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
50 using namespace llvm;
51
52 #define DEBUG_TYPE "pgo-memop-opt"
53
54 STATISTIC(NumOfPGOMemOPOpt, "Number of memop intrinsics optimized.");
55 STATISTIC(NumOfPGOMemOPAnnotate, "Number of memop intrinsics annotated.");
56
57 // The minimum call count to optimize memory intrinsic calls.
58 static cl::opt<unsigned>
59 MemOPCountThreshold("pgo-memop-count-threshold", cl::Hidden, cl::init(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.
65 static cl::opt<bool> DisableMemOPOPT("disable-memop-opt", cl::init(false),
66 cl::Hidden, cl::desc("Disable optimize"));
67
68 // The percent threshold to optimize memory intrinsic calls.
69 static cl::opt<unsigned>
70 MemOPPercentThreshold("pgo-memop-percent-threshold", cl::init(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.
76 static cl::opt<unsigned>
77 MemOPMaxVersion("pgo-memop-max-version", cl::init(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.
82 static cl::opt<bool>
83 MemOPScaleCount("pgo-memop-scale-count", cl::init(true), cl::Hidden,
84 cl::desc("Scale the memop size counts using the basic "
85 " block count value"));
86
87 cl::opt<bool>
88 MemOPOptMemcmpBcmp("pgo-memop-optimize-memcmp-bcmp", cl::init(true),
89 cl::Hidden,
90 cl::desc("Size-specialize memcmp and bcmp calls"));
91
92 static cl::opt<unsigned>
93 MemOpMaxOptSize("memop-value-prof-max-opt-size", cl::Hidden, cl::init(128),
94 cl::desc("Optimize the memop size <= this value"));
95
96 namespace {
97
getMIName(const MemIntrinsic * MI)98 static 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).
112 struct MemOp {
113 Instruction *I;
MemOp__anona03ef4830111::MemOp114 MemOp(MemIntrinsic *MI) : I(MI) {}
MemOp__anona03ef4830111::MemOp115 MemOp(CallInst *CI) : I(CI) {}
asMI__anona03ef4830111::MemOp116 MemIntrinsic *asMI() { return dyn_cast<MemIntrinsic>(I); }
asCI__anona03ef4830111::MemOp117 CallInst *asCI() { return cast<CallInst>(I); }
clone__anona03ef4830111::MemOp118 MemOp clone() {
119 if (auto MI = asMI())
120 return MemOp(cast<MemIntrinsic>(MI->clone()));
121 return MemOp(cast<CallInst>(asCI()->clone()));
122 }
getLength__anona03ef4830111::MemOp123 Value *getLength() {
124 if (auto MI = asMI())
125 return MI->getLength();
126 return asCI()->getArgOperand(2);
127 }
setLength__anona03ef4830111::MemOp128 void setLength(Value *Length) {
129 if (auto MI = asMI())
130 return MI->setLength(Length);
131 asCI()->setArgOperand(2, Length);
132 }
getFuncName__anona03ef4830111::MemOp133 StringRef getFuncName() {
134 if (auto MI = asMI())
135 return MI->getCalledFunction()->getName();
136 return asCI()->getCalledFunction()->getName();
137 }
isMemmove__anona03ef4830111::MemOp138 bool isMemmove() {
139 if (auto MI = asMI())
140 if (MI->getIntrinsicID() == Intrinsic::memmove)
141 return true;
142 return false;
143 }
isMemcmp__anona03ef4830111::MemOp144 bool isMemcmp(TargetLibraryInfo &TLI) {
145 LibFunc Func;
146 if (asMI() == nullptr && TLI.getLibFunc(*asCI(), Func) &&
147 Func == LibFunc_memcmp) {
148 return true;
149 }
150 return false;
151 }
isBcmp__anona03ef4830111::MemOp152 bool isBcmp(TargetLibraryInfo &TLI) {
153 LibFunc Func;
154 if (asMI() == nullptr && TLI.getLibFunc(*asCI(), Func) &&
155 Func == LibFunc_bcmp) {
156 return true;
157 }
158 return false;
159 }
getName__anona03ef4830111::MemOp160 const char *getName(TargetLibraryInfo &TLI) {
161 if (auto MI = asMI())
162 return getMIName(MI);
163 LibFunc Func;
164 if (TLI.getLibFunc(*asCI(), 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
175 class MemOPSizeOpt : public InstVisitor<MemOPSizeOpt> {
176 public:
MemOPSizeOpt(Function & Func,BlockFrequencyInfo & BFI,OptimizationRemarkEmitter & ORE,DominatorTree * DT,TargetLibraryInfo & TLI)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) {}
isChanged() const181 bool isChanged() const { return Changed; }
perform()182 void perform() {
183 WorkList.clear();
184 visit(Func);
185
186 for (auto &MO : WorkList) {
187 ++NumOfPGOMemOPAnnotate;
188 if (perform(MO)) {
189 Changed = true;
190 ++NumOfPGOMemOPOpt;
191 LLVM_DEBUG(dbgs() << "MemOP call: " << MO.getFuncName()
192 << "is Transformed.\n");
193 }
194 }
195 }
196
visitMemIntrinsic(MemIntrinsic & MI)197 void visitMemIntrinsic(MemIntrinsic &MI) {
198 Value *Length = MI.getLength();
199 // Not perform on constant length calls.
200 if (isa<ConstantInt>(Length))
201 return;
202 WorkList.push_back(MemOp(&MI));
203 }
204
visitCallInst(CallInst & CI)205 void visitCallInst(CallInst &CI) {
206 LibFunc Func;
207 if (TLI.getLibFunc(CI, Func) &&
208 (Func == LibFunc_memcmp || Func == LibFunc_bcmp) &&
209 !isa<ConstantInt>(CI.getArgOperand(2))) {
210 WorkList.push_back(MemOp(&CI));
211 }
212 }
213
214 private:
215 Function &Func;
216 BlockFrequencyInfo &BFI;
217 OptimizationRemarkEmitter &ORE;
218 DominatorTree *DT;
219 TargetLibraryInfo &TLI;
220 bool Changed;
221 std::vector<MemOp> WorkList;
222 bool perform(MemOp MO);
223 };
224
isProfitable(uint64_t Count,uint64_t TotalCount)225 static bool isProfitable(uint64_t Count, uint64_t TotalCount) {
226 assert(Count <= TotalCount);
227 if (Count < MemOPCountThreshold)
228 return false;
229 if (Count < TotalCount * MemOPPercentThreshold / 100)
230 return false;
231 return true;
232 }
233
getScaledCount(uint64_t Count,uint64_t Num,uint64_t Denom)234 static inline uint64_t getScaledCount(uint64_t Count, uint64_t Num,
235 uint64_t Denom) {
236 if (!MemOPScaleCount)
237 return Count;
238 bool Overflowed;
239 uint64_t ScaleCount = SaturatingMultiply(Count, Num, &Overflowed);
240 return ScaleCount / Denom;
241 }
242
perform(MemOp MO)243 bool MemOPSizeOpt::perform(MemOp MO) {
244 assert(MO.I);
245 if (MO.isMemmove())
246 return false;
247 if (!MemOPOptMemcmpBcmp && (MO.isMemcmp(TLI) || MO.isBcmp(TLI)))
248 return false;
249
250 uint32_t MaxNumVals = INSTR_PROF_NUM_BUCKETS;
251 uint64_t TotalCount;
252 auto VDs =
253 getValueProfDataFromInst(*MO.I, IPVK_MemOPSize, MaxNumVals, TotalCount);
254 if (VDs.empty())
255 return false;
256
257 uint64_t ActualCount = TotalCount;
258 uint64_t SavedTotalCount = TotalCount;
259 if (MemOPScaleCount) {
260 auto BBEdgeCount = BFI.getBlockProfileCount(MO.I->getParent());
261 if (!BBEdgeCount)
262 return false;
263 ActualCount = *BBEdgeCount;
264 }
265
266 LLVM_DEBUG(dbgs() << "Read one memory intrinsic profile with count "
267 << ActualCount << "\n");
268 LLVM_DEBUG(
269 for (auto &VD
270 : VDs) { dbgs() << " (" << VD.Value << "," << VD.Count << ")\n"; });
271
272 if (ActualCount < MemOPCountThreshold)
273 return false;
274 // Skip if the total value profiled count is 0, in which case we can't
275 // scale up the counts properly (and there is no profitable transformation).
276 if (TotalCount == 0)
277 return false;
278
279 TotalCount = ActualCount;
280 if (MemOPScaleCount)
281 LLVM_DEBUG(dbgs() << "Scale counts: numerator = " << ActualCount
282 << " denominator = " << SavedTotalCount << "\n");
283
284 // Keeping track of the count of the default case:
285 uint64_t RemainCount = TotalCount;
286 uint64_t SavedRemainCount = SavedTotalCount;
287 SmallVector<uint64_t, 16> SizeIds;
288 SmallVector<uint64_t, 16> CaseCounts;
289 SmallDenseSet<uint64_t, 16> SeenSizeId;
290 uint64_t MaxCount = 0;
291 unsigned Version = 0;
292 // Default case is in the front -- save the slot here.
293 CaseCounts.push_back(0);
294 SmallVector<InstrProfValueData, 24> RemainingVDs;
295 for (auto I = VDs.begin(), E = VDs.end(); I != E; ++I) {
296 auto &VD = *I;
297 int64_t V = VD.Value;
298 uint64_t C = VD.Count;
299 if (MemOPScaleCount)
300 C = getScaledCount(C, ActualCount, SavedTotalCount);
301
302 if (!InstrProfIsSingleValRange(V) || V > MemOpMaxOptSize) {
303 RemainingVDs.push_back(VD);
304 continue;
305 }
306
307 // ValueCounts are sorted on the count. Break at the first un-profitable
308 // value.
309 if (!isProfitable(C, RemainCount)) {
310 RemainingVDs.insert(RemainingVDs.end(), I, E);
311 break;
312 }
313
314 if (!SeenSizeId.insert(V).second) {
315 errs() << "warning: Invalid Profile Data in Function " << Func.getName()
316 << ": Two identical values in MemOp value counts.\n";
317 return false;
318 }
319
320 SizeIds.push_back(V);
321 CaseCounts.push_back(C);
322 if (C > MaxCount)
323 MaxCount = C;
324
325 assert(RemainCount >= C);
326 RemainCount -= C;
327 assert(SavedRemainCount >= VD.Count);
328 SavedRemainCount -= VD.Count;
329
330 if (++Version >= MemOPMaxVersion && MemOPMaxVersion != 0) {
331 RemainingVDs.insert(RemainingVDs.end(), I + 1, E);
332 break;
333 }
334 }
335
336 if (Version == 0)
337 return false;
338
339 CaseCounts[0] = RemainCount;
340 if (RemainCount > MaxCount)
341 MaxCount = RemainCount;
342
343 uint64_t SumForOpt = TotalCount - RemainCount;
344
345 LLVM_DEBUG(dbgs() << "Optimize one memory intrinsic call to " << Version
346 << " Versions (covering " << SumForOpt << " out of "
347 << TotalCount << ")\n");
348
349 // mem_op(..., size)
350 // ==>
351 // switch (size) {
352 // case s1:
353 // mem_op(..., s1);
354 // goto merge_bb;
355 // case s2:
356 // mem_op(..., s2);
357 // goto merge_bb;
358 // ...
359 // default:
360 // mem_op(..., size);
361 // goto merge_bb;
362 // }
363 // merge_bb:
364
365 BasicBlock *BB = MO.I->getParent();
366 LLVM_DEBUG(dbgs() << "\n\n== Basic Block Before ==\n");
367 LLVM_DEBUG(dbgs() << *BB << "\n");
368 auto OrigBBFreq = BFI.getBlockFreq(BB);
369
370 BasicBlock *DefaultBB = SplitBlock(BB, MO.I, DT);
371 BasicBlock::iterator It(*MO.I);
372 ++It;
373 assert(It != DefaultBB->end());
374 BasicBlock *MergeBB = SplitBlock(DefaultBB, &(*It), DT);
375 MergeBB->setName("MemOP.Merge");
376 BFI.setBlockFreq(MergeBB, OrigBBFreq);
377 DefaultBB->setName("MemOP.Default");
378
379 DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Eager);
380 auto &Ctx = Func.getContext();
381 IRBuilder<> IRB(BB);
382 BB->getTerminator()->eraseFromParent();
383 Value *SizeVar = MO.getLength();
384 SwitchInst *SI = IRB.CreateSwitch(SizeVar, DefaultBB, SizeIds.size());
385 Type *MemOpTy = MO.I->getType();
386 PHINode *PHI = nullptr;
387 if (!MemOpTy->isVoidTy()) {
388 // Insert a phi for the return values at the merge block.
389 IRBuilder<> IRBM(MergeBB->getFirstNonPHI());
390 PHI = IRBM.CreatePHI(MemOpTy, SizeIds.size() + 1, "MemOP.RVMerge");
391 MO.I->replaceAllUsesWith(PHI);
392 PHI->addIncoming(MO.I, DefaultBB);
393 }
394
395 // Clear the value profile data.
396 MO.I->setMetadata(LLVMContext::MD_prof, nullptr);
397 // If all promoted, we don't need the MD.prof metadata.
398 if (SavedRemainCount > 0 || Version != VDs.size()) {
399 // Otherwise we need update with the un-promoted records back.
400 annotateValueSite(*Func.getParent(), *MO.I, RemainingVDs, SavedRemainCount,
401 IPVK_MemOPSize, VDs.size());
402 }
403
404 LLVM_DEBUG(dbgs() << "\n\n== Basic Block After==\n");
405
406 std::vector<DominatorTree::UpdateType> Updates;
407 if (DT)
408 Updates.reserve(2 * SizeIds.size());
409
410 for (uint64_t SizeId : SizeIds) {
411 BasicBlock *CaseBB = BasicBlock::Create(
412 Ctx, Twine("MemOP.Case.") + Twine(SizeId), &Func, DefaultBB);
413 MemOp NewMO = MO.clone();
414 // Fix the argument.
415 auto *SizeType = dyn_cast<IntegerType>(NewMO.getLength()->getType());
416 assert(SizeType && "Expected integer type size argument.");
417 ConstantInt *CaseSizeId = ConstantInt::get(SizeType, SizeId);
418 NewMO.setLength(CaseSizeId);
419 NewMO.I->insertInto(CaseBB, CaseBB->end());
420 IRBuilder<> IRBCase(CaseBB);
421 IRBCase.CreateBr(MergeBB);
422 SI->addCase(CaseSizeId, CaseBB);
423 if (!MemOpTy->isVoidTy())
424 PHI->addIncoming(NewMO.I, CaseBB);
425 if (DT) {
426 Updates.push_back({DominatorTree::Insert, CaseBB, MergeBB});
427 Updates.push_back({DominatorTree::Insert, BB, CaseBB});
428 }
429 LLVM_DEBUG(dbgs() << *CaseBB << "\n");
430 }
431 DTU.applyUpdates(Updates);
432 Updates.clear();
433
434 if (MaxCount)
435 setProfMetadata(Func.getParent(), SI, CaseCounts, MaxCount);
436
437 LLVM_DEBUG(dbgs() << *BB << "\n");
438 LLVM_DEBUG(dbgs() << *DefaultBB << "\n");
439 LLVM_DEBUG(dbgs() << *MergeBB << "\n");
440
441 ORE.emit([&]() {
442 using namespace ore;
443 return OptimizationRemark(DEBUG_TYPE, "memopt-opt", MO.I)
444 << "optimized " << NV("Memop", MO.getName(TLI)) << " with count "
445 << NV("Count", SumForOpt) << " out of " << NV("Total", TotalCount)
446 << " for " << NV("Versions", Version) << " versions";
447 });
448
449 return true;
450 }
451 } // namespace
452
PGOMemOPSizeOptImpl(Function & F,BlockFrequencyInfo & BFI,OptimizationRemarkEmitter & ORE,DominatorTree * DT,TargetLibraryInfo & TLI)453 static bool PGOMemOPSizeOptImpl(Function &F, BlockFrequencyInfo &BFI,
454 OptimizationRemarkEmitter &ORE,
455 DominatorTree *DT, TargetLibraryInfo &TLI) {
456 if (DisableMemOPOPT)
457 return false;
458
459 if (F.hasFnAttribute(Attribute::OptimizeForSize))
460 return false;
461 MemOPSizeOpt MemOPSizeOpt(F, BFI, ORE, DT, TLI);
462 MemOPSizeOpt.perform();
463 return MemOPSizeOpt.isChanged();
464 }
465
run(Function & F,FunctionAnalysisManager & FAM)466 PreservedAnalyses PGOMemOPSizeOpt::run(Function &F,
467 FunctionAnalysisManager &FAM) {
468 auto &BFI = FAM.getResult<BlockFrequencyAnalysis>(F);
469 auto &ORE = FAM.getResult<OptimizationRemarkEmitterAnalysis>(F);
470 auto *DT = FAM.getCachedResult<DominatorTreeAnalysis>(F);
471 auto &TLI = FAM.getResult<TargetLibraryAnalysis>(F);
472 bool Changed = PGOMemOPSizeOptImpl(F, BFI, ORE, DT, TLI);
473 if (!Changed)
474 return PreservedAnalyses::all();
475 auto PA = PreservedAnalyses();
476 PA.preserve<DominatorTreeAnalysis>();
477 return PA;
478 }
479