From 95294b879685dd36b59f77ce0d7fb821c854ef37 Mon Sep 17 00:00:00 2001 From: Chris Lattner Date: Fri, 14 Jan 2011 19:36:13 +0000 Subject: [PATCH] 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. llvm-svn: 123456 --- .../llvm/Transforms/Utils/SSAUpdater.h | 32 ++++ llvm/lib/Transforms/Utils/SSAUpdater.cpp | 154 ++++++++++++++++++ 2 files changed, 186 insertions(+) diff --git a/llvm/include/llvm/Transforms/Utils/SSAUpdater.h b/llvm/include/llvm/Transforms/Utils/SSAUpdater.h index e50a6b15df81..9e79aca50e6d 100644 --- a/llvm/include/llvm/Transforms/Utils/SSAUpdater.h +++ b/llvm/include/llvm/Transforms/Utils/SSAUpdater.h @@ -108,6 +108,38 @@ private: 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 &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 &Insts) const { + for (unsigned i = 0, e = Insts.size(); i != e; ++i) + if (Insts[i] == I) + return true; + return false; + } +}; } // End llvm namespace diff --git a/llvm/lib/Transforms/Utils/SSAUpdater.cpp b/llvm/lib/Transforms/Utils/SSAUpdater.cpp index 2b21fdf6678e..2ecae356ff96 100644 --- a/llvm/lib/Transforms/Utils/SSAUpdater.cpp +++ b/llvm/lib/Transforms/Utils/SSAUpdater.cpp @@ -343,3 +343,157 @@ Value *SSAUpdater::GetValueAtEndOfBlockInternal(BasicBlock *BB) { SSAUpdaterImpl Impl(this, &AvailableVals, InsertedPHIs); return Impl.GetValue(BB); } + +//===----------------------------------------------------------------------===// +// LoadAndStorePromoter Implementation +//===----------------------------------------------------------------------===// + +void LoadAndStorePromoter::run(StringRef BaseName, + const SmallVectorImpl &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(Insts[0])) + ValTy = LI->getType(); + else + ValTy = cast(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 since there is often 0/1 element. + DenseMap > 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 LiveInLoads; + DenseMap ReplacedLoads; + + for (unsigned i = 0, e = Insts.size(); i != e; ++i) { + Instruction *User = Insts[i]; + BasicBlock *BB = User->getParent(); + std::vector &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(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(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(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(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(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(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::iterator RLI = ReplacedLoads.find(NewVal); + while (RLI != ReplacedLoads.end()) { + NewVal = RLI->second; + RLI = ReplacedLoads.find(NewVal); + } + + User->replaceAllUsesWith(NewVal); + } + + User->eraseFromParent(); + } +} -- GitLab