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/Support/AtomicOrdering.h"
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 ///
25 bool isSafeToDestroyConstant(const Constant *C);
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.
41     NotStored,
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.
45     InitializerStored,
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.
51     StoredOnce,
52 
53     /// This global is stored to by multiple values or something else that we
54     /// cannot track.
55     Stored
56   } StoredType = NotStored;
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;
66   bool HasMultipleAccessingFunctions = false;
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.
73   AtomicOrdering Ordering = AtomicOrdering::NotAtomic;
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
86