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/Support/CommandLine.h"
23#include "llvm/Support/FileSystem.h"
24#include "llvm/Support/GraphWriter.h"
25
26using namespace llvm;
27
28static cl::opt<std::string>
29 CFGFuncName("cfg-func-name", cl::Hidden,
30 cl::desc("The name of a function (or its substring)"
31 " whose CFG is viewed/printed."));
32
33static cl::opt<std::string> CFGDotFilenamePrefix(
34 "cfg-dot-filename-prefix", cl::Hidden,
35 cl::desc("The prefix used for the CFG dot file names."));
36
37static cl::opt<bool> HideUnreachablePaths("cfg-hide-unreachable-paths",
38 cl::init(Val: false));
39
40static cl::opt<bool> HideDeoptimizePaths("cfg-hide-deoptimize-paths",
41 cl::init(Val: false));
42
43static cl::opt<double> HideColdPaths(
44 "cfg-hide-cold-paths", cl::init(Val: 0.0),
45 cl::desc("Hide blocks with relative frequency below the given value"));
46
47static cl::opt<bool> ShowHeatColors("cfg-heat-colors", cl::init(Val: true),
48 cl::Hidden,
49 cl::desc("Show heat colors in CFG"));
50
51static cl::opt<bool> UseRawEdgeWeight("cfg-raw-weights", cl::init(Val: false),
52 cl::Hidden,
53 cl::desc("Use raw weights for labels. "
54 "Use percentages as default."));
55
56static cl::opt<bool>
57 ShowEdgeWeight("cfg-weights", cl::init(Val: false), cl::Hidden,
58 cl::desc("Show edges labeled with weights"));
59
60static void writeCFGToDotFile(Function &F, BlockFrequencyInfo *BFI,
61 BranchProbabilityInfo *BPI, uint64_t MaxFreq,
62 bool CFGOnly = false) {
63 std::string Filename =
64 (CFGDotFilenamePrefix + "." + F.getName() + ".dot").str();
65 errs() << "Writing '" << Filename << "'...";
66
67 std::error_code EC;
68 raw_fd_ostream File(Filename, EC, sys::fs::OF_Text);
69
70 DOTFuncInfo CFGInfo(&F, BFI, BPI, MaxFreq);
71 CFGInfo.setHeatColors(ShowHeatColors);
72 CFGInfo.setEdgeWeights(ShowEdgeWeight);
73 CFGInfo.setRawEdgeWeights(UseRawEdgeWeight);
74
75 if (!EC)
76 WriteGraph(O&: File, G: &CFGInfo, ShortNames: CFGOnly);
77 else
78 errs() << " error opening file for writing!";
79 errs() << "\n";
80}
81
82static void viewCFG(Function &F, const BlockFrequencyInfo *BFI,
83 const BranchProbabilityInfo *BPI, uint64_t MaxFreq,
84 bool CFGOnly = false) {
85 DOTFuncInfo CFGInfo(&F, BFI, BPI, MaxFreq);
86 CFGInfo.setHeatColors(ShowHeatColors);
87 CFGInfo.setEdgeWeights(ShowEdgeWeight);
88 CFGInfo.setRawEdgeWeights(UseRawEdgeWeight);
89
90 ViewGraph(G: &CFGInfo, Name: "cfg." + F.getName(), ShortNames: CFGOnly);
91}
92
93PreservedAnalyses CFGViewerPass::run(Function &F, FunctionAnalysisManager &AM) {
94 if (!CFGFuncName.empty() && !F.getName().contains(Other: CFGFuncName))
95 return PreservedAnalyses::all();
96 auto *BFI = &AM.getResult<BlockFrequencyAnalysis>(IR&: F);
97 auto *BPI = &AM.getResult<BranchProbabilityAnalysis>(IR&: F);
98 viewCFG(F, BFI, BPI, MaxFreq: getMaxFreq(F, BFI));
99 return PreservedAnalyses::all();
100}
101
102PreservedAnalyses CFGOnlyViewerPass::run(Function &F,
103 FunctionAnalysisManager &AM) {
104 if (!CFGFuncName.empty() && !F.getName().contains(Other: CFGFuncName))
105 return PreservedAnalyses::all();
106 auto *BFI = &AM.getResult<BlockFrequencyAnalysis>(IR&: F);
107 auto *BPI = &AM.getResult<BranchProbabilityAnalysis>(IR&: F);
108 viewCFG(F, BFI, BPI, MaxFreq: getMaxFreq(F, BFI), /*CFGOnly=*/true);
109 return PreservedAnalyses::all();
110}
111
112PreservedAnalyses CFGPrinterPass::run(Function &F,
113 FunctionAnalysisManager &AM) {
114 if (!CFGFuncName.empty() && !F.getName().contains(Other: CFGFuncName))
115 return PreservedAnalyses::all();
116 auto *BFI = &AM.getResult<BlockFrequencyAnalysis>(IR&: F);
117 auto *BPI = &AM.getResult<BranchProbabilityAnalysis>(IR&: F);
118 writeCFGToDotFile(F, BFI, BPI, MaxFreq: getMaxFreq(F, BFI));
119 return PreservedAnalyses::all();
120}
121
122PreservedAnalyses CFGOnlyPrinterPass::run(Function &F,
123 FunctionAnalysisManager &AM) {
124 if (!CFGFuncName.empty() && !F.getName().contains(Other: CFGFuncName))
125 return PreservedAnalyses::all();
126 auto *BFI = &AM.getResult<BlockFrequencyAnalysis>(IR&: F);
127 auto *BPI = &AM.getResult<BranchProbabilityAnalysis>(IR&: F);
128 writeCFGToDotFile(F, BFI, BPI, MaxFreq: getMaxFreq(F, BFI), /*CFGOnly=*/true);
129 return PreservedAnalyses::all();
130}
131
132/// viewCFG - This function is meant for use from the debugger. You can just
133/// say 'call F->viewCFG()' and a ghostview window should pop up from the
134/// program, displaying the CFG of the current function. This depends on there
135/// being a 'dot' and 'gv' program in your path.
136///
137void Function::viewCFG() const { viewCFG(ViewCFGOnly: false, BFI: nullptr, BPI: nullptr); }
138
139void Function::viewCFG(bool ViewCFGOnly, const BlockFrequencyInfo *BFI,
140 const BranchProbabilityInfo *BPI) const {
141 if (!CFGFuncName.empty() && !getName().contains(Other: CFGFuncName))
142 return;
143 DOTFuncInfo CFGInfo(this, BFI, BPI, BFI ? getMaxFreq(F: *this, BFI) : 0);
144 ViewGraph(G: &CFGInfo, Name: "cfg" + getName(), ShortNames: ViewCFGOnly);
145}
146
147/// viewCFGOnly - This function is meant for use from the debugger. It works
148/// just like viewCFG, but it does not include the contents of basic blocks
149/// into the nodes, just the label. If you are only interested in the CFG
150/// this can make the graph smaller.
151///
152void Function::viewCFGOnly() const { viewCFGOnly(BFI: nullptr, BPI: nullptr); }
153
154void Function::viewCFGOnly(const BlockFrequencyInfo *BFI,
155 const BranchProbabilityInfo *BPI) const {
156 viewCFG(ViewCFGOnly: true, BFI, BPI);
157}
158
159/// Find all blocks on the paths which terminate with a deoptimize or
160/// unreachable (i.e. all blocks which are post-dominated by a deoptimize
161/// or unreachable). These paths are hidden if the corresponding cl::opts
162/// are enabled.
163void DOTGraphTraits<DOTFuncInfo *>::computeDeoptOrUnreachablePaths(
164 const Function *F) {
165 auto evaluateBB = [&](const BasicBlock *Node) {
166 if (succ_empty(BB: Node)) {
167 const Instruction *TI = Node->getTerminator();
168 isOnDeoptOrUnreachablePath[Node] =
169 (HideUnreachablePaths && isa<UnreachableInst>(Val: TI)) ||
170 (HideDeoptimizePaths && Node->getTerminatingDeoptimizeCall());
171 return;
172 }
173 isOnDeoptOrUnreachablePath[Node] =
174 llvm::all_of(Range: successors(BB: Node), P: [this](const BasicBlock *BB) {
175 return isOnDeoptOrUnreachablePath[BB];
176 });
177 };
178 /// The post order traversal iteration is done to know the status of
179 /// isOnDeoptOrUnreachablePath for all the successors on the current BB.
180 llvm::for_each(Range: post_order(G: &F->getEntryBlock()), F: evaluateBB);
181}
182
183bool DOTGraphTraits<DOTFuncInfo *>::isNodeHidden(const BasicBlock *Node,
184 const DOTFuncInfo *CFGInfo) {
185 if (HideColdPaths.getNumOccurrences() > 0)
186 if (auto *BFI = CFGInfo->getBFI()) {
187 BlockFrequency NodeFreq = BFI->getBlockFreq(BB: Node);
188 BlockFrequency EntryFreq = BFI->getEntryFreq();
189 // Hide blocks with relative frequency below HideColdPaths threshold.
190 if ((double)NodeFreq.getFrequency() / EntryFreq.getFrequency() <
191 HideColdPaths)
192 return true;
193 }
194 if (HideUnreachablePaths || HideDeoptimizePaths) {
195 if (!isOnDeoptOrUnreachablePath.contains(Val: Node))
196 computeDeoptOrUnreachablePaths(F: Node->getParent());
197 return isOnDeoptOrUnreachablePath[Node];
198 }
199 return false;
200}
201

source code of llvm/lib/Analysis/CFGPrinter.cpp