LLVM  14.0.0git
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  // If the result of the constantexpr isn't pointer type, then we won't
70  // know to expect it in various places. Just reject early.
71  if (!isa<PointerType>(CE->getType()))
72  return true;
73 
74  // FIXME: Do we need to add constexpr selects to VisitedUsers?
75  if (analyzeGlobalAux(CE, GS, VisitedUsers))
76  return true;
77  } else if (const Instruction *I = dyn_cast<Instruction>(UR)) {
78  if (!GS.HasMultipleAccessingFunctions) {
79  const Function *F = I->getParent()->getParent();
80  if (!GS.AccessingFunction)
81  GS.AccessingFunction = F;
82  else if (GS.AccessingFunction != F)
83  GS.HasMultipleAccessingFunctions = true;
84  }
85  if (const LoadInst *LI = dyn_cast<LoadInst>(I)) {
86  GS.IsLoaded = true;
87  // Don't hack on volatile loads.
88  if (LI->isVolatile())
89  return true;
90  GS.Ordering = strongerOrdering(GS.Ordering, LI->getOrdering());
91  } else if (const StoreInst *SI = dyn_cast<StoreInst>(I)) {
92  // Don't allow a store OF the address, only stores TO the address.
93  if (SI->getOperand(0) == V)
94  return true;
95 
96  // Don't hack on volatile stores.
97  if (SI->isVolatile())
98  return true;
99 
100  GS.Ordering = strongerOrdering(GS.Ordering, SI->getOrdering());
101 
102  // If this is a direct store to the global (i.e., the global is a scalar
103  // value, not an aggregate), keep more specific information about
104  // stores.
105  if (GS.StoredType != GlobalStatus::Stored) {
106  const Value *Ptr = SI->getPointerOperand()->stripPointerCasts();
107  if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) {
108  Value *StoredVal = SI->getOperand(0);
109 
110  if (Constant *C = dyn_cast<Constant>(StoredVal)) {
111  if (C->isThreadDependent()) {
112  // The stored value changes between threads; don't track it.
113  return true;
114  }
115  }
116 
117  if (GV->hasInitializer() && StoredVal == GV->getInitializer()) {
118  if (GS.StoredType < GlobalStatus::InitializerStored)
119  GS.StoredType = GlobalStatus::InitializerStored;
120  } else if (isa<LoadInst>(StoredVal) &&
121  cast<LoadInst>(StoredVal)->getOperand(0) == GV) {
122  if (GS.StoredType < GlobalStatus::InitializerStored)
123  GS.StoredType = GlobalStatus::InitializerStored;
124  } else if (GS.StoredType < GlobalStatus::StoredOnce) {
125  GS.StoredType = GlobalStatus::StoredOnce;
126  GS.StoredOnceStore = SI;
127  } else if (GS.StoredType == GlobalStatus::StoredOnce &&
128  GS.getStoredOnceValue() == StoredVal) {
129  // noop.
130  } else {
131  GS.StoredType = GlobalStatus::Stored;
132  }
133  } else {
134  GS.StoredType = GlobalStatus::Stored;
135  }
136  }
137  } else if (isa<BitCastInst>(I) || isa<GetElementPtrInst>(I) ||
138  isa<AddrSpaceCastInst>(I)) {
139  // Skip over bitcasts and GEPs; we don't care about the type or offset
140  // of the pointer.
141  if (analyzeGlobalAux(I, GS, VisitedUsers))
142  return true;
143  } else if (isa<SelectInst>(I) || isa<PHINode>(I)) {
144  // Look through selects and PHIs to find if the pointer is
145  // conditionally accessed. Make sure we only visit an instruction
146  // once; otherwise, we can get infinite recursion or exponential
147  // compile time.
148  if (VisitedUsers.insert(I).second)
149  if (analyzeGlobalAux(I, GS, VisitedUsers))
150  return true;
151  } else if (isa<CmpInst>(I)) {
152  GS.IsCompared = true;
153  } else if (const MemTransferInst *MTI = dyn_cast<MemTransferInst>(I)) {
154  if (MTI->isVolatile())
155  return true;
156  if (MTI->getArgOperand(0) == V)
157  GS.StoredType = GlobalStatus::Stored;
158  if (MTI->getArgOperand(1) == V)
159  GS.IsLoaded = true;
160  } else if (const MemSetInst *MSI = dyn_cast<MemSetInst>(I)) {
161  assert(MSI->getArgOperand(0) == V && "Memset only takes one pointer!");
162  if (MSI->isVolatile())
163  return true;
164  GS.StoredType = GlobalStatus::Stored;
165  } else if (const auto *CB = dyn_cast<CallBase>(I)) {
166  if (!CB->isCallee(&U))
167  return true;
168  GS.IsLoaded = true;
169  } else {
170  return true; // Any other non-load instruction might take address!
171  }
172  } else if (const Constant *C = dyn_cast<Constant>(UR)) {
173  // We might have a dead and dangling constant hanging off of here.
175  return true;
176  } else {
177  // Otherwise must be some other user.
178  return true;
179  }
180  }
181 
182  return false;
183 }
184 
185 GlobalStatus::GlobalStatus() = default;
186 
188  SmallPtrSet<const Value *, 16> VisitedUsers;
189  return analyzeGlobalAux(V, GS, VisitedUsers);
190 }
llvm::AtomicOrdering::AcquireRelease
@ AcquireRelease
llvm
This is an optimization pass for GlobalISel generic memory operations.
Definition: AllocatorList.h:23
IntrinsicInst.h
AtomicOrdering.h
llvm::MemTransferInst
This class wraps the llvm.memcpy/memmove intrinsics.
Definition: IntrinsicInst.h:969
llvm::Function
Definition: Function.h:62
llvm::GlobalVariable
Definition: GlobalVariable.h:39
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:187
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:55
Instruction.h
llvm::GlobalStatus
As we analyze each global, keep track of some information about it.
Definition: GlobalStatus.h:30
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:376
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:957
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:309
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:58
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:55
llvm::GlobalStatus::InitializerStored
@ InitializerStored
This global is stored to, but the only thing stored is the constant it was initialized with.
Definition: GlobalStatus.h:45
llvm::LoadInst
An instruction for reading from memory.
Definition: Instructions.h:180
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:971
GlobalVariable.h
Casting.h
llvm::GlobalStatus::GlobalStatus
GlobalStatus()
llvm::X86AS::GS
@ GS
Definition: X86.h:187
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:51
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:504
llvm::Value
LLVM Value Representation.
Definition: Value.h:74
llvm::Value::users
iterator_range< user_iterator > users()
Definition: Value.h:421
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