[llvm] [NFC] Refactoring MCDXBC to support out of order storage of root parameters (PR #137284)

[via llvm-commits]

================
@@ -9,18 +9,81 @@
 #include "llvm/BinaryFormat/DXContainer.h"
 #include <cstdint>
 #include <limits>
+#include <variant>
 
 namespace llvm {
 
 class raw_ostream;
 namespace mcdxbc {
 
-struct RootParameter {
+struct RootParameterInfo {
   dxbc::RootParameterHeader Header;
-  union {
-    dxbc::RootConstants Constants;
-    dxbc::RTS0::v2::RootDescriptor Descriptor;
-  };
+  size_t Location;
+
+  RootParameterInfo() = default;
+
+  RootParameterInfo(dxbc::RootParameterHeader H, size_t L)
+      : Header(H), Location(L) {}
+};
+
+using RootDescriptor = std::variant<dxbc::RTS0::v1::RootDescriptor,
+                                    dxbc::RTS0::v2::RootDescriptor>;
+using ParametersView = std::variant<const dxbc::RootConstants *,
+                                    const dxbc::RTS0::v1::RootDescriptor *,
+                                    const dxbc::RTS0::v2::RootDescriptor *>;
+struct RootParametersContainer {
+  SmallVector<RootParameterInfo> ParametersInfo;
+
+  SmallVector<dxbc::RootConstants> Constants;
+  SmallVector<RootDescriptor> Descriptors;
+
+  void addInfo(dxbc::RootParameterHeader H, size_t L) {
+    ParametersInfo.push_back(RootParameterInfo(H, L));
+  }
+
+  void addParameter(dxbc::RootParameterHeader H, dxbc::RootConstants C) {
+    addInfo(H, Constants.size());
+    Constants.push_back(C);
+  }
+
+  void addParameter(dxbc::RootParameterHeader H,
+                    dxbc::RTS0::v1::RootDescriptor D) {
+    addInfo(H, Descriptors.size());
+    Descriptors.push_back(D);
+  }
+
+  void addParameter(dxbc::RootParameterHeader H,
+                    dxbc::RTS0::v2::RootDescriptor D) {
+    addInfo(H, Descriptors.size());
+    Descriptors.push_back(D);
+  }
+
+  std::optional<ParametersView> getParameter(const RootParameterInfo *H) const {
+    switch (H->Header.ParameterType) {
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joaosaffran wrote:

Sure. Some context, Root Parameters are split into a Header and a Data section. The Header contains a RootParameter type field, specifying which kind of data is being stored: Root Constants, Root Descriptors or Descriptor Tables. The header also contains an offset, pointing to the exact location of the data in the binary file. Here is an test example showing what an invalid root signature look like: https://github.com/llvm/llvm-project/blob/038d357dde4907d39f6a3fabbaf48dc39cf9dc60/llvm/test/ObjectYAML/DXContainer/RootSignature-InvalidType.yaml.

Notice that in such test there is no data section, only the header section. Since I don't know what kind of data it is/the data is not supported, it is not possible to write it. 

https://github.com/llvm/llvm-project/pull/137284