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 /// 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 via StoredOnceStore 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 via the store instruction. 60 const StoreInst *StoredOnceStore = nullptr; 61 62 /// If only one value (besides the initializer constant) is ever stored to 63 /// this global return the stored value. 64 Value *getStoredOnceValue() const { 65 return (StoredType == StoredOnce && StoredOnceStore) 66 ? StoredOnceStore->getOperand(0) 67 : nullptr; 68 } 69 70 /// These start out null/false. When the first accessing function is noticed, 71 /// it is recorded. When a second different accessing function is noticed, 72 /// HasMultipleAccessingFunctions is set to true. 73 const Function *AccessingFunction = nullptr; 74 bool HasMultipleAccessingFunctions = false; 75 76 /// Set to the strongest atomic ordering requirement. 77 AtomicOrdering Ordering = AtomicOrdering::NotAtomic; 78 79 GlobalStatus(); 80 81 /// Look at all uses of the global and fill in the GlobalStatus structure. If 82 /// the global has its address taken, return true to indicate we can't do 83 /// anything with it. 84 static bool analyzeGlobal(const Value *V, GlobalStatus &GS); 85 }; 86 87 } // end namespace llvm 88 89 #endif // LLVM_TRANSFORMS_UTILS_GLOBALSTATUS_H 90