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/Analysis/BlockFrequencyInfoImpl.h"
16 #include "llvm/Analysis/BranchProbabilityInfo.h"
17 #include "llvm/Analysis/LoopInfo.h"
18 #include "llvm/Analysis/Passes.h"
19 #include "llvm/IR/CFG.h"
20 #include "llvm/InitializePasses.h"
21 #include "llvm/Support/CommandLine.h"
22 #include "llvm/Support/Debug.h"
23 #include "llvm/Support/GraphWriter.h"
24 
25 using namespace llvm;
26 
27 #define DEBUG_TYPE "block-freq"
28 
29 #ifndef NDEBUG
30 enum GVDAGType {
31   GVDT_None,
32   GVDT_Fraction,
33   GVDT_Integer
34 };
35 
36 static cl::opt<GVDAGType>
37 ViewBlockFreqPropagationDAG("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(
41             clEnumValN(GVDT_None, "none",
42                        "do not display graphs."),
43             clEnumValN(GVDT_Fraction, "fraction", "display a graph using the "
44                        "fractional block frequency representation."),
45             clEnumValN(GVDT_Integer, "integer", "display a graph using the raw "
46                        "integer fractional block frequency representation."),
47             clEnumValEnd));
48 
49 namespace llvm {
50 
51 template <>
52 struct GraphTraits<BlockFrequencyInfo *> {
53   typedef const BasicBlock NodeType;
54   typedef succ_const_iterator ChildIteratorType;
55   typedef Function::const_iterator nodes_iterator;
56 
57   static inline const NodeType *getEntryNode(const BlockFrequencyInfo *G) {
58     return &G->getFunction()->front();
59   }
60   static ChildIteratorType child_begin(const NodeType *N) {
61     return succ_begin(N);
62   }
63   static ChildIteratorType child_end(const NodeType *N) {
64     return succ_end(N);
65   }
66   static nodes_iterator nodes_begin(const BlockFrequencyInfo *G) {
67     return G->getFunction()->begin();
68   }
69   static nodes_iterator nodes_end(const BlockFrequencyInfo *G) {
70     return G->getFunction()->end();
71   }
72 };
73 
74 template<>
75 struct DOTGraphTraits<BlockFrequencyInfo*> : public DefaultDOTGraphTraits {
76   explicit DOTGraphTraits(bool isSimple=false) :
77     DefaultDOTGraphTraits(isSimple) {}
78 
79   static std::string getGraphName(const BlockFrequencyInfo *G) {
80     return G->getFunction()->getName();
81   }
82 
83   std::string getNodeLabel(const BasicBlock *Node,
84                            const BlockFrequencyInfo *Graph) {
85     std::string Result;
86     raw_string_ostream OS(Result);
87 
88     OS << Node->getName() << ":";
89     switch (ViewBlockFreqPropagationDAG) {
90     case GVDT_Fraction:
91       Graph->printBlockFreq(OS, Node);
92       break;
93     case GVDT_Integer:
94       OS << Graph->getBlockFreq(Node).getFrequency();
95       break;
96     case GVDT_None:
97       llvm_unreachable("If we are not supposed to render a graph we should "
98                        "never reach this point.");
99     }
100 
101     return Result;
102   }
103 };
104 
105 } // end namespace llvm
106 #endif
107 
108 BlockFrequencyInfo::BlockFrequencyInfo() {}
109 
110 BlockFrequencyInfo::BlockFrequencyInfo(const Function &F,
111                                        const BranchProbabilityInfo &BPI,
112                                        const LoopInfo &LI) {
113   calculate(F, BPI, LI);
114 }
115 
116 void BlockFrequencyInfo::calculate(const Function &F,
117                                    const BranchProbabilityInfo &BPI,
118                                    const LoopInfo &LI) {
119   if (!BFI)
120     BFI.reset(new ImplType);
121   BFI->calculate(F, BPI, LI);
122 #ifndef NDEBUG
123   if (ViewBlockFreqPropagationDAG != GVDT_None)
124     view();
125 #endif
126 }
127 
128 BlockFrequency BlockFrequencyInfo::getBlockFreq(const BasicBlock *BB) const {
129   return BFI ? BFI->getBlockFreq(BB) : 0;
130 }
131 
132 Optional<uint64_t>
133 BlockFrequencyInfo::getBlockProfileCount(const BasicBlock *BB) const {
134   auto EntryCount = getFunction()->getEntryCount();
135   if (!EntryCount)
136     return None;
137   // Use 128 bit APInt to do the arithmetic to avoid overflow.
138   APInt BlockCount(128, EntryCount.getValue());
139   APInt BlockFreq(128, getBlockFreq(BB).getFrequency());
140   APInt EntryFreq(128, getEntryFreq());
141   BlockCount *= BlockFreq;
142   BlockCount = BlockCount.udiv(EntryFreq);
143   return BlockCount.getLimitedValue();
144 }
145 
146 void BlockFrequencyInfo::setBlockFreq(const BasicBlock *BB,
147                                       uint64_t Freq) {
148   assert(BFI && "Expected analysis to be available");
149   BFI->setBlockFreq(BB, Freq);
150 }
151 
152 /// Pop up a ghostview window with the current block frequency propagation
153 /// rendered using dot.
154 void BlockFrequencyInfo::view() const {
155 // This code is only for debugging.
156 #ifndef NDEBUG
157   ViewGraph(const_cast<BlockFrequencyInfo *>(this), "BlockFrequencyDAGs");
158 #else
159   errs() << "BlockFrequencyInfo::view is only available in debug builds on "
160             "systems with Graphviz or gv!\n";
161 #endif // NDEBUG
162 }
163 
164 const Function *BlockFrequencyInfo::getFunction() const {
165   return BFI ? BFI->getFunction() : nullptr;
166 }
167 
168 raw_ostream &BlockFrequencyInfo::
169 printBlockFreq(raw_ostream &OS, const BlockFrequency Freq) const {
170   return BFI ? BFI->printBlockFreq(OS, Freq) : OS;
171 }
172 
173 raw_ostream &
174 BlockFrequencyInfo::printBlockFreq(raw_ostream &OS,
175                                    const BasicBlock *BB) const {
176   return BFI ? BFI->printBlockFreq(OS, BB) : OS;
177 }
178 
179 uint64_t BlockFrequencyInfo::getEntryFreq() const {
180   return BFI ? BFI->getEntryFreq() : 0;
181 }
182 
183 void BlockFrequencyInfo::releaseMemory() { BFI.reset(); }
184 
185 void BlockFrequencyInfo::print(raw_ostream &OS) const {
186   if (BFI)
187     BFI->print(OS);
188 }
189 
190 
191 INITIALIZE_PASS_BEGIN(BlockFrequencyInfoWrapperPass, "block-freq",
192                       "Block Frequency Analysis", true, true)
193 INITIALIZE_PASS_DEPENDENCY(BranchProbabilityInfoWrapperPass)
194 INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
195 INITIALIZE_PASS_END(BlockFrequencyInfoWrapperPass, "block-freq",
196                     "Block Frequency Analysis", true, true)
197 
198 char BlockFrequencyInfoWrapperPass::ID = 0;
199 
200 
201 BlockFrequencyInfoWrapperPass::BlockFrequencyInfoWrapperPass()
202     : FunctionPass(ID) {
203   initializeBlockFrequencyInfoWrapperPassPass(*PassRegistry::getPassRegistry());
204 }
205 
206 BlockFrequencyInfoWrapperPass::~BlockFrequencyInfoWrapperPass() {}
207 
208 void BlockFrequencyInfoWrapperPass::print(raw_ostream &OS,
209                                           const Module *) const {
210   BFI.print(OS);
211 }
212 
213 void BlockFrequencyInfoWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
214   AU.addRequired<BranchProbabilityInfoWrapperPass>();
215   AU.addRequired<LoopInfoWrapperPass>();
216   AU.setPreservesAll();
217 }
218 
219 void BlockFrequencyInfoWrapperPass::releaseMemory() { BFI.releaseMemory(); }
220 
221 bool BlockFrequencyInfoWrapperPass::runOnFunction(Function &F) {
222   BranchProbabilityInfo &BPI =
223       getAnalysis<BranchProbabilityInfoWrapperPass>().getBPI();
224   LoopInfo &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
225   BFI.calculate(F, BPI, LI);
226   return false;
227 }
228