// Currently this just loops over all alloca instructions, looking for
// instructions that are only used in simple load and stores.
//
-// After this, the code is transformed by...
+// After this, the code is transformed by...something magical :)
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar/PromoteMemoryToRegister.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/iMemory.h"
+#include "llvm/iPHINode.h"
+#include "llvm/iTerminators.h"
#include "llvm/Pass.h"
-#include "llvm/Method.h"
-#include "llvm/Assembly/Writer.h" // For debugging
-using cfg::DominanceFrontier;
+#include "llvm/Function.h"
+#include "llvm/BasicBlock.h"
+#include "llvm/Constant.h"
-// PromotePass - This class is implements the PromoteMemoryToRegister pass
+using std::vector;
+using std::map;
+using std::set;
+
+namespace {
+ struct PromotePass : public FunctionPass {
+ vector<AllocaInst*> Allocas; // the alloca instruction..
+ map<Instruction*, unsigned> AllocaLookup; // reverse mapping of above
+
+ vector<vector<BasicBlock*> > PhiNodes; // index corresponds to Allocas
+
+ // List of instructions to remove at end of pass
+ vector<Instruction *> KillList;
+
+ map<BasicBlock*,vector<PHINode*> > NewPhiNodes; // the PhiNodes we're adding
+
+ public:
+ const char *getPassName() const { return "Promote Memory to Register"; }
+
+ // runOnFunction - To run this pass, first we calculate the alloca
+ // instructions that are safe for promotion, then we promote each one.
+ //
+ virtual bool runOnFunction(Function *F);
+
+ // getAnalysisUsage - We need dominance frontiers
+ //
+ virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.addRequired(DominanceFrontier::ID);
+ AU.preservesCFG();
+ }
+
+ private:
+ void Traverse(BasicBlock *BB, BasicBlock *Pred, vector<Value*> &IncVals,
+ set<BasicBlock*> &Visited);
+ bool QueuePhiNode(BasicBlock *BB, unsigned AllocaIdx);
+ void FindSafeAllocas(Function *F);
+ };
+
+} // end of anonymous namespace
+
+
+// isSafeAlloca - This predicate controls what types of alloca instructions are
+// allowed to be promoted...
//
-class PromotePass : public MethodPass {
-public:
- // runOnMethod - To run this pass, first we calculate the alloca instructions
- // that are safe for promotion, then we promote each one.
- //
- virtual bool runOnMethod(Method *M) {
- std::vector<AllocaInst*> Allocas;
- findSafeAllocas(M, Allocas); // Calculate safe allocas
+static inline bool isSafeAlloca(const AllocaInst *AI) {
+ if (AI->isArrayAllocation()) return false;
+
+ for (Value::use_const_iterator UI = AI->use_begin(), UE = AI->use_end();
+ UI != UE; ++UI) { // Loop over all of the uses of the alloca
+
+ // Only allow nonindexed memory access instructions...
+ if (MemAccessInst *MAI = dyn_cast<MemAccessInst>(*UI)) {
+ if (MAI->hasIndices()) { // indexed?
+ // Allow the access if there is only one index and the index is
+ // zero.
+ if (*MAI->idx_begin() != Constant::getNullValue(Type::UIntTy) ||
+ MAI->idx_begin()+1 != MAI->idx_end())
+ return false;
+ }
+ } else {
+ return false; // Not a load or store?
+ }
+ }
+
+ return true;
+}
+
+// FindSafeAllocas - Find allocas that are safe to promote
+//
+void PromotePass::FindSafeAllocas(Function *F) {
+ BasicBlock *BB = F->getEntryNode(); // Get the entry node for the function
+
+ // Look at all instructions in the entry node
+ for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
+ if (AllocaInst *AI = dyn_cast<AllocaInst>(*I)) // Is it an alloca?
+ if (isSafeAlloca(AI)) { // If safe alloca, add alloca to safe list
+ AllocaLookup[AI] = Allocas.size(); // Keep reverse mapping
+ Allocas.push_back(AI);
+ }
+}
+
+
- // Get dominance frontier information...
- DominanceFrontier &DF = getAnalysis<DominanceFrontier>();
+bool PromotePass::runOnFunction(Function *F) {
+ // Calculate the set of safe allocas
+ FindSafeAllocas(F);
- // Transform each alloca in turn...
- for (std::vector<AllocaInst*>::iterator I = Allocas.begin(),
- E = Allocas.end(); I != E; ++I)
- promoteAlloca(*I, DF);
+ // If there is nothing to do, bail out...
+ if (Allocas.empty()) return false;
- return !Allocas.empty();
+ // Add each alloca to the KillList. Note: KillList is destroyed MOST recently
+ // added to least recently.
+ KillList.assign(Allocas.begin(), Allocas.end());
+
+ // Calculate the set of write-locations for each alloca. This is analogous to
+ // counting the number of 'redefinitions' of each variable.
+ vector<vector<BasicBlock*> > WriteSets; // index corresponds to Allocas
+ WriteSets.resize(Allocas.size());
+ for (unsigned i = 0; i != Allocas.size(); ++i) {
+ AllocaInst *AI = Allocas[i];
+ for (Value::use_iterator U =AI->use_begin(), E = AI->use_end(); U != E; ++U)
+ if (StoreInst *SI = dyn_cast<StoreInst>(*U))
+ // jot down the basic-block it came from
+ WriteSets[i].push_back(SI->getParent());
}
+ // Get dominance frontier information...
+ DominanceFrontier &DF = getAnalysis<DominanceFrontier>();
- // getAnalysisUsageInfo - We need dominance frontiers
+ // Compute the locations where PhiNodes need to be inserted. Look at the
+ // dominance frontier of EACH basic-block we have a write in
//
- virtual void getAnalysisUsageInfo(Pass::AnalysisSet &Requires,
- Pass::AnalysisSet &Destroyed,
- Pass::AnalysisSet &Provided) {
- Requires.push_back(DominanceFrontier::ID);
+ PhiNodes.resize(Allocas.size());
+ for (unsigned i = 0; i != Allocas.size(); ++i) {
+ for (unsigned j = 0; j != WriteSets[i].size(); j++) {
+ // Look up the DF for this write, add it to PhiNodes
+ DominanceFrontier::const_iterator it = DF.find(WriteSets[i][j]);
+ DominanceFrontier::DomSetType S = it->second;
+ for (DominanceFrontier::DomSetType::iterator P = S.begin(), PE = S.end();
+ P != PE; ++P)
+ QueuePhiNode(*P, i);
+ }
+
+ // Perform iterative step
+ for (unsigned k = 0; k != PhiNodes[i].size(); k++) {
+ DominanceFrontier::const_iterator it = DF.find(PhiNodes[i][k]);
+ DominanceFrontier::DomSetType S = it->second;
+ for (DominanceFrontier::DomSetType::iterator P = S.begin(), PE = S.end();
+ P != PE; ++P)
+ QueuePhiNode(*P, i);
+ }
}
-private:
- // findSafeAllocas - Find allocas that are safe to promote
+ // Set the incoming values for the basic block to be null values for all of
+ // the alloca's. We do this in case there is a load of a value that has not
+ // been stored yet. In this case, it will get this null value.
+ //
+ vector<Value *> Values(Allocas.size());
+ for (unsigned i = 0, e = Allocas.size(); i != e; ++i)
+ Values[i] = Constant::getNullValue(Allocas[i]->getType()->getElementType());
+
+ // Walks all basic blocks in the function performing the SSA rename algorithm
+ // and inserting the phi nodes we marked as necessary
//
- void findSafeAllocas(Method *M, std::vector<AllocaInst*> &Allocas) const;
+ set<BasicBlock*> Visited; // The basic blocks we've already visited
+ Traverse(F->front(), 0, Values, Visited);
- // promoteAlloca - Convert the use chain of an alloca instruction into
- // register references.
+ // Remove all instructions marked by being placed in the KillList...
//
- void promoteAlloca(AllocaInst *AI, DominanceFrontier &DF);
-};
+ while (!KillList.empty()) {
+ Instruction *I = KillList.back();
+ KillList.pop_back();
+
+ I->getParent()->getInstList().remove(I);
+ delete I;
+ }
+
+ // Purge data structurse so they are available the next iteration...
+ Allocas.clear();
+ AllocaLookup.clear();
+ PhiNodes.clear();
+ NewPhiNodes.clear();
+ return true;
+}
-// findSafeAllocas - Find allocas that are safe to promote
+// QueuePhiNode - queues a phi-node to be added to a basic-block for a specific
+// Alloca returns true if there wasn't already a phi-node for that variable
//
-void PromotePass::findSafeAllocas(Method *M,
- std::vector<AllocaInst*> &Allocas) const {
- BasicBlock *BB = M->front(); // Get the entry node for the method
+bool PromotePass::QueuePhiNode(BasicBlock *BB, unsigned AllocaNo) {
+ // Look up the basic-block in question
+ vector<PHINode*> &BBPNs = NewPhiNodes[BB];
+ if (BBPNs.empty()) BBPNs.resize(Allocas.size());
- // Look at all instructions in the entry node
- for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
- if (AllocaInst *AI = dyn_cast<AllocaInst>(*I)) // Is it an alloca?
- if (!AI->isArrayAllocation()) {
- bool isSafe = true;
- for (Value::use_iterator UI = AI->use_begin(), UE = AI->use_end();
- UI != UE; ++UI) { // Loop over all of the uses of the alloca
- // Only allow nonindexed memory access instructions...
- if (MemAccessInst *MAI = dyn_cast<MemAccessInst>(*UI)) {
- if (MAI->hasIndices()) { isSafe = false; break; } // indexed?
- } else {
- isSafe = false; break; // Not a load or store?
- }
- }
+ // If the BB already has a phi node added for the i'th alloca then we're done!
+ if (BBPNs[AllocaNo]) return false;
- if (isSafe) // If all checks pass, add alloca to safe list
- Allocas.push_back(AI);
- }
+ // Create a PhiNode using the dereferenced type...
+ PHINode *PN = new PHINode(Allocas[AllocaNo]->getType()->getElementType(),
+ Allocas[AllocaNo]->getName()+".mem2reg");
+ BBPNs[AllocaNo] = PN;
+ // Add the phi-node to the basic-block
+ BB->getInstList().push_front(PN);
+
+ PhiNodes[AllocaNo].push_back(BB);
+ return true;
}
+void PromotePass::Traverse(BasicBlock *BB, BasicBlock *Pred,
+ vector<Value*> &IncomingVals,
+ set<BasicBlock*> &Visited) {
+ // If this is a BB needing a phi node, lookup/create the phinode for each
+ // variable we need phinodes for.
+ vector<PHINode *> &BBPNs = NewPhiNodes[BB];
+ for (unsigned k = 0; k != BBPNs.size(); ++k)
+ if (PHINode *PN = BBPNs[k]) {
+ // at this point we can assume that the array has phi nodes.. let's add
+ // the incoming data
+ PN->addIncoming(IncomingVals[k], Pred);
+ // also note that the active variable IS designated by the phi node
+ IncomingVals[k] = PN;
+ }
-// promoteAlloca - Convert the use chain of an alloca instruction into
-// register references.
-//
-void PromotePass::promoteAlloca(AllocaInst *AI, DominanceFrontier &DFInfo) {
- cerr << "TODO: Should process: " << AI;
+ // don't revisit nodes
+ if (Visited.count(BB)) return;
+
+ // mark as visited
+ Visited.insert(BB);
+
+ // keep track of the value of each variable we're watching.. how?
+ for (BasicBlock::iterator II = BB->begin(); II != BB->end(); ++II) {
+ Instruction *I = *II; //get the instruction
+
+ if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
+ Value *Ptr = LI->getPointerOperand();
+
+ if (AllocaInst *Src = dyn_cast<AllocaInst>(Ptr)) {
+ map<Instruction*, unsigned>::iterator AI = AllocaLookup.find(Src);
+ if (AI != AllocaLookup.end()) {
+ Value *V = IncomingVals[AI->second];
+
+ // walk the use list of this load and replace all uses with r
+ LI->replaceAllUsesWith(V);
+ KillList.push_back(LI); // Mark the load to be deleted
+ }
+ }
+ } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
+ // delete this instruction and mark the name as the current holder of the
+ // value
+ Value *Ptr = SI->getPointerOperand();
+ if (AllocaInst *Dest = dyn_cast<AllocaInst>(Ptr)) {
+ map<Instruction *, unsigned>::iterator ai = AllocaLookup.find(Dest);
+ if (ai != AllocaLookup.end()) {
+ // what value were we writing?
+ IncomingVals[ai->second] = SI->getOperand(0);
+ KillList.push_back(SI); // Mark the store to be deleted
+ }
+ }
+
+ } else if (TerminatorInst *TI = dyn_cast<TerminatorInst>(I)) {
+ // Recurse across our successors
+ for (unsigned i = 0; i != TI->getNumSuccessors(); i++) {
+ vector<Value*> OutgoingVals(IncomingVals);
+ Traverse(TI->getSuccessor(i), BB, OutgoingVals, Visited);
+ }
+ }
+ }
}
-// newPromoteMemoryToRegister - Provide an entry point to create this pass.
+// createPromoteMemoryToRegister - Provide an entry point to create this pass.
//
-Pass *newPromoteMemoryToRegister() {
+Pass *createPromoteMemoryToRegister() {
return new PromotePass();
}
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