#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/Dominators.h"
-#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/SSAUpdater.h"
#include "llvm/Support/CFG.h"
AU.addRequiredID(LoopSimplifyID);
AU.addRequired<AliasAnalysis>();
AU.addPreserved<AliasAnalysis>();
- AU.addPreserved<ScalarEvolution>();
+ AU.addPreserved("scalar-evolution");
AU.addPreservedID(LoopSimplifyID);
}
///
bool inSubLoop(BasicBlock *BB) {
assert(CurLoop->contains(BB) && "Only valid if BB is IN the loop");
- for (Loop::iterator I = CurLoop->begin(), E = CurLoop->end(); I != E; ++I)
- if ((*I)->contains(BB))
- return true; // A subloop actually contains this block!
- return false;
- }
-
- /// isExitBlockDominatedByBlockInLoop - This method checks to see if the
- /// specified exit block of the loop is dominated by the specified block
- /// that is in the body of the loop. We use these constraints to
- /// dramatically limit the amount of the dominator tree that needs to be
- /// searched.
- bool isExitBlockDominatedByBlockInLoop(BasicBlock *ExitBlock,
- BasicBlock *BlockInLoop) const {
- // If the block in the loop is the loop header, it must be dominated!
- BasicBlock *LoopHeader = CurLoop->getHeader();
- if (BlockInLoop == LoopHeader)
- return true;
-
- DomTreeNode *BlockInLoopNode = DT->getNode(BlockInLoop);
- DomTreeNode *IDom = DT->getNode(ExitBlock);
-
- // Because the exit block is not in the loop, we know we have to get _at
- // least_ its immediate dominator.
- IDom = IDom->getIDom();
-
- while (IDom && IDom != BlockInLoopNode) {
- // If we have got to the header of the loop, then the instructions block
- // did not dominate the exit node, so we can't hoist it.
- if (IDom->getBlock() == LoopHeader)
- return false;
-
- // Get next Immediate Dominator.
- IDom = IDom->getIDom();
- };
-
- return true;
+ return LI->getLoopFor(BB) != CurLoop;
}
/// sink - When an instruction is found to only be used outside of the loop,
/// pointerInvalidatedByLoop - Return true if the body of this loop may
/// store into the memory location pointed to by V.
///
- bool pointerInvalidatedByLoop(Value *V, unsigned Size,
+ bool pointerInvalidatedByLoop(Value *V, uint64_t Size,
const MDNode *TBAAInfo) {
// Check to see if any of the basic blocks in CurLoop invalidate *V.
return CurAST->getAliasSetForPointer(V, Size, TBAAInfo).isMod();
return true;
// Don't hoist loads which have may-aliased stores in loop.
- unsigned Size = 0;
+ uint64_t Size = 0;
if (LI->getType()->isSized())
Size = AA->getTypeStoreSize(LI->getType());
return !pointerInvalidatedByLoop(LI->getOperand(0), Size,
LI->getMetadata(LLVMContext::MD_tbaa));
} else if (CallInst *CI = dyn_cast<CallInst>(&I)) {
- // Handle obvious cases efficiently.
+ // Don't sink or hoist dbg info; it's legal, but not useful.
+ if (isa<DbgInfoIntrinsic>(I))
+ return false;
+
+ // Handle simple cases by querying alias analysis.
AliasAnalysis::ModRefBehavior Behavior = AA->getModRefBehavior(CI);
if (Behavior == AliasAnalysis::DoesNotAccessMemory)
return true;
- else if (Behavior == AliasAnalysis::OnlyReadsMemory) {
+ if (AliasAnalysis::onlyReadsMemory(Behavior)) {
// If this call only reads from memory and there are no writes to memory
// in the loop, we can hoist or sink the call as appropriate.
bool FoundMod = false;
// enough that we handle it as a special (more efficient) case. It is more
// efficient to handle because there are no PHI nodes that need to be placed.
if (ExitBlocks.size() == 1) {
- if (!isExitBlockDominatedByBlockInLoop(ExitBlocks[0], I.getParent())) {
+ if (!DT->dominates(I.getParent(), ExitBlocks[0])) {
// Instruction is not used, just delete it.
CurAST->deleteValue(&I);
// If I has users in unreachable blocks, eliminate.
for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
BasicBlock *ExitBlock = ExitBlocks[i];
- if (!isExitBlockDominatedByBlockInLoop(ExitBlock, InstOrigBB))
+ if (!DT->dominates(InstOrigBB, ExitBlock))
continue;
// Insert the code after the last PHI node.
SmallVector<BasicBlock*, 8> ExitBlocks;
CurLoop->getExitBlocks(ExitBlocks);
- // For each exit block, get the DT node and walk up the DT until the
- // instruction's basic block is found or we exit the loop.
+ // Verify that the block dominates each of the exit blocks of the loop.
for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
- if (!isExitBlockDominatedByBlockInLoop(ExitBlocks[i], Inst.getParent()))
+ if (!DT->dominates(Inst.getParent(), ExitBlocks[i]))
return false;
return true;
}
+namespace {
+ class LoopPromoter : public LoadAndStorePromoter {
+ Value *SomePtr; // Designated pointer to store to.
+ SmallPtrSet<Value*, 4> &PointerMustAliases;
+ SmallVectorImpl<BasicBlock*> &LoopExitBlocks;
+ AliasSetTracker &AST;
+ DebugLoc DL;
+ int Alignment;
+ public:
+ LoopPromoter(Value *SP,
+ const SmallVectorImpl<Instruction*> &Insts, SSAUpdater &S,
+ SmallPtrSet<Value*, 4> &PMA,
+ SmallVectorImpl<BasicBlock*> &LEB, AliasSetTracker &ast,
+ DebugLoc dl, int alignment)
+ : LoadAndStorePromoter(Insts, S, 0, 0), SomePtr(SP),
+ PointerMustAliases(PMA), LoopExitBlocks(LEB), AST(ast), DL(dl),
+ Alignment(alignment) {}
+
+ virtual bool isInstInList(Instruction *I,
+ const SmallVectorImpl<Instruction*> &) const {
+ Value *Ptr;
+ if (LoadInst *LI = dyn_cast<LoadInst>(I))
+ Ptr = LI->getOperand(0);
+ else
+ Ptr = cast<StoreInst>(I)->getPointerOperand();
+ return PointerMustAliases.count(Ptr);
+ }
+
+ virtual void doExtraRewritesBeforeFinalDeletion() const {
+ // Insert stores after in the loop exit blocks. Each exit block gets a
+ // store of the live-out values that feed them. Since we've already told
+ // the SSA updater about the defs in the loop and the preheader
+ // definition, it is all set and we can start using it.
+ for (unsigned i = 0, e = LoopExitBlocks.size(); i != e; ++i) {
+ BasicBlock *ExitBlock = LoopExitBlocks[i];
+ Value *LiveInValue = SSA.GetValueInMiddleOfBlock(ExitBlock);
+ Instruction *InsertPos = ExitBlock->getFirstNonPHI();
+ StoreInst *NewSI = new StoreInst(LiveInValue, SomePtr, InsertPos);
+ NewSI->setAlignment(Alignment);
+ NewSI->setDebugLoc(DL);
+ }
+ }
+
+ virtual void replaceLoadWithValue(LoadInst *LI, Value *V) const {
+ // Update alias analysis.
+ AST.copyValue(LI, V);
+ }
+ virtual void instructionDeleted(Instruction *I) const {
+ AST.deleteValue(I);
+ }
+ };
+} // end anon namespace
+
/// PromoteAliasSet - Try to promote memory values to scalars by sinking
/// stores out of the loop and moving loads to before the loop. We do this by
/// looping over the stores in the loop, looking for stores to Must pointers
// It is safe to promote P if all uses are direct load/stores and if at
// least one is guaranteed to be executed.
bool GuaranteedToExecute = false;
-
+
SmallVector<Instruction*, 64> LoopUses;
SmallPtrSet<Value*, 4> PointerMustAliases;
+ // We start with an alignment of one and try to find instructions that allow
+ // us to prove better alignment.
+ unsigned Alignment = 1;
+
// Check that all of the pointers in the alias set have the same type. We
// cannot (yet) promote a memory location that is loaded and stored in
// different sizes.
// If there is an non-load/store instruction in the loop, we can't promote
// it.
- if (isa<LoadInst>(Use))
+ unsigned InstAlignment;
+ if (LoadInst *load = dyn_cast<LoadInst>(Use)) {
assert(!cast<LoadInst>(Use)->isVolatile() && "AST broken");
- else if (isa<StoreInst>(Use)) {
+ InstAlignment = load->getAlignment();
+ } else if (StoreInst *store = dyn_cast<StoreInst>(Use)) {
+ // Stores *of* the pointer are not interesting, only stores *to* the
+ // pointer.
+ if (Use->getOperand(1) != ASIV)
+ continue;
+ InstAlignment = store->getAlignment();
assert(!cast<StoreInst>(Use)->isVolatile() && "AST broken");
- if (Use->getOperand(0) == ASIV) return;
} else
return; // Not a load or store.
-
+
+ // If the alignment of this instruction allows us to specify a more
+ // restrictive (and performant) alignment and if we are sure this
+ // instruction will be executed, update the alignment.
+ // Larger is better, with the exception of 0 being the best alignment.
+ if ((InstAlignment > Alignment || InstAlignment == 0)
+ && (Alignment != 0))
+ if (isSafeToExecuteUnconditionally(*Use)) {
+ GuaranteedToExecute = true;
+ Alignment = InstAlignment;
+ }
+
if (!GuaranteedToExecute)
GuaranteedToExecute = isSafeToExecuteUnconditionally(*Use);
LoopUses.push_back(Use);
}
}
-
+
// If there isn't a guaranteed-to-execute instruction, we can't promote.
if (!GuaranteedToExecute)
return;
Changed = true;
++NumPromoted;
+ // Grab a debug location for the inserted loads/stores; given that the
+ // inserted loads/stores have little relation to the original loads/stores,
+ // this code just arbitrarily picks a location from one, since any debug
+ // location is better than none.
+ DebugLoc DL = LoopUses[0]->getDebugLoc();
+
+ SmallVector<BasicBlock*, 8> ExitBlocks;
+ CurLoop->getUniqueExitBlocks(ExitBlocks);
+
// We use the SSAUpdater interface to insert phi nodes as required.
SmallVector<PHINode*, 16> NewPHIs;
SSAUpdater SSA(&NewPHIs);
+ LoopPromoter Promoter(SomePtr, LoopUses, SSA, PointerMustAliases, ExitBlocks,
+ *CurAST, DL, Alignment);
- // It wants to know some value of the same type as what we'll be inserting.
- Value *SomeValue;
- if (isa<LoadInst>(LoopUses[0]))
- SomeValue = LoopUses[0];
- else
- SomeValue = cast<StoreInst>(LoopUses[0])->getOperand(0);
- SSA.Initialize(SomeValue->getType(), SomeValue->getName());
-
- // First step: bucket up uses of the pointers 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 usually 0/1 element.
- DenseMap<BasicBlock*, std::vector<Instruction*> > UsesByBlock;
- for (unsigned i = 0, e = LoopUses.size(); i != e; ++i) {
- Instruction *User = LoopUses[i];
- UsesByBlock[User->getParent()].push_back(User);
- }
-
- // Okay, now we can iterate over all the blocks in the loop with uses,
- // processing them. Keep track of which loads are loading a live-in value.
- SmallVector<LoadInst*, 32> LiveInLoads;
- DenseMap<Value*, Value*> ReplacedLoads;
-
- for (unsigned LoopUse = 0, e = LoopUses.size(); LoopUse != e; ++LoopUse) {
- Instruction *User = LoopUses[LoopUse];
- std::vector<Instruction*> &BlockUses = UsesByBlock[User->getParent()];
-
- // 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 (isa<StoreInst>(User)) {
- SSA.AddAvailableValue(User->getParent(),
- cast<StoreInst>(User)->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. If so, we can queue
- // them all as live in loads.
- bool HasStore = false;
- for (unsigned i = 0, e = BlockUses.size(); i != e; ++i) {
- if (isa<StoreInst>(BlockUses[i])) {
- HasStore = true;
- break;
- }
- }
-
- 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.
- BasicBlock *BB = User->getParent();
- 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 (!PointerMustAliases.count(L->getOperand(0))) 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 (!PointerMustAliases.count(S->getOperand(1))) 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();
- }
-
- // Now that all the intra-loop values are classified, set up the preheader.
- // It gets a load of the pointer we're promoting, and it is the live-out value
- // from the preheader.
- LoadInst *PreheaderLoad = new LoadInst(SomePtr,SomePtr->getName()+".promoted",
- Preheader->getTerminator());
+ // Set up the preheader to have a definition of the value. It is the live-out
+ // value from the preheader that uses in the loop will use.
+ LoadInst *PreheaderLoad =
+ new LoadInst(SomePtr, SomePtr->getName()+".promoted",
+ Preheader->getTerminator());
+ PreheaderLoad->setAlignment(Alignment);
+ PreheaderLoad->setDebugLoc(DL);
SSA.AddAvailableValue(Preheader, PreheaderLoad);
- // Now that the preheader is good to go, set up the exit blocks. Each exit
- // block gets a store of the live-out values that feed them. Since we've
- // already told the SSA updater about the defs in the loop and the preheader
- // definition, it is all set and we can start using it.
- SmallVector<BasicBlock*, 8> ExitBlocks;
- CurLoop->getUniqueExitBlocks(ExitBlocks);
- for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
- BasicBlock *ExitBlock = ExitBlocks[i];
- Value *LiveInValue = SSA.GetValueInMiddleOfBlock(ExitBlock);
- Instruction *InsertPos = ExitBlock->getFirstNonPHI();
- new StoreInst(LiveInValue, SomePtr, InsertPos);
- }
+ // Rewrite all the loads in the loop and remember all the definitions from
+ // stores in the loop.
+ Promoter.run(LoopUses);
- // 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);
- CurAST->copyValue(ALoad, NewVal);
- ReplacedLoads[ALoad] = NewVal;
- }
-
- // If the preheader load is itself a pointer, we need to tell alias analysis
- // about the new pointer we created in the preheader block and about any PHI
- // nodes that just got inserted.
- if (PreheaderLoad->getType()->isPointerTy()) {
- // Copy any value stored to or loaded from a must-alias of the pointer.
- CurAST->copyValue(SomeValue, PreheaderLoad);
-
- for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i)
- CurAST->copyValue(SomeValue, NewPHIs[i]);
- }
-
- // Now that everything is rewritten, delete the old instructions from the body
- // of the loop. They should all be dead now.
- for (unsigned i = 0, e = LoopUses.size(); i != e; ++i) {
- Instruction *User = LoopUses[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);
- CurAST->copyValue(User, NewVal);
- }
-
- CurAST->deleteValue(User);
- User->eraseFromParent();
- }
-
- // fwew, we're done!
+ // If the SSAUpdater didn't use the load in the preheader, just zap it now.
+ if (PreheaderLoad->use_empty())
+ PreheaderLoad->eraseFromParent();
}
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