.
if (SimpleValue::canHandle(Inst)) {
// See if the instruction has an available value. If so, use it.
if (Value *V = AvailableValues->lookup(Inst)) {
DEBUG(dbgs() << "EarlyCSE CSE: " << *Inst << " to: " << *V << '\n');
Inst->replaceAllUsesWith(V);
Inst->eraseFromParent();
Changed = true;
++NumCSE;
continue;
}
// Otherwise, just remember that this value is available.
AvailableValues->insert(Inst, Inst);
continue;
}
// If this is a non-volatile load, process it.
if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
// Ignore volatile loads.
if (!LI->isSimple()) {
LastStore = 0;
continue;
}
// If we have an available version of this load, and if it is the right
// generation, replace this instruction.
std::pair<Value*, unsigned> InVal =
AvailableLoads->lookup(Inst->getOperand(0));
if (InVal.first != 0 && InVal.second == CurrentGeneration) {
DEBUG(dbgs() << "EarlyCSE CSE LOAD: " << *Inst << " to: "
<< *InVal.first << '\n');
if (!Inst->use_empty()) Inst->replaceAllUsesWith(InVal.first);
Inst->eraseFromParent();
Changed = true;
++NumCSELoad;
continue;
}
// Otherwise, remember that we have this instruction.
AvailableLoads->insert(Inst->getOperand(0),
std::pair<Value*, unsigned>(Inst, CurrentGeneration));
LastStore = 0;
continue;
}
// If this instruction may read from memory, forget LastStore.
if (Inst->mayReadFromMemory())
LastStore = 0;
// If this is a read-only call, process it.
if (CallValue::canHandle(Inst)) {
// If we have an available version of this call, and if it is the right
// generation, replace this instruction.
std::pair<Value*, unsigned> InVal = AvailableCalls->lookup(Inst);
if (InVal.first != 0 && InVal.second == CurrentGeneration) {
DEBUG(dbgs() << "EarlyCSE CSE CALL: " << *Inst << " to: "
<< *InVal.first << '\n');
if (!Inst->use_empty()) Inst->replaceAllUsesWith(InVal.first);
Inst->eraseFromParent();
Changed = true;
++NumCSECall;
continue;
}
// Otherwise, remember that we have this instruction.
AvailableCalls->insert(Inst,
std::pair<Value*, unsigned>(Inst, CurrentGeneration));
continue;
}
// Okay, this isn't something we can CSE at all. Check to see if it is
// something that could modify memory. If so, our available memory values
// cannot be used so bump the generation count.
if (Inst->mayWriteToMemory()) {
++CurrentGeneration;
if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
// We do a trivial form of DSE if there are two stores to the same
// location with no intervening loads. Delete the earlier store.
if (LastStore &&
LastStore->getPointerOperand() == SI->getPointerOperand()) {
DEBUG(dbgs() << "EarlyCSE DEAD STORE: " << *LastStore << " due to: "
<< *Inst << '\n');
LastStore->eraseFromParent();
Changed = true;
++NumDSE;
LastStore = 0;
continue;
}
// Okay, we just invalidated anything we knew about loaded values. Try
// to salvage *something* by remembering that the stored value is a live
// version of the pointer. It is safe to forward from volatile stores
// to non-volatile loads, so we don't have to check for volatility of
// the store.
AvailableLoads->insert(SI->getPointerOperand(),
std::pair<Value*, unsigned>(SI->getValueOperand(), CurrentGeneration));
// Remember that this was the last store we saw for DSE.
if (SI->isSimple())
LastStore = SI;
}
}
}
return Changed;
}
bool EarlyCSE::runOnFunction(Function &F) {
std::deque<StackNode *> nodesToProcess;
TD = getAnalysisIfAvailable<TargetData>();
TLI = &getAnalysis<TargetLibraryInfo>();
DT = &getAnalysis<DominatorTree>();
// Tables that the pass uses when walking the domtree.
ScopedHTType AVTable;
AvailableValues = &AVTable;
LoadHTType LoadTable;
AvailableLoads = &LoadTable;
CallHTType CallTable;
AvailableCalls = &CallTable;
CurrentGeneration = 0;
bool Changed = false;
// Process the root node.
nodesToProcess.push_front(
new StackNode(AvailableValues, AvailableLoads, AvailableCalls,
CurrentGeneration, DT->getRootNode(),
DT->getRootNode()->begin(),
DT->getRootNode()->end()));
// Save the current generation.
unsigned LiveOutGeneration = CurrentGeneration;
// Process the stack.
while (!nodesToProcess.empty()) {
// Grab the first item off the stack. Set the current generation, remove
// the node from the stack, and process it.
StackNode *NodeToProcess = nodesToProcess.front();
// Initialize class members.
CurrentGeneration = NodeToProcess->currentGeneration();
// Check if the node needs to be processed.
if (!NodeToProcess->isProcessed()) {
// Process the node.
Changed |= processNode(NodeToProcess->node());
NodeToProcess->childGeneration(CurrentGeneration);
NodeToProcess->process();
} else if (NodeToProcess->childIter() != NodeToProcess->end()) {
// Push the next child onto the stack.
DomTreeNode *child = NodeToProcess->nextChild();
nodesToProcess.push_front(
new StackNode(AvailableValues,
AvailableLoads,
AvailableCalls,
NodeToProcess->childGeneration(), child,
child->begin(), child->end()));
} else {
// It has been processed, and there are no more children to process,
// so delete it and pop it off the stack.
delete NodeToProcess;
nodesToProcess.pop_front();
}
} // while (!nodes...)
// Reset the current generation.
CurrentGeneration = LiveOutGeneration;
return Changed;
}