1//===-- PGOMemOPSizeOpt.cpp - Optimizations based on value profiling ===//
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 transformation that optimizes memory intrinsics
10// such as memcpy using the size value profile. When memory intrinsic size
11// value profile metadata is available, a single memory intrinsic is expanded
12// to a sequence of guarded specialized versions that are called with the
13// hottest size(s), for later expansion into more optimal inline sequences.
14//
15//===----------------------------------------------------------------------===//
16
17#include "llvm/ADT/ArrayRef.h"
18#include "llvm/ADT/Statistic.h"
19#include "llvm/ADT/StringRef.h"
20#include "llvm/ADT/Twine.h"
21#include "llvm/Analysis/BlockFrequencyInfo.h"
22#include "llvm/Analysis/DomTreeUpdater.h"
23#include "llvm/Analysis/OptimizationRemarkEmitter.h"
24#include "llvm/Analysis/TargetLibraryInfo.h"
25#include "llvm/IR/BasicBlock.h"
26#include "llvm/IR/DerivedTypes.h"
27#include "llvm/IR/Dominators.h"
28#include "llvm/IR/Function.h"
29#include "llvm/IR/IRBuilder.h"
30#include "llvm/IR/InstVisitor.h"
31#include "llvm/IR/Instruction.h"
32#include "llvm/IR/Instructions.h"
33#include "llvm/IR/LLVMContext.h"
34#include "llvm/IR/PassManager.h"
35#include "llvm/IR/Type.h"
36#include "llvm/ProfileData/InstrProf.h"
37#define INSTR_PROF_VALUE_PROF_MEMOP_API
38#include "llvm/ProfileData/InstrProfData.inc"
39#include "llvm/Support/Casting.h"
40#include "llvm/Support/CommandLine.h"
41#include "llvm/Support/Debug.h"
42#include "llvm/Support/ErrorHandling.h"
43#include "llvm/Support/MathExtras.h"
44#include "llvm/Transforms/Instrumentation/PGOInstrumentation.h"
45#include "llvm/Transforms/Utils/BasicBlockUtils.h"
46#include <cassert>
47#include <cstdint>
48#include <vector>
49
50using namespace llvm;
51
52#define DEBUG_TYPE "pgo-memop-opt"
53
54STATISTIC(NumOfPGOMemOPOpt, "Number of memop intrinsics optimized.");
55STATISTIC(NumOfPGOMemOPAnnotate, "Number of memop intrinsics annotated.");
56
57// The minimum call count to optimize memory intrinsic calls.
58static cl::opt<unsigned>
59 MemOPCountThreshold("pgo-memop-count-threshold", cl::Hidden, cl::init(Val: 1000),
60 cl::desc("The minimum count to optimize memory "
61 "intrinsic calls"));
62
63// Command line option to disable memory intrinsic optimization. The default is
64// false. This is for debug purpose.
65static cl::opt<bool> DisableMemOPOPT("disable-memop-opt", cl::init(Val: false),
66 cl::Hidden, cl::desc("Disable optimize"));
67
68// The percent threshold to optimize memory intrinsic calls.
69static cl::opt<unsigned>
70 MemOPPercentThreshold("pgo-memop-percent-threshold", cl::init(Val: 40),
71 cl::Hidden,
72 cl::desc("The percentage threshold for the "
73 "memory intrinsic calls optimization"));
74
75// Maximum number of versions for optimizing memory intrinsic call.
76static cl::opt<unsigned>
77 MemOPMaxVersion("pgo-memop-max-version", cl::init(Val: 3), cl::Hidden,
78 cl::desc("The max version for the optimized memory "
79 " intrinsic calls"));
80
81// Scale the counts from the annotation using the BB count value.
82static cl::opt<bool>
83 MemOPScaleCount("pgo-memop-scale-count", cl::init(Val: true), cl::Hidden,
84 cl::desc("Scale the memop size counts using the basic "
85 " block count value"));
86
87cl::opt<bool>
88 MemOPOptMemcmpBcmp("pgo-memop-optimize-memcmp-bcmp", cl::init(Val: true),
89 cl::Hidden,
90 cl::desc("Size-specialize memcmp and bcmp calls"));
91
92static cl::opt<unsigned>
93 MemOpMaxOptSize("memop-value-prof-max-opt-size", cl::Hidden, cl::init(Val: 128),
94 cl::desc("Optimize the memop size <= this value"));
95
96namespace {
97
98static const char *getMIName(const MemIntrinsic *MI) {
99 switch (MI->getIntrinsicID()) {
100 case Intrinsic::memcpy:
101 return "memcpy";
102 case Intrinsic::memmove:
103 return "memmove";
104 case Intrinsic::memset:
105 return "memset";
106 default:
107 return "unknown";
108 }
109}
110
111// A class that abstracts a memop (memcpy, memmove, memset, memcmp and bcmp).
112struct MemOp {
113 Instruction *I;
114 MemOp(MemIntrinsic *MI) : I(MI) {}
115 MemOp(CallInst *CI) : I(CI) {}
116 MemIntrinsic *asMI() { return dyn_cast<MemIntrinsic>(Val: I); }
117 CallInst *asCI() { return cast<CallInst>(Val: I); }
118 MemOp clone() {
119 if (auto MI = asMI())
120 return MemOp(cast<MemIntrinsic>(Val: MI->clone()));
121 return MemOp(cast<CallInst>(Val: asCI()->clone()));
122 }
123 Value *getLength() {
124 if (auto MI = asMI())
125 return MI->getLength();
126 return asCI()->getArgOperand(i: 2);
127 }
128 void setLength(Value *Length) {
129 if (auto MI = asMI())
130 return MI->setLength(Length);
131 asCI()->setArgOperand(i: 2, v: Length);
132 }
133 StringRef getFuncName() {
134 if (auto MI = asMI())
135 return MI->getCalledFunction()->getName();
136 return asCI()->getCalledFunction()->getName();
137 }
138 bool isMemmove() {
139 if (auto MI = asMI())
140 if (MI->getIntrinsicID() == Intrinsic::memmove)
141 return true;
142 return false;
143 }
144 bool isMemcmp(TargetLibraryInfo &TLI) {
145 LibFunc Func;
146 if (asMI() == nullptr && TLI.getLibFunc(CB: *asCI(), F&: Func) &&
147 Func == LibFunc_memcmp) {
148 return true;
149 }
150 return false;
151 }
152 bool isBcmp(TargetLibraryInfo &TLI) {
153 LibFunc Func;
154 if (asMI() == nullptr && TLI.getLibFunc(CB: *asCI(), F&: Func) &&
155 Func == LibFunc_bcmp) {
156 return true;
157 }
158 return false;
159 }
160 const char *getName(TargetLibraryInfo &TLI) {
161 if (auto MI = asMI())
162 return getMIName(MI);
163 LibFunc Func;
164 if (TLI.getLibFunc(CB: *asCI(), F&: Func)) {
165 if (Func == LibFunc_memcmp)
166 return "memcmp";
167 if (Func == LibFunc_bcmp)
168 return "bcmp";
169 }
170 llvm_unreachable("Must be MemIntrinsic or memcmp/bcmp CallInst");
171 return nullptr;
172 }
173};
174
175class MemOPSizeOpt : public InstVisitor<MemOPSizeOpt> {
176public:
177 MemOPSizeOpt(Function &Func, BlockFrequencyInfo &BFI,
178 OptimizationRemarkEmitter &ORE, DominatorTree *DT,
179 TargetLibraryInfo &TLI)
180 : Func(Func), BFI(BFI), ORE(ORE), DT(DT), TLI(TLI), Changed(false) {
181 ValueDataArray =
182 std::make_unique<InstrProfValueData[]>(INSTR_PROF_NUM_BUCKETS);
183 }
184 bool isChanged() const { return Changed; }
185 void perform() {
186 WorkList.clear();
187 visit(F&: Func);
188
189 for (auto &MO : WorkList) {
190 ++NumOfPGOMemOPAnnotate;
191 if (perform(MO)) {
192 Changed = true;
193 ++NumOfPGOMemOPOpt;
194 LLVM_DEBUG(dbgs() << "MemOP call: " << MO.getFuncName()
195 << "is Transformed.\n");
196 }
197 }
198 }
199
200 void visitMemIntrinsic(MemIntrinsic &MI) {
201 Value *Length = MI.getLength();
202 // Not perform on constant length calls.
203 if (isa<ConstantInt>(Val: Length))
204 return;
205 WorkList.push_back(x: MemOp(&MI));
206 }
207
208 void visitCallInst(CallInst &CI) {
209 LibFunc Func;
210 if (TLI.getLibFunc(CB: CI, F&: Func) &&
211 (Func == LibFunc_memcmp || Func == LibFunc_bcmp) &&
212 !isa<ConstantInt>(Val: CI.getArgOperand(i: 2))) {
213 WorkList.push_back(x: MemOp(&CI));
214 }
215 }
216
217private:
218 Function &Func;
219 BlockFrequencyInfo &BFI;
220 OptimizationRemarkEmitter &ORE;
221 DominatorTree *DT;
222 TargetLibraryInfo &TLI;
223 bool Changed;
224 std::vector<MemOp> WorkList;
225 // The space to read the profile annotation.
226 std::unique_ptr<InstrProfValueData[]> ValueDataArray;
227 bool perform(MemOp MO);
228};
229
230static bool isProfitable(uint64_t Count, uint64_t TotalCount) {
231 assert(Count <= TotalCount);
232 if (Count < MemOPCountThreshold)
233 return false;
234 if (Count < TotalCount * MemOPPercentThreshold / 100)
235 return false;
236 return true;
237}
238
239static inline uint64_t getScaledCount(uint64_t Count, uint64_t Num,
240 uint64_t Denom) {
241 if (!MemOPScaleCount)
242 return Count;
243 bool Overflowed;
244 uint64_t ScaleCount = SaturatingMultiply(X: Count, Y: Num, ResultOverflowed: &Overflowed);
245 return ScaleCount / Denom;
246}
247
248bool MemOPSizeOpt::perform(MemOp MO) {
249 assert(MO.I);
250 if (MO.isMemmove())
251 return false;
252 if (!MemOPOptMemcmpBcmp && (MO.isMemcmp(TLI) || MO.isBcmp(TLI)))
253 return false;
254
255 uint32_t NumVals, MaxNumVals = INSTR_PROF_NUM_BUCKETS;
256 uint64_t TotalCount;
257 if (!getValueProfDataFromInst(Inst: *MO.I, ValueKind: IPVK_MemOPSize, MaxNumValueData: MaxNumVals,
258 ValueData: ValueDataArray.get(), ActualNumValueData&: NumVals, TotalC&: TotalCount))
259 return false;
260
261 uint64_t ActualCount = TotalCount;
262 uint64_t SavedTotalCount = TotalCount;
263 if (MemOPScaleCount) {
264 auto BBEdgeCount = BFI.getBlockProfileCount(BB: MO.I->getParent());
265 if (!BBEdgeCount)
266 return false;
267 ActualCount = *BBEdgeCount;
268 }
269
270 ArrayRef<InstrProfValueData> VDs(ValueDataArray.get(), NumVals);
271 LLVM_DEBUG(dbgs() << "Read one memory intrinsic profile with count "
272 << ActualCount << "\n");
273 LLVM_DEBUG(
274 for (auto &VD
275 : VDs) { dbgs() << " (" << VD.Value << "," << VD.Count << ")\n"; });
276
277 if (ActualCount < MemOPCountThreshold)
278 return false;
279 // Skip if the total value profiled count is 0, in which case we can't
280 // scale up the counts properly (and there is no profitable transformation).
281 if (TotalCount == 0)
282 return false;
283
284 TotalCount = ActualCount;
285 if (MemOPScaleCount)
286 LLVM_DEBUG(dbgs() << "Scale counts: numerator = " << ActualCount
287 << " denominator = " << SavedTotalCount << "\n");
288
289 // Keeping track of the count of the default case:
290 uint64_t RemainCount = TotalCount;
291 uint64_t SavedRemainCount = SavedTotalCount;
292 SmallVector<uint64_t, 16> SizeIds;
293 SmallVector<uint64_t, 16> CaseCounts;
294 SmallDenseSet<uint64_t, 16> SeenSizeId;
295 uint64_t MaxCount = 0;
296 unsigned Version = 0;
297 // Default case is in the front -- save the slot here.
298 CaseCounts.push_back(Elt: 0);
299 SmallVector<InstrProfValueData, 24> RemainingVDs;
300 for (auto I = VDs.begin(), E = VDs.end(); I != E; ++I) {
301 auto &VD = *I;
302 int64_t V = VD.Value;
303 uint64_t C = VD.Count;
304 if (MemOPScaleCount)
305 C = getScaledCount(Count: C, Num: ActualCount, Denom: SavedTotalCount);
306
307 if (!InstrProfIsSingleValRange(Value: V) || V > MemOpMaxOptSize) {
308 RemainingVDs.push_back(Elt: VD);
309 continue;
310 }
311
312 // ValueCounts are sorted on the count. Break at the first un-profitable
313 // value.
314 if (!isProfitable(Count: C, TotalCount: RemainCount)) {
315 RemainingVDs.insert(I: RemainingVDs.end(), From: I, To: E);
316 break;
317 }
318
319 if (!SeenSizeId.insert(V).second) {
320 errs() << "warning: Invalid Profile Data in Function " << Func.getName()
321 << ": Two identical values in MemOp value counts.\n";
322 return false;
323 }
324
325 SizeIds.push_back(Elt: V);
326 CaseCounts.push_back(Elt: C);
327 if (C > MaxCount)
328 MaxCount = C;
329
330 assert(RemainCount >= C);
331 RemainCount -= C;
332 assert(SavedRemainCount >= VD.Count);
333 SavedRemainCount -= VD.Count;
334
335 if (++Version >= MemOPMaxVersion && MemOPMaxVersion != 0) {
336 RemainingVDs.insert(I: RemainingVDs.end(), From: I + 1, To: E);
337 break;
338 }
339 }
340
341 if (Version == 0)
342 return false;
343
344 CaseCounts[0] = RemainCount;
345 if (RemainCount > MaxCount)
346 MaxCount = RemainCount;
347
348 uint64_t SumForOpt = TotalCount - RemainCount;
349
350 LLVM_DEBUG(dbgs() << "Optimize one memory intrinsic call to " << Version
351 << " Versions (covering " << SumForOpt << " out of "
352 << TotalCount << ")\n");
353
354 // mem_op(..., size)
355 // ==>
356 // switch (size) {
357 // case s1:
358 // mem_op(..., s1);
359 // goto merge_bb;
360 // case s2:
361 // mem_op(..., s2);
362 // goto merge_bb;
363 // ...
364 // default:
365 // mem_op(..., size);
366 // goto merge_bb;
367 // }
368 // merge_bb:
369
370 BasicBlock *BB = MO.I->getParent();
371 LLVM_DEBUG(dbgs() << "\n\n== Basic Block Before ==\n");
372 LLVM_DEBUG(dbgs() << *BB << "\n");
373 auto OrigBBFreq = BFI.getBlockFreq(BB);
374
375 BasicBlock *DefaultBB = SplitBlock(Old: BB, SplitPt: MO.I, DT);
376 BasicBlock::iterator It(*MO.I);
377 ++It;
378 assert(It != DefaultBB->end());
379 BasicBlock *MergeBB = SplitBlock(Old: DefaultBB, SplitPt: &(*It), DT);
380 MergeBB->setName("MemOP.Merge");
381 BFI.setBlockFreq(BB: MergeBB, Freq: OrigBBFreq);
382 DefaultBB->setName("MemOP.Default");
383
384 DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Eager);
385 auto &Ctx = Func.getContext();
386 IRBuilder<> IRB(BB);
387 BB->getTerminator()->eraseFromParent();
388 Value *SizeVar = MO.getLength();
389 SwitchInst *SI = IRB.CreateSwitch(V: SizeVar, Dest: DefaultBB, NumCases: SizeIds.size());
390 Type *MemOpTy = MO.I->getType();
391 PHINode *PHI = nullptr;
392 if (!MemOpTy->isVoidTy()) {
393 // Insert a phi for the return values at the merge block.
394 IRBuilder<> IRBM(MergeBB->getFirstNonPHI());
395 PHI = IRBM.CreatePHI(Ty: MemOpTy, NumReservedValues: SizeIds.size() + 1, Name: "MemOP.RVMerge");
396 MO.I->replaceAllUsesWith(V: PHI);
397 PHI->addIncoming(V: MO.I, BB: DefaultBB);
398 }
399
400 // Clear the value profile data.
401 MO.I->setMetadata(KindID: LLVMContext::MD_prof, Node: nullptr);
402 // If all promoted, we don't need the MD.prof metadata.
403 if (SavedRemainCount > 0 || Version != NumVals) {
404 // Otherwise we need update with the un-promoted records back.
405 ArrayRef<InstrProfValueData> RemVDs(RemainingVDs);
406 annotateValueSite(M&: *Func.getParent(), Inst&: *MO.I, VDs: RemVDs, Sum: SavedRemainCount,
407 ValueKind: IPVK_MemOPSize, MaxMDCount: NumVals);
408 }
409
410 LLVM_DEBUG(dbgs() << "\n\n== Basic Block After==\n");
411
412 std::vector<DominatorTree::UpdateType> Updates;
413 if (DT)
414 Updates.reserve(n: 2 * SizeIds.size());
415
416 for (uint64_t SizeId : SizeIds) {
417 BasicBlock *CaseBB = BasicBlock::Create(
418 Context&: Ctx, Name: Twine("MemOP.Case.") + Twine(SizeId), Parent: &Func, InsertBefore: DefaultBB);
419 MemOp NewMO = MO.clone();
420 // Fix the argument.
421 auto *SizeType = dyn_cast<IntegerType>(Val: NewMO.getLength()->getType());
422 assert(SizeType && "Expected integer type size argument.");
423 ConstantInt *CaseSizeId = ConstantInt::get(Ty: SizeType, V: SizeId);
424 NewMO.setLength(CaseSizeId);
425 NewMO.I->insertInto(ParentBB: CaseBB, It: CaseBB->end());
426 IRBuilder<> IRBCase(CaseBB);
427 IRBCase.CreateBr(Dest: MergeBB);
428 SI->addCase(OnVal: CaseSizeId, Dest: CaseBB);
429 if (!MemOpTy->isVoidTy())
430 PHI->addIncoming(V: NewMO.I, BB: CaseBB);
431 if (DT) {
432 Updates.push_back(x: {DominatorTree::Insert, CaseBB, MergeBB});
433 Updates.push_back(x: {DominatorTree::Insert, BB, CaseBB});
434 }
435 LLVM_DEBUG(dbgs() << *CaseBB << "\n");
436 }
437 DTU.applyUpdates(Updates);
438 Updates.clear();
439
440 if (MaxCount)
441 setProfMetadata(M: Func.getParent(), TI: SI, EdgeCounts: CaseCounts, MaxCount);
442
443 LLVM_DEBUG(dbgs() << *BB << "\n");
444 LLVM_DEBUG(dbgs() << *DefaultBB << "\n");
445 LLVM_DEBUG(dbgs() << *MergeBB << "\n");
446
447 ORE.emit(RemarkBuilder: [&]() {
448 using namespace ore;
449 return OptimizationRemark(DEBUG_TYPE, "memopt-opt", MO.I)
450 << "optimized " << NV("Memop", MO.getName(TLI)) << " with count "
451 << NV("Count", SumForOpt) << " out of " << NV("Total", TotalCount)
452 << " for " << NV("Versions", Version) << " versions";
453 });
454
455 return true;
456}
457} // namespace
458
459static bool PGOMemOPSizeOptImpl(Function &F, BlockFrequencyInfo &BFI,
460 OptimizationRemarkEmitter &ORE,
461 DominatorTree *DT, TargetLibraryInfo &TLI) {
462 if (DisableMemOPOPT)
463 return false;
464
465 if (F.hasFnAttribute(Attribute::OptimizeForSize))
466 return false;
467 MemOPSizeOpt MemOPSizeOpt(F, BFI, ORE, DT, TLI);
468 MemOPSizeOpt.perform();
469 return MemOPSizeOpt.isChanged();
470}
471
472PreservedAnalyses PGOMemOPSizeOpt::run(Function &F,
473 FunctionAnalysisManager &FAM) {
474 auto &BFI = FAM.getResult<BlockFrequencyAnalysis>(IR&: F);
475 auto &ORE = FAM.getResult<OptimizationRemarkEmitterAnalysis>(IR&: F);
476 auto *DT = FAM.getCachedResult<DominatorTreeAnalysis>(IR&: F);
477 auto &TLI = FAM.getResult<TargetLibraryAnalysis>(IR&: F);
478 bool Changed = PGOMemOPSizeOptImpl(F, BFI, ORE, DT, TLI);
479 if (!Changed)
480 return PreservedAnalyses::all();
481 auto PA = PreservedAnalyses();
482 PA.preserve<DominatorTreeAnalysis>();
483 return PA;
484}
485

source code of llvm/lib/Transforms/Instrumentation/PGOMemOPSizeOpt.cpp