-//===- GVN.cpp - Eliminate redundant values and loads ------------===//
+//===- GVN.cpp - Eliminate redundant values and loads ---------------------===//
//
// The LLVM Compiler Infrastructure
//
#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");
+STATISTIC(NumPRELoad, "Number of loads PRE'd");
static cl::opt<bool> EnablePRE("enable-pre",
cl::init(true), cl::Hidden);
+cl::opt<bool> EnableLoadPRE("enable-load-pre"/*, cl::init(true)*/);
//===----------------------------------------------------------------------===//
// ValueTable Class
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; }
};
}
return nextValueNumber++;
}
- Instruction* local_dep = MD->getDependency(C);
+ MemDepResult local_dep = MD->getDependency(C);
- if (local_dep == MemoryDependenceAnalysis::None) {
+ if (!local_dep.isDef() && !local_dep.isNonLocal()) {
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
- } else if (local_dep != MemoryDependenceAnalysis::NonLocal) {
- if (!isa<CallInst>(local_dep)) {
- valueNumbering.insert(std::make_pair(V, nextValueNumber));
- return nextValueNumber++;
- }
-
- CallInst* local_cdep = cast<CallInst>(local_dep);
+ }
+
+ if (local_dep.isDef()) {
+ CallInst* local_cdep = cast<CallInst>(local_dep.getInst());
- if (local_cdep->getCalledFunction() != C->getCalledFunction() ||
- local_cdep->getNumOperands() != C->getNumOperands()) {
+ if (local_cdep->getNumOperands() != C->getNumOperands()) {
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
- } else if (!C->getCalledFunction()) {
- valueNumbering.insert(std::make_pair(V, nextValueNumber));
- return nextValueNumber++;
- } else {
- 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++;
- }
+ }
+
+ 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;
}
- }
-
- DenseMap<BasicBlock*, Value*> deps;
- MD->getNonLocalDependency(C, deps);
+ uint32_t v = lookup_or_add(local_cdep);
+ valueNumbering.insert(std::make_pair(V, v));
+ return v;
+ }
+
+ // Non-local case.
+ const MemoryDependenceAnalysis::NonLocalDepInfo &deps =
+ MD->getNonLocalCallDependency(CallSite(C));
+ // FIXME: call/call dependencies for readonly calls should return def, not
+ // clobber! Move the checking logic to MemDep!
CallInst* cdep = 0;
- for (DenseMap<BasicBlock*, Value*>::iterator I = deps.begin(),
- E = deps.end(); I != E; ++I) {
- if (I->second == MemoryDependenceAnalysis::None) {
- valueNumbering.insert(std::make_pair(V, nextValueNumber));
+ // 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;
- return nextValueNumber++;
- } else if (I->second != MemoryDependenceAnalysis::NonLocal) {
- if (DT->properlyDominates(I->first, C->getParent())) {
- if (CallInst* CD = dyn_cast<CallInst>(I->second))
- cdep = CD;
- else {
- valueNumbering.insert(std::make_pair(V, nextValueNumber));
- return nextValueNumber++;
- }
- } else {
- valueNumbering.insert(std::make_pair(V, nextValueNumber));
- return nextValueNumber++;
- }
+ // We don't handle non-depedencies. If we already have a call, reject
+ // instruction dependencies.
+ if (I->second.isClobber() || 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) {
return nextValueNumber++;
}
- if (cdep->getCalledFunction() != C->getCalledFunction() ||
- cdep->getNumOperands() != C->getNumOperands()) {
+ if (cdep->getNumOperands() != C->getNumOperands()) {
valueNumbering.insert(std::make_pair(V, nextValueNumber));
return nextValueNumber++;
- } else if (!C->getCalledFunction()) {
- valueNumbering.insert(std::make_pair(V, nextValueNumber));
- return nextValueNumber++;
- } else {
- 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++;
- }
+ }
+ 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;
}
+ 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++;
// GVN Pass
//===----------------------------------------------------------------------===//
-namespace llvm {
- template<> struct DenseMapInfo<uint32_t> {
- static inline uint32_t getEmptyKey() { return ~0; }
- static inline uint32_t getTombstoneKey() { return ~0 - 1; }
- static unsigned getHashValue(const uint32_t& Val) { return Val * 37; }
- static bool isPod() { return true; }
- static bool isEqual(const uint32_t& LHS, const uint32_t& RHS) {
- return LHS == RHS;
- }
- };
-}
-
namespace {
struct VISIBILITY_HIDDEN ValueNumberScope {
ValueNumberScope* parent;
bool runOnFunction(Function &F);
public:
static char ID; // Pass identification, replacement for typeid
- GVN() : FunctionPass((intptr_t)&ID) { }
+ GVN() : FunctionPass(&ID) { }
private:
+ MemoryDependenceAnalysis *MD;
+ DominatorTree *DT;
+
ValueTable VN;
DenseMap<BasicBlock*, ValueNumberScope*> localAvail;
// This transformation requires dominator postdominator info
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
- AU.setPreservesCFG();
AU.addRequired<DominatorTree>();
AU.addRequired<MemoryDependenceAnalysis>();
AU.addRequired<AliasAnalysis>();
+
+ AU.addPreserved<DominatorTree>();
AU.addPreserved<AliasAnalysis>();
- AU.addPreserved<MemoryDependenceAnalysis>();
}
// 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 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;
}
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 (DT->dominates(inst, p))
if (isSafeReplacement(p, inst))
return inst;
return 0;
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);
+ // 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());
+
+ if (BasicBlock *Pred = BB->getSinglePredecessor()) {
+ Value *ret = GetValueForBlock(Pred, orig, Phis);
Phis[BB] = ret;
return ret;
}
+
+ // Get the number of predecessors of this block so we can reserve space later.
+ // If there is already a PHI in it, use the #preds from it, otherwise count.
+ // Getting it from the PHI is constant time.
+ unsigned NumPreds;
+ if (PHINode *ExistingPN = dyn_cast<PHINode>(BB->begin()))
+ NumPreds = ExistingPN->getNumIncomingValues();
+ else
+ NumPreds = std::distance(pred_begin(BB), pred_end(BB));
// 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)));
+ PN->reserveOperandSpace(NumPreds);
- if (Phis.count(BB) == 0)
- Phis.insert(std::make_pair(BB, PN));
+ 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) {
PN->addIncoming(val, *PI);
}
- AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
- AA.copyValue(orig, PN);
+ VN.getAliasAnalysis()->copyValue(orig, PN);
// Attempt to collapse PHI nodes that are trivially redundant
Value* v = CollapsePhi(PN);
return PN;
}
- MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
-
- MD.removeInstruction(PN);
PN->replaceAllUsesWith(v);
for (DenseMap<BasicBlock*, Value*>::iterator I = Phis.begin(),
if (I->second == PN)
I->second = v;
+ DEBUG(cerr << "GVN removed: " << *PN);
+ MD->removeInstruction(PN);
PN->eraseFromParent();
Phis[BB] = v;
return v;
}
+/// IsValueFullyAvailableInBlock - Return true if we can prove that the value
+/// we're analyzing is fully available in the specified block. As we go, keep
+/// track of which blocks we know are fully alive in FullyAvailableBlocks. This
+/// map is actually a tri-state map with the following values:
+/// 0) we know the block *is not* fully available.
+/// 1) we know the block *is* fully available.
+/// 2) we do not know whether the block is fully available or not, but we are
+/// currently speculating that it will be.
+/// 3) we are speculating for this block and have used that to speculate for
+/// other blocks.
+static bool IsValueFullyAvailableInBlock(BasicBlock *BB,
+ DenseMap<BasicBlock*, char> &FullyAvailableBlocks) {
+ // Optimistically assume that the block is fully available and check to see
+ // if we already know about this block in one lookup.
+ std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV =
+ FullyAvailableBlocks.insert(std::make_pair(BB, 2));
+
+ // If the entry already existed for this block, return the precomputed value.
+ if (!IV.second) {
+ // If this is a speculative "available" value, mark it as being used for
+ // speculation of other blocks.
+ if (IV.first->second == 2)
+ IV.first->second = 3;
+ return IV.first->second != 0;
+ }
+
+ // Otherwise, see if it is fully available in all predecessors.
+ pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
+
+ // If this block has no predecessors, it isn't live-in here.
+ if (PI == PE)
+ goto SpeculationFailure;
+
+ for (; PI != PE; ++PI)
+ // If the value isn't fully available in one of our predecessors, then it
+ // isn't fully available in this block either. Undo our previous
+ // optimistic assumption and bail out.
+ if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks))
+ goto SpeculationFailure;
+
+ return true;
+
+// SpeculationFailure - If we get here, we found out that this is not, after
+// all, a fully-available block. We have a problem if we speculated on this and
+// used the speculation to mark other blocks as available.
+SpeculationFailure:
+ char &BBVal = FullyAvailableBlocks[BB];
+
+ // If we didn't speculate on this, just return with it set to false.
+ if (BBVal == 2) {
+ BBVal = 0;
+ return false;
+ }
+
+ // If we did speculate on this value, we could have blocks set to 1 that are
+ // incorrect. Walk the (transitive) successors of this block and mark them as
+ // 0 if set to one.
+ SmallVector<BasicBlock*, 32> BBWorklist;
+ BBWorklist.push_back(BB);
+
+ while (!BBWorklist.empty()) {
+ BasicBlock *Entry = BBWorklist.pop_back_val();
+ // Note that this sets blocks to 0 (unavailable) if they happen to not
+ // already be in FullyAvailableBlocks. This is safe.
+ char &EntryVal = FullyAvailableBlocks[Entry];
+ if (EntryVal == 0) continue; // Already unavailable.
+
+ // Mark as unavailable.
+ EntryVal = 0;
+
+ for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I)
+ BBWorklist.push_back(*I);
+ }
+
+ return false;
+}
+
/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are
/// non-local by performing PHI construction.
-bool GVN::processNonLocalLoad(LoadInst* L,
+bool GVN::processNonLocalLoad(LoadInst *LI,
SmallVectorImpl<Instruction*> &toErase) {
- MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
-
- // Find the non-local dependencies of the load
- DenseMap<BasicBlock*, Value*> deps;
- MD.getNonLocalDependency(L, deps);
+ // Find the non-local dependencies of the load.
+ SmallVector<MemoryDependenceAnalysis::NonLocalDepEntry, 64> Deps;
+ MD->getNonLocalPointerDependency(LI->getOperand(0), true, LI->getParent(),
+ Deps);
+ //DEBUG(cerr << "INVESTIGATING NONLOCAL LOAD: " << Deps.size() << *LI);
+
+ // 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;
- DenseMap<BasicBlock*, Value*> repl;
+ // Filter out useless results (non-locals, etc). Keep track of the blocks
+ // where we have a value available in repl, also keep track of whether we see
+ // dependencies that produce an unknown value for the load (such as a call
+ // that could potentially clobber the load).
+ SmallVector<std::pair<BasicBlock*, Value*>, 16> ValuesPerBlock;
+ SmallVector<BasicBlock*, 16> UnavailableBlocks;
- // 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)
+ for (unsigned i = 0, e = Deps.size(); i != e; ++i) {
+ BasicBlock *DepBB = Deps[i].first;
+ MemDepResult DepInfo = Deps[i].second;
+
+ if (DepInfo.isClobber()) {
+ UnavailableBlocks.push_back(DepBB);
continue;
+ }
+
+ Instruction *DepInst = DepInfo.getInst();
+
+ // Loading the allocation -> undef.
+ if (isa<AllocationInst>(DepInst)) {
+ ValuesPerBlock.push_back(std::make_pair(DepBB,
+ UndefValue::get(LI->getType())));
+ 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;
+ if (StoreInst* S = dyn_cast<StoreInst>(DepInst)) {
+ // 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() != LI->getType()) {
+ UnavailableBlocks.push_back(DepBB);
+ continue;
+ }
+
+ ValuesPerBlock.push_back(std::make_pair(DepBB, S->getOperand(0)));
+
+ } else if (LoadInst* LD = dyn_cast<LoadInst>(DepInst)) {
+ if (LD->getType() != LI->getType()) {
+ UnavailableBlocks.push_back(DepBB);
+ continue;
+ }
+ ValuesPerBlock.push_back(std::make_pair(DepBB, LD));
} else {
- return false;
+ UnavailableBlocks.push_back(DepBB);
+ continue;
}
}
- // 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;
+ // If we have no predecessors that produce a known value for this load, exit
+ // early.
+ if (ValuesPerBlock.empty()) return false;
+
+ // If all of the instructions we depend on produce a known value for this
+ // load, then it is fully redundant and we can use PHI insertion to compute
+ // its value. Insert PHIs and remove the fully redundant value now.
+ if (UnavailableBlocks.empty()) {
+ // Use cached PHI construction information from previous runs
+ SmallPtrSet<Instruction*, 4> &p = phiMap[LI->getPointerOperand()];
+ // FIXME: What does phiMap do? Are we positive it isn't getting invalidated?
+ for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end();
+ I != E; ++I) {
+ if ((*I)->getParent() == LI->getParent()) {
+ DEBUG(cerr << "GVN REMOVING NONLOCAL LOAD #1: " << *LI);
+ LI->replaceAllUsesWith(*I);
+ toErase.push_back(LI);
+ NumGVNLoad++;
+ return true;
+ }
+
+ ValuesPerBlock.push_back(std::make_pair((*I)->getParent(), *I));
}
- repl.insert(std::make_pair((*I)->getParent(), *I));
+ DEBUG(cerr << "GVN REMOVING NONLOCAL LOAD: " << *LI);
+
+ DenseMap<BasicBlock*, Value*> BlockReplValues;
+ BlockReplValues.insert(ValuesPerBlock.begin(), ValuesPerBlock.end());
+ // Perform PHI construction.
+ Value* v = GetValueForBlock(LI->getParent(), LI, BlockReplValues, true);
+ LI->replaceAllUsesWith(v);
+ toErase.push_back(LI);
+ NumGVNLoad++;
+ return true;
}
- // Perform PHI construction
- SmallPtrSet<BasicBlock*, 4> visited;
- Value* v = GetValueForBlock(L->getParent(), L, repl, true);
+ if (!EnablePRE || !EnableLoadPRE)
+ return false;
+
+ // Okay, we have *some* definitions of the value. This means that the value
+ // is available in some of our (transitive) predecessors. Lets think about
+ // doing PRE of this load. This will involve inserting a new load into the
+ // predecessor when it's not available. We could do this in general, but
+ // prefer to not increase code size. As such, we only do this when we know
+ // that we only have to insert *one* load (which means we're basically moving
+ // the load, not inserting a new one).
+
+ // Everything we do here is based on local predecessors of LI's block. If it
+ // only has one predecessor, bail now.
+ BasicBlock *LoadBB = LI->getParent();
+ if (LoadBB->getSinglePredecessor())
+ return false;
+
+ // If we have a repl set with LI itself in it, this means we have a loop where
+ // at least one of the values is LI. Since this means that we won't be able
+ // to eliminate LI even if we insert uses in the other predecessors, we will
+ // end up increasing code size. Reject this by scanning for LI.
+ for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
+ if (ValuesPerBlock[i].second == LI)
+ return false;
- MD.removeInstruction(L);
- L->replaceAllUsesWith(v);
- toErase.push_back(L);
- NumGVNLoad++;
+ // Okay, we have some hope :). Check to see if the loaded value is fully
+ // available in all but one predecessor.
+ // FIXME: If we could restructure the CFG, we could make a common pred with
+ // all the preds that don't have an available LI and insert a new load into
+ // that one block.
+ BasicBlock *UnavailablePred = 0;
+ DenseMap<BasicBlock*, char> FullyAvailableBlocks;
+ for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
+ FullyAvailableBlocks[ValuesPerBlock[i].first] = true;
+ for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
+ FullyAvailableBlocks[UnavailableBlocks[i]] = false;
+
+ for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB);
+ PI != E; ++PI) {
+ if (IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks))
+ continue;
+
+ // If this load is not available in multiple predecessors, reject it.
+ if (UnavailablePred && UnavailablePred != *PI)
+ return false;
+ UnavailablePred = *PI;
+ }
+
+ assert(UnavailablePred != 0 &&
+ "Fully available value should be eliminated above!");
+
+ // If the loaded pointer is PHI node defined in this block, do PHI translation
+ // to get its value in the predecessor.
+ Value *LoadPtr = LI->getOperand(0)->DoPHITranslation(LoadBB, UnavailablePred);
+
+ // Make sure the value is live in the predecessor. If it was defined by a
+ // non-PHI instruction in this block, we don't know how to recompute it above.
+ if (Instruction *LPInst = dyn_cast<Instruction>(LoadPtr))
+ if (!DT->dominates(LPInst->getParent(), UnavailablePred)) {
+ DEBUG(cerr << "COULDN'T PRE LOAD BECAUSE PTR IS UNAVAILABLE IN PRED: "
+ << *LPInst << *LI << "\n");
+ return false;
+ }
+
+ // We don't currently handle critical edges :(
+ if (UnavailablePred->getTerminator()->getNumSuccessors() != 1) {
+ DEBUG(cerr << "COULD NOT PRE LOAD BECAUSE OF CRITICAL EDGE '"
+ << UnavailablePred->getName() << "': " << *LI);
+ return false;
+ }
+
+ // Okay, we can eliminate this load by inserting a reload in the predecessor
+ // and using PHI construction to get the value in the other predecessors, do
+ // it.
+ DEBUG(cerr << "GVN REMOVING PRE LOAD: " << *LI);
+
+ Value *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false,
+ LI->getAlignment(),
+ UnavailablePred->getTerminator());
+
+ DenseMap<BasicBlock*, Value*> BlockReplValues;
+ BlockReplValues.insert(ValuesPerBlock.begin(), ValuesPerBlock.end());
+ BlockReplValues[UnavailablePred] = NewLoad;
+
+ // Perform PHI construction.
+ Value* v = GetValueForBlock(LI->getParent(), LI, BlockReplValues, true);
+ LI->replaceAllUsesWith(v);
+ v->takeName(LI);
+ toErase.push_back(LI);
+ NumPRELoad++;
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;
+bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) {
+ if (L->isVolatile())
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);
+ MemDepResult dep = MD->getDependency(L);
+
+ // If the value isn't available, don't do anything!
+ if (dep.isClobber())
+ return false;
+
+ // If it is defined in another block, try harder.
+ if (dep.isNonLocal())
+ return processNonLocalLoad(L, toErase);
+
+ Instruction *DepInst = dep.getInst();
+ if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) {
+ // Only forward substitute stores to loads of the same type.
+ // FIXME: Could do better!
+ if (DepSI->getPointerOperand()->getType() != pointer->getType())
+ return false;
- if (!removedNonLocal)
- last = L;
+ // Remove it!
+ L->replaceAllUsesWith(DepSI->getOperand(0));
+ toErase.push_back(L);
+ NumGVNLoad++;
+ return true;
+ }
+
+ if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) {
+ // Only forward substitute stores to loads of the same type.
+ // FIXME: Could do better! load i32 -> load i8 -> truncate on little endian.
+ if (DepLI->getType() != L->getType())
+ return false;
- return removedNonLocal;
+ // Remove it!
+ L->replaceAllUsesWith(DepLI);
+ toErase.push_back(L);
+ NumGVNLoad++;
+ return true;
}
-
- 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 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 (isa<AllocationInst>(DepInst)) {
+ L->replaceAllUsesWith(UndefValue::get(L->getType()));
+ toErase.push_back(L);
+ NumGVNLoad++;
+ return true;
}
- if (!deletedLoad)
- last = L;
-
- return deletedLoad;
+ return false;
}
Value* GVN::lookupNumber(BasicBlock* BB, uint32_t num) {
- ValueNumberScope* locals = localAvail[BB];
+ 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);
/// 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);
+ bool changed = processLoad(L, toErase);
if (!changed) {
unsigned num = VN.lookup_or_add(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)) {
+ if (isa<AllocationInst>(I) || isa<TerminatorInst>(I)) {
localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
return false;
}
if (constVal) {
for (PhiMapType::iterator PI = phiMap.begin(), PE = phiMap.end();
PI != PE; ++PI)
- if (PI->second.count(p))
- PI->second.erase(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!
- MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
- MD.removeInstruction(I);
-
VN.erase(I);
I->replaceAllUsesWith(repl);
toErase.push_back(I);
return true;
- } else if (!I->isTerminator()) {
+ } else {
localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
}
// function.
//
bool GVN::runOnFunction(Function& F) {
+ MD = &getAnalysis<MemoryDependenceAnalysis>();
+ DT = &getAnalysis<DominatorTree>();
VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>());
- VN.setMemDep(&getAnalysis<MemoryDependenceAnalysis>());
- VN.setDomTree(&getAnalysis<DominatorTree>());
+ 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;
+ }
+
+ unsigned Iteration = 0;
+
while (shouldContinue) {
+ DEBUG(cerr << "GVN iteration: " << Iteration << "\n");
shouldContinue = iterateOnFunction(F);
changed |= shouldContinue;
+ ++Iteration;
}
+ if (EnablePRE) {
+ bool PREChanged = true;
+ while (PREChanged) {
+ PREChanged = performPRE(F);
+ changed |= PREChanged;
+ }
+ }
+ // FIXME: Should perform GVN again after PRE does something. PRE can move
+ // computations into blocks where they become fully redundant. Note that
+ // we can't do this until PRE's critical edge splitting updates memdep.
+ // Actually, when this happens, we should just fully integrate PRE into GVN.
+
+ cleanupGlobalSets();
+
return changed;
}
bool GVN::processBlock(DomTreeNode* DTN) {
BasicBlock* BB = DTN->getBlock();
-
+ // FIXME: Kill off toErase by doing erasing eagerly in a helper function (and
+ // incrementing BI before processing an instruction).
SmallVector<Instruction*, 8> toErase;
- DenseMap<Value*, LoadInst*> lastSeenLoad;
bool changed_function = false;
if (DTN->getIDom())
for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
BI != BE;) {
- changed_function |= processInstruction(BI, lastSeenLoad, toErase);
+ changed_function |= processInstruction(BI, toErase);
if (toErase.empty()) {
++BI;
continue;
--BI;
for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
- E = toErase.end(); I != E; ++I)
+ E = toErase.end(); I != E; ++I) {
+ DEBUG(cerr << "GVN removed: " << **I);
+ MD->removeInstruction(*I);
(*I)->eraseFromParent();
+ }
+ toErase.clear();
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;
+ bool Changed = false;
SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit;
+ DenseMap<BasicBlock*, Value*> predMap;
for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()),
DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) {
BasicBlock* CurrentBlock = *DI;
for (BasicBlock::iterator BI = CurrentBlock->begin(),
BE = CurrentBlock->end(); BI != BE; ) {
- if (isa<AllocaInst>(BI) || isa<TerminatorInst>(BI) ||
- isa<LoadInst>(BI) || isa<StoreInst>(BI) ||
- isa<CallInst>(BI) || isa<PHINode>(BI)) {
- BI++;
+ Instruction *CurInst = BI++;
+
+ if (isa<AllocationInst>(CurInst) || isa<TerminatorInst>(CurInst) ||
+ isa<PHINode>(CurInst) || CurInst->mayReadFromMemory() ||
+ CurInst->mayWriteToMemory())
continue;
- }
- uint32_t valno = VN.lookup(BI);
+ uint32_t valno = VN.lookup(CurInst);
// Look for the predecessors for PRE opportunities. We're
// only trying to solve the basic diamond case, where
unsigned numWith = 0;
unsigned numWithout = 0;
BasicBlock* PREPred = 0;
- DenseMap<BasicBlock*, Value*> predMap;
+ predMap.clear();
+
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
if (predV == localAvail[*PI]->table.end()) {
PREPred = *PI;
numWithout++;
- } else if (predV->second == BI) {
+ } else if (predV->second == CurInst) {
numWithout = 2;
} else {
predMap[*PI] = predV->second;
// 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++;
+ if (numWithout != 1 || numWith == 0)
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
unsigned succNum = 0;
for (unsigned i = 0, e = PREPred->getTerminator()->getNumSuccessors();
i != e; ++i)
- if (PREPred->getTerminator()->getSuccessor(i) == PREPred) {
+ 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;
}
// 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();
+ Instruction* PREInstr = CurInst->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 if (!lookupNumber(PREPred, VN.lookup(op))) {
+ for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) {
+ Value *Op = PREInstr->getOperand(i);
+ if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op))
+ continue;
+
+ if (Value *V = lookupNumber(PREPred, VN.lookup(Op))) {
+ PREInstr->setOperand(i, V);
+ } else {
success = false;
break;
- } else
- PREInstr->setOperand(i, lookupNumber(PREPred, VN.lookup(op)));
+ }
}
// Fail out if we encounter an operand that is not available in
// are not value numbered precisely.
if (!success) {
delete PREInstr;
- BI++;
continue;
}
PREInstr->insertBefore(PREPred->getTerminator());
- PREInstr->setName(BI->getName() + ".pre");
+ PREInstr->setName(CurInst->getName() + ".pre");
predMap[PREPred] = PREInstr;
VN.add(PREInstr, valno);
NumGVNPRE++;
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",
+ PHINode* Phi = PHINode::Create(CurInst->getType(),
+ CurInst->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);
-
- // The newly created PHI completely replaces the old instruction,
- // so we need to update the maps to reflect this.
- DomTreeNode* DTN = getAnalysis<DominatorTree>()[CurrentBlock];
- for (DomTreeNode::iterator UI = DTN->begin(), UE = DTN->end();
- UI != UE; ++UI)
- localAvail[(*UI)->getBlock()]->table[valno] = Phi;
localAvail[CurrentBlock]->table[valno] = Phi;
- BI->replaceAllUsesWith(Phi);
- VN.erase(BI);
-
- Instruction* erase = BI;
- BI++;
- erase->eraseFromParent();
+ CurInst->replaceAllUsesWith(Phi);
+ VN.erase(CurInst);
- changed = true;
+ DEBUG(cerr << "GVN PRE removed: " << *CurInst);
+ MD->removeInstruction(CurInst);
+ CurInst->eraseFromParent();
+ Changed = true;
}
}
I = toSplit.begin(), E = toSplit.end(); I != E; ++I)
SplitCriticalEdge(I->first, I->second, this);
- return changed;
+ return Changed || toSplit.size();
}
-// GVN::iterateOnFunction - Executes one iteration of GVN
+// iterateOnFunction - Executes one iteration of GVN
bool GVN::iterateOnFunction(Function &F) {
- // Clean out global sets from any previous functions
- VN.clear();
- phiMap.clear();
-
- for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator
- I = localAvail.begin(), E = localAvail.end(); I != E; ++I)
- delete I->second;
- localAvail.clear();
-
- DominatorTree &DT = getAnalysis<DominatorTree>();
+ 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)
+ for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
+ DE = df_end(DT->getRootNode()); DI != DE; ++DI)
changed |= processBlock(*DI);
- if (EnablePRE)
- changed |= performPRE(F);
-
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();
+}
projects / oota-llvm.git / blobdiff