Debug Info: remove duplication of DIEs when a DIE is part of the type system

and it is shared across CUs.

We add a few maps in DwarfDebug to map MDNodes for the type system to the
corresponding DIEs: MDTypeNodeToDieMap, MDSPNodeToDieMap, and
MDStaticMemberNodeToDieMap. These DIEs can be shared across CUs, that is why we
keep the maps in DwarfDebug instead of CompileUnit.

Sometimes, when we try to add an attribute to a DIE, the DIE is not yet added
to its owner yet, so we don't know whether we should use ref_addr or ref4.
We create a worklist that will be processed during finalization to add
attributes with the correct form (ref_addr or ref4).

We add addDIEEntry to DwarfDebug to be a wrapper around DIE->addValue. It checks
whether we know the correct form, if not, we update the worklist
(DIEEntryWorklist).

A testing case is added to show that we only create a single DIE for a type
MDNode and we use ref_addr to refer to the type DIE.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191792 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/AsmPrinter/DIE.cpp

@@ -113,13 +113,21 @@ DIE::~DIE() {
 /// Climb up the parent chain to get the compile unit DIE to which this DIE
 /// belongs.
 DIE *DIE::getCompileUnit() {
+  DIE *Cu = checkCompileUnit();
+  assert(Cu && "We should not have orphaned DIEs.");
+  return Cu;
+}
+
+/// Climb up the parent chain to get the compile unit DIE this DIE belongs
+/// to. Return NULL if DIE is not added to an owner yet.
+DIE *DIE::checkCompileUnit() {
   DIE *p = this;
   while (p) {
     if (p->getTag() == dwarf::DW_TAG_compile_unit)
       return p;
     p = p->getParent();
   }
-  llvm_unreachable("We should not have orphaned DIEs.");
+  return NULL;
 }
 
 DIEValue *DIE::findAttribute(uint16_t Attribute) {