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
