1 | //===- GlobalStatus.h - Compute status info for globals ---------*- C++ -*-===// |
2 | // |
3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
4 | // See https://llvm.org/LICENSE.txt for license information. |
5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
6 | // |
7 | //===----------------------------------------------------------------------===// |
8 | |
9 | #ifndef LLVM_TRANSFORMS_UTILS_GLOBALSTATUS_H |
10 | #define LLVM_TRANSFORMS_UTILS_GLOBALSTATUS_H |
11 | |
12 | #include "llvm/IR/Instructions.h" |
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 | /// Number of stores to the global. |
39 | unsigned NumStores = 0; |
40 | |
41 | /// Keep track of what stores to the global look like. |
42 | enum StoredType { |
43 | /// There is no store to this global. It can thus be marked constant. |
44 | NotStored, |
45 | |
46 | /// This global is stored to, but the only thing stored is the constant it |
47 | /// was initialized with. This is only tracked for scalar globals. |
48 | InitializerStored, |
49 | |
50 | /// This global is stored to, but only its initializer and one other value |
51 | /// is ever stored to it. If this global isStoredOnce, we track the value |
52 | /// stored to it via StoredOnceStore below. This is only tracked for scalar |
53 | /// globals. |
54 | StoredOnce, |
55 | |
56 | /// This global is stored to by multiple values or something else that we |
57 | /// cannot track. |
58 | Stored |
59 | } StoredType = NotStored; |
60 | |
61 | /// If only one value (besides the initializer constant) is ever stored to |
62 | /// this global, keep track of what value it is via the store instruction. |
63 | const StoreInst *StoredOnceStore = nullptr; |
64 | |
65 | /// If only one value (besides the initializer constant) is ever stored to |
66 | /// this global return the stored value. |
67 | Value *getStoredOnceValue() const { |
68 | return (StoredType == StoredOnce && StoredOnceStore) |
69 | ? StoredOnceStore->getOperand(i_nocapture: 0) |
70 | : nullptr; |
71 | } |
72 | |
73 | /// These start out null/false. When the first accessing function is noticed, |
74 | /// it is recorded. When a second different accessing function is noticed, |
75 | /// HasMultipleAccessingFunctions is set to true. |
76 | const Function *AccessingFunction = nullptr; |
77 | bool HasMultipleAccessingFunctions = false; |
78 | |
79 | /// Set to the strongest atomic ordering requirement. |
80 | AtomicOrdering Ordering = AtomicOrdering::NotAtomic; |
81 | |
82 | GlobalStatus(); |
83 | |
84 | /// Look at all uses of the global and fill in the GlobalStatus structure. If |
85 | /// the global has its address taken, return true to indicate we can't do |
86 | /// anything with it. |
87 | static bool analyzeGlobal(const Value *V, GlobalStatus &GS); |
88 | }; |
89 | |
90 | } // end namespace llvm |
91 | |
92 | #endif // LLVM_TRANSFORMS_UTILS_GLOBALSTATUS_H |
93 | |