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 independently, 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 static const 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 inline bool operator<(InterfaceValue LHS, InterfaceValue RHS) {
124 return LHS.Index < RHS.Index ||
125 (LHS.Index == RHS.Index && LHS.DerefLevel < RHS.DerefLevel);
126 }
127 inline bool operator>(InterfaceValue LHS, InterfaceValue RHS) {
128 return RHS < LHS;
129 }
130 inline bool operator<=(InterfaceValue LHS, InterfaceValue RHS) {
131 return !(RHS < LHS);
132 }
133 inline bool operator>=(InterfaceValue LHS, InterfaceValue RHS) {
134 return !(LHS < RHS);
135 }
136
137 // We use UnknownOffset to represent pointer offsets that cannot be determined
138 // at compile time. Note that MemoryLocation::UnknownSize cannot be used here
139 // because we require a signed value.
140 static const int64_t UnknownOffset = INT64_MAX;
141
addOffset(int64_t LHS,int64_t RHS)142 inline int64_t addOffset(int64_t LHS, int64_t RHS) {
143 if (LHS == UnknownOffset || RHS == UnknownOffset)
144 return UnknownOffset;
145 // FIXME: Do we need to guard against integer overflow here?
146 return LHS + RHS;
147 }
148
149 /// We use ExternalRelation to describe an externally visible aliasing relations
150 /// between parameters/return value of a function.
151 struct ExternalRelation {
152 InterfaceValue From, To;
153 int64_t Offset;
154 };
155
156 inline bool operator==(ExternalRelation LHS, ExternalRelation RHS) {
157 return LHS.From == RHS.From && LHS.To == RHS.To && LHS.Offset == RHS.Offset;
158 }
159 inline bool operator!=(ExternalRelation LHS, ExternalRelation RHS) {
160 return !(LHS == RHS);
161 }
162 inline bool operator<(ExternalRelation LHS, ExternalRelation RHS) {
163 if (LHS.From < RHS.From)
164 return true;
165 if (LHS.From > RHS.From)
166 return false;
167 if (LHS.To < RHS.To)
168 return true;
169 if (LHS.To > RHS.To)
170 return false;
171 return LHS.Offset < RHS.Offset;
172 }
173 inline bool operator>(ExternalRelation LHS, ExternalRelation RHS) {
174 return RHS < LHS;
175 }
176 inline bool operator<=(ExternalRelation LHS, ExternalRelation RHS) {
177 return !(RHS < LHS);
178 }
179 inline bool operator>=(ExternalRelation LHS, ExternalRelation RHS) {
180 return !(LHS < RHS);
181 }
182
183 /// We use ExternalAttribute to describe an externally visible AliasAttrs
184 /// for parameters/return value.
185 struct ExternalAttribute {
186 InterfaceValue IValue;
187 AliasAttrs Attr;
188 };
189
190 /// AliasSummary is just a collection of ExternalRelation and ExternalAttribute
191 struct AliasSummary {
192 // RetParamRelations is a collection of ExternalRelations.
193 SmallVector<ExternalRelation, 8> RetParamRelations;
194
195 // RetParamAttributes is a collection of ExternalAttributes.
196 SmallVector<ExternalAttribute, 8> RetParamAttributes;
197 };
198
199 /// This is the result of instantiating InterfaceValue at a particular callsite
200 struct InstantiatedValue {
201 Value *Val;
202 unsigned DerefLevel;
203 };
204 Optional<InstantiatedValue> instantiateInterfaceValue(InterfaceValue, CallSite);
205
206 inline bool operator==(InstantiatedValue LHS, InstantiatedValue RHS) {
207 return LHS.Val == RHS.Val && LHS.DerefLevel == RHS.DerefLevel;
208 }
209 inline bool operator!=(InstantiatedValue LHS, InstantiatedValue RHS) {
210 return !(LHS == RHS);
211 }
212 inline bool operator<(InstantiatedValue LHS, InstantiatedValue RHS) {
213 return std::less<Value *>()(LHS.Val, RHS.Val) ||
214 (LHS.Val == RHS.Val && LHS.DerefLevel < RHS.DerefLevel);
215 }
216 inline bool operator>(InstantiatedValue LHS, InstantiatedValue RHS) {
217 return RHS < LHS;
218 }
219 inline bool operator<=(InstantiatedValue LHS, InstantiatedValue RHS) {
220 return !(RHS < LHS);
221 }
222 inline bool operator>=(InstantiatedValue LHS, InstantiatedValue RHS) {
223 return !(LHS < RHS);
224 }
225
226 /// This is the result of instantiating ExternalRelation at a particular
227 /// callsite
228 struct InstantiatedRelation {
229 InstantiatedValue From, To;
230 int64_t Offset;
231 };
232 Optional<InstantiatedRelation> instantiateExternalRelation(ExternalRelation,
233 CallSite);
234
235 /// This is the result of instantiating ExternalAttribute at a particular
236 /// callsite
237 struct InstantiatedAttr {
238 InstantiatedValue IValue;
239 AliasAttrs Attr;
240 };
241 Optional<InstantiatedAttr> instantiateExternalAttribute(ExternalAttribute,
242 CallSite);
243 }
244
245 template <> struct DenseMapInfo<cflaa::InstantiatedValue> {
246 static inline cflaa::InstantiatedValue getEmptyKey() {
247 return cflaa::InstantiatedValue{DenseMapInfo<Value *>::getEmptyKey(),
248 DenseMapInfo<unsigned>::getEmptyKey()};
249 }
250 static inline cflaa::InstantiatedValue getTombstoneKey() {
251 return cflaa::InstantiatedValue{DenseMapInfo<Value *>::getTombstoneKey(),
252 DenseMapInfo<unsigned>::getTombstoneKey()};
253 }
254 static unsigned getHashValue(const cflaa::InstantiatedValue &IV) {
255 return DenseMapInfo<std::pair<Value *, unsigned>>::getHashValue(
256 std::make_pair(IV.Val, IV.DerefLevel));
257 }
258 static bool isEqual(const cflaa::InstantiatedValue &LHS,
259 const cflaa::InstantiatedValue &RHS) {
260 return LHS.Val == RHS.Val && LHS.DerefLevel == RHS.DerefLevel;
261 }
262 };
263 }
264
265 #endif
266