LLVM  6.0.0svn
GlobalStatus.h
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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 
14 
15 namespace llvm {
16 
17 class Constant;
18 class Function;
19 class Value;
20 
21 /// It is safe to destroy a constant iff it is only used by constants itself.
22 /// Note that constants cannot be cyclic, so this test is pretty easy to
23 /// implement recursively.
24 ///
26 
27 /// As we analyze each global, keep track of some information about it. If we
28 /// find out that the address of the global is taken, none of this info will be
29 /// accurate.
30 struct GlobalStatus {
31  /// True if the global's address is used in a comparison.
32  bool IsCompared = false;
33 
34  /// True if the global is ever loaded. If the global isn't ever loaded it
35  /// can be deleted.
36  bool IsLoaded = false;
37 
38  /// Keep track of what stores to the global look like.
39  enum StoredType {
40  /// There is no store to this global. It can thus be marked constant.
42 
43  /// This global is stored to, but the only thing stored is the constant it
44  /// was initialized with. This is only tracked for scalar globals.
46 
47  /// This global is stored to, but only its initializer and one other value
48  /// is ever stored to it. If this global isStoredOnce, we track the value
49  /// stored to it in StoredOnceValue below. This is only tracked for scalar
50  /// globals.
52 
53  /// This global is stored to by multiple values or something else that we
54  /// cannot track.
57 
58  /// If only one value (besides the initializer constant) is ever stored to
59  /// this global, keep track of what value it is.
60  Value *StoredOnceValue = nullptr;
61 
62  /// These start out null/false. When the first accessing function is noticed,
63  /// it is recorded. When a second different accessing function is noticed,
64  /// HasMultipleAccessingFunctions is set to true.
65  const Function *AccessingFunction = nullptr;
67 
68  /// Set to true if this global has a user that is not an instruction (e.g. a
69  /// constant expr or GV initializer).
70  bool HasNonInstructionUser = false;
71 
72  /// Set to the strongest atomic ordering requirement.
74 
75  GlobalStatus();
76 
77  /// Look at all uses of the global and fill in the GlobalStatus structure. If
78  /// the global has its address taken, return true to indicate we can't do
79  /// anything with it.
80  static bool analyzeGlobal(const Value *V, GlobalStatus &GS);
81 };
82 
83 } // end namespace llvm
84 
85 #endif // LLVM_TRANSFORMS_UTILS_GLOBALSTATUS_H
uint64_t CallInst * C
bool IsLoaded
True if the global is ever loaded.
Definition: GlobalStatus.h:36
Value * StoredOnceValue
If only one value (besides the initializer constant) is ever stored to this global, keep track of what value it is.
Definition: GlobalStatus.h:60
const Function * AccessingFunction
These start out null/false.
Definition: GlobalStatus.h:65
Atomic ordering constants.
Compute iterated dominance frontiers using a linear time algorithm.
Definition: AllocatorList.h:24
bool HasMultipleAccessingFunctions
Definition: GlobalStatus.h:66
This global is stored to, but the only thing stored is the constant it was initialized with...
Definition: GlobalStatus.h:45
StoredType
Keep track of what stores to the global look like.
Definition: GlobalStatus.h:39
bool HasNonInstructionUser
Set to true if this global has a user that is not an instruction (e.g.
Definition: GlobalStatus.h:70
AtomicOrdering
Atomic ordering for LLVM's memory model.
This global is stored to, but only its initializer and one other value is ever stored to it...
Definition: GlobalStatus.h:51
As we analyze each global, keep track of some information about it.
Definition: GlobalStatus.h:30
static bool analyzeGlobal(const Value *V, GlobalStatus &GS)
Look at all uses of the global and fill in the GlobalStatus structure.
bool isSafeToDestroyConstant(const Constant *C)
It is safe to destroy a constant iff it is only used by constants itself.
This global is stored to by multiple values or something else that we cannot track.
Definition: GlobalStatus.h:55
bool IsCompared
True if the global's address is used in a comparison.
Definition: GlobalStatus.h:32
AtomicOrdering Ordering
Set to the strongest atomic ordering requirement.
Definition: GlobalStatus.h:73
LLVM Value Representation.
Definition: Value.h:73
There is no store to this global. It can thus be marked constant.
Definition: GlobalStatus.h:41