[clang] [HLSL] Implement output parameter (PR #101083)

[Chris B via cfe-commits]

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@@ -11427,6 +11427,19 @@ static void AnalyzeImplicitConversions(
     return;
   }
 
+  if (auto *OutArgE = dyn_cast<HLSLOutArgExpr>(E)) {
+    // The base expression is only used to initialize the parameter for
+    // arguments to `inout` parameters, so we only traverse down the base
+    // expression for `inout` cases.
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llvm-beanz wrote:

I should have commented on this. If SemaChecking traverses down both sides we get warnings for the conversion that would "initialize" the `out` parameter, but those warnings aren't accurate because no initialization occurs.

If we only traverse down the write back side we only get the warning for the copy back to the l-value, which is the behavior we want.

clang/test/SemaHLSL/Language/OutputParameters.hlsl verifies the behavior for `out` arguments of only diagnosing the write back conversion, removing the condition breaks that test by emitting diagnostics on the initialization as well.

https://github.com/llvm/llvm-project/pull/101083