[WIP] Initial code for module flags.

Module flags are key-value pairs associated with the module. They include a
'behavior' value, indicating how module flags react when mergine two
files. Normally, it's just the union of the two module flags. But if two module
flags have the same key, then the resulting flags are dictated by the behaviors.

Allowable behaviors are:

     Error
       Emits an error if two values disagree.

     Warning
       Emits a warning if two values disagree.

     Require
       Emits an error when the specified value is not present
       or doesn't have the specified value. It is an error for
       two (or more) llvm.module.flags with the same ID to have
       the Require behavior but different values. There may be
       multiple Require flags per ID.

     Override
       Uses the specified value if the two values disagree. It
       is an error for two (or more) llvm.module.flags with the
       same ID to have the Override behavior but different
       values.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@150300 91177308-0d34-0410-b5e6-96231b3b80d8

lib/VMCore/Module.cpp

@@ -321,11 +321,51 @@ NamedMDNode *Module::getOrInsertNamedMetadata(StringRef Name) {
   return NMD;
 }
 
+/// eraseNamedMetadata - Remove the given NamedMDNode from this module and
+/// delete it.
 void Module::eraseNamedMetadata(NamedMDNode *NMD) {
   static_cast<StringMap<NamedMDNode *> *>(NamedMDSymTab)->erase(NMD->getName());
   NamedMDList.erase(NMD);
 }
 
+/// getModuleFlagsMetadata - Returns the NamedMDNode in the module that
+/// represents module-level flags. This method returns null if there are no
+/// module-level flags.
+NamedMDNode *Module::getModuleFlagsMetadata() const {
+  return getNamedMetadata("llvm.module.flags");
+}
+
+/// getOrInsertModuleFlagsMetadata - Returns the NamedMDNode in the module that
+/// represents module-level flags. If module-level flags aren't found, it
+/// creates the named metadata that contains them.
+NamedMDNode *Module::getOrInsertModuleFlagsMetadata() {
+  return getOrInsertNamedMetadata("llvm.module.flags");
+}
+
+/// addModuleFlag - Add a module-level flag to the module-level flags
+/// metadata. It will create the module-level flags named metadata if it doesn't
+/// already exist.
+void Module::addModuleFlag(ModAttrBehavior Behavior, StringRef Key,
+                           Value *Val) {
+  Type *Int32Ty = Type::getInt32Ty(Context);
+  Value *Ops[3] = {
+    ConstantInt::get(Int32Ty, Behavior), MDString::get(Context, Key), Val
+  };
+  getOrInsertModuleFlagsMetadata()->addOperand(MDNode::get(Context, Ops));
+}
+void Module::addModuleFlag(ModAttrBehavior Behavior, StringRef Key,
+                           uint32_t Val) {
+  Type *Int32Ty = Type::getInt32Ty(Context);
+  addModuleFlag(Behavior, Key, ConstantInt::get(Int32Ty, Val));
+}
+void Module::addModuleFlag(MDNode *Node) {
+  assert(Node->getNumOperands() == 3 &&
+         "Invalid number of operands for module flag!");
+  assert(isa<ConstantInt>(Node->getOperand(0)) &&
+         isa<MDString>(Node->getOperand(1)) &&
+         "Invalid operand types for module flag!");
+  getOrInsertModuleFlagsMetadata()->addOperand(Node);
+}
 
 //===----------------------------------------------------------------------===//
 // Methods to control the materialization of GlobalValues in the Module.