1 //===- CanonicalizeAliases.cpp - ThinLTO Support: Canonicalize Aliases ----===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // Currently this file implements partial alias canonicalization, to
11 // flatten chains of aliases (also done by GlobalOpt, but not on for
13 // @a = alias i8, i8 *@b
14 // @b = alias i8, i8 *@g
16 // will be converted to:
17 // @a = alias i8, i8 *@g <-- @a is now an alias to base object @g
18 // @b = alias i8, i8 *@g
20 // Eventually this file will implement full alias canonicalation, so that
21 // all aliasees are private anonymous values. E.g.
22 // @a = alias i8, i8 *@g
25 // will be converted to:
26 // @0 = private global
27 // @a = alias i8, i8* @0
28 // @g = alias i8, i8* @0
30 // This simplifies optimization and ThinLTO linking of the original symbols.
31 //===----------------------------------------------------------------------===//
33 #include "llvm/Transforms/Utils/CanonicalizeAliases.h"
35 #include "llvm/IR/Operator.h"
36 #include "llvm/IR/ValueHandle.h"
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);
52 auto *CE = dyn_cast<ConstantExpr>(C);
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);
62 /// Convert aliases to canonical form.
63 static bool canonicalizeAliases(Module &M) {
65 for (auto &GA : M.aliases())
66 canonicalizeAlias(&GA, Changed);
70 // Legacy pass that canonicalizes aliases.
71 class CanonicalizeAliasesLegacyPass : public ModulePass {
74 /// Pass identification, replacement for typeid
77 /// Specify pass name for debug output
78 StringRef getPassName() const override { return "Canonicalize Aliases"; }
80 explicit CanonicalizeAliasesLegacyPass() : ModulePass(ID) {}
82 bool runOnModule(Module &M) override { return canonicalizeAliases(M); }
84 char CanonicalizeAliasesLegacyPass::ID = 0;
86 } // anonymous namespace
88 PreservedAnalyses CanonicalizeAliasesPass::run(Module &M,
89 ModuleAnalysisManager &AM) {
90 if (!canonicalizeAliases(M))
91 return PreservedAnalyses::all();
93 return PreservedAnalyses::none();
96 INITIALIZE_PASS_BEGIN(CanonicalizeAliasesLegacyPass, "canonicalize-aliases",
97 "Canonicalize aliases", false, false)
98 INITIALIZE_PASS_END(CanonicalizeAliasesLegacyPass, "canonicalize-aliases",
99 "Canonicalize aliases", false, false)
102 ModulePass *createCanonicalizeAliasesPass() {
103 return new CanonicalizeAliasesLegacyPass();