LLVM  13.0.0git
GlobalStatus.cpp
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1 //===-- GlobalStatus.cpp - Compute status info for globals -----------------==//
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 
10 #include "llvm/ADT/SmallPtrSet.h"
11 #include "llvm/IR/BasicBlock.h"
12 #include "llvm/IR/Constant.h"
13 #include "llvm/IR/Constants.h"
14 #include "llvm/IR/GlobalValue.h"
15 #include "llvm/IR/GlobalVariable.h"
16 #include "llvm/IR/InstrTypes.h"
17 #include "llvm/IR/Instruction.h"
18 #include "llvm/IR/Instructions.h"
19 #include "llvm/IR/IntrinsicInst.h"
20 #include "llvm/IR/Use.h"
21 #include "llvm/IR/User.h"
22 #include "llvm/IR/Value.h"
24 #include "llvm/Support/Casting.h"
25 #include <algorithm>
26 #include <cassert>
27 
28 using namespace llvm;
29 
30 /// Return the stronger of the two ordering. If the two orderings are acquire
31 /// and release, then return AcquireRelease.
32 ///
37  return (AtomicOrdering)std::max((unsigned)X, (unsigned)Y);
38 }
39 
40 /// It is safe to destroy a constant iff it is only used by constants itself.
41 /// Note that constants cannot be cyclic, so this test is pretty easy to
42 /// implement recursively.
43 ///
45  if (isa<GlobalValue>(C))
46  return false;
47 
48  if (isa<ConstantData>(C))
49  return false;
50 
51  for (const User *U : C->users())
52  if (const Constant *CU = dyn_cast<Constant>(U)) {
54  return false;
55  } else
56  return false;
57  return true;
58 }
59 
60 static bool analyzeGlobalAux(const Value *V, GlobalStatus &GS,
61  SmallPtrSetImpl<const Value *> &VisitedUsers) {
62  if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
63  if (GV->isExternallyInitialized())
64  GS.StoredType = GlobalStatus::StoredOnce;
65 
66  for (const Use &U : V->uses()) {
67  const User *UR = U.getUser();
68  if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(UR)) {
69  GS.HasNonInstructionUser = true;
70 
71  // If the result of the constantexpr isn't pointer type, then we won't
72  // know to expect it in various places. Just reject early.
73  if (!isa<PointerType>(CE->getType()))
74  return true;
75 
76  // FIXME: Do we need to add constexpr selects to VisitedUsers?
77  if (analyzeGlobalAux(CE, GS, VisitedUsers))
78  return true;
79  } else if (const Instruction *I = dyn_cast<Instruction>(UR)) {
80  if (!GS.HasMultipleAccessingFunctions) {
81  const Function *F = I->getParent()->getParent();
82  if (!GS.AccessingFunction)
83  GS.AccessingFunction = F;
84  else if (GS.AccessingFunction != F)
85  GS.HasMultipleAccessingFunctions = true;
86  }
87  if (const LoadInst *LI = dyn_cast<LoadInst>(I)) {
88  GS.IsLoaded = true;
89  // Don't hack on volatile loads.
90  if (LI->isVolatile())
91  return true;
92  GS.Ordering = strongerOrdering(GS.Ordering, LI->getOrdering());
93  } else if (const StoreInst *SI = dyn_cast<StoreInst>(I)) {
94  // Don't allow a store OF the address, only stores TO the address.
95  if (SI->getOperand(0) == V)
96  return true;
97 
98  // Don't hack on volatile stores.
99  if (SI->isVolatile())
100  return true;
101 
102  GS.Ordering = strongerOrdering(GS.Ordering, SI->getOrdering());
103 
104  // If this is a direct store to the global (i.e., the global is a scalar
105  // value, not an aggregate), keep more specific information about
106  // stores.
107  if (GS.StoredType != GlobalStatus::Stored) {
108  if (const GlobalVariable *GV =
109  dyn_cast<GlobalVariable>(SI->getOperand(1))) {
110  Value *StoredVal = SI->getOperand(0);
111 
112  if (Constant *C = dyn_cast<Constant>(StoredVal)) {
113  if (C->isThreadDependent()) {
114  // The stored value changes between threads; don't track it.
115  return true;
116  }
117  }
118 
119  if (GV->hasInitializer() && StoredVal == GV->getInitializer()) {
120  if (GS.StoredType < GlobalStatus::InitializerStored)
121  GS.StoredType = GlobalStatus::InitializerStored;
122  } else if (isa<LoadInst>(StoredVal) &&
123  cast<LoadInst>(StoredVal)->getOperand(0) == GV) {
124  if (GS.StoredType < GlobalStatus::InitializerStored)
125  GS.StoredType = GlobalStatus::InitializerStored;
126  } else if (GS.StoredType < GlobalStatus::StoredOnce) {
127  GS.StoredType = GlobalStatus::StoredOnce;
128  GS.StoredOnceValue = StoredVal;
129  } else if (GS.StoredType == GlobalStatus::StoredOnce &&
130  GS.StoredOnceValue == StoredVal) {
131  // noop.
132  } else {
133  GS.StoredType = GlobalStatus::Stored;
134  }
135  } else {
136  GS.StoredType = GlobalStatus::Stored;
137  }
138  }
139  } else if (isa<BitCastInst>(I) || isa<GetElementPtrInst>(I) ||
140  isa<AddrSpaceCastInst>(I)) {
141  // Skip over bitcasts and GEPs; we don't care about the type or offset
142  // of the pointer.
143  if (analyzeGlobalAux(I, GS, VisitedUsers))
144  return true;
145  } else if (isa<SelectInst>(I) || isa<PHINode>(I)) {
146  // Look through selects and PHIs to find if the pointer is
147  // conditionally accessed. Make sure we only visit an instruction
148  // once; otherwise, we can get infinite recursion or exponential
149  // compile time.
150  if (VisitedUsers.insert(I).second)
151  if (analyzeGlobalAux(I, GS, VisitedUsers))
152  return true;
153  } else if (isa<CmpInst>(I)) {
154  GS.IsCompared = true;
155  } else if (const MemTransferInst *MTI = dyn_cast<MemTransferInst>(I)) {
156  if (MTI->isVolatile())
157  return true;
158  if (MTI->getArgOperand(0) == V)
159  GS.StoredType = GlobalStatus::Stored;
160  if (MTI->getArgOperand(1) == V)
161  GS.IsLoaded = true;
162  } else if (const MemSetInst *MSI = dyn_cast<MemSetInst>(I)) {
163  assert(MSI->getArgOperand(0) == V && "Memset only takes one pointer!");
164  if (MSI->isVolatile())
165  return true;
166  GS.StoredType = GlobalStatus::Stored;
167  } else if (const auto *CB = dyn_cast<CallBase>(I)) {
168  if (!CB->isCallee(&U))
169  return true;
170  GS.IsLoaded = true;
171  } else {
172  return true; // Any other non-load instruction might take address!
173  }
174  } else if (const Constant *C = dyn_cast<Constant>(UR)) {
175  GS.HasNonInstructionUser = true;
176  // We might have a dead and dangling constant hanging off of here.
178  return true;
179  } else {
180  GS.HasNonInstructionUser = true;
181  // Otherwise must be some other user.
182  return true;
183  }
184  }
185 
186  return false;
187 }
188 
189 GlobalStatus::GlobalStatus() = default;
190 
192  SmallPtrSet<const Value *, 16> VisitedUsers;
193  return analyzeGlobalAux(V, GS, VisitedUsers);
194 }
llvm::AtomicOrdering::AcquireRelease
@ AcquireRelease
llvm
Definition: AllocatorList.h:23
IntrinsicInst.h
AtomicOrdering.h
llvm::MemTransferInst
This class wraps the llvm.memcpy/memmove intrinsics.
Definition: IntrinsicInst.h:877
llvm::Function
Definition: Function.h:61
llvm::GlobalVariable
Definition: GlobalVariable.h:40
llvm::X86AS::GS
@ GS
Definition: X86.h:187
llvm::GlobalStatus::analyzeGlobal
static bool analyzeGlobal(const Value *V, GlobalStatus &GS)
Look at all uses of the global and fill in the GlobalStatus structure.
Definition: GlobalStatus.cpp:191
llvm::SmallPtrSet
SmallPtrSet - This class implements a set which is optimized for holding SmallSize or less elements.
Definition: SmallPtrSet.h:449
Use.h
F
#define F(x, y, z)
Definition: MD5.cpp:56
Instruction.h
llvm::GlobalStatus
As we analyze each global, keep track of some information about it.
Definition: GlobalStatus.h:29
GlobalValue.h
Constants.h
llvm::User
Definition: User.h:44
C
(vector float) vec_cmpeq(*A, *B) C
Definition: README_ALTIVEC.txt:86
InstrTypes.h
Y
static GCMetadataPrinterRegistry::Add< OcamlGCMetadataPrinter > Y("ocaml", "ocaml 3.10-compatible collector")
strongerOrdering
static AtomicOrdering strongerOrdering(AtomicOrdering X, AtomicOrdering Y)
Return the stronger of the two ordering.
Definition: GlobalStatus.cpp:33
llvm::Value::uses
iterator_range< use_iterator > uses()
Definition: Value.h:377
llvm::Instruction
Definition: Instruction.h:45
llvm::AtomicOrdering::Acquire
@ Acquire
SmallPtrSet.h
llvm::isSafeToDestroyConstant
bool isSafeToDestroyConstant(const Constant *C)
It is safe to destroy a constant iff it is only used by constants itself.
Definition: GlobalStatus.cpp:44
X
static GCMetadataPrinterRegistry::Add< ErlangGCPrinter > X("erlang", "erlang-compatible garbage collector")
llvm::MemSetInst
This class wraps the llvm.memset intrinsic.
Definition: IntrinsicInst.h:865
llvm::AtomicOrdering
AtomicOrdering
Atomic ordering for LLVM's memory model.
Definition: AtomicOrdering.h:56
BasicBlock.h
llvm::StoreInst
An instruction for storing to memory.
Definition: Instructions.h:303
llvm::Constant
This is an important base class in LLVM.
Definition: Constant.h:41
GlobalStatus.h
I
#define I(x, y, z)
Definition: MD5.cpp:59
assert
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
SI
StandardInstrumentations SI(Debug, VerifyEach)
llvm::GlobalStatus::Stored
@ Stored
This global is stored to by multiple values or something else that we cannot track.
Definition: GlobalStatus.h:54
llvm::GlobalStatus::InitializerStored
@ InitializerStored
This global is stored to, but the only thing stored is the constant it was initialized with.
Definition: GlobalStatus.h:44
llvm::LoadInst
An instruction for reading from memory.
Definition: Instructions.h:174
llvm::AtomicOrdering::Release
@ Release
analyzeGlobalAux
static bool analyzeGlobalAux(const Value *V, GlobalStatus &GS, SmallPtrSetImpl< const Value * > &VisitedUsers)
Definition: GlobalStatus.cpp:60
Constant.h
llvm::ConstantExpr
A constant value that is initialized with an expression using other constant values.
Definition: Constants.h:931
GlobalVariable.h
Casting.h
llvm::GlobalStatus::GlobalStatus
GlobalStatus()
llvm::GlobalStatus::StoredOnce
@ StoredOnce
This global is stored to, but only its initializer and one other value is ever stored to it.
Definition: GlobalStatus.h:50
Instructions.h
User.h
llvm::max
Align max(MaybeAlign Lhs, Align Rhs)
Definition: Alignment.h:340
llvm::SmallPtrSetImpl< const Value * >
Value.h
CU
Definition: AArch64AsmBackend.cpp:499
llvm::Value
LLVM Value Representation.
Definition: Value.h:75
llvm::Value::users
iterator_range< user_iterator > users()
Definition: Value.h:422
llvm::Use
A Use represents the edge between a Value definition and its users.
Definition: Use.h:44
llvm::SmallPtrSetImpl::insert
std::pair< iterator, bool > insert(PtrType Ptr)
Inserts Ptr if and only if there is no element in the container equal to Ptr.
Definition: SmallPtrSet.h:364