1 //===- BlockFrequencyInfo.cpp - Block Frequency Analysis ------------------===//
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 // Loops should be simplified before this analysis.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #include "llvm/Analysis/BlockFrequencyInfo.h"
14 #include "llvm/ADT/APInt.h"
15 #include "llvm/ADT/None.h"
16 #include "llvm/ADT/iterator.h"
17 #include "llvm/Analysis/BlockFrequencyInfoImpl.h"
18 #include "llvm/Analysis/BranchProbabilityInfo.h"
19 #include "llvm/Analysis/LoopInfo.h"
20 #include "llvm/IR/CFG.h"
21 #include "llvm/IR/Function.h"
22 #include "llvm/IR/PassManager.h"
23 #include "llvm/InitializePasses.h"
24 #include "llvm/Pass.h"
25 #include "llvm/Support/CommandLine.h"
26 #include "llvm/Support/GraphWriter.h"
27 #include "llvm/Support/raw_ostream.h"
28 #include <algorithm>
29 #include <cassert>
30 #include <string>
31 
32 using namespace llvm;
33 
34 #define DEBUG_TYPE "block-freq"
35 
36 static cl::opt<GVDAGType> ViewBlockFreqPropagationDAG(
37     "view-block-freq-propagation-dags", cl::Hidden,
38     cl::desc("Pop up a window to show a dag displaying how block "
39              "frequencies propagation through the CFG."),
40     cl::values(clEnumValN(GVDT_None, "none", "do not display graphs."),
41                clEnumValN(GVDT_Fraction, "fraction",
42                           "display a graph using the "
43                           "fractional block frequency representation."),
44                clEnumValN(GVDT_Integer, "integer",
45                           "display a graph using the raw "
46                           "integer fractional block frequency representation."),
47                clEnumValN(GVDT_Count, "count", "display a graph using the real "
48                                                "profile count if available.")));
49 
50 cl::opt<std::string>
51     ViewBlockFreqFuncName("view-bfi-func-name", cl::Hidden,
52                           cl::desc("The option to specify "
53                                    "the name of the function "
54                                    "whose CFG will be displayed."));
55 
56 cl::opt<unsigned>
57     ViewHotFreqPercent("view-hot-freq-percent", cl::init(10), cl::Hidden,
58                        cl::desc("An integer in percent used to specify "
59                                 "the hot blocks/edges to be displayed "
60                                 "in red: a block or edge whose frequency "
61                                 "is no less than the max frequency of the "
62                                 "function multiplied by this percent."));
63 
64 // Command line option to turn on CFG dot or text dump after profile annotation.
65 cl::opt<PGOViewCountsType> PGOViewCounts(
66     "pgo-view-counts", cl::Hidden,
67     cl::desc("A boolean option to show CFG dag or text with "
68              "block profile counts and branch probabilities "
69              "right after PGO profile annotation step. The "
70              "profile counts are computed using branch "
71              "probabilities from the runtime profile data and "
72              "block frequency propagation algorithm. To view "
73              "the raw counts from the profile, use option "
74              "-pgo-view-raw-counts instead. To limit graph "
75              "display to only one function, use filtering option "
76              "-view-bfi-func-name."),
77     cl::values(clEnumValN(PGOVCT_None, "none", "do not show."),
78                clEnumValN(PGOVCT_Graph, "graph", "show a graph."),
79                clEnumValN(PGOVCT_Text, "text", "show in text.")));
80 
81 static cl::opt<bool> PrintBlockFreq(
82     "print-bfi", cl::init(false), cl::Hidden,
83     cl::desc("Print the block frequency info."));
84 
85 cl::opt<std::string> PrintBlockFreqFuncName(
86     "print-bfi-func-name", cl::Hidden,
87     cl::desc("The option to specify the name of the function "
88              "whose block frequency info is printed."));
89 
90 namespace llvm {
91 
92 static GVDAGType getGVDT() {
93   if (PGOViewCounts == PGOVCT_Graph)
94     return GVDT_Count;
95   return ViewBlockFreqPropagationDAG;
96 }
97 
98 template <>
99 struct GraphTraits<BlockFrequencyInfo *> {
100   using NodeRef = const BasicBlock *;
101   using ChildIteratorType = const_succ_iterator;
102   using nodes_iterator = pointer_iterator<Function::const_iterator>;
103 
104   static NodeRef getEntryNode(const BlockFrequencyInfo *G) {
105     return &G->getFunction()->front();
106   }
107 
108   static ChildIteratorType child_begin(const NodeRef N) {
109     return succ_begin(N);
110   }
111 
112   static ChildIteratorType child_end(const NodeRef N) { return succ_end(N); }
113 
114   static nodes_iterator nodes_begin(const BlockFrequencyInfo *G) {
115     return nodes_iterator(G->getFunction()->begin());
116   }
117 
118   static nodes_iterator nodes_end(const BlockFrequencyInfo *G) {
119     return nodes_iterator(G->getFunction()->end());
120   }
121 };
122 
123 using BFIDOTGTraitsBase =
124     BFIDOTGraphTraitsBase<BlockFrequencyInfo, BranchProbabilityInfo>;
125 
126 template <>
127 struct DOTGraphTraits<BlockFrequencyInfo *> : public BFIDOTGTraitsBase {
128   explicit DOTGraphTraits(bool isSimple = false)
129       : BFIDOTGTraitsBase(isSimple) {}
130 
131   std::string getNodeLabel(const BasicBlock *Node,
132                            const BlockFrequencyInfo *Graph) {
133 
134     return BFIDOTGTraitsBase::getNodeLabel(Node, Graph, getGVDT());
135   }
136 
137   std::string getNodeAttributes(const BasicBlock *Node,
138                                 const BlockFrequencyInfo *Graph) {
139     return BFIDOTGTraitsBase::getNodeAttributes(Node, Graph,
140                                                 ViewHotFreqPercent);
141   }
142 
143   std::string getEdgeAttributes(const BasicBlock *Node, EdgeIter EI,
144                                 const BlockFrequencyInfo *BFI) {
145     return BFIDOTGTraitsBase::getEdgeAttributes(Node, EI, BFI, BFI->getBPI(),
146                                                 ViewHotFreqPercent);
147   }
148 };
149 
150 } // end namespace llvm
151 
152 BlockFrequencyInfo::BlockFrequencyInfo() = default;
153 
154 BlockFrequencyInfo::BlockFrequencyInfo(const Function &F,
155                                        const BranchProbabilityInfo &BPI,
156                                        const LoopInfo &LI) {
157   calculate(F, BPI, LI);
158 }
159 
160 BlockFrequencyInfo::BlockFrequencyInfo(BlockFrequencyInfo &&Arg)
161     : BFI(std::move(Arg.BFI)) {}
162 
163 BlockFrequencyInfo &BlockFrequencyInfo::operator=(BlockFrequencyInfo &&RHS) {
164   releaseMemory();
165   BFI = std::move(RHS.BFI);
166   return *this;
167 }
168 
169 // Explicitly define the default constructor otherwise it would be implicitly
170 // defined at the first ODR-use which is the BFI member in the
171 // LazyBlockFrequencyInfo header.  The dtor needs the BlockFrequencyInfoImpl
172 // template instantiated which is not available in the header.
173 BlockFrequencyInfo::~BlockFrequencyInfo() = default;
174 
175 bool BlockFrequencyInfo::invalidate(Function &F, const PreservedAnalyses &PA,
176                                     FunctionAnalysisManager::Invalidator &) {
177   // Check whether the analysis, all analyses on functions, or the function's
178   // CFG have been preserved.
179   auto PAC = PA.getChecker<BlockFrequencyAnalysis>();
180   return !(PAC.preserved() || PAC.preservedSet<AllAnalysesOn<Function>>() ||
181            PAC.preservedSet<CFGAnalyses>());
182 }
183 
184 void BlockFrequencyInfo::calculate(const Function &F,
185                                    const BranchProbabilityInfo &BPI,
186                                    const LoopInfo &LI) {
187   if (!BFI)
188     BFI.reset(new ImplType);
189   BFI->calculate(F, BPI, LI);
190   if (ViewBlockFreqPropagationDAG != GVDT_None &&
191       (ViewBlockFreqFuncName.empty() ||
192        F.getName().equals(ViewBlockFreqFuncName))) {
193     view();
194   }
195   if (PrintBlockFreq &&
196       (PrintBlockFreqFuncName.empty() ||
197        F.getName().equals(PrintBlockFreqFuncName))) {
198     print(dbgs());
199   }
200 }
201 
202 BlockFrequency BlockFrequencyInfo::getBlockFreq(const BasicBlock *BB) const {
203   return BFI ? BFI->getBlockFreq(BB) : 0;
204 }
205 
206 Optional<uint64_t>
207 BlockFrequencyInfo::getBlockProfileCount(const BasicBlock *BB,
208                                          bool AllowSynthetic) const {
209   if (!BFI)
210     return None;
211 
212   return BFI->getBlockProfileCount(*getFunction(), BB, AllowSynthetic);
213 }
214 
215 Optional<uint64_t>
216 BlockFrequencyInfo::getProfileCountFromFreq(uint64_t Freq) const {
217   if (!BFI)
218     return None;
219   return BFI->getProfileCountFromFreq(*getFunction(), Freq);
220 }
221 
222 bool BlockFrequencyInfo::isIrrLoopHeader(const BasicBlock *BB) {
223   assert(BFI && "Expected analysis to be available");
224   return BFI->isIrrLoopHeader(BB);
225 }
226 
227 void BlockFrequencyInfo::setBlockFreq(const BasicBlock *BB, uint64_t Freq) {
228   assert(BFI && "Expected analysis to be available");
229   BFI->setBlockFreq(BB, Freq);
230 }
231 
232 void BlockFrequencyInfo::setBlockFreqAndScale(
233     const BasicBlock *ReferenceBB, uint64_t Freq,
234     SmallPtrSetImpl<BasicBlock *> &BlocksToScale) {
235   assert(BFI && "Expected analysis to be available");
236   // Use 128 bits APInt to avoid overflow.
237   APInt NewFreq(128, Freq);
238   APInt OldFreq(128, BFI->getBlockFreq(ReferenceBB).getFrequency());
239   APInt BBFreq(128, 0);
240   for (auto *BB : BlocksToScale) {
241     BBFreq = BFI->getBlockFreq(BB).getFrequency();
242     // Multiply first by NewFreq and then divide by OldFreq
243     // to minimize loss of precision.
244     BBFreq *= NewFreq;
245     // udiv is an expensive operation in the general case. If this ends up being
246     // a hot spot, one of the options proposed in
247     // https://reviews.llvm.org/D28535#650071 could be used to avoid this.
248     BBFreq = BBFreq.udiv(OldFreq);
249     BFI->setBlockFreq(BB, BBFreq.getLimitedValue());
250   }
251   BFI->setBlockFreq(ReferenceBB, Freq);
252 }
253 
254 /// Pop up a ghostview window with the current block frequency propagation
255 /// rendered using dot.
256 void BlockFrequencyInfo::view(StringRef title) const {
257   ViewGraph(const_cast<BlockFrequencyInfo *>(this), title);
258 }
259 
260 const Function *BlockFrequencyInfo::getFunction() const {
261   return BFI ? BFI->getFunction() : nullptr;
262 }
263 
264 const BranchProbabilityInfo *BlockFrequencyInfo::getBPI() const {
265   return BFI ? &BFI->getBPI() : nullptr;
266 }
267 
268 raw_ostream &BlockFrequencyInfo::
269 printBlockFreq(raw_ostream &OS, const BlockFrequency Freq) const {
270   return BFI ? BFI->printBlockFreq(OS, Freq) : OS;
271 }
272 
273 raw_ostream &
274 BlockFrequencyInfo::printBlockFreq(raw_ostream &OS,
275                                    const BasicBlock *BB) const {
276   return BFI ? BFI->printBlockFreq(OS, BB) : OS;
277 }
278 
279 uint64_t BlockFrequencyInfo::getEntryFreq() const {
280   return BFI ? BFI->getEntryFreq() : 0;
281 }
282 
283 void BlockFrequencyInfo::releaseMemory() { BFI.reset(); }
284 
285 void BlockFrequencyInfo::print(raw_ostream &OS) const {
286   if (BFI)
287     BFI->print(OS);
288 }
289 
290 void BlockFrequencyInfo::verifyMatch(BlockFrequencyInfo &Other) const {
291   if (BFI)
292     BFI->verifyMatch(*Other.BFI);
293 }
294 
295 INITIALIZE_PASS_BEGIN(BlockFrequencyInfoWrapperPass, "block-freq",
296                       "Block Frequency Analysis", true, true)
297 INITIALIZE_PASS_DEPENDENCY(BranchProbabilityInfoWrapperPass)
298 INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
299 INITIALIZE_PASS_END(BlockFrequencyInfoWrapperPass, "block-freq",
300                     "Block Frequency Analysis", true, true)
301 
302 char BlockFrequencyInfoWrapperPass::ID = 0;
303 
304 BlockFrequencyInfoWrapperPass::BlockFrequencyInfoWrapperPass()
305     : FunctionPass(ID) {
306   initializeBlockFrequencyInfoWrapperPassPass(*PassRegistry::getPassRegistry());
307 }
308 
309 BlockFrequencyInfoWrapperPass::~BlockFrequencyInfoWrapperPass() = default;
310 
311 void BlockFrequencyInfoWrapperPass::print(raw_ostream &OS,
312                                           const Module *) const {
313   BFI.print(OS);
314 }
315 
316 void BlockFrequencyInfoWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
317   AU.addRequired<BranchProbabilityInfoWrapperPass>();
318   AU.addRequired<LoopInfoWrapperPass>();
319   AU.setPreservesAll();
320 }
321 
322 void BlockFrequencyInfoWrapperPass::releaseMemory() { BFI.releaseMemory(); }
323 
324 bool BlockFrequencyInfoWrapperPass::runOnFunction(Function &F) {
325   BranchProbabilityInfo &BPI =
326       getAnalysis<BranchProbabilityInfoWrapperPass>().getBPI();
327   LoopInfo &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
328   BFI.calculate(F, BPI, LI);
329   return false;
330 }
331 
332 AnalysisKey BlockFrequencyAnalysis::Key;
333 BlockFrequencyInfo BlockFrequencyAnalysis::run(Function &F,
334                                                FunctionAnalysisManager &AM) {
335   BlockFrequencyInfo BFI;
336   BFI.calculate(F, AM.getResult<BranchProbabilityAnalysis>(F),
337                 AM.getResult<LoopAnalysis>(F));
338   return BFI;
339 }
340 
341 PreservedAnalyses
342 BlockFrequencyPrinterPass::run(Function &F, FunctionAnalysisManager &AM) {
343   OS << "Printing analysis results of BFI for function "
344      << "'" << F.getName() << "':"
345      << "\n";
346   AM.getResult<BlockFrequencyAnalysis>(F).print(OS);
347   return PreservedAnalyses::all();
348 }
349