1 files changed, 290 insertions, 0 deletions
diff --git a/llvm/lib/Transforms/IPO/Internalize.cpp b/llvm/lib/Transforms/IPO/Internalize.cpp
new file mode 100644
index 000000000000..2e269604e379
--- /dev/null
+++ b/llvm/lib/Transforms/IPO/Internalize.cpp
@@ -0,0 +1,290 @@
+//===-- Internalize.cpp - Mark functions internal -------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass loops over all of the functions and variables in the input module.
+// If the function or variable does not need to be preserved according to the
+// client supplied callback, it is marked as internal.
+//
+// This transformation would not be legal in a regular compilation, but it gets
+// extra information from the linker about what is safe.
+//
+// For example: Internalizing a function with external linkage. Only if we are
+// told it is only used from within this module, it is safe to do it.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/IPO/Internalize.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/StringSet.h"
+#include "llvm/Analysis/CallGraph.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/LineIterator.h"
+#include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/IPO.h"
+#include "llvm/Transforms/Utils/GlobalStatus.h"
+using namespace llvm;
+
+#define DEBUG_TYPE "internalize"
+
+STATISTIC(NumAliases, "Number of aliases internalized");
+STATISTIC(NumFunctions, "Number of functions internalized");
+STATISTIC(NumGlobals, "Number of global vars internalized");
+
+// APIFile - A file which contains a list of symbols that should not be marked
+// external.
+static cl::opt<std::string>
+    APIFile("internalize-public-api-file", cl::value_desc("filename"),
+            cl::desc("A file containing list of symbol names to preserve"));
+
+// APIList - A list of symbols that should not be marked internal.
+static cl::list<std::string>
+    APIList("internalize-public-api-list", cl::value_desc("list"),
+            cl::desc("A list of symbol names to preserve"), cl::CommaSeparated);
+
+namespace {
+// Helper to load an API list to preserve from file and expose it as a functor
+// for internalization.
+class PreserveAPIList {
+public:
+  PreserveAPIList() {
+    if (!APIFile.empty())
+      LoadFile(APIFile);
+    ExternalNames.insert(APIList.begin(), APIList.end());
+  }
+
+  bool operator()(const GlobalValue &GV) {
+    return ExternalNames.count(GV.getName());
+  }
+
+private:
+  // Contains the set of symbols loaded from file
+  StringSet<> ExternalNames;
+
+  void LoadFile(StringRef Filename) {
+    // Load the APIFile...
+    ErrorOr<std::unique_ptr<MemoryBuffer>> Buf =
+        MemoryBuffer::getFile(Filename);
+    if (!Buf) {
+      errs() << "WARNING: Internalize couldn't load file '" << Filename
+             << "'! Continuing as if it's empty.\n";
+      return; // Just continue as if the file were empty
+    }
+    for (line_iterator I(*Buf->get(), true), E; I != E; ++I)
+      ExternalNames.insert(*I);
+  }
+};
+} // end anonymous namespace
+
+bool InternalizePass::shouldPreserveGV(const GlobalValue &GV) {
+  // Function must be defined here
+  if (GV.isDeclaration())
+    return true;
+
+  // Available externally is really just a "declaration with a body".
+  if (GV.hasAvailableExternallyLinkage())
+    return true;
+
+  // Assume that dllexported symbols are referenced elsewhere
+  if (GV.hasDLLExportStorageClass())
+    return true;
+
+  // Already local, has nothing to do.
+  if (GV.hasLocalLinkage())
+    return false;
+
+  // Check some special cases
+  if (AlwaysPreserved.count(GV.getName()))
+    return true;
+
+  return MustPreserveGV(GV);
+}
+
+bool InternalizePass::maybeInternalize(
+    GlobalValue &GV, const DenseSet<const Comdat *> &ExternalComdats) {
+  if (Comdat *C = GV.getComdat()) {
+    if (ExternalComdats.count(C))
+      return false;
+
+    // If a comdat is not externally visible we can drop it.
+    if (auto GO = dyn_cast<GlobalObject>(&GV))
+      GO->setComdat(nullptr);
+
+    if (GV.hasLocalLinkage())
+      return false;
+  } else {
+    if (GV.hasLocalLinkage())
+      return false;
+
+    if (shouldPreserveGV(GV))
+      return false;
+  }
+
+  GV.setVisibility(GlobalValue::DefaultVisibility);
+  GV.setLinkage(GlobalValue::InternalLinkage);
+  return true;
+}
+
+// If GV is part of a comdat and is externally visible, keep track of its
+// comdat so that we don't internalize any of its members.
+void InternalizePass::checkComdatVisibility(
+    GlobalValue &GV, DenseSet<const Comdat *> &ExternalComdats) {
+  Comdat *C = GV.getComdat();
+  if (!C)
+    return;
+
+  if (shouldPreserveGV(GV))
+    ExternalComdats.insert(C);
+}
+
+bool InternalizePass::internalizeModule(Module &M, CallGraph *CG) {
+  bool Changed = false;
+  CallGraphNode *ExternalNode = CG ? CG->getExternalCallingNode() : nullptr;
+
+  SmallPtrSet<GlobalValue *, 8> Used;
+  collectUsedGlobalVariables(M, Used, false);
+
+  // Collect comdat visiblity information for the module.
+  DenseSet<const Comdat *> ExternalComdats;
+  if (!M.getComdatSymbolTable().empty()) {
+    for (Function &F : M)
+      checkComdatVisibility(F, ExternalComdats);
+    for (GlobalVariable &GV : M.globals())
+      checkComdatVisibility(GV, ExternalComdats);
+    for (GlobalAlias &GA : M.aliases())
+      checkComdatVisibility(GA, ExternalComdats);
+  }
+
+  // We must assume that globals in llvm.used have a reference that not even
+  // the linker can see, so we don't internalize them.
+  // For llvm.compiler.used the situation is a bit fuzzy. The assembler and
+  // linker can drop those symbols. If this pass is running as part of LTO,
+  // one might think that it could just drop llvm.compiler.used. The problem
+  // is that even in LTO llvm doesn't see every reference. For example,
+  // we don't see references from function local inline assembly. To be
+  // conservative, we internalize symbols in llvm.compiler.used, but we
+  // keep llvm.compiler.used so that the symbol is not deleted by llvm.
+  for (GlobalValue *V : Used) {
+    AlwaysPreserved.insert(V->getName());
+  }
+
+  // Mark all functions not in the api as internal.
+  for (Function &I : M) {
+    if (!maybeInternalize(I, ExternalComdats))
+      continue;
+    Changed = true;
+
+    if (ExternalNode)
+      // Remove a callgraph edge from the external node to this function.
+      ExternalNode->removeOneAbstractEdgeTo((*CG)[&I]);
+
+    ++NumFunctions;
+    LLVM_DEBUG(dbgs() << "Internalizing func " << I.getName() << "\n");
+  }
+
+  // Never internalize the llvm.used symbol.  It is used to implement
+  // attribute((used)).
+  // FIXME: Shouldn't this just filter on llvm.metadata section??
+  AlwaysPreserved.insert("llvm.used");
+  AlwaysPreserved.insert("llvm.compiler.used");
+
+  // Never internalize anchors used by the machine module info, else the info
+  // won't find them.  (see MachineModuleInfo.)
+  AlwaysPreserved.insert("llvm.global_ctors");
+  AlwaysPreserved.insert("llvm.global_dtors");
+  AlwaysPreserved.insert("llvm.global.annotations");
+
+  // Never internalize symbols code-gen inserts.
+  // FIXME: We should probably add this (and the __stack_chk_guard) via some
+  // type of call-back in CodeGen.
+  AlwaysPreserved.insert("__stack_chk_fail");
+  AlwaysPreserved.insert("__stack_chk_guard");
+
+  // Mark all global variables with initializers that are not in the api as
+  // internal as well.
+  for (auto &GV : M.globals()) {
+    if (!maybeInternalize(GV, ExternalComdats))
+      continue;
+    Changed = true;
+
+    ++NumGlobals;
+    LLVM_DEBUG(dbgs() << "Internalized gvar " << GV.getName() << "\n");
+  }
+
+  // Mark all aliases that are not in the api as internal as well.
+  for (auto &GA : M.aliases()) {
+    if (!maybeInternalize(GA, ExternalComdats))
+      continue;
+    Changed = true;
+
+    ++NumAliases;
+    LLVM_DEBUG(dbgs() << "Internalized alias " << GA.getName() << "\n");
+  }
+
+  return Changed;
+}
+
+InternalizePass::InternalizePass() : MustPreserveGV(PreserveAPIList()) {}
+
+PreservedAnalyses InternalizePass::run(Module &M, ModuleAnalysisManager &AM) {
+  if (!internalizeModule(M, AM.getCachedResult<CallGraphAnalysis>(M)))
+    return PreservedAnalyses::all();
+
+  PreservedAnalyses PA;
+  PA.preserve<CallGraphAnalysis>();
+  return PA;
+}
+
+namespace {
+class InternalizeLegacyPass : public ModulePass {
+  // Client supplied callback to control wheter a symbol must be preserved.
+  std::function<bool(const GlobalValue &)> MustPreserveGV;
+
+public:
+  static char ID; // Pass identification, replacement for typeid
+
+  InternalizeLegacyPass() : ModulePass(ID), MustPreserveGV(PreserveAPIList()) {}
+
+  InternalizeLegacyPass(std::function<bool(const GlobalValue &)> MustPreserveGV)
+      : ModulePass(ID), MustPreserveGV(std::move(MustPreserveGV)) {
+    initializeInternalizeLegacyPassPass(*PassRegistry::getPassRegistry());
+  }
+
+  bool runOnModule(Module &M) override {
+    if (skipModule(M))
+      return false;
+
+    CallGraphWrapperPass *CGPass =
+        getAnalysisIfAvailable<CallGraphWrapperPass>();
+    CallGraph *CG = CGPass ? &CGPass->getCallGraph() : nullptr;
+    return internalizeModule(M, MustPreserveGV, CG);
+  }
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.setPreservesCFG();
+    AU.addPreserved<CallGraphWrapperPass>();
+  }
+};
+}
+
+char InternalizeLegacyPass::ID = 0;
+INITIALIZE_PASS(InternalizeLegacyPass, "internalize",
+                "Internalize Global Symbols", false, false)
+
+ModulePass *llvm::createInternalizePass() {
+  return new InternalizeLegacyPass();
+}
+
+ModulePass *llvm::createInternalizePass(
+    std::function<bool(const GlobalValue &)> MustPreserveGV) {
+  return new InternalizeLegacyPass(std::move(MustPreserveGV));
+}