[llvm] [DirectX] Adding support for Root Descriptors in obj2yaml/yaml2obj (PR #137259)

[Damyan Pepper via llvm-commits]

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@@ -121,16 +121,19 @@ namespace DirectX {
 struct RootParameterView {
   const dxbc::RootParameterHeader &Header;
   StringRef ParamData;
-  RootParameterView(const dxbc::RootParameterHeader &H, StringRef P)
+  RootParameterView(uint32_t V, const dxbc::RootParameterHeader &H, StringRef P)
       : Header(H), ParamData(P) {}
 
-  template <typename T> Expected<T> readParameter() {
-    T Struct;
-    if (sizeof(T) != ParamData.size())
+  template <typename T, typename VersionT = T> Expected<T> readParameter() {
+    assert(sizeof(VersionT) <= sizeof(T) &&
+           "Parameter of higher version must inherit all previous version data "
+           "members");
+    if (sizeof(VersionT) != ParamData.size())
       return make_error<GenericBinaryError>(
           "Reading structure out of file bounds", object_error::parse_failed);
 
-    memcpy(&Struct, ParamData.data(), sizeof(T));
+    T Struct;
+    memcpy(&Struct, ParamData.data(), sizeof(VersionT));
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damyanp wrote:

I'm getting pretty lost trying to read this and understand what T vs VersionT is meant to mean.

But it looks like we expect VersionT to be smaller than T.  Which means that this memcpy won't overwrite everything in T, which means that the rest of it is uninitialized?

https://github.com/llvm/llvm-project/pull/137259