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

[Justin Bogner via llvm-commits]

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@@ -274,27 +274,39 @@ void DXContainerWriter::writeParts(raw_ostream &OS) {
       RS.StaticSamplersOffset = P.RootSignature->StaticSamplersOffset;
 
       for (const auto &Param : P.RootSignature->Parameters) {
-        mcdxbc::RootParameter NewParam;
-        NewParam.Header = dxbc::RootParameterHeader{
-            Param.Type, Param.Visibility, Param.Offset};
+        auto Header = dxbc::RootParameterHeader{Param.Type, Param.Visibility,
+                                                Param.Offset};
 
         switch (Param.Type) {
         case llvm::to_underlying(dxbc::RootParameterType::Constants32Bit):
-          NewParam.Constants.Num32BitValues = Param.Constants.Num32BitValues;
-          NewParam.Constants.RegisterSpace = Param.Constants.RegisterSpace;
-          NewParam.Constants.ShaderRegister = Param.Constants.ShaderRegister;
+          dxbc::RootConstants Constants;
+          Constants.Num32BitValues = Param.Constants.Num32BitValues;
+          Constants.RegisterSpace = Param.Constants.RegisterSpace;
+          Constants.ShaderRegister = Param.Constants.ShaderRegister;
+          RS.ParametersContainer.addParameter(Header, Constants);
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bogner wrote:

It might be more convenient to use a couple of specific named functions rather than having a generic addParameter:
```c++
  void addConstant(uint32_t Type, uint32_t Visibility, uint32_t Offset,
                   uint32_t ShaderRegister, uint32_t RegisterSpace,
                   uint32_t Num32BitValues);
```

On the other hand that's quite a few int parameters to remember the order of, so YMMV. I'll let you judge which is more ergonomic.

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