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//===- CanonicalizeAliases.cpp - ThinLTO Support: Canonicalize Aliases ----===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// Currently this file implements partial alias canonicalization, to
// flatten chains of aliases (also done by GlobalOpt, but not on for
// O0 compiles). E.g.
// @a = alias i8, i8 *@b
// @b = alias i8, i8 *@g
//
// will be converted to:
// @a = alias i8, i8 *@g <-- @a is now an alias to base object @g
// @b = alias i8, i8 *@g
//
// Eventually this file will implement full alias canonicalation, so that
// all aliasees are private anonymous values. E.g.
// @a = alias i8, i8 *@g
// @g = global i8 0
//
// will be converted to:
// @0 = private global
// @a = alias i8, i8* @0
// @g = alias i8, i8* @0
//
// This simplifies optimization and ThinLTO linking of the original symbols.
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Utils/CanonicalizeAliases.h"
#include "llvm/IR/Constants.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
using namespace llvm;
namespace {
static Constant *canonicalizeAlias(Constant *C, bool &Changed) {
if (auto *GA = dyn_cast<GlobalAlias>(C)) {
auto *NewAliasee = canonicalizeAlias(GA->getAliasee(), Changed);
if (NewAliasee != GA->getAliasee()) {
GA->setAliasee(NewAliasee);
Changed = true;
}
return NewAliasee;
}
auto *CE = dyn_cast<ConstantExpr>(C);
if (!CE)
return C;
std::vector<Constant *> Ops;
for (Use &U : CE->operands())
Ops.push_back(canonicalizeAlias(cast<Constant>(U), Changed));
return CE->getWithOperands(Ops);
}
/// Convert aliases to canonical form.
static bool canonicalizeAliases(Module &M) {
bool Changed = false;
for (auto &GA : M.aliases())
canonicalizeAlias(&GA, Changed);
return Changed;
}
} // anonymous namespace
PreservedAnalyses CanonicalizeAliasesPass::run(Module &M,
ModuleAnalysisManager &AM) {
if (!canonicalizeAliases(M))
return PreservedAnalyses::all();
return PreservedAnalyses::none();
}
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