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Generalize LoadAndStorePromoter a bit and switch LICM

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to use it.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@123501 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner
2011-01-15 00:12:35 +00:00
parent ca3f06963c
commit deaf55f698
4 changed files with 131 additions and 193 deletions
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lib/Transforms/Scalar/LICM.cpp
+70 -159
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@@ -595,6 +595,53 @@ bool LICM::isSafeToExecuteUnconditionally(Instruction &Inst) {
return true;
}
namespace {
class LoopPromoter : public LoadAndStorePromoter {
Value *SomePtr; // Designated pointer to store to.
SmallPtrSet<Value*, 4> &PointerMustAliases;
SmallVectorImpl<BasicBlock*> &LoopExitBlocks;
AliasSetTracker &AST;
public:
LoopPromoter(Value *SP,
const SmallVectorImpl<Instruction*> &Insts, SSAUpdater &S,
SmallPtrSet<Value*, 4> &PMA,
SmallVectorImpl<BasicBlock*> &LEB, AliasSetTracker &ast)
: LoadAndStorePromoter(Insts, S), SomePtr(SP), PointerMustAliases(PMA),
LoopExitBlocks(LEB), AST(ast) {}
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();
new StoreInst(LiveInValue, SomePtr, InsertPos);
}
}
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
@@ -679,179 +726,43 @@ void LICM::PromoteAliasSet(AliasSet &AS) {
Changed = true;
++NumPromoted;
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);
// 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());
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);
// Copy any value stored to or loaded from a must-alias of the pointer.
if (PreheaderLoad->getType()->isPointerTy()) {
Value *SomeValue;
if (LoadInst *LI = dyn_cast<LoadInst>(LoopUses[0]))
SomeValue = LI;
else
SomeValue = cast<StoreInst>(LoopUses[0])->getValueOperand();
CurAST->copyValue(SomeValue, PreheaderLoad);
}
// 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;
}
// Rewrite all the loads in the loop and remember all the definitions from
// stores in the loop.
Promoter.run(LoopUses);
// 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();
CurAST->copyValue(PreheaderLoad, NewPHIs[i]);
}
// fwew, we're done!