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 
15 namespace llvm {
16 class Value;
17 class 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 ///
23 bool 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.
28 struct 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