1 //===- ConstantHoisting.cpp - Prepare code for expensive constants --------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This pass identifies expensive constants to hoist and coalesces them to
11 // better prepare it for SelectionDAG-based code generation. This works around
12 // the limitations of the basic-block-at-a-time approach.
14 // First it scans all instructions for integer constants and calculates its
15 // cost. If the constant can be folded into the instruction (the cost is
16 // TCC_Free) or the cost is just a simple operation (TCC_BASIC), then we don't
17 // consider it expensive and leave it alone. This is the default behavior and
18 // the default implementation of getIntImmCost will always return TCC_Free.
20 // If the cost is more than TCC_BASIC, then the integer constant can't be folded
21 // into the instruction and it might be beneficial to hoist the constant.
22 // Similar constants are coalesced to reduce register pressure and
23 // materialization code.
25 // When a constant is hoisted, it is also hidden behind a bitcast to force it to
26 // be live-out of the basic block. Otherwise the constant would be just
27 // duplicated and each basic block would have its own copy in the SelectionDAG.
28 // The SelectionDAG recognizes such constants as opaque and doesn't perform
29 // certain transformations on them, which would create a new expensive constant.
31 // This optimization is only applied to integer constants in instructions and
32 // simple (this means not nested) constant cast expressions. For example:
33 // %0 = load i64* inttoptr (i64 big_constant to i64*)
34 //===----------------------------------------------------------------------===//
36 #include "llvm/Transforms/Scalar/ConstantHoisting.h"
37 #include "llvm/ADT/SmallSet.h"
38 #include "llvm/ADT/SmallVector.h"
39 #include "llvm/ADT/Statistic.h"
40 #include "llvm/IR/Constants.h"
41 #include "llvm/IR/IntrinsicInst.h"
42 #include "llvm/Pass.h"
43 #include "llvm/Support/Debug.h"
44 #include "llvm/Support/raw_ostream.h"
45 #include "llvm/Transforms/Scalar.h"
49 using namespace consthoist;
51 #define DEBUG_TYPE "consthoist"
53 STATISTIC(NumConstantsHoisted, "Number of constants hoisted");
54 STATISTIC(NumConstantsRebased, "Number of constants rebased");
57 /// \brief The constant hoisting pass.
58 class ConstantHoistingLegacyPass : public FunctionPass {
60 static char ID; // Pass identification, replacement for typeid
61 ConstantHoistingLegacyPass() : FunctionPass(ID) {
62 initializeConstantHoistingLegacyPassPass(*PassRegistry::getPassRegistry());
65 bool runOnFunction(Function &Fn) override;
67 StringRef getPassName() const override { return "Constant Hoisting"; }
69 void getAnalysisUsage(AnalysisUsage &AU) const override {
71 AU.addRequired<DominatorTreeWrapperPass>();
72 AU.addRequired<TargetTransformInfoWrapperPass>();
75 void releaseMemory() override { Impl.releaseMemory(); }
78 ConstantHoistingPass Impl;
82 char ConstantHoistingLegacyPass::ID = 0;
83 INITIALIZE_PASS_BEGIN(ConstantHoistingLegacyPass, "consthoist",
84 "Constant Hoisting", false, false)
85 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
86 INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
87 INITIALIZE_PASS_END(ConstantHoistingLegacyPass, "consthoist",
88 "Constant Hoisting", false, false)
90 FunctionPass *llvm::createConstantHoistingPass() {
91 return new ConstantHoistingLegacyPass();
94 /// \brief Perform the constant hoisting optimization for the given function.
95 bool ConstantHoistingLegacyPass::runOnFunction(Function &Fn) {
99 DEBUG(dbgs() << "********** Begin Constant Hoisting **********\n");
100 DEBUG(dbgs() << "********** Function: " << Fn.getName() << '\n');
102 bool MadeChange = Impl.runImpl(
103 Fn, getAnalysis<TargetTransformInfoWrapperPass>().getTTI(Fn),
104 getAnalysis<DominatorTreeWrapperPass>().getDomTree(), Fn.getEntryBlock());
107 DEBUG(dbgs() << "********** Function after Constant Hoisting: "
108 << Fn.getName() << '\n');
111 DEBUG(dbgs() << "********** End Constant Hoisting **********\n");
117 /// \brief Find the constant materialization insertion point.
118 Instruction *ConstantHoistingPass::findMatInsertPt(Instruction *Inst,
119 unsigned Idx) const {
120 // If the operand is a cast instruction, then we have to materialize the
121 // constant before the cast instruction.
123 Value *Opnd = Inst->getOperand(Idx);
124 if (auto CastInst = dyn_cast<Instruction>(Opnd))
125 if (CastInst->isCast())
129 // The simple and common case. This also includes constant expressions.
130 if (!isa<PHINode>(Inst) && !Inst->isEHPad())
133 // We can't insert directly before a phi node or an eh pad. Insert before
134 // the terminator of the incoming or dominating block.
135 assert(Entry != Inst->getParent() && "PHI or landing pad in entry block!");
136 if (Idx != ~0U && isa<PHINode>(Inst))
137 return cast<PHINode>(Inst)->getIncomingBlock(Idx)->getTerminator();
139 BasicBlock *IDom = DT->getNode(Inst->getParent())->getIDom()->getBlock();
140 return IDom->getTerminator();
143 /// \brief Find an insertion point that dominates all uses.
144 Instruction *ConstantHoistingPass::findConstantInsertionPoint(
145 const ConstantInfo &ConstInfo) const {
146 assert(!ConstInfo.RebasedConstants.empty() && "Invalid constant info entry.");
147 // Collect all basic blocks.
148 SmallPtrSet<BasicBlock *, 8> BBs;
149 for (auto const &RCI : ConstInfo.RebasedConstants)
150 for (auto const &U : RCI.Uses)
151 BBs.insert(findMatInsertPt(U.Inst, U.OpndIdx)->getParent());
153 if (BBs.count(Entry))
154 return &Entry->front();
156 while (BBs.size() >= 2) {
157 BasicBlock *BB, *BB1, *BB2;
159 BB2 = *std::next(BBs.begin());
160 BB = DT->findNearestCommonDominator(BB1, BB2);
162 return &Entry->front();
167 assert((BBs.size() == 1) && "Expected only one element.");
168 Instruction &FirstInst = (*BBs.begin())->front();
169 return findMatInsertPt(&FirstInst);
173 /// \brief Record constant integer ConstInt for instruction Inst at operand
176 /// The operand at index Idx is not necessarily the constant integer itself. It
177 /// could also be a cast instruction or a constant expression that uses the
179 void ConstantHoistingPass::collectConstantCandidates(
180 ConstCandMapType &ConstCandMap, Instruction *Inst, unsigned Idx,
181 ConstantInt *ConstInt) {
183 // Ask the target about the cost of materializing the constant for the given
184 // instruction and operand index.
185 if (auto IntrInst = dyn_cast<IntrinsicInst>(Inst))
186 Cost = TTI->getIntImmCost(IntrInst->getIntrinsicID(), Idx,
187 ConstInt->getValue(), ConstInt->getType());
189 Cost = TTI->getIntImmCost(Inst->getOpcode(), Idx, ConstInt->getValue(),
190 ConstInt->getType());
192 // Ignore cheap integer constants.
193 if (Cost > TargetTransformInfo::TCC_Basic) {
194 ConstCandMapType::iterator Itr;
196 std::tie(Itr, Inserted) = ConstCandMap.insert(std::make_pair(ConstInt, 0));
198 ConstCandVec.push_back(ConstantCandidate(ConstInt));
199 Itr->second = ConstCandVec.size() - 1;
201 ConstCandVec[Itr->second].addUser(Inst, Idx, Cost);
202 DEBUG(if (isa<ConstantInt>(Inst->getOperand(Idx)))
203 dbgs() << "Collect constant " << *ConstInt << " from " << *Inst
204 << " with cost " << Cost << '\n';
206 dbgs() << "Collect constant " << *ConstInt << " indirectly from "
207 << *Inst << " via " << *Inst->getOperand(Idx) << " with cost "
213 /// \brief Scan the instruction for expensive integer constants and record them
214 /// in the constant candidate vector.
215 void ConstantHoistingPass::collectConstantCandidates(
216 ConstCandMapType &ConstCandMap, Instruction *Inst) {
217 // Skip all cast instructions. They are visited indirectly later on.
221 // Can't handle inline asm. Skip it.
222 if (auto Call = dyn_cast<CallInst>(Inst))
223 if (isa<InlineAsm>(Call->getCalledValue()))
226 // Switch cases must remain constant, and if the value being tested is
227 // constant the entire thing should disappear.
228 if (isa<SwitchInst>(Inst))
231 // Static allocas (constant size in the entry block) are handled by
232 // prologue/epilogue insertion so they're free anyway. We definitely don't
233 // want to make them non-constant.
234 auto AI = dyn_cast<AllocaInst>(Inst);
235 if (AI && AI->isStaticAlloca())
238 // Scan all operands.
239 for (unsigned Idx = 0, E = Inst->getNumOperands(); Idx != E; ++Idx) {
240 Value *Opnd = Inst->getOperand(Idx);
242 // Visit constant integers.
243 if (auto ConstInt = dyn_cast<ConstantInt>(Opnd)) {
244 collectConstantCandidates(ConstCandMap, Inst, Idx, ConstInt);
248 // Visit cast instructions that have constant integers.
249 if (auto CastInst = dyn_cast<Instruction>(Opnd)) {
250 // Only visit cast instructions, which have been skipped. All other
251 // instructions should have already been visited.
252 if (!CastInst->isCast())
255 if (auto *ConstInt = dyn_cast<ConstantInt>(CastInst->getOperand(0))) {
256 // Pretend the constant is directly used by the instruction and ignore
257 // the cast instruction.
258 collectConstantCandidates(ConstCandMap, Inst, Idx, ConstInt);
263 // Visit constant expressions that have constant integers.
264 if (auto ConstExpr = dyn_cast<ConstantExpr>(Opnd)) {
265 // Only visit constant cast expressions.
266 if (!ConstExpr->isCast())
269 if (auto ConstInt = dyn_cast<ConstantInt>(ConstExpr->getOperand(0))) {
270 // Pretend the constant is directly used by the instruction and ignore
271 // the constant expression.
272 collectConstantCandidates(ConstCandMap, Inst, Idx, ConstInt);
276 } // end of for all operands
279 /// \brief Collect all integer constants in the function that cannot be folded
280 /// into an instruction itself.
281 void ConstantHoistingPass::collectConstantCandidates(Function &Fn) {
282 ConstCandMapType ConstCandMap;
283 for (BasicBlock &BB : Fn)
284 for (Instruction &Inst : BB)
285 collectConstantCandidates(ConstCandMap, &Inst);
288 // This helper function is necessary to deal with values that have different
289 // bit widths (APInt Operator- does not like that). If the value cannot be
290 // represented in uint64 we return an "empty" APInt. This is then interpreted
291 // as the value is not in range.
292 static llvm::Optional<APInt> calculateOffsetDiff(APInt V1, APInt V2)
294 llvm::Optional<APInt> Res = None;
295 unsigned BW = V1.getBitWidth() > V2.getBitWidth() ?
296 V1.getBitWidth() : V2.getBitWidth();
297 uint64_t LimVal1 = V1.getLimitedValue();
298 uint64_t LimVal2 = V2.getLimitedValue();
300 if (LimVal1 == ~0ULL || LimVal2 == ~0ULL)
303 uint64_t Diff = LimVal1 - LimVal2;
304 return APInt(BW, Diff, true);
307 // From a list of constants, one needs to picked as the base and the other
308 // constants will be transformed into an offset from that base constant. The
309 // question is which we can pick best? For example, consider these constants
310 // and their number of uses:
312 // Constants| 2 | 4 | 12 | 42 |
313 // NumUses | 3 | 2 | 8 | 7 |
315 // Selecting constant 12 because it has the most uses will generate negative
316 // offsets for constants 2 and 4 (i.e. -10 and -8 respectively). If negative
317 // offsets lead to less optimal code generation, then there might be better
318 // solutions. Suppose immediates in the range of 0..35 are most optimally
319 // supported by the architecture, then selecting constant 2 is most optimal
320 // because this will generate offsets: 0, 2, 10, 40. Offsets 0, 2 and 10 are in
321 // range 0..35, and thus 3 + 2 + 8 = 13 uses are in range. Selecting 12 would
322 // have only 8 uses in range, so choosing 2 as a base is more optimal. Thus, in
323 // selecting the base constant the range of the offsets is a very important
324 // factor too that we take into account here. This algorithm calculates a total
325 // costs for selecting a constant as the base and substract the costs if
326 // immediates are out of range. It has quadratic complexity, so we call this
327 // function only when we're optimising for size and there are less than 100
328 // constants, we fall back to the straightforward algorithm otherwise
329 // which does not do all the offset calculations.
331 ConstantHoistingPass::maximizeConstantsInRange(ConstCandVecType::iterator S,
332 ConstCandVecType::iterator E,
333 ConstCandVecType::iterator &MaxCostItr) {
334 unsigned NumUses = 0;
336 if(!Entry->getParent()->optForSize() || std::distance(S,E) > 100) {
337 for (auto ConstCand = S; ConstCand != E; ++ConstCand) {
338 NumUses += ConstCand->Uses.size();
339 if (ConstCand->CumulativeCost > MaxCostItr->CumulativeCost)
340 MaxCostItr = ConstCand;
345 DEBUG(dbgs() << "== Maximize constants in range ==\n");
347 for (auto ConstCand = S; ConstCand != E; ++ConstCand) {
348 auto Value = ConstCand->ConstInt->getValue();
349 Type *Ty = ConstCand->ConstInt->getType();
351 NumUses += ConstCand->Uses.size();
352 DEBUG(dbgs() << "= Constant: " << ConstCand->ConstInt->getValue() << "\n");
354 for (auto User : ConstCand->Uses) {
355 unsigned Opcode = User.Inst->getOpcode();
356 unsigned OpndIdx = User.OpndIdx;
357 Cost += TTI->getIntImmCost(Opcode, OpndIdx, Value, Ty);
358 DEBUG(dbgs() << "Cost: " << Cost << "\n");
360 for (auto C2 = S; C2 != E; ++C2) {
361 llvm::Optional<APInt> Diff = calculateOffsetDiff(
362 C2->ConstInt->getValue(),
363 ConstCand->ConstInt->getValue());
366 TTI->getIntImmCodeSizeCost(Opcode, OpndIdx, Diff.getValue(), Ty);
368 DEBUG(dbgs() << "Offset " << Diff.getValue() << " "
369 << "has penalty: " << ImmCosts << "\n"
370 << "Adjusted cost: " << Cost << "\n");
374 DEBUG(dbgs() << "Cumulative cost: " << Cost << "\n");
375 if (Cost > MaxCost) {
377 MaxCostItr = ConstCand;
378 DEBUG(dbgs() << "New candidate: " << MaxCostItr->ConstInt->getValue()
385 /// \brief Find the base constant within the given range and rebase all other
386 /// constants with respect to the base constant.
387 void ConstantHoistingPass::findAndMakeBaseConstant(
388 ConstCandVecType::iterator S, ConstCandVecType::iterator E) {
390 unsigned NumUses = maximizeConstantsInRange(S, E, MaxCostItr);
392 // Don't hoist constants that have only one use.
396 ConstantInfo ConstInfo;
397 ConstInfo.BaseConstant = MaxCostItr->ConstInt;
398 Type *Ty = ConstInfo.BaseConstant->getType();
400 // Rebase the constants with respect to the base constant.
401 for (auto ConstCand = S; ConstCand != E; ++ConstCand) {
402 APInt Diff = ConstCand->ConstInt->getValue() -
403 ConstInfo.BaseConstant->getValue();
404 Constant *Offset = Diff == 0 ? nullptr : ConstantInt::get(Ty, Diff);
405 ConstInfo.RebasedConstants.push_back(
406 RebasedConstantInfo(std::move(ConstCand->Uses), Offset));
408 ConstantVec.push_back(std::move(ConstInfo));
411 /// \brief Finds and combines constant candidates that can be easily
412 /// rematerialized with an add from a common base constant.
413 void ConstantHoistingPass::findBaseConstants() {
414 // Sort the constants by value and type. This invalidates the mapping!
415 std::sort(ConstCandVec.begin(), ConstCandVec.end(),
416 [](const ConstantCandidate &LHS, const ConstantCandidate &RHS) {
417 if (LHS.ConstInt->getType() != RHS.ConstInt->getType())
418 return LHS.ConstInt->getType()->getBitWidth() <
419 RHS.ConstInt->getType()->getBitWidth();
420 return LHS.ConstInt->getValue().ult(RHS.ConstInt->getValue());
423 // Simple linear scan through the sorted constant candidate vector for viable
425 auto MinValItr = ConstCandVec.begin();
426 for (auto CC = std::next(ConstCandVec.begin()), E = ConstCandVec.end();
428 if (MinValItr->ConstInt->getType() == CC->ConstInt->getType()) {
429 // Check if the constant is in range of an add with immediate.
430 APInt Diff = CC->ConstInt->getValue() - MinValItr->ConstInt->getValue();
431 if ((Diff.getBitWidth() <= 64) &&
432 TTI->isLegalAddImmediate(Diff.getSExtValue()))
435 // We either have now a different constant type or the constant is not in
436 // range of an add with immediate anymore.
437 findAndMakeBaseConstant(MinValItr, CC);
438 // Start a new base constant search.
441 // Finalize the last base constant search.
442 findAndMakeBaseConstant(MinValItr, ConstCandVec.end());
445 /// \brief Updates the operand at Idx in instruction Inst with the result of
446 /// instruction Mat. If the instruction is a PHI node then special
447 /// handling for duplicate values form the same incoming basic block is
449 /// \return The update will always succeed, but the return value indicated if
450 /// Mat was used for the update or not.
451 static bool updateOperand(Instruction *Inst, unsigned Idx, Instruction *Mat) {
452 if (auto PHI = dyn_cast<PHINode>(Inst)) {
453 // Check if any previous operand of the PHI node has the same incoming basic
454 // block. This is a very odd case that happens when the incoming basic block
455 // has a switch statement. In this case use the same value as the previous
456 // operand(s), otherwise we will fail verification due to different values.
457 // The values are actually the same, but the variable names are different
458 // and the verifier doesn't like that.
459 BasicBlock *IncomingBB = PHI->getIncomingBlock(Idx);
460 for (unsigned i = 0; i < Idx; ++i) {
461 if (PHI->getIncomingBlock(i) == IncomingBB) {
462 Value *IncomingVal = PHI->getIncomingValue(i);
463 Inst->setOperand(Idx, IncomingVal);
469 Inst->setOperand(Idx, Mat);
473 /// \brief Emit materialization code for all rebased constants and update their
475 void ConstantHoistingPass::emitBaseConstants(Instruction *Base,
477 const ConstantUser &ConstUser) {
478 Instruction *Mat = Base;
480 Instruction *InsertionPt = findMatInsertPt(ConstUser.Inst,
482 Mat = BinaryOperator::Create(Instruction::Add, Base, Offset,
483 "const_mat", InsertionPt);
485 DEBUG(dbgs() << "Materialize constant (" << *Base->getOperand(0)
486 << " + " << *Offset << ") in BB "
487 << Mat->getParent()->getName() << '\n' << *Mat << '\n');
488 Mat->setDebugLoc(ConstUser.Inst->getDebugLoc());
490 Value *Opnd = ConstUser.Inst->getOperand(ConstUser.OpndIdx);
492 // Visit constant integer.
493 if (isa<ConstantInt>(Opnd)) {
494 DEBUG(dbgs() << "Update: " << *ConstUser.Inst << '\n');
495 if (!updateOperand(ConstUser.Inst, ConstUser.OpndIdx, Mat) && Offset)
496 Mat->eraseFromParent();
497 DEBUG(dbgs() << "To : " << *ConstUser.Inst << '\n');
501 // Visit cast instruction.
502 if (auto CastInst = dyn_cast<Instruction>(Opnd)) {
503 assert(CastInst->isCast() && "Expected an cast instruction!");
504 // Check if we already have visited this cast instruction before to avoid
505 // unnecessary cloning.
506 Instruction *&ClonedCastInst = ClonedCastMap[CastInst];
507 if (!ClonedCastInst) {
508 ClonedCastInst = CastInst->clone();
509 ClonedCastInst->setOperand(0, Mat);
510 ClonedCastInst->insertAfter(CastInst);
511 // Use the same debug location as the original cast instruction.
512 ClonedCastInst->setDebugLoc(CastInst->getDebugLoc());
513 DEBUG(dbgs() << "Clone instruction: " << *CastInst << '\n'
514 << "To : " << *ClonedCastInst << '\n');
517 DEBUG(dbgs() << "Update: " << *ConstUser.Inst << '\n');
518 updateOperand(ConstUser.Inst, ConstUser.OpndIdx, ClonedCastInst);
519 DEBUG(dbgs() << "To : " << *ConstUser.Inst << '\n');
523 // Visit constant expression.
524 if (auto ConstExpr = dyn_cast<ConstantExpr>(Opnd)) {
525 Instruction *ConstExprInst = ConstExpr->getAsInstruction();
526 ConstExprInst->setOperand(0, Mat);
527 ConstExprInst->insertBefore(findMatInsertPt(ConstUser.Inst,
530 // Use the same debug location as the instruction we are about to update.
531 ConstExprInst->setDebugLoc(ConstUser.Inst->getDebugLoc());
533 DEBUG(dbgs() << "Create instruction: " << *ConstExprInst << '\n'
534 << "From : " << *ConstExpr << '\n');
535 DEBUG(dbgs() << "Update: " << *ConstUser.Inst << '\n');
536 if (!updateOperand(ConstUser.Inst, ConstUser.OpndIdx, ConstExprInst)) {
537 ConstExprInst->eraseFromParent();
539 Mat->eraseFromParent();
541 DEBUG(dbgs() << "To : " << *ConstUser.Inst << '\n');
546 /// \brief Hoist and hide the base constant behind a bitcast and emit
547 /// materialization code for derived constants.
548 bool ConstantHoistingPass::emitBaseConstants() {
549 bool MadeChange = false;
550 for (auto const &ConstInfo : ConstantVec) {
551 // Hoist and hide the base constant behind a bitcast.
552 Instruction *IP = findConstantInsertionPoint(ConstInfo);
553 IntegerType *Ty = ConstInfo.BaseConstant->getType();
555 new BitCastInst(ConstInfo.BaseConstant, Ty, "const", IP);
556 DEBUG(dbgs() << "Hoist constant (" << *ConstInfo.BaseConstant << ") to BB "
557 << IP->getParent()->getName() << '\n' << *Base << '\n');
558 NumConstantsHoisted++;
560 // Emit materialization code for all rebased constants.
561 for (auto const &RCI : ConstInfo.RebasedConstants) {
562 NumConstantsRebased++;
563 for (auto const &U : RCI.Uses)
564 emitBaseConstants(Base, RCI.Offset, U);
567 // Use the same debug location as the last user of the constant.
568 assert(!Base->use_empty() && "The use list is empty!?");
569 assert(isa<Instruction>(Base->user_back()) &&
570 "All uses should be instructions.");
571 Base->setDebugLoc(cast<Instruction>(Base->user_back())->getDebugLoc());
573 // Correct for base constant, which we counted above too.
574 NumConstantsRebased--;
580 /// \brief Check all cast instructions we made a copy of and remove them if they
581 /// have no more users.
582 void ConstantHoistingPass::deleteDeadCastInst() const {
583 for (auto const &I : ClonedCastMap)
584 if (I.first->use_empty())
585 I.first->eraseFromParent();
588 /// \brief Optimize expensive integer constants in the given function.
589 bool ConstantHoistingPass::runImpl(Function &Fn, TargetTransformInfo &TTI,
590 DominatorTree &DT, BasicBlock &Entry) {
593 this->Entry = &Entry;
594 // Collect all constant candidates.
595 collectConstantCandidates(Fn);
597 // There are no constant candidates to worry about.
598 if (ConstCandVec.empty())
601 // Combine constants that can be easily materialized with an add from a common
605 // There are no constants to emit.
606 if (ConstantVec.empty())
609 // Finally hoist the base constant and emit materialization code for dependent
611 bool MadeChange = emitBaseConstants();
613 // Cleanup dead instructions.
614 deleteDeadCastInst();
619 PreservedAnalyses ConstantHoistingPass::run(Function &F,
620 FunctionAnalysisManager &AM) {
621 auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
622 auto &TTI = AM.getResult<TargetIRAnalysis>(F);
623 if (!runImpl(F, TTI, DT, F.getEntryBlock()))
624 return PreservedAnalyses::all();
626 // FIXME: This should also 'preserve the CFG'.
627 return PreservedAnalyses::none();