[llvm] [DXIL] Add support for root signature flag element in DXContainer (PR #123147)

[Justin Bogner via llvm-commits]

================
@@ -144,6 +150,30 @@ void DXContainerGlobals::addSignature(Module &M,
   Globals.emplace_back(buildSignature(M, OutputSig, "dx.osg1", "OSG1"));
 }
 
+void DXContainerGlobals::addRootSignature(Module &M,
+                                          SmallVector<GlobalValue *> &Globals) {
+
+  auto &RSA = getAnalysis<RootSignatureAnalysisWrapper>();
+  std::optional<ModuleRootSignature> MaybeRootSignature = RSA.getResult();
+
+  if (!MaybeRootSignature.has_value())
+    return;
+
+  ModuleRootSignature MRS = MaybeRootSignature.value();
----------------
bogner wrote:

I generally find it clearer to use the pointer-like API of optional rather than unwrapping into a second variable,
```c++
std::optional<ModuleRootSignature> MRS= RSA.getResult();
if (!MRS.has_value())
  return;
// ...
RSH.Flags = MRS->Flags;
```

This is mostly personal preference though, so feel free to take it or leave it.

https://github.com/llvm/llvm-project/pull/123147