LLVM  10.0.0svn
CanonicalizeAliases.cpp
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1 //===- CanonicalizeAliases.cpp - ThinLTO Support: Canonicalize Aliases ----===//
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 // Currently this file implements partial alias canonicalization, to
10 // flatten chains of aliases (also done by GlobalOpt, but not on for
11 // O0 compiles). E.g.
12 // @a = alias i8, i8 *@b
13 // @b = alias i8, i8 *@g
14 //
15 // will be converted to:
16 // @a = alias i8, i8 *@g <-- @a is now an alias to base object @g
17 // @b = alias i8, i8 *@g
18 //
19 // Eventually this file will implement full alias canonicalation, so that
20 // all aliasees are private anonymous values. E.g.
21 // @a = alias i8, i8 *@g
22 // @g = global i8 0
23 //
24 // will be converted to:
25 // @0 = private global
26 // @a = alias i8, i8* @0
27 // @g = alias i8, i8* @0
28 //
29 // This simplifies optimization and ThinLTO linking of the original symbols.
30 //===----------------------------------------------------------------------===//
31 
33 
34 #include "llvm/IR/Operator.h"
35 #include "llvm/IR/ValueHandle.h"
36 #include "llvm/Pass.h"
37 
38 using namespace llvm;
39 
40 namespace {
41 
42 static Constant *canonicalizeAlias(Constant *C, bool &Changed) {
43  if (auto *GA = dyn_cast<GlobalAlias>(C)) {
44  auto *NewAliasee = canonicalizeAlias(GA->getAliasee(), Changed);
45  if (NewAliasee != GA->getAliasee()) {
46  GA->setAliasee(NewAliasee);
47  Changed = true;
48  }
49  return NewAliasee;
50  }
51 
52  auto *CE = dyn_cast<ConstantExpr>(C);
53  if (!CE)
54  return C;
55 
56  std::vector<Constant *> Ops;
57  for (Use &U : CE->operands())
58  Ops.push_back(canonicalizeAlias(cast<Constant>(U), Changed));
59  return CE->getWithOperands(Ops);
60 }
61 
62 /// Convert aliases to canonical form.
63 static bool canonicalizeAliases(Module &M) {
64  bool Changed = false;
65  for (auto &GA : M.aliases())
66  canonicalizeAlias(&GA, Changed);
67  return Changed;
68 }
69 
70 // Legacy pass that canonicalizes aliases.
71 class CanonicalizeAliasesLegacyPass : public ModulePass {
72 
73 public:
74  /// Pass identification, replacement for typeid
75  static char ID;
76 
77  /// Specify pass name for debug output
78  StringRef getPassName() const override { return "Canonicalize Aliases"; }
79 
80  explicit CanonicalizeAliasesLegacyPass() : ModulePass(ID) {}
81 
82  bool runOnModule(Module &M) override { return canonicalizeAliases(M); }
83 };
85 
86 } // anonymous namespace
87 
90  if (!canonicalizeAliases(M))
91  return PreservedAnalyses::all();
92 
93  return PreservedAnalyses::none();
94 }
95 
96 INITIALIZE_PASS_BEGIN(CanonicalizeAliasesLegacyPass, "canonicalize-aliases",
97  "Canonicalize aliases", false, false)
98 INITIALIZE_PASS_END(CanonicalizeAliasesLegacyPass, "canonicalize-aliases",
99  "Canonicalize aliases", false, false)
100 
101 namespace llvm {
103  return new CanonicalizeAliasesLegacyPass();
104 }
105 } // namespace llvm
uint64_t CallInst * C
This class represents lattice values for constants.
Definition: AllocatorList.h:23
A Module instance is used to store all the information related to an LLVM module. ...
Definition: Module.h:66
INITIALIZE_PASS_BEGIN(CanonicalizeAliasesLegacyPass, "canonicalize-aliases", "Canonicalize aliases", false, false) INITIALIZE_PASS_END(CanonicalizeAliasesLegacyPass
ModulePass * createCanonicalizeAliasesPass()
PreservedAnalyses run(Module &M, ModuleAnalysisManager &AM)
A Use represents the edge between a Value definition and its users.
Definition: Use.h:55
Windows NT (Windows on ARM)
A constant value that is initialized with an expression using other constant values.
Definition: Constants.h:888
canonicalize aliases
static PreservedAnalyses none()
Convenience factory function for the empty preserved set.
Definition: PassManager.h:157
A set of analyses that are preserved following a run of a transformation pass.
Definition: PassManager.h:154
This is an important base class in LLVM.
Definition: Constant.h:41
static PreservedAnalyses all()
Construct a special preserved set that preserves all passes.
Definition: PassManager.h:160
INITIALIZE_PASS_END(RegBankSelect, DEBUG_TYPE, "Assign register bank of generic virtual registers", false, false) RegBankSelect
ModulePass class - This class is used to implement unstructured interprocedural optimizations and ana...
Definition: Pass.h:224
LLVM_NODISCARD std::enable_if<!is_simple_type< Y >::value, typename cast_retty< X, const Y >::ret_type >::type dyn_cast(const Y &Val)
Definition: Casting.h:332
StringRef - Represent a constant reference to a string, i.e.
Definition: StringRef.h:48
A container for analyses that lazily runs them and caches their results.
iterator_range< alias_iterator > aliases()
Definition: Module.h:628