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
