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1 //=====- CFLSummary.h - Abstract stratified sets implementation. --------=====//
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 /// \file
10 /// This file defines various utility types and functions useful to
11 /// summary-based alias analysis.
12 ///
13 /// Summary-based analysis, also known as bottom-up analysis, is a style of
14 /// interprocedrual static analysis that tries to analyze the callees before the
15 /// callers get analyzed. The key idea of summary-based analysis is to first
16 /// process each function indepedently, outline its behavior in a condensed
17 /// summary, and then instantiate the summary at the callsite when the said
18 /// function is called elsewhere. This is often in contrast to another style
19 /// called top-down analysis, in which callers are always analyzed first before
20 /// the callees.
21 ///
22 /// In a summary-based analysis, functions must be examined independently and
23 /// out-of-context. We have no information on the state of the memory, the
24 /// arguments, the global values, and anything else external to the function. To
25 /// carry out the analysis conservative assumptions have to be made about those
26 /// external states. In exchange for the potential loss of precision, the
27 /// summary we obtain this way is highly reusable, which makes the analysis
28 /// easier to scale to large programs even if carried out context-sensitively.
29 ///
30 /// Currently, all CFL-based alias analyses adopt the summary-based approach
31 /// and therefore heavily rely on this header.
32 ///
33 //===----------------------------------------------------------------------===//
34 
35 #ifndef LLVM_ANALYSIS_ALIASANALYSISSUMMARY_H
36 #define LLVM_ANALYSIS_ALIASANALYSISSUMMARY_H
37 
38 #include "llvm/ADT/DenseMapInfo.h"
39 #include "llvm/ADT/Optional.h"
40 #include "llvm/ADT/SmallVector.h"
41 #include "llvm/IR/CallSite.h"
42 #include <bitset>
43 
44 namespace llvm {
45 namespace cflaa {
46 
47 //===----------------------------------------------------------------------===//
48 // AliasAttr related stuffs
49 //===----------------------------------------------------------------------===//
50 
51 /// The number of attributes that AliasAttr should contain. Attributes are
52 /// described below, and 32 was an arbitrary choice because it fits nicely in 32
53 /// bits (because we use a bitset for AliasAttr).
54 static const unsigned NumAliasAttrs = 32;
55 
56 /// These are attributes that an alias analysis can use to mark certain special
57 /// properties of a given pointer. Refer to the related functions below to see
58 /// what kinds of attributes are currently defined.
59 typedef std::bitset<NumAliasAttrs> AliasAttrs;
60 
61 /// Attr represent whether the said pointer comes from an unknown source
62 /// (such as opaque memory or an integer cast).
63 AliasAttrs getAttrNone();
64 
65 /// AttrUnknown represent whether the said pointer comes from a source not known
66 /// to alias analyses (such as opaque memory or an integer cast).
67 AliasAttrs getAttrUnknown();
68 bool hasUnknownAttr(AliasAttrs);
69 
70 /// AttrCaller represent whether the said pointer comes from a source not known
71 /// to the current function but known to the caller. Values pointed to by the
72 /// arguments of the current function have this attribute set
73 AliasAttrs getAttrCaller();
74 bool hasCallerAttr(AliasAttrs);
75 bool hasUnknownOrCallerAttr(AliasAttrs);
76 
77 /// AttrEscaped represent whether the said pointer comes from a known source but
78 /// escapes to the unknown world (e.g. casted to an integer, or passed as an
79 /// argument to opaque function). Unlike non-escaped pointers, escaped ones may
80 /// alias pointers coming from unknown sources.
81 AliasAttrs getAttrEscaped();
82 bool hasEscapedAttr(AliasAttrs);
83 
84 /// AttrGlobal represent whether the said pointer is a global value.
85 /// AttrArg represent whether the said pointer is an argument, and if so, what
86 /// index the argument has.
87 AliasAttrs getGlobalOrArgAttrFromValue(const Value &);
88 bool isGlobalOrArgAttr(AliasAttrs);
89 
90 /// Given an AliasAttrs, return a new AliasAttrs that only contains attributes
91 /// meaningful to the caller. This function is primarily used for
92 /// interprocedural analysis
93 /// Currently, externally visible AliasAttrs include AttrUnknown, AttrGlobal,
94 /// and AttrEscaped
95 AliasAttrs getExternallyVisibleAttrs(AliasAttrs);
96 
97 //===----------------------------------------------------------------------===//
98 // Function summary related stuffs
99 //===----------------------------------------------------------------------===//
100 
101 /// The maximum number of arguments we can put into a summary.
102 LLVM_CONSTEXPR static unsigned MaxSupportedArgsInSummary = 50;
103 
104 /// We use InterfaceValue to describe parameters/return value, as well as
105 /// potential memory locations that are pointed to by parameters/return value,
106 /// of a function.
107 /// Index is an integer which represents a single parameter or a return value.
108 /// When the index is 0, it refers to the return value. Non-zero index i refers
109 /// to the i-th parameter.
110 /// DerefLevel indicates the number of dereferences one must perform on the
111 /// parameter/return value to get this InterfaceValue.
112 struct InterfaceValue {
113   unsigned Index;
114   unsigned DerefLevel;
115 };
116 
117 inline bool operator==(InterfaceValue lhs, InterfaceValue rhs) {
118   return lhs.Index == rhs.Index && lhs.DerefLevel == rhs.DerefLevel;
119 }
120 inline bool operator!=(InterfaceValue lhs, InterfaceValue rhs) {
121   return !(lhs == rhs);
122 }
123 
124 /// We use ExternalRelation to describe an externally visible aliasing relations
125 /// between parameters/return value of a function.
126 struct ExternalRelation {
127   InterfaceValue From, To;
128 };
129 
130 /// We use ExternalAttribute to describe an externally visible AliasAttrs
131 /// for parameters/return value.
132 struct ExternalAttribute {
133   InterfaceValue IValue;
134   AliasAttrs Attr;
135 };
136 
137 /// AliasSummary is just a collection of ExternalRelation and ExternalAttribute
138 struct AliasSummary {
139   // RetParamRelations is a collection of ExternalRelations.
140   SmallVector<ExternalRelation, 8> RetParamRelations;
141 
142   // RetParamAttributes is a collection of ExternalAttributes.
143   SmallVector<ExternalAttribute, 8> RetParamAttributes;
144 };
145 
146 /// This is the result of instantiating InterfaceValue at a particular callsite
147 struct InstantiatedValue {
148   Value *Val;
149   unsigned DerefLevel;
150 };
151 Optional<InstantiatedValue> instantiateInterfaceValue(InterfaceValue, CallSite);
152 
153 /// This is the result of instantiating ExternalRelation at a particular
154 /// callsite
155 struct InstantiatedRelation {
156   InstantiatedValue From, To;
157 };
158 Optional<InstantiatedRelation> instantiateExternalRelation(ExternalRelation,
159                                                            CallSite);
160 
161 /// This is the result of instantiating ExternalAttribute at a particular
162 /// callsite
163 struct InstantiatedAttr {
164   InstantiatedValue IValue;
165   AliasAttrs Attr;
166 };
167 Optional<InstantiatedAttr> instantiateExternalAttribute(ExternalAttribute,
168                                                         CallSite);
169 }
170 
171 template <> struct DenseMapInfo<cflaa::InstantiatedValue> {
172   static inline cflaa::InstantiatedValue getEmptyKey() {
173     return cflaa::InstantiatedValue{DenseMapInfo<Value *>::getEmptyKey(),
174                                     DenseMapInfo<unsigned>::getEmptyKey()};
175   }
176   static inline cflaa::InstantiatedValue getTombstoneKey() {
177     return cflaa::InstantiatedValue{DenseMapInfo<Value *>::getTombstoneKey(),
178                                     DenseMapInfo<unsigned>::getTombstoneKey()};
179   }
180   static unsigned getHashValue(const cflaa::InstantiatedValue &IV) {
181     return DenseMapInfo<std::pair<Value *, unsigned>>::getHashValue(
182         std::make_pair(IV.Val, IV.DerefLevel));
183   }
184   static bool isEqual(const cflaa::InstantiatedValue &LHS,
185                       const cflaa::InstantiatedValue &RHS) {
186     return LHS.Val == RHS.Val && LHS.DerefLevel == RHS.DerefLevel;
187   }
188 };
189 }
190 
191 #endif
192