//===-- LICM.cpp - Loop Invariant Code Motion Pass ------------------------===//
+//
+// The LLVM Compiler Infrastructure
//
-// This pass is a simple loop invariant code motion pass. An interesting aspect
-// of this pass is that it uses alias analysis for two purposes:
+// 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
+// code from the body of a loop as possible. It does this by either hoisting
+// code into the preheader block, or by sinking code to the exit blocks if it is
+// safe. This pass also promotes must-aliased memory locations in the loop to
+// live in registers.
+//
+// This pass uses alias analysis for two purposes:
//
// 1. Moving loop invariant loads out of loops. If we can determine that a
// load inside of a loop never aliases anything stored to, we can hoist it
-// like any other instruction.
+// or sink it like any other instruction.
// 2. Scalar Promotion of Memory - If there is a store instruction inside of
// the loop, we try to move the store to happen AFTER the loop instead of
// inside of the loop. This can only happen if a few conditions are true:
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Analysis/AliasSetTracker.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Instructions.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Target/TargetData.h"
-#include "llvm/Support/InstVisitor.h"
#include "llvm/Support/CFG.h"
-#include "Support/Statistic.h"
#include "Support/CommandLine.h"
+#include "Support/Debug.h"
+#include "Support/Statistic.h"
#include "llvm/Assembly/Writer.h"
#include <algorithm>
+using namespace llvm;
namespace {
- cl::opt<bool> DisablePromotion("disable-licm-promotion", cl::Hidden,
- cl::desc("Disable memory promotion in LICM pass"));
+ 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<> NumHoistedLoads("licm", "Number of load insts hoisted");
- Statistic<> NumPromoted("licm", "Number of memory locations promoted to registers");
-
- /// LoopBodyInfo - We recursively traverse loops from most-deeply-nested to
- /// least-deeply-nested. For all of the loops nested within the current one,
- /// we keep track of information so that we don't have to repeat queries.
- ///
- struct LoopBodyInfo {
- std::vector<CallInst*> Calls; // Call instructions in loop
- std::vector<InvokeInst*> Invokes; // Invoke instructions in loop
-
- // StoredPointers - Targets of store instructions...
- std::set<Value*> StoredPointers;
-
- // LoadedPointers - Source pointers for load instructions...
- std::set<Value*> LoadedPointers;
-
- enum PointerClass {
- PointerUnknown = 0, // Nothing is known about this pointer yet
- PointerMustStore, // Memory is stored to ONLY through this pointer
- PointerMayStore, // Memory is stored to through this or other pointers
- PointerNoStore // Memory is not modified in this loop
- };
-
- // PointerIsModified - Keep track of information as we find out about it in
- // the loop body...
- //
- std::map<Value*, enum PointerClass> PointerIsModified;
-
- /// CantModifyAnyPointers - Return true if no memory modifying instructions
- /// occur in this loop. This is just a conservative approximation, because
- /// a call may not actually store anything.
- bool CantModifyAnyPointers() const {
- return Calls.empty() && Invokes.empty() && StoredPointers.empty();
- }
-
- /// incorporate - Incorporate information about a subloop into the current
- /// loop.
- void incorporate(const LoopBodyInfo &OtherLBI);
- void incorporate(BasicBlock &BB); // do the same for a basic block
-
- PointerClass getPointerInfo(Value *V, AliasAnalysis &AA) {
- PointerClass &VInfo = PointerIsModified[V];
- if (VInfo == PointerUnknown)
- VInfo = calculatePointerInfo(V, AA);
- return VInfo;
- }
- private:
- /// calculatePointerInfo - Calculate information about the specified
- /// pointer.
- PointerClass calculatePointerInfo(Value *V, AliasAnalysis &AA) const;
- };
-}
+ Statistic<> NumMovedLoads("licm", "Number of load insts hoisted or sunk");
+ Statistic<> NumPromoted("licm",
+ "Number of memory locations promoted to registers");
-/// incorporate - Incorporate information about a subloop into the current loop.
-void LoopBodyInfo::incorporate(const LoopBodyInfo &OtherLBI) {
- // Do not incorporate NonModifiedPointers (which is just a cache) because it
- // is too much trouble to make sure it's still valid.
- Calls.insert (Calls.end(), OtherLBI.Calls.begin(), OtherLBI.Calls.end());
- Invokes.insert(Invokes.end(),OtherLBI.Invokes.begin(),OtherLBI.Invokes.end());
- StoredPointers.insert(OtherLBI.StoredPointers.begin(),
- OtherLBI.StoredPointers.end());
- LoadedPointers.insert(OtherLBI.LoadedPointers.begin(),
- OtherLBI.LoadedPointers.end());
-}
-
-void LoopBodyInfo::incorporate(BasicBlock &BB) {
- for (BasicBlock::iterator I = BB.begin(), E = --BB.end(); I != E; ++I)
- if (CallInst *CI = dyn_cast<CallInst>(&*I))
- Calls.push_back(CI);
- else if (StoreInst *SI = dyn_cast<StoreInst>(&*I))
- StoredPointers.insert(SI->getOperand(1));
- else if (LoadInst *LI = dyn_cast<LoadInst>(&*I))
- LoadedPointers.insert(LI->getOperand(0));
-
- if (InvokeInst *II = dyn_cast<InvokeInst>(BB.getTerminator()))
- Invokes.push_back(II);
-}
-
-
-// calculatePointerInfo - Calculate information about the specified pointer.
-LoopBodyInfo::PointerClass LoopBodyInfo::calculatePointerInfo(Value *V,
- AliasAnalysis &AA) const {
- for (unsigned i = 0, e = Calls.size(); i != e; ++i)
- if (AA.getModRefInfo(Calls[i], V, ~0))
- return PointerMayStore;
-
- for (unsigned i = 0, e = Invokes.size(); i != e; ++i)
- if (AA.getModRefInfo(Invokes[i], V, ~0))
- return PointerMayStore;
-
- PointerClass Result = PointerNoStore;
- for (std::set<Value*>::const_iterator I = StoredPointers.begin(),
- E = StoredPointers.end(); I != E; ++I)
- if (AA.alias(V, ~0, *I, ~0))
- if (V == *I)
- Result = PointerMustStore; // If this is the only alias, return must
- else
- return PointerMayStore; // We have to return may
- return Result;
-}
-
-namespace {
- struct LICM : public FunctionPass, public InstVisitor<LICM> {
+ struct LICM : public FunctionPass {
virtual bool runOnFunction(Function &F);
/// This transformation requires natural loop information & requires that
///
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
- AU.addRequiredID(LoopPreheadersID);
+ AU.addRequiredID(LoopSimplifyID);
AU.addRequired<LoopInfo>();
AU.addRequired<DominatorTree>();
- AU.addRequired<DominanceFrontier>();
+ AU.addRequired<DominanceFrontier>(); // For scalar promotion (mem2reg)
AU.addRequired<AliasAnalysis>();
}
private:
- LoopInfo *LI; // Current LoopInfo
+ // Various analyses that we use...
AliasAnalysis *AA; // Current AliasAnalysis information
+ LoopInfo *LI; // Current LoopInfo
+ DominatorTree *DT; // Dominator Tree for the current Loop...
+ DominanceFrontier *DF; // Current Dominance Frontier
+
+ // State that is updated as we process loops
bool Changed; // Set to true when we change anything.
BasicBlock *Preheader; // The preheader block of the current loop...
Loop *CurLoop; // The current loop we are working on...
- LoopBodyInfo *CurLBI; // Information about the current loop...
+ AliasSetTracker *CurAST; // AliasSet information for the current loop...
/// visitLoop - Hoist expressions out of the specified loop...
///
- void visitLoop(Loop *L, LoopBodyInfo &LBI);
+ void visitLoop(Loop *L, AliasSetTracker &AST);
/// HoistRegion - Walk the specified region of the CFG (defined by all
/// blocks dominated by the specified block, and that are in the current
/// loop) in depth first order w.r.t the DominatorTree. This allows us to
- /// visit defintions before uses, allowing us to hoist a loop body in one
+ /// visit definitions before uses, allowing us to hoist a loop body in one
/// pass without iteration.
///
void HoistRegion(DominatorTree::Node *N);
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;
+
+ 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_ it's 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;
+ }
+
+ /// sink - When an instruction is found to only be used outside of the loop,
+ /// this function moves it to the exit blocks and patches up SSA form as
+ /// needed.
+ ///
+ void sink(Instruction &I);
+
/// hoist - When an instruction is found to only use loop invariant operands
/// that is safe to hoist, this instruction is called to do the dirty work.
///
void hoist(Instruction &I);
+ /// isSafeToExecuteUnconditionally - Only sink or hoist an instruction if it
+ /// is not a trapping instruction or if it is a trapping instruction and is
+ /// guaranteed to execute.
+ ///
+ bool isSafeToExecuteUnconditionally(Instruction &I);
+
/// pointerInvalidatedByLoop - Return true if the body of this loop may
/// store into the memory location pointed to by V.
///
bool pointerInvalidatedByLoop(Value *V) {
- // Check to see if any of the basic blocks in CurLoop invalidate V.
- return CurLBI->getPointerInfo(V, *AA) != LoopBodyInfo::PointerNoStore;
+ // Check to see if any of the basic blocks in CurLoop invalidate *V.
+ return CurAST->getAliasSetForPointer(V, 0).isMod();
}
/// isLoopInvariant - Return true if the specified value is loop invariant
return true; // All non-instructions are loop invariant
}
+ bool canSinkOrHoistInst(Instruction &I);
+ bool isLoopInvariantInst(Instruction &I);
+ bool isNotUsedInLoop(Instruction &I);
+
/// PromoteValuesInLoop - Look at the stores in the loop and promote as many
/// to scalars as we can.
///
void PromoteValuesInLoop();
/// findPromotableValuesInLoop - Check the current loop for stores to
- /// definate pointers, which are not loaded and stored through may aliases.
+ /// 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(
std::vector<std::pair<AllocaInst*, Value*> > &PromotedValues,
std::map<Value*, AllocaInst*> &Val2AlMap);
-
-
- /// Instruction visitation handlers... these basically control whether or
- /// not the specified instruction types are hoisted.
- ///
- friend class InstVisitor<LICM>;
- void visitBinaryOperator(Instruction &I) {
- if (isLoopInvariant(I.getOperand(0)) && isLoopInvariant(I.getOperand(1)))
- hoist(I);
- }
- void visitCastInst(CastInst &CI) {
- Instruction &I = (Instruction&)CI;
- if (isLoopInvariant(I.getOperand(0))) hoist(I);
- }
- void visitShiftInst(ShiftInst &I) { visitBinaryOperator((Instruction&)I); }
-
- void visitLoadInst(LoadInst &LI);
-
- void visitGetElementPtrInst(GetElementPtrInst &GEPI) {
- Instruction &I = (Instruction&)GEPI;
- for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i)
- if (!isLoopInvariant(I.getOperand(i))) return;
- hoist(I);
- }
};
RegisterOpt<LICM> X("licm", "Loop Invariant Code Motion");
}
-Pass *createLICMPass() { return new LICM(); }
+FunctionPass *llvm::createLICMPass() { return new LICM(); }
/// runOnFunction - For LICM, this simply traverses the loop structure of the
/// function, hoisting expressions out of loops if possible.
// Get our Loop and Alias Analysis information...
LI = &getAnalysis<LoopInfo>();
AA = &getAnalysis<AliasAnalysis>();
+ DF = &getAnalysis<DominanceFrontier>();
+ DT = &getAnalysis<DominatorTree>();
// Hoist expressions out of all of the top-level loops.
const std::vector<Loop*> &TopLevelLoops = LI->getTopLevelLoops();
for (std::vector<Loop*>::const_iterator I = TopLevelLoops.begin(),
E = TopLevelLoops.end(); I != E; ++I) {
- LoopBodyInfo LBI;
- LICM::visitLoop(*I, LBI);
+ AliasSetTracker AST(*AA);
+ visitLoop(*I, AST);
}
return Changed;
}
/// visitLoop - Hoist expressions out of the specified loop...
///
-void LICM::visitLoop(Loop *L, LoopBodyInfo &LBI) {
+void LICM::visitLoop(Loop *L, AliasSetTracker &AST) {
// Recurse through all subloops before we process this loop...
for (std::vector<Loop*>::const_iterator I = L->getSubLoops().begin(),
E = L->getSubLoops().end(); I != E; ++I) {
- LoopBodyInfo SubLBI;
- LICM::visitLoop(*I, SubLBI);
+ AliasSetTracker SubAST(*AA);
+ visitLoop(*I, SubAST);
// Incorporate information about the subloops into this loop...
- LBI.incorporate(SubLBI);
+ AST.add(SubAST);
}
CurLoop = L;
- CurLBI = &LBI;
+ CurAST = &AST;
// Get the preheader block to move instructions into...
Preheader = L->getLoopPreheader();
assert(Preheader&&"Preheader insertion pass guarantees we have a preheader!");
// Loop over the body of this loop, looking for calls, invokes, and stores.
- // Because subloops have already been incorporated into LBI, we skip blocks in
+ // Because subloops have already been incorporated into AST, we skip blocks in
// subloops.
//
- const std::vector<BasicBlock*> &LoopBBs = L->getBlocks();
- for (std::vector<BasicBlock*>::const_iterator I = LoopBBs.begin(),
- E = LoopBBs.end(); I != E; ++I)
+ 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...
- LBI.incorporate(**I); // Incorporate the specified basic block
+ AST.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
// that we are guaranteed to see definitions before we see uses. This allows
// us to perform the LICM transformation in one pass, without iteration.
//
- HoistRegion(getAnalysis<DominatorTree>()[L->getHeader()]);
+ HoistRegion(DT->getNode(L->getHeader()));
// Now that all loop invariants have been removed from the loop, promote any
// memory references to scalars that we can...
/// HoistRegion - Walk the specified region of the CFG (defined by all blocks
/// dominated by the specified block, and that are in the current loop) in depth
-/// first order w.r.t the DominatorTree. This allows us to visit defintions
+/// first order w.r.t the DominatorTree. This allows us to visit definitions
/// before uses, allowing us to hoist a loop body in one pass without iteration.
///
void LICM::HoistRegion(DominatorTree::Node *N) {
assert(N != 0 && "Null dominator tree node?");
+ BasicBlock *BB = N->getBlock();
// If this subregion is not in the top level loop at all, exit.
- if (!CurLoop->contains(N->getNode())) return;
-
- // Only need to hoist the contents of this block if it is not part of a
- // subloop (which would already have been hoisted)
- if (!inSubLoop(N->getNode()))
- visit(*N->getNode());
+ if (!CurLoop->contains(BB)) return;
+
+ // Only need to process the contents of this block if it is not part of a
+ // subloop (which would already have been processed).
+ if (!inSubLoop(BB))
+ for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E; ) {
+ Instruction &I = *II++;
+
+ // We can only handle simple expressions and loads with this code.
+ if (canSinkOrHoistInst(I)) {
+ // First check to see if we can sink this instruction to the exit blocks
+ // of the loop. We can do this if the only 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 (isNotUsedInLoop(I))
+ sink(I);
+
+ // If we can't sink the instruction, try hoisting it 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.
+ //
+ else if (isLoopInvariantInst(I) && isSafeToExecuteUnconditionally(I))
+ hoist(I);
+ }
+ }
const std::vector<DominatorTree::Node*> &Children = N->getChildren();
for (unsigned i = 0, e = Children.size(); i != e; ++i)
HoistRegion(Children[i]);
}
+/// canSinkOrHoistInst - Return true if the hoister and sinker can handle this
+/// instruction.
+///
+bool LICM::canSinkOrHoistInst(Instruction &I) {
+ // Loads have extra constraints we have to verify before we can hoist them.
+ if (LoadInst *LI = dyn_cast<LoadInst>(&I)) {
+ if (LI->isVolatile())
+ return false; // Don't hoist volatile loads!
+
+ // Don't hoist loads which have may-aliased stores in loop.
+ return !pointerInvalidatedByLoop(LI->getOperand(0));
+ }
+
+ return isa<BinaryOperator>(I) || isa<ShiftInst>(I) || isa<CastInst>(I) ||
+ isa<GetElementPtrInst>(I) || isa<VANextInst>(I) || isa<VAArgInst>(I);
+}
+
+/// isNotUsedInLoop - Return true if the only users of this instruction are
+/// outside of the loop. If this is true, we can sink the instruction to the
+/// exit blocks of the loop.
+///
+bool LICM::isNotUsedInLoop(Instruction &I) {
+ for (Value::use_iterator UI = I.use_begin(), E = I.use_end(); UI != E; ++UI)
+ if (CurLoop->contains(cast<Instruction>(*UI)->getParent()))
+ return false;
+ return true;
+}
+
+
+/// isLoopInvariantInst - Return true if all operands of this instruction are
+/// loop invariant. We also filter out non-hoistable instructions here just for
+/// efficiency.
+///
+bool LICM::isLoopInvariantInst(Instruction &I) {
+ // The instruction is loop invariant if all of its operands are loop-invariant
+ for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i)
+ if (!isLoopInvariant(I.getOperand(i)))
+ return false;
+
+ // If we got this far, the instruction is loop invariant!
+ return true;
+}
+
+/// sink - When an instruction is found to only be used outside of the loop,
+/// this function moves it to the exit blocks and patches up SSA form as
+/// needed.
+///
+void LICM::sink(Instruction &I) {
+ DEBUG(std::cerr << "LICM sinking instruction: " << I);
+
+ const std::vector<BasicBlock*> &ExitBlocks = CurLoop->getExitBlocks();
+
+ // 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.
+ if (ExitBlocks.size() == 1) {
+ if (!isExitBlockDominatedByBlockInLoop(ExitBlocks[0], I.getParent())) {
+ // Instruction is not used, just delete it.
+ I.getParent()->getInstList().erase(&I);
+ } else {
+ // Move the instruction to the start of the exit block, after any PHI
+ // nodes in it.
+ I.getParent()->getInstList().remove(&I);
+
+ 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.
+ I.getParent()->getInstList().erase(&I);
+ return; // Don't count this as a sunk instruction, don't check operands.
+ } 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());
+
+ // Secondly, insert load instructions for each use of the instruction
+ // outside of the loop.
+ while (!I.use_empty()) {
+ Instruction *U = cast<Instruction>(I.use_back());
+
+ // If the user is a PHI Node, we actually have to insert load instructions
+ // in all predecessor blocks, not in the PHI block itself!
+ if (PHINode *UPN = dyn_cast<PHINode>(U)) {
+ // Only insert into each predecessor once, so that we don't have
+ // different incoming values from the same block!
+ std::map<BasicBlock*, Value*> InsertedBlocks;
+ for (unsigned i = 0, e = UPN->getNumIncomingValues(); i != e; ++i)
+ if (UPN->getIncomingValue(i) == &I) {
+ BasicBlock *Pred = UPN->getIncomingBlock(i);
+ Value *&PredVal = InsertedBlocks[Pred];
+ if (!PredVal) {
+ // Insert a new load instruction right before the terminator in
+ // the predecessor block.
+ PredVal = new LoadInst(AI, "", Pred->getTerminator());
+ }
+
+ UPN->setIncomingValue(i, PredVal);
+ }
+
+ } else {
+ LoadInst *L = new LoadInst(AI, "", U);
+ U->replaceUsesOfWith(&I, L);
+ }
+ }
+
+ // Thirdly, insert a copy of the instruction in each exit block of the loop
+ // that is dominated by the instruction, storing the result into the memory
+ // location. Be careful not to insert the instruction into any particular
+ // basic block more than once.
+ std::set<BasicBlock*> InsertedBlocks;
+ BasicBlock *InstOrigBB = I.getParent();
+
+ for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
+ BasicBlock *ExitBlock = ExitBlocks[i];
+
+ if (isExitBlockDominatedByBlockInLoop(ExitBlock, InstOrigBB)) {
+ // 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;
+
+ // 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.empty()) {
+ I.getParent()->getInstList().remove(&I);
+ ExitBlock->getInstList().insert(InsertPt, &I);
+ New = &I;
+ } else {
+ New = I.clone();
+ 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);
+ }
+ }
+ }
+
+ // Finally, promote the fine value to SSA form.
+ std::vector<AllocaInst*> Allocas;
+ Allocas.push_back(AI);
+ PromoteMemToReg(Allocas, *DT, *DF, AA->getTargetData());
+ }
+
+ if (isa<LoadInst>(I)) ++NumMovedLoads;
+ ++NumSunk;
+ Changed = true;
+
+ // Since we just sunk an instruction, check to see if any other instructions
+ // used by this instruction are now sinkable. If so, sink them too.
+ for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i)
+ if (Instruction *OpI = dyn_cast<Instruction>(I.getOperand(i)))
+ if (CurLoop->contains(OpI->getParent()) && canSinkOrHoistInst(*OpI) &&
+ isNotUsedInLoop(*OpI) &&
+ isSafeToExecuteUnconditionally(*OpI))
+ sink(*OpI);
+}
/// hoist - When an instruction is found to only use loop invariant operands
/// that is safe to hoist, this instruction is called to do the dirty work.
///
-void LICM::hoist(Instruction &Inst) {
+void LICM::hoist(Instruction &I) {
DEBUG(std::cerr << "LICM hoisting to";
WriteAsOperand(std::cerr, Preheader, false);
- std::cerr << ": " << Inst);
+ std::cerr << ": " << I);
// Remove the instruction from its current basic block... but don't delete the
// instruction.
- Inst.getParent()->getInstList().remove(&Inst);
+ I.getParent()->getInstList().remove(&I);
// Insert the new node in Preheader, before the terminator.
- Preheader->getInstList().insert(Preheader->getTerminator(), &Inst);
+ Preheader->getInstList().insert(Preheader->getTerminator(), &I);
+ if (isa<LoadInst>(I)) ++NumMovedLoads;
++NumHoisted;
Changed = true;
}
-
-void LICM::visitLoadInst(LoadInst &LI) {
- if (isLoopInvariant(LI.getOperand(0)) &&
- !pointerInvalidatedByLoop(LI.getOperand(0))) {
- hoist(LI);
- ++NumHoistedLoads;
- }
+/// isSafeToExecuteUnconditionally - Only sink or hoist an instruction if it is
+/// not a trapping instruction or if it is a trapping instruction and is
+/// guaranteed to execute.
+///
+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 the instruction is in the header block for the loop (which is very
+ // common), it is always guaranteed to dominate the exit blocks. Since this
+ // is a common case, and can save some work, check it now.
+ if (Inst.getParent() == CurLoop->getHeader())
+ return true;
+
+ // Get the exit blocks for the current loop.
+ const std::vector<BasicBlock*> &ExitBlocks = CurLoop->getExitBlocks();
+
+ // 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.
+ for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
+ if (!isExitBlockDominatedByBlockInLoop(ExitBlocks[i], Inst.getParent()))
+ return false;
+
+ return true;
}
+
/// PromoteValuesInLoop - 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
///
void LICM::PromoteValuesInLoop() {
// PromotedValues - List of values that are promoted out of the loop. Each
- // value has an alloca instruction for it, and a cannonical version of the
+ // value has an alloca instruction for it, and a canonical version of the
// pointer.
std::vector<std::pair<AllocaInst*, Value*> > PromotedValues;
std::map<Value*, AllocaInst*> ValueToAllocaMap; // Map of ptr to alloca
}
// Scan the basic blocks in the loop, replacing uses of our pointers with
- // uses of the allocas in question. If we find a branch that exits the
- // loop, make sure to put reload code into all of the successors of the
- // loop.
+ // uses of the allocas in question.
//
const std::vector<BasicBlock*> &LoopBBs = CurLoop->getBlocks();
for (std::vector<BasicBlock*>::const_iterator I = LoopBBs.begin(),
// Rewrite all loads and stores in the block of the pointer...
for (BasicBlock::iterator II = (*I)->begin(), E = (*I)->end();
II != E; ++II) {
- if (LoadInst *L = dyn_cast<LoadInst>(&*II)) {
+ if (LoadInst *L = dyn_cast<LoadInst>(II)) {
std::map<Value*, AllocaInst*>::iterator
I = ValueToAllocaMap.find(L->getOperand(0));
if (I != ValueToAllocaMap.end())
L->setOperand(0, I->second); // Rewrite load instruction...
- } else if (StoreInst *S = dyn_cast<StoreInst>(&*II)) {
+ } else if (StoreInst *S = dyn_cast<StoreInst>(II)) {
std::map<Value*, AllocaInst*>::iterator
I = ValueToAllocaMap.find(S->getOperand(1));
if (I != ValueToAllocaMap.end())
S->setOperand(1, I->second); // Rewrite store instruction...
}
}
+ }
- // Check to see if any successors of this block are outside of the loop.
- // If so, we need to copy the value from the alloca back into the memory
- // location...
- //
- for (succ_iterator SI = succ_begin(*I), SE = succ_end(*I); SI != SE; ++SI)
- if (!CurLoop->contains(*SI)) {
- // Copy all of the allocas into their memory locations...
- BasicBlock::iterator BI = (*SI)->begin();
- while (isa<PHINode>(*BI))
- ++BI; // Skip over all of the phi nodes in the block...
- Instruction *InsertPos = BI;
- for (unsigned i = 0, e = PromotedValues.size(); i != e; ++i) {
- // Load from the alloca...
- LoadInst *LI = new LoadInst(PromotedValues[i].first, "", InsertPos);
- // Store into the memory we promoted...
- new StoreInst(LI, PromotedValues[i].second, InsertPos);
- }
+ // Now that the body of the loop uses the allocas instead of the original
+ // memory locations, insert code to copy the alloca value back into the
+ // original memory location on all exits from the loop. Note that we only
+ // 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;
+
+ const std::vector<BasicBlock*> &ExitBlocks = CurLoop->getExitBlocks();
+ 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;
+ for (unsigned i = 0, e = PromotedValues.size(); i != e; ++i) {
+ // Load from the alloca...
+ LoadInst *LI = new LoadInst(PromotedValues[i].first, "", InsertPos);
+ // 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, getAnalysis<DominanceFrontier>(),
- AA->getTargetData());
+ PromoteMemToReg(PromotedAllocas, *DT, *DF, AA->getTargetData());
}
-/// findPromotableValuesInLoop - Check the current loop for stores to definate
+/// 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...
std::map<Value*, AllocaInst*> &ValueToAllocaMap) {
Instruction *FnStart = CurLoop->getHeader()->getParent()->begin()->begin();
- for (std::set<Value*>::iterator I = CurLBI->StoredPointers.begin(),
- E = CurLBI->StoredPointers.end(); I != E; ++I) {
- Value *V = *I;
- if (isLoopInvariant(V) &&
- CurLBI->getPointerInfo(V, *AA) == LoopBodyInfo::PointerMustStore) {
-
- // Don't add a new entry for this stored pointer if it aliases something
- // we have already processed.
- std::map<Value*, AllocaInst*>::iterator V2AMI =
- ValueToAllocaMap.lower_bound(V);
- if (V2AMI == ValueToAllocaMap.end() || V2AMI->first != V) {
- // Check to make sure that any loads in the loop are either NO or MUST
- // aliases. We cannot rewrite loads that _might_ come from this memory
- // location.
-
- bool PointerOk = true;
- for (std::set<Value*>::const_iterator I =CurLBI->LoadedPointers.begin(),
- E = CurLBI->LoadedPointers.end(); PointerOk && I != E; ++I)
- switch (AA->alias(V, ~0, *I, ~0)) {
- case AliasAnalysis::MustAlias:
- if (V->getType() != (*I)->getType())
- PointerOk = false;
- break;
- case AliasAnalysis::MayAlias:
- PointerOk = false;
- case AliasAnalysis::NoAlias:
- 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));
- ValueToAllocaMap.insert(V2AMI, std::make_pair(V, AI));
-
- DEBUG(std::cerr << "LICM: Promoting value: " << *V << "\n");
-
- // Loop over all of the loads and stores that alias this pointer,
- // adding them to the Value2AllocaMap as well...
- for (std::set<Value*>::const_iterator
- I = CurLBI->LoadedPointers.begin(),
- E = CurLBI->LoadedPointers.end(); I != E; ++I)
- if (AA->alias(V, ~0, *I, ~0) == AliasAnalysis::MustAlias)
- ValueToAllocaMap[*I] = AI;
-
- for (std::set<Value*>::const_iterator
- I = CurLBI->StoredPointers.begin(),
- E = CurLBI->StoredPointers.end(); I != E; ++I)
- if (AA->alias(V, ~0, *I, ~0) == AliasAnalysis::MustAlias)
- ValueToAllocaMap[*I] = AI;
+ // 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, and if the pointer is loop invariant.
+ if (!AS.isForwardingAliasSet() && AS.isMod() && AS.isMustAlias() &&
+ isLoopInvariant(AS.begin()->first)) {
+ assert(AS.begin() != AS.end() &&
+ "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.
+ bool PointerOk = true;
+ for (AliasSet::iterator I = AS.begin(), E = AS.end(); I != E; ++I)
+ if (V->getType() != I->first->getType()) {
+ PointerOk = false;
+ 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));
+
+ 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");
}
}
}
projects / oota-llvm.git / blobdiff