1//===- GlobalStatus.h - Compute status info for globals ---------*- C++ -*-===//
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#ifndef LLVM_TRANSFORMS_UTILS_GLOBALSTATUS_H
11#define LLVM_TRANSFORMS_UTILS_GLOBALSTATUS_H
12
13#include "llvm/IR/Instructions.h"
14
15namespace llvm {
16class Value;
17class Function;
18
19/// It is safe to destroy a constant iff it is only used by constants itself.
20/// Note that constants cannot be cyclic, so this test is pretty easy to
21/// implement recursively.
22///
23bool isSafeToDestroyConstant(const Constant *C);
24
25/// As we analyze each global, keep track of some information about it.  If we
26/// find out that the address of the global is taken, none of this info will be
27/// accurate.
28struct GlobalStatus {
29  /// True if the global's address is used in a comparison.
30  bool IsCompared;
31
32  /// True if the global is ever loaded.  If the global isn't ever loaded it
33  /// can be deleted.
34  bool IsLoaded;
35
36  /// Keep track of what stores to the global look like.
37  enum StoredType {
38    /// There is no store to this global.  It can thus be marked constant.
39    NotStored,
40
41    /// This global is stored to, but the only thing stored is the constant it
42    /// was initialized with. This is only tracked for scalar globals.
43    InitializerStored,
44
45    /// This global is stored to, but only its initializer and one other value
46    /// is ever stored to it.  If this global isStoredOnce, we track the value
47    /// stored to it in StoredOnceValue below.  This is only tracked for scalar
48    /// globals.
49    StoredOnce,
50
51    /// This global is stored to by multiple values or something else that we
52    /// cannot track.
53    Stored
54  } StoredType;
55
56  /// If only one value (besides the initializer constant) is ever stored to
57  /// this global, keep track of what value it is.
58  Value *StoredOnceValue;
59
60  /// These start out null/false.  When the first accessing function is noticed,
61  /// it is recorded. When a second different accessing function is noticed,
62  /// HasMultipleAccessingFunctions is set to true.
63  const Function *AccessingFunction;
64  bool HasMultipleAccessingFunctions;
65
66  /// Set to true if this global has a user that is not an instruction (e.g. a
67  /// constant expr or GV initializer).
68  bool HasNonInstructionUser;
69
70  /// Set to the strongest atomic ordering requirement.
71  AtomicOrdering Ordering;
72
73  /// Look at all uses of the global and fill in the GlobalStatus structure.  If
74  /// the global has its address taken, return true to indicate we can't do
75  /// anything with it.
76  static bool analyzeGlobal(const Value *V, GlobalStatus &GS);
77
78  GlobalStatus();
79};
80}
81
82#endif
83