TransformUtils: Introduce module splitter.

The module splitter splits a module into linkable partitions. It will
be used to implement parallel LTO code generation.

This initial version of the splitter does not attempt to deal with the
somewhat subtle symbol visibility issues around module splitting. These
will be dealt with in a future change.

Differential Revision: http://reviews.llvm.org/D12132

llvm-svn: 245662

1 files changed, 39 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Utils/CloneModule.cpp b/llvm/lib/Transforms/Utils/CloneModule.cpp
index 61f1811e7b4..5e7cae5364a 100644
--- a/llvm/lib/Transforms/Utils/CloneModule.cpp
+++ b/llvm/lib/Transforms/Utils/CloneModule.cpp
@@ -33,6 +33,12 @@ Module *llvm::CloneModule(const Module *M) {
 }
 
 Module *llvm::CloneModule(const Module *M, ValueToValueMapTy &VMap) {
+  return CloneModule(M, VMap, [](const GlobalValue *GV) { return true; });
+}
+
+Module *llvm::CloneModule(
+    const Module *M, ValueToValueMapTy &VMap,
+    std::function<bool(const GlobalValue *)> ShouldCloneDefinition) {
   // First off, we need to create the new module.
   Module *New = new Module(M->getModuleIdentifier(), M->getContext());
   New->setDataLayout(M->getDataLayout());
@@ -68,6 +74,26 @@ Module *llvm::CloneModule(const Module *M, ValueToValueMapTy &VMap) {
   // Loop over the aliases in the module
   for (Module::const_alias_iterator I = M->alias_begin(), E = M->alias_end();
        I != E; ++I) {
+    if (!ShouldCloneDefinition(I)) {
+      // An alias cannot act as an external reference, so we need to create
+      // either a function or a global variable depending on the value type.
+      // FIXME: Once pointee types are gone we can probably pick one or the
+      // other.
+      GlobalValue *GV;
+      if (I->getValueType()->isFunctionTy())
+        GV = Function::Create(cast<FunctionType>(I->getValueType()),
+                              GlobalValue::ExternalLinkage, I->getName(), New);
+      else
+        GV = new GlobalVariable(
+            *New, I->getValueType(), false, GlobalValue::ExternalLinkage,
+            (Constant *)nullptr, I->getName(), (GlobalVariable *)nullptr,
+            I->getThreadLocalMode(), I->getType()->getAddressSpace());
+      VMap[I] = GV;
+      // We do not copy attributes (mainly because copying between different
+      // kinds of globals is forbidden), but this is generally not required for
+      // correctness.
+      continue;
+    }
     auto *PTy = cast<PointerType>(I->getType());
     auto *GA = GlobalAlias::create(PTy, I->getLinkage(), I->getName(), New);
     GA->copyAttributesFrom(I);
@@ -81,6 +107,11 @@ Module *llvm::CloneModule(const Module *M, ValueToValueMapTy &VMap) {
   for (Module::const_global_iterator I = M->global_begin(), E = M->global_end();
        I != E; ++I) {
     GlobalVariable *GV = cast<GlobalVariable>(VMap[I]);
+    if (!ShouldCloneDefinition(I)) {
+      // Skip after setting the correct linkage for an external reference.
+      GV->setLinkage(GlobalValue::ExternalLinkage);
+      continue;
+    }
     if (I->hasInitializer())
       GV->setInitializer(MapValue(I->getInitializer(), VMap));
   }
@@ -89,6 +120,11 @@ Module *llvm::CloneModule(const Module *M, ValueToValueMapTy &VMap) {
   //
   for (Module::const_iterator I = M->begin(), E = M->end(); I != E; ++I) {
     Function *F = cast<Function>(VMap[I]);
+    if (!ShouldCloneDefinition(I)) {
+      // Skip after setting the correct linkage for an external reference.
+      F->setLinkage(GlobalValue::ExternalLinkage);
+      continue;
+    }
     if (!I->isDeclaration()) {
       Function::arg_iterator DestI = F->arg_begin();
       for (Function::const_arg_iterator J = I->arg_begin(); J != I->arg_end();
@@ -109,6 +145,9 @@ Module *llvm::CloneModule(const Module *M, ValueToValueMapTy &VMap) {
   // And aliases
   for (Module::const_alias_iterator I = M->alias_begin(), E = M->alias_end();
        I != E; ++I) {
+    // We already dealt with undefined aliases above.
+    if (!ShouldCloneDefinition(I))
+      continue;
     GlobalAlias *GA = cast<GlobalAlias>(VMap[I]);
     if (const Constant *C = I->getAliasee())
       GA->setAliasee(MapValue(C, VMap));