self-review: recompute offsets instead of storing them

llvm/lib/ObjCopy/DXContainer/DXContainerObject.h

@@ -22,13 +22,22 @@ using namespace object;
 
 struct Part {
   StringRef Name;
-  uint32_t Offset;
   ArrayRef<uint8_t> Data;
+
+  size_t size() const {
+    return sizeof(dxbc::PartHeader) // base header
+           + Data.size();           // contents size
+  }
 };
 
 struct Object {
   dxbc::Header Header;
   SmallVector<Part> Parts;
+
+  size_t headerSize() const {
+    return sizeof(dxbc::Header)               // base header
+           + sizeof(uint32_t) * Parts.size(); // part offset values
+  }
 };
 
 } // end namespace dxc

llvm/lib/ObjCopy/DXContainer/DXContainerReader.cpp

@@ -22,13 +22,14 @@ Expected<std::unique_ptr<Object>> DXContainerReader::create() const {
     Expected<StringRef> Name = DXContainerObj.getSectionName(PartDRI);
     if (auto E = Name.takeError())
       return createStringError(inconvertibleErrorCode(), "Missing Part Name");
-    uint32_t Offset = DXContainerObj.getSectionAddress(PartDRI);
+    assert(Name->size() == 4 &&
+           "Valid DXIL Part name consists of 4 characters");
     Expected<ArrayRef<uint8_t>> Data =
         DXContainerObj.getSectionContents(PartDRI);
     if (auto E = Data.takeError())
       return createStringError(inconvertibleErrorCode(),
                                "Missing Part Contents");
-    Obj->Parts.push_back({*Name, Offset, *Data});
+    Obj->Parts.push_back({*Name, *Data});
   }
   return std::move(Obj);
 }

llvm/lib/ObjCopy/DXContainer/DXContainerWriter.cpp

@@ -15,16 +15,13 @@ namespace dxc {
 using namespace object;
 
 size_t DXContainerWriter::finalize() {
-  size_t ObjectSize = sizeof(dxbc::Header);
-  ObjectSize += Obj.Parts.size() * sizeof(uint32_t);
   Offsets.reserve(Obj.Parts.size());
+  size_t Offset = Obj.headerSize();
   for (const Part &P : Obj.Parts) {
-    Offsets.push_back(ObjectSize);
-    assert(P.Name.size() == 4 &&
-           "Valid DXIL Part name consists of 4 characters");
-    ObjectSize += 4 + sizeof(uint32_t) + P.Data.size();
+    Offsets.push_back(Offset);
+    Offset += P.size();
   }
-  return ObjectSize;
+  return Obj.Header.FileSize;
 }
 
 Error DXContainerWriter::write() {