[llvm-commits] [llvm] r123456 - in /llvm/trunk: include/llvm/Transforms/Utils/SSAUpdater.h lib/Transforms/Utils/SSAUpdater.cpp
Chris Lattner
sabre at nondot.org
Fri Jan 14 11:36:13 PST 2011
Author: lattner
Date: Fri Jan 14 13:36:13 2011
New Revision: 123456
URL: http://llvm.org/viewvc/llvm-project?rev=123456&view=rev
Log:
Add a new LoadAndStorePromoter class, which implements the general
"promote a bunch of load and stores" logic, allowing the code to
be shared and reused.
Modified:
llvm/trunk/include/llvm/Transforms/Utils/SSAUpdater.h
llvm/trunk/lib/Transforms/Utils/SSAUpdater.cpp
Modified: llvm/trunk/include/llvm/Transforms/Utils/SSAUpdater.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Transforms/Utils/SSAUpdater.h?rev=123456&r1=123455&r2=123456&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Transforms/Utils/SSAUpdater.h (original)
+++ llvm/trunk/include/llvm/Transforms/Utils/SSAUpdater.h Fri Jan 14 13:36:13 2011
@@ -108,6 +108,38 @@
void operator=(const SSAUpdater&); // DO NOT IMPLEMENT
SSAUpdater(const SSAUpdater&); // DO NOT IMPLEMENT
};
+
+/// LoadAndStorePromoter - This little helper class provides a convenient way to
+/// promote a collection of loads and stores into SSA Form using the SSAUpdater.
+/// This handles complexities that SSAUpdater doesn't, such as multiple loads
+/// and stores in one block.
+///
+/// Clients of this class are expected to subclass this and implement the
+/// virtual methods.
+///
+class LoadAndStorePromoter {
+public:
+ LoadAndStorePromoter() {}
+ virtual ~LoadAndStorePromoter() {}
+
+ /// run - This does the promotion. Insts is a list of loads and stores to
+ /// promote, and Name is the basename for the PHIs to insert. After this is
+ /// complete, the loads and stores are removed from the code.
+ void run(StringRef Name, const SmallVectorImpl<Instruction*> &Insts,
+ SSAUpdater *SSA = 0);
+
+
+ /// Return true if the specified instruction is in the Inst list (which was
+ /// passed into the run method). Clients should implement this with a more
+ /// efficient version if possible.
+ virtual bool isInstInList(Instruction *I,
+ const SmallVectorImpl<Instruction*> &Insts) const {
+ for (unsigned i = 0, e = Insts.size(); i != e; ++i)
+ if (Insts[i] == I)
+ return true;
+ return false;
+ }
+};
} // End llvm namespace
Modified: llvm/trunk/lib/Transforms/Utils/SSAUpdater.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/SSAUpdater.cpp?rev=123456&r1=123455&r2=123456&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/SSAUpdater.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/SSAUpdater.cpp Fri Jan 14 13:36:13 2011
@@ -343,3 +343,157 @@
SSAUpdaterImpl<SSAUpdater> Impl(this, &AvailableVals, InsertedPHIs);
return Impl.GetValue(BB);
}
+
+//===----------------------------------------------------------------------===//
+// LoadAndStorePromoter Implementation
+//===----------------------------------------------------------------------===//
+
+void LoadAndStorePromoter::run(StringRef BaseName,
+ const SmallVectorImpl<Instruction*> &Insts,
+ SSAUpdater *SSA) {
+ if (Insts.empty()) return;
+
+ // If no SSAUpdater was provided, use a default one. This allows the client
+ // to capture inserted PHI nodes etc if they want.
+ SSAUpdater DefaultSSA;
+ if (SSA == 0) SSA = &DefaultSSA;
+
+ const Type *ValTy;
+ if (LoadInst *LI = dyn_cast<LoadInst>(Insts[0]))
+ ValTy = LI->getType();
+ else
+ ValTy = cast<StoreInst>(Insts[0])->getOperand(0)->getType();
+
+ SSA->Initialize(ValTy, BaseName);
+
+ // 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 (unsigned i = 0, e = Insts.size(); i != e; ++i) {
+ Instruction *User = Insts[i];
+ 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 (unsigned i = 0, e = Insts.size(); i != e; ++i) {
+ Instruction *User = Insts[i];
+ 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 (!isInstInList(L, Insts)) 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 (!isInstInList(S, Insts)) 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 (unsigned i = 0, e = Insts.size(); i != e; ++i) {
+ Instruction *User = Insts[i];
+
+ // 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();
+ }
+}
More information about the llvm-commits
mailing list