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For details, See: docs/2002-06-25-MegaPatchInfo.txt git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@2779 91177308-0d34-0410-b5e6-96231b3b80d8
294 lines
10 KiB
C++
294 lines
10 KiB
C++
//===- PromoteMemoryToRegister.cpp - Convert memory refs to regs ----------===//
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//
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// This pass is used to promote memory references to be register references. A
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// simple example of the transformation performed by this pass is:
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//
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// FROM CODE TO CODE
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// %X = alloca int, uint 1 ret int 42
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// store int 42, int *%X
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// %Y = load int* %X
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// ret int %Y
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//
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// To do this transformation, a simple analysis is done to ensure it is safe.
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// Currently this just loops over all alloca instructions, looking for
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// instructions that are only used in simple load and stores.
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//
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// After this, the code is transformed by...something magical :)
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Analysis/Dominators.h"
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#include "llvm/iMemory.h"
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#include "llvm/iPHINode.h"
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#include "llvm/iTerminators.h"
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#include "llvm/Function.h"
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#include "llvm/BasicBlock.h"
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#include "llvm/Constant.h"
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#include "llvm/Type.h"
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#include "Support/StatisticReporter.h"
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static Statistic<> NumPromoted("mem2reg\t\t- Number of alloca's promoted");
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using std::vector;
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using std::map;
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using std::set;
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namespace {
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struct PromotePass : public FunctionPass {
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vector<AllocaInst*> Allocas; // the alloca instruction..
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map<Instruction*, unsigned> AllocaLookup; // reverse mapping of above
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vector<vector<BasicBlock*> > PhiNodes; // index corresponds to Allocas
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// List of instructions to remove at end of pass
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vector<Instruction *> KillList;
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map<BasicBlock*,vector<PHINode*> > NewPhiNodes; // the PhiNodes we're adding
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public:
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const char *getPassName() const { return "Promote Memory to Register"; }
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// runOnFunction - To run this pass, first we calculate the alloca
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// instructions that are safe for promotion, then we promote each one.
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//
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virtual bool runOnFunction(Function &F);
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// getAnalysisUsage - We need dominance frontiers
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//
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequired(DominanceFrontier::ID);
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AU.preservesCFG();
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}
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private:
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void Traverse(BasicBlock *BB, BasicBlock *Pred, vector<Value*> &IncVals,
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set<BasicBlock*> &Visited);
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bool QueuePhiNode(BasicBlock *BB, unsigned AllocaIdx);
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void FindSafeAllocas(Function &F);
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};
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} // end of anonymous namespace
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// isSafeAlloca - This predicate controls what types of alloca instructions are
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// allowed to be promoted...
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//
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static inline bool isSafeAlloca(const AllocaInst *AI) {
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if (AI->isArrayAllocation()) return false;
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for (Value::use_const_iterator UI = AI->use_begin(), UE = AI->use_end();
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UI != UE; ++UI) { // Loop over all of the uses of the alloca
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// Only allow nonindexed memory access instructions...
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if (MemAccessInst *MAI = dyn_cast<MemAccessInst>(*UI)) {
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if (MAI->getPointerOperand() != (Value*)AI)
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return false; // Reject stores of alloca pointer into some other loc.
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if (MAI->hasIndices()) { // indexed?
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// Allow the access if there is only one index and the index is
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// zero.
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if (*MAI->idx_begin() != Constant::getNullValue(Type::UIntTy) ||
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MAI->idx_begin()+1 != MAI->idx_end())
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return false;
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}
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} else {
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return false; // Not a load or store?
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}
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}
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return true;
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}
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// FindSafeAllocas - Find allocas that are safe to promote
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//
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void PromotePass::FindSafeAllocas(Function &F) {
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BasicBlock &BB = F.getEntryNode(); // Get the entry node for the function
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// Look at all instructions in the entry node
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for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ++I)
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if (AllocaInst *AI = dyn_cast<AllocaInst>(&*I)) // Is it an alloca?
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if (isSafeAlloca(AI)) { // If safe alloca, add alloca to safe list
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AllocaLookup[AI] = Allocas.size(); // Keep reverse mapping
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Allocas.push_back(AI);
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}
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}
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bool PromotePass::runOnFunction(Function &F) {
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// Calculate the set of safe allocas
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FindSafeAllocas(F);
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// If there is nothing to do, bail out...
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if (Allocas.empty()) return false;
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// Add each alloca to the KillList. Note: KillList is destroyed MOST recently
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// added to least recently.
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KillList.assign(Allocas.begin(), Allocas.end());
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// Calculate the set of write-locations for each alloca. This is analogous to
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// counting the number of 'redefinitions' of each variable.
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vector<vector<BasicBlock*> > WriteSets; // index corresponds to Allocas
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WriteSets.resize(Allocas.size());
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for (unsigned i = 0; i != Allocas.size(); ++i) {
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AllocaInst *AI = Allocas[i];
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for (Value::use_iterator U =AI->use_begin(), E = AI->use_end(); U != E; ++U)
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if (StoreInst *SI = dyn_cast<StoreInst>(*U))
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// jot down the basic-block it came from
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WriteSets[i].push_back(SI->getParent());
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}
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// Get dominance frontier information...
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DominanceFrontier &DF = getAnalysis<DominanceFrontier>();
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// Compute the locations where PhiNodes need to be inserted. Look at the
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// dominance frontier of EACH basic-block we have a write in
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//
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PhiNodes.resize(Allocas.size());
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for (unsigned i = 0; i != Allocas.size(); ++i) {
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for (unsigned j = 0; j != WriteSets[i].size(); j++) {
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// Look up the DF for this write, add it to PhiNodes
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DominanceFrontier::const_iterator it = DF.find(WriteSets[i][j]);
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DominanceFrontier::DomSetType S = it->second;
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for (DominanceFrontier::DomSetType::iterator P = S.begin(), PE = S.end();
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P != PE; ++P)
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QueuePhiNode(*P, i);
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}
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// Perform iterative step
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for (unsigned k = 0; k != PhiNodes[i].size(); k++) {
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DominanceFrontier::const_iterator it = DF.find(PhiNodes[i][k]);
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DominanceFrontier::DomSetType S = it->second;
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for (DominanceFrontier::DomSetType::iterator P = S.begin(), PE = S.end();
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P != PE; ++P)
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QueuePhiNode(*P, i);
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}
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}
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// Set the incoming values for the basic block to be null values for all of
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// the alloca's. We do this in case there is a load of a value that has not
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// been stored yet. In this case, it will get this null value.
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//
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vector<Value *> Values(Allocas.size());
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for (unsigned i = 0, e = Allocas.size(); i != e; ++i)
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Values[i] = Constant::getNullValue(Allocas[i]->getAllocatedType());
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// Walks all basic blocks in the function performing the SSA rename algorithm
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// and inserting the phi nodes we marked as necessary
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//
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set<BasicBlock*> Visited; // The basic blocks we've already visited
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Traverse(F.begin(), 0, Values, Visited);
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// Remove all instructions marked by being placed in the KillList...
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//
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while (!KillList.empty()) {
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Instruction *I = KillList.back();
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KillList.pop_back();
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I->getParent()->getInstList().erase(I);
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}
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NumPromoted += Allocas.size();
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// Purge data structurse so they are available the next iteration...
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Allocas.clear();
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AllocaLookup.clear();
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PhiNodes.clear();
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NewPhiNodes.clear();
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return true;
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}
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// QueuePhiNode - queues a phi-node to be added to a basic-block for a specific
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// Alloca returns true if there wasn't already a phi-node for that variable
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//
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bool PromotePass::QueuePhiNode(BasicBlock *BB, unsigned AllocaNo) {
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// Look up the basic-block in question
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vector<PHINode*> &BBPNs = NewPhiNodes[BB];
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if (BBPNs.empty()) BBPNs.resize(Allocas.size());
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// If the BB already has a phi node added for the i'th alloca then we're done!
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if (BBPNs[AllocaNo]) return false;
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// Create a PhiNode using the dereferenced type...
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PHINode *PN = new PHINode(Allocas[AllocaNo]->getAllocatedType(),
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Allocas[AllocaNo]->getName()+".mem2reg");
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BBPNs[AllocaNo] = PN;
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// Add the phi-node to the basic-block
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BB->getInstList().push_front(PN);
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PhiNodes[AllocaNo].push_back(BB);
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return true;
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}
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void PromotePass::Traverse(BasicBlock *BB, BasicBlock *Pred,
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vector<Value*> &IncomingVals,
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set<BasicBlock*> &Visited) {
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// If this is a BB needing a phi node, lookup/create the phinode for each
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// variable we need phinodes for.
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vector<PHINode *> &BBPNs = NewPhiNodes[BB];
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for (unsigned k = 0; k != BBPNs.size(); ++k)
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if (PHINode *PN = BBPNs[k]) {
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// at this point we can assume that the array has phi nodes.. let's add
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// the incoming data
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PN->addIncoming(IncomingVals[k], Pred);
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// also note that the active variable IS designated by the phi node
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IncomingVals[k] = PN;
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}
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// don't revisit nodes
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if (Visited.count(BB)) return;
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// mark as visited
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Visited.insert(BB);
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// keep track of the value of each variable we're watching.. how?
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for (BasicBlock::iterator II = BB->begin(); II != BB->end(); ++II) {
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Instruction *I = II; // get the instruction
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if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
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Value *Ptr = LI->getPointerOperand();
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if (AllocaInst *Src = dyn_cast<AllocaInst>(Ptr)) {
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map<Instruction*, unsigned>::iterator AI = AllocaLookup.find(Src);
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if (AI != AllocaLookup.end()) {
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Value *V = IncomingVals[AI->second];
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// walk the use list of this load and replace all uses with r
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LI->replaceAllUsesWith(V);
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KillList.push_back(LI); // Mark the load to be deleted
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}
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}
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} else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
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// delete this instruction and mark the name as the current holder of the
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// value
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Value *Ptr = SI->getPointerOperand();
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if (AllocaInst *Dest = dyn_cast<AllocaInst>(Ptr)) {
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map<Instruction *, unsigned>::iterator ai = AllocaLookup.find(Dest);
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if (ai != AllocaLookup.end()) {
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// what value were we writing?
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IncomingVals[ai->second] = SI->getOperand(0);
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KillList.push_back(SI); // Mark the store to be deleted
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}
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}
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} else if (TerminatorInst *TI = dyn_cast<TerminatorInst>(I)) {
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// Recurse across our successors
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for (unsigned i = 0; i != TI->getNumSuccessors(); i++) {
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vector<Value*> OutgoingVals(IncomingVals);
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Traverse(TI->getSuccessor(i), BB, OutgoingVals, Visited);
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}
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}
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}
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}
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// createPromoteMemoryToRegister - Provide an entry point to create this pass.
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//
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Pass *createPromoteMemoryToRegister() {
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return new PromotePass();
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}
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