#include "llvm/Value.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DepthFirstIterator.h"
-#include "llvm/ADT/ScopedHashTable.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) {
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; }
+ 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;
};
}
-typedef ScopedHashTable<uint32_t, Value*> ValueNumberMap;
-typedef ScopedHashTableScope<uint32_t, Value*> ValueNumberScope;
-
namespace {
class VISIBILITY_HIDDEN GVN : public FunctionPass {
private:
ValueTable VN;
-
- DenseMap<BasicBlock*, ValueNumberScope> availableOut;
- ValueNumberMap BaseMap;
+ DenseMap<BasicBlock*, DenseMap<uint32_t, Value*> > localAvail;
typedef DenseMap<Value*, SmallPtrSet<Instruction*, 4> > PhiMapType;
PhiMapType phiMap;
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");
-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");
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 (BaseMap.begin(num) != BaseMap.end()) {
- Value* repl = *BaseMap.begin(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()) {
- BaseMap.insert(num, I);
+ localAvail[I->getParent()].insert(std::make_pair(num, I));
}
return false;
bool GVN::processBlock(DomTreeNode* DTN) {
BasicBlock* BB = DTN->getBlock();
- ValueNumberScope NewScope(BaseMap);
SmallVector<Instruction*, 8> toErase;
DenseMap<Value*, LoadInst*> lastSeenLoad;
bool changed_function = false;
-
+
+ if (DTN->getIDom())
+ localAvail.insert(std::make_pair(BB,
+ localAvail[DTN->getIDom()->getBlock()]));
+
for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
BI != BE;) {
changed_function |= processInstruction(BI, lastSeenLoad, toErase);
toErase.clear();
}
- for (DomTreeNode::iterator I = DTN->begin(), E = DTN->end(); I != E; ++I)
- changed_function |= processBlock(*I);
-
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;
+ }
+
+ 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;
+ 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++;
+ }
+ }
+
+ // 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;
+ }
+
+ // 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)]);
+ }
+
+ // 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);
+
+ // 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);
+
+ Instruction* erase = BI;
+ BI++;
+ erase->eraseFromParent();
+
+ changed = true;
+ }
+ }
+
+ return changed;
+}
+
// GVN::iterateOnFunction - Executes one iteration of GVN
bool GVN::iterateOnFunction(Function &F) {
// Clean out global sets from any previous functions
VN.clear();
- availableOut.clear();
+ localAvail.clear();
phiMap.clear();
DominatorTree &DT = getAnalysis<DominatorTree>();
// Top-down walk of the dominator tree
- return processBlock(DT.getRootNode());
+ 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;
}
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