1 //===- IndirectCallPromotion.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 promotes indirect calls to
10 // conditional direct calls when the indirect-call value profile metadata is
11 // available.
12 //
13 //===----------------------------------------------------------------------===//
14 
15 #include "llvm/ADT/ArrayRef.h"
16 #include "llvm/ADT/STLExtras.h"
17 #include "llvm/ADT/SmallVector.h"
18 #include "llvm/ADT/Statistic.h"
19 #include "llvm/ADT/StringRef.h"
20 #include "llvm/Analysis/IndirectCallPromotionAnalysis.h"
21 #include "llvm/Analysis/IndirectCallVisitor.h"
22 #include "llvm/Analysis/OptimizationRemarkEmitter.h"
23 #include "llvm/Analysis/ProfileSummaryInfo.h"
24 #include "llvm/IR/Attributes.h"
25 #include "llvm/IR/BasicBlock.h"
26 #include "llvm/IR/CallSite.h"
27 #include "llvm/IR/DerivedTypes.h"
28 #include "llvm/IR/DiagnosticInfo.h"
29 #include "llvm/IR/Function.h"
30 #include "llvm/IR/IRBuilder.h"
31 #include "llvm/IR/InstrTypes.h"
32 #include "llvm/IR/Instruction.h"
33 #include "llvm/IR/Instructions.h"
34 #include "llvm/IR/LLVMContext.h"
35 #include "llvm/IR/MDBuilder.h"
36 #include "llvm/IR/PassManager.h"
37 #include "llvm/IR/Type.h"
38 #include "llvm/IR/Value.h"
39 #include "llvm/InitializePasses.h"
40 #include "llvm/Pass.h"
41 #include "llvm/ProfileData/InstrProf.h"
42 #include "llvm/Support/Casting.h"
43 #include "llvm/Support/CommandLine.h"
44 #include "llvm/Support/Debug.h"
45 #include "llvm/Support/Error.h"
46 #include "llvm/Support/raw_ostream.h"
47 #include "llvm/Transforms/Instrumentation.h"
48 #include "llvm/Transforms/Instrumentation/PGOInstrumentation.h"
49 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
50 #include "llvm/Transforms/Utils/CallPromotionUtils.h"
51 #include <cassert>
52 #include <cstdint>
53 #include <memory>
54 #include <string>
55 #include <utility>
56 #include <vector>
57 
58 using namespace llvm;
59 
60 #define DEBUG_TYPE "pgo-icall-prom"
61 
62 STATISTIC(NumOfPGOICallPromotion, "Number of indirect call promotions.");
63 STATISTIC(NumOfPGOICallsites, "Number of indirect call candidate sites.");
64 
65 // Command line option to disable indirect-call promotion with the default as
66 // false. This is for debug purpose.
67 static cl::opt<bool> DisableICP("disable-icp", cl::init(false), cl::Hidden,
68                                 cl::desc("Disable indirect call promotion"));
69 
70 // Set the cutoff value for the promotion. If the value is other than 0, we
71 // stop the transformation once the total number of promotions equals the cutoff
72 // value.
73 // For debug use only.
74 static cl::opt<unsigned>
75     ICPCutOff("icp-cutoff", cl::init(0), cl::Hidden, cl::ZeroOrMore,
76               cl::desc("Max number of promotions for this compilation"));
77 
78 // If ICPCSSkip is non zero, the first ICPCSSkip callsites will be skipped.
79 // For debug use only.
80 static cl::opt<unsigned>
81     ICPCSSkip("icp-csskip", cl::init(0), cl::Hidden, cl::ZeroOrMore,
82               cl::desc("Skip Callsite up to this number for this compilation"));
83 
84 // Set if the pass is called in LTO optimization. The difference for LTO mode
85 // is the pass won't prefix the source module name to the internal linkage
86 // symbols.
87 static cl::opt<bool> ICPLTOMode("icp-lto", cl::init(false), cl::Hidden,
88                                 cl::desc("Run indirect-call promotion in LTO "
89                                          "mode"));
90 
91 // Set if the pass is called in SamplePGO mode. The difference for SamplePGO
92 // mode is it will add prof metadatato the created direct call.
93 static cl::opt<bool>
94     ICPSamplePGOMode("icp-samplepgo", cl::init(false), cl::Hidden,
95                      cl::desc("Run indirect-call promotion in SamplePGO mode"));
96 
97 // If the option is set to true, only call instructions will be considered for
98 // transformation -- invoke instructions will be ignored.
99 static cl::opt<bool>
100     ICPCallOnly("icp-call-only", cl::init(false), cl::Hidden,
101                 cl::desc("Run indirect-call promotion for call instructions "
102                          "only"));
103 
104 // If the option is set to true, only invoke instructions will be considered for
105 // transformation -- call instructions will be ignored.
106 static cl::opt<bool> ICPInvokeOnly("icp-invoke-only", cl::init(false),
107                                    cl::Hidden,
108                                    cl::desc("Run indirect-call promotion for "
109                                             "invoke instruction only"));
110 
111 // Dump the function level IR if the transformation happened in this
112 // function. For debug use only.
113 static cl::opt<bool>
114     ICPDUMPAFTER("icp-dumpafter", cl::init(false), cl::Hidden,
115                  cl::desc("Dump IR after transformation happens"));
116 
117 namespace {
118 
119 class PGOIndirectCallPromotionLegacyPass : public ModulePass {
120 public:
121   static char ID;
122 
123   PGOIndirectCallPromotionLegacyPass(bool InLTO = false, bool SamplePGO = false)
124       : ModulePass(ID), InLTO(InLTO), SamplePGO(SamplePGO) {
125     initializePGOIndirectCallPromotionLegacyPassPass(
126         *PassRegistry::getPassRegistry());
127   }
128 
129   void getAnalysisUsage(AnalysisUsage &AU) const override {
130     AU.addRequired<ProfileSummaryInfoWrapperPass>();
131   }
132 
133   StringRef getPassName() const override { return "PGOIndirectCallPromotion"; }
134 
135 private:
136   bool runOnModule(Module &M) override;
137 
138   // If this pass is called in LTO. We need to special handling the PGOFuncName
139   // for the static variables due to LTO's internalization.
140   bool InLTO;
141 
142   // If this pass is called in SamplePGO. We need to add the prof metadata to
143   // the promoted direct call.
144   bool SamplePGO;
145 };
146 
147 } // end anonymous namespace
148 
149 char PGOIndirectCallPromotionLegacyPass::ID = 0;
150 
151 INITIALIZE_PASS_BEGIN(PGOIndirectCallPromotionLegacyPass, "pgo-icall-prom",
152                       "Use PGO instrumentation profile to promote indirect "
153                       "calls to direct calls.",
154                       false, false)
155 INITIALIZE_PASS_DEPENDENCY(ProfileSummaryInfoWrapperPass)
156 INITIALIZE_PASS_END(PGOIndirectCallPromotionLegacyPass, "pgo-icall-prom",
157                     "Use PGO instrumentation profile to promote indirect "
158                     "calls to direct calls.",
159                     false, false)
160 
161 ModulePass *llvm::createPGOIndirectCallPromotionLegacyPass(bool InLTO,
162                                                            bool SamplePGO) {
163   return new PGOIndirectCallPromotionLegacyPass(InLTO, SamplePGO);
164 }
165 
166 namespace {
167 
168 // The class for main data structure to promote indirect calls to conditional
169 // direct calls.
170 class ICallPromotionFunc {
171 private:
172   Function &F;
173   Module *M;
174 
175   // Symtab that maps indirect call profile values to function names and
176   // defines.
177   InstrProfSymtab *Symtab;
178 
179   bool SamplePGO;
180 
181   OptimizationRemarkEmitter &ORE;
182 
183   // A struct that records the direct target and it's call count.
184   struct PromotionCandidate {
185     Function *TargetFunction;
186     uint64_t Count;
187 
188     PromotionCandidate(Function *F, uint64_t C) : TargetFunction(F), Count(C) {}
189   };
190 
191   // Check if the indirect-call call site should be promoted. Return the number
192   // of promotions. Inst is the candidate indirect call, ValueDataRef
193   // contains the array of value profile data for profiled targets,
194   // TotalCount is the total profiled count of call executions, and
195   // NumCandidates is the number of candidate entries in ValueDataRef.
196   std::vector<PromotionCandidate> getPromotionCandidatesForCallSite(
197       Instruction *Inst, const ArrayRef<InstrProfValueData> &ValueDataRef,
198       uint64_t TotalCount, uint32_t NumCandidates);
199 
200   // Promote a list of targets for one indirect-call callsite. Return
201   // the number of promotions.
202   uint32_t tryToPromote(Instruction *Inst,
203                         const std::vector<PromotionCandidate> &Candidates,
204                         uint64_t &TotalCount);
205 
206 public:
207   ICallPromotionFunc(Function &Func, Module *Modu, InstrProfSymtab *Symtab,
208                      bool SamplePGO, OptimizationRemarkEmitter &ORE)
209       : F(Func), M(Modu), Symtab(Symtab), SamplePGO(SamplePGO), ORE(ORE) {}
210   ICallPromotionFunc(const ICallPromotionFunc &) = delete;
211   ICallPromotionFunc &operator=(const ICallPromotionFunc &) = delete;
212 
213   bool processFunction(ProfileSummaryInfo *PSI);
214 };
215 
216 } // end anonymous namespace
217 
218 // Indirect-call promotion heuristic. The direct targets are sorted based on
219 // the count. Stop at the first target that is not promoted.
220 std::vector<ICallPromotionFunc::PromotionCandidate>
221 ICallPromotionFunc::getPromotionCandidatesForCallSite(
222     Instruction *Inst, const ArrayRef<InstrProfValueData> &ValueDataRef,
223     uint64_t TotalCount, uint32_t NumCandidates) {
224   std::vector<PromotionCandidate> Ret;
225 
226   LLVM_DEBUG(dbgs() << " \nWork on callsite #" << NumOfPGOICallsites << *Inst
227                     << " Num_targets: " << ValueDataRef.size()
228                     << " Num_candidates: " << NumCandidates << "\n");
229   NumOfPGOICallsites++;
230   if (ICPCSSkip != 0 && NumOfPGOICallsites <= ICPCSSkip) {
231     LLVM_DEBUG(dbgs() << " Skip: User options.\n");
232     return Ret;
233   }
234 
235   for (uint32_t I = 0; I < NumCandidates; I++) {
236     uint64_t Count = ValueDataRef[I].Count;
237     assert(Count <= TotalCount);
238     uint64_t Target = ValueDataRef[I].Value;
239     LLVM_DEBUG(dbgs() << " Candidate " << I << " Count=" << Count
240                       << "  Target_func: " << Target << "\n");
241 
242     if (ICPInvokeOnly && isa<CallInst>(Inst)) {
243       LLVM_DEBUG(dbgs() << " Not promote: User options.\n");
244       ORE.emit([&]() {
245         return OptimizationRemarkMissed(DEBUG_TYPE, "UserOptions", Inst)
246                << " Not promote: User options";
247       });
248       break;
249     }
250     if (ICPCallOnly && isa<InvokeInst>(Inst)) {
251       LLVM_DEBUG(dbgs() << " Not promote: User option.\n");
252       ORE.emit([&]() {
253         return OptimizationRemarkMissed(DEBUG_TYPE, "UserOptions", Inst)
254                << " Not promote: User options";
255       });
256       break;
257     }
258     if (ICPCutOff != 0 && NumOfPGOICallPromotion >= ICPCutOff) {
259       LLVM_DEBUG(dbgs() << " Not promote: Cutoff reached.\n");
260       ORE.emit([&]() {
261         return OptimizationRemarkMissed(DEBUG_TYPE, "CutOffReached", Inst)
262                << " Not promote: Cutoff reached";
263       });
264       break;
265     }
266 
267     Function *TargetFunction = Symtab->getFunction(Target);
268     if (TargetFunction == nullptr) {
269       LLVM_DEBUG(dbgs() << " Not promote: Cannot find the target\n");
270       ORE.emit([&]() {
271         return OptimizationRemarkMissed(DEBUG_TYPE, "UnableToFindTarget", Inst)
272                << "Cannot promote indirect call: target with md5sum "
273                << ore::NV("target md5sum", Target) << " not found";
274       });
275       break;
276     }
277 
278     const char *Reason = nullptr;
279     if (!isLegalToPromote(CallSite(Inst), TargetFunction, &Reason)) {
280       using namespace ore;
281 
282       ORE.emit([&]() {
283         return OptimizationRemarkMissed(DEBUG_TYPE, "UnableToPromote", Inst)
284                << "Cannot promote indirect call to "
285                << NV("TargetFunction", TargetFunction) << " with count of "
286                << NV("Count", Count) << ": " << Reason;
287       });
288       break;
289     }
290 
291     Ret.push_back(PromotionCandidate(TargetFunction, Count));
292     TotalCount -= Count;
293   }
294   return Ret;
295 }
296 
297 Instruction *llvm::pgo::promoteIndirectCall(Instruction *Inst,
298                                             Function *DirectCallee,
299                                             uint64_t Count, uint64_t TotalCount,
300                                             bool AttachProfToDirectCall,
301                                             OptimizationRemarkEmitter *ORE) {
302 
303   uint64_t ElseCount = TotalCount - Count;
304   uint64_t MaxCount = (Count >= ElseCount ? Count : ElseCount);
305   uint64_t Scale = calculateCountScale(MaxCount);
306   MDBuilder MDB(Inst->getContext());
307   MDNode *BranchWeights = MDB.createBranchWeights(
308       scaleBranchCount(Count, Scale), scaleBranchCount(ElseCount, Scale));
309 
310   Instruction *NewInst =
311       promoteCallWithIfThenElse(CallSite(Inst), DirectCallee, BranchWeights);
312 
313   if (AttachProfToDirectCall) {
314     MDBuilder MDB(NewInst->getContext());
315     NewInst->setMetadata(
316         LLVMContext::MD_prof,
317         MDB.createBranchWeights({static_cast<uint32_t>(Count)}));
318   }
319 
320   using namespace ore;
321 
322   if (ORE)
323     ORE->emit([&]() {
324       return OptimizationRemark(DEBUG_TYPE, "Promoted", Inst)
325              << "Promote indirect call to " << NV("DirectCallee", DirectCallee)
326              << " with count " << NV("Count", Count) << " out of "
327              << NV("TotalCount", TotalCount);
328     });
329   return NewInst;
330 }
331 
332 // Promote indirect-call to conditional direct-call for one callsite.
333 uint32_t ICallPromotionFunc::tryToPromote(
334     Instruction *Inst, const std::vector<PromotionCandidate> &Candidates,
335     uint64_t &TotalCount) {
336   uint32_t NumPromoted = 0;
337 
338   for (auto &C : Candidates) {
339     uint64_t Count = C.Count;
340     pgo::promoteIndirectCall(Inst, C.TargetFunction, Count, TotalCount,
341                              SamplePGO, &ORE);
342     assert(TotalCount >= Count);
343     TotalCount -= Count;
344     NumOfPGOICallPromotion++;
345     NumPromoted++;
346   }
347   return NumPromoted;
348 }
349 
350 // Traverse all the indirect-call callsite and get the value profile
351 // annotation to perform indirect-call promotion.
352 bool ICallPromotionFunc::processFunction(ProfileSummaryInfo *PSI) {
353   bool Changed = false;
354   ICallPromotionAnalysis ICallAnalysis;
355   for (auto &I : findIndirectCalls(F)) {
356     uint32_t NumVals, NumCandidates;
357     uint64_t TotalCount;
358     auto ICallProfDataRef = ICallAnalysis.getPromotionCandidatesForInstruction(
359         I, NumVals, TotalCount, NumCandidates);
360     if (!NumCandidates ||
361         (PSI && PSI->hasProfileSummary() && !PSI->isHotCount(TotalCount)))
362       continue;
363     auto PromotionCandidates = getPromotionCandidatesForCallSite(
364         I, ICallProfDataRef, TotalCount, NumCandidates);
365     uint32_t NumPromoted = tryToPromote(I, PromotionCandidates, TotalCount);
366     if (NumPromoted == 0)
367       continue;
368 
369     Changed = true;
370     // Adjust the MD.prof metadata. First delete the old one.
371     I->setMetadata(LLVMContext::MD_prof, nullptr);
372     // If all promoted, we don't need the MD.prof metadata.
373     if (TotalCount == 0 || NumPromoted == NumVals)
374       continue;
375     // Otherwise we need update with the un-promoted records back.
376     annotateValueSite(*M, *I, ICallProfDataRef.slice(NumPromoted), TotalCount,
377                       IPVK_IndirectCallTarget, NumCandidates);
378   }
379   return Changed;
380 }
381 
382 // A wrapper function that does the actual work.
383 static bool promoteIndirectCalls(Module &M, ProfileSummaryInfo *PSI,
384                                  bool InLTO, bool SamplePGO,
385                                  ModuleAnalysisManager *AM = nullptr) {
386   if (DisableICP)
387     return false;
388   InstrProfSymtab Symtab;
389   if (Error E = Symtab.create(M, InLTO)) {
390     std::string SymtabFailure = toString(std::move(E));
391     LLVM_DEBUG(dbgs() << "Failed to create symtab: " << SymtabFailure << "\n");
392     (void)SymtabFailure;
393     return false;
394   }
395   bool Changed = false;
396   for (auto &F : M) {
397     if (F.isDeclaration() || F.hasOptNone())
398       continue;
399 
400     std::unique_ptr<OptimizationRemarkEmitter> OwnedORE;
401     OptimizationRemarkEmitter *ORE;
402     if (AM) {
403       auto &FAM =
404           AM->getResult<FunctionAnalysisManagerModuleProxy>(M).getManager();
405       ORE = &FAM.getResult<OptimizationRemarkEmitterAnalysis>(F);
406     } else {
407       OwnedORE = std::make_unique<OptimizationRemarkEmitter>(&F);
408       ORE = OwnedORE.get();
409     }
410 
411     ICallPromotionFunc ICallPromotion(F, &M, &Symtab, SamplePGO, *ORE);
412     bool FuncChanged = ICallPromotion.processFunction(PSI);
413     if (ICPDUMPAFTER && FuncChanged) {
414       LLVM_DEBUG(dbgs() << "\n== IR Dump After =="; F.print(dbgs()));
415       LLVM_DEBUG(dbgs() << "\n");
416     }
417     Changed |= FuncChanged;
418     if (ICPCutOff != 0 && NumOfPGOICallPromotion >= ICPCutOff) {
419       LLVM_DEBUG(dbgs() << " Stop: Cutoff reached.\n");
420       break;
421     }
422   }
423   return Changed;
424 }
425 
426 bool PGOIndirectCallPromotionLegacyPass::runOnModule(Module &M) {
427   ProfileSummaryInfo *PSI =
428       &getAnalysis<ProfileSummaryInfoWrapperPass>().getPSI();
429 
430   // Command-line option has the priority for InLTO.
431   return promoteIndirectCalls(M, PSI, InLTO | ICPLTOMode,
432                               SamplePGO | ICPSamplePGOMode);
433 }
434 
435 PreservedAnalyses PGOIndirectCallPromotion::run(Module &M,
436                                                 ModuleAnalysisManager &AM) {
437   ProfileSummaryInfo *PSI = &AM.getResult<ProfileSummaryAnalysis>(M);
438 
439   if (!promoteIndirectCalls(M, PSI, InLTO | ICPLTOMode,
440                             SamplePGO | ICPSamplePGOMode, &AM))
441     return PreservedAnalyses::all();
442 
443   return PreservedAnalyses::none();
444 }
445