Debug Info: remove duplication of DIEs when a DIE can be shared across CUs.

We add a map in DwarfDebug to map MDNodes that are shareable across CUs to the
corresponding DIEs: MDTypeNodeToDieMap. These DIEs can be shared across CUs,
that is why we keep the maps in DwarfDebug instead of CompileUnit.

We make the assumption that if a DIE is not added to an owner yet, we assume
it belongs to the current CU. Since DIEs for the type system are added to
their owners immediately after creation, and other DIEs belong to the current
CU, the assumption should be true.

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.

We also add a testing case to show ref_addr relocations for non-darwin
platforms.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@193779 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 46 insertions, 4 deletions

diff --git a/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp b/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
index 703e2c12d8..575cf31eaa 100644
--- a/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
+++ b/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
@@ -98,6 +98,35 @@ int64_t CompileUnit::getDefaultLowerBound() const {
   return -1;
 }
 
+/// Check whether the DIE for this MDNode can be shared across CUs.
+static bool isShareableAcrossCUs(const MDNode *N) {
+  // When the MDNode can be part of the type system, the DIE can be
+  // shared across CUs.
+  return DIDescriptor(N).isType() ||
+         (DIDescriptor(N).isSubprogram() && !DISubprogram(N).isDefinition());
+}
+
+/// getDIE - Returns the debug information entry map slot for the
+/// specified debug variable. We delegate the request to DwarfDebug
+/// when the DIE for this MDNode can be shared across CUs. The mappings
+/// will be kept in DwarfDebug for shareable DIEs.
+DIE *CompileUnit::getDIE(const MDNode *N) const {
+  if (isShareableAcrossCUs(N))
+    return DD->getDIE(N);
+  return MDNodeToDieMap.lookup(N);
+}
+
+/// insertDIE - Insert DIE into the map. We delegate the request to DwarfDebug
+/// when the DIE for this MDNode can be shared across CUs. The mappings
+/// will be kept in DwarfDebug for shareable DIEs.
+void CompileUnit::insertDIE(const MDNode *N, DIE *D) {
+  if (isShareableAcrossCUs(N)) {
+    DD->insertDIE(N, D);
+    return;
+  }
+  MDNodeToDieMap.insert(std::make_pair(N, D));
+}
+
 /// addFlag - Add a flag that is true.
 void CompileUnit::addFlag(DIE *Die, dwarf::Attribute Attribute) {
   if (DD->getDwarfVersion() >= 4)
@@ -245,8 +274,21 @@ void CompileUnit::addDelta(DIE *Die, dwarf::Attribute Attribute, dwarf::Form For
 /// addDIEEntry - Add a DIE attribute data and value.
 ///
 void CompileUnit::addDIEEntry(DIE *Die, dwarf::Attribute Attribute, DIE *Entry) {
-  // We currently only use ref4.
-  Die->addValue(Attribute, dwarf::DW_FORM_ref4, createDIEEntry(Entry));
+  addDIEEntry(Die, Attribute, createDIEEntry(Entry));
+}
+
+void CompileUnit::addDIEEntry(DIE *Die, dwarf::Attribute Attribute,
+                              DIEEntry *Entry) {
+  const DIE *DieCU = Die->getCompileUnitOrNull();
+  const DIE *EntryCU = Entry->getEntry()->getCompileUnitOrNull();
+  if (!DieCU)
+    // We assume that Die belongs to this CU, if it is not linked to any CU yet.
+    DieCU = getCUDie();
+  if (!EntryCU)
+    EntryCU = getCUDie();
+  Die->addValue(Attribute, EntryCU == DieCU ? dwarf::DW_FORM_ref4
+                                            : dwarf::DW_FORM_ref_addr,
+                Entry);
 }
 
 /// Create a DIE with the given Tag, add the DIE to its parent, and
@@ -882,7 +924,7 @@ void CompileUnit::addType(DIE *Entity, DIType Ty, dwarf::Attribute Attribute) {
   DIEEntry *Entry = getDIEEntry(Ty);
   // If it exists then use the existing value.
   if (Entry) {
-    Entity->addValue(Attribute, dwarf::DW_FORM_ref4, Entry);
+    addDIEEntry(Entity, Attribute, Entry);
     return;
   }
 
@@ -892,7 +934,7 @@ void CompileUnit::addType(DIE *Entity, DIType Ty, dwarf::Attribute Attribute) {
   // Set up proxy.
   Entry = createDIEEntry(Buffer);
   insertDIEEntry(Ty, Entry);
-  Entity->addValue(Attribute, dwarf::DW_FORM_ref4, Entry);
+  addDIEEntry(Entity, Attribute, Entry);
 
   // If this is a complete composite type then include it in the
   // list of global types.