#include "llvm/Target/TargetData.h"
#include "llvm/Transforms/Utils/PromoteMemToReg.h"
#include "llvm/Transforms/Utils/Local.h"
+#include "llvm/Transforms/Utils/SSAUpdater.h"
#include "llvm/Support/CallSite.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
STATISTIC(NumConverted, "Number of aggregates converted to scalar");
STATISTIC(NumGlobals, "Number of allocas copied from constant global");
+enum {
+ UsePromoteMemToReg = 1
+};
+
namespace {
struct SROA : public FunctionPass {
static char ID; // Pass identification, replacement for typeid
// getAnalysisUsage - This pass does not require any passes, but we know it
// will not alter the CFG, so say so.
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
- AU.addRequired<DominatorTree>();
- AU.addRequired<DominanceFrontier>();
+ if (UsePromoteMemToReg) {
+ AU.addRequired<DominatorTree>();
+ AU.addRequired<DominanceFrontier>();
+ }
AU.setPreservesCFG();
}
return Changed;
}
+/// PromoteAlloca - Promote an alloca to registers, using SSAUpdater.
+static void PromoteAlloca(AllocaInst *AI, SSAUpdater &SSA) {
+ SSA.Initialize(AI->getType()->getElementType(), AI->getName());
+
+ // First step: bucket up uses of the alloca by the block they occur in.
+ // This is important because we have to handle multiple defs/uses in a block
+ // ourselves: SSAUpdater is purely for cross-block references.
+ // FIXME: Want a TinyVector<Instruction*> since there is often 0/1 element.
+ DenseMap<BasicBlock*, std::vector<Instruction*> > UsesByBlock;
+
+ for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end();
+ UI != E; ++UI) {
+ Instruction *User = cast<Instruction>(*UI);
+ UsesByBlock[User->getParent()].push_back(User);
+ }
+
+ // Okay, now we can iterate over all the blocks in the function with uses,
+ // processing them. Keep track of which loads are loading a live-in value.
+ // Walk the uses in the use-list order to be determinstic.
+ SmallVector<LoadInst*, 32> LiveInLoads;
+ DenseMap<Value*, Value*> ReplacedLoads;
+
+ for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end();
+ UI != E; ++UI) {
+ Instruction *User = cast<Instruction>(*UI);
+ BasicBlock *BB = User->getParent();
+ std::vector<Instruction*> &BlockUses = UsesByBlock[BB];
+
+ // If this block has already been processed, ignore this repeat use.
+ if (BlockUses.empty()) continue;
+
+ // Okay, this is the first use in the block. If this block just has a
+ // single user in it, we can rewrite it trivially.
+ if (BlockUses.size() == 1) {
+ // If it is a store, it is a trivial def of the value in the block.
+ if (StoreInst *SI = dyn_cast<StoreInst>(User))
+ SSA.AddAvailableValue(BB, SI->getOperand(0));
+ else
+ // Otherwise it is a load, queue it to rewrite as a live-in load.
+ LiveInLoads.push_back(cast<LoadInst>(User));
+ BlockUses.clear();
+ continue;
+ }
+
+ // Otherwise, check to see if this block is all loads.
+ bool HasStore = false;
+ for (unsigned i = 0, e = BlockUses.size(); i != e; ++i) {
+ if (isa<StoreInst>(BlockUses[i])) {
+ HasStore = true;
+ break;
+ }
+ }
+
+ // If so, we can queue them all as live in loads. We don't have an
+ // efficient way to tell which on is first in the block and don't want to
+ // scan large blocks, so just add all loads as live ins.
+ if (!HasStore) {
+ for (unsigned i = 0, e = BlockUses.size(); i != e; ++i)
+ LiveInLoads.push_back(cast<LoadInst>(BlockUses[i]));
+ BlockUses.clear();
+ continue;
+ }
+
+ // Otherwise, we have mixed loads and stores (or just a bunch of stores).
+ // Since SSAUpdater is purely for cross-block values, we need to determine
+ // the order of these instructions in the block. If the first use in the
+ // block is a load, then it uses the live in value. The last store defines
+ // the live out value. We handle this by doing a linear scan of the block.
+ Value *StoredValue = 0;
+ for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E; ++II) {
+ if (LoadInst *L = dyn_cast<LoadInst>(II)) {
+ // If this is a load from an unrelated pointer, ignore it.
+ if (L->getOperand(0) != AI) continue;
+
+ // If we haven't seen a store yet, this is a live in use, otherwise
+ // use the stored value.
+ if (StoredValue) {
+ L->replaceAllUsesWith(StoredValue);
+ ReplacedLoads[L] = StoredValue;
+ } else {
+ LiveInLoads.push_back(L);
+ }
+ continue;
+ }
+
+ if (StoreInst *S = dyn_cast<StoreInst>(II)) {
+ // If this is a store to an unrelated pointer, ignore it.
+ if (S->getPointerOperand() != AI) continue;
+
+ // Remember that this is the active value in the block.
+ StoredValue = S->getOperand(0);
+ }
+ }
+
+ // The last stored value that happened is the live-out for the block.
+ assert(StoredValue && "Already checked that there is a store in block");
+ SSA.AddAvailableValue(BB, StoredValue);
+ BlockUses.clear();
+ }
+
+ // Okay, now we rewrite all loads that use live-in values in the loop,
+ // inserting PHI nodes as necessary.
+ for (unsigned i = 0, e = LiveInLoads.size(); i != e; ++i) {
+ LoadInst *ALoad = LiveInLoads[i];
+ Value *NewVal = SSA.GetValueInMiddleOfBlock(ALoad->getParent());
+ ALoad->replaceAllUsesWith(NewVal);
+ ReplacedLoads[ALoad] = NewVal;
+ }
+
+ // Now that everything is rewritten, delete the old instructions from the
+ // function. They should all be dead now.
+ for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); UI != E; ) {
+ Instruction *User = cast<Instruction>(*UI++);
+
+ // If this is a load that still has uses, then the load must have been added
+ // as a live value in the SSAUpdate data structure for a block (e.g. because
+ // the loaded value was stored later). In this case, we need to recursively
+ // propagate the updates until we get to the real value.
+ if (!User->use_empty()) {
+ Value *NewVal = ReplacedLoads[User];
+ assert(NewVal && "not a replaced load?");
+
+ // Propagate down to the ultimate replacee. The intermediately loads
+ // could theoretically already have been deleted, so we don't want to
+ // dereference the Value*'s.
+ DenseMap<Value*, Value*>::iterator RLI = ReplacedLoads.find(NewVal);
+ while (RLI != ReplacedLoads.end()) {
+ NewVal = RLI->second;
+ RLI = ReplacedLoads.find(NewVal);
+ }
+
+ User->replaceAllUsesWith(NewVal);
+ }
+
+ User->eraseFromParent();
+ }
+}
+
bool SROA::performPromotion(Function &F) {
std::vector<AllocaInst*> Allocas;
- DominatorTree &DT = getAnalysis<DominatorTree>();
- DominanceFrontier &DF = getAnalysis<DominanceFrontier>();
+ DominatorTree *DT = 0;
+ DominanceFrontier *DF = 0;
+ if (UsePromoteMemToReg) {
+ DT = &getAnalysis<DominatorTree>();
+ DF = &getAnalysis<DominanceFrontier>();
+ }
BasicBlock &BB = F.getEntryBlock(); // Get the entry node for the function
if (Allocas.empty()) break;
- PromoteMemToReg(Allocas, DT, DF);
+ if (UsePromoteMemToReg)
+ PromoteMemToReg(Allocas, *DT, *DF);
+ else {
+ SSAUpdater SSA;
+ for (unsigned i = 0, e = Allocas.size(); i != e; ++i) {
+ PromoteAlloca(Allocas[i], SSA);
+ Allocas[i]->eraseFromParent();
+ }
+ }
NumPromoted += Allocas.size();
Changed = true;
}
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