//
// 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 file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Instructions.h"
+#include "llvm/LLVMContext.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/raw_ostream.h"
#include "llvm/Support/Debug.h"
#include "llvm/ADT/Statistic.h"
#include <algorithm>
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"));
+static cl::opt<bool>
+DisablePromotion("disable-licm-promotion", cl::Hidden,
+ cl::desc("Disable memory promotion in LICM pass"));
+
+// This feature is currently disabled by default because CodeGen is not yet
+// capable of rematerializing these constants in PIC mode, so it can lead to
+// degraded performance. Compile test/CodeGen/X86/remat-constant.ll with
+// -relocation-model=pic to see an example of this.
+static cl::opt<bool>
+EnableLICMConstantMotion("enable-licm-constant-variables", cl::Hidden,
+ cl::desc("Enable hoisting/sinking of constant "
+ "global variables"));
+namespace {
struct VISIBILITY_HIDDEN LICM : public LoopPass {
static char ID; // Pass identification, replacement for typeid
- LICM() : LoopPass((intptr_t)&ID) {}
+ LICM() : LoopPass(&ID) {}
virtual bool runOnLoop(Loop *L, LPPassManager &LPM);
std::vector<std::pair<AllocaInst*, Value*> > &PromotedValues,
std::map<Value*, AllocaInst*> &Val2AlMap);
};
-
- char LICM::ID = 0;
- RegisterPass<LICM> X("licm", "Loop Invariant Code Motion");
}
-LoopPass *llvm::createLICMPass() { return new LICM(); }
+char LICM::ID = 0;
+static RegisterPass<LICM> X("licm", "Loop Invariant Code Motion");
+
+Pass *llvm::createLICMPass() { return new LICM(); }
/// Hoist expressions out of the specified loop. Note, alias info for inner
/// loop is not preserved so it is not a good idea to run LICM multiple
// Because subloops have already been incorporated into AST, we skip blocks in
// subloops.
//
- 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...
- CurAST->add(**I); // Incorporate the specified basic block
+ for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
+ I != E; ++I) {
+ BasicBlock *BB = *I;
+ if (LI->getLoopFor(BB) == L) // Ignore blocks in subloops...
+ CurAST->add(*BB); // 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
if (LI->isVolatile())
return false; // Don't hoist volatile loads!
+ // Loads from constant memory are always safe to move, even if they end up
+ // in the same alias set as something that ends up being modified.
+ if (EnableLICMConstantMotion &&
+ AA->pointsToConstantMemory(LI->getOperand(0)))
+ return true;
+
// Don't hoist loads which have may-aliased stores in loop.
unsigned Size = 0;
if (LI->getType()->isSized())
- Size = AA->getTargetData().getTypeStoreSize(LI->getType());
+ Size = AA->getTypeStoreSize(LI->getType());
return !pointerInvalidatedByLoop(LI->getOperand(0), Size);
} else if (CallInst *CI = dyn_cast<CallInst>(&I)) {
// Handle obvious cases efficiently.
++NumSunk;
Changed = true;
+ LLVMContext &Context = I.getContext();
+
// The case where there is only a single exit node of this loop is common
// 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.
// Instruction is not used, just delete it.
CurAST->deleteValue(&I);
if (!I.use_empty()) // If I has users in unreachable blocks, eliminate.
- I.replaceAllUsesWith(UndefValue::get(I.getType()));
+ I.replaceAllUsesWith(Context.getUndef(I.getType()));
I.eraseFromParent();
} else {
// Move the instruction to the start of the exit block, after any PHI
// nodes in it.
I.removeFromParent();
- BasicBlock::iterator InsertPt = ExitBlocks[0]->begin();
- while (isa<PHINode>(InsertPt)) ++InsertPt;
+ BasicBlock::iterator InsertPt = ExitBlocks[0]->getFirstNonPHI();
ExitBlocks[0]->getInstList().insert(InsertPt, &I);
}
- } else if (ExitBlocks.size() == 0) {
+ } else if (ExitBlocks.empty()) {
// The instruction is actually dead if there ARE NO exit blocks.
CurAST->deleteValue(&I);
if (!I.use_empty()) // If I has users in unreachable blocks, eliminate.
- I.replaceAllUsesWith(UndefValue::get(I.getType()));
+ I.replaceAllUsesWith(Context.getUndef(I.getType()));
I.eraseFromParent();
} else {
// Otherwise, if we have multiple exits, use the PromoteMem2Reg function to
// If we haven't already processed this exit block, do so now.
if (InsertedBlocks.insert(ExitBlock).second) {
// Insert the code after the last PHI node...
- BasicBlock::iterator InsertPt = ExitBlock->begin();
- while (isa<PHINode>(InsertPt)) ++InsertPt;
+ BasicBlock::iterator InsertPt = ExitBlock->getFirstNonPHI();
// If this is the first exit block processed, just move the original
// instruction, otherwise clone the original instruction and insert
ExitBlock->getInstList().insert(InsertPt, &I);
New = &I;
} else {
- New = I.clone();
+ New = I.clone(Context);
CurAST->copyValue(&I, New);
if (!I.getName().empty())
New->setName(I.getName()+".le");
if (AI) {
std::vector<AllocaInst*> Allocas;
Allocas.push_back(AI);
- PromoteMemToReg(Allocas, *DT, *DF, CurAST);
+ PromoteMemToReg(Allocas, *DT, *DF, Context, CurAST);
}
}
}
/// that is safe to hoist, this instruction is called to do the dirty work.
///
void LICM::hoist(Instruction &I) {
- DOUT << "LICM hoisting to " << Preheader->getName() << ": " << I;
+ DEBUG(errs() << "LICM hoisting to " << Preheader->getName() << ": " << I);
// Remove the instruction from its current basic block... but don't delete the
// instruction.
///
bool LICM::isSafeToExecuteUnconditionally(Instruction &Inst) {
// If it is not a trapping instruction, it is always safe to hoist.
- if (!Inst.isTrapping()) return true;
+ if (Inst.isSafeToSpeculativelyExecute())
+ 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
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.
SmallVector<BasicBlock*, 8> ExitBlocks;
CurLoop->getExitBlocks(ExitBlocks);
// Scan the basic blocks in the loop, replacing uses of our pointers with
// uses of the allocas in question.
//
- const std::vector<BasicBlock*> &LoopBBs = CurLoop->getBlocks();
- for (std::vector<BasicBlock*>::const_iterator I = LoopBBs.begin(),
- E = LoopBBs.end(); I != E; ++I) {
+ for (Loop::block_iterator I = CurLoop->block_begin(),
+ E = CurLoop->block_end(); I != E; ++I) {
+ BasicBlock *BB = *I;
// Rewrite all loads and stores in the block of the pointer...
- for (BasicBlock::iterator II = (*I)->begin(), E = (*I)->end();
- II != E; ++II) {
+ for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E; ++II) {
if (LoadInst *L = dyn_cast<LoadInst>(II)) {
std::map<Value*, AllocaInst*>::iterator
I = ValueToAllocaMap.find(L->getOperand(0));
// want to insert one copy of the code in each exit block, though the loop may
// exit to the same block more than once.
//
- std::set<BasicBlock*> ProcessedBlocks;
+ SmallPtrSet<BasicBlock*, 16> ProcessedBlocks;
SmallVector<BasicBlock*, 8> ExitBlocks;
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.
- BasicBlock::iterator BI = ExitBlocks[i]->begin();
- while (isa<PHINode>(*BI))
- ++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.
- LoadInst *LI = new LoadInst(PromotedValues[i].first, "", InsertPos);
-
- // 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);
- }
+ for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
+ if (!ProcessedBlocks.insert(ExitBlocks[i]))
+ continue;
+
+ // Copy all of the allocas into their memory locations.
+ BasicBlock::iterator BI = ExitBlocks[i]->getFirstNonPHI();
+ Instruction *InsertPos = BI;
+ unsigned PVN = 0;
+ for (unsigned i = 0, e = PromotedValues.size(); i != e; ++i) {
+ // Load from the alloca.
+ LoadInst *LI = new LoadInst(PromotedValues[i].first, "", InsertPos);
+
+ // 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.
PromotedAllocas.reserve(PromotedValues.size());
for (unsigned i = 0, e = PromotedValues.size(); i != e; ++i)
PromotedAllocas.push_back(PromotedValues[i].first);
- PromoteMemToReg(PromotedAllocas, *DT, *DF, CurAST);
+ PromoteMemToReg(PromotedAllocas, *DT, *DF, Preheader->getContext(), CurAST);
}
/// FindPromotableValuesInLoop - Check the current loop for stores to definite
std::map<Value*, AllocaInst*> &ValueToAllocaMap) {
Instruction *FnStart = CurLoop->getHeader()->getParent()->begin()->begin();
- SmallVector<Instruction *, 4> LoopExits;
- SmallVector<BasicBlock *, 4> Blocks;
- CurLoop->getExitingBlocks(Blocks);
- for (SmallVector<BasicBlock *, 4>::iterator BI = Blocks.begin(),
- BE = Blocks.end(); BI != BE; ++BI) {
- BasicBlock *BB = *BI;
- LoopExits.push_back(BB->getTerminator());
- }
-
// Loop over all of the alias sets in the tracker object.
for (AliasSetTracker::iterator I = CurAST->begin(), E = CurAST->end();
I != E; ++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, 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)) {
- assert(!AS.empty() &&
- "Must alias set should have at least one pointer element in it!");
- Value *V = AS.begin()->first;
-
- // 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 (AS.isForwardingAliasSet() || !AS.isMod() || !AS.isMustAlias() ||
+ AS.isVolatile() || !CurLoop->isLoopInvariant(AS.begin()->getValue()))
+ continue;
+
+ assert(!AS.empty() &&
+ "Must alias set should have at least one pointer element in it!");
+ Value *V = AS.begin()->getValue();
+
+ // 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.
+ {
bool PointerOk = true;
for (AliasSet::iterator I = AS.begin(), E = AS.end(); I != E; ++I)
- if (V->getType() != I->first->getType()) {
+ if (V->getType() != I->getValue()->getType()) {
PointerOk = false;
break;
}
+ if (!PointerOk)
+ continue;
+ }
- // If one use of value V inside the loop is safe then it is OK to promote
- // this value. On the otherside if there is not any unsafe use inside the
- // loop then also it is OK to promote this value. Otherwise it is
- // unsafe to promote this value.
- if (PointerOk) {
- bool oneSafeUse = false;
- bool oneUnsafeUse = false;
- for(Value::use_iterator UI = V->use_begin(), UE = V->use_end();
- UI != UE; ++UI) {
- Instruction *Use = dyn_cast<Instruction>(*UI);
- if (!Use || !CurLoop->contains(Use->getParent()))
- continue;
- for (SmallVector<Instruction *, 4>::iterator
- ExitI = LoopExits.begin(), ExitE = LoopExits.end();
- ExitI != ExitE; ++ExitI) {
- Instruction *Ex = *ExitI;
- if (!isa<PHINode>(Use) && DT->dominates(Use, Ex)) {
- oneSafeUse = true;
- break;
- }
- else
- oneUnsafeUse = true;
- }
-
- if (oneSafeUse)
- break;
- }
-
- if (oneSafeUse)
- PointerOk = true;
- else if (!oneUnsafeUse)
- PointerOk = true;
- else
- PointerOk = false;
+ // It isn't safe to promote a load/store from the loop if the load/store is
+ // conditional. For example, turning:
+ //
+ // for () { if (c) *P += 1; }
+ //
+ // into:
+ //
+ // tmp = *P; for () { if (c) tmp +=1; } *P = tmp;
+ //
+ // is not safe, because *P may only be valid to access if 'c' is true.
+ //
+ // 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;
+ bool InvalidInst = false;
+ for (Value::use_iterator UI = V->use_begin(), UE = V->use_end();
+ UI != UE; ++UI) {
+ // Ignore instructions not in this loop.
+ Instruction *Use = dyn_cast<Instruction>(*UI);
+ if (!Use || !CurLoop->contains(Use->getParent()))
+ continue;
+
+ if (!isa<LoadInst>(Use) && !isa<StoreInst>(Use)) {
+ InvalidInst = true;
+ break;
}
- if (PointerOk) {
- 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));
+ if (!GuaranteedToExecute)
+ GuaranteedToExecute = isSafeToExecuteUnconditionally(*Use);
+ }
- // Update the AST and alias analysis.
- CurAST->copyValue(V, AI);
+ // If there is an non-load/store instruction in the loop, we can't promote
+ // it. If there isn't a guaranteed-to-execute instruction, we can't
+ // promote.
+ if (InvalidInst || !GuaranteedToExecute)
+ continue;
+
+ 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));
- for (AliasSet::iterator I = AS.begin(), E = AS.end(); I != E; ++I)
- ValueToAllocaMap.insert(std::make_pair(I->first, AI));
+ // Update the AST and alias analysis.
+ CurAST->copyValue(V, AI);
- DOUT << "LICM: Promoting value: " << *V << "\n";
- }
- }
+ for (AliasSet::iterator I = AS.begin(), E = AS.end(); I != E; ++I)
+ ValueToAllocaMap.insert(std::make_pair(I->getValue(), AI));
+
+ DOUT << "LICM: Promoting value: " << *V << "\n";
}
}
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