//===-- LICM.cpp - Loop Invariant Code Motion Pass ------------------------===//
-//
+//
// The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
-//
+//
//===----------------------------------------------------------------------===//
//
// This pass performs loop invariant code motion, attempting to remove as much
//
//===----------------------------------------------------------------------===//
+#define DEBUG_TYPE "licm"
#include "llvm/Transforms/Scalar.h"
+#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Instructions.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/AliasSetTracker.h"
#include "llvm/Analysis/Dominators.h"
-#include "llvm/Support/CFG.h"
#include "llvm/Transforms/Utils/PromoteMemToReg.h"
-#include "llvm/Transforms/Utils/Local.h"
-#include "Support/CommandLine.h"
-#include "Support/Debug.h"
-#include "Support/Statistic.h"
+#include "llvm/Support/CFG.h"
+#include "llvm/Support/Compiler.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/ADT/Statistic.h"
#include <algorithm>
using namespace llvm;
+STATISTIC(NumSunk , "Number of instructions sunk out of loop");
+STATISTIC(NumHoisted , "Number of instructions hoisted out of loop");
+STATISTIC(NumMovedLoads, "Number of load insts hoisted or sunk");
+STATISTIC(NumMovedCalls, "Number of call insts hoisted or sunk");
+STATISTIC(NumPromoted , "Number of memory locations promoted to registers");
+
namespace {
cl::opt<bool>
DisablePromotion("disable-licm-promotion", cl::Hidden,
cl::desc("Disable memory promotion in LICM pass"));
- Statistic<> NumSunk("licm", "Number of instructions sunk out of loop");
- Statistic<> NumHoisted("licm", "Number of instructions hoisted out of loop");
- Statistic<> NumMovedLoads("licm", "Number of load insts hoisted or sunk");
- Statistic<> NumMovedCalls("licm", "Number of call insts hoisted or sunk");
- Statistic<> NumPromoted("licm",
- "Number of memory locations promoted to registers");
+ struct VISIBILITY_HIDDEN LICM : public LoopPass {
+ static char ID; // Pass identification, replacement for typeid
+ LICM() : LoopPass((intptr_t)&ID) {}
- struct LICM : public FunctionPass {
- virtual bool runOnFunction(Function &F);
+ virtual bool runOnLoop(Loop *L, LPPassManager &LPM);
/// This transformation requires natural loop information & requires that
/// loop preheaders be inserted into the CFG...
AU.addRequiredID(LoopSimplifyID);
AU.addRequired<LoopInfo>();
AU.addRequired<DominatorTree>();
+ AU.addRequired<ETForest>();
AU.addRequired<DominanceFrontier>(); // For scalar promotion (mem2reg)
AU.addRequired<AliasAnalysis>();
}
+ bool doFinalization() {
+ LoopToAliasMap.clear();
+ return false;
+ }
+
private:
// Various analyses that we use...
AliasAnalysis *AA; // Current AliasAnalysis information
LoopInfo *LI; // Current LoopInfo
+ ETForest *ET; // ETForest for the current loop..
DominatorTree *DT; // Dominator Tree for the current Loop...
DominanceFrontier *DF; // Current Dominance Frontier
BasicBlock *Preheader; // The preheader block of the current loop...
Loop *CurLoop; // The current loop we are working on...
AliasSetTracker *CurAST; // AliasSet information for the current loop...
-
- /// visitLoop - Hoist expressions out of the specified loop...
- ///
- void visitLoop(Loop *L, AliasSetTracker &AST);
+ std::map<Loop *, AliasSetTracker *> LoopToAliasMap;
/// SinkRegion - Walk the specified region of the CFG (defined by all blocks
/// dominated by the specified block, and that are in the current loop) in
BasicBlock *LoopHeader = CurLoop->getHeader();
if (BlockInLoop == LoopHeader)
return true;
-
+
DominatorTree::Node *BlockInLoopNode = DT->getNode(BlockInLoop);
DominatorTree::Node *IDom = DT->getNode(ExitBlock);
-
+
// Because the exit block is not in the loop, we know we have to get _at
// least_ its immediate dominator.
do {
// Get next Immediate Dominator.
IDom = IDom->getIDom();
-
+
// 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;
-
+
} while (IDom != BlockInLoopNode);
return true;
/// pointerInvalidatedByLoop - Return true if the body of this loop may
/// store into the memory location pointed to by V.
- ///
- bool pointerInvalidatedByLoop(Value *V) {
+ ///
+ bool pointerInvalidatedByLoop(Value *V, unsigned Size) {
// Check to see if any of the basic blocks in CurLoop invalidate *V.
- return CurAST->getAliasSetForPointer(V, 0).isMod();
+ return CurAST->getAliasSetForPointer(V, Size).isMod();
}
bool canSinkOrHoistInst(Instruction &I);
///
void PromoteValuesInLoop();
- /// findPromotableValuesInLoop - Check the current loop for stores to
+ /// FindPromotableValuesInLoop - Check the current loop for stores to
/// definite pointers, which are not loaded and stored through may aliases.
/// If these are found, create an alloca for the value, add it to the
/// PromotedValues list, and keep track of the mapping from value to
/// alloca...
///
- void findPromotableValuesInLoop(
+ void FindPromotableValuesInLoop(
std::vector<std::pair<AllocaInst*, Value*> > &PromotedValues,
std::map<Value*, AllocaInst*> &Val2AlMap);
};
- RegisterOpt<LICM> X("licm", "Loop Invariant Code Motion");
+ char LICM::ID = 0;
+ RegisterPass<LICM> X("licm", "Loop Invariant Code Motion");
}
-FunctionPass *llvm::createLICMPass() { return new LICM(); }
+LoopPass *llvm::createLICMPass() { return new LICM(); }
-/// runOnFunction - For LICM, this simply traverses the loop structure of the
-/// function, hoisting expressions out of loops if possible.
+/// Hoist expressions out of the specified loop...
///
-bool LICM::runOnFunction(Function &) {
+bool LICM::runOnLoop(Loop *L, LPPassManager &LPM) {
Changed = false;
// Get our Loop and Alias Analysis information...
AA = &getAnalysis<AliasAnalysis>();
DF = &getAnalysis<DominanceFrontier>();
DT = &getAnalysis<DominatorTree>();
-
- // Hoist expressions out of all of the top-level loops.
- for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I) {
- AliasSetTracker AST(*AA);
- visitLoop(*I, AST);
- }
- return Changed;
-}
-
-
-/// visitLoop - Hoist expressions out of the specified loop...
-///
-void LICM::visitLoop(Loop *L, AliasSetTracker &AST) {
- // Recurse through all subloops before we process this loop...
- for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I) {
- AliasSetTracker SubAST(*AA);
- visitLoop(*I, SubAST);
-
- // Incorporate information about the subloops into this loop...
- AST.add(SubAST);
+ ET = &getAnalysis<ETForest>();
+
+ CurAST = new AliasSetTracker(*AA);
+ // Collect Alias info from subloops
+ for (Loop::iterator LoopItr = L->begin(), LoopItrE = L->end();
+ LoopItr != LoopItrE; ++LoopItr) {
+ Loop *InnerL = *LoopItr;
+ AliasSetTracker *InnerAST = LoopToAliasMap[InnerL];
+ assert (InnerAST && "Where is my AST?");
+
+ // What if InnerLoop was modified by other passes ?
+ CurAST->add(*InnerAST);
}
+
CurLoop = L;
- CurAST = &AST;
// Get the preheader block to move instructions into...
Preheader = L->getLoopPreheader();
for (std::vector<BasicBlock*>::const_iterator I = L->getBlocks().begin(),
E = L->getBlocks().end(); I != E; ++I)
if (LI->getLoopFor(*I) == L) // Ignore blocks in subloops...
- AST.add(**I); // Incorporate the specified basic block
+ CurAST->add(**I); // Incorporate the specified basic block
// We want to visit all of the instructions in this loop... that are not parts
// of our subloops (they have already had their invariants hoisted out of
// Clear out loops state information for the next iteration
CurLoop = 0;
Preheader = 0;
+
+ LoopToAliasMap[L] = CurAST;
+ return Changed;
}
/// SinkRegion - Walk the specified region of the CFG (defined by all blocks
for (BasicBlock::iterator II = BB->end(); II != BB->begin(); ) {
Instruction &I = *--II;
-
+
// Check to see if we can sink this instruction to the exit blocks
// of the loop. We can do this if the all users of the instruction are
// outside of the loop. In this case, it doesn't even matter if the
// operands of the instruction are loop invariant.
//
- if (canSinkOrHoistInst(I) && isNotUsedInLoop(I)) {
+ if (isNotUsedInLoop(I) && canSinkOrHoistInst(I)) {
++II;
sink(I);
}
if (!inSubLoop(BB))
for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E; ) {
Instruction &I = *II++;
-
+
// Try hoisting the instruction out to the preheader. We can only do this
// if all of the operands of the instruction are loop invariant and if it
// is safe to hoist the instruction.
//
- if (isLoopInvariantInst(I) && canSinkOrHoistInst(I) &&
+ if (isLoopInvariantInst(I) && canSinkOrHoistInst(I) &&
isSafeToExecuteUnconditionally(I))
- hoist(I);
+ hoist(I);
}
const std::vector<DominatorTree::Node*> &Children = N->getChildren();
return false; // Don't hoist volatile loads!
// Don't hoist loads which have may-aliased stores in loop.
- return !pointerInvalidatedByLoop(LI->getOperand(0));
+ unsigned Size = 0;
+ if (LI->getType()->isSized())
+ Size = AA->getTargetData().getTypeSize(LI->getType());
+ return !pointerInvalidatedByLoop(LI->getOperand(0), Size);
} else if (CallInst *CI = dyn_cast<CallInst>(&I)) {
// Handle obvious cases efficiently.
if (Function *Callee = CI->getCalledFunction()) {
- if (AA->doesNotAccessMemory(Callee))
+ AliasAnalysis::ModRefBehavior Behavior =AA->getModRefBehavior(Callee, CI);
+ if (Behavior == AliasAnalysis::DoesNotAccessMemory)
return true;
- else if (AA->onlyReadsMemory(Callee)) {
+ else if (Behavior == AliasAnalysis::OnlyReadsMemory) {
// 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;
// FIXME: This should use mod/ref information to see if we can hoist or sink
// the call.
-
+
return false;
}
- return isa<BinaryOperator>(I) || isa<ShiftInst>(I) || isa<CastInst>(I) ||
- isa<SelectInst>(I) ||
- isa<GetElementPtrInst>(I) || isa<VANextInst>(I) || isa<VAArgInst>(I);
+ // Otherwise these instructions are hoistable/sinkable
+ return isa<BinaryOperator>(I) || isa<CastInst>(I) ||
+ isa<SelectInst>(I) || isa<GetElementPtrInst>(I) || isa<CmpInst>(I);
}
/// isNotUsedInLoop - Return true if the only users of this instruction are
/// position, and may either delete it or move it to outside of the loop.
///
void LICM::sink(Instruction &I) {
- DEBUG(std::cerr << "LICM sinking instruction: " << I);
+ DOUT << "LICM sinking instruction: " << I;
std::vector<BasicBlock*> ExitBlocks;
CurLoop->getExitBlocks(ExitBlocks);
if (!isExitBlockDominatedByBlockInLoop(ExitBlocks[0], I.getParent())) {
// Instruction is not used, just delete it.
CurAST->deleteValue(&I);
- I.getParent()->getInstList().erase(&I);
+ if (!I.use_empty()) // If I has users in unreachable blocks, eliminate.
+ I.replaceAllUsesWith(UndefValue::get(I.getType()));
+ I.eraseFromParent();
} else {
// Move the instruction to the start of the exit block, after any PHI
// nodes in it.
- I.getParent()->getInstList().remove(&I);
-
+ I.removeFromParent();
+
BasicBlock::iterator InsertPt = ExitBlocks[0]->begin();
while (isa<PHINode>(InsertPt)) ++InsertPt;
ExitBlocks[0]->getInstList().insert(InsertPt, &I);
} else if (ExitBlocks.size() == 0) {
// The instruction is actually dead if there ARE NO exit blocks.
CurAST->deleteValue(&I);
- I.getParent()->getInstList().erase(&I);
+ if (!I.use_empty()) // If I has users in unreachable blocks, eliminate.
+ I.replaceAllUsesWith(UndefValue::get(I.getType()));
+ I.eraseFromParent();
} else {
// Otherwise, if we have multiple exits, use the PromoteMem2Reg function to
// do all of the hard work of inserting PHI nodes as necessary. We convert
// the value into a stack object to get it to do this.
// Firstly, we create a stack object to hold the value...
- AllocaInst *AI = new AllocaInst(I.getType(), 0, I.getName(),
- I.getParent()->getParent()->front().begin());
+ AllocaInst *AI = 0;
+
+ if (I.getType() != Type::VoidTy) {
+ AI = new AllocaInst(I.getType(), 0, I.getName(),
+ I.getParent()->getParent()->getEntryBlock().begin());
+ CurAST->add(AI);
+ }
// Secondly, insert load instructions for each use of the instruction
// outside of the loop.
// Insert a new load instruction right before the terminator in
// the predecessor block.
PredVal = new LoadInst(AI, "", Pred->getTerminator());
+ CurAST->add(cast<LoadInst>(PredVal));
}
UPN->setIncomingValue(i, PredVal);
} else {
LoadInst *L = new LoadInst(AI, "", U);
U->replaceUsesOfWith(&I, L);
+ CurAST->add(L);
}
}
// Insert the code after the last PHI node...
BasicBlock::iterator InsertPt = ExitBlock->begin();
while (isa<PHINode>(InsertPt)) ++InsertPt;
-
+
// If this is the first exit block processed, just move the original
// instruction, otherwise clone the original instruction and insert
// the copy.
Instruction *New;
if (InsertedBlocks.size() == 1) {
- I.getParent()->getInstList().remove(&I);
+ I.removeFromParent();
ExitBlock->getInstList().insert(InsertPt, &I);
New = &I;
} else {
New = I.clone();
- New->setName(I.getName()+".le");
+ CurAST->copyValue(&I, New);
+ if (!I.getName().empty())
+ New->setName(I.getName()+".le");
ExitBlock->getInstList().insert(InsertPt, New);
}
-
+
// Now that we have inserted the instruction, store it into the alloca
- new StoreInst(New, AI, InsertPt);
+ if (AI) new StoreInst(New, AI, InsertPt);
}
}
}
// If the instruction doesn't dominate any exit blocks, it must be dead.
if (InsertedBlocks.empty()) {
CurAST->deleteValue(&I);
- I.getParent()->getInstList().erase(&I);
+ I.eraseFromParent();
}
-
+
// Finally, promote the fine value to SSA form.
- std::vector<AllocaInst*> Allocas;
- Allocas.push_back(AI);
- PromoteMemToReg(Allocas, *DT, *DF, AA->getTargetData());
+ if (AI) {
+ std::vector<AllocaInst*> Allocas;
+ Allocas.push_back(AI);
+ PromoteMemToReg(Allocas, *ET, *DF, CurAST);
+ }
}
}
/// that is safe to hoist, this instruction is called to do the dirty work.
///
void LICM::hoist(Instruction &I) {
- DEBUG(std::cerr << "LICM hoisting to " << Preheader->getName()
- << ": " << I);
+ DOUT << "LICM hoisting to " << Preheader->getName() << ": " << I;
// Remove the instruction from its current basic block... but don't delete the
// instruction.
- I.getParent()->getInstList().remove(&I);
+ I.removeFromParent();
// Insert the new node in Preheader, before the terminator.
Preheader->getInstList().insert(Preheader->getTerminator(), &I);
-
+
if (isa<LoadInst>(I)) ++NumMovedLoads;
else if (isa<CallInst>(I)) ++NumMovedCalls;
++NumHoisted;
bool LICM::isSafeToExecuteUnconditionally(Instruction &Inst) {
// If it is not a trapping instruction, it is always safe to hoist.
if (!Inst.isTrapping()) return true;
-
+
// Otherwise we have to check to make sure that the instruction dominates all
// of the exit blocks. If it doesn't, then there is a path out of the loop
// which does not execute this instruction, so we can't hoist it.
if (Inst.getParent() == CurLoop->getHeader())
return true;
+ // It's always safe to load from a global or alloca.
+ if (isa<LoadInst>(Inst))
+ if (isa<AllocationInst>(Inst.getOperand(0)) ||
+ isa<GlobalVariable>(Inst.getOperand(0)))
+ return true;
+
// Get the exit blocks for the current loop.
std::vector<BasicBlock*> ExitBlocks;
CurLoop->getExitBlocks(ExitBlocks);
for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
if (!isExitBlockDominatedByBlockInLoop(ExitBlocks[i], Inst.getParent()))
return false;
-
+
return true;
}
std::vector<std::pair<AllocaInst*, Value*> > PromotedValues;
std::map<Value*, AllocaInst*> ValueToAllocaMap; // Map of ptr to alloca
- findPromotableValuesInLoop(PromotedValues, ValueToAllocaMap);
- if (ValueToAllocaMap.empty()) return; // If there are values to promote...
+ FindPromotableValuesInLoop(PromotedValues, ValueToAllocaMap);
+ if (ValueToAllocaMap.empty()) return; // If there are values to promote.
Changed = true;
NumPromoted += PromotedValues.size();
+ std::vector<Value*> PointerValueNumbers;
+
// Emit a copy from the value into the alloca'd value in the loop preheader
TerminatorInst *LoopPredInst = Preheader->getTerminator();
for (unsigned i = 0, e = PromotedValues.size(); i != e; ++i) {
- // Load from the memory we are promoting...
- LoadInst *LI = new LoadInst(PromotedValues[i].second,
- PromotedValues[i].second->getName()+".promoted",
- LoopPredInst);
- // Store into the temporary alloca...
+ Value *Ptr = PromotedValues[i].second;
+
+ // If we are promoting a pointer value, update alias information for the
+ // inserted load.
+ Value *LoadValue = 0;
+ if (isa<PointerType>(cast<PointerType>(Ptr->getType())->getElementType())) {
+ // Locate a load or store through the pointer, and assign the same value
+ // to LI as we are loading or storing. Since we know that the value is
+ // stored in this loop, this will always succeed.
+ for (Value::use_iterator UI = Ptr->use_begin(), E = Ptr->use_end();
+ UI != E; ++UI)
+ if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
+ LoadValue = LI;
+ break;
+ } else if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
+ if (SI->getOperand(1) == Ptr) {
+ LoadValue = SI->getOperand(0);
+ break;
+ }
+ }
+ assert(LoadValue && "No store through the pointer found!");
+ PointerValueNumbers.push_back(LoadValue); // Remember this for later.
+ }
+
+ // Load from the memory we are promoting.
+ LoadInst *LI = new LoadInst(Ptr, Ptr->getName()+".promoted", LoopPredInst);
+
+ if (LoadValue) CurAST->copyValue(LoadValue, LI);
+
+ // Store into the temporary alloca.
new StoreInst(LI, PromotedValues[i].first, LoopPredInst);
}
-
+
// Scan the basic blocks in the loop, replacing uses of our pointers with
// uses of the allocas in question.
//
CurLoop->getExitBlocks(ExitBlocks);
for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
if (ProcessedBlocks.insert(ExitBlocks[i]).second) {
- // Copy all of the allocas into their memory locations...
+ // Copy all of the allocas into their memory locations.
BasicBlock::iterator BI = ExitBlocks[i]->begin();
while (isa<PHINode>(*BI))
- ++BI; // Skip over all of the phi nodes in the block...
+ ++BI; // Skip over all of the phi nodes in the block.
Instruction *InsertPos = BI;
+ unsigned PVN = 0;
for (unsigned i = 0, e = PromotedValues.size(); i != e; ++i) {
- // Load from the alloca...
+ // Load from the alloca.
LoadInst *LI = new LoadInst(PromotedValues[i].first, "", InsertPos);
- // Store into the memory we promoted...
+
+ // If this is a pointer type, update alias info appropriately.
+ if (isa<PointerType>(LI->getType()))
+ CurAST->copyValue(PointerValueNumbers[PVN++], LI);
+
+ // Store into the memory we promoted.
new StoreInst(LI, PromotedValues[i].second, InsertPos);
}
}
// Now that we have done the deed, use the mem2reg functionality to promote
- // all of the new allocas we just created into real SSA registers...
+ // all of the new allocas we just created into real SSA registers.
//
std::vector<AllocaInst*> PromotedAllocas;
PromotedAllocas.reserve(PromotedValues.size());
for (unsigned i = 0, e = PromotedValues.size(); i != e; ++i)
PromotedAllocas.push_back(PromotedValues[i].first);
- PromoteMemToReg(PromotedAllocas, *DT, *DF, AA->getTargetData());
+ PromoteMemToReg(PromotedAllocas, *ET, *DF, CurAST);
}
-/// findPromotableValuesInLoop - Check the current loop for stores to definite
+/// FindPromotableValuesInLoop - Check the current loop for stores to definite
/// pointers, which are not loaded and stored through may aliases. If these are
/// found, create an alloca for the value, add it to the PromotedValues list,
-/// and keep track of the mapping from value to alloca...
+/// and keep track of the mapping from value to alloca.
///
-void LICM::findPromotableValuesInLoop(
+void LICM::FindPromotableValuesInLoop(
std::vector<std::pair<AllocaInst*, Value*> > &PromotedValues,
std::map<Value*, AllocaInst*> &ValueToAllocaMap) {
Instruction *FnStart = CurLoop->getHeader()->getParent()->begin()->begin();
- // Loop over all of the alias sets in the tracker object...
+ // Loop over all of the alias sets in the tracker object.
for (AliasSetTracker::iterator I = CurAST->begin(), E = CurAST->end();
I != E; ++I) {
AliasSet &AS = *I;
// We can promote this alias set if it has a store, if it is a "Must" alias
- // set, if the pointer is loop invariant, if if we are not eliminating any
+ // set, if the pointer is loop invariant, and if we are not eliminating any
// volatile loads or stores.
if (!AS.isForwardingAliasSet() && AS.isMod() && AS.isMustAlias() &&
!AS.isVolatile() && CurLoop->isLoopInvariant(AS.begin()->first)) {
const Type *Ty = cast<PointerType>(V->getType())->getElementType();
AllocaInst *AI = new AllocaInst(Ty, 0, V->getName()+".tmp", FnStart);
PromotedValues.push_back(std::make_pair(AI, V));
-
+
+ // Update the AST and alias analysis.
+ CurAST->copyValue(V, AI);
+
for (AliasSet::iterator I = AS.begin(), E = AS.end(); I != E; ++I)
ValueToAllocaMap.insert(std::make_pair(I->first, AI));
-
- DEBUG(std::cerr << "LICM: Promoting value: " << *V << "\n");
+
+ DOUT << "LICM: Promoting value: " << *V << "\n";
}
}
}
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