LibCallSemantics.h revision b2143b6247901ae4eca2192ee134564c4f5f7853 
1//===- LibCallSemantics.h - Describe library semantics --------------------===//
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//
10// This file defines interfaces that can be used to describe language specific
11// runtime library interfaces (e.g. libc, libm, etc) to LLVM optimizers.
12//
13//===----------------------------------------------------------------------===//
14
15#ifndef LLVM_ANALYSIS_LIBCALLSEMANTICS_H
16#define LLVM_ANALYSIS_LIBCALLSEMANTICS_H
17
18#include "llvm/Analysis/AliasAnalysis.h"
19
20namespace llvm {
21
22  /// LibCallLocationInfo - This struct describes a set of memory locations that
23  /// are accessed by libcalls.  Identification of a location is doing with a
24  /// simple callback function.
25  ///
26  /// For example, the LibCallInfo may be set up to model the behavior of
27  /// standard libm functions.  The location that they may be interested in is
28  /// an abstract location that represents errno for the current target.  In
29  /// this case, a location for errno is anything such that the predicate
30  /// returns true.  On Mac OS/X, this predicate would return true if the
31  /// pointer is the result of a call to "__error()".
32  ///
33  /// Locations can also be defined in a constant-sensitive way.  For example,
34  /// it is possible to define a location that returns true iff it is passed
35  /// into the call as a specific argument.  This is useful for modeling things
36  /// like "printf", which can store to memory, but only through pointers passed
37  /// with a '%n' constraint.
38  ///
39  struct LibCallLocationInfo {
40    // TODO: Flags: isContextSensitive etc.
41
42    /// isLocation - Return a LocResult if the specified pointer refers to this
43    /// location for the specified call site.  This returns "Yes" if we can tell
44    /// that the pointer *does definitely* refer to the location, "No" if we can
45    /// tell that the location *definitely does not* refer to the location, and
46    /// returns "Unknown" if we cannot tell for certain.
47    enum LocResult {
48      Yes, No, Unknown
49    };
50    LocResult (*isLocation)(ImmutableCallSite CS,
51                            const AliasAnalysis::Location &Loc);
52  };
53
54  /// LibCallFunctionInfo - Each record in the array of FunctionInfo structs
55  /// records the behavior of one libcall that is known by the optimizer.  This
56  /// captures things like the side effects of the call.  Side effects are
57  /// modeled both universally (in the readnone/readonly) sense, but also
58  /// potentially against a set of abstract locations defined by the optimizer.
59  /// This allows an optimizer to define that some libcall (e.g. sqrt) is
60  /// side-effect free except that it might modify errno (thus, the call is
61  /// *not* universally readonly).  Or it might say that the side effects
62  /// are unknown other than to say that errno is not modified.
63  ///
64  struct LibCallFunctionInfo {
65    /// Name - This is the name of the libcall this describes.
66    const char *Name;
67
68    /// TODO: Constant folding function: Constant* vector -> Constant*.
69
70    /// UniversalBehavior - This captures the absolute mod/ref behavior without
71    /// any specific context knowledge.  For example, if the function is known
72    /// to be readonly, this would be set to 'ref'.  If known to be readnone,
73    /// this is set to NoModRef.
74    AliasAnalysis::ModRefResult UniversalBehavior;
75
76    /// LocationMRInfo - This pair captures info about whether a specific
77    /// location is modified or referenced by a libcall.
78    struct LocationMRInfo {
79      /// LocationID - ID # of the accessed location or ~0U for array end.
80      unsigned LocationID;
81      /// MRInfo - Mod/Ref info for this location.
82      AliasAnalysis::ModRefResult MRInfo;
83    };
84
85    /// DetailsType - Indicate the sense of the LocationDetails array.  This
86    /// controls how the LocationDetails array is interpreted.
87    enum {
88      /// DoesOnly - If DetailsType is set to DoesOnly, then we know that the
89      /// *only* mod/ref behavior of this function is captured by the
90      /// LocationDetails array.  If we are trying to say that 'sqrt' can only
91      /// modify errno, we'd have the {errnoloc,mod} in the LocationDetails
92      /// array and have DetailsType set to DoesOnly.
93      DoesOnly,
94
95      /// DoesNot - If DetailsType is set to DoesNot, then the sense of the
96      /// LocationDetails array is completely inverted.  This means that we *do
97      /// not* know everything about the side effects of this libcall, but we do
98      /// know things that the libcall cannot do.  This is useful for complex
99      /// functions like 'ctime' which have crazy mod/ref behavior, but are
100      /// known to never read or write errno.  In this case, we'd have
101      /// {errnoloc,modref} in the LocationDetails array and DetailsType would
102      /// be set to DoesNot, indicating that ctime does not read or write the
103      /// errno location.
104      DoesNot
105    } DetailsType;
106
107    /// LocationDetails - This is a pointer to an array of LocationMRInfo
108    /// structs which indicates the behavior of the libcall w.r.t. specific
109    /// locations.  For example, if this libcall is known to only modify
110    /// 'errno', it would have a LocationDetails array with the errno ID and
111    /// 'mod' in it.  See the DetailsType field for how this is interpreted.
112    ///
113    /// In the "DoesOnly" case, this information is 'may' information for: there
114    /// is no guarantee that the specified side effect actually does happen,
115    /// just that it could.  In the "DoesNot" case, this is 'must not' info.
116    ///
117    /// If this pointer is null, no details are known.
118    ///
119    const LocationMRInfo *LocationDetails;
120  };
121
122
123  /// LibCallInfo - Abstract interface to query about library call information.
124  /// Instances of this class return known information about some set of
125  /// libcalls.
126  ///
127  class LibCallInfo {
128    // Implementation details of this object, private.
129    mutable void *Impl;
130    mutable const LibCallLocationInfo *Locations;
131    mutable unsigned NumLocations;
132  public:
133    LibCallInfo() : Impl(0), Locations(0), NumLocations(0) {}
134    virtual ~LibCallInfo();
135
136    //===------------------------------------------------------------------===//
137    //  Accessor Methods: Efficient access to contained data.
138    //===------------------------------------------------------------------===//
139
140    /// getLocationInfo - Return information about the specified LocationID.
141    const LibCallLocationInfo &getLocationInfo(unsigned LocID) const;
142
143
144    /// getFunctionInfo - Return the LibCallFunctionInfo object corresponding to
145    /// the specified function if we have it.  If not, return null.
146    const LibCallFunctionInfo *getFunctionInfo(const Function *F) const;
147
148
149    //===------------------------------------------------------------------===//
150    //  Implementation Methods: Subclasses should implement these.
151    //===------------------------------------------------------------------===//
152
153    /// getLocationInfo - Return descriptors for the locations referenced by
154    /// this set of libcalls.
155    virtual unsigned getLocationInfo(const LibCallLocationInfo *&Array) const {
156      return 0;
157    }
158
159    /// getFunctionInfoArray - Return an array of descriptors that describe the
160    /// set of libcalls represented by this LibCallInfo object.  This array is
161    /// terminated by an entry with a NULL name.
162    virtual const LibCallFunctionInfo *getFunctionInfoArray() const = 0;
163  };
164
165} // end namespace llvm
166
167#endif
168