1 //===-- LoopUnswitch.cpp - Hoist loop-invariant conditionals in loop ------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This pass transforms loops that contain branches on loop-invariant conditions
11 // to have multiple loops. For example, it turns the left into the right code:
20 // This can increase the size of the code exponentially (doubling it every time
21 // a loop is unswitched) so we only unswitch if the resultant code will be
22 // smaller than a threshold.
24 // This pass expects LICM to be run before it to hoist invariant conditions out
25 // of the loop, to make the unswitching opportunity obvious.
27 //===----------------------------------------------------------------------===//
29 #define DEBUG_TYPE "loop-unswitch"
30 #include "llvm/Transforms/Scalar.h"
31 #include "llvm/Constants.h"
32 #include "llvm/Function.h"
33 #include "llvm/Instructions.h"
34 #include "llvm/Analysis/LoopInfo.h"
35 #include "llvm/Transforms/Utils/Cloning.h"
36 #include "llvm/Transforms/Utils/Local.h"
37 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
38 #include "llvm/ADT/Statistic.h"
39 #include "llvm/Support/Debug.h"
40 #include "llvm/Support/CommandLine.h"
47 Statistic<> NumUnswitched("loop-unswitch", "Number of loops unswitched");
49 Threshold("loop-unswitch-threshold", cl::desc("Max loop size to unswitch"),
50 cl::init(10), cl::Hidden);
52 class LoopUnswitch : public FunctionPass {
53 LoopInfo *LI; // Loop information
55 virtual bool runOnFunction(Function &F);
56 bool visitLoop(Loop *L);
58 /// This transformation requires natural loop information & requires that
59 /// loop preheaders be inserted into the CFG...
61 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
62 AU.addRequiredID(LoopSimplifyID);
63 AU.addPreservedID(LoopSimplifyID);
64 AU.addRequired<LoopInfo>();
65 AU.addPreserved<LoopInfo>();
69 bool UnswitchIfProfitable(Value *LoopCond, Constant *Val,Loop *L);
70 unsigned getLoopUnswitchCost(Loop *L, Value *LIC);
71 void VersionLoop(Value *LIC, Constant *OnVal,
72 Loop *L, Loop *&Out1, Loop *&Out2);
73 BasicBlock *SplitEdge(BasicBlock *From, BasicBlock *To);
74 void RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,Constant *Val,
76 void UnswitchTrivialCondition(Loop *L, Value *Cond, bool EntersLoopOnCond,
77 BasicBlock *ExitBlock);
79 RegisterOpt<LoopUnswitch> X("loop-unswitch", "Unswitch loops");
82 FunctionPass *llvm::createLoopUnswitchPass() { return new LoopUnswitch(); }
84 bool LoopUnswitch::runOnFunction(Function &F) {
86 LI = &getAnalysis<LoopInfo>();
88 // Transform all the top-level loops. Copy the loop list so that the child
89 // can update the loop tree if it needs to delete the loop.
90 std::vector<Loop*> SubLoops(LI->begin(), LI->end());
91 for (unsigned i = 0, e = SubLoops.size(); i != e; ++i)
92 Changed |= visitLoop(SubLoops[i]);
98 /// LoopValuesUsedOutsideLoop - Return true if there are any values defined in
99 /// the loop that are used by instructions outside of it.
100 static bool LoopValuesUsedOutsideLoop(Loop *L) {
101 // We will be doing lots of "loop contains block" queries. Loop::contains is
102 // linear time, use a set to speed this up.
103 std::set<BasicBlock*> LoopBlocks;
105 for (Loop::block_iterator BB = L->block_begin(), E = L->block_end();
107 LoopBlocks.insert(*BB);
109 for (Loop::block_iterator BB = L->block_begin(), E = L->block_end();
111 for (BasicBlock::iterator I = (*BB)->begin(), E = (*BB)->end(); I != E; ++I)
112 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;
114 BasicBlock *UserBB = cast<Instruction>(*UI)->getParent();
115 if (!LoopBlocks.count(UserBB))
122 /// FindTrivialLoopExitBlock - We know that we have a branch from the loop
123 /// header to the specified latch block. See if one of the successors of the
124 /// latch block is an exit, and if so what block it is.
125 static BasicBlock *FindTrivialLoopExitBlock(Loop *L, BasicBlock *Latch) {
126 BasicBlock *Header = L->getHeader();
127 BranchInst *LatchBranch = dyn_cast<BranchInst>(Latch->getTerminator());
128 if (!LatchBranch || !LatchBranch->isConditional()) return 0;
130 // Simple case, the latch block is a conditional branch. The target that
131 // doesn't go to the loop header is our block if it is not in the loop.
132 if (LatchBranch->getSuccessor(0) == Header) {
133 if (L->contains(LatchBranch->getSuccessor(1))) return false;
134 return LatchBranch->getSuccessor(1);
136 assert(LatchBranch->getSuccessor(1) == Header);
137 if (L->contains(LatchBranch->getSuccessor(0))) return false;
138 return LatchBranch->getSuccessor(0);
143 /// IsTrivialUnswitchCondition - Check to see if this unswitch condition is
144 /// trivial: that is, that the condition controls whether or not the loop does
145 /// anything at all. If this is a trivial condition, unswitching produces no
146 /// code duplications (equivalently, it produces a simpler loop and a new empty
147 /// loop, which gets deleted).
149 /// If this is a trivial condition, return ConstantBool::True if the loop body
150 /// runs when the condition is true, False if the loop body executes when the
151 /// condition is false. Otherwise, return null to indicate a complex condition.
152 static bool IsTrivialUnswitchCondition(Loop *L, Value *Cond,
153 bool *CondEntersLoop = 0,
154 BasicBlock **LoopExit = 0) {
155 BasicBlock *Header = L->getHeader();
156 BranchInst *HeaderTerm = dyn_cast<BranchInst>(Header->getTerminator());
158 // If the header block doesn't end with a conditional branch on Cond, we can't
160 if (!HeaderTerm || !HeaderTerm->isConditional() ||
161 HeaderTerm->getCondition() != Cond)
164 // Check to see if the conditional branch goes to the latch block. If not,
165 // it's not trivial. This also determines the value of Cond that will execute
167 BasicBlock *Latch = L->getLoopLatch();
168 if (HeaderTerm->getSuccessor(1) == Latch) {
169 if (CondEntersLoop) *CondEntersLoop = true;
170 } else if (HeaderTerm->getSuccessor(0) == Latch)
171 if (CondEntersLoop) *CondEntersLoop = false;
173 return false; // Doesn't branch to latch block.
175 // The latch block must end with a conditional branch where one edge goes to
176 // the header (this much we know) and one edge goes OUT of the loop.
177 BasicBlock *LoopExitBlock = FindTrivialLoopExitBlock(L, Latch);
178 if (!LoopExitBlock) return 0;
179 if (LoopExit) *LoopExit = LoopExitBlock;
181 // We already know that nothing uses any scalar values defined inside of this
182 // loop. As such, we just have to check to see if this loop will execute any
183 // side-effecting instructions (e.g. stores, calls, volatile loads) in the
184 // part of the loop that the code *would* execute.
185 for (BasicBlock::iterator I = Header->begin(), E = Header->end(); I != E; ++I)
186 if (I->mayWriteToMemory())
188 for (BasicBlock::iterator I = Latch->begin(), E = Latch->end(); I != E; ++I)
189 if (I->mayWriteToMemory())
194 /// getLoopUnswitchCost - Return the cost (code size growth) that will happen if
195 /// we choose to unswitch the specified loop on the specified value.
197 unsigned LoopUnswitch::getLoopUnswitchCost(Loop *L, Value *LIC) {
198 // If the condition is trivial, always unswitch. There is no code growth for
200 if (IsTrivialUnswitchCondition(L, LIC))
204 // FIXME: this is brain dead. It should take into consideration code
206 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
209 // Do not include empty blocks in the cost calculation. This happen due to
210 // loop canonicalization and will be removed.
211 if (BB->begin() == BasicBlock::iterator(BB->getTerminator()))
214 // Count basic blocks.
221 /// FindLIVLoopCondition - Cond is a condition that occurs in L. If it is
222 /// invariant in the loop, or has an invariant piece, return the invariant.
223 /// Otherwise, return null.
224 static Value *FindLIVLoopCondition(Value *Cond, Loop *L, bool &Changed) {
225 // Constants should be folded, not unswitched on!
226 if (isa<Constant>(Cond)) return false;
228 // TODO: Handle: br (VARIANT|INVARIANT).
229 // TODO: Hoist simple expressions out of loops.
230 if (L->isLoopInvariant(Cond)) return Cond;
232 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Cond))
233 if (BO->getOpcode() == Instruction::And ||
234 BO->getOpcode() == Instruction::Or) {
235 // If either the left or right side is invariant, we can unswitch on this,
236 // which will cause the branch to go away in one loop and the condition to
237 // simplify in the other one.
238 if (Value *LHS = FindLIVLoopCondition(BO->getOperand(0), L, Changed))
240 if (Value *RHS = FindLIVLoopCondition(BO->getOperand(1), L, Changed))
247 bool LoopUnswitch::visitLoop(Loop *L) {
248 bool Changed = false;
250 // Recurse through all subloops before we process this loop. Copy the loop
251 // list so that the child can update the loop tree if it needs to delete the
253 std::vector<Loop*> SubLoops(L->begin(), L->end());
254 for (unsigned i = 0, e = SubLoops.size(); i != e; ++i)
255 Changed |= visitLoop(SubLoops[i]);
257 // Loop over all of the basic blocks in the loop. If we find an interior
258 // block that is branching on a loop-invariant condition, we can unswitch this
260 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
262 TerminatorInst *TI = (*I)->getTerminator();
263 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
264 // If this isn't branching on an invariant condition, we can't unswitch
266 if (BI->isConditional()) {
267 // See if this, or some part of it, is loop invariant. If so, we can
268 // unswitch on it if we desire.
269 Value *LoopCond = FindLIVLoopCondition(BI->getCondition(), L, Changed);
270 if (LoopCond && UnswitchIfProfitable(LoopCond, ConstantBool::True, L))
273 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
274 Value *LoopCond = FindLIVLoopCondition(SI->getCondition(), L, Changed);
275 if (LoopCond && SI->getNumCases() > 1) {
276 // Find a value to unswitch on:
277 // FIXME: this should chose the most expensive case!
278 Constant *UnswitchVal = SI->getCaseValue(1);
279 if (UnswitchIfProfitable(LoopCond, UnswitchVal, L))
284 // Scan the instructions to check for unswitchable values.
285 for (BasicBlock::iterator BBI = (*I)->begin(), E = (*I)->end();
287 if (SelectInst *SI = dyn_cast<SelectInst>(BBI)) {
288 Value *LoopCond = FindLIVLoopCondition(SI->getCondition(), L, Changed);
289 if (LoopCond && UnswitchIfProfitable(LoopCond, ConstantBool::True, L))
297 /// UnswitchIfProfitable - We have found that we can unswitch L when
298 /// LoopCond == Val to simplify the loop. If we decide that this is profitable,
299 /// unswitch the loop, reprocess the pieces, then return true.
300 bool LoopUnswitch::UnswitchIfProfitable(Value *LoopCond, Constant *Val,Loop *L){
301 // Check to see if it would be profitable to unswitch this loop.
302 if (getLoopUnswitchCost(L, LoopCond) > Threshold) {
303 // FIXME: this should estimate growth by the amount of code shared by the
304 // resultant unswitched loops.
306 DEBUG(std::cerr << "NOT unswitching loop %"
307 << L->getHeader()->getName() << ", cost too high: "
308 << L->getBlocks().size() << "\n");
312 // If this loop has live-out values, we can't unswitch it. We need something
313 // like loop-closed SSA form in order to know how to insert PHI nodes for
315 if (LoopValuesUsedOutsideLoop(L)) {
316 DEBUG(std::cerr << "NOT unswitching loop %" << L->getHeader()->getName()
317 << ", a loop value is used outside loop!\n");
321 //std::cerr << "BEFORE:\n"; LI->dump();
322 Loop *NewLoop1 = 0, *NewLoop2 = 0;
324 // If this is a trivial condition to unswitch (which results in no code
325 // duplication), do it now.
326 bool EntersLoopOnCond;
327 BasicBlock *ExitBlock;
328 if (IsTrivialUnswitchCondition(L, LoopCond, &EntersLoopOnCond, &ExitBlock)){
329 UnswitchTrivialCondition(L, LoopCond, EntersLoopOnCond, ExitBlock);
332 VersionLoop(LoopCond, Val, L, NewLoop1, NewLoop2);
336 //std::cerr << "AFTER:\n"; LI->dump();
338 // Try to unswitch each of our new loops now!
339 if (NewLoop1) visitLoop(NewLoop1);
340 if (NewLoop2) visitLoop(NewLoop2);
344 BasicBlock *LoopUnswitch::SplitEdge(BasicBlock *BB, BasicBlock *Succ) {
345 TerminatorInst *LatchTerm = BB->getTerminator();
346 unsigned SuccNum = 0;
347 for (unsigned i = 0, e = LatchTerm->getNumSuccessors(); ; ++i) {
348 assert(i != e && "Didn't find edge?");
349 if (LatchTerm->getSuccessor(i) == Succ) {
355 // If this is a critical edge, let SplitCriticalEdge do it.
356 if (SplitCriticalEdge(BB->getTerminator(), SuccNum, this))
357 return LatchTerm->getSuccessor(SuccNum);
359 // If the edge isn't critical, then BB has a single successor or Succ has a
360 // single pred. Split the block.
361 BasicBlock *BlockToSplit;
362 BasicBlock::iterator SplitPoint;
363 if (BasicBlock *SP = Succ->getSinglePredecessor()) {
364 // If the successor only has a single pred, split the top of the successor
366 assert(SP == BB && "CFG broken");
368 SplitPoint = Succ->begin();
370 // Otherwise, if BB has a single successor, split it at the bottom of the
372 assert(BB->getTerminator()->getNumSuccessors() == 1 &&
373 "Should have a single succ!");
375 SplitPoint = BB->getTerminator();
379 BlockToSplit->splitBasicBlock(SplitPoint,
380 BlockToSplit->getName()+".tail");
381 // New now lives in whichever loop that BB used to.
382 if (Loop *L = LI->getLoopFor(BlockToSplit))
383 L->addBasicBlockToLoop(New, *LI);
389 // RemapInstruction - Convert the instruction operands from referencing the
390 // current values into those specified by ValueMap.
392 static inline void RemapInstruction(Instruction *I,
393 std::map<const Value *, Value*> &ValueMap) {
394 for (unsigned op = 0, E = I->getNumOperands(); op != E; ++op) {
395 Value *Op = I->getOperand(op);
396 std::map<const Value *, Value*>::iterator It = ValueMap.find(Op);
397 if (It != ValueMap.end()) Op = It->second;
398 I->setOperand(op, Op);
402 /// CloneLoop - Recursively clone the specified loop and all of its children,
403 /// mapping the blocks with the specified map.
404 static Loop *CloneLoop(Loop *L, Loop *PL, std::map<const Value*, Value*> &VM,
406 Loop *New = new Loop();
409 PL->addChildLoop(New);
411 LI->addTopLevelLoop(New);
413 // Add all of the blocks in L to the new loop.
414 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
416 if (LI->getLoopFor(*I) == L)
417 New->addBasicBlockToLoop(cast<BasicBlock>(VM[*I]), *LI);
419 // Add all of the subloops to the new loop.
420 for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
421 CloneLoop(*I, New, VM, LI);
426 /// UnswitchTrivialCondition - Given a loop that has a trivial unswitchable
427 /// condition in it (a cond branch from its header block to its latch block,
428 /// where the path through the loop that doesn't execute its body has no
429 /// side-effects), unswitch it. This doesn't involve any code duplication, just
430 /// moving the conditional branch outside of the loop and updating loop info.
431 void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond,
433 BasicBlock *ExitBlock) {
434 DEBUG(std::cerr << "loop-unswitch: Trivial-Unswitch loop %"
435 << L->getHeader()->getName() << " [" << L->getBlocks().size()
436 << " blocks] in Function " << L->getHeader()->getParent()->getName()
437 << " on cond:" << *Cond << "\n");
439 // First step, split the preheader, so that we know that there is a safe place
440 // to insert the conditional branch. We will change 'OrigPH' to have a
441 // conditional branch on Cond.
442 BasicBlock *OrigPH = L->getLoopPreheader();
443 BasicBlock *NewPH = SplitEdge(OrigPH, L->getHeader());
445 // Now that we have a place to insert the conditional branch, create a place
446 // to branch to: this is the exit block out of the loop that we should
449 // Split this edge now, so that the loop maintains its exit block.
450 assert(!L->contains(ExitBlock) && "Exit block is in the loop?");
451 BasicBlock *NewExit = SplitEdge(L->getLoopLatch(), ExitBlock);
452 assert(NewExit != ExitBlock && "Edge not split!");
454 // Okay, now we have a position to branch from and a position to branch to,
455 // insert the new conditional branch.
456 new BranchInst(EnterOnCond ? NewPH : NewExit, EnterOnCond ? NewExit : NewPH,
457 Cond, OrigPH->getTerminator());
458 OrigPH->getTerminator()->eraseFromParent();
460 // Now that we know that the loop is never entered when this condition is a
461 // particular value, rewrite the loop with this info. We know that this will
462 // at least eliminate the old branch.
463 RewriteLoopBodyWithConditionConstant(L, Cond, ConstantBool::get(EnterOnCond),
468 /// VersionLoop - We determined that the loop is profitable to unswitch when LIC
469 /// equal Val. Split it into loop versions and test the condition outside of
470 /// either loop. Return the loops created as Out1/Out2.
471 void LoopUnswitch::VersionLoop(Value *LIC, Constant *Val, Loop *L,
472 Loop *&Out1, Loop *&Out2) {
473 Function *F = L->getHeader()->getParent();
475 DEBUG(std::cerr << "loop-unswitch: Unswitching loop %"
476 << L->getHeader()->getName() << " [" << L->getBlocks().size()
477 << " blocks] in Function " << F->getName()
478 << " when '" << *Val << "' == " << *LIC << "\n");
480 // LoopBlocks contains all of the basic blocks of the loop, including the
481 // preheader of the loop, the body of the loop, and the exit blocks of the
482 // loop, in that order.
483 std::vector<BasicBlock*> LoopBlocks;
485 // First step, split the preheader and exit blocks, and add these blocks to
486 // the LoopBlocks list.
487 BasicBlock *OrigPreheader = L->getLoopPreheader();
488 LoopBlocks.push_back(SplitEdge(OrigPreheader, L->getHeader()));
490 // We want the loop to come after the preheader, but before the exit blocks.
491 LoopBlocks.insert(LoopBlocks.end(), L->block_begin(), L->block_end());
493 std::vector<BasicBlock*> ExitBlocks;
494 L->getExitBlocks(ExitBlocks);
495 std::sort(ExitBlocks.begin(), ExitBlocks.end());
496 ExitBlocks.erase(std::unique(ExitBlocks.begin(), ExitBlocks.end()),
498 // Split all of the edges from inside the loop to their exit blocks. This
499 // unswitching trivial: no phi nodes to update.
500 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
501 BasicBlock *ExitBlock = ExitBlocks[i];
502 std::vector<BasicBlock*> Preds(pred_begin(ExitBlock), pred_end(ExitBlock));
504 for (unsigned j = 0, e = Preds.size(); j != e; ++j) {
505 assert(L->contains(Preds[j]) &&
506 "All preds of loop exit blocks must be the same loop!");
507 SplitEdge(Preds[j], ExitBlock);
511 // The exit blocks may have been changed due to edge splitting, recompute.
513 L->getExitBlocks(ExitBlocks);
514 std::sort(ExitBlocks.begin(), ExitBlocks.end());
515 ExitBlocks.erase(std::unique(ExitBlocks.begin(), ExitBlocks.end()),
518 // Add exit blocks to the loop blocks.
519 LoopBlocks.insert(LoopBlocks.end(), ExitBlocks.begin(), ExitBlocks.end());
521 // Next step, clone all of the basic blocks that make up the loop (including
522 // the loop preheader and exit blocks), keeping track of the mapping between
523 // the instructions and blocks.
524 std::vector<BasicBlock*> NewBlocks;
525 NewBlocks.reserve(LoopBlocks.size());
526 std::map<const Value*, Value*> ValueMap;
527 for (unsigned i = 0, e = LoopBlocks.size(); i != e; ++i) {
528 NewBlocks.push_back(CloneBasicBlock(LoopBlocks[i], ValueMap, ".us", F));
529 ValueMap[LoopBlocks[i]] = NewBlocks.back(); // Keep the BB mapping.
532 // Splice the newly inserted blocks into the function right before the
533 // original preheader.
534 F->getBasicBlockList().splice(LoopBlocks[0], F->getBasicBlockList(),
535 NewBlocks[0], F->end());
537 // Now we create the new Loop object for the versioned loop.
538 Loop *NewLoop = CloneLoop(L, L->getParentLoop(), ValueMap, LI);
539 Loop *ParentLoop = L->getParentLoop();
541 // Make sure to add the cloned preheader and exit blocks to the parent loop
543 ParentLoop->addBasicBlockToLoop(NewBlocks[0], *LI);
546 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
547 BasicBlock *NewExit = cast<BasicBlock>(ValueMap[ExitBlocks[i]]);
549 ParentLoop->addBasicBlockToLoop(cast<BasicBlock>(NewExit), *LI);
551 assert(NewExit->getTerminator()->getNumSuccessors() == 1 &&
552 "Exit block should have been split to have one successor!");
553 BasicBlock *ExitSucc = NewExit->getTerminator()->getSuccessor(0);
555 // If the successor of the exit block had PHI nodes, add an entry for
558 for (BasicBlock::iterator I = ExitSucc->begin();
559 (PN = dyn_cast<PHINode>(I)); ++I) {
560 Value *V = PN->getIncomingValueForBlock(ExitBlocks[i]);
561 std::map<const Value *, Value*>::iterator It = ValueMap.find(V);
562 if (It != ValueMap.end()) V = It->second;
563 PN->addIncoming(V, NewExit);
567 // Rewrite the code to refer to itself.
568 for (unsigned i = 0, e = NewBlocks.size(); i != e; ++i)
569 for (BasicBlock::iterator I = NewBlocks[i]->begin(),
570 E = NewBlocks[i]->end(); I != E; ++I)
571 RemapInstruction(I, ValueMap);
573 // Rewrite the original preheader to select between versions of the loop.
574 assert(isa<BranchInst>(OrigPreheader->getTerminator()) &&
575 cast<BranchInst>(OrigPreheader->getTerminator())->isUnconditional() &&
576 OrigPreheader->getTerminator()->getSuccessor(0) == LoopBlocks[0] &&
577 "Preheader splitting did not work correctly!");
579 // Insert a conditional branch on LIC to the two preheaders. The original
580 // code is the true version and the new code is the false version.
581 Value *BranchVal = LIC;
582 if (!isa<ConstantBool>(BranchVal)) {
583 BranchVal = BinaryOperator::createSetEQ(LIC, Val, "tmp",
584 OrigPreheader->getTerminator());
585 } else if (Val != ConstantBool::True) {
586 // We want to enter the new loop when the condition is true.
587 BranchVal = BinaryOperator::createNot(BranchVal, "tmp",
588 OrigPreheader->getTerminator());
591 // Remove the unconditional branch to LoopBlocks[0] and insert the new branch.
592 OrigPreheader->getInstList().pop_back();
593 new BranchInst(NewBlocks[0], LoopBlocks[0], BranchVal, OrigPreheader);
595 // Now we rewrite the original code to know that the condition is true and the
596 // new code to know that the condition is false.
597 RewriteLoopBodyWithConditionConstant(L, LIC, Val, false);
598 RewriteLoopBodyWithConditionConstant(NewLoop, LIC, Val, true);
603 // RewriteLoopBodyWithConditionConstant - We know either that the value LIC has
604 // the value specified by Val in the specified loop, or we know it does NOT have
605 // that value. Rewrite any uses of LIC or of properties correlated to it.
606 void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
609 assert(!isa<Constant>(LIC) && "Why are we unswitching on a constant?");
611 // FIXME: Support correlated properties, like:
618 // NotVal - If Val is a bool, this contains its inverse.
619 Constant *NotVal = 0;
620 if (ConstantBool *CB = dyn_cast<ConstantBool>(Val))
621 NotVal = ConstantBool::get(!CB->getValue());
623 // FOLD boolean conditions (X|LIC), (X&LIC). Fold conditional branches,
624 // selects, switches.
625 std::vector<User*> Users(LIC->use_begin(), LIC->use_end());
627 // Haha, this loop could be unswitched. Get it? The unswitch pass could
628 // unswitch itself. Amazing.
629 for (unsigned i = 0, e = Users.size(); i != e; ++i)
630 if (Instruction *U = cast<Instruction>(Users[i]))
631 if (L->contains(U->getParent()))
633 U->replaceUsesOfWith(LIC, Val);
635 U->replaceUsesOfWith(LIC, NotVal);
637 // If we know that LIC is not Val, use this info to simplify code.
638 if (SwitchInst *SI = dyn_cast<SwitchInst>(U)) {
639 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) {
640 if (SI->getCaseValue(i) == Val) {
641 // Found a dead case value. Don't remove PHI nodes in the
642 // successor if they become single-entry, those PHI nodes may
643 // be in the Users list.
644 SI->getSuccessor(i)->removePredecessor(SI->getParent(), true);
651 // TODO: We could simplify stuff like X == C.