PNaCl ABI: add passes to cleanup/finalize some linkage types and resolve aliases.

R=mseaborn@chromium.org,eliben@chromium.org
BUG= https://code.google.com/p/nativeclient/issues/detail?id=3339

Review URL: https://codereview.chromium.org/13036005

2 files changed, 110 insertions, 0 deletions

diff --git a/lib/Transforms/NaCl/CMakeLists.txt b/lib/Transforms/NaCl/CMakeLists.txt
index 6ba9dcc68b..5b1de88dc4 100644
--- a/lib/Transforms/NaCl/CMakeLists.txt
+++ b/lib/Transforms/NaCl/CMakeLists.txt
@@ -4,6 +4,7 @@ add_llvm_library(LLVMTransformsNaCl
   ExpandTls.cpp
   ExpandTlsConstantExpr.cpp
   ExpandVarArgs.cpp
+  GlobalCleanup.cpp
   )
 
 add_dependencies(LLVMTransformsNaCl intrinsics_gen)
diff --git a/lib/Transforms/NaCl/GlobalCleanup.cpp b/lib/Transforms/NaCl/GlobalCleanup.cpp
new file mode 100644
index 0000000000..9a28063af6
--- /dev/null
+++ b/lib/Transforms/NaCl/GlobalCleanup.cpp
@@ -0,0 +1,109 @@
+//===- GlobalCleanup.cpp - Cleanup global symbols post-bitcode-link -------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+// ===---------------------------------------------------------------------===//
+//
+// PNaCl executables should have no external symbols or aliases. These passes
+// internalize (or otherwise remove/resolve) GlobalValues and resolve all
+// GlobalAliases.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DerivedTypes.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Pass.h"
+#include "llvm/Transforms/NaCl.h"
+
+using namespace llvm;
+
+namespace {
+  class GlobalCleanup : public ModulePass {
+  public:
+    static char ID;
+    GlobalCleanup() : ModulePass(ID) {
+      initializeGlobalCleanupPass(*PassRegistry::getPassRegistry());
+    }
+    virtual bool runOnModule(Module &M);
+  };
+
+  class ResolveAliases : public ModulePass {
+  public:
+    static char ID;
+    ResolveAliases() : ModulePass(ID) {
+      initializeResolveAliasesPass(*PassRegistry::getPassRegistry());
+    }
+    virtual bool runOnModule(Module &M);
+  };
+}
+
+char GlobalCleanup::ID = 0;
+INITIALIZE_PASS(GlobalCleanup, "nacl-global-cleanup",
+                "GlobalValue cleanup for PNaCl", false, false)
+
+static bool CleanUpLinkage(GlobalValue *GV) {
+  // TODO(dschuff): handle the rest of the linkage types as necessary without
+  // running afoul of the IR verifier or breaking the native link
+  switch (GV->getLinkage()) {
+    case GlobalValue::ExternalWeakLinkage: {
+      Constant *NullRef = Constant::getNullValue(GV->getType());
+      GV->replaceAllUsesWith(NullRef);
+      GV->eraseFromParent();
+      return true;
+    }
+    default:
+      // default with fall through to avoid compiler warning
+      return false;
+  }
+  return false;
+}
+
+bool GlobalCleanup::runOnModule(Module &M) {
+  bool Modified = false;
+
+  if (GlobalVariable *GV = M.getNamedGlobal("llvm.compiler.used")) {
+    GV->eraseFromParent();
+    Modified = true;
+  }
+  if (GlobalVariable *GV = M.getNamedGlobal("llvm.used")) {
+    GV->eraseFromParent();
+    Modified = true;
+  }
+
+  for (Module::global_iterator I = M.global_begin(), E = M.global_end();
+       I != E; ) {
+    GlobalVariable *GV = I++;
+    Modified |= CleanUpLinkage(GV);
+  }
+  return Modified;
+}
+
+ModulePass *llvm::createGlobalCleanupPass() {
+  return new GlobalCleanup();
+}
+
+char ResolveAliases::ID = 0;
+INITIALIZE_PASS(ResolveAliases, "resolve-aliases",
+                "resolve global variable and function aliases", false, false)
+
+bool ResolveAliases::runOnModule(Module &M) {
+  bool Modified = false;
+
+  for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end();
+       I != E; ) {
+    GlobalAlias *Alias = I++;
+    Alias->replaceAllUsesWith(Alias->getAliasee());
+    Alias->eraseFromParent();
+    Modified = true;
+  }
+  return Modified;
+}
+
+ModulePass *createResolveAliasesPass() {
+  return new ResolveAliases();
+}