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/iterator.h"
16 #include "llvm/Analysis/BlockFrequencyInfoImpl.h"
17 #include "llvm/Analysis/BranchProbabilityInfo.h"
18 #include "llvm/Analysis/LoopInfo.h"
19 #include "llvm/IR/CFG.h"
20 #include "llvm/IR/Function.h"
21 #include "llvm/IR/PassManager.h"
22 #include "llvm/InitializePasses.h"
23 #include "llvm/Pass.h"
24 #include "llvm/Support/CommandLine.h"
25 #include "llvm/Support/GraphWriter.h"
26 #include "llvm/Support/raw_ostream.h"
27 #include <cassert>
28 #include <optional>
29 #include <string>
30
31 using namespace llvm;
32
33 #define DEBUG_TYPE "block-freq"
34
35 static cl::opt<GVDAGType> ViewBlockFreqPropagationDAG(
36 "view-block-freq-propagation-dags", cl::Hidden,
37 cl::desc("Pop up a window to show a dag displaying how block "
38 "frequencies propagation through the CFG."),
39 cl::values(clEnumValN(GVDT_None, "none", "do not display graphs."),
40 clEnumValN(GVDT_Fraction, "fraction",
41 "display a graph using the "
42 "fractional block frequency representation."),
43 clEnumValN(GVDT_Integer, "integer",
44 "display a graph using the raw "
45 "integer fractional block frequency representation."),
46 clEnumValN(GVDT_Count, "count", "display a graph using the real "
47 "profile count if available.")));
48
49 namespace llvm {
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 } // namespace llvm
90
91 namespace llvm {
92
getGVDT()93 static GVDAGType getGVDT() {
94 if (PGOViewCounts == PGOVCT_Graph)
95 return GVDT_Count;
96 return ViewBlockFreqPropagationDAG;
97 }
98
99 template <>
100 struct GraphTraits<BlockFrequencyInfo *> {
101 using NodeRef = const BasicBlock *;
102 using ChildIteratorType = const_succ_iterator;
103 using nodes_iterator = pointer_iterator<Function::const_iterator>;
104
getEntryNodellvm::GraphTraits105 static NodeRef getEntryNode(const BlockFrequencyInfo *G) {
106 return &G->getFunction()->front();
107 }
108
child_beginllvm::GraphTraits109 static ChildIteratorType child_begin(const NodeRef N) {
110 return succ_begin(N);
111 }
112
child_endllvm::GraphTraits113 static ChildIteratorType child_end(const NodeRef N) { return succ_end(N); }
114
nodes_beginllvm::GraphTraits115 static nodes_iterator nodes_begin(const BlockFrequencyInfo *G) {
116 return nodes_iterator(G->getFunction()->begin());
117 }
118
nodes_endllvm::GraphTraits119 static nodes_iterator nodes_end(const BlockFrequencyInfo *G) {
120 return nodes_iterator(G->getFunction()->end());
121 }
122 };
123
124 using BFIDOTGTraitsBase =
125 BFIDOTGraphTraitsBase<BlockFrequencyInfo, BranchProbabilityInfo>;
126
127 template <>
128 struct DOTGraphTraits<BlockFrequencyInfo *> : public BFIDOTGTraitsBase {
DOTGraphTraitsllvm::DOTGraphTraits129 explicit DOTGraphTraits(bool isSimple = false)
130 : BFIDOTGTraitsBase(isSimple) {}
131
getNodeLabelllvm::DOTGraphTraits132 std::string getNodeLabel(const BasicBlock *Node,
133 const BlockFrequencyInfo *Graph) {
134
135 return BFIDOTGTraitsBase::getNodeLabel(Node, Graph, getGVDT());
136 }
137
getNodeAttributesllvm::DOTGraphTraits138 std::string getNodeAttributes(const BasicBlock *Node,
139 const BlockFrequencyInfo *Graph) {
140 return BFIDOTGTraitsBase::getNodeAttributes(Node, Graph,
141 ViewHotFreqPercent);
142 }
143
getEdgeAttributesllvm::DOTGraphTraits144 std::string getEdgeAttributes(const BasicBlock *Node, EdgeIter EI,
145 const BlockFrequencyInfo *BFI) {
146 return BFIDOTGTraitsBase::getEdgeAttributes(Node, EI, BFI, BFI->getBPI(),
147 ViewHotFreqPercent);
148 }
149 };
150
151 } // end namespace llvm
152
153 BlockFrequencyInfo::BlockFrequencyInfo() = default;
154
BlockFrequencyInfo(const Function & F,const BranchProbabilityInfo & BPI,const LoopInfo & LI)155 BlockFrequencyInfo::BlockFrequencyInfo(const Function &F,
156 const BranchProbabilityInfo &BPI,
157 const LoopInfo &LI) {
158 calculate(F, BPI, LI);
159 }
160
BlockFrequencyInfo(BlockFrequencyInfo && Arg)161 BlockFrequencyInfo::BlockFrequencyInfo(BlockFrequencyInfo &&Arg)
162 : BFI(std::move(Arg.BFI)) {}
163
operator =(BlockFrequencyInfo && RHS)164 BlockFrequencyInfo &BlockFrequencyInfo::operator=(BlockFrequencyInfo &&RHS) {
165 releaseMemory();
166 BFI = std::move(RHS.BFI);
167 return *this;
168 }
169
170 // Explicitly define the default constructor otherwise it would be implicitly
171 // defined at the first ODR-use which is the BFI member in the
172 // LazyBlockFrequencyInfo header. The dtor needs the BlockFrequencyInfoImpl
173 // template instantiated which is not available in the header.
174 BlockFrequencyInfo::~BlockFrequencyInfo() = default;
175
invalidate(Function & F,const PreservedAnalyses & PA,FunctionAnalysisManager::Invalidator &)176 bool BlockFrequencyInfo::invalidate(Function &F, const PreservedAnalyses &PA,
177 FunctionAnalysisManager::Invalidator &) {
178 // Check whether the analysis, all analyses on functions, or the function's
179 // CFG have been preserved.
180 auto PAC = PA.getChecker<BlockFrequencyAnalysis>();
181 return !(PAC.preserved() || PAC.preservedSet<AllAnalysesOn<Function>>() ||
182 PAC.preservedSet<CFGAnalyses>());
183 }
184
calculate(const Function & F,const BranchProbabilityInfo & BPI,const LoopInfo & LI)185 void BlockFrequencyInfo::calculate(const Function &F,
186 const BranchProbabilityInfo &BPI,
187 const LoopInfo &LI) {
188 if (!BFI)
189 BFI.reset(new ImplType);
190 BFI->calculate(F, BPI, LI);
191 if (ViewBlockFreqPropagationDAG != GVDT_None &&
192 (ViewBlockFreqFuncName.empty() ||
193 F.getName().equals(ViewBlockFreqFuncName))) {
194 view();
195 }
196 if (PrintBlockFreq &&
197 (PrintBlockFreqFuncName.empty() ||
198 F.getName().equals(PrintBlockFreqFuncName))) {
199 print(dbgs());
200 }
201 }
202
getBlockFreq(const BasicBlock * BB) const203 BlockFrequency BlockFrequencyInfo::getBlockFreq(const BasicBlock *BB) const {
204 return BFI ? BFI->getBlockFreq(BB) : 0;
205 }
206
207 std::optional<uint64_t>
getBlockProfileCount(const BasicBlock * BB,bool AllowSynthetic) const208 BlockFrequencyInfo::getBlockProfileCount(const BasicBlock *BB,
209 bool AllowSynthetic) const {
210 if (!BFI)
211 return std::nullopt;
212
213 return BFI->getBlockProfileCount(*getFunction(), BB, AllowSynthetic);
214 }
215
216 std::optional<uint64_t>
getProfileCountFromFreq(uint64_t Freq) const217 BlockFrequencyInfo::getProfileCountFromFreq(uint64_t Freq) const {
218 if (!BFI)
219 return std::nullopt;
220 return BFI->getProfileCountFromFreq(*getFunction(), Freq);
221 }
222
isIrrLoopHeader(const BasicBlock * BB)223 bool BlockFrequencyInfo::isIrrLoopHeader(const BasicBlock *BB) {
224 assert(BFI && "Expected analysis to be available");
225 return BFI->isIrrLoopHeader(BB);
226 }
227
setBlockFreq(const BasicBlock * BB,uint64_t Freq)228 void BlockFrequencyInfo::setBlockFreq(const BasicBlock *BB, uint64_t Freq) {
229 assert(BFI && "Expected analysis to be available");
230 BFI->setBlockFreq(BB, Freq);
231 }
232
setBlockFreqAndScale(const BasicBlock * ReferenceBB,uint64_t Freq,SmallPtrSetImpl<BasicBlock * > & BlocksToScale)233 void BlockFrequencyInfo::setBlockFreqAndScale(
234 const BasicBlock *ReferenceBB, uint64_t Freq,
235 SmallPtrSetImpl<BasicBlock *> &BlocksToScale) {
236 assert(BFI && "Expected analysis to be available");
237 // Use 128 bits APInt to avoid overflow.
238 APInt NewFreq(128, Freq);
239 APInt OldFreq(128, BFI->getBlockFreq(ReferenceBB).getFrequency());
240 APInt BBFreq(128, 0);
241 for (auto *BB : BlocksToScale) {
242 BBFreq = BFI->getBlockFreq(BB).getFrequency();
243 // Multiply first by NewFreq and then divide by OldFreq
244 // to minimize loss of precision.
245 BBFreq *= NewFreq;
246 // udiv is an expensive operation in the general case. If this ends up being
247 // a hot spot, one of the options proposed in
248 // https://reviews.llvm.org/D28535#650071 could be used to avoid this.
249 BBFreq = BBFreq.udiv(OldFreq);
250 BFI->setBlockFreq(BB, BBFreq.getLimitedValue());
251 }
252 BFI->setBlockFreq(ReferenceBB, Freq);
253 }
254
255 /// Pop up a ghostview window with the current block frequency propagation
256 /// rendered using dot.
view(StringRef title) const257 void BlockFrequencyInfo::view(StringRef title) const {
258 ViewGraph(const_cast<BlockFrequencyInfo *>(this), title);
259 }
260
getFunction() const261 const Function *BlockFrequencyInfo::getFunction() const {
262 return BFI ? BFI->getFunction() : nullptr;
263 }
264
getBPI() const265 const BranchProbabilityInfo *BlockFrequencyInfo::getBPI() const {
266 return BFI ? &BFI->getBPI() : nullptr;
267 }
268
269 raw_ostream &BlockFrequencyInfo::
printBlockFreq(raw_ostream & OS,const BlockFrequency Freq) const270 printBlockFreq(raw_ostream &OS, const BlockFrequency Freq) const {
271 return BFI ? BFI->printBlockFreq(OS, Freq) : OS;
272 }
273
274 raw_ostream &
printBlockFreq(raw_ostream & OS,const BasicBlock * BB) const275 BlockFrequencyInfo::printBlockFreq(raw_ostream &OS,
276 const BasicBlock *BB) const {
277 return BFI ? BFI->printBlockFreq(OS, BB) : OS;
278 }
279
getEntryFreq() const280 uint64_t BlockFrequencyInfo::getEntryFreq() const {
281 return BFI ? BFI->getEntryFreq() : 0;
282 }
283
releaseMemory()284 void BlockFrequencyInfo::releaseMemory() { BFI.reset(); }
285
print(raw_ostream & OS) const286 void BlockFrequencyInfo::print(raw_ostream &OS) const {
287 if (BFI)
288 BFI->print(OS);
289 }
290
verifyMatch(BlockFrequencyInfo & Other) const291 void BlockFrequencyInfo::verifyMatch(BlockFrequencyInfo &Other) const {
292 if (BFI)
293 BFI->verifyMatch(*Other.BFI);
294 }
295
296 INITIALIZE_PASS_BEGIN(BlockFrequencyInfoWrapperPass, "block-freq",
297 "Block Frequency Analysis", true, true)
298 INITIALIZE_PASS_DEPENDENCY(BranchProbabilityInfoWrapperPass)
299 INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
300 INITIALIZE_PASS_END(BlockFrequencyInfoWrapperPass, "block-freq",
301 "Block Frequency Analysis", true, true)
302
303 char BlockFrequencyInfoWrapperPass::ID = 0;
304
BlockFrequencyInfoWrapperPass()305 BlockFrequencyInfoWrapperPass::BlockFrequencyInfoWrapperPass()
306 : FunctionPass(ID) {
307 initializeBlockFrequencyInfoWrapperPassPass(*PassRegistry::getPassRegistry());
308 }
309
310 BlockFrequencyInfoWrapperPass::~BlockFrequencyInfoWrapperPass() = default;
311
print(raw_ostream & OS,const Module *) const312 void BlockFrequencyInfoWrapperPass::print(raw_ostream &OS,
313 const Module *) const {
314 BFI.print(OS);
315 }
316
getAnalysisUsage(AnalysisUsage & AU) const317 void BlockFrequencyInfoWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
318 AU.addRequired<BranchProbabilityInfoWrapperPass>();
319 AU.addRequired<LoopInfoWrapperPass>();
320 AU.setPreservesAll();
321 }
322
releaseMemory()323 void BlockFrequencyInfoWrapperPass::releaseMemory() { BFI.releaseMemory(); }
324
runOnFunction(Function & F)325 bool BlockFrequencyInfoWrapperPass::runOnFunction(Function &F) {
326 BranchProbabilityInfo &BPI =
327 getAnalysis<BranchProbabilityInfoWrapperPass>().getBPI();
328 LoopInfo &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
329 BFI.calculate(F, BPI, LI);
330 return false;
331 }
332
333 AnalysisKey BlockFrequencyAnalysis::Key;
run(Function & F,FunctionAnalysisManager & AM)334 BlockFrequencyInfo BlockFrequencyAnalysis::run(Function &F,
335 FunctionAnalysisManager &AM) {
336 BlockFrequencyInfo BFI;
337 BFI.calculate(F, AM.getResult<BranchProbabilityAnalysis>(F),
338 AM.getResult<LoopAnalysis>(F));
339 return BFI;
340 }
341
342 PreservedAnalyses
run(Function & F,FunctionAnalysisManager & AM)343 BlockFrequencyPrinterPass::run(Function &F, FunctionAnalysisManager &AM) {
344 OS << "Printing analysis results of BFI for function "
345 << "'" << F.getName() << "':"
346 << "\n";
347 AM.getResult<BlockFrequencyAnalysis>(F).print(OS);
348 return PreservedAnalyses::all();
349 }
350