Add a pass to strip the bodies of available_externally functions so string

literals and `TypeInfo`s only referenced by them can be deleted by `-globaldce`.

gen/optimizer.cpp

@@ -222,6 +222,9 @@ static void addPassesForOptLevel(PassManager& pm) {
     }
 
     if (optimizeLevel >= 1) {
+#if LLVM_REV >= 68940
+        addPass(pm, createStripExternalsPass());
+#endif
         addPass(pm, createGlobalDCEPass());
     }
 

gen/passes/Passes.h

@@ -12,8 +12,11 @@ llvm::FunctionPass* createSimplifyDRuntimeCalls();
 
 #ifdef USE_METADATA
 llvm::FunctionPass* createGarbageCollect2Stack();
-llvm::ModulePass *createStripMetaData();
+llvm::ModulePass* createStripMetaData();
 #endif
 
+#if LLVM_REV >= 68940
+llvm::ModulePass* createStripExternalsPass();
+#endif
 
 #endif

gen/passes/StripExternals.cpp

@@ -0,0 +1,92 @@
+//===-- StripExternals.cpp - Strip available_externally symbols -----------===//
+//
+//                             The LLVM D Compiler
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This transform stips the bodies of available_externally functions and
+// initializers of available_externally globals, turning them into external
+// declarations.
+// This is useful to allow Global DCE (-globaldce) to clean up references to
+// globals only used by available_externally functions and initializers.
+//
+//===----------------------------------------------------------------------===//
+
+#include "gen/llvm-version.h"
+
+#if LLVM_REV >= 68940
+
+
+#define DEBUG_TYPE "strip-externals"
+
+#include "Passes.h"
+
+#include "llvm/Module.h"
+#include "llvm/Pass.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Support/Compiler.h"
+#include "llvm/Support/Debug.h"
+using namespace llvm;
+
+STATISTIC(NumFunctions, "Number of function bodies removed");
+STATISTIC(NumVariables, "Number of global initializers removed");
+
+namespace {
+  struct VISIBILITY_HIDDEN StripExternals : public ModulePass {
+    static char ID; // Pass identification, replacement for typeid
+    StripExternals() : ModulePass(&ID) {}
+
+    // run - Do the StripExternals pass on the specified module.
+    //
+    bool runOnModule(Module &M);
+  };
+}
+
+char StripExternals::ID = 0;
+static RegisterPass<StripExternals>
+X("strip-externals", "Strip available_externally bodies and initializers");
+
+ModulePass *createStripExternalsPass() { return new StripExternals(); }
+
+bool StripExternals::runOnModule(Module &M) {
+  bool Changed = false;
+
+  for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
+    if (I->hasAvailableExternallyLinkage()) {
+      assert(!I->isDeclaration()&&"Declarations can't be available_externally");
+      Changed = true;
+      ++NumFunctions;
+      if (I->use_empty()) {
+        DOUT << "Deleting function: " << *I;
+        I->eraseFromParent();
+      } else {
+        I->deleteBody();
+        DOUT << "Deleted function body: " << *I;
+      }
+    }
+  }
+
+  for (Module::global_iterator I = M.global_begin(), E = M.global_end();
+       I != E; ++I) {
+    if (I->hasAvailableExternallyLinkage()) {
+      assert(!I->isDeclaration()&&"Declarations can't be available_externally");
+      Changed = true;
+      ++NumVariables;
+      if (I->use_empty()) {
+        DOUT << "Deleting global: " << *I;
+        I->eraseFromParent();
+      } else {
+        I->setInitializer(0);
+        I->setLinkage(GlobalValue::ExternalLinkage);
+        DOUT << "Deleted initializer: " << *I;
+      }
+    }
+  }
+
+  return Changed;
+}
+
+#endif //LLVM_REV >= 68940