[DWARFLinker] Release input DWARF after object has been linked

dsymutil is using an excessive amount of memory because it's holding on
to the DWARF Context, even after it's done processing the corresponding
object file. This patch releases the input DWARF after cloning, at which
point it is no longer needed. This has always been the intended
behavior, though I didn't bisect to figure out when this regressed.

When linking swift, this reduces peak (dirty) memory usage from 25 to 15
gigabytes.

rdar://111525100

Author: JDevlieghere

llvm/include/llvm/DWARFLinker/DWARFLinker.h

@@ -13,13 +13,13 @@
 #include "llvm/CodeGen/AccelTable.h"
 #include "llvm/CodeGen/NonRelocatableStringpool.h"
 #include "llvm/DWARFLinker/DWARFLinkerCompileUnit.h"
+#include "llvm/DebugInfo/DWARF/DWARFContext.h"
 #include "llvm/DebugInfo/DWARF/DWARFDebugLine.h"
 #include "llvm/DebugInfo/DWARF/DWARFDebugRangeList.h"
 #include "llvm/DebugInfo/DWARF/DWARFDie.h"
 #include <map>
 
 namespace llvm {
-class DWARFContext;
 class DWARFExpression;
 class DWARFUnit;
 class DataExtractor;
@@ -196,19 +196,26 @@ using UnitListTy = std::vector<std::unique_ptr<CompileUnit>>;
 /// and it`s address map.
 class DWARFFile {
 public:
-  DWARFFile(StringRef Name, DWARFContext *Dwarf, AddressesMap *Addresses,
+  DWARFFile(StringRef Name, std::unique_ptr<DWARFContext> Dwarf,
+            std::unique_ptr<AddressesMap> Addresses,
             const std::vector<std::string> &Warnings)
-      : FileName(Name), Dwarf(Dwarf), Addresses(Addresses), Warnings(Warnings) {
-  }
+      : FileName(Name), Dwarf(std::move(Dwarf)),
+        Addresses(std::move(Addresses)), Warnings(Warnings) {}
 
   /// object file name.
   StringRef FileName;
-  /// source DWARF information.
-  DWARFContext *Dwarf = nullptr;
-  /// helpful address information(list of valid address ranges, relocations).
-  AddressesMap *Addresses = nullptr;
+  /// The source DWARF information.
+  std::unique_ptr<DWARFContext> Dwarf;
+  /// Helpful address information(list of valid address ranges, relocations).
+  std::unique_ptr<AddressesMap> Addresses;
   /// warnings for object file.
   const std::vector<std::string> &Warnings;
+
+  /// Unloads object file and corresponding AddressesMap and Dwarf Context.
+  void unload() {
+    Addresses.reset();
+    Dwarf.reset();
+  }
 };
 
 typedef std::function<void(const Twine &Warning, StringRef Context,
@@ -445,7 +452,8 @@ class DWARFLinker {
     /// the debug object.
     void clear() {
       CompileUnits.clear();
-      File.Addresses->clear();
+      ModuleUnits.clear();
+      File.unload();
     }
   };
 

llvm/tools/dsymutil/DwarfLinkerForBinary.cpp

@@ -272,14 +272,9 @@ DwarfLinkerForBinary::loadObject(const DebugMapObject &Obj,
   auto ErrorOrObj = loadObject(Obj, DebugMap.getTriple());
 
   if (ErrorOrObj) {
-    ContextForLinking.push_back(
-        std::unique_ptr<DWARFContext>(DWARFContext::create(*ErrorOrObj)));
-    AddressMapForLinking.push_back(
-        std::make_unique<AddressManager>(*this, *ErrorOrObj, Obj));
-
     ObjectsForLinking.push_back(std::make_unique<DWARFFile>(
-        Obj.getObjectFilename(), ContextForLinking.back().get(),
-        AddressMapForLinking.back().get(),
+        Obj.getObjectFilename(), DWARFContext::create(*ErrorOrObj),
+        std::make_unique<AddressManager>(*this, *ErrorOrObj, Obj),
         Obj.empty() ? Obj.getWarnings() : EmptyWarnings));
 
     Error E = RL.link(*ErrorOrObj);
@@ -554,8 +549,6 @@ bool DwarfLinkerForBinary::link(const DebugMap &Map) {
     return false;
 
   ObjectsForLinking.clear();
-  ContextForLinking.clear();
-  AddressMapForLinking.clear();
 
   DebugMap DebugMap(Map.getTriple(), Map.getBinaryPath());
 

llvm/tools/dsymutil/DwarfLinkerForBinary.h

@@ -221,8 +221,6 @@ class DwarfLinkerForBinary {
   LinkOptions Options;
   std::unique_ptr<DwarfStreamer> Streamer;
   std::vector<std::unique_ptr<DWARFFile>> ObjectsForLinking;
-  std::vector<std::unique_ptr<DWARFContext>> ContextForLinking;
-  std::vector<std::unique_ptr<AddressManager>> AddressMapForLinking;
   std::vector<std::string> EmptyWarnings;
 
   /// A list of all .swiftinterface files referenced by the debug

llvm/tools/llvm-dwarfutil/DebugInfoLinker.cpp

@@ -305,7 +305,6 @@ Error linkDebugInfo(object::ObjectFile &File, const Options &Options,
   DebugInfoLinker.setUpdate(!Options.DoGarbageCollection);
 
   std::vector<std::unique_ptr<DWARFFile>> ObjectsForLinking(1);
-  std::vector<std::unique_ptr<AddressesMap>> AddresssMapForLinking(1);
   std::vector<std::string> EmptyWarnings;
 
   // Unknown debug sections would be removed. Display warning
@@ -319,11 +318,9 @@ Error linkDebugInfo(object::ObjectFile &File, const Options &Options,
   }
 
   // Add object files to the DWARFLinker.
-  AddresssMapForLinking[0] =
-      std::make_unique<ObjFileAddressMap>(*Context, Options, File);
-
   ObjectsForLinking[0] = std::make_unique<DWARFFile>(
-      File.getFileName(), &*Context, AddresssMapForLinking[0].get(),
+      File.getFileName(), DWARFContext::create(File),
+      std::make_unique<ObjFileAddressMap>(*Context, Options, File),
       EmptyWarnings);
 
   for (size_t I = 0; I < ObjectsForLinking.size(); I++)