1 files changed, 101 insertions, 0 deletions
diff --git a/llvm/lib/Transforms/IPO/ElimAvailExtern.cpp b/llvm/lib/Transforms/IPO/ElimAvailExtern.cpp
new file mode 100644
index 000000000000..fc52db562c62
--- /dev/null
+++ b/llvm/lib/Transforms/IPO/ElimAvailExtern.cpp
@@ -0,0 +1,101 @@
+//===- ElimAvailExtern.cpp - DCE unreachable internal functions -----------===//
+//
+// 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 transform is designed to eliminate available external global
+// definitions from the program, turning them into declarations.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/IPO/ElimAvailExtern.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/IR/Constant.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/GlobalValue.h"
+#include "llvm/IR/GlobalVariable.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Pass.h"
+#include "llvm/Transforms/IPO.h"
+#include "llvm/Transforms/Utils/GlobalStatus.h"
+
+using namespace llvm;
+
+#define DEBUG_TYPE "elim-avail-extern"
+
+STATISTIC(NumFunctions, "Number of functions removed");
+STATISTIC(NumVariables, "Number of global variables removed");
+
+static bool eliminateAvailableExternally(Module &M) {
+  bool Changed = false;
+
+  // Drop initializers of available externally global variables.
+  for (GlobalVariable &GV : M.globals()) {
+    if (!GV.hasAvailableExternallyLinkage())
+      continue;
+    if (GV.hasInitializer()) {
+      Constant *Init = GV.getInitializer();
+      GV.setInitializer(nullptr);
+      if (isSafeToDestroyConstant(Init))
+        Init->destroyConstant();
+    }
+    GV.removeDeadConstantUsers();
+    GV.setLinkage(GlobalValue::ExternalLinkage);
+    NumVariables++;
+    Changed = true;
+  }
+
+  // Drop the bodies of available externally functions.
+  for (Function &F : M) {
+    if (!F.hasAvailableExternallyLinkage())
+      continue;
+    if (!F.isDeclaration())
+      // This will set the linkage to external
+      F.deleteBody();
+    F.removeDeadConstantUsers();
+    NumFunctions++;
+    Changed = true;
+  }
+
+  return Changed;
+}
+
+PreservedAnalyses
+EliminateAvailableExternallyPass::run(Module &M, ModuleAnalysisManager &) {
+  if (!eliminateAvailableExternally(M))
+    return PreservedAnalyses::all();
+  return PreservedAnalyses::none();
+}
+
+namespace {
+
+struct EliminateAvailableExternallyLegacyPass : public ModulePass {
+  static char ID; // Pass identification, replacement for typeid
+
+  EliminateAvailableExternallyLegacyPass() : ModulePass(ID) {
+    initializeEliminateAvailableExternallyLegacyPassPass(
+        *PassRegistry::getPassRegistry());
+  }
+
+  // run - Do the EliminateAvailableExternally pass on the specified module,
+  // optionally updating the specified callgraph to reflect the changes.
+  bool runOnModule(Module &M) override {
+    if (skipModule(M))
+      return false;
+    return eliminateAvailableExternally(M);
+  }
+};
+
+} // end anonymous namespace
+
+char EliminateAvailableExternallyLegacyPass::ID = 0;
+
+INITIALIZE_PASS(EliminateAvailableExternallyLegacyPass, "elim-avail-extern",
+                "Eliminate Available Externally Globals", false, false)
+
+ModulePass *llvm::createEliminateAvailableExternallyPass() {
+  return new EliminateAvailableExternallyLegacyPass();
+}