1 files changed, 105 insertions, 0 deletions
diff --git a/llvm/lib/Transforms/Utils/CanonicalizeAliases.cpp b/llvm/lib/Transforms/Utils/CanonicalizeAliases.cpp
new file mode 100644
index 000000000000..3c7c8d872595
--- /dev/null
+++ b/llvm/lib/Transforms/Utils/CanonicalizeAliases.cpp
@@ -0,0 +1,105 @@
+//===- 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/Operator.h"
+#include "llvm/IR/ValueHandle.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;
+}
+
+// Legacy pass that canonicalizes aliases.
+class CanonicalizeAliasesLegacyPass : public ModulePass {
+
+public:
+  /// Pass identification, replacement for typeid
+  static char ID;
+
+  /// Specify pass name for debug output
+  StringRef getPassName() const override { return "Canonicalize Aliases"; }
+
+  explicit CanonicalizeAliasesLegacyPass() : ModulePass(ID) {}
+
+  bool runOnModule(Module &M) override { return canonicalizeAliases(M); }
+};
+char CanonicalizeAliasesLegacyPass::ID = 0;
+
+} // anonymous namespace
+
+PreservedAnalyses CanonicalizeAliasesPass::run(Module &M,
+                                               ModuleAnalysisManager &AM) {
+  if (!canonicalizeAliases(M))
+    return PreservedAnalyses::all();
+
+  return PreservedAnalyses::none();
+}
+
+INITIALIZE_PASS_BEGIN(CanonicalizeAliasesLegacyPass, "canonicalize-aliases",
+                      "Canonicalize aliases", false, false)
+INITIALIZE_PASS_END(CanonicalizeAliasesLegacyPass, "canonicalize-aliases",
+                    "Canonicalize aliases", false, false)
+
+namespace llvm {
+ModulePass *createCanonicalizeAliasesPass() {
+  return new CanonicalizeAliasesLegacyPass();
+}
+} // namespace llvm