1 //===- BlockFrequencyInfo.cpp - Block Frequency Analysis ------------------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // Loops should be simplified before this analysis.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "llvm/Analysis/BlockFrequencyInfo.h"
15 #include "llvm/ADT/APInt.h"
16 #include "llvm/ADT/None.h"
17 #include "llvm/ADT/iterator.h"
18 #include "llvm/Analysis/BlockFrequencyInfoImpl.h"
19 #include "llvm/Analysis/BranchProbabilityInfo.h"
20 #include "llvm/Analysis/LoopInfo.h"
21 #include "llvm/IR/CFG.h"
22 #include "llvm/IR/Function.h"
23 #include "llvm/IR/PassManager.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 dump after profile annotation.
65 cl::opt<bool>
66     PGOViewCounts("pgo-view-counts", cl::init(false), cl::Hidden,
67                   cl::desc("A boolean option to show CFG dag 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 
78 static cl::opt<bool> PrintBlockFreq(
79     "print-bfi", cl::init(false), cl::Hidden,
80     cl::desc("Print the block frequency info."));
81 
82 cl::opt<std::string> PrintBlockFreqFuncName(
83     "print-bfi-func-name", cl::Hidden,
84     cl::desc("The option to specify the name of the function "
85              "whose block frequency info is printed."));
86 
87 namespace llvm {
88 
89 static GVDAGType getGVDT() {
90   if (PGOViewCounts)
91     return GVDT_Count;
92   return ViewBlockFreqPropagationDAG;
93 }
94 
95 template <>
96 struct GraphTraits<BlockFrequencyInfo *> {
97   using NodeRef = const BasicBlock *;
98   using ChildIteratorType = succ_const_iterator;
99   using nodes_iterator = pointer_iterator<Function::const_iterator>;
100 
101   static NodeRef getEntryNode(const BlockFrequencyInfo *G) {
102     return &G->getFunction()->front();
103   }
104 
105   static ChildIteratorType child_begin(const NodeRef N) {
106     return succ_begin(N);
107   }
108 
109   static ChildIteratorType child_end(const NodeRef N) { return succ_end(N); }
110 
111   static nodes_iterator nodes_begin(const BlockFrequencyInfo *G) {
112     return nodes_iterator(G->getFunction()->begin());
113   }
114 
115   static nodes_iterator nodes_end(const BlockFrequencyInfo *G) {
116     return nodes_iterator(G->getFunction()->end());
117   }
118 };
119 
120 using BFIDOTGTraitsBase =
121     BFIDOTGraphTraitsBase<BlockFrequencyInfo, BranchProbabilityInfo>;
122 
123 template <>
124 struct DOTGraphTraits<BlockFrequencyInfo *> : public BFIDOTGTraitsBase {
125   explicit DOTGraphTraits(bool isSimple = false)
126       : BFIDOTGTraitsBase(isSimple) {}
127 
128   std::string getNodeLabel(const BasicBlock *Node,
129                            const BlockFrequencyInfo *Graph) {
130 
131     return BFIDOTGTraitsBase::getNodeLabel(Node, Graph, getGVDT());
132   }
133 
134   std::string getNodeAttributes(const BasicBlock *Node,
135                                 const BlockFrequencyInfo *Graph) {
136     return BFIDOTGTraitsBase::getNodeAttributes(Node, Graph,
137                                                 ViewHotFreqPercent);
138   }
139 
140   std::string getEdgeAttributes(const BasicBlock *Node, EdgeIter EI,
141                                 const BlockFrequencyInfo *BFI) {
142     return BFIDOTGTraitsBase::getEdgeAttributes(Node, EI, BFI, BFI->getBPI(),
143                                                 ViewHotFreqPercent);
144   }
145 };
146 
147 } // end namespace llvm
148 
149 BlockFrequencyInfo::BlockFrequencyInfo() = default;
150 
151 BlockFrequencyInfo::BlockFrequencyInfo(const Function &F,
152                                        const BranchProbabilityInfo &BPI,
153                                        const LoopInfo &LI) {
154   calculate(F, BPI, LI);
155 }
156 
157 BlockFrequencyInfo::BlockFrequencyInfo(BlockFrequencyInfo &&Arg)
158     : BFI(std::move(Arg.BFI)) {}
159 
160 BlockFrequencyInfo &BlockFrequencyInfo::operator=(BlockFrequencyInfo &&RHS) {
161   releaseMemory();
162   BFI = std::move(RHS.BFI);
163   return *this;
164 }
165 
166 // Explicitly define the default constructor otherwise it would be implicitly
167 // defined at the first ODR-use which is the BFI member in the
168 // LazyBlockFrequencyInfo header.  The dtor needs the BlockFrequencyInfoImpl
169 // template instantiated which is not available in the header.
170 BlockFrequencyInfo::~BlockFrequencyInfo() = default;
171 
172 bool BlockFrequencyInfo::invalidate(Function &F, const PreservedAnalyses &PA,
173                                     FunctionAnalysisManager::Invalidator &) {
174   // Check whether the analysis, all analyses on functions, or the function's
175   // CFG have been preserved.
176   auto PAC = PA.getChecker<BlockFrequencyAnalysis>();
177   return !(PAC.preserved() || PAC.preservedSet<AllAnalysesOn<Function>>() ||
178            PAC.preservedSet<CFGAnalyses>());
179 }
180 
181 void BlockFrequencyInfo::calculate(const Function &F,
182                                    const BranchProbabilityInfo &BPI,
183                                    const LoopInfo &LI) {
184   if (!BFI)
185     BFI.reset(new ImplType);
186   BFI->calculate(F, BPI, LI);
187   if (ViewBlockFreqPropagationDAG != GVDT_None &&
188       (ViewBlockFreqFuncName.empty() ||
189        F.getName().equals(ViewBlockFreqFuncName))) {
190     view();
191   }
192   if (PrintBlockFreq &&
193       (PrintBlockFreqFuncName.empty() ||
194        F.getName().equals(PrintBlockFreqFuncName))) {
195     print(dbgs());
196   }
197 }
198 
199 BlockFrequency BlockFrequencyInfo::getBlockFreq(const BasicBlock *BB) const {
200   return BFI ? BFI->getBlockFreq(BB) : 0;
201 }
202 
203 Optional<uint64_t>
204 BlockFrequencyInfo::getBlockProfileCount(const BasicBlock *BB) const {
205   if (!BFI)
206     return None;
207 
208   return BFI->getBlockProfileCount(*getFunction(), BB);
209 }
210 
211 Optional<uint64_t>
212 BlockFrequencyInfo::getProfileCountFromFreq(uint64_t Freq) const {
213   if (!BFI)
214     return None;
215   return BFI->getProfileCountFromFreq(*getFunction(), Freq);
216 }
217 
218 void BlockFrequencyInfo::setBlockFreq(const BasicBlock *BB, uint64_t Freq) {
219   assert(BFI && "Expected analysis to be available");
220   BFI->setBlockFreq(BB, Freq);
221 }
222 
223 void BlockFrequencyInfo::setBlockFreqAndScale(
224     const BasicBlock *ReferenceBB, uint64_t Freq,
225     SmallPtrSetImpl<BasicBlock *> &BlocksToScale) {
226   assert(BFI && "Expected analysis to be available");
227   // Use 128 bits APInt to avoid overflow.
228   APInt NewFreq(128, Freq);
229   APInt OldFreq(128, BFI->getBlockFreq(ReferenceBB).getFrequency());
230   APInt BBFreq(128, 0);
231   for (auto *BB : BlocksToScale) {
232     BBFreq = BFI->getBlockFreq(BB).getFrequency();
233     // Multiply first by NewFreq and then divide by OldFreq
234     // to minimize loss of precision.
235     BBFreq *= NewFreq;
236     // udiv is an expensive operation in the general case. If this ends up being
237     // a hot spot, one of the options proposed in
238     // https://reviews.llvm.org/D28535#650071 could be used to avoid this.
239     BBFreq = BBFreq.udiv(OldFreq);
240     BFI->setBlockFreq(BB, BBFreq.getLimitedValue());
241   }
242   BFI->setBlockFreq(ReferenceBB, Freq);
243 }
244 
245 /// Pop up a ghostview window with the current block frequency propagation
246 /// rendered using dot.
247 void BlockFrequencyInfo::view() const {
248   ViewGraph(const_cast<BlockFrequencyInfo *>(this), "BlockFrequencyDAGs");
249 }
250 
251 const Function *BlockFrequencyInfo::getFunction() const {
252   return BFI ? BFI->getFunction() : nullptr;
253 }
254 
255 const BranchProbabilityInfo *BlockFrequencyInfo::getBPI() const {
256   return BFI ? &BFI->getBPI() : nullptr;
257 }
258 
259 raw_ostream &BlockFrequencyInfo::
260 printBlockFreq(raw_ostream &OS, const BlockFrequency Freq) const {
261   return BFI ? BFI->printBlockFreq(OS, Freq) : OS;
262 }
263 
264 raw_ostream &
265 BlockFrequencyInfo::printBlockFreq(raw_ostream &OS,
266                                    const BasicBlock *BB) const {
267   return BFI ? BFI->printBlockFreq(OS, BB) : OS;
268 }
269 
270 uint64_t BlockFrequencyInfo::getEntryFreq() const {
271   return BFI ? BFI->getEntryFreq() : 0;
272 }
273 
274 void BlockFrequencyInfo::releaseMemory() { BFI.reset(); }
275 
276 void BlockFrequencyInfo::print(raw_ostream &OS) const {
277   if (BFI)
278     BFI->print(OS);
279 }
280 
281 INITIALIZE_PASS_BEGIN(BlockFrequencyInfoWrapperPass, "block-freq",
282                       "Block Frequency Analysis", true, true)
283 INITIALIZE_PASS_DEPENDENCY(BranchProbabilityInfoWrapperPass)
284 INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
285 INITIALIZE_PASS_END(BlockFrequencyInfoWrapperPass, "block-freq",
286                     "Block Frequency Analysis", true, true)
287 
288 char BlockFrequencyInfoWrapperPass::ID = 0;
289 
290 BlockFrequencyInfoWrapperPass::BlockFrequencyInfoWrapperPass()
291     : FunctionPass(ID) {
292   initializeBlockFrequencyInfoWrapperPassPass(*PassRegistry::getPassRegistry());
293 }
294 
295 BlockFrequencyInfoWrapperPass::~BlockFrequencyInfoWrapperPass() = default;
296 
297 void BlockFrequencyInfoWrapperPass::print(raw_ostream &OS,
298                                           const Module *) const {
299   BFI.print(OS);
300 }
301 
302 void BlockFrequencyInfoWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
303   AU.addRequired<BranchProbabilityInfoWrapperPass>();
304   AU.addRequired<LoopInfoWrapperPass>();
305   AU.setPreservesAll();
306 }
307 
308 void BlockFrequencyInfoWrapperPass::releaseMemory() { BFI.releaseMemory(); }
309 
310 bool BlockFrequencyInfoWrapperPass::runOnFunction(Function &F) {
311   BranchProbabilityInfo &BPI =
312       getAnalysis<BranchProbabilityInfoWrapperPass>().getBPI();
313   LoopInfo &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
314   BFI.calculate(F, BPI, LI);
315   return false;
316 }
317 
318 AnalysisKey BlockFrequencyAnalysis::Key;
319 BlockFrequencyInfo BlockFrequencyAnalysis::run(Function &F,
320                                                FunctionAnalysisManager &AM) {
321   BlockFrequencyInfo BFI;
322   BFI.calculate(F, AM.getResult<BranchProbabilityAnalysis>(F),
323                 AM.getResult<LoopAnalysis>(F));
324   return BFI;
325 }
326 
327 PreservedAnalyses
328 BlockFrequencyPrinterPass::run(Function &F, FunctionAnalysisManager &AM) {
329   OS << "Printing analysis results of BFI for function "
330      << "'" << F.getName() << "':"
331      << "\n";
332   AM.getResult<BlockFrequencyAnalysis>(F).print(OS);
333   return PreservedAnalyses::all();
334 }
335