include/llvm/Transforms/Utils/GlobalStatus.h

   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/Support/AtomicOrdering.h"
  13
  14 namespace llvm {
  15
  16 class Constant;
  17 class Function;
  18 class Value;
  19
  20 /// It is safe to destroy a constant iff it is only used by constants itself.
  21 /// Note that constants cannot be cyclic, so this test is pretty easy to
  22 /// implement recursively.
  23 ///
  24 bool isSafeToDestroyConstant(const Constant *C);
  25
  26 /// As we analyze each global, keep track of some information about it.  If we
  27 /// find out that the address of the global is taken, none of this info will be
  28 /// accurate.
  29 struct GlobalStatus {
  30   /// True if the global's address is used in a comparison.
  31   bool IsCompared = false;
  32
  33   /// True if the global is ever loaded.  If the global isn't ever loaded it
  34   /// can be deleted.
  35   bool IsLoaded = false;
  36
  37   /// Keep track of what stores to the global look like.
  38   enum StoredType {
  39     /// There is no store to this global.  It can thus be marked constant.
  40     NotStored,
  41
  42     /// This global is stored to, but the only thing stored is the constant it
  43     /// was initialized with. This is only tracked for scalar globals.
  44     InitializerStored,
  45
  46     /// This global is stored to, but only its initializer and one other value
  47     /// is ever stored to it.  If this global isStoredOnce, we track the value
  48     /// stored to it in StoredOnceValue below.  This is only tracked for scalar
  49     /// globals.
  50     StoredOnce,
  51
  52     /// This global is stored to by multiple values or something else that we
  53     /// cannot track.
  54     Stored
  55   } StoredType = NotStored;
  56
  57   /// If only one value (besides the initializer constant) is ever stored to
  58   /// this global, keep track of what value it is.
  59   Value *StoredOnceValue = nullptr;
  60
  61   /// These start out null/false.  When the first accessing function is noticed,
  62   /// it is recorded. When a second different accessing function is noticed,
  63   /// HasMultipleAccessingFunctions is set to true.
  64   const Function *AccessingFunction = nullptr;
  65   bool HasMultipleAccessingFunctions = false;
  66
  67   /// Set to true if this global has a user that is not an instruction (e.g. a
  68   /// constant expr or GV initializer).
  69   bool HasNonInstructionUser = false;
  70
  71   /// Set to the strongest atomic ordering requirement.
  72   AtomicOrdering Ordering = AtomicOrdering::NotAtomic;
  73
  74   GlobalStatus();
  75
  76   /// Look at all uses of the global and fill in the GlobalStatus structure.  If
  77   /// the global has its address taken, return true to indicate we can't do
  78   /// anything with it.
  79   static bool analyzeGlobal(const Value *V, GlobalStatus &GS);
  80 };
  81
  82 } // end namespace llvm
  83
  84 #endif // LLVM_TRANSFORMS_UTILS_GLOBALSTATUS_H