1 //===-- LICM.cpp - Loop Invariant Code Motion Pass ------------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This pass performs loop invariant code motion, attempting to remove as much
11 // code from the body of a loop as possible. It does this by either hoisting
12 // code into the preheader block, or by sinking code to the exit blocks if it is
13 // safe. This pass also promotes must-aliased memory locations in the loop to
14 // live in registers, thus hoisting and sinking "invariant" loads and stores.
16 // This pass uses alias analysis for two purposes:
18 // 1. Moving loop invariant loads and calls out of loops. If we can determine
19 // that a load or call inside of a loop never aliases anything stored to,
20 // we can hoist it or sink it like any other instruction.
21 // 2. Scalar Promotion of Memory - If there is a store instruction inside of
22 // the loop, we try to move the store to happen AFTER the loop instead of
23 // inside of the loop. This can only happen if a few conditions are true:
24 // A. The pointer stored through is loop invariant
25 // B. There are no stores or loads in the loop which _may_ alias the
26 // pointer. There are no calls in the loop which mod/ref the pointer.
27 // If these conditions are true, we can promote the loads and stores in the
28 // loop of the pointer to use a temporary alloca'd variable. We then use
29 // the SSAUpdater to construct the appropriate SSA form for the value.
31 //===----------------------------------------------------------------------===//
33 #define DEBUG_TYPE "licm"
34 #include "llvm/Transforms/Scalar.h"
35 #include "llvm/Constants.h"
36 #include "llvm/DerivedTypes.h"
37 #include "llvm/IntrinsicInst.h"
38 #include "llvm/Instructions.h"
39 #include "llvm/Target/TargetData.h"
40 #include "llvm/Analysis/LoopInfo.h"
41 #include "llvm/Analysis/LoopPass.h"
42 #include "llvm/Analysis/AliasAnalysis.h"
43 #include "llvm/Analysis/AliasSetTracker.h"
44 #include "llvm/Analysis/Dominators.h"
45 #include "llvm/Analysis/ScalarEvolution.h"
46 #include "llvm/Transforms/Utils/SSAUpdater.h"
47 #include "llvm/Support/CFG.h"
48 #include "llvm/Support/CommandLine.h"
49 #include "llvm/Support/raw_ostream.h"
50 #include "llvm/Support/Debug.h"
51 #include "llvm/ADT/Statistic.h"
55 STATISTIC(NumSunk , "Number of instructions sunk out of loop");
56 STATISTIC(NumHoisted , "Number of instructions hoisted out of loop");
57 STATISTIC(NumMovedLoads, "Number of load insts hoisted or sunk");
58 STATISTIC(NumMovedCalls, "Number of call insts hoisted or sunk");
59 STATISTIC(NumPromoted , "Number of memory locations promoted to registers");
62 DisablePromotion("disable-licm-promotion", cl::Hidden,
63 cl::desc("Disable memory promotion in LICM pass"));
66 struct LICM : public LoopPass {
67 static char ID; // Pass identification, replacement for typeid
68 LICM() : LoopPass(ID) {}
70 virtual bool runOnLoop(Loop *L, LPPassManager &LPM);
72 /// This transformation requires natural loop information & requires that
73 /// loop preheaders be inserted into the CFG...
75 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
77 AU.addRequired<DominatorTree>();
78 AU.addRequired<LoopInfo>();
79 AU.addRequiredID(LoopSimplifyID);
80 AU.addRequired<AliasAnalysis>();
81 AU.addPreserved<ScalarEvolution>();
82 AU.addPreserved<DominanceFrontier>();
83 AU.addPreservedID(LoopSimplifyID);
86 bool doFinalization() {
87 // Free the values stored in the map
88 for (std::map<Loop *, AliasSetTracker *>::iterator
89 I = LoopToAliasMap.begin(), E = LoopToAliasMap.end(); I != E; ++I)
92 LoopToAliasMap.clear();
97 // Various analyses that we use...
98 AliasAnalysis *AA; // Current AliasAnalysis information
99 LoopInfo *LI; // Current LoopInfo
100 DominatorTree *DT; // Dominator Tree for the current Loop.
102 // State that is updated as we process loops
103 bool Changed; // Set to true when we change anything.
104 BasicBlock *Preheader; // The preheader block of the current loop...
105 Loop *CurLoop; // The current loop we are working on...
106 AliasSetTracker *CurAST; // AliasSet information for the current loop...
107 std::map<Loop *, AliasSetTracker *> LoopToAliasMap;
109 /// cloneBasicBlockAnalysis - Simple Analysis hook. Clone alias set info.
110 void cloneBasicBlockAnalysis(BasicBlock *From, BasicBlock *To, Loop *L);
112 /// deleteAnalysisValue - Simple Analysis hook. Delete value V from alias
114 void deleteAnalysisValue(Value *V, Loop *L);
116 /// SinkRegion - Walk the specified region of the CFG (defined by all blocks
117 /// dominated by the specified block, and that are in the current loop) in
118 /// reverse depth first order w.r.t the DominatorTree. This allows us to
119 /// visit uses before definitions, allowing us to sink a loop body in one
120 /// pass without iteration.
122 void SinkRegion(DomTreeNode *N);
124 /// HoistRegion - Walk the specified region of the CFG (defined by all
125 /// blocks dominated by the specified block, and that are in the current
126 /// loop) in depth first order w.r.t the DominatorTree. This allows us to
127 /// visit definitions before uses, allowing us to hoist a loop body in one
128 /// pass without iteration.
130 void HoistRegion(DomTreeNode *N);
132 /// inSubLoop - Little predicate that returns true if the specified basic
133 /// block is in a subloop of the current one, not the current one itself.
135 bool inSubLoop(BasicBlock *BB) {
136 assert(CurLoop->contains(BB) && "Only valid if BB is IN the loop");
137 for (Loop::iterator I = CurLoop->begin(), E = CurLoop->end(); I != E; ++I)
138 if ((*I)->contains(BB))
139 return true; // A subloop actually contains this block!
143 /// isExitBlockDominatedByBlockInLoop - This method checks to see if the
144 /// specified exit block of the loop is dominated by the specified block
145 /// that is in the body of the loop. We use these constraints to
146 /// dramatically limit the amount of the dominator tree that needs to be
148 bool isExitBlockDominatedByBlockInLoop(BasicBlock *ExitBlock,
149 BasicBlock *BlockInLoop) const {
150 // If the block in the loop is the loop header, it must be dominated!
151 BasicBlock *LoopHeader = CurLoop->getHeader();
152 if (BlockInLoop == LoopHeader)
155 DomTreeNode *BlockInLoopNode = DT->getNode(BlockInLoop);
156 DomTreeNode *IDom = DT->getNode(ExitBlock);
158 // Because the exit block is not in the loop, we know we have to get _at
159 // least_ its immediate dominator.
160 IDom = IDom->getIDom();
162 while (IDom && IDom != BlockInLoopNode) {
163 // If we have got to the header of the loop, then the instructions block
164 // did not dominate the exit node, so we can't hoist it.
165 if (IDom->getBlock() == LoopHeader)
168 // Get next Immediate Dominator.
169 IDom = IDom->getIDom();
175 /// sink - When an instruction is found to only be used outside of the loop,
176 /// this function moves it to the exit blocks and patches up SSA form as
179 void sink(Instruction &I);
181 /// hoist - When an instruction is found to only use loop invariant operands
182 /// that is safe to hoist, this instruction is called to do the dirty work.
184 void hoist(Instruction &I);
186 /// isSafeToExecuteUnconditionally - Only sink or hoist an instruction if it
187 /// is not a trapping instruction or if it is a trapping instruction and is
188 /// guaranteed to execute.
190 bool isSafeToExecuteUnconditionally(Instruction &I);
192 /// pointerInvalidatedByLoop - Return true if the body of this loop may
193 /// store into the memory location pointed to by V.
195 bool pointerInvalidatedByLoop(Value *V, unsigned Size) {
196 // Check to see if any of the basic blocks in CurLoop invalidate *V.
197 return CurAST->getAliasSetForPointer(V, Size).isMod();
200 bool canSinkOrHoistInst(Instruction &I);
201 bool isLoopInvariantInst(Instruction &I);
202 bool isNotUsedInLoop(Instruction &I);
204 void PromoteAliasSet(AliasSet &AS);
209 INITIALIZE_PASS(LICM, "licm", "Loop Invariant Code Motion", false, false);
211 Pass *llvm::createLICMPass() { return new LICM(); }
213 /// Hoist expressions out of the specified loop. Note, alias info for inner
214 /// loop is not preserved so it is not a good idea to run LICM multiple
215 /// times on one loop.
217 bool LICM::runOnLoop(Loop *L, LPPassManager &LPM) {
220 // Get our Loop and Alias Analysis information...
221 LI = &getAnalysis<LoopInfo>();
222 AA = &getAnalysis<AliasAnalysis>();
223 DT = &getAnalysis<DominatorTree>();
225 CurAST = new AliasSetTracker(*AA);
226 // Collect Alias info from subloops
227 for (Loop::iterator LoopItr = L->begin(), LoopItrE = L->end();
228 LoopItr != LoopItrE; ++LoopItr) {
229 Loop *InnerL = *LoopItr;
230 AliasSetTracker *InnerAST = LoopToAliasMap[InnerL];
231 assert (InnerAST && "Where is my AST?");
233 // What if InnerLoop was modified by other passes ?
234 CurAST->add(*InnerAST);
239 // Get the preheader block to move instructions into...
240 Preheader = L->getLoopPreheader();
242 // Loop over the body of this loop, looking for calls, invokes, and stores.
243 // Because subloops have already been incorporated into AST, we skip blocks in
246 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
249 if (LI->getLoopFor(BB) == L) // Ignore blocks in subloops...
250 CurAST->add(*BB); // Incorporate the specified basic block
253 // We want to visit all of the instructions in this loop... that are not parts
254 // of our subloops (they have already had their invariants hoisted out of
255 // their loop, into this loop, so there is no need to process the BODIES of
258 // Traverse the body of the loop in depth first order on the dominator tree so
259 // that we are guaranteed to see definitions before we see uses. This allows
260 // us to sink instructions in one pass, without iteration. After sinking
261 // instructions, we perform another pass to hoist them out of the loop.
263 if (L->hasDedicatedExits())
264 SinkRegion(DT->getNode(L->getHeader()));
266 HoistRegion(DT->getNode(L->getHeader()));
268 // Now that all loop invariants have been removed from the loop, promote any
269 // memory references to scalars that we can.
270 if (!DisablePromotion && Preheader && L->hasDedicatedExits()) {
271 // Loop over all of the alias sets in the tracker object.
272 for (AliasSetTracker::iterator I = CurAST->begin(), E = CurAST->end();
277 // Clear out loops state information for the next iteration
281 LoopToAliasMap[L] = CurAST;
285 /// SinkRegion - Walk the specified region of the CFG (defined by all blocks
286 /// dominated by the specified block, and that are in the current loop) in
287 /// reverse depth first order w.r.t the DominatorTree. This allows us to visit
288 /// uses before definitions, allowing us to sink a loop body in one pass without
291 void LICM::SinkRegion(DomTreeNode *N) {
292 assert(N != 0 && "Null dominator tree node?");
293 BasicBlock *BB = N->getBlock();
295 // If this subregion is not in the top level loop at all, exit.
296 if (!CurLoop->contains(BB)) return;
298 // We are processing blocks in reverse dfo, so process children first...
299 const std::vector<DomTreeNode*> &Children = N->getChildren();
300 for (unsigned i = 0, e = Children.size(); i != e; ++i)
301 SinkRegion(Children[i]);
303 // Only need to process the contents of this block if it is not part of a
304 // subloop (which would already have been processed).
305 if (inSubLoop(BB)) return;
307 for (BasicBlock::iterator II = BB->end(); II != BB->begin(); ) {
308 Instruction &I = *--II;
310 // Check to see if we can sink this instruction to the exit blocks
311 // of the loop. We can do this if the all users of the instruction are
312 // outside of the loop. In this case, it doesn't even matter if the
313 // operands of the instruction are loop invariant.
315 if (isNotUsedInLoop(I) && canSinkOrHoistInst(I)) {
322 /// HoistRegion - Walk the specified region of the CFG (defined by all blocks
323 /// dominated by the specified block, and that are in the current loop) in depth
324 /// first order w.r.t the DominatorTree. This allows us to visit definitions
325 /// before uses, allowing us to hoist a loop body in one pass without iteration.
327 void LICM::HoistRegion(DomTreeNode *N) {
328 assert(N != 0 && "Null dominator tree node?");
329 BasicBlock *BB = N->getBlock();
331 // If this subregion is not in the top level loop at all, exit.
332 if (!CurLoop->contains(BB)) return;
334 // Only need to process the contents of this block if it is not part of a
335 // subloop (which would already have been processed).
337 for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E; ) {
338 Instruction &I = *II++;
340 // Try hoisting the instruction out to the preheader. We can only do this
341 // if all of the operands of the instruction are loop invariant and if it
342 // is safe to hoist the instruction.
344 if (isLoopInvariantInst(I) && canSinkOrHoistInst(I) &&
345 isSafeToExecuteUnconditionally(I))
349 const std::vector<DomTreeNode*> &Children = N->getChildren();
350 for (unsigned i = 0, e = Children.size(); i != e; ++i)
351 HoistRegion(Children[i]);
354 /// canSinkOrHoistInst - Return true if the hoister and sinker can handle this
357 bool LICM::canSinkOrHoistInst(Instruction &I) {
358 // Loads have extra constraints we have to verify before we can hoist them.
359 if (LoadInst *LI = dyn_cast<LoadInst>(&I)) {
360 if (LI->isVolatile())
361 return false; // Don't hoist volatile loads!
363 // Loads from constant memory are always safe to move, even if they end up
364 // in the same alias set as something that ends up being modified.
365 if (AA->pointsToConstantMemory(LI->getOperand(0)))
368 // Don't hoist loads which have may-aliased stores in loop.
370 if (LI->getType()->isSized())
371 Size = AA->getTypeStoreSize(LI->getType());
372 return !pointerInvalidatedByLoop(LI->getOperand(0), Size);
373 } else if (CallInst *CI = dyn_cast<CallInst>(&I)) {
374 // Handle obvious cases efficiently.
375 AliasAnalysis::ModRefBehavior Behavior = AA->getModRefBehavior(CI);
376 if (Behavior == AliasAnalysis::DoesNotAccessMemory)
378 else if (Behavior == AliasAnalysis::OnlyReadsMemory) {
379 // If this call only reads from memory and there are no writes to memory
380 // in the loop, we can hoist or sink the call as appropriate.
381 bool FoundMod = false;
382 for (AliasSetTracker::iterator I = CurAST->begin(), E = CurAST->end();
385 if (!AS.isForwardingAliasSet() && AS.isMod()) {
390 if (!FoundMod) return true;
393 // FIXME: This should use mod/ref information to see if we can hoist or sink
399 // Otherwise these instructions are hoistable/sinkable
400 return isa<BinaryOperator>(I) || isa<CastInst>(I) ||
401 isa<SelectInst>(I) || isa<GetElementPtrInst>(I) || isa<CmpInst>(I) ||
402 isa<InsertElementInst>(I) || isa<ExtractElementInst>(I) ||
403 isa<ShuffleVectorInst>(I);
406 /// isNotUsedInLoop - Return true if the only users of this instruction are
407 /// outside of the loop. If this is true, we can sink the instruction to the
408 /// exit blocks of the loop.
410 bool LICM::isNotUsedInLoop(Instruction &I) {
411 for (Value::use_iterator UI = I.use_begin(), E = I.use_end(); UI != E; ++UI) {
412 Instruction *User = cast<Instruction>(*UI);
413 if (PHINode *PN = dyn_cast<PHINode>(User)) {
414 // PHI node uses occur in predecessor blocks!
415 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
416 if (PN->getIncomingValue(i) == &I)
417 if (CurLoop->contains(PN->getIncomingBlock(i)))
419 } else if (CurLoop->contains(User)) {
427 /// isLoopInvariantInst - Return true if all operands of this instruction are
428 /// loop invariant. We also filter out non-hoistable instructions here just for
431 bool LICM::isLoopInvariantInst(Instruction &I) {
432 // The instruction is loop invariant if all of its operands are loop-invariant
433 for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i)
434 if (!CurLoop->isLoopInvariant(I.getOperand(i)))
437 // If we got this far, the instruction is loop invariant!
441 /// sink - When an instruction is found to only be used outside of the loop,
442 /// this function moves it to the exit blocks and patches up SSA form as needed.
443 /// This method is guaranteed to remove the original instruction from its
444 /// position, and may either delete it or move it to outside of the loop.
446 void LICM::sink(Instruction &I) {
447 DEBUG(dbgs() << "LICM sinking instruction: " << I << "\n");
449 SmallVector<BasicBlock*, 8> ExitBlocks;
450 CurLoop->getUniqueExitBlocks(ExitBlocks);
452 if (isa<LoadInst>(I)) ++NumMovedLoads;
453 else if (isa<CallInst>(I)) ++NumMovedCalls;
457 // The case where there is only a single exit node of this loop is common
458 // enough that we handle it as a special (more efficient) case. It is more
459 // efficient to handle because there are no PHI nodes that need to be placed.
460 if (ExitBlocks.size() == 1) {
461 if (!isExitBlockDominatedByBlockInLoop(ExitBlocks[0], I.getParent())) {
462 // Instruction is not used, just delete it.
463 CurAST->deleteValue(&I);
464 // If I has users in unreachable blocks, eliminate.
465 // If I is not void type then replaceAllUsesWith undef.
466 // This allows ValueHandlers and custom metadata to adjust itself.
468 I.replaceAllUsesWith(UndefValue::get(I.getType()));
471 // Move the instruction to the start of the exit block, after any PHI
473 I.removeFromParent();
474 BasicBlock::iterator InsertPt = ExitBlocks[0]->getFirstNonPHI();
475 ExitBlocks[0]->getInstList().insert(InsertPt, &I);
480 if (ExitBlocks.empty()) {
481 // The instruction is actually dead if there ARE NO exit blocks.
482 CurAST->deleteValue(&I);
483 // If I has users in unreachable blocks, eliminate.
484 // If I is not void type then replaceAllUsesWith undef.
485 // This allows ValueHandlers and custom metadata to adjust itself.
487 I.replaceAllUsesWith(UndefValue::get(I.getType()));
492 // Otherwise, if we have multiple exits, use the SSAUpdater to do all of the
493 // hard work of inserting PHI nodes as necessary.
494 SmallVector<PHINode*, 8> NewPHIs;
495 SSAUpdater SSA(&NewPHIs);
500 // Insert a copy of the instruction in each exit block of the loop that is
501 // dominated by the instruction. Each exit block is known to only be in the
502 // ExitBlocks list once.
503 BasicBlock *InstOrigBB = I.getParent();
504 unsigned NumInserted = 0;
506 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
507 BasicBlock *ExitBlock = ExitBlocks[i];
509 if (!isExitBlockDominatedByBlockInLoop(ExitBlock, InstOrigBB))
512 // Insert the code after the last PHI node.
513 BasicBlock::iterator InsertPt = ExitBlock->getFirstNonPHI();
515 // If this is the first exit block processed, just move the original
516 // instruction, otherwise clone the original instruction and insert
519 if (NumInserted++ == 0) {
520 I.moveBefore(InsertPt);
524 CurAST->copyValue(&I, New);
525 if (!I.getName().empty())
526 New->setName(I.getName()+".le");
527 ExitBlock->getInstList().insert(InsertPt, New);
530 // Now that we have inserted the instruction, inform SSAUpdater.
532 SSA.AddAvailableValue(ExitBlock, New);
535 // If the instruction doesn't dominate any exit blocks, it must be dead.
536 if (NumInserted == 0) {
537 CurAST->deleteValue(&I);
539 I.replaceAllUsesWith(UndefValue::get(I.getType()));
544 // Next, rewrite uses of the instruction, inserting PHI nodes as needed.
545 for (Value::use_iterator UI = I.use_begin(), UE = I.use_end(); UI != UE; ) {
546 // Grab the use before incrementing the iterator.
547 Use &U = UI.getUse();
548 // Increment the iterator before removing the use from the list.
550 SSA.RewriteUseAfterInsertions(U);
553 // Update CurAST for NewPHIs if I had pointer type.
554 if (I.getType()->isPointerTy())
555 for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i)
556 CurAST->copyValue(NewPHIs[i], &I);
559 /// hoist - When an instruction is found to only use loop invariant operands
560 /// that is safe to hoist, this instruction is called to do the dirty work.
562 void LICM::hoist(Instruction &I) {
563 DEBUG(dbgs() << "LICM hoisting to " << Preheader->getName() << ": "
566 // Remove the instruction from its current basic block... but don't delete the
568 I.removeFromParent();
570 // Insert the new node in Preheader, before the terminator.
571 Preheader->getInstList().insert(Preheader->getTerminator(), &I);
573 if (isa<LoadInst>(I)) ++NumMovedLoads;
574 else if (isa<CallInst>(I)) ++NumMovedCalls;
579 /// isSafeToExecuteUnconditionally - Only sink or hoist an instruction if it is
580 /// not a trapping instruction or if it is a trapping instruction and is
581 /// guaranteed to execute.
583 bool LICM::isSafeToExecuteUnconditionally(Instruction &Inst) {
584 // If it is not a trapping instruction, it is always safe to hoist.
585 if (Inst.isSafeToSpeculativelyExecute())
588 // Otherwise we have to check to make sure that the instruction dominates all
589 // of the exit blocks. If it doesn't, then there is a path out of the loop
590 // which does not execute this instruction, so we can't hoist it.
592 // If the instruction is in the header block for the loop (which is very
593 // common), it is always guaranteed to dominate the exit blocks. Since this
594 // is a common case, and can save some work, check it now.
595 if (Inst.getParent() == CurLoop->getHeader())
598 // Get the exit blocks for the current loop.
599 SmallVector<BasicBlock*, 8> ExitBlocks;
600 CurLoop->getExitBlocks(ExitBlocks);
602 // For each exit block, get the DT node and walk up the DT until the
603 // instruction's basic block is found or we exit the loop.
604 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
605 if (!isExitBlockDominatedByBlockInLoop(ExitBlocks[i], Inst.getParent()))
611 /// PromoteAliasSet - Try to promote memory values to scalars by sinking
612 /// stores out of the loop and moving loads to before the loop. We do this by
613 /// looping over the stores in the loop, looking for stores to Must pointers
614 /// which are loop invariant.
616 void LICM::PromoteAliasSet(AliasSet &AS) {
617 // We can promote this alias set if it has a store, if it is a "Must" alias
618 // set, if the pointer is loop invariant, and if we are not eliminating any
619 // volatile loads or stores.
620 if (AS.isForwardingAliasSet() || !AS.isMod() || !AS.isMustAlias() ||
621 AS.isVolatile() || !CurLoop->isLoopInvariant(AS.begin()->getValue()))
624 assert(!AS.empty() &&
625 "Must alias set should have at least one pointer element in it!");
626 Value *SomePtr = AS.begin()->getValue();
628 // It isn't safe to promote a load/store from the loop if the load/store is
629 // conditional. For example, turning:
631 // for () { if (c) *P += 1; }
635 // tmp = *P; for () { if (c) tmp +=1; } *P = tmp;
637 // is not safe, because *P may only be valid to access if 'c' is true.
639 // It is safe to promote P if all uses are direct load/stores and if at
640 // least one is guaranteed to be executed.
641 bool GuaranteedToExecute = false;
643 SmallVector<Instruction*, 64> LoopUses;
644 SmallPtrSet<Value*, 4> PointerMustAliases;
646 // Check that all of the pointers in the alias set have the same type. We
647 // cannot (yet) promote a memory location that is loaded and stored in
649 for (AliasSet::iterator ASI = AS.begin(), E = AS.end(); ASI != E; ++ASI) {
650 Value *ASIV = ASI->getValue();
651 PointerMustAliases.insert(ASIV);
653 // Check that all of the pointers in the alias set have the same type. We
654 // cannot (yet) promote a memory location that is loaded and stored in
656 if (SomePtr->getType() != ASIV->getType())
659 for (Value::use_iterator UI = ASIV->use_begin(), UE = ASIV->use_end();
661 // Ignore instructions that are outside the loop.
662 Instruction *Use = dyn_cast<Instruction>(*UI);
663 if (!Use || !CurLoop->contains(Use))
666 // If there is an non-load/store instruction in the loop, we can't promote
668 if (isa<LoadInst>(Use))
669 assert(!cast<LoadInst>(Use)->isVolatile() && "AST broken");
670 else if (isa<StoreInst>(Use))
671 assert(!cast<StoreInst>(Use)->isVolatile() &&
672 Use->getOperand(0) != ASIV && "AST broken");
674 return; // Not a load or store.
676 if (!GuaranteedToExecute)
677 GuaranteedToExecute = isSafeToExecuteUnconditionally(*Use);
679 LoopUses.push_back(Use);
683 // If there isn't a guaranteed-to-execute instruction, we can't promote.
684 if (!GuaranteedToExecute)
687 // Otherwise, this is safe to promote, lets do it!
688 DEBUG(dbgs() << "LICM: Promoting value stored to in loop: " <<*SomePtr<<'\n');
692 // We use the SSAUpdater interface to insert phi nodes as required.
693 SmallVector<PHINode*, 16> NewPHIs;
694 SSAUpdater SSA(&NewPHIs);
696 // It wants to know some value of the same type as what we'll be inserting.
698 if (isa<LoadInst>(LoopUses[0]))
699 SomeValue = LoopUses[0];
701 SomeValue = cast<StoreInst>(LoopUses[0])->getOperand(0);
702 SSA.Initialize(SomeValue);
704 // First step: bucket up uses of the pointers by the block they occur in.
705 // This is important because we have to handle multiple defs/uses in a block
706 // ourselves: SSAUpdater is purely for cross-block references.
707 // FIXME: Want a TinyVector<Instruction*> since there is usually 0/1 element.
708 DenseMap<BasicBlock*, std::vector<Instruction*> > UsesByBlock;
709 for (unsigned i = 0, e = LoopUses.size(); i != e; ++i) {
710 Instruction *User = LoopUses[i];
711 UsesByBlock[User->getParent()].push_back(User);
714 // Okay, now we can iterate over all the blocks in the loop with uses,
715 // processing them. Keep track of which loads are loading a live-in value.
716 SmallVector<LoadInst*, 32> LiveInLoads;
718 for (unsigned LoopUse = 0, e = LoopUses.size(); LoopUse != e; ++LoopUse) {
719 Instruction *User = LoopUses[LoopUse];
720 std::vector<Instruction*> &BlockUses = UsesByBlock[User->getParent()];
722 // If this block has already been processed, ignore this repeat use.
723 if (BlockUses.empty()) continue;
725 // Okay, this is the first use in the block. If this block just has a
726 // single user in it, we can rewrite it trivially.
727 if (BlockUses.size() == 1) {
728 // If it is a store, it is a trivial def of the value in the block.
729 if (isa<StoreInst>(User)) {
730 SSA.AddAvailableValue(User->getParent(),
731 cast<StoreInst>(User)->getOperand(0));
733 // Otherwise it is a load, queue it to rewrite as a live-in load.
734 LiveInLoads.push_back(cast<LoadInst>(User));
740 // Otherwise, check to see if this block is all loads. If so, we can queue
741 // them all as live in loads.
742 bool HasStore = false;
743 for (unsigned i = 0, e = BlockUses.size(); i != e; ++i) {
744 if (isa<StoreInst>(BlockUses[i])) {
751 for (unsigned i = 0, e = BlockUses.size(); i != e; ++i)
752 LiveInLoads.push_back(cast<LoadInst>(BlockUses[i]));
757 // Otherwise, we have mixed loads and stores (or just a bunch of stores).
758 // Since SSAUpdater is purely for cross-block values, we need to determine
759 // the order of these instructions in the block. If the first use in the
760 // block is a load, then it uses the live in value. The last store defines
761 // the live out value. We handle this by doing a linear scan of the block.
762 BasicBlock *BB = User->getParent();
763 Value *StoredValue = 0;
764 for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E; ++II) {
765 if (LoadInst *L = dyn_cast<LoadInst>(II)) {
766 // If this is a load to an unrelated pointer, ignore it.
767 if (!PointerMustAliases.count(L->getOperand(0))) continue;
769 // If we haven't seen a store yet, this is a live in use, otherwise
770 // use the stored value.
772 L->replaceAllUsesWith(StoredValue);
774 LiveInLoads.push_back(L);
778 if (StoreInst *S = dyn_cast<StoreInst>(II)) {
779 // If this is a load to an unrelated pointer, ignore it.
780 if (!PointerMustAliases.count(S->getOperand(1))) continue;
782 // Remember that this is the active value in the block.
783 StoredValue = S->getOperand(0);
787 // The last stored value that happened is the live-out for the block.
788 assert(StoredValue && "Already checked that there is a store in block");
789 SSA.AddAvailableValue(BB, StoredValue);
793 // Now that all the intra-loop values are classified, set up the preheader.
794 // It gets a load of the pointer we're promoting, and it is the live-out value
795 // from the preheader.
796 LoadInst *PreheaderLoad = new LoadInst(SomePtr,SomePtr->getName()+".promoted",
797 Preheader->getTerminator());
798 SSA.AddAvailableValue(Preheader, PreheaderLoad);
800 // Now that the preheader is good to go, set up the exit blocks. Each exit
801 // block gets a store of the live-out values that feed them. Since we've
802 // already told the SSA updater about the defs in the loop and the preheader
803 // definition, it is all set and we can start using it.
804 SmallVector<BasicBlock*, 8> ExitBlocks;
805 CurLoop->getUniqueExitBlocks(ExitBlocks);
806 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
807 BasicBlock *ExitBlock = ExitBlocks[i];
808 Value *LiveInValue = SSA.GetValueInMiddleOfBlock(ExitBlock);
809 Instruction *InsertPos = ExitBlock->getFirstNonPHI();
810 new StoreInst(LiveInValue, SomePtr, InsertPos);
813 // Okay, now we rewrite all loads that use live-in values in the loop,
814 // inserting PHI nodes as necessary.
815 for (unsigned i = 0, e = LiveInLoads.size(); i != e; ++i) {
816 LoadInst *ALoad = LiveInLoads[i];
817 ALoad->replaceAllUsesWith(SSA.GetValueInMiddleOfBlock(ALoad->getParent()));
820 // Now that everything is rewritten, delete the old instructions from the body
821 // of the loop. They should all be dead now.
822 for (unsigned i = 0, e = LoopUses.size(); i != e; ++i) {
823 Instruction *User = LoopUses[i];
824 CurAST->deleteValue(User);
825 User->eraseFromParent();
828 // If the preheader load is itself a pointer, we need to tell alias analysis
829 // about the new pointer we created in the preheader block and about any PHI
830 // nodes that just got inserted.
831 if (PreheaderLoad->getType()->isPointerTy()) {
832 // Copy any value stored to or loaded from a must-alias of the pointer.
833 CurAST->copyValue(SomeValue, PreheaderLoad);
835 for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i)
836 CurAST->copyValue(SomeValue, NewPHIs[i]);
843 /// cloneBasicBlockAnalysis - Simple Analysis hook. Clone alias set info.
844 void LICM::cloneBasicBlockAnalysis(BasicBlock *From, BasicBlock *To, Loop *L) {
845 AliasSetTracker *AST = LoopToAliasMap[L];
849 AST->copyValue(From, To);
852 /// deleteAnalysisValue - Simple Analysis hook. Delete value V from alias
854 void LICM::deleteAnalysisValue(Value *V, Loop *L) {
855 AliasSetTracker *AST = LoopToAliasMap[L];