LLVM  9.0.0svn
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/CallSite.h"
13 #include "llvm/IR/Constant.h"
14 #include "llvm/IR/Constants.h"
15 #include "llvm/IR/GlobalValue.h"
16 #include "llvm/IR/GlobalVariable.h"
17 #include "llvm/IR/InstrTypes.h"
18 #include "llvm/IR/Instruction.h"
19 #include "llvm/IR/Instructions.h"
20 #include "llvm/IR/IntrinsicInst.h"
21 #include "llvm/IR/Use.h"
22 #include "llvm/IR/User.h"
23 #include "llvm/IR/Value.h"
25 #include "llvm/Support/Casting.h"
26 #include <algorithm>
27 #include <cassert>
28 
29 using namespace llvm;
30 
31 /// Return the stronger of the two ordering. If the two orderings are acquire
32 /// and release, then return AcquireRelease.
33 ///
38  return (AtomicOrdering)std::max((unsigned)X, (unsigned)Y);
39 }
40 
41 /// It is safe to destroy a constant iff it is only used by constants itself.
42 /// Note that constants cannot be cyclic, so this test is pretty easy to
43 /// implement recursively.
44 ///
46  if (isa<GlobalValue>(C))
47  return false;
48 
49  if (isa<ConstantData>(C))
50  return false;
51 
52  for (const User *U : C->users())
53  if (const Constant *CU = dyn_cast<Constant>(U)) {
55  return false;
56  } else
57  return false;
58  return true;
59 }
60 
61 static bool analyzeGlobalAux(const Value *V, GlobalStatus &GS,
62  SmallPtrSetImpl<const Value *> &VisitedUsers) {
63  if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
64  if (GV->isExternallyInitialized())
66 
67  for (const Use &U : V->uses()) {
68  const User *UR = U.getUser();
69  if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(UR)) {
70  GS.HasNonInstructionUser = true;
71 
72  // If the result of the constantexpr isn't pointer type, then we won't
73  // know to expect it in various places. Just reject early.
74  if (!isa<PointerType>(CE->getType()))
75  return true;
76 
77  // FIXME: Do we need to add constexpr selects to VisitedUsers?
78  if (analyzeGlobalAux(CE, GS, VisitedUsers))
79  return true;
80  } else if (const Instruction *I = dyn_cast<Instruction>(UR)) {
82  const Function *F = I->getParent()->getParent();
83  if (!GS.AccessingFunction)
84  GS.AccessingFunction = F;
85  else if (GS.AccessingFunction != F)
87  }
88  if (const LoadInst *LI = dyn_cast<LoadInst>(I)) {
89  GS.IsLoaded = true;
90  // Don't hack on volatile loads.
91  if (LI->isVolatile())
92  return true;
93  GS.Ordering = strongerOrdering(GS.Ordering, LI->getOrdering());
94  } else if (const StoreInst *SI = dyn_cast<StoreInst>(I)) {
95  // Don't allow a store OF the address, only stores TO the address.
96  if (SI->getOperand(0) == V)
97  return true;
98 
99  // Don't hack on volatile stores.
100  if (SI->isVolatile())
101  return true;
102 
103  GS.Ordering = strongerOrdering(GS.Ordering, SI->getOrdering());
104 
105  // If this is a direct store to the global (i.e., the global is a scalar
106  // value, not an aggregate), keep more specific information about
107  // stores.
108  if (GS.StoredType != GlobalStatus::Stored) {
109  if (const GlobalVariable *GV =
110  dyn_cast<GlobalVariable>(SI->getOperand(1))) {
111  Value *StoredVal = SI->getOperand(0);
112 
113  if (Constant *C = dyn_cast<Constant>(StoredVal)) {
114  if (C->isThreadDependent()) {
115  // The stored value changes between threads; don't track it.
116  return true;
117  }
118  }
119 
120  if (GV->hasInitializer() && StoredVal == GV->getInitializer()) {
123  } else if (isa<LoadInst>(StoredVal) &&
124  cast<LoadInst>(StoredVal)->getOperand(0) == GV) {
127  } else if (GS.StoredType < GlobalStatus::StoredOnce) {
129  GS.StoredOnceValue = StoredVal;
130  } else if (GS.StoredType == GlobalStatus::StoredOnce &&
131  GS.StoredOnceValue == StoredVal) {
132  // noop.
133  } else {
135  }
136  } else {
138  }
139  }
140  } else if (isa<BitCastInst>(I) || isa<GetElementPtrInst>(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)
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;
167  } else if (auto C = ImmutableCallSite(I)) {
168  if (!C.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 }
uint64_t CallInst * C
bool IsLoaded
True if the global is ever loaded.
Definition: GlobalStatus.h:35
static GCMetadataPrinterRegistry::Add< ErlangGCPrinter > X("erlang", "erlang-compatible garbage collector")
iterator_range< use_iterator > uses()
Definition: Value.h:354
Value * StoredOnceValue
If only one value (besides the initializer constant) is ever stored to this global, keep track of what value it is.
Definition: GlobalStatus.h:59
const Function * AccessingFunction
These start out null/false.
Definition: GlobalStatus.h:64
GCNRegPressure max(const GCNRegPressure &P1, const GCNRegPressure &P2)
Atomic ordering constants.
This class represents lattice values for constants.
Definition: AllocatorList.h:23
bool HasMultipleAccessingFunctions
Definition: GlobalStatus.h:65
This class wraps the llvm.memset intrinsic.
F(f)
An instruction for reading from memory.
Definition: Instructions.h:167
This defines the Use class.
This global is stored to, but the only thing stored is the constant it was initialized with...
Definition: GlobalStatus.h:44
static GCMetadataPrinterRegistry::Add< OcamlGCMetadataPrinter > Y("ocaml", "ocaml 3.10-compatible collector")
static bool analyzeGlobalAux(const Value *V, GlobalStatus &GS, SmallPtrSetImpl< const Value *> &VisitedUsers)
A Use represents the edge between a Value definition and its users.
Definition: Use.h:55
StoredType
Keep track of what stores to the global look like.
Definition: GlobalStatus.h:38
bool HasNonInstructionUser
Set to true if this global has a user that is not an instruction (e.g.
Definition: GlobalStatus.h:69
AtomicOrdering
Atomic ordering for LLVM&#39;s memory model.
A constant value that is initialized with an expression using other constant values.
Definition: Constants.h:888
An instruction for storing to memory.
Definition: Instructions.h:320
This global is stored to, but only its initializer and one other value is ever stored to it...
Definition: GlobalStatus.h:50
static AtomicOrdering strongerOrdering(AtomicOrdering X, AtomicOrdering Y)
Return the stronger of the two ordering.
As we analyze each global, keep track of some information about it.
Definition: GlobalStatus.h:29
* if(!EatIfPresent(lltok::kw_thread_local)) return false
ParseOptionalThreadLocal := /*empty.
This is an important base class in LLVM.
Definition: Constant.h:41
This file contains the declarations for the subclasses of Constant, which represent the different fla...
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:370
static bool analyzeGlobal(const Value *V, GlobalStatus &GS)
Look at all uses of the global and fill in the GlobalStatus structure.
bool isSafeToDestroyConstant(const Constant *C)
It is safe to destroy a constant iff it is only used by constants itself.
SmallPtrSet - This class implements a set which is optimized for holding SmallSize or less elements...
Definition: SmallPtrSet.h:417
bool isCallee(Value::const_user_iterator UI) const
Determine whether the passed iterator points to the callee operand&#39;s Use.
Definition: InstrTypes.h:1295
This global is stored to by multiple values or something else that we cannot track.
Definition: GlobalStatus.h:54
iterator_range< user_iterator > users()
Definition: Value.h:399
This class wraps the llvm.memcpy/memmove intrinsics.
bool IsCompared
True if the global&#39;s address is used in a comparison.
Definition: GlobalStatus.h:31
AtomicOrdering Ordering
Set to the strongest atomic ordering requirement.
Definition: GlobalStatus.h:72
Establish a view to a call site for examination.
Definition: CallSite.h:897
#define I(x, y, z)
Definition: MD5.cpp:58
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
LLVM Value Representation.
Definition: Value.h:72
for(unsigned i=Desc.getNumOperands(), e=OldMI.getNumOperands();i !=e;++i)