1 //===- IndVarSimplify.cpp - Induction Variable Elimination ----------------===//
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 transformation analyzes and transforms the induction variables (and
11 // computations derived from them) into simpler forms suitable for subsequent
12 // analysis and transformation.
14 // If the trip count of a loop is computable, this pass also makes the following
16 // 1. The exit condition for the loop is canonicalized to compare the
17 // induction value against the exit value. This turns loops like:
18 // 'for (i = 7; i*i < 1000; ++i)' into 'for (i = 0; i != 25; ++i)'
19 // 2. Any use outside of the loop of an expression derived from the indvar
20 // is changed to compute the derived value outside of the loop, eliminating
21 // the dependence on the exit value of the induction variable. If the only
22 // purpose of the loop is to compute the exit value of some derived
23 // expression, this transformation will make the loop dead.
25 //===----------------------------------------------------------------------===//
27 #include "llvm/Transforms/Scalar.h"
28 #include "llvm/ADT/DenseMap.h"
29 #include "llvm/ADT/SmallVector.h"
30 #include "llvm/ADT/Statistic.h"
31 #include "llvm/Analysis/LoopInfo.h"
32 #include "llvm/Analysis/LoopPass.h"
33 #include "llvm/Analysis/ScalarEvolutionExpander.h"
34 #include "llvm/Analysis/TargetTransformInfo.h"
35 #include "llvm/IR/BasicBlock.h"
36 #include "llvm/IR/CFG.h"
37 #include "llvm/IR/Constants.h"
38 #include "llvm/IR/DataLayout.h"
39 #include "llvm/IR/Dominators.h"
40 #include "llvm/IR/Instructions.h"
41 #include "llvm/IR/IntrinsicInst.h"
42 #include "llvm/IR/LLVMContext.h"
43 #include "llvm/IR/Type.h"
44 #include "llvm/Support/CommandLine.h"
45 #include "llvm/Support/Debug.h"
46 #include "llvm/Support/raw_ostream.h"
47 #include "llvm/Analysis/TargetLibraryInfo.h"
48 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
49 #include "llvm/Transforms/Utils/Local.h"
50 #include "llvm/Transforms/Utils/SimplifyIndVar.h"
53 #define DEBUG_TYPE "indvars"
55 STATISTIC(NumWidened , "Number of indvars widened");
56 STATISTIC(NumReplaced , "Number of exit values replaced");
57 STATISTIC(NumLFTR , "Number of loop exit tests replaced");
58 STATISTIC(NumElimExt , "Number of IV sign/zero extends eliminated");
59 STATISTIC(NumElimIV , "Number of congruent IVs eliminated");
61 // Trip count verification can be enabled by default under NDEBUG if we
62 // implement a strong expression equivalence checker in SCEV. Until then, we
63 // use the verify-indvars flag, which may assert in some cases.
64 static cl::opt<bool> VerifyIndvars(
65 "verify-indvars", cl::Hidden,
66 cl::desc("Verify the ScalarEvolution result after running indvars"));
68 static cl::opt<bool> ReduceLiveIVs("liv-reduce", cl::Hidden,
69 cl::desc("Reduce live induction variables."));
72 class IndVarSimplify : public LoopPass {
76 TargetLibraryInfo *TLI;
77 const TargetTransformInfo *TTI;
79 SmallVector<WeakVH, 16> DeadInsts;
83 static char ID; // Pass identification, replacement for typeid
85 : LoopPass(ID), LI(nullptr), SE(nullptr), DT(nullptr), Changed(false) {
86 initializeIndVarSimplifyPass(*PassRegistry::getPassRegistry());
89 bool runOnLoop(Loop *L, LPPassManager &LPM) override;
91 void getAnalysisUsage(AnalysisUsage &AU) const override {
92 AU.addRequired<DominatorTreeWrapperPass>();
93 AU.addRequired<LoopInfoWrapperPass>();
94 AU.addRequired<ScalarEvolution>();
95 AU.addRequiredID(LoopSimplifyID);
96 AU.addRequiredID(LCSSAID);
97 AU.addPreserved<ScalarEvolution>();
98 AU.addPreservedID(LoopSimplifyID);
99 AU.addPreservedID(LCSSAID);
100 AU.setPreservesCFG();
104 void releaseMemory() override {
108 bool isValidRewrite(Value *FromVal, Value *ToVal);
110 void HandleFloatingPointIV(Loop *L, PHINode *PH);
111 void RewriteNonIntegerIVs(Loop *L);
113 void SimplifyAndExtend(Loop *L, SCEVExpander &Rewriter, LPPassManager &LPM);
115 void RewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter);
117 Value *LinearFunctionTestReplace(Loop *L, const SCEV *BackedgeTakenCount,
118 PHINode *IndVar, SCEVExpander &Rewriter);
120 void SinkUnusedInvariants(Loop *L);
124 char IndVarSimplify::ID = 0;
125 INITIALIZE_PASS_BEGIN(IndVarSimplify, "indvars",
126 "Induction Variable Simplification", false, false)
127 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
128 INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
129 INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
130 INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
131 INITIALIZE_PASS_DEPENDENCY(LCSSA)
132 INITIALIZE_PASS_END(IndVarSimplify, "indvars",
133 "Induction Variable Simplification", false, false)
135 Pass *llvm::createIndVarSimplifyPass() {
136 return new IndVarSimplify();
139 /// isValidRewrite - Return true if the SCEV expansion generated by the
140 /// rewriter can replace the original value. SCEV guarantees that it
141 /// produces the same value, but the way it is produced may be illegal IR.
142 /// Ideally, this function will only be called for verification.
143 bool IndVarSimplify::isValidRewrite(Value *FromVal, Value *ToVal) {
144 // If an SCEV expression subsumed multiple pointers, its expansion could
145 // reassociate the GEP changing the base pointer. This is illegal because the
146 // final address produced by a GEP chain must be inbounds relative to its
147 // underlying object. Otherwise basic alias analysis, among other things,
148 // could fail in a dangerous way. Ultimately, SCEV will be improved to avoid
149 // producing an expression involving multiple pointers. Until then, we must
152 // Retrieve the pointer operand of the GEP. Don't use GetUnderlyingObject
153 // because it understands lcssa phis while SCEV does not.
154 Value *FromPtr = FromVal;
155 Value *ToPtr = ToVal;
156 if (GEPOperator *GEP = dyn_cast<GEPOperator>(FromVal)) {
157 FromPtr = GEP->getPointerOperand();
159 if (GEPOperator *GEP = dyn_cast<GEPOperator>(ToVal)) {
160 ToPtr = GEP->getPointerOperand();
162 if (FromPtr != FromVal || ToPtr != ToVal) {
163 // Quickly check the common case
164 if (FromPtr == ToPtr)
167 // SCEV may have rewritten an expression that produces the GEP's pointer
168 // operand. That's ok as long as the pointer operand has the same base
169 // pointer. Unlike GetUnderlyingObject(), getPointerBase() will find the
170 // base of a recurrence. This handles the case in which SCEV expansion
171 // converts a pointer type recurrence into a nonrecurrent pointer base
172 // indexed by an integer recurrence.
174 // If the GEP base pointer is a vector of pointers, abort.
175 if (!FromPtr->getType()->isPointerTy() || !ToPtr->getType()->isPointerTy())
178 const SCEV *FromBase = SE->getPointerBase(SE->getSCEV(FromPtr));
179 const SCEV *ToBase = SE->getPointerBase(SE->getSCEV(ToPtr));
180 if (FromBase == ToBase)
183 DEBUG(dbgs() << "INDVARS: GEP rewrite bail out "
184 << *FromBase << " != " << *ToBase << "\n");
191 /// Determine the insertion point for this user. By default, insert immediately
192 /// before the user. SCEVExpander or LICM will hoist loop invariants out of the
193 /// loop. For PHI nodes, there may be multiple uses, so compute the nearest
194 /// common dominator for the incoming blocks.
195 static Instruction *getInsertPointForUses(Instruction *User, Value *Def,
197 PHINode *PHI = dyn_cast<PHINode>(User);
201 Instruction *InsertPt = nullptr;
202 for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i) {
203 if (PHI->getIncomingValue(i) != Def)
206 BasicBlock *InsertBB = PHI->getIncomingBlock(i);
208 InsertPt = InsertBB->getTerminator();
211 InsertBB = DT->findNearestCommonDominator(InsertPt->getParent(), InsertBB);
212 InsertPt = InsertBB->getTerminator();
214 assert(InsertPt && "Missing phi operand");
215 assert((!isa<Instruction>(Def) ||
216 DT->dominates(cast<Instruction>(Def), InsertPt)) &&
217 "def does not dominate all uses");
221 //===----------------------------------------------------------------------===//
222 // RewriteNonIntegerIVs and helpers. Prefer integer IVs.
223 //===----------------------------------------------------------------------===//
225 /// ConvertToSInt - Convert APF to an integer, if possible.
226 static bool ConvertToSInt(const APFloat &APF, int64_t &IntVal) {
227 bool isExact = false;
228 // See if we can convert this to an int64_t
230 if (APF.convertToInteger(&UIntVal, 64, true, APFloat::rmTowardZero,
231 &isExact) != APFloat::opOK || !isExact)
237 /// HandleFloatingPointIV - If the loop has floating induction variable
238 /// then insert corresponding integer induction variable if possible.
240 /// for(double i = 0; i < 10000; ++i)
242 /// is converted into
243 /// for(int i = 0; i < 10000; ++i)
246 void IndVarSimplify::HandleFloatingPointIV(Loop *L, PHINode *PN) {
247 unsigned IncomingEdge = L->contains(PN->getIncomingBlock(0));
248 unsigned BackEdge = IncomingEdge^1;
250 // Check incoming value.
251 ConstantFP *InitValueVal =
252 dyn_cast<ConstantFP>(PN->getIncomingValue(IncomingEdge));
255 if (!InitValueVal || !ConvertToSInt(InitValueVal->getValueAPF(), InitValue))
258 // Check IV increment. Reject this PN if increment operation is not
259 // an add or increment value can not be represented by an integer.
260 BinaryOperator *Incr =
261 dyn_cast<BinaryOperator>(PN->getIncomingValue(BackEdge));
262 if (Incr == nullptr || Incr->getOpcode() != Instruction::FAdd) return;
264 // If this is not an add of the PHI with a constantfp, or if the constant fp
265 // is not an integer, bail out.
266 ConstantFP *IncValueVal = dyn_cast<ConstantFP>(Incr->getOperand(1));
268 if (IncValueVal == nullptr || Incr->getOperand(0) != PN ||
269 !ConvertToSInt(IncValueVal->getValueAPF(), IncValue))
272 // Check Incr uses. One user is PN and the other user is an exit condition
273 // used by the conditional terminator.
274 Value::user_iterator IncrUse = Incr->user_begin();
275 Instruction *U1 = cast<Instruction>(*IncrUse++);
276 if (IncrUse == Incr->user_end()) return;
277 Instruction *U2 = cast<Instruction>(*IncrUse++);
278 if (IncrUse != Incr->user_end()) return;
280 // Find exit condition, which is an fcmp. If it doesn't exist, or if it isn't
281 // only used by a branch, we can't transform it.
282 FCmpInst *Compare = dyn_cast<FCmpInst>(U1);
284 Compare = dyn_cast<FCmpInst>(U2);
285 if (!Compare || !Compare->hasOneUse() ||
286 !isa<BranchInst>(Compare->user_back()))
289 BranchInst *TheBr = cast<BranchInst>(Compare->user_back());
291 // We need to verify that the branch actually controls the iteration count
292 // of the loop. If not, the new IV can overflow and no one will notice.
293 // The branch block must be in the loop and one of the successors must be out
295 assert(TheBr->isConditional() && "Can't use fcmp if not conditional");
296 if (!L->contains(TheBr->getParent()) ||
297 (L->contains(TheBr->getSuccessor(0)) &&
298 L->contains(TheBr->getSuccessor(1))))
302 // If it isn't a comparison with an integer-as-fp (the exit value), we can't
304 ConstantFP *ExitValueVal = dyn_cast<ConstantFP>(Compare->getOperand(1));
306 if (ExitValueVal == nullptr ||
307 !ConvertToSInt(ExitValueVal->getValueAPF(), ExitValue))
310 // Find new predicate for integer comparison.
311 CmpInst::Predicate NewPred = CmpInst::BAD_ICMP_PREDICATE;
312 switch (Compare->getPredicate()) {
313 default: return; // Unknown comparison.
314 case CmpInst::FCMP_OEQ:
315 case CmpInst::FCMP_UEQ: NewPred = CmpInst::ICMP_EQ; break;
316 case CmpInst::FCMP_ONE:
317 case CmpInst::FCMP_UNE: NewPred = CmpInst::ICMP_NE; break;
318 case CmpInst::FCMP_OGT:
319 case CmpInst::FCMP_UGT: NewPred = CmpInst::ICMP_SGT; break;
320 case CmpInst::FCMP_OGE:
321 case CmpInst::FCMP_UGE: NewPred = CmpInst::ICMP_SGE; break;
322 case CmpInst::FCMP_OLT:
323 case CmpInst::FCMP_ULT: NewPred = CmpInst::ICMP_SLT; break;
324 case CmpInst::FCMP_OLE:
325 case CmpInst::FCMP_ULE: NewPred = CmpInst::ICMP_SLE; break;
328 // We convert the floating point induction variable to a signed i32 value if
329 // we can. This is only safe if the comparison will not overflow in a way
330 // that won't be trapped by the integer equivalent operations. Check for this
332 // TODO: We could use i64 if it is native and the range requires it.
334 // The start/stride/exit values must all fit in signed i32.
335 if (!isInt<32>(InitValue) || !isInt<32>(IncValue) || !isInt<32>(ExitValue))
338 // If not actually striding (add x, 0.0), avoid touching the code.
342 // Positive and negative strides have different safety conditions.
344 // If we have a positive stride, we require the init to be less than the
346 if (InitValue >= ExitValue)
349 uint32_t Range = uint32_t(ExitValue-InitValue);
350 // Check for infinite loop, either:
351 // while (i <= Exit) or until (i > Exit)
352 if (NewPred == CmpInst::ICMP_SLE || NewPred == CmpInst::ICMP_SGT) {
353 if (++Range == 0) return; // Range overflows.
356 unsigned Leftover = Range % uint32_t(IncValue);
358 // If this is an equality comparison, we require that the strided value
359 // exactly land on the exit value, otherwise the IV condition will wrap
360 // around and do things the fp IV wouldn't.
361 if ((NewPred == CmpInst::ICMP_EQ || NewPred == CmpInst::ICMP_NE) &&
365 // If the stride would wrap around the i32 before exiting, we can't
367 if (Leftover != 0 && int32_t(ExitValue+IncValue) < ExitValue)
371 // If we have a negative stride, we require the init to be greater than the
373 if (InitValue <= ExitValue)
376 uint32_t Range = uint32_t(InitValue-ExitValue);
377 // Check for infinite loop, either:
378 // while (i >= Exit) or until (i < Exit)
379 if (NewPred == CmpInst::ICMP_SGE || NewPred == CmpInst::ICMP_SLT) {
380 if (++Range == 0) return; // Range overflows.
383 unsigned Leftover = Range % uint32_t(-IncValue);
385 // If this is an equality comparison, we require that the strided value
386 // exactly land on the exit value, otherwise the IV condition will wrap
387 // around and do things the fp IV wouldn't.
388 if ((NewPred == CmpInst::ICMP_EQ || NewPred == CmpInst::ICMP_NE) &&
392 // If the stride would wrap around the i32 before exiting, we can't
394 if (Leftover != 0 && int32_t(ExitValue+IncValue) > ExitValue)
398 IntegerType *Int32Ty = Type::getInt32Ty(PN->getContext());
400 // Insert new integer induction variable.
401 PHINode *NewPHI = PHINode::Create(Int32Ty, 2, PN->getName()+".int", PN);
402 NewPHI->addIncoming(ConstantInt::get(Int32Ty, InitValue),
403 PN->getIncomingBlock(IncomingEdge));
406 BinaryOperator::CreateAdd(NewPHI, ConstantInt::get(Int32Ty, IncValue),
407 Incr->getName()+".int", Incr);
408 NewPHI->addIncoming(NewAdd, PN->getIncomingBlock(BackEdge));
410 ICmpInst *NewCompare = new ICmpInst(TheBr, NewPred, NewAdd,
411 ConstantInt::get(Int32Ty, ExitValue),
414 // In the following deletions, PN may become dead and may be deleted.
415 // Use a WeakVH to observe whether this happens.
418 // Delete the old floating point exit comparison. The branch starts using the
420 NewCompare->takeName(Compare);
421 Compare->replaceAllUsesWith(NewCompare);
422 RecursivelyDeleteTriviallyDeadInstructions(Compare, TLI);
424 // Delete the old floating point increment.
425 Incr->replaceAllUsesWith(UndefValue::get(Incr->getType()));
426 RecursivelyDeleteTriviallyDeadInstructions(Incr, TLI);
428 // If the FP induction variable still has uses, this is because something else
429 // in the loop uses its value. In order to canonicalize the induction
430 // variable, we chose to eliminate the IV and rewrite it in terms of an
433 // We give preference to sitofp over uitofp because it is faster on most
436 Value *Conv = new SIToFPInst(NewPHI, PN->getType(), "indvar.conv",
437 PN->getParent()->getFirstInsertionPt());
438 PN->replaceAllUsesWith(Conv);
439 RecursivelyDeleteTriviallyDeadInstructions(PN, TLI);
444 void IndVarSimplify::RewriteNonIntegerIVs(Loop *L) {
445 // First step. Check to see if there are any floating-point recurrences.
446 // If there are, change them into integer recurrences, permitting analysis by
447 // the SCEV routines.
449 BasicBlock *Header = L->getHeader();
451 SmallVector<WeakVH, 8> PHIs;
452 for (BasicBlock::iterator I = Header->begin();
453 PHINode *PN = dyn_cast<PHINode>(I); ++I)
456 for (unsigned i = 0, e = PHIs.size(); i != e; ++i)
457 if (PHINode *PN = dyn_cast_or_null<PHINode>(&*PHIs[i]))
458 HandleFloatingPointIV(L, PN);
460 // If the loop previously had floating-point IV, ScalarEvolution
461 // may not have been able to compute a trip count. Now that we've done some
462 // re-writing, the trip count may be computable.
467 //===----------------------------------------------------------------------===//
468 // RewriteLoopExitValues - Optimize IV users outside the loop.
469 // As a side effect, reduces the amount of IV processing within the loop.
470 //===----------------------------------------------------------------------===//
472 /// RewriteLoopExitValues - Check to see if this loop has a computable
473 /// loop-invariant execution count. If so, this means that we can compute the
474 /// final value of any expressions that are recurrent in the loop, and
475 /// substitute the exit values from the loop into any instructions outside of
476 /// the loop that use the final values of the current expressions.
478 /// This is mostly redundant with the regular IndVarSimplify activities that
479 /// happen later, except that it's more powerful in some cases, because it's
480 /// able to brute-force evaluate arbitrary instructions as long as they have
481 /// constant operands at the beginning of the loop.
482 void IndVarSimplify::RewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter) {
483 // Verify the input to the pass in already in LCSSA form.
484 assert(L->isLCSSAForm(*DT));
486 SmallVector<BasicBlock*, 8> ExitBlocks;
487 L->getUniqueExitBlocks(ExitBlocks);
489 // Find all values that are computed inside the loop, but used outside of it.
490 // Because of LCSSA, these values will only occur in LCSSA PHI Nodes. Scan
491 // the exit blocks of the loop to find them.
492 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
493 BasicBlock *ExitBB = ExitBlocks[i];
495 // If there are no PHI nodes in this exit block, then no values defined
496 // inside the loop are used on this path, skip it.
497 PHINode *PN = dyn_cast<PHINode>(ExitBB->begin());
500 unsigned NumPreds = PN->getNumIncomingValues();
502 // We would like to be able to RAUW single-incoming value PHI nodes. We
503 // have to be certain this is safe even when this is an LCSSA PHI node.
504 // While the computed exit value is no longer varying in *this* loop, the
505 // exit block may be an exit block for an outer containing loop as well,
506 // the exit value may be varying in the outer loop, and thus it may still
507 // require an LCSSA PHI node. The safe case is when this is
508 // single-predecessor PHI node (LCSSA) and the exit block containing it is
509 // part of the enclosing loop, or this is the outer most loop of the nest.
510 // In either case the exit value could (at most) be varying in the same
511 // loop body as the phi node itself. Thus if it is in turn used outside of
512 // an enclosing loop it will only be via a separate LCSSA node.
513 bool LCSSASafePhiForRAUW =
515 (!L->getParentLoop() || L->getParentLoop() == LI->getLoopFor(ExitBB));
517 // Iterate over all of the PHI nodes.
518 BasicBlock::iterator BBI = ExitBB->begin();
519 while ((PN = dyn_cast<PHINode>(BBI++))) {
521 continue; // dead use, don't replace it
523 // SCEV only supports integer expressions for now.
524 if (!PN->getType()->isIntegerTy() && !PN->getType()->isPointerTy())
527 // It's necessary to tell ScalarEvolution about this explicitly so that
528 // it can walk the def-use list and forget all SCEVs, as it may not be
529 // watching the PHI itself. Once the new exit value is in place, there
530 // may not be a def-use connection between the loop and every instruction
531 // which got a SCEVAddRecExpr for that loop.
534 // Iterate over all of the values in all the PHI nodes.
535 for (unsigned i = 0; i != NumPreds; ++i) {
536 // If the value being merged in is not integer or is not defined
537 // in the loop, skip it.
538 Value *InVal = PN->getIncomingValue(i);
539 if (!isa<Instruction>(InVal))
542 // If this pred is for a subloop, not L itself, skip it.
543 if (LI->getLoopFor(PN->getIncomingBlock(i)) != L)
544 continue; // The Block is in a subloop, skip it.
546 // Check that InVal is defined in the loop.
547 Instruction *Inst = cast<Instruction>(InVal);
548 if (!L->contains(Inst))
551 // Okay, this instruction has a user outside of the current loop
552 // and varies predictably *inside* the loop. Evaluate the value it
553 // contains when the loop exits, if possible.
554 const SCEV *ExitValue = SE->getSCEVAtScope(Inst, L->getParentLoop());
555 if (!SE->isLoopInvariant(ExitValue, L) ||
556 !isSafeToExpand(ExitValue, *SE))
559 // Computing the value outside of the loop brings no benefit if :
560 // - it is definitely used inside the loop in a way which can not be
562 // - no use outside of the loop can take advantage of hoisting the
563 // computation out of the loop
564 if (ExitValue->getSCEVType()>=scMulExpr) {
565 unsigned NumHardInternalUses = 0;
566 unsigned NumSoftExternalUses = 0;
567 unsigned NumUses = 0;
568 for (auto IB = Inst->user_begin(), IE = Inst->user_end();
569 IB != IE && NumUses <= 6; ++IB) {
570 Instruction *UseInstr = cast<Instruction>(*IB);
571 unsigned Opc = UseInstr->getOpcode();
573 if (L->contains(UseInstr)) {
574 if (Opc == Instruction::Call || Opc == Instruction::Ret)
575 NumHardInternalUses++;
577 if (Opc == Instruction::PHI) {
578 // Do not count the Phi as a use. LCSSA may have inserted
579 // plenty of trivial ones.
581 for (auto PB = UseInstr->user_begin(),
582 PE = UseInstr->user_end();
583 PB != PE && NumUses <= 6; ++PB, ++NumUses) {
584 unsigned PhiOpc = cast<Instruction>(*PB)->getOpcode();
585 if (PhiOpc != Instruction::Call && PhiOpc != Instruction::Ret)
586 NumSoftExternalUses++;
590 if (Opc != Instruction::Call && Opc != Instruction::Ret)
591 NumSoftExternalUses++;
594 if (NumUses <= 6 && NumHardInternalUses && !NumSoftExternalUses)
598 Value *ExitVal = Rewriter.expandCodeFor(ExitValue, PN->getType(), Inst);
600 DEBUG(dbgs() << "INDVARS: RLEV: AfterLoopVal = " << *ExitVal << '\n'
601 << " LoopVal = " << *Inst << "\n");
603 if (!isValidRewrite(Inst, ExitVal)) {
604 DeadInsts.push_back(ExitVal);
610 PN->setIncomingValue(i, ExitVal);
612 // If this instruction is dead now, delete it. Don't do it now to avoid
613 // invalidating iterators.
614 if (isInstructionTriviallyDead(Inst, TLI))
615 DeadInsts.push_back(Inst);
617 // If we determined that this PHI is safe to replace even if an LCSSA
619 if (LCSSASafePhiForRAUW) {
620 PN->replaceAllUsesWith(ExitVal);
621 PN->eraseFromParent();
625 // If we were unable to completely replace the PHI node, clone the PHI
626 // and delete the original one. This lets IVUsers and any other maps
627 // purge the original user from their records.
628 if (!LCSSASafePhiForRAUW) {
629 PHINode *NewPN = cast<PHINode>(PN->clone());
631 NewPN->insertBefore(PN);
632 PN->replaceAllUsesWith(NewPN);
633 PN->eraseFromParent();
638 // The insertion point instruction may have been deleted; clear it out
639 // so that the rewriter doesn't trip over it later.
640 Rewriter.clearInsertPoint();
643 //===----------------------------------------------------------------------===//
644 // IV Widening - Extend the width of an IV to cover its widest uses.
645 //===----------------------------------------------------------------------===//
648 // Collect information about induction variables that are used by sign/zero
649 // extend operations. This information is recorded by CollectExtend and
650 // provides the input to WidenIV.
653 Type *WidestNativeType; // Widest integer type created [sz]ext
654 bool IsSigned; // Was a sext user seen before a zext?
656 WideIVInfo() : NarrowIV(nullptr), WidestNativeType(nullptr),
661 /// visitCast - Update information about the induction variable that is
662 /// extended by this sign or zero extend operation. This is used to determine
663 /// the final width of the IV before actually widening it.
664 static void visitIVCast(CastInst *Cast, WideIVInfo &WI, ScalarEvolution *SE,
665 const TargetTransformInfo *TTI) {
666 bool IsSigned = Cast->getOpcode() == Instruction::SExt;
667 if (!IsSigned && Cast->getOpcode() != Instruction::ZExt)
670 Type *Ty = Cast->getType();
671 uint64_t Width = SE->getTypeSizeInBits(Ty);
672 if (!Cast->getModule()->getDataLayout().isLegalInteger(Width))
675 // Cast is either an sext or zext up to this point.
676 // We should not widen an indvar if arithmetics on the wider indvar are more
677 // expensive than those on the narrower indvar. We check only the cost of ADD
678 // because at least an ADD is required to increment the induction variable. We
679 // could compute more comprehensively the cost of all instructions on the
680 // induction variable when necessary.
682 TTI->getArithmeticInstrCost(Instruction::Add, Ty) >
683 TTI->getArithmeticInstrCost(Instruction::Add,
684 Cast->getOperand(0)->getType())) {
688 if (!WI.WidestNativeType) {
689 WI.WidestNativeType = SE->getEffectiveSCEVType(Ty);
690 WI.IsSigned = IsSigned;
694 // We extend the IV to satisfy the sign of its first user, arbitrarily.
695 if (WI.IsSigned != IsSigned)
698 if (Width > SE->getTypeSizeInBits(WI.WidestNativeType))
699 WI.WidestNativeType = SE->getEffectiveSCEVType(Ty);
704 /// NarrowIVDefUse - Record a link in the Narrow IV def-use chain along with the
705 /// WideIV that computes the same value as the Narrow IV def. This avoids
706 /// caching Use* pointers.
707 struct NarrowIVDefUse {
708 Instruction *NarrowDef;
709 Instruction *NarrowUse;
710 Instruction *WideDef;
712 NarrowIVDefUse(): NarrowDef(nullptr), NarrowUse(nullptr), WideDef(nullptr) {}
714 NarrowIVDefUse(Instruction *ND, Instruction *NU, Instruction *WD):
715 NarrowDef(ND), NarrowUse(NU), WideDef(WD) {}
718 /// WidenIV - The goal of this transform is to remove sign and zero extends
719 /// without creating any new induction variables. To do this, it creates a new
720 /// phi of the wider type and redirects all users, either removing extends or
721 /// inserting truncs whenever we stop propagating the type.
737 Instruction *WideInc;
738 const SCEV *WideIncExpr;
739 SmallVectorImpl<WeakVH> &DeadInsts;
741 SmallPtrSet<Instruction*,16> Widened;
742 SmallVector<NarrowIVDefUse, 8> NarrowIVUsers;
745 WidenIV(const WideIVInfo &WI, LoopInfo *LInfo,
746 ScalarEvolution *SEv, DominatorTree *DTree,
747 SmallVectorImpl<WeakVH> &DI) :
748 OrigPhi(WI.NarrowIV),
749 WideType(WI.WidestNativeType),
750 IsSigned(WI.IsSigned),
752 L(LI->getLoopFor(OrigPhi->getParent())),
757 WideIncExpr(nullptr),
759 assert(L->getHeader() == OrigPhi->getParent() && "Phi must be an IV");
762 PHINode *CreateWideIV(SCEVExpander &Rewriter);
765 Value *getExtend(Value *NarrowOper, Type *WideType, bool IsSigned,
768 Instruction *CloneIVUser(NarrowIVDefUse DU);
770 const SCEVAddRecExpr *GetWideRecurrence(Instruction *NarrowUse);
772 const SCEVAddRecExpr* GetExtendedOperandRecurrence(NarrowIVDefUse DU);
774 const SCEV *GetSCEVByOpCode(const SCEV *LHS, const SCEV *RHS,
775 unsigned OpCode) const;
777 Instruction *WidenIVUse(NarrowIVDefUse DU, SCEVExpander &Rewriter);
779 bool WidenLoopCompare(NarrowIVDefUse DU);
781 void pushNarrowIVUsers(Instruction *NarrowDef, Instruction *WideDef);
783 } // anonymous namespace
785 /// isLoopInvariant - Perform a quick domtree based check for loop invariance
786 /// assuming that V is used within the loop. LoopInfo::isLoopInvariant() seems
787 /// gratuitous for this purpose.
788 static bool isLoopInvariant(Value *V, const Loop *L, const DominatorTree *DT) {
789 Instruction *Inst = dyn_cast<Instruction>(V);
793 return DT->properlyDominates(Inst->getParent(), L->getHeader());
796 Value *WidenIV::getExtend(Value *NarrowOper, Type *WideType, bool IsSigned,
798 // Set the debug location and conservative insertion point.
799 IRBuilder<> Builder(Use);
800 // Hoist the insertion point into loop preheaders as far as possible.
801 for (const Loop *L = LI->getLoopFor(Use->getParent());
802 L && L->getLoopPreheader() && isLoopInvariant(NarrowOper, L, DT);
803 L = L->getParentLoop())
804 Builder.SetInsertPoint(L->getLoopPreheader()->getTerminator());
806 return IsSigned ? Builder.CreateSExt(NarrowOper, WideType) :
807 Builder.CreateZExt(NarrowOper, WideType);
810 /// CloneIVUser - Instantiate a wide operation to replace a narrow
811 /// operation. This only needs to handle operations that can evaluation to
812 /// SCEVAddRec. It can safely return 0 for any operation we decide not to clone.
813 Instruction *WidenIV::CloneIVUser(NarrowIVDefUse DU) {
814 unsigned Opcode = DU.NarrowUse->getOpcode();
818 case Instruction::Add:
819 case Instruction::Mul:
820 case Instruction::UDiv:
821 case Instruction::Sub:
822 case Instruction::And:
823 case Instruction::Or:
824 case Instruction::Xor:
825 case Instruction::Shl:
826 case Instruction::LShr:
827 case Instruction::AShr:
828 DEBUG(dbgs() << "Cloning IVUser: " << *DU.NarrowUse << "\n");
830 // Replace NarrowDef operands with WideDef. Otherwise, we don't know
831 // anything about the narrow operand yet so must insert a [sz]ext. It is
832 // probably loop invariant and will be folded or hoisted. If it actually
833 // comes from a widened IV, it should be removed during a future call to
835 Value *LHS = (DU.NarrowUse->getOperand(0) == DU.NarrowDef) ? DU.WideDef :
836 getExtend(DU.NarrowUse->getOperand(0), WideType, IsSigned, DU.NarrowUse);
837 Value *RHS = (DU.NarrowUse->getOperand(1) == DU.NarrowDef) ? DU.WideDef :
838 getExtend(DU.NarrowUse->getOperand(1), WideType, IsSigned, DU.NarrowUse);
840 BinaryOperator *NarrowBO = cast<BinaryOperator>(DU.NarrowUse);
841 BinaryOperator *WideBO = BinaryOperator::Create(NarrowBO->getOpcode(),
843 NarrowBO->getName());
844 IRBuilder<> Builder(DU.NarrowUse);
845 Builder.Insert(WideBO);
846 if (const OverflowingBinaryOperator *OBO =
847 dyn_cast<OverflowingBinaryOperator>(NarrowBO)) {
848 if (OBO->hasNoUnsignedWrap()) WideBO->setHasNoUnsignedWrap();
849 if (OBO->hasNoSignedWrap()) WideBO->setHasNoSignedWrap();
855 const SCEV *WidenIV::GetSCEVByOpCode(const SCEV *LHS, const SCEV *RHS,
856 unsigned OpCode) const {
857 if (OpCode == Instruction::Add)
858 return SE->getAddExpr(LHS, RHS);
859 if (OpCode == Instruction::Sub)
860 return SE->getMinusSCEV(LHS, RHS);
861 if (OpCode == Instruction::Mul)
862 return SE->getMulExpr(LHS, RHS);
864 llvm_unreachable("Unsupported opcode.");
867 /// No-wrap operations can transfer sign extension of their result to their
868 /// operands. Generate the SCEV value for the widened operation without
869 /// actually modifying the IR yet. If the expression after extending the
870 /// operands is an AddRec for this loop, return it.
871 const SCEVAddRecExpr* WidenIV::GetExtendedOperandRecurrence(NarrowIVDefUse DU) {
873 // Handle the common case of add<nsw/nuw>
874 const unsigned OpCode = DU.NarrowUse->getOpcode();
875 // Only Add/Sub/Mul instructions supported yet.
876 if (OpCode != Instruction::Add && OpCode != Instruction::Sub &&
877 OpCode != Instruction::Mul)
880 // One operand (NarrowDef) has already been extended to WideDef. Now determine
881 // if extending the other will lead to a recurrence.
882 const unsigned ExtendOperIdx =
883 DU.NarrowUse->getOperand(0) == DU.NarrowDef ? 1 : 0;
884 assert(DU.NarrowUse->getOperand(1-ExtendOperIdx) == DU.NarrowDef && "bad DU");
886 const SCEV *ExtendOperExpr = nullptr;
887 const OverflowingBinaryOperator *OBO =
888 cast<OverflowingBinaryOperator>(DU.NarrowUse);
889 if (IsSigned && OBO->hasNoSignedWrap())
890 ExtendOperExpr = SE->getSignExtendExpr(
891 SE->getSCEV(DU.NarrowUse->getOperand(ExtendOperIdx)), WideType);
892 else if(!IsSigned && OBO->hasNoUnsignedWrap())
893 ExtendOperExpr = SE->getZeroExtendExpr(
894 SE->getSCEV(DU.NarrowUse->getOperand(ExtendOperIdx)), WideType);
898 // When creating this SCEV expr, don't apply the current operations NSW or NUW
899 // flags. This instruction may be guarded by control flow that the no-wrap
900 // behavior depends on. Non-control-equivalent instructions can be mapped to
901 // the same SCEV expression, and it would be incorrect to transfer NSW/NUW
902 // semantics to those operations.
903 const SCEV *lhs = SE->getSCEV(DU.WideDef);
904 const SCEV *rhs = ExtendOperExpr;
906 // Let's swap operands to the initial order for the case of non-commutative
907 // operations, like SUB. See PR21014.
908 if (ExtendOperIdx == 0)
910 const SCEVAddRecExpr *AddRec =
911 dyn_cast<SCEVAddRecExpr>(GetSCEVByOpCode(lhs, rhs, OpCode));
913 if (!AddRec || AddRec->getLoop() != L)
918 /// GetWideRecurrence - Is this instruction potentially interesting from
919 /// IVUsers' perspective after widening it's type? In other words, can the
920 /// extend be safely hoisted out of the loop with SCEV reducing the value to a
921 /// recurrence on the same loop. If so, return the sign or zero extended
922 /// recurrence. Otherwise return NULL.
923 const SCEVAddRecExpr *WidenIV::GetWideRecurrence(Instruction *NarrowUse) {
924 if (!SE->isSCEVable(NarrowUse->getType()))
927 const SCEV *NarrowExpr = SE->getSCEV(NarrowUse);
928 if (SE->getTypeSizeInBits(NarrowExpr->getType())
929 >= SE->getTypeSizeInBits(WideType)) {
930 // NarrowUse implicitly widens its operand. e.g. a gep with a narrow
931 // index. So don't follow this use.
935 const SCEV *WideExpr = IsSigned ?
936 SE->getSignExtendExpr(NarrowExpr, WideType) :
937 SE->getZeroExtendExpr(NarrowExpr, WideType);
938 const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(WideExpr);
939 if (!AddRec || AddRec->getLoop() != L)
944 /// This IV user cannot be widen. Replace this use of the original narrow IV
945 /// with a truncation of the new wide IV to isolate and eliminate the narrow IV.
946 static void truncateIVUse(NarrowIVDefUse DU, DominatorTree *DT) {
947 DEBUG(dbgs() << "INDVARS: Truncate IV " << *DU.WideDef
948 << " for user " << *DU.NarrowUse << "\n");
949 IRBuilder<> Builder(getInsertPointForUses(DU.NarrowUse, DU.NarrowDef, DT));
950 Value *Trunc = Builder.CreateTrunc(DU.WideDef, DU.NarrowDef->getType());
951 DU.NarrowUse->replaceUsesOfWith(DU.NarrowDef, Trunc);
954 /// If the narrow use is a compare instruction, then widen the compare
955 // (and possibly the other operand). The extend operation is hoisted into the
956 // loop preheader as far as possible.
957 bool WidenIV::WidenLoopCompare(NarrowIVDefUse DU) {
958 ICmpInst *Cmp = dyn_cast<ICmpInst>(DU.NarrowUse);
962 // Sign of IV user and compare must match.
963 if (IsSigned != CmpInst::isSigned(Cmp->getPredicate()))
966 Value *Op = Cmp->getOperand(Cmp->getOperand(0) == DU.NarrowDef ? 1 : 0);
967 unsigned CastWidth = SE->getTypeSizeInBits(Op->getType());
968 unsigned IVWidth = SE->getTypeSizeInBits(WideType);
969 assert (CastWidth <= IVWidth && "Unexpected width while widening compare.");
971 // Widen the compare instruction.
972 IRBuilder<> Builder(getInsertPointForUses(DU.NarrowUse, DU.NarrowDef, DT));
973 DU.NarrowUse->replaceUsesOfWith(DU.NarrowDef, DU.WideDef);
975 // Widen the other operand of the compare, if necessary.
976 if (CastWidth < IVWidth) {
977 Value *ExtOp = getExtend(Op, WideType, IsSigned, Cmp);
978 DU.NarrowUse->replaceUsesOfWith(Op, ExtOp);
983 /// WidenIVUse - Determine whether an individual user of the narrow IV can be
984 /// widened. If so, return the wide clone of the user.
985 Instruction *WidenIV::WidenIVUse(NarrowIVDefUse DU, SCEVExpander &Rewriter) {
987 // Stop traversing the def-use chain at inner-loop phis or post-loop phis.
988 if (PHINode *UsePhi = dyn_cast<PHINode>(DU.NarrowUse)) {
989 if (LI->getLoopFor(UsePhi->getParent()) != L) {
990 // For LCSSA phis, sink the truncate outside the loop.
991 // After SimplifyCFG most loop exit targets have a single predecessor.
992 // Otherwise fall back to a truncate within the loop.
993 if (UsePhi->getNumOperands() != 1)
994 truncateIVUse(DU, DT);
997 PHINode::Create(DU.WideDef->getType(), 1, UsePhi->getName() + ".wide",
999 WidePhi->addIncoming(DU.WideDef, UsePhi->getIncomingBlock(0));
1000 IRBuilder<> Builder(WidePhi->getParent()->getFirstInsertionPt());
1001 Value *Trunc = Builder.CreateTrunc(WidePhi, DU.NarrowDef->getType());
1002 UsePhi->replaceAllUsesWith(Trunc);
1003 DeadInsts.push_back(UsePhi);
1004 DEBUG(dbgs() << "INDVARS: Widen lcssa phi " << *UsePhi
1005 << " to " << *WidePhi << "\n");
1010 // Our raison d'etre! Eliminate sign and zero extension.
1011 if (IsSigned ? isa<SExtInst>(DU.NarrowUse) : isa<ZExtInst>(DU.NarrowUse)) {
1012 Value *NewDef = DU.WideDef;
1013 if (DU.NarrowUse->getType() != WideType) {
1014 unsigned CastWidth = SE->getTypeSizeInBits(DU.NarrowUse->getType());
1015 unsigned IVWidth = SE->getTypeSizeInBits(WideType);
1016 if (CastWidth < IVWidth) {
1017 // The cast isn't as wide as the IV, so insert a Trunc.
1018 IRBuilder<> Builder(DU.NarrowUse);
1019 NewDef = Builder.CreateTrunc(DU.WideDef, DU.NarrowUse->getType());
1022 // A wider extend was hidden behind a narrower one. This may induce
1023 // another round of IV widening in which the intermediate IV becomes
1024 // dead. It should be very rare.
1025 DEBUG(dbgs() << "INDVARS: New IV " << *WidePhi
1026 << " not wide enough to subsume " << *DU.NarrowUse << "\n");
1027 DU.NarrowUse->replaceUsesOfWith(DU.NarrowDef, DU.WideDef);
1028 NewDef = DU.NarrowUse;
1031 if (NewDef != DU.NarrowUse) {
1032 DEBUG(dbgs() << "INDVARS: eliminating " << *DU.NarrowUse
1033 << " replaced by " << *DU.WideDef << "\n");
1035 DU.NarrowUse->replaceAllUsesWith(NewDef);
1036 DeadInsts.push_back(DU.NarrowUse);
1038 // Now that the extend is gone, we want to expose it's uses for potential
1039 // further simplification. We don't need to directly inform SimplifyIVUsers
1040 // of the new users, because their parent IV will be processed later as a
1041 // new loop phi. If we preserved IVUsers analysis, we would also want to
1042 // push the uses of WideDef here.
1044 // No further widening is needed. The deceased [sz]ext had done it for us.
1048 // Does this user itself evaluate to a recurrence after widening?
1049 const SCEVAddRecExpr *WideAddRec = GetWideRecurrence(DU.NarrowUse);
1051 WideAddRec = GetExtendedOperandRecurrence(DU);
1054 // If use is a loop condition, try to promote the condition instead of
1055 // truncating the IV first.
1056 if (WidenLoopCompare(DU))
1059 // This user does not evaluate to a recurence after widening, so don't
1060 // follow it. Instead insert a Trunc to kill off the original use,
1061 // eventually isolating the original narrow IV so it can be removed.
1062 truncateIVUse(DU, DT);
1065 // Assume block terminators cannot evaluate to a recurrence. We can't to
1066 // insert a Trunc after a terminator if there happens to be a critical edge.
1067 assert(DU.NarrowUse != DU.NarrowUse->getParent()->getTerminator() &&
1068 "SCEV is not expected to evaluate a block terminator");
1070 // Reuse the IV increment that SCEVExpander created as long as it dominates
1072 Instruction *WideUse = nullptr;
1073 if (WideAddRec == WideIncExpr
1074 && Rewriter.hoistIVInc(WideInc, DU.NarrowUse))
1077 WideUse = CloneIVUser(DU);
1081 // Evaluation of WideAddRec ensured that the narrow expression could be
1082 // extended outside the loop without overflow. This suggests that the wide use
1083 // evaluates to the same expression as the extended narrow use, but doesn't
1084 // absolutely guarantee it. Hence the following failsafe check. In rare cases
1085 // where it fails, we simply throw away the newly created wide use.
1086 if (WideAddRec != SE->getSCEV(WideUse)) {
1087 DEBUG(dbgs() << "Wide use expression mismatch: " << *WideUse
1088 << ": " << *SE->getSCEV(WideUse) << " != " << *WideAddRec << "\n");
1089 DeadInsts.push_back(WideUse);
1093 // Returning WideUse pushes it on the worklist.
1097 /// pushNarrowIVUsers - Add eligible users of NarrowDef to NarrowIVUsers.
1099 void WidenIV::pushNarrowIVUsers(Instruction *NarrowDef, Instruction *WideDef) {
1100 for (User *U : NarrowDef->users()) {
1101 Instruction *NarrowUser = cast<Instruction>(U);
1103 // Handle data flow merges and bizarre phi cycles.
1104 if (!Widened.insert(NarrowUser).second)
1107 NarrowIVUsers.push_back(NarrowIVDefUse(NarrowDef, NarrowUser, WideDef));
1111 /// CreateWideIV - Process a single induction variable. First use the
1112 /// SCEVExpander to create a wide induction variable that evaluates to the same
1113 /// recurrence as the original narrow IV. Then use a worklist to forward
1114 /// traverse the narrow IV's def-use chain. After WidenIVUse has processed all
1115 /// interesting IV users, the narrow IV will be isolated for removal by
1118 /// It would be simpler to delete uses as they are processed, but we must avoid
1119 /// invalidating SCEV expressions.
1121 PHINode *WidenIV::CreateWideIV(SCEVExpander &Rewriter) {
1122 // Is this phi an induction variable?
1123 const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(OrigPhi));
1127 // Widen the induction variable expression.
1128 const SCEV *WideIVExpr = IsSigned ?
1129 SE->getSignExtendExpr(AddRec, WideType) :
1130 SE->getZeroExtendExpr(AddRec, WideType);
1132 assert(SE->getEffectiveSCEVType(WideIVExpr->getType()) == WideType &&
1133 "Expect the new IV expression to preserve its type");
1135 // Can the IV be extended outside the loop without overflow?
1136 AddRec = dyn_cast<SCEVAddRecExpr>(WideIVExpr);
1137 if (!AddRec || AddRec->getLoop() != L)
1140 // An AddRec must have loop-invariant operands. Since this AddRec is
1141 // materialized by a loop header phi, the expression cannot have any post-loop
1142 // operands, so they must dominate the loop header.
1143 assert(SE->properlyDominates(AddRec->getStart(), L->getHeader()) &&
1144 SE->properlyDominates(AddRec->getStepRecurrence(*SE), L->getHeader())
1145 && "Loop header phi recurrence inputs do not dominate the loop");
1147 // The rewriter provides a value for the desired IV expression. This may
1148 // either find an existing phi or materialize a new one. Either way, we
1149 // expect a well-formed cyclic phi-with-increments. i.e. any operand not part
1150 // of the phi-SCC dominates the loop entry.
1151 Instruction *InsertPt = L->getHeader()->begin();
1152 WidePhi = cast<PHINode>(Rewriter.expandCodeFor(AddRec, WideType, InsertPt));
1154 // Remembering the WideIV increment generated by SCEVExpander allows
1155 // WidenIVUse to reuse it when widening the narrow IV's increment. We don't
1156 // employ a general reuse mechanism because the call above is the only call to
1157 // SCEVExpander. Henceforth, we produce 1-to-1 narrow to wide uses.
1158 if (BasicBlock *LatchBlock = L->getLoopLatch()) {
1160 cast<Instruction>(WidePhi->getIncomingValueForBlock(LatchBlock));
1161 WideIncExpr = SE->getSCEV(WideInc);
1164 DEBUG(dbgs() << "Wide IV: " << *WidePhi << "\n");
1167 // Traverse the def-use chain using a worklist starting at the original IV.
1168 assert(Widened.empty() && NarrowIVUsers.empty() && "expect initial state" );
1170 Widened.insert(OrigPhi);
1171 pushNarrowIVUsers(OrigPhi, WidePhi);
1173 while (!NarrowIVUsers.empty()) {
1174 NarrowIVDefUse DU = NarrowIVUsers.pop_back_val();
1176 // Process a def-use edge. This may replace the use, so don't hold a
1177 // use_iterator across it.
1178 Instruction *WideUse = WidenIVUse(DU, Rewriter);
1180 // Follow all def-use edges from the previous narrow use.
1182 pushNarrowIVUsers(DU.NarrowUse, WideUse);
1184 // WidenIVUse may have removed the def-use edge.
1185 if (DU.NarrowDef->use_empty())
1186 DeadInsts.push_back(DU.NarrowDef);
1191 //===----------------------------------------------------------------------===//
1192 // Live IV Reduction - Minimize IVs live across the loop.
1193 //===----------------------------------------------------------------------===//
1196 //===----------------------------------------------------------------------===//
1197 // Simplification of IV users based on SCEV evaluation.
1198 //===----------------------------------------------------------------------===//
1201 class IndVarSimplifyVisitor : public IVVisitor {
1202 ScalarEvolution *SE;
1203 const TargetTransformInfo *TTI;
1209 IndVarSimplifyVisitor(PHINode *IV, ScalarEvolution *SCEV,
1210 const TargetTransformInfo *TTI,
1211 const DominatorTree *DTree)
1212 : SE(SCEV), TTI(TTI), IVPhi(IV) {
1214 WI.NarrowIV = IVPhi;
1216 setSplitOverflowIntrinsics();
1219 // Implement the interface used by simplifyUsersOfIV.
1220 void visitCast(CastInst *Cast) override { visitIVCast(Cast, WI, SE, TTI); }
1224 /// SimplifyAndExtend - Iteratively perform simplification on a worklist of IV
1225 /// users. Each successive simplification may push more users which may
1226 /// themselves be candidates for simplification.
1228 /// Sign/Zero extend elimination is interleaved with IV simplification.
1230 void IndVarSimplify::SimplifyAndExtend(Loop *L,
1231 SCEVExpander &Rewriter,
1232 LPPassManager &LPM) {
1233 SmallVector<WideIVInfo, 8> WideIVs;
1235 SmallVector<PHINode*, 8> LoopPhis;
1236 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I) {
1237 LoopPhis.push_back(cast<PHINode>(I));
1239 // Each round of simplification iterates through the SimplifyIVUsers worklist
1240 // for all current phis, then determines whether any IVs can be
1241 // widened. Widening adds new phis to LoopPhis, inducing another round of
1242 // simplification on the wide IVs.
1243 while (!LoopPhis.empty()) {
1244 // Evaluate as many IV expressions as possible before widening any IVs. This
1245 // forces SCEV to set no-wrap flags before evaluating sign/zero
1246 // extension. The first time SCEV attempts to normalize sign/zero extension,
1247 // the result becomes final. So for the most predictable results, we delay
1248 // evaluation of sign/zero extend evaluation until needed, and avoid running
1249 // other SCEV based analysis prior to SimplifyAndExtend.
1251 PHINode *CurrIV = LoopPhis.pop_back_val();
1253 // Information about sign/zero extensions of CurrIV.
1254 IndVarSimplifyVisitor Visitor(CurrIV, SE, TTI, DT);
1256 Changed |= simplifyUsersOfIV(CurrIV, SE, &LPM, DeadInsts, &Visitor);
1258 if (Visitor.WI.WidestNativeType) {
1259 WideIVs.push_back(Visitor.WI);
1261 } while(!LoopPhis.empty());
1263 for (; !WideIVs.empty(); WideIVs.pop_back()) {
1264 WidenIV Widener(WideIVs.back(), LI, SE, DT, DeadInsts);
1265 if (PHINode *WidePhi = Widener.CreateWideIV(Rewriter)) {
1267 LoopPhis.push_back(WidePhi);
1273 //===----------------------------------------------------------------------===//
1274 // LinearFunctionTestReplace and its kin. Rewrite the loop exit condition.
1275 //===----------------------------------------------------------------------===//
1277 /// Check for expressions that ScalarEvolution generates to compute
1278 /// BackedgeTakenInfo. If these expressions have not been reduced, then
1279 /// expanding them may incur additional cost (albeit in the loop preheader).
1280 static bool isHighCostExpansion(const SCEV *S, BranchInst *BI,
1281 SmallPtrSetImpl<const SCEV*> &Processed,
1282 ScalarEvolution *SE) {
1283 if (!Processed.insert(S).second)
1286 // If the backedge-taken count is a UDiv, it's very likely a UDiv that
1287 // ScalarEvolution's HowFarToZero or HowManyLessThans produced to compute a
1288 // precise expression, rather than a UDiv from the user's code. If we can't
1289 // find a UDiv in the code with some simple searching, assume the former and
1290 // forego rewriting the loop.
1291 if (isa<SCEVUDivExpr>(S)) {
1292 ICmpInst *OrigCond = dyn_cast<ICmpInst>(BI->getCondition());
1293 if (!OrigCond) return true;
1294 const SCEV *R = SE->getSCEV(OrigCond->getOperand(1));
1295 R = SE->getMinusSCEV(R, SE->getConstant(R->getType(), 1));
1297 const SCEV *L = SE->getSCEV(OrigCond->getOperand(0));
1298 L = SE->getMinusSCEV(L, SE->getConstant(L->getType(), 1));
1304 // Recurse past add expressions, which commonly occur in the
1305 // BackedgeTakenCount. They may already exist in program code, and if not,
1306 // they are not too expensive rematerialize.
1307 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
1308 for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end();
1310 if (isHighCostExpansion(*I, BI, Processed, SE))
1316 // HowManyLessThans uses a Max expression whenever the loop is not guarded by
1317 // the exit condition.
1318 if (isa<SCEVSMaxExpr>(S) || isa<SCEVUMaxExpr>(S))
1321 // If we haven't recognized an expensive SCEV pattern, assume it's an
1322 // expression produced by program code.
1326 /// canExpandBackedgeTakenCount - Return true if this loop's backedge taken
1327 /// count expression can be safely and cheaply expanded into an instruction
1328 /// sequence that can be used by LinearFunctionTestReplace.
1330 /// TODO: This fails for pointer-type loop counters with greater than one byte
1331 /// strides, consequently preventing LFTR from running. For the purpose of LFTR
1332 /// we could skip this check in the case that the LFTR loop counter (chosen by
1333 /// FindLoopCounter) is also pointer type. Instead, we could directly convert
1334 /// the loop test to an inequality test by checking the target data's alignment
1335 /// of element types (given that the initial pointer value originates from or is
1336 /// used by ABI constrained operation, as opposed to inttoptr/ptrtoint).
1337 /// However, we don't yet have a strong motivation for converting loop tests
1338 /// into inequality tests.
1339 static bool canExpandBackedgeTakenCount(Loop *L, ScalarEvolution *SE) {
1340 const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L);
1341 if (isa<SCEVCouldNotCompute>(BackedgeTakenCount) ||
1342 BackedgeTakenCount->isZero())
1345 if (!L->getExitingBlock())
1348 // Can't rewrite non-branch yet.
1349 BranchInst *BI = dyn_cast<BranchInst>(L->getExitingBlock()->getTerminator());
1353 SmallPtrSet<const SCEV*, 8> Processed;
1354 if (isHighCostExpansion(BackedgeTakenCount, BI, Processed, SE))
1360 /// getLoopPhiForCounter - Return the loop header phi IFF IncV adds a loop
1361 /// invariant value to the phi.
1362 static PHINode *getLoopPhiForCounter(Value *IncV, Loop *L, DominatorTree *DT) {
1363 Instruction *IncI = dyn_cast<Instruction>(IncV);
1367 switch (IncI->getOpcode()) {
1368 case Instruction::Add:
1369 case Instruction::Sub:
1371 case Instruction::GetElementPtr:
1372 // An IV counter must preserve its type.
1373 if (IncI->getNumOperands() == 2)
1379 PHINode *Phi = dyn_cast<PHINode>(IncI->getOperand(0));
1380 if (Phi && Phi->getParent() == L->getHeader()) {
1381 if (isLoopInvariant(IncI->getOperand(1), L, DT))
1385 if (IncI->getOpcode() == Instruction::GetElementPtr)
1388 // Allow add/sub to be commuted.
1389 Phi = dyn_cast<PHINode>(IncI->getOperand(1));
1390 if (Phi && Phi->getParent() == L->getHeader()) {
1391 if (isLoopInvariant(IncI->getOperand(0), L, DT))
1397 /// Return the compare guarding the loop latch, or NULL for unrecognized tests.
1398 static ICmpInst *getLoopTest(Loop *L) {
1399 assert(L->getExitingBlock() && "expected loop exit");
1401 BasicBlock *LatchBlock = L->getLoopLatch();
1402 // Don't bother with LFTR if the loop is not properly simplified.
1406 BranchInst *BI = dyn_cast<BranchInst>(L->getExitingBlock()->getTerminator());
1407 assert(BI && "expected exit branch");
1409 return dyn_cast<ICmpInst>(BI->getCondition());
1412 /// needsLFTR - LinearFunctionTestReplace policy. Return true unless we can show
1413 /// that the current exit test is already sufficiently canonical.
1414 static bool needsLFTR(Loop *L, DominatorTree *DT) {
1415 // Do LFTR to simplify the exit condition to an ICMP.
1416 ICmpInst *Cond = getLoopTest(L);
1420 // Do LFTR to simplify the exit ICMP to EQ/NE
1421 ICmpInst::Predicate Pred = Cond->getPredicate();
1422 if (Pred != ICmpInst::ICMP_NE && Pred != ICmpInst::ICMP_EQ)
1425 // Look for a loop invariant RHS
1426 Value *LHS = Cond->getOperand(0);
1427 Value *RHS = Cond->getOperand(1);
1428 if (!isLoopInvariant(RHS, L, DT)) {
1429 if (!isLoopInvariant(LHS, L, DT))
1431 std::swap(LHS, RHS);
1433 // Look for a simple IV counter LHS
1434 PHINode *Phi = dyn_cast<PHINode>(LHS);
1436 Phi = getLoopPhiForCounter(LHS, L, DT);
1441 // Do LFTR if PHI node is defined in the loop, but is *not* a counter.
1442 int Idx = Phi->getBasicBlockIndex(L->getLoopLatch());
1446 // Do LFTR if the exit condition's IV is *not* a simple counter.
1447 Value *IncV = Phi->getIncomingValue(Idx);
1448 return Phi != getLoopPhiForCounter(IncV, L, DT);
1451 /// Recursive helper for hasConcreteDef(). Unfortunately, this currently boils
1452 /// down to checking that all operands are constant and listing instructions
1453 /// that may hide undef.
1454 static bool hasConcreteDefImpl(Value *V, SmallPtrSetImpl<Value*> &Visited,
1456 if (isa<Constant>(V))
1457 return !isa<UndefValue>(V);
1462 // Conservatively handle non-constant non-instructions. For example, Arguments
1464 Instruction *I = dyn_cast<Instruction>(V);
1468 // Load and return values may be undef.
1469 if(I->mayReadFromMemory() || isa<CallInst>(I) || isa<InvokeInst>(I))
1472 // Optimistically handle other instructions.
1473 for (User::op_iterator OI = I->op_begin(), E = I->op_end(); OI != E; ++OI) {
1474 if (!Visited.insert(*OI).second)
1476 if (!hasConcreteDefImpl(*OI, Visited, Depth+1))
1482 /// Return true if the given value is concrete. We must prove that undef can
1485 /// TODO: If we decide that this is a good approach to checking for undef, we
1486 /// may factor it into a common location.
1487 static bool hasConcreteDef(Value *V) {
1488 SmallPtrSet<Value*, 8> Visited;
1490 return hasConcreteDefImpl(V, Visited, 0);
1493 /// AlmostDeadIV - Return true if this IV has any uses other than the (soon to
1494 /// be rewritten) loop exit test.
1495 static bool AlmostDeadIV(PHINode *Phi, BasicBlock *LatchBlock, Value *Cond) {
1496 int LatchIdx = Phi->getBasicBlockIndex(LatchBlock);
1497 Value *IncV = Phi->getIncomingValue(LatchIdx);
1499 for (User *U : Phi->users())
1500 if (U != Cond && U != IncV) return false;
1502 for (User *U : IncV->users())
1503 if (U != Cond && U != Phi) return false;
1507 /// FindLoopCounter - Find an affine IV in canonical form.
1509 /// BECount may be an i8* pointer type. The pointer difference is already
1510 /// valid count without scaling the address stride, so it remains a pointer
1511 /// expression as far as SCEV is concerned.
1513 /// Currently only valid for LFTR. See the comments on hasConcreteDef below.
1515 /// FIXME: Accept -1 stride and set IVLimit = IVInit - BECount
1517 /// FIXME: Accept non-unit stride as long as SCEV can reduce BECount * Stride.
1518 /// This is difficult in general for SCEV because of potential overflow. But we
1519 /// could at least handle constant BECounts.
1520 static PHINode *FindLoopCounter(Loop *L, const SCEV *BECount,
1521 ScalarEvolution *SE, DominatorTree *DT) {
1522 uint64_t BCWidth = SE->getTypeSizeInBits(BECount->getType());
1525 cast<BranchInst>(L->getExitingBlock()->getTerminator())->getCondition();
1527 // Loop over all of the PHI nodes, looking for a simple counter.
1528 PHINode *BestPhi = nullptr;
1529 const SCEV *BestInit = nullptr;
1530 BasicBlock *LatchBlock = L->getLoopLatch();
1531 assert(LatchBlock && "needsLFTR should guarantee a loop latch");
1533 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I) {
1534 PHINode *Phi = cast<PHINode>(I);
1535 if (!SE->isSCEVable(Phi->getType()))
1538 // Avoid comparing an integer IV against a pointer Limit.
1539 if (BECount->getType()->isPointerTy() && !Phi->getType()->isPointerTy())
1542 const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(Phi));
1543 if (!AR || AR->getLoop() != L || !AR->isAffine())
1546 // AR may be a pointer type, while BECount is an integer type.
1547 // AR may be wider than BECount. With eq/ne tests overflow is immaterial.
1548 // AR may not be a narrower type, or we may never exit.
1549 uint64_t PhiWidth = SE->getTypeSizeInBits(AR->getType());
1550 if (PhiWidth < BCWidth ||
1551 !L->getHeader()->getModule()->getDataLayout().isLegalInteger(PhiWidth))
1554 const SCEV *Step = dyn_cast<SCEVConstant>(AR->getStepRecurrence(*SE));
1555 if (!Step || !Step->isOne())
1558 int LatchIdx = Phi->getBasicBlockIndex(LatchBlock);
1559 Value *IncV = Phi->getIncomingValue(LatchIdx);
1560 if (getLoopPhiForCounter(IncV, L, DT) != Phi)
1563 // Avoid reusing a potentially undef value to compute other values that may
1564 // have originally had a concrete definition.
1565 if (!hasConcreteDef(Phi)) {
1566 // We explicitly allow unknown phis as long as they are already used by
1567 // the loop test. In this case we assume that performing LFTR could not
1568 // increase the number of undef users.
1569 if (ICmpInst *Cond = getLoopTest(L)) {
1570 if (Phi != getLoopPhiForCounter(Cond->getOperand(0), L, DT)
1571 && Phi != getLoopPhiForCounter(Cond->getOperand(1), L, DT)) {
1576 const SCEV *Init = AR->getStart();
1578 if (BestPhi && !AlmostDeadIV(BestPhi, LatchBlock, Cond)) {
1579 // Don't force a live loop counter if another IV can be used.
1580 if (AlmostDeadIV(Phi, LatchBlock, Cond))
1583 // Prefer to count-from-zero. This is a more "canonical" counter form. It
1584 // also prefers integer to pointer IVs.
1585 if (BestInit->isZero() != Init->isZero()) {
1586 if (BestInit->isZero())
1589 // If two IVs both count from zero or both count from nonzero then the
1590 // narrower is likely a dead phi that has been widened. Use the wider phi
1591 // to allow the other to be eliminated.
1592 else if (PhiWidth <= SE->getTypeSizeInBits(BestPhi->getType()))
1601 /// genLoopLimit - Help LinearFunctionTestReplace by generating a value that
1602 /// holds the RHS of the new loop test.
1603 static Value *genLoopLimit(PHINode *IndVar, const SCEV *IVCount, Loop *L,
1604 SCEVExpander &Rewriter, ScalarEvolution *SE) {
1605 const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(IndVar));
1606 assert(AR && AR->getLoop() == L && AR->isAffine() && "bad loop counter");
1607 const SCEV *IVInit = AR->getStart();
1609 // IVInit may be a pointer while IVCount is an integer when FindLoopCounter
1610 // finds a valid pointer IV. Sign extend BECount in order to materialize a
1611 // GEP. Avoid running SCEVExpander on a new pointer value, instead reusing
1612 // the existing GEPs whenever possible.
1613 if (IndVar->getType()->isPointerTy()
1614 && !IVCount->getType()->isPointerTy()) {
1616 // IVOffset will be the new GEP offset that is interpreted by GEP as a
1617 // signed value. IVCount on the other hand represents the loop trip count,
1618 // which is an unsigned value. FindLoopCounter only allows induction
1619 // variables that have a positive unit stride of one. This means we don't
1620 // have to handle the case of negative offsets (yet) and just need to zero
1622 Type *OfsTy = SE->getEffectiveSCEVType(IVInit->getType());
1623 const SCEV *IVOffset = SE->getTruncateOrZeroExtend(IVCount, OfsTy);
1625 // Expand the code for the iteration count.
1626 assert(SE->isLoopInvariant(IVOffset, L) &&
1627 "Computed iteration count is not loop invariant!");
1628 BranchInst *BI = cast<BranchInst>(L->getExitingBlock()->getTerminator());
1629 Value *GEPOffset = Rewriter.expandCodeFor(IVOffset, OfsTy, BI);
1631 Value *GEPBase = IndVar->getIncomingValueForBlock(L->getLoopPreheader());
1632 assert(AR->getStart() == SE->getSCEV(GEPBase) && "bad loop counter");
1633 // We could handle pointer IVs other than i8*, but we need to compensate for
1634 // gep index scaling. See canExpandBackedgeTakenCount comments.
1635 assert(SE->getSizeOfExpr(IntegerType::getInt64Ty(IndVar->getContext()),
1636 cast<PointerType>(GEPBase->getType())->getElementType())->isOne()
1637 && "unit stride pointer IV must be i8*");
1639 IRBuilder<> Builder(L->getLoopPreheader()->getTerminator());
1640 return Builder.CreateGEP(GEPBase, GEPOffset, "lftr.limit");
1643 // In any other case, convert both IVInit and IVCount to integers before
1644 // comparing. This may result in SCEV expension of pointers, but in practice
1645 // SCEV will fold the pointer arithmetic away as such:
1646 // BECount = (IVEnd - IVInit - 1) => IVLimit = IVInit (postinc).
1648 // Valid Cases: (1) both integers is most common; (2) both may be pointers
1649 // for simple memset-style loops.
1651 // IVInit integer and IVCount pointer would only occur if a canonical IV
1652 // were generated on top of case #2, which is not expected.
1654 const SCEV *IVLimit = nullptr;
1655 // For unit stride, IVCount = Start + BECount with 2's complement overflow.
1656 // For non-zero Start, compute IVCount here.
1657 if (AR->getStart()->isZero())
1660 assert(AR->getStepRecurrence(*SE)->isOne() && "only handles unit stride");
1661 const SCEV *IVInit = AR->getStart();
1663 // For integer IVs, truncate the IV before computing IVInit + BECount.
1664 if (SE->getTypeSizeInBits(IVInit->getType())
1665 > SE->getTypeSizeInBits(IVCount->getType()))
1666 IVInit = SE->getTruncateExpr(IVInit, IVCount->getType());
1668 IVLimit = SE->getAddExpr(IVInit, IVCount);
1670 // Expand the code for the iteration count.
1671 BranchInst *BI = cast<BranchInst>(L->getExitingBlock()->getTerminator());
1672 IRBuilder<> Builder(BI);
1673 assert(SE->isLoopInvariant(IVLimit, L) &&
1674 "Computed iteration count is not loop invariant!");
1675 // Ensure that we generate the same type as IndVar, or a smaller integer
1676 // type. In the presence of null pointer values, we have an integer type
1677 // SCEV expression (IVInit) for a pointer type IV value (IndVar).
1678 Type *LimitTy = IVCount->getType()->isPointerTy() ?
1679 IndVar->getType() : IVCount->getType();
1680 return Rewriter.expandCodeFor(IVLimit, LimitTy, BI);
1684 /// LinearFunctionTestReplace - This method rewrites the exit condition of the
1685 /// loop to be a canonical != comparison against the incremented loop induction
1686 /// variable. This pass is able to rewrite the exit tests of any loop where the
1687 /// SCEV analysis can determine a loop-invariant trip count of the loop, which
1688 /// is actually a much broader range than just linear tests.
1689 Value *IndVarSimplify::
1690 LinearFunctionTestReplace(Loop *L,
1691 const SCEV *BackedgeTakenCount,
1693 SCEVExpander &Rewriter) {
1694 assert(canExpandBackedgeTakenCount(L, SE) && "precondition");
1696 // Initialize CmpIndVar and IVCount to their preincremented values.
1697 Value *CmpIndVar = IndVar;
1698 const SCEV *IVCount = BackedgeTakenCount;
1700 // If the exiting block is the same as the backedge block, we prefer to
1701 // compare against the post-incremented value, otherwise we must compare
1702 // against the preincremented value.
1703 if (L->getExitingBlock() == L->getLoopLatch()) {
1704 // Add one to the "backedge-taken" count to get the trip count.
1705 // This addition may overflow, which is valid as long as the comparison is
1706 // truncated to BackedgeTakenCount->getType().
1707 IVCount = SE->getAddExpr(BackedgeTakenCount,
1708 SE->getConstant(BackedgeTakenCount->getType(), 1));
1709 // The BackedgeTaken expression contains the number of times that the
1710 // backedge branches to the loop header. This is one less than the
1711 // number of times the loop executes, so use the incremented indvar.
1712 CmpIndVar = IndVar->getIncomingValueForBlock(L->getExitingBlock());
1715 Value *ExitCnt = genLoopLimit(IndVar, IVCount, L, Rewriter, SE);
1716 assert(ExitCnt->getType()->isPointerTy() == IndVar->getType()->isPointerTy()
1717 && "genLoopLimit missed a cast");
1719 // Insert a new icmp_ne or icmp_eq instruction before the branch.
1720 BranchInst *BI = cast<BranchInst>(L->getExitingBlock()->getTerminator());
1721 ICmpInst::Predicate P;
1722 if (L->contains(BI->getSuccessor(0)))
1723 P = ICmpInst::ICMP_NE;
1725 P = ICmpInst::ICMP_EQ;
1727 DEBUG(dbgs() << "INDVARS: Rewriting loop exit condition to:\n"
1728 << " LHS:" << *CmpIndVar << '\n'
1730 << (P == ICmpInst::ICMP_NE ? "!=" : "==") << "\n"
1731 << " RHS:\t" << *ExitCnt << "\n"
1732 << " IVCount:\t" << *IVCount << "\n");
1734 IRBuilder<> Builder(BI);
1736 // LFTR can ignore IV overflow and truncate to the width of
1737 // BECount. This avoids materializing the add(zext(add)) expression.
1738 unsigned CmpIndVarSize = SE->getTypeSizeInBits(CmpIndVar->getType());
1739 unsigned ExitCntSize = SE->getTypeSizeInBits(ExitCnt->getType());
1740 if (CmpIndVarSize > ExitCntSize) {
1741 const SCEVAddRecExpr *AR = cast<SCEVAddRecExpr>(SE->getSCEV(IndVar));
1742 const SCEV *ARStart = AR->getStart();
1743 const SCEV *ARStep = AR->getStepRecurrence(*SE);
1744 // For constant IVCount, avoid truncation.
1745 if (isa<SCEVConstant>(ARStart) && isa<SCEVConstant>(IVCount)) {
1746 const APInt &Start = cast<SCEVConstant>(ARStart)->getValue()->getValue();
1747 APInt Count = cast<SCEVConstant>(IVCount)->getValue()->getValue();
1748 // Note that the post-inc value of BackedgeTakenCount may have overflowed
1749 // above such that IVCount is now zero.
1750 if (IVCount != BackedgeTakenCount && Count == 0) {
1751 Count = APInt::getMaxValue(Count.getBitWidth()).zext(CmpIndVarSize);
1755 Count = Count.zext(CmpIndVarSize);
1757 if (cast<SCEVConstant>(ARStep)->getValue()->isNegative())
1758 NewLimit = Start - Count;
1760 NewLimit = Start + Count;
1761 ExitCnt = ConstantInt::get(CmpIndVar->getType(), NewLimit);
1763 DEBUG(dbgs() << " Widen RHS:\t" << *ExitCnt << "\n");
1765 CmpIndVar = Builder.CreateTrunc(CmpIndVar, ExitCnt->getType(),
1769 Value *Cond = Builder.CreateICmp(P, CmpIndVar, ExitCnt, "exitcond");
1770 Value *OrigCond = BI->getCondition();
1771 // It's tempting to use replaceAllUsesWith here to fully replace the old
1772 // comparison, but that's not immediately safe, since users of the old
1773 // comparison may not be dominated by the new comparison. Instead, just
1774 // update the branch to use the new comparison; in the common case this
1775 // will make old comparison dead.
1776 BI->setCondition(Cond);
1777 DeadInsts.push_back(OrigCond);
1784 //===----------------------------------------------------------------------===//
1785 // SinkUnusedInvariants. A late subpass to cleanup loop preheaders.
1786 //===----------------------------------------------------------------------===//
1788 /// If there's a single exit block, sink any loop-invariant values that
1789 /// were defined in the preheader but not used inside the loop into the
1790 /// exit block to reduce register pressure in the loop.
1791 void IndVarSimplify::SinkUnusedInvariants(Loop *L) {
1792 BasicBlock *ExitBlock = L->getExitBlock();
1793 if (!ExitBlock) return;
1795 BasicBlock *Preheader = L->getLoopPreheader();
1796 if (!Preheader) return;
1798 Instruction *InsertPt = ExitBlock->getFirstInsertionPt();
1799 BasicBlock::iterator I = Preheader->getTerminator();
1800 while (I != Preheader->begin()) {
1802 // New instructions were inserted at the end of the preheader.
1803 if (isa<PHINode>(I))
1806 // Don't move instructions which might have side effects, since the side
1807 // effects need to complete before instructions inside the loop. Also don't
1808 // move instructions which might read memory, since the loop may modify
1809 // memory. Note that it's okay if the instruction might have undefined
1810 // behavior: LoopSimplify guarantees that the preheader dominates the exit
1812 if (I->mayHaveSideEffects() || I->mayReadFromMemory())
1815 // Skip debug info intrinsics.
1816 if (isa<DbgInfoIntrinsic>(I))
1819 // Skip landingpad instructions.
1820 if (isa<LandingPadInst>(I))
1823 // Don't sink alloca: we never want to sink static alloca's out of the
1824 // entry block, and correctly sinking dynamic alloca's requires
1825 // checks for stacksave/stackrestore intrinsics.
1826 // FIXME: Refactor this check somehow?
1827 if (isa<AllocaInst>(I))
1830 // Determine if there is a use in or before the loop (direct or
1832 bool UsedInLoop = false;
1833 for (Use &U : I->uses()) {
1834 Instruction *User = cast<Instruction>(U.getUser());
1835 BasicBlock *UseBB = User->getParent();
1836 if (PHINode *P = dyn_cast<PHINode>(User)) {
1838 PHINode::getIncomingValueNumForOperand(U.getOperandNo());
1839 UseBB = P->getIncomingBlock(i);
1841 if (UseBB == Preheader || L->contains(UseBB)) {
1847 // If there is, the def must remain in the preheader.
1851 // Otherwise, sink it to the exit block.
1852 Instruction *ToMove = I;
1855 if (I != Preheader->begin()) {
1856 // Skip debug info intrinsics.
1859 } while (isa<DbgInfoIntrinsic>(I) && I != Preheader->begin());
1861 if (isa<DbgInfoIntrinsic>(I) && I == Preheader->begin())
1867 ToMove->moveBefore(InsertPt);
1873 //===----------------------------------------------------------------------===//
1874 // IndVarSimplify driver. Manage several subpasses of IV simplification.
1875 //===----------------------------------------------------------------------===//
1877 bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
1878 if (skipOptnoneFunction(L))
1881 // If LoopSimplify form is not available, stay out of trouble. Some notes:
1882 // - LSR currently only supports LoopSimplify-form loops. Indvars'
1883 // canonicalization can be a pessimization without LSR to "clean up"
1885 // - We depend on having a preheader; in particular,
1886 // Loop::getCanonicalInductionVariable only supports loops with preheaders,
1887 // and we're in trouble if we can't find the induction variable even when
1888 // we've manually inserted one.
1889 if (!L->isLoopSimplifyForm())
1892 LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
1893 SE = &getAnalysis<ScalarEvolution>();
1894 DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
1895 auto *TLIP = getAnalysisIfAvailable<TargetLibraryInfoWrapperPass>();
1896 TLI = TLIP ? &TLIP->getTLI() : nullptr;
1897 auto *TTIP = getAnalysisIfAvailable<TargetTransformInfoWrapperPass>();
1898 TTI = TTIP ? &TTIP->getTTI(*L->getHeader()->getParent()) : nullptr;
1899 const DataLayout &DL = L->getHeader()->getModule()->getDataLayout();
1904 // If there are any floating-point recurrences, attempt to
1905 // transform them to use integer recurrences.
1906 RewriteNonIntegerIVs(L);
1908 const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L);
1910 // Create a rewriter object which we'll use to transform the code with.
1911 SCEVExpander Rewriter(*SE, DL, "indvars");
1913 Rewriter.setDebugType(DEBUG_TYPE);
1916 // Eliminate redundant IV users.
1918 // Simplification works best when run before other consumers of SCEV. We
1919 // attempt to avoid evaluating SCEVs for sign/zero extend operations until
1920 // other expressions involving loop IVs have been evaluated. This helps SCEV
1921 // set no-wrap flags before normalizing sign/zero extension.
1922 Rewriter.disableCanonicalMode();
1923 SimplifyAndExtend(L, Rewriter, LPM);
1925 // Check to see if this loop has a computable loop-invariant execution count.
1926 // If so, this means that we can compute the final value of any expressions
1927 // that are recurrent in the loop, and substitute the exit values from the
1928 // loop into any instructions outside of the loop that use the final values of
1929 // the current expressions.
1931 if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount))
1932 RewriteLoopExitValues(L, Rewriter);
1934 // Eliminate redundant IV cycles.
1935 NumElimIV += Rewriter.replaceCongruentIVs(L, DT, DeadInsts);
1937 // If we have a trip count expression, rewrite the loop's exit condition
1938 // using it. We can currently only handle loops with a single exit.
1939 if (canExpandBackedgeTakenCount(L, SE) && needsLFTR(L, DT)) {
1940 PHINode *IndVar = FindLoopCounter(L, BackedgeTakenCount, SE, DT);
1942 // Check preconditions for proper SCEVExpander operation. SCEV does not
1943 // express SCEVExpander's dependencies, such as LoopSimplify. Instead any
1944 // pass that uses the SCEVExpander must do it. This does not work well for
1945 // loop passes because SCEVExpander makes assumptions about all loops,
1946 // while LoopPassManager only forces the current loop to be simplified.
1948 // FIXME: SCEV expansion has no way to bail out, so the caller must
1949 // explicitly check any assumptions made by SCEV. Brittle.
1950 const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(BackedgeTakenCount);
1951 if (!AR || AR->getLoop()->getLoopPreheader())
1952 (void)LinearFunctionTestReplace(L, BackedgeTakenCount, IndVar,
1956 // Clear the rewriter cache, because values that are in the rewriter's cache
1957 // can be deleted in the loop below, causing the AssertingVH in the cache to
1961 // Now that we're done iterating through lists, clean up any instructions
1962 // which are now dead.
1963 while (!DeadInsts.empty())
1964 if (Instruction *Inst =
1965 dyn_cast_or_null<Instruction>(&*DeadInsts.pop_back_val()))
1966 RecursivelyDeleteTriviallyDeadInstructions(Inst, TLI);
1968 // The Rewriter may not be used from this point on.
1970 // Loop-invariant instructions in the preheader that aren't used in the
1971 // loop may be sunk below the loop to reduce register pressure.
1972 SinkUnusedInvariants(L);
1974 // Clean up dead instructions.
1975 Changed |= DeleteDeadPHIs(L->getHeader(), TLI);
1976 // Check a post-condition.
1977 assert(L->isLCSSAForm(*DT) &&
1978 "Indvars did not leave the loop in lcssa form!");
1980 // Verify that LFTR, and any other change have not interfered with SCEV's
1981 // ability to compute trip count.
1983 if (VerifyIndvars && !isa<SCEVCouldNotCompute>(BackedgeTakenCount)) {
1985 const SCEV *NewBECount = SE->getBackedgeTakenCount(L);
1986 if (SE->getTypeSizeInBits(BackedgeTakenCount->getType()) <
1987 SE->getTypeSizeInBits(NewBECount->getType()))
1988 NewBECount = SE->getTruncateOrNoop(NewBECount,
1989 BackedgeTakenCount->getType());
1991 BackedgeTakenCount = SE->getTruncateOrNoop(BackedgeTakenCount,
1992 NewBECount->getType());
1993 assert(BackedgeTakenCount == NewBECount && "indvars must preserve SCEV");