1//==- AArch64PromoteConstant.cpp - Promote constant to global for AArch64 --==//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file implements the AArch64PromoteConstant pass which promotes constants
10// to global variables when this is likely to be more efficient. Currently only
11// types related to constant vector (i.e., constant vector, array of constant
12// vectors, constant structure with a constant vector field, etc.) are promoted
13// to global variables. Constant vectors are likely to be lowered in target
14// constant pool during instruction selection already; therefore, the access
15// will remain the same (memory load), but the structure types are not split
16// into different constant pool accesses for each field. A bonus side effect is
17// that created globals may be merged by the global merge pass.
18//
19// FIXME: This pass may be useful for other targets too.
20//===----------------------------------------------------------------------===//
21
22#include "AArch64.h"
23#include "llvm/ADT/DenseMap.h"
24#include "llvm/ADT/SmallVector.h"
25#include "llvm/ADT/Statistic.h"
26#include "llvm/IR/BasicBlock.h"
27#include "llvm/IR/Constant.h"
28#include "llvm/IR/Constants.h"
29#include "llvm/IR/Dominators.h"
30#include "llvm/IR/Function.h"
31#include "llvm/IR/GlobalValue.h"
32#include "llvm/IR/GlobalVariable.h"
33#include "llvm/IR/IRBuilder.h"
34#include "llvm/IR/InstIterator.h"
35#include "llvm/IR/Instruction.h"
36#include "llvm/IR/Instructions.h"
37#include "llvm/IR/IntrinsicInst.h"
38#include "llvm/IR/Module.h"
39#include "llvm/IR/Type.h"
40#include "llvm/InitializePasses.h"
41#include "llvm/Pass.h"
42#include "llvm/Support/Casting.h"
43#include "llvm/Support/CommandLine.h"
44#include "llvm/Support/Debug.h"
45#include "llvm/Support/raw_ostream.h"
46#include <cassert>
47#include <utility>
48
49using namespace llvm;
50
51#define DEBUG_TYPE "aarch64-promote-const"
52
53// Stress testing mode - disable heuristics.
54static cl::opt<bool> Stress("aarch64-stress-promote-const", cl::Hidden,
55 cl::desc("Promote all vector constants"));
56
57STATISTIC(NumPromoted, "Number of promoted constants");
58STATISTIC(NumPromotedUses, "Number of promoted constants uses");
59
60//===----------------------------------------------------------------------===//
61// AArch64PromoteConstant
62//===----------------------------------------------------------------------===//
63
64namespace {
65
66/// Promotes interesting constant into global variables.
67/// The motivating example is:
68/// static const uint16_t TableA[32] = {
69/// 41944, 40330, 38837, 37450, 36158, 34953, 33826, 32768,
70/// 31776, 30841, 29960, 29128, 28340, 27595, 26887, 26215,
71/// 25576, 24967, 24386, 23832, 23302, 22796, 22311, 21846,
72/// 21400, 20972, 20561, 20165, 19785, 19419, 19066, 18725,
73/// };
74///
75/// uint8x16x4_t LoadStatic(void) {
76/// uint8x16x4_t ret;
77/// ret.val[0] = vld1q_u16(TableA + 0);
78/// ret.val[1] = vld1q_u16(TableA + 8);
79/// ret.val[2] = vld1q_u16(TableA + 16);
80/// ret.val[3] = vld1q_u16(TableA + 24);
81/// return ret;
82/// }
83///
84/// The constants in this example are folded into the uses. Thus, 4 different
85/// constants are created.
86///
87/// As their type is vector the cheapest way to create them is to load them
88/// for the memory.
89///
90/// Therefore the final assembly final has 4 different loads. With this pass
91/// enabled, only one load is issued for the constants.
92class AArch64PromoteConstant : public ModulePass {
93public:
94 struct PromotedConstant {
95 bool ShouldConvert = false;
96 GlobalVariable *GV = nullptr;
97 };
98 using PromotionCacheTy = SmallDenseMap<Constant *, PromotedConstant, 16>;
99
100 struct UpdateRecord {
101 Constant *C;
102 Instruction *User;
103 unsigned Op;
104
105 UpdateRecord(Constant *C, Instruction *User, unsigned Op)
106 : C(C), User(User), Op(Op) {}
107 };
108
109 static char ID;
110
111 AArch64PromoteConstant() : ModulePass(ID) {}
112
113 StringRef getPassName() const override { return "AArch64 Promote Constant"; }
114
115 /// Iterate over the functions and promote the interesting constants into
116 /// global variables with module scope.
117 bool runOnModule(Module &M) override {
118 LLVM_DEBUG(dbgs() << getPassName() << '\n');
119 if (skipModule(M))
120 return false;
121 bool Changed = false;
122 PromotionCacheTy PromotionCache;
123 for (auto &MF : M) {
124 Changed |= runOnFunction(F&: MF, PromotionCache);
125 }
126 return Changed;
127 }
128
129private:
130 /// Look for interesting constants used within the given function.
131 /// Promote them into global variables, load these global variables within
132 /// the related function, so that the number of inserted load is minimal.
133 bool runOnFunction(Function &F, PromotionCacheTy &PromotionCache);
134
135 // This transformation requires dominator info
136 void getAnalysisUsage(AnalysisUsage &AU) const override {
137 AU.setPreservesCFG();
138 AU.addRequired<DominatorTreeWrapperPass>();
139 AU.addPreserved<DominatorTreeWrapperPass>();
140 }
141
142 /// Type to store a list of Uses.
143 using Uses = SmallVector<std::pair<Instruction *, unsigned>, 4>;
144 /// Map an insertion point to all the uses it dominates.
145 using InsertionPoints = DenseMap<Instruction *, Uses>;
146
147 /// Find the closest point that dominates the given Use.
148 Instruction *findInsertionPoint(Instruction &User, unsigned OpNo);
149
150 /// Check if the given insertion point is dominated by an existing
151 /// insertion point.
152 /// If true, the given use is added to the list of dominated uses for
153 /// the related existing point.
154 /// \param NewPt the insertion point to be checked
155 /// \param User the user of the constant
156 /// \param OpNo the operand number of the use
157 /// \param InsertPts existing insertion points
158 /// \pre NewPt and all instruction in InsertPts belong to the same function
159 /// \return true if one of the insertion point in InsertPts dominates NewPt,
160 /// false otherwise
161 bool isDominated(Instruction *NewPt, Instruction *User, unsigned OpNo,
162 InsertionPoints &InsertPts);
163
164 /// Check if the given insertion point can be merged with an existing
165 /// insertion point in a common dominator.
166 /// If true, the given use is added to the list of the created insertion
167 /// point.
168 /// \param NewPt the insertion point to be checked
169 /// \param User the user of the constant
170 /// \param OpNo the operand number of the use
171 /// \param InsertPts existing insertion points
172 /// \pre NewPt and all instruction in InsertPts belong to the same function
173 /// \pre isDominated returns false for the exact same parameters.
174 /// \return true if it exists an insertion point in InsertPts that could
175 /// have been merged with NewPt in a common dominator,
176 /// false otherwise
177 bool tryAndMerge(Instruction *NewPt, Instruction *User, unsigned OpNo,
178 InsertionPoints &InsertPts);
179
180 /// Compute the minimal insertion points to dominates all the interesting
181 /// uses of value.
182 /// Insertion points are group per function and each insertion point
183 /// contains a list of all the uses it dominates within the related function
184 /// \param User the user of the constant
185 /// \param OpNo the operand number of the constant
186 /// \param[out] InsertPts output storage of the analysis
187 void computeInsertionPoint(Instruction *User, unsigned OpNo,
188 InsertionPoints &InsertPts);
189
190 /// Insert a definition of a new global variable at each point contained in
191 /// InsPtsPerFunc and update the related uses (also contained in
192 /// InsPtsPerFunc).
193 void insertDefinitions(Function &F, GlobalVariable &GV,
194 InsertionPoints &InsertPts);
195
196 /// Do the constant promotion indicated by the Updates records, keeping track
197 /// of globals in PromotionCache.
198 void promoteConstants(Function &F, SmallVectorImpl<UpdateRecord> &Updates,
199 PromotionCacheTy &PromotionCache);
200
201 /// Transfer the list of dominated uses of IPI to NewPt in InsertPts.
202 /// Append Use to this list and delete the entry of IPI in InsertPts.
203 static void appendAndTransferDominatedUses(Instruction *NewPt,
204 Instruction *User, unsigned OpNo,
205 InsertionPoints::iterator &IPI,
206 InsertionPoints &InsertPts) {
207 // Record the dominated use.
208 IPI->second.emplace_back(Args&: User, Args&: OpNo);
209 // Transfer the dominated uses of IPI to NewPt
210 // Inserting into the DenseMap may invalidate existing iterator.
211 // Keep a copy of the key to find the iterator to erase. Keep a copy of the
212 // value so that we don't have to dereference IPI->second.
213 Instruction *OldInstr = IPI->first;
214 Uses OldUses = std::move(IPI->second);
215 InsertPts[NewPt] = std::move(OldUses);
216 // Erase IPI.
217 InsertPts.erase(Val: OldInstr);
218 }
219};
220
221} // end anonymous namespace
222
223char AArch64PromoteConstant::ID = 0;
224
225INITIALIZE_PASS_BEGIN(AArch64PromoteConstant, "aarch64-promote-const",
226 "AArch64 Promote Constant Pass", false, false)
227INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
228INITIALIZE_PASS_END(AArch64PromoteConstant, "aarch64-promote-const",
229 "AArch64 Promote Constant Pass", false, false)
230
231ModulePass *llvm::createAArch64PromoteConstantPass() {
232 return new AArch64PromoteConstant();
233}
234
235/// Check if the given type uses a vector type.
236static bool isConstantUsingVectorTy(const Type *CstTy) {
237 if (CstTy->isVectorTy())
238 return true;
239 if (CstTy->isStructTy()) {
240 for (unsigned EltIdx = 0, EndEltIdx = CstTy->getStructNumElements();
241 EltIdx < EndEltIdx; ++EltIdx)
242 if (isConstantUsingVectorTy(CstTy: CstTy->getStructElementType(N: EltIdx)))
243 return true;
244 } else if (CstTy->isArrayTy())
245 return isConstantUsingVectorTy(CstTy: CstTy->getArrayElementType());
246 return false;
247}
248
249// Returns true if \p C contains only ConstantData leafs and no global values,
250// block addresses or constant expressions. Traverses ConstantAggregates.
251static bool containsOnlyConstantData(const Constant *C) {
252 if (isa<ConstantData>(Val: C))
253 return true;
254
255 if (isa<GlobalValue>(Val: C) || isa<BlockAddress>(Val: C) || isa<ConstantExpr>(Val: C))
256 return false;
257
258 return all_of(Range: C->operands(), P: [](const Use &U) {
259 return containsOnlyConstantData(C: cast<Constant>(Val: &U));
260 });
261}
262
263/// Check if the given use (Instruction + OpIdx) of Cst should be converted into
264/// a load of a global variable initialized with Cst.
265/// A use should be converted if it is legal to do so.
266/// For instance, it is not legal to turn the mask operand of a shuffle vector
267/// into a load of a global variable.
268static bool shouldConvertUse(const Constant *Cst, const Instruction *Instr,
269 unsigned OpIdx) {
270 // shufflevector instruction expects a const for the mask argument, i.e., the
271 // third argument. Do not promote this use in that case.
272 if (isa<const ShuffleVectorInst>(Val: Instr) && OpIdx == 2)
273 return false;
274
275 // extractvalue instruction expects a const idx.
276 if (isa<const ExtractValueInst>(Val: Instr) && OpIdx > 0)
277 return false;
278
279 // extractvalue instruction expects a const idx.
280 if (isa<const InsertValueInst>(Val: Instr) && OpIdx > 1)
281 return false;
282
283 if (isa<const AllocaInst>(Val: Instr) && OpIdx > 0)
284 return false;
285
286 // Alignment argument must be constant.
287 if (isa<const LoadInst>(Val: Instr) && OpIdx > 0)
288 return false;
289
290 // Alignment argument must be constant.
291 if (isa<const StoreInst>(Val: Instr) && OpIdx > 1)
292 return false;
293
294 // Index must be constant.
295 if (isa<const GetElementPtrInst>(Val: Instr) && OpIdx > 0)
296 return false;
297
298 // Personality function and filters must be constant.
299 // Give up on that instruction.
300 if (isa<const LandingPadInst>(Val: Instr))
301 return false;
302
303 // Switch instruction expects constants to compare to.
304 if (isa<const SwitchInst>(Val: Instr))
305 return false;
306
307 // Expected address must be a constant.
308 if (isa<const IndirectBrInst>(Val: Instr))
309 return false;
310
311 // Do not mess with intrinsics.
312 if (isa<const IntrinsicInst>(Val: Instr))
313 return false;
314
315 // Do not mess with inline asm.
316 const CallInst *CI = dyn_cast<const CallInst>(Val: Instr);
317 return !(CI && CI->isInlineAsm());
318}
319
320/// Check if the given Cst should be converted into
321/// a load of a global variable initialized with Cst.
322/// A constant should be converted if it is likely that the materialization of
323/// the constant will be tricky. Thus, we give up on zero or undef values.
324///
325/// \todo Currently, accept only vector related types.
326/// Also we give up on all simple vector type to keep the existing
327/// behavior. Otherwise, we should push here all the check of the lowering of
328/// BUILD_VECTOR. By giving up, we lose the potential benefit of merging
329/// constant via global merge and the fact that the same constant is stored
330/// only once with this method (versus, as many function that uses the constant
331/// for the regular approach, even for float).
332/// Again, the simplest solution would be to promote every
333/// constant and rematerialize them when they are actually cheap to create.
334static bool shouldConvertImpl(const Constant *Cst) {
335 if (isa<const UndefValue>(Val: Cst))
336 return false;
337
338 // FIXME: In some cases, it may be interesting to promote in memory
339 // a zero initialized constant.
340 // E.g., when the type of Cst require more instructions than the
341 // adrp/add/load sequence or when this sequence can be shared by several
342 // instances of Cst.
343 // Ideally, we could promote this into a global and rematerialize the constant
344 // when it was a bad idea.
345 if (Cst->isZeroValue())
346 return false;
347
348 if (Stress)
349 return true;
350
351 // FIXME: see function \todo
352 if (Cst->getType()->isVectorTy())
353 return false;
354 return isConstantUsingVectorTy(CstTy: Cst->getType());
355}
356
357static bool
358shouldConvert(Constant &C,
359 AArch64PromoteConstant::PromotionCacheTy &PromotionCache) {
360 auto Converted = PromotionCache.insert(
361 KV: std::make_pair(x: &C, y: AArch64PromoteConstant::PromotedConstant()));
362 if (Converted.second)
363 Converted.first->second.ShouldConvert = shouldConvertImpl(Cst: &C);
364 return Converted.first->second.ShouldConvert;
365}
366
367Instruction *AArch64PromoteConstant::findInsertionPoint(Instruction &User,
368 unsigned OpNo) {
369 // If this user is a phi, the insertion point is in the related
370 // incoming basic block.
371 if (PHINode *PhiInst = dyn_cast<PHINode>(Val: &User))
372 return PhiInst->getIncomingBlock(i: OpNo)->getTerminator();
373
374 return &User;
375}
376
377bool AArch64PromoteConstant::isDominated(Instruction *NewPt, Instruction *User,
378 unsigned OpNo,
379 InsertionPoints &InsertPts) {
380 DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>(
381 F&: *NewPt->getParent()->getParent()).getDomTree();
382
383 // Traverse all the existing insertion points and check if one is dominating
384 // NewPt. If it is, remember that.
385 for (auto &IPI : InsertPts) {
386 if (NewPt == IPI.first || DT.dominates(Def: IPI.first, User: NewPt) ||
387 // When IPI.first is a terminator instruction, DT may think that
388 // the result is defined on the edge.
389 // Here we are testing the insertion point, not the definition.
390 (IPI.first->getParent() != NewPt->getParent() &&
391 DT.dominates(A: IPI.first->getParent(), B: NewPt->getParent()))) {
392 // No need to insert this point. Just record the dominated use.
393 LLVM_DEBUG(dbgs() << "Insertion point dominated by:\n");
394 LLVM_DEBUG(IPI.first->print(dbgs()));
395 LLVM_DEBUG(dbgs() << '\n');
396 IPI.second.emplace_back(Args&: User, Args&: OpNo);
397 return true;
398 }
399 }
400 return false;
401}
402
403bool AArch64PromoteConstant::tryAndMerge(Instruction *NewPt, Instruction *User,
404 unsigned OpNo,
405 InsertionPoints &InsertPts) {
406 DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>(
407 F&: *NewPt->getParent()->getParent()).getDomTree();
408 BasicBlock *NewBB = NewPt->getParent();
409
410 // Traverse all the existing insertion point and check if one is dominated by
411 // NewPt and thus useless or can be combined with NewPt into a common
412 // dominator.
413 for (InsertionPoints::iterator IPI = InsertPts.begin(),
414 EndIPI = InsertPts.end();
415 IPI != EndIPI; ++IPI) {
416 BasicBlock *CurBB = IPI->first->getParent();
417 if (NewBB == CurBB) {
418 // Instructions are in the same block.
419 // By construction, NewPt is dominating the other.
420 // Indeed, isDominated returned false with the exact same arguments.
421 LLVM_DEBUG(dbgs() << "Merge insertion point with:\n");
422 LLVM_DEBUG(IPI->first->print(dbgs()));
423 LLVM_DEBUG(dbgs() << "\nat considered insertion point.\n");
424 appendAndTransferDominatedUses(NewPt, User, OpNo, IPI, InsertPts);
425 return true;
426 }
427
428 // Look for a common dominator
429 BasicBlock *CommonDominator = DT.findNearestCommonDominator(A: NewBB, B: CurBB);
430 // If none exists, we cannot merge these two points.
431 if (!CommonDominator)
432 continue;
433
434 if (CommonDominator != NewBB) {
435 // By construction, the CommonDominator cannot be CurBB.
436 assert(CommonDominator != CurBB &&
437 "Instruction has not been rejected during isDominated check!");
438 // Take the last instruction of the CommonDominator as insertion point
439 NewPt = CommonDominator->getTerminator();
440 }
441 // else, CommonDominator is the block of NewBB, hence NewBB is the last
442 // possible insertion point in that block.
443 LLVM_DEBUG(dbgs() << "Merge insertion point with:\n");
444 LLVM_DEBUG(IPI->first->print(dbgs()));
445 LLVM_DEBUG(dbgs() << '\n');
446 LLVM_DEBUG(NewPt->print(dbgs()));
447 LLVM_DEBUG(dbgs() << '\n');
448 appendAndTransferDominatedUses(NewPt, User, OpNo, IPI, InsertPts);
449 return true;
450 }
451 return false;
452}
453
454void AArch64PromoteConstant::computeInsertionPoint(
455 Instruction *User, unsigned OpNo, InsertionPoints &InsertPts) {
456 LLVM_DEBUG(dbgs() << "Considered use, opidx " << OpNo << ":\n");
457 LLVM_DEBUG(User->print(dbgs()));
458 LLVM_DEBUG(dbgs() << '\n');
459
460 Instruction *InsertionPoint = findInsertionPoint(User&: *User, OpNo);
461
462 LLVM_DEBUG(dbgs() << "Considered insertion point:\n");
463 LLVM_DEBUG(InsertionPoint->print(dbgs()));
464 LLVM_DEBUG(dbgs() << '\n');
465
466 if (isDominated(NewPt: InsertionPoint, User, OpNo, InsertPts))
467 return;
468 // This insertion point is useful, check if we can merge some insertion
469 // point in a common dominator or if NewPt dominates an existing one.
470 if (tryAndMerge(NewPt: InsertionPoint, User, OpNo, InsertPts))
471 return;
472
473 LLVM_DEBUG(dbgs() << "Keep considered insertion point\n");
474
475 // It is definitely useful by its own
476 InsertPts[InsertionPoint].emplace_back(Args&: User, Args&: OpNo);
477}
478
479static void ensurePromotedGV(Function &F, Constant &C,
480 AArch64PromoteConstant::PromotedConstant &PC) {
481 assert(PC.ShouldConvert &&
482 "Expected that we should convert this to a global");
483 if (PC.GV)
484 return;
485 PC.GV = new GlobalVariable(
486 *F.getParent(), C.getType(), true, GlobalValue::InternalLinkage, nullptr,
487 "_PromotedConst", nullptr, GlobalVariable::NotThreadLocal);
488 PC.GV->setInitializer(&C);
489 LLVM_DEBUG(dbgs() << "Global replacement: ");
490 LLVM_DEBUG(PC.GV->print(dbgs()));
491 LLVM_DEBUG(dbgs() << '\n');
492 ++NumPromoted;
493}
494
495void AArch64PromoteConstant::insertDefinitions(Function &F,
496 GlobalVariable &PromotedGV,
497 InsertionPoints &InsertPts) {
498#ifndef NDEBUG
499 // Do more checking for debug purposes.
500 DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>(F).getDomTree();
501#endif
502 assert(!InsertPts.empty() && "Empty uses does not need a definition");
503
504 for (const auto &IPI : InsertPts) {
505 // Create the load of the global variable.
506 IRBuilder<> Builder(IPI.first);
507 LoadInst *LoadedCst =
508 Builder.CreateLoad(Ty: PromotedGV.getValueType(), Ptr: &PromotedGV);
509 LLVM_DEBUG(dbgs() << "**********\n");
510 LLVM_DEBUG(dbgs() << "New def: ");
511 LLVM_DEBUG(LoadedCst->print(dbgs()));
512 LLVM_DEBUG(dbgs() << '\n');
513
514 // Update the dominated uses.
515 for (auto Use : IPI.second) {
516#ifndef NDEBUG
517 assert(DT.dominates(LoadedCst,
518 findInsertionPoint(*Use.first, Use.second)) &&
519 "Inserted definition does not dominate all its uses!");
520#endif
521 LLVM_DEBUG({
522 dbgs() << "Use to update " << Use.second << ":";
523 Use.first->print(dbgs());
524 dbgs() << '\n';
525 });
526 Use.first->setOperand(i: Use.second, Val: LoadedCst);
527 ++NumPromotedUses;
528 }
529 }
530}
531
532void AArch64PromoteConstant::promoteConstants(
533 Function &F, SmallVectorImpl<UpdateRecord> &Updates,
534 PromotionCacheTy &PromotionCache) {
535 // Promote the constants.
536 for (auto U = Updates.begin(), E = Updates.end(); U != E;) {
537 LLVM_DEBUG(dbgs() << "** Compute insertion points **\n");
538 auto First = U;
539 Constant *C = First->C;
540 InsertionPoints InsertPts;
541 do {
542 computeInsertionPoint(User: U->User, OpNo: U->Op, InsertPts);
543 } while (++U != E && U->C == C);
544
545 auto &Promotion = PromotionCache[C];
546 ensurePromotedGV(F, C&: *C, PC&: Promotion);
547 insertDefinitions(F, PromotedGV&: *Promotion.GV, InsertPts);
548 }
549}
550
551bool AArch64PromoteConstant::runOnFunction(Function &F,
552 PromotionCacheTy &PromotionCache) {
553 // Look for instructions using constant vector. Promote that constant to a
554 // global variable. Create as few loads of this variable as possible and
555 // update the uses accordingly.
556 SmallVector<UpdateRecord, 64> Updates;
557 for (Instruction &I : instructions(F: &F)) {
558 // Traverse the operand, looking for constant vectors. Replace them by a
559 // load of a global variable of constant vector type.
560 for (Use &U : I.operands()) {
561 Constant *Cst = dyn_cast<Constant>(Val&: U);
562 // There is no point in promoting global values as they are already
563 // global. Do not promote constants containing constant expression, global
564 // values or blockaddresses either, as they may require some code
565 // expansion.
566 if (!Cst || isa<GlobalValue>(Val: Cst) || !containsOnlyConstantData(C: Cst))
567 continue;
568
569 // Check if this constant is worth promoting.
570 if (!shouldConvert(C&: *Cst, PromotionCache))
571 continue;
572
573 // Check if this use should be promoted.
574 unsigned OpNo = &U - I.op_begin();
575 if (!shouldConvertUse(Cst, Instr: &I, OpIdx: OpNo))
576 continue;
577
578 Updates.emplace_back(Args&: Cst, Args: &I, Args&: OpNo);
579 }
580 }
581
582 if (Updates.empty())
583 return false;
584
585 promoteConstants(F, Updates, PromotionCache);
586 return true;
587}
588