1 //===- CFGPrinter.cpp - DOT printer for the control flow graph ------------===//
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 defines a `-dot-cfg` analysis pass, which emits the
10 // `<prefix>.<fnname>.dot` file for each function in the program, with a graph
11 // of the CFG for that function. The default value for `<prefix>` is `cfg` but
12 // can be customized as needed.
13 //
14 // The other main feature of this file is that it implements the
15 // Function::viewCFG method, which is useful for debugging passes which operate
16 // on the CFG.
17 //
18 //===----------------------------------------------------------------------===//
19
20 #include "llvm/Analysis/CFGPrinter.h"
21 #include "llvm/ADT/PostOrderIterator.h"
22 #include "llvm/IR/ModuleSlotTracker.h"
23 #include "llvm/Support/CommandLine.h"
24 #include "llvm/Support/FileSystem.h"
25 #include "llvm/Support/GraphWriter.h"
26
27 using namespace llvm;
28
29 static cl::opt<std::string>
30 CFGFuncName("cfg-func-name", cl::Hidden,
31 cl::desc("The name of a function (or its substring)"
32 " whose CFG is viewed/printed."));
33
34 static cl::opt<std::string> CFGDotFilenamePrefix(
35 "cfg-dot-filename-prefix", cl::Hidden,
36 cl::desc("The prefix used for the CFG dot file names."));
37
38 static cl::opt<bool> HideUnreachablePaths("cfg-hide-unreachable-paths",
39 cl::init(false));
40
41 static cl::opt<bool> HideDeoptimizePaths("cfg-hide-deoptimize-paths",
42 cl::init(false));
43
44 static cl::opt<double> HideColdPaths(
45 "cfg-hide-cold-paths", cl::init(0.0),
46 cl::desc("Hide blocks with relative frequency below the given value"));
47
48 static cl::opt<bool> ShowHeatColors("cfg-heat-colors", cl::init(true),
49 cl::Hidden,
50 cl::desc("Show heat colors in CFG"));
51
52 static cl::opt<bool> UseRawEdgeWeight("cfg-raw-weights", cl::init(false),
53 cl::Hidden,
54 cl::desc("Use raw weights for labels. "
55 "Use percentages as default."));
56
57 static cl::opt<bool>
58 ShowEdgeWeight("cfg-weights", cl::init(false), cl::Hidden,
59 cl::desc("Show edges labeled with weights"));
60
writeCFGToDotFile(Function & F,BlockFrequencyInfo * BFI,BranchProbabilityInfo * BPI,uint64_t MaxFreq,bool CFGOnly=false)61 static void writeCFGToDotFile(Function &F, BlockFrequencyInfo *BFI,
62 BranchProbabilityInfo *BPI, uint64_t MaxFreq,
63 bool CFGOnly = false) {
64 std::string Filename =
65 (CFGDotFilenamePrefix + "." + F.getName() + ".dot").str();
66 errs() << "Writing '" << Filename << "'...";
67
68 std::error_code EC;
69 raw_fd_ostream File(Filename, EC, sys::fs::OF_Text);
70
71 DOTFuncInfo CFGInfo(&F, BFI, BPI, MaxFreq);
72 CFGInfo.setHeatColors(ShowHeatColors);
73 CFGInfo.setEdgeWeights(ShowEdgeWeight);
74 CFGInfo.setRawEdgeWeights(UseRawEdgeWeight);
75
76 if (!EC)
77 WriteGraph(File, &CFGInfo, CFGOnly);
78 else
79 errs() << " error opening file for writing!";
80 errs() << "\n";
81 }
82
viewCFG(Function & F,const BlockFrequencyInfo * BFI,const BranchProbabilityInfo * BPI,uint64_t MaxFreq,bool CFGOnly=false)83 static void viewCFG(Function &F, const BlockFrequencyInfo *BFI,
84 const BranchProbabilityInfo *BPI, uint64_t MaxFreq,
85 bool CFGOnly = false) {
86 DOTFuncInfo CFGInfo(&F, BFI, BPI, MaxFreq);
87 CFGInfo.setHeatColors(ShowHeatColors);
88 CFGInfo.setEdgeWeights(ShowEdgeWeight);
89 CFGInfo.setRawEdgeWeights(UseRawEdgeWeight);
90
91 ViewGraph(&CFGInfo, "cfg." + F.getName(), CFGOnly);
92 }
93
DOTFuncInfo(const Function * F,const BlockFrequencyInfo * BFI,const BranchProbabilityInfo * BPI,uint64_t MaxFreq)94 DOTFuncInfo::DOTFuncInfo(const Function *F, const BlockFrequencyInfo *BFI,
95 const BranchProbabilityInfo *BPI, uint64_t MaxFreq)
96 : F(F), BFI(BFI), BPI(BPI), MaxFreq(MaxFreq) {
97 ShowHeat = false;
98 EdgeWeights = !!BPI; // Print EdgeWeights when BPI is available.
99 RawWeights = !!BFI; // Print RawWeights when BFI is available.
100 }
101
102 DOTFuncInfo::~DOTFuncInfo() = default;
103
getModuleSlotTracker()104 ModuleSlotTracker *DOTFuncInfo::getModuleSlotTracker() {
105 if (!MSTStorage)
106 MSTStorage = std::make_unique<ModuleSlotTracker>(F->getParent());
107 return &*MSTStorage;
108 }
109
run(Function & F,FunctionAnalysisManager & AM)110 PreservedAnalyses CFGViewerPass::run(Function &F, FunctionAnalysisManager &AM) {
111 if (!CFGFuncName.empty() && !F.getName().contains(CFGFuncName))
112 return PreservedAnalyses::all();
113 auto *BFI = &AM.getResult<BlockFrequencyAnalysis>(F);
114 auto *BPI = &AM.getResult<BranchProbabilityAnalysis>(F);
115 viewCFG(F, BFI, BPI, getMaxFreq(F, BFI));
116 return PreservedAnalyses::all();
117 }
118
run(Function & F,FunctionAnalysisManager & AM)119 PreservedAnalyses CFGOnlyViewerPass::run(Function &F,
120 FunctionAnalysisManager &AM) {
121 if (!CFGFuncName.empty() && !F.getName().contains(CFGFuncName))
122 return PreservedAnalyses::all();
123 auto *BFI = &AM.getResult<BlockFrequencyAnalysis>(F);
124 auto *BPI = &AM.getResult<BranchProbabilityAnalysis>(F);
125 viewCFG(F, BFI, BPI, getMaxFreq(F, BFI), /*CFGOnly=*/true);
126 return PreservedAnalyses::all();
127 }
128
run(Function & F,FunctionAnalysisManager & AM)129 PreservedAnalyses CFGPrinterPass::run(Function &F,
130 FunctionAnalysisManager &AM) {
131 if (!CFGFuncName.empty() && !F.getName().contains(CFGFuncName))
132 return PreservedAnalyses::all();
133 auto *BFI = &AM.getResult<BlockFrequencyAnalysis>(F);
134 auto *BPI = &AM.getResult<BranchProbabilityAnalysis>(F);
135 writeCFGToDotFile(F, BFI, BPI, getMaxFreq(F, BFI));
136 return PreservedAnalyses::all();
137 }
138
run(Function & F,FunctionAnalysisManager & AM)139 PreservedAnalyses CFGOnlyPrinterPass::run(Function &F,
140 FunctionAnalysisManager &AM) {
141 if (!CFGFuncName.empty() && !F.getName().contains(CFGFuncName))
142 return PreservedAnalyses::all();
143 auto *BFI = &AM.getResult<BlockFrequencyAnalysis>(F);
144 auto *BPI = &AM.getResult<BranchProbabilityAnalysis>(F);
145 writeCFGToDotFile(F, BFI, BPI, getMaxFreq(F, BFI), /*CFGOnly=*/true);
146 return PreservedAnalyses::all();
147 }
148
149 /// viewCFG - This function is meant for use from the debugger. You can just
150 /// say 'call F->viewCFG()' and a ghostview window should pop up from the
151 /// program, displaying the CFG of the current function. This depends on there
152 /// being a 'dot' and 'gv' program in your path.
153 ///
viewCFG() const154 void Function::viewCFG() const { viewCFG(false, nullptr, nullptr); }
155
viewCFG(const char * OutputFileName) const156 void Function::viewCFG(const char *OutputFileName) const {
157 viewCFG(false, nullptr, nullptr, OutputFileName);
158 }
159
viewCFG(bool ViewCFGOnly,const BlockFrequencyInfo * BFI,const BranchProbabilityInfo * BPI,const char * OutputFileName) const160 void Function::viewCFG(bool ViewCFGOnly, const BlockFrequencyInfo *BFI,
161 const BranchProbabilityInfo *BPI,
162 const char *OutputFileName) const {
163 if (!CFGFuncName.empty() && !getName().contains(CFGFuncName))
164 return;
165 DOTFuncInfo CFGInfo(this, BFI, BPI, BFI ? getMaxFreq(*this, BFI) : 0);
166 ViewGraph(&CFGInfo, OutputFileName ? OutputFileName : "cfg" + getName(),
167 ViewCFGOnly);
168 }
169
170 /// viewCFGOnly - This function is meant for use from the debugger. It works
171 /// just like viewCFG, but it does not include the contents of basic blocks
172 /// into the nodes, just the label. If you are only interested in the CFG
173 /// this can make the graph smaller.
174 ///
viewCFGOnly() const175 void Function::viewCFGOnly() const { viewCFGOnly(nullptr, nullptr); }
176
viewCFGOnly(const char * OutputFileName) const177 void Function::viewCFGOnly(const char *OutputFileName) const {
178 viewCFG(true, nullptr, nullptr, OutputFileName);
179 }
180
viewCFGOnly(const BlockFrequencyInfo * BFI,const BranchProbabilityInfo * BPI) const181 void Function::viewCFGOnly(const BlockFrequencyInfo *BFI,
182 const BranchProbabilityInfo *BPI) const {
183 viewCFG(true, BFI, BPI);
184 }
185
186 /// Find all blocks on the paths which terminate with a deoptimize or
187 /// unreachable (i.e. all blocks which are post-dominated by a deoptimize
188 /// or unreachable). These paths are hidden if the corresponding cl::opts
189 /// are enabled.
computeDeoptOrUnreachablePaths(const Function * F)190 void DOTGraphTraits<DOTFuncInfo *>::computeDeoptOrUnreachablePaths(
191 const Function *F) {
192 auto evaluateBB = [&](const BasicBlock *Node) {
193 if (succ_empty(Node)) {
194 const Instruction *TI = Node->getTerminator();
195 isOnDeoptOrUnreachablePath[Node] =
196 (HideUnreachablePaths && isa<UnreachableInst>(TI)) ||
197 (HideDeoptimizePaths && Node->getTerminatingDeoptimizeCall());
198 return;
199 }
200 isOnDeoptOrUnreachablePath[Node] =
201 llvm::all_of(successors(Node), [this](const BasicBlock *BB) {
202 return isOnDeoptOrUnreachablePath[BB];
203 });
204 };
205 /// The post order traversal iteration is done to know the status of
206 /// isOnDeoptOrUnreachablePath for all the successors on the current BB.
207 llvm::for_each(post_order(&F->getEntryBlock()), evaluateBB);
208 }
209
isNodeHidden(const BasicBlock * Node,const DOTFuncInfo * CFGInfo)210 bool DOTGraphTraits<DOTFuncInfo *>::isNodeHidden(const BasicBlock *Node,
211 const DOTFuncInfo *CFGInfo) {
212 if (HideColdPaths.getNumOccurrences() > 0)
213 if (auto *BFI = CFGInfo->getBFI()) {
214 BlockFrequency NodeFreq = BFI->getBlockFreq(Node);
215 BlockFrequency EntryFreq = BFI->getEntryFreq();
216 // Hide blocks with relative frequency below HideColdPaths threshold.
217 if ((double)NodeFreq.getFrequency() / EntryFreq.getFrequency() <
218 HideColdPaths)
219 return true;
220 }
221 if (HideUnreachablePaths || HideDeoptimizePaths) {
222 if (!isOnDeoptOrUnreachablePath.contains(Node))
223 computeDeoptOrUnreachablePaths(Node->getParent());
224 return isOnDeoptOrUnreachablePath[Node];
225 }
226 return false;
227 }
228
getCompleteNodeLabel(const BasicBlock * Node,DOTFuncInfo * CFGInfo,function_ref<void (raw_string_ostream &,const BasicBlock &)> HandleBasicBlock,function_ref<void (std::string &,unsigned &,unsigned)> HandleComment)229 std::string DOTGraphTraits<DOTFuncInfo *>::getCompleteNodeLabel(
230 const BasicBlock *Node, DOTFuncInfo *CFGInfo,
231 function_ref<void(raw_string_ostream &, const BasicBlock &)>
232 HandleBasicBlock,
233 function_ref<void(std::string &, unsigned &, unsigned)> HandleComment) {
234 if (HandleBasicBlock)
235 return CompleteNodeLabelString(Node, HandleBasicBlock, HandleComment);
236
237 // Default basic block printing
238 std::optional<ModuleSlotTracker> MSTStorage;
239 ModuleSlotTracker *MST = nullptr;
240
241 if (CFGInfo) {
242 MST = CFGInfo->getModuleSlotTracker();
243 } else {
244 MSTStorage.emplace(Node->getModule());
245 MST = &*MSTStorage;
246 }
247
248 return CompleteNodeLabelString(
249 Node,
250 function_ref<void(raw_string_ostream &, const BasicBlock &)>(
251 [MST](raw_string_ostream &OS, const BasicBlock &Node) -> void {
252 // Prepend label name
253 Node.printAsOperand(OS, false, *MST);
254 OS << ":\n";
255
256 for (const Instruction &Inst : Node) {
257 Inst.print(OS, *MST, /* IsForDebug */ false);
258 OS << '\n';
259 }
260 }),
261 HandleComment);
262 }
263