1 //===- bolt/Passes/FrameOptimizer.cpp -------------------------------------===//
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 FrameOptimizerPass class.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #include "bolt/Passes/FrameOptimizer.h"
14 #include "bolt/Core/ParallelUtilities.h"
15 #include "bolt/Passes/BinaryFunctionCallGraph.h"
16 #include "bolt/Passes/DataflowInfoManager.h"
17 #include "bolt/Passes/ShrinkWrapping.h"
18 #include "bolt/Passes/StackAvailableExpressions.h"
19 #include "bolt/Passes/StackReachingUses.h"
20 #include "llvm/Support/Timer.h"
21 #include <deque>
22 #include <unordered_map>
23 
24 #define DEBUG_TYPE "fop"
25 
26 using namespace llvm;
27 
28 namespace opts {
29 extern cl::opt<unsigned> Verbosity;
30 extern cl::opt<bool> TimeOpts;
31 extern cl::OptionCategory BoltOptCategory;
32 
33 using namespace bolt;
34 
35 cl::opt<FrameOptimizationType>
36 FrameOptimization("frame-opt",
37   cl::init(FOP_NONE),
38   cl::desc("optimize stack frame accesses"),
39   cl::values(
40     clEnumValN(FOP_NONE, "none", "do not perform frame optimization"),
41     clEnumValN(FOP_HOT, "hot", "perform FOP on hot functions"),
42     clEnumValN(FOP_ALL, "all", "perform FOP on all functions")),
43   cl::ZeroOrMore,
44   cl::cat(BoltOptCategory));
45 
46 cl::opt<bool>
47 RemoveStores("frame-opt-rm-stores",
48   cl::init(FOP_NONE),
49   cl::desc("apply additional analysis to remove stores (experimental)"),
50   cl::init(false),
51   cl::ZeroOrMore,
52   cl::cat(BoltOptCategory));
53 
54 } // namespace opts
55 
56 namespace llvm {
57 namespace bolt {
58 
59 void FrameOptimizerPass::removeUnnecessaryLoads(const RegAnalysis &RA,
60                                                 const FrameAnalysis &FA,
61                                                 BinaryFunction &BF) {
62   StackAvailableExpressions SAE(RA, FA, BF);
63   SAE.run();
64 
65   LLVM_DEBUG(dbgs() << "Performing unnecessary loads removal\n");
66   std::deque<std::pair<BinaryBasicBlock *, MCInst *>> ToErase;
67   bool Changed = false;
68   const auto ExprEnd = SAE.expr_end();
69   MCPlusBuilder *MIB = BF.getBinaryContext().MIB.get();
70   for (BinaryBasicBlock &BB : BF) {
71     LLVM_DEBUG(dbgs() << "\tNow at BB " << BB.getName() << "\n");
72     const MCInst *Prev = nullptr;
73     for (MCInst &Inst : BB) {
74       LLVM_DEBUG({
75         dbgs() << "\t\tNow at ";
76         Inst.dump();
77         for (auto I = Prev ? SAE.expr_begin(*Prev) : SAE.expr_begin(BB);
78              I != ExprEnd; ++I) {
79           dbgs() << "\t\t\tReached by: ";
80           (*I)->dump();
81         }
82       });
83       // if Inst is a load from stack and the current available expressions show
84       // this value is available in a register or immediate, replace this load
85       // with move from register or from immediate.
86       ErrorOr<const FrameIndexEntry &> FIEX = FA.getFIEFor(Inst);
87       if (!FIEX) {
88         Prev = &Inst;
89         continue;
90       }
91       // FIXME: Change to remove IsSimple == 0. We're being conservative here,
92       // but once replaceMemOperandWithReg is ready, we should feed it with all
93       // sorts of complex instructions.
94       if (FIEX->IsLoad == false || FIEX->IsSimple == false ||
95           FIEX->StackOffset >= 0) {
96         Prev = &Inst;
97         continue;
98       }
99 
100       for (auto I = Prev ? SAE.expr_begin(*Prev) : SAE.expr_begin(BB);
101            I != ExprEnd; ++I) {
102         const MCInst *AvailableInst = *I;
103         ErrorOr<const FrameIndexEntry &> FIEY = FA.getFIEFor(*AvailableInst);
104         if (!FIEY)
105           continue;
106         assert(FIEY->IsStore && FIEY->IsSimple);
107         if (FIEX->StackOffset != FIEY->StackOffset || FIEX->Size != FIEY->Size)
108           continue;
109         // TODO: Change push/pops to stack adjustment instruction
110         if (MIB->isPop(Inst))
111           continue;
112 
113         ++NumRedundantLoads;
114         Changed = true;
115         LLVM_DEBUG(dbgs() << "Redundant load instruction: ");
116         LLVM_DEBUG(Inst.dump());
117         LLVM_DEBUG(dbgs() << "Related store instruction: ");
118         LLVM_DEBUG(AvailableInst->dump());
119         LLVM_DEBUG(dbgs() << "@BB: " << BB.getName() << "\n");
120         // Replace load
121         if (FIEY->IsStoreFromReg) {
122           if (!MIB->replaceMemOperandWithReg(Inst, FIEY->RegOrImm)) {
123             LLVM_DEBUG(dbgs() << "FAILED to change operand to a reg\n");
124             break;
125           }
126           ++NumLoadsChangedToReg;
127           MIB->removeAnnotation(Inst, "FrameAccessEntry");
128           LLVM_DEBUG(dbgs() << "Changed operand to a reg\n");
129           if (MIB->isRedundantMove(Inst)) {
130             ++NumLoadsDeleted;
131             LLVM_DEBUG(dbgs() << "Created a redundant move\n");
132             // Delete it!
133             ToErase.push_front(std::make_pair(&BB, &Inst));
134           }
135         } else {
136           char Buf[8] = {0, 0, 0, 0, 0, 0, 0, 0};
137           support::ulittle64_t::ref(Buf + 0) = FIEY->RegOrImm;
138           LLVM_DEBUG(dbgs() << "Changing operand to an imm... ");
139           if (!MIB->replaceMemOperandWithImm(Inst, StringRef(Buf, 8), 0)) {
140             LLVM_DEBUG(dbgs() << "FAILED\n");
141           } else {
142             ++NumLoadsChangedToImm;
143             MIB->removeAnnotation(Inst, "FrameAccessEntry");
144             LLVM_DEBUG(dbgs() << "Ok\n");
145           }
146         }
147         LLVM_DEBUG(dbgs() << "Changed to: ");
148         LLVM_DEBUG(Inst.dump());
149         break;
150       }
151       Prev = &Inst;
152     }
153   }
154   if (Changed)
155     LLVM_DEBUG(dbgs() << "FOP modified \"" << BF.getPrintName() << "\"\n");
156 
157   // TODO: Implement an interface of eraseInstruction that works out the
158   // complete list of elements to remove.
159   for (std::pair<BinaryBasicBlock *, MCInst *> I : ToErase)
160     I.first->eraseInstruction(I.first->findInstruction(I.second));
161 }
162 
163 void FrameOptimizerPass::removeUnusedStores(const FrameAnalysis &FA,
164                                             BinaryFunction &BF) {
165   StackReachingUses SRU(FA, BF);
166   SRU.run();
167 
168   LLVM_DEBUG(dbgs() << "Performing unused stores removal\n");
169   std::vector<std::pair<BinaryBasicBlock *, MCInst *>> ToErase;
170   bool Changed = false;
171   for (BinaryBasicBlock &BB : BF) {
172     LLVM_DEBUG(dbgs() << "\tNow at BB " << BB.getName() << "\n");
173     const MCInst *Prev = nullptr;
174     for (auto I = BB.rbegin(), E = BB.rend(); I != E; ++I) {
175       MCInst &Inst = *I;
176       LLVM_DEBUG({
177         dbgs() << "\t\tNow at ";
178         Inst.dump();
179         for (auto I = Prev ? SRU.expr_begin(*Prev) : SRU.expr_begin(BB);
180              I != SRU.expr_end(); ++I) {
181           dbgs() << "\t\t\tReached by: ";
182           (*I)->dump();
183         }
184       });
185       ErrorOr<const FrameIndexEntry &> FIEX = FA.getFIEFor(Inst);
186       if (!FIEX) {
187         Prev = &Inst;
188         continue;
189       }
190       if (FIEX->IsLoad || !FIEX->IsSimple || FIEX->StackOffset >= 0) {
191         Prev = &Inst;
192         continue;
193       }
194 
195       if (SRU.isStoreUsed(*FIEX,
196                           Prev ? SRU.expr_begin(*Prev) : SRU.expr_begin(BB))) {
197         Prev = &Inst;
198         continue;
199       }
200       // TODO: Change push/pops to stack adjustment instruction
201       if (BF.getBinaryContext().MIB->isPush(Inst))
202         continue;
203 
204       ++NumRedundantStores;
205       Changed = true;
206       LLVM_DEBUG(dbgs() << "Unused store instruction: ");
207       LLVM_DEBUG(Inst.dump());
208       LLVM_DEBUG(dbgs() << "@BB: " << BB.getName() << "\n");
209       LLVM_DEBUG(dbgs() << "FIE offset = " << FIEX->StackOffset
210                         << " size = " << (int)FIEX->Size << "\n");
211       // Delete it!
212       ToErase.emplace_back(&BB, &Inst);
213       Prev = &Inst;
214     }
215   }
216 
217   for (std::pair<BinaryBasicBlock *, MCInst *> I : ToErase)
218     I.first->eraseInstruction(I.first->findInstruction(I.second));
219 
220   if (Changed)
221     LLVM_DEBUG(dbgs() << "FOP modified \"" << BF.getPrintName() << "\"\n");
222 }
223 
224 void FrameOptimizerPass::runOnFunctions(BinaryContext &BC) {
225   if (opts::FrameOptimization == FOP_NONE)
226     return;
227 
228   std::unique_ptr<BinaryFunctionCallGraph> CG;
229   std::unique_ptr<FrameAnalysis> FA;
230   std::unique_ptr<RegAnalysis> RA;
231 
232   {
233     NamedRegionTimer T1("callgraph", "create call graph", "FOP",
234                         "FOP breakdown", opts::TimeOpts);
235     CG = std::make_unique<BinaryFunctionCallGraph>(buildCallGraph(BC));
236   }
237 
238   {
239     NamedRegionTimer T1("frameanalysis", "frame analysis", "FOP",
240                         "FOP breakdown", opts::TimeOpts);
241     FA = std::make_unique<FrameAnalysis>(BC, *CG);
242   }
243 
244   {
245     NamedRegionTimer T1("reganalysis", "reg analysis", "FOP", "FOP breakdown",
246                         opts::TimeOpts);
247     RA = std::make_unique<RegAnalysis>(BC, &BC.getBinaryFunctions(), CG.get());
248   }
249 
250   // Perform caller-saved register optimizations, then callee-saved register
251   // optimizations (shrink wrapping)
252   for (auto &I : BC.getBinaryFunctions()) {
253     if (!FA->hasFrameInfo(I.second))
254       continue;
255     // Restrict pass execution if user asked to only run on hot functions
256     if (opts::FrameOptimization == FOP_HOT) {
257       if (I.second.getKnownExecutionCount() < BC.getHotThreshold())
258         continue;
259       LLVM_DEBUG(
260           dbgs() << "Considering " << I.second.getPrintName()
261                  << " for frame optimizations because its execution count ( "
262                  << I.second.getKnownExecutionCount()
263                  << " ) exceeds our hotness threshold ( "
264                  << BC.getHotThreshold() << " )\n");
265     }
266 
267     {
268       NamedRegionTimer T1("removeloads", "remove loads", "FOP", "FOP breakdown",
269                           opts::TimeOpts);
270       removeUnnecessaryLoads(*RA, *FA, I.second);
271     }
272 
273     if (opts::RemoveStores) {
274       NamedRegionTimer T1("removestores", "remove stores", "FOP",
275                           "FOP breakdown", opts::TimeOpts);
276       removeUnusedStores(*FA, I.second);
277     }
278     // Don't even start shrink wrapping if no profiling info is available
279     if (I.second.getKnownExecutionCount() == 0)
280       continue;
281   }
282 
283   {
284     NamedRegionTimer T1("shrinkwrapping", "shrink wrapping", "FOP",
285                         "FOP breakdown", opts::TimeOpts);
286     performShrinkWrapping(*RA, *FA, BC);
287   }
288 
289   outs() << "BOLT-INFO: FOP optimized " << NumRedundantLoads
290          << " redundant load(s) and " << NumRedundantStores
291          << " unused store(s)\n";
292   outs() << "BOLT-INFO: FOP changed " << NumLoadsChangedToReg
293          << " load(s) to use a register instead of a stack access, and "
294          << NumLoadsChangedToImm << " to use an immediate.\n"
295          << "BOLT-INFO: FOP deleted " << NumLoadsDeleted << " load(s) and "
296          << NumRedundantStores << " store(s).\n";
297   FA->printStats();
298   ShrinkWrapping::printStats();
299 }
300 
301 void FrameOptimizerPass::performShrinkWrapping(const RegAnalysis &RA,
302                                                const FrameAnalysis &FA,
303                                                BinaryContext &BC) {
304   // Initialize necessary annotations to allow safe parallel accesses to
305   // annotation index in MIB
306   BC.MIB->getOrCreateAnnotationIndex(CalleeSavedAnalysis::getSaveTagName());
307   BC.MIB->getOrCreateAnnotationIndex(CalleeSavedAnalysis::getRestoreTagName());
308   BC.MIB->getOrCreateAnnotationIndex(StackLayoutModifier::getTodoTagName());
309   BC.MIB->getOrCreateAnnotationIndex(StackLayoutModifier::getSlotTagName());
310   BC.MIB->getOrCreateAnnotationIndex(
311       StackLayoutModifier::getOffsetCFIRegTagName());
312   BC.MIB->getOrCreateAnnotationIndex("ReachingDefs");
313   BC.MIB->getOrCreateAnnotationIndex("ReachingUses");
314   BC.MIB->getOrCreateAnnotationIndex("LivenessAnalysis");
315   BC.MIB->getOrCreateAnnotationIndex("StackReachingUses");
316   BC.MIB->getOrCreateAnnotationIndex("PostDominatorAnalysis");
317   BC.MIB->getOrCreateAnnotationIndex("DominatorAnalysis");
318   BC.MIB->getOrCreateAnnotationIndex("StackPointerTracking");
319   BC.MIB->getOrCreateAnnotationIndex("StackPointerTrackingForInternalCalls");
320   BC.MIB->getOrCreateAnnotationIndex("StackAvailableExpressions");
321   BC.MIB->getOrCreateAnnotationIndex("StackAllocationAnalysis");
322   BC.MIB->getOrCreateAnnotationIndex("ShrinkWrap-Todo");
323   BC.MIB->getOrCreateAnnotationIndex("PredictiveStackPointerTracking");
324   BC.MIB->getOrCreateAnnotationIndex("ReachingInsnsBackward");
325   BC.MIB->getOrCreateAnnotationIndex("ReachingInsns");
326   BC.MIB->getOrCreateAnnotationIndex("AccessesDeletedPos");
327   BC.MIB->getOrCreateAnnotationIndex("DeleteMe");
328 
329   ParallelUtilities::PredicateTy SkipPredicate = [&](const BinaryFunction &BF) {
330     if (!FA.hasFrameInfo(BF))
331       return true;
332 
333     if (opts::FrameOptimization == FOP_HOT &&
334         (BF.getKnownExecutionCount() < BC.getHotThreshold()))
335       return true;
336 
337     if (BF.getKnownExecutionCount() == 0)
338       return true;
339 
340     return false;
341   };
342 
343   ParallelUtilities::WorkFuncWithAllocTy WorkFunction =
344       [&](BinaryFunction &BF, MCPlusBuilder::AllocatorIdTy AllocatorId) {
345         DataflowInfoManager Info(BF, &RA, &FA, AllocatorId);
346         ShrinkWrapping SW(FA, BF, Info, AllocatorId);
347 
348         if (SW.perform()) {
349           std::lock_guard<std::mutex> Lock(FuncsChangedMutex);
350           FuncsChanged.insert(&BF);
351         }
352       };
353 
354   ParallelUtilities::runOnEachFunctionWithUniqueAllocId(
355       BC, ParallelUtilities::SchedulingPolicy::SP_INST_QUADRATIC, WorkFunction,
356       SkipPredicate, "shrink-wrapping");
357 }
358 
359 } // namespace bolt
360 } // namespace llvm
361