#define DEBUG_TYPE "early-cse"
#include "llvm/Transforms/Scalar.h"
-#include "llvm/Analysis/Dominators.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/Transforms/Utils/Local.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/RecyclingAllocator.h"
+#include "llvm/ADT/ScopedHashTable.h"
+#include "llvm/ADT/Statistic.h"
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;
+
+ 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;
+ }
+
+ // 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
/// cases.
class EarlyCSE : public FunctionPass {
public:
+ const TargetData *TD;
+ 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) {
+ explicit EarlyCSE() : FunctionPass(ID) {
initializeEarlyCSEPass(*PassRegistry::getPassRegistry());
}
bool runOnFunction(Function &F);
private:
+
+ bool processNode(DomTreeNode *Node);
+
// This transformation requires dominator postdominator info
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<DominatorTree>();
INITIALIZE_PASS_DEPENDENCY(DominatorTree)
INITIALIZE_PASS_END(EarlyCSE, "early-cse", "Early CSE", false, false)
+bool EarlyCSE::processNode(DomTreeNode *Node) {
+ // Define a scope in the scoped hash table. When we are done processing this
+ // domtree node and recurse back up to our parent domtree node, this will pop
+ // off all the values we install.
+ ScopedHTType::ScopeTy Scope(*AvailableValues);
+
+ // Define a scope for the load values so that anything we add will get
+ // popped when we recurse back up to our parent domtree node.
+ LoadHTType::ScopeTy LoadScope(*AvailableLoads);
+
+ // Define a scope for the call values so that anything we add will get
+ // popped when we recurse back up to our parent domtree node.
+ CallHTType::ScopeTy CallScope(*AvailableCalls);
+
+ 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, 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->isVolatile()) {
+ 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->isVolatile())
+ LastStore = SI;
+ }
+ }
+ }
+
+ unsigned LiveOutGeneration = CurrentGeneration;
+ for (DomTreeNode::iterator I = Node->begin(), E = Node->end(); I != E; ++I) {
+ Changed |= processNode(*I);
+ // Pop any generation changes off the stack from the recursive walk.
+ CurrentGeneration = LiveOutGeneration;
+ }
+ return Changed;
+}
+
+
bool EarlyCSE::runOnFunction(Function &F) {
- DominatorTree &DT = getAnalysis<DominatorTree>();
- (void)DT;
- return false;
+ TD = getAnalysisIfAvailable<TargetData>();
+ 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;
+ return processNode(DT->getRootNode());
}
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