#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
-#include "llvm/ADT/SparseBitVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/AliasAnalysis.h"
STATISTIC(NumGVNInstr, "Number of instructions deleted");
STATISTIC(NumGVNLoad, "Number of loads deleted");
+STATISTIC(NumGVNPRE, "Number of instructions PRE'd");
//===----------------------------------------------------------------------===//
// ValueTable Class
// 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) {
return nextValueNumber++;
} else if (I->second != MemoryDependenceAnalysis::NonLocal) {
- if (DT->dominates(I->first, C->getParent())) {
+ if (DT->properlyDominates(I->first, C->getParent())) {
if (CallInst* CD = dyn_cast<CallInst>(I->second))
cdep = CD;
else {
}
//===----------------------------------------------------------------------===//
-// ValueNumberedSet Class
+// GVN Pass
//===----------------------------------------------------------------------===//
-namespace {
-class VISIBILITY_HIDDEN ValueNumberedSet {
- private:
- SmallPtrSet<Value*, 8> contents;
- SparseBitVector<64> numbers;
- public:
- ValueNumberedSet() { }
- ValueNumberedSet(const ValueNumberedSet& other) {
- numbers = other.numbers;
- contents = other.contents;
- }
-
- typedef SmallPtrSet<Value*, 8>::iterator iterator;
-
- iterator begin() { return contents.begin(); }
- iterator end() { return contents.end(); }
-
- bool insert(Value* v) { return contents.insert(v); }
- void insert(iterator I, iterator E) { contents.insert(I, E); }
- void erase(Value* v) { contents.erase(v); }
- unsigned count(Value* v) { return contents.count(v); }
- size_t size() { return contents.size(); }
-
- void set(unsigned i) {
- numbers.set(i);
- }
-
- void operator=(const ValueNumberedSet& other) {
- contents = other.contents;
- numbers = other.numbers;
- }
-
- void reset(unsigned i) {
- numbers.reset(i);
- }
-
- bool test(unsigned i) {
- return numbers.test(i);
+
+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;
}
-};
+ };
}
-//===----------------------------------------------------------------------===//
-// GVN Pass
-//===----------------------------------------------------------------------===//
-
namespace {
class VISIBILITY_HIDDEN GVN : public FunctionPass {
private:
ValueTable VN;
-
- DenseMap<BasicBlock*, ValueNumberedSet> availableOut;
+ DenseMap<BasicBlock*, DenseMap<uint32_t, Value*> > localAvail;
typedef DenseMap<Value*, SmallPtrSet<Instruction*, 4> > PhiMapType;
PhiMapType phiMap;
// Helper fuctions
// FIXME: eliminate or document these better
- Value* find_leader(ValueNumberedSet& vals, uint32_t v) ;
- void val_insert(ValueNumberedSet& s, Value* v);
bool processLoad(LoadInst* L,
DenseMap<Value*, LoadInst*> &lastLoad,
SmallVectorImpl<Instruction*> &toErase);
bool processInstruction(Instruction* I,
- ValueNumberedSet& currAvail,
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<BasicBlock*, Value*>& d);
+ 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);
};
char GVN::ID = 0;
static RegisterPass<GVN> X("gvn",
"Global Value Numbering");
-/// find_leader - Given a set and a value number, return the first
-/// element of the set with that value number, or 0 if no such element
-/// is present
-Value* GVN::find_leader(ValueNumberedSet& vals, uint32_t v) {
- if (!vals.test(v))
- return 0;
-
- for (ValueNumberedSet::iterator I = vals.begin(), E = vals.end();
- I != E; ++I)
- if (v == VN.lookup(*I))
- return *I;
-
- assert(0 && "No leader found, but present bit is set?");
- return 0;
-}
-
-/// val_insert - Insert a value into a set only if there is not a value
-/// with the same value number already in the set
-void GVN::val_insert(ValueNumberedSet& s, Value* v) {
- uint32_t num = VN.lookup(v);
- if (!s.test(num))
- s.insert(v);
-}
-
-void GVN::dump(DenseMap<BasicBlock*, Value*>& d) {
+void GVN::dump(DenseMap<uint32_t, Value*>& d) {
printf("{\n");
- for (DenseMap<BasicBlock*, Value*>::iterator I = d.begin(),
+ for (DenseMap<uint32_t, Value*>::iterator I = d.begin(),
E = d.end(); I != E; ++I) {
- if (I->second == MemoryDependenceAnalysis::None)
- printf("None\n");
- else
+ printf("%d\n", I->first);
I->second->dump();
}
printf("}\n");
/// processInstruction - When calculating availability, handle an instruction
/// by inserting it into the appropriate sets
-bool GVN::processInstruction(Instruction *I, ValueNumberedSet &currAvail,
+bool GVN::processInstruction(Instruction *I,
DenseMap<Value*, LoadInst*> &lastSeenLoad,
SmallVectorImpl<Instruction*> &toErase) {
- if (LoadInst* L = dyn_cast<LoadInst>(I))
- return processLoad(L, lastSeenLoad, 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()].insert(std::make_pair(num, L));
+ }
+
+ return changed;
+ }
+
+ 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)) {
+ localAvail[I->getParent()].insert(std::make_pair(num, I));
return false;
-
- unsigned num = VN.lookup_or_add(I);
+ }
// Collapse PHI nodes
if (PHINode* p = dyn_cast<PHINode>(I)) {
p->replaceAllUsesWith(constVal);
toErase.push_back(p);
+ } else {
+ localAvail[I->getParent()].insert(std::make_pair(num, I));
}
// Perform value-number based elimination
- } else if (currAvail.test(num)) {
- Value* repl = find_leader(currAvail, num);
+ } else if (localAvail[I->getParent()].count(num)) {
+ Value* repl = localAvail[I->getParent()][num];
// Remove it!
MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
toErase.push_back(I);
return true;
} else if (!I->isTerminator()) {
- currAvail.set(num);
- currAvail.insert(I);
+ localAvail[I->getParent()].insert(std::make_pair(num, I));
}
return false;
}
-// GVN::iterateOnFunction - Executes one iteration of GVN
-bool GVN::iterateOnFunction(Function &F) {
- // Clean out global sets from any previous functions
- VN.clear();
- availableOut.clear();
- phiMap.clear();
-
+bool GVN::processBlock(DomTreeNode* DTN) {
+ BasicBlock* BB = DTN->getBlock();
+
+ SmallVector<Instruction*, 8> toErase;
+ DenseMap<Value*, LoadInst*> lastSeenLoad;
bool changed_function = false;
- DominatorTree &DT = getAnalysis<DominatorTree>();
+ if (DTN->getIDom())
+ localAvail.insert(std::make_pair(BB,
+ localAvail[DTN->getIDom()->getBlock()]));
- SmallVector<Instruction*, 8> toErase;
- DenseMap<Value*, LoadInst*> lastSeenLoad;
- DenseMap<DomTreeNode*, size_t> numChildrenVisited;
-
- // Top-down walk of the dominator tree
- for (df_iterator<DomTreeNode*> DI = df_begin(DT.getRootNode()),
- E = df_end(DT.getRootNode()); DI != E; ++DI) {
+ for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
+ BI != BE;) {
+ changed_function |= processInstruction(BI, lastSeenLoad, toErase);
+ if (toErase.empty()) {
+ ++BI;
+ continue;
+ }
- // Get the set to update for this block
- ValueNumberedSet& currAvail = availableOut[DI->getBlock()];
- lastSeenLoad.clear();
+ // If we need some instructions deleted, do it now.
+ NumGVNInstr += toErase.size();
+
+ // Avoid iterator invalidation.
+ bool AtStart = BI == BB->begin();
+ if (!AtStart)
+ --BI;
+
+ for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
+ E = toErase.end(); I != E; ++I)
+ (*I)->eraseFromParent();
- BasicBlock* BB = DI->getBlock();
+ if (AtStart)
+ BI = BB->begin();
+ else
+ ++BI;
+
+ toErase.clear();
+ }
- // A block inherits AVAIL_OUT from its dominator
- if (DI->getIDom() != 0) {
- currAvail = availableOut[DI->getIDom()->getBlock()];
+ 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;
+ 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<AllocaInst>(BI) || isa<TerminatorInst>(BI) ||
+ isa<LoadInst>(BI) || isa<StoreInst>(BI) ||
+ isa<CallInst>(BI) || isa<PHINode>(BI)) {
+ BI++;
+ continue;
+ }
- numChildrenVisited[DI->getIDom()]++;
+ uint32_t valno = VN.lookup(BI);
- if (numChildrenVisited[DI->getIDom()] == DI->getIDom()->getNumChildren()) {
- availableOut.erase(DI->getIDom()->getBlock());
- numChildrenVisited.erase(DI->getIDom());
+ // 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;
+ 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.
+ if (*PI == CurrentBlock)
+ numWithout = 2;
+
+ if (!localAvail[*PI].count(valno)) {
+ PREPred = *PI;
+ numWithout++;
+ } else if (localAvail[*PI][valno] == BI) {
+ numWithout = 2;
+ } else {
+ numWith++;
+ }
}
- }
-
- for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
- BI != BE;) {
- changed_function |= processInstruction(BI, currAvail,
- lastSeenLoad, toErase);
- if (toErase.empty()) {
- ++BI;
+
+ // 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;
}
- // If we need some instructions deleted, do it now.
- NumGVNInstr += toErase.size();
+ // 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 if (!localAvail[PREPred].count(VN.lookup(op))) {
+ success = false;
+ break;
+ } else
+ PREInstr->setOperand(i, localAvail[PREPred][VN.lookup(op)]);
+ }
- // Avoid iterator invalidation.
- bool AtStart = BI == BB->begin();
- if (!AtStart)
- --BI;
-
- for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
- E = toErase.end(); I != E; ++I)
- (*I)->eraseFromParent();
-
- if (AtStart)
- BI = BB->begin();
- else
- ++BI;
+ // 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");
+ VN.add(PREInstr, valno);
+ NumGVNPRE++;
+
+ // Update the availability map to include the new instruction.
+ localAvail[PREPred].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(localAvail[*PI][valno], *PI);
+
+ VN.add(Phi, valno);
- toErase.clear();
+ // The newly created PHI completely replaces the old instruction,
+ // so we need to update the maps to reflect this.
+ for (DenseMap<BasicBlock*, DenseMap<uint32_t, Value*> >::iterator
+ UI = localAvail.begin(), UE = localAvail.end(); UI != UE; ++UI)
+ for (DenseMap<uint32_t, Value*>::iterator UUI = UI->second.begin(),
+ UUE = UI->second.end(); UUI != UUE; ++UUI)
+ if (UUI->second == BI)
+ UUI->second = Phi;
+
+ BI->replaceAllUsesWith(Phi);
+ VN.erase(BI);
+
+ Instruction* erase = BI;
+ BI++;
+ erase->eraseFromParent();
+
+ changed = true;
}
}
- return changed_function;
+ return changed;
+}
+
+// GVN::iterateOnFunction - Executes one iteration of GVN
+bool GVN::iterateOnFunction(Function &F) {
+ // Clean out global sets from any previous functions
+ VN.clear();
+ localAvail.clear();
+ phiMap.clear();
+
+ DominatorTree &DT = getAnalysis<DominatorTree>();
+
+ // 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);
+
+ changed |= performPRE(F);
+ return changed;
}
projects / oota-llvm.git / blobdiff