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

[John McCall via cfe-commits]

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@@ -4689,6 +4720,31 @@ void CodeGenFunction::EmitCallArg(CallArgList &args, const Expr *E,
   assert(type->isReferenceType() == E->isGLValue() &&
          "reference binding to unmaterialized r-value!");
 
+  // Add writeback for HLSLOutParamExpr.
+  if (const HLSLOutArgExpr *OE = dyn_cast<HLSLOutArgExpr>(E)) {
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rjmccall wrote:

Please pull the body of this out into a helper function.

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