1 //===- CallGraphSCCPass.h - Pass that operates BU on call graph -*- C++ -*-===//
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 the CallGraphSCCPass class, which is used for passes which
10 // are implemented as bottom-up traversals on the call graph.  Because there may
11 // be cycles in the call graph, passes of this type operate on the call-graph in
12 // SCC order: that is, they process function bottom-up, except for recursive
13 // functions, which they process all at once.
14 //
15 // These passes are inherently interprocedural, and are required to keep the
16 // call graph up-to-date if they do anything which could modify it.
17 //
18 //===----------------------------------------------------------------------===//
19 
20 #ifndef LLVM_ANALYSIS_CALLGRAPHSCCPASS_H
21 #define LLVM_ANALYSIS_CALLGRAPHSCCPASS_H
22 
23 #include "llvm/ADT/ArrayRef.h"
24 #include "llvm/Pass.h"
25 #include <vector>
26 
27 namespace llvm {
28 
29 class CallGraph;
30 class CallGraphNode;
31 class CallGraphSCC;
32 class PMStack;
33 
34 class CallGraphSCCPass : public Pass {
35 public:
36   explicit CallGraphSCCPass(char &pid) : Pass(PT_CallGraphSCC, pid) {}
37 
38   /// createPrinterPass - Get a pass that prints the Module
39   /// corresponding to a CallGraph.
40   Pass *createPrinterPass(raw_ostream &OS,
41                           const std::string &Banner) const override;
42 
43   using llvm::Pass::doInitialization;
44   using llvm::Pass::doFinalization;
45 
46   /// doInitialization - This method is called before the SCC's of the program
47   /// has been processed, allowing the pass to do initialization as necessary.
48   virtual bool doInitialization(CallGraph &CG) {
49     return false;
50   }
51 
52   /// runOnSCC - This method should be implemented by the subclass to perform
53   /// whatever action is necessary for the specified SCC.  Note that
54   /// non-recursive (or only self-recursive) functions will have an SCC size of
55   /// 1, where recursive portions of the call graph will have SCC size > 1.
56   ///
57   /// SCC passes that add or delete functions to the SCC are required to update
58   /// the SCC list, otherwise stale pointers may be dereferenced.
59   virtual bool runOnSCC(CallGraphSCC &SCC) = 0;
60 
61   /// doFinalization - This method is called after the SCC's of the program has
62   /// been processed, allowing the pass to do final cleanup as necessary.
63   virtual bool doFinalization(CallGraph &CG) {
64     return false;
65   }
66 
67   /// Assign pass manager to manager this pass
68   void assignPassManager(PMStack &PMS, PassManagerType PMT) override;
69 
70   ///  Return what kind of Pass Manager can manage this pass.
71   PassManagerType getPotentialPassManagerType() const override {
72     return PMT_CallGraphPassManager;
73   }
74 
75   /// getAnalysisUsage - For this class, we declare that we require and preserve
76   /// the call graph.  If the derived class implements this method, it should
77   /// always explicitly call the implementation here.
78   void getAnalysisUsage(AnalysisUsage &Info) const override;
79 
80 protected:
81   /// Optional passes call this function to check whether the pass should be
82   /// skipped. This is the case when optimization bisect is over the limit.
83   bool skipSCC(CallGraphSCC &SCC) const;
84 };
85 
86 /// CallGraphSCC - This is a single SCC that a CallGraphSCCPass is run on.
87 class CallGraphSCC {
88   const CallGraph &CG; // The call graph for this SCC.
89   void *Context; // The CGPassManager object that is vending this.
90   std::vector<CallGraphNode *> Nodes;
91 
92 public:
93   CallGraphSCC(CallGraph &cg, void *context) : CG(cg), Context(context) {}
94 
95   void initialize(ArrayRef<CallGraphNode *> NewNodes) {
96     Nodes.assign(NewNodes.begin(), NewNodes.end());
97   }
98 
99   bool isSingular() const { return Nodes.size() == 1; }
100   unsigned size() const { return Nodes.size(); }
101 
102   /// ReplaceNode - This informs the SCC and the pass manager that the specified
103   /// Old node has been deleted, and New is to be used in its place.
104   void ReplaceNode(CallGraphNode *Old, CallGraphNode *New);
105 
106   /// DeleteNode - This informs the SCC and the pass manager that the specified
107   /// Old node has been deleted.
108   void DeleteNode(CallGraphNode *Old);
109 
110   using iterator = std::vector<CallGraphNode *>::const_iterator;
111 
112   iterator begin() const { return Nodes.begin(); }
113   iterator end() const { return Nodes.end(); }
114 
115   const CallGraph &getCallGraph() { return CG; }
116 };
117 
118 void initializeDummyCGSCCPassPass(PassRegistry &);
119 
120 /// This pass is required by interprocedural register allocation. It forces
121 /// codegen to follow bottom up order on call graph.
122 class DummyCGSCCPass : public CallGraphSCCPass {
123 public:
124   static char ID;
125 
126   DummyCGSCCPass() : CallGraphSCCPass(ID) {
127     PassRegistry &Registry = *PassRegistry::getPassRegistry();
128     initializeDummyCGSCCPassPass(Registry);
129   }
130 
131   bool runOnSCC(CallGraphSCC &SCC) override { return false; }
132 
133   void getAnalysisUsage(AnalysisUsage &AU) const override {
134     AU.setPreservesAll();
135   }
136 };
137 
138 } // end namespace llvm
139 
140 #endif // LLVM_ANALYSIS_CALLGRAPHSCCPASS_H
141