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

[John McCall via cfe-commits]

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@@ -4148,6 +4152,30 @@ static void emitWriteback(CodeGenFunction &CGF,
   assert(!isProvablyNull(srcAddr.getBasePointer()) &&
          "shouldn't have writeback for provably null argument");
 
+  if (CGF.getLangOpts().HLSL) {
+    if (!isa<OpaqueValueExpr>(writeback.CastExpr)) {
+      RValue TmpVal = CGF.EmitAnyExprToTemp(writeback.CastExpr);
+      if (TmpVal.isScalar())
+        CGF.EmitStoreThroughLValue(TmpVal, srcLV);
+      else {
+        llvm::Value *Val = CGF.Builder.CreateLoad(TmpVal.getAggregateAddress());
+        CGF.EmitAggregateStore(Val, srcLV.getAddress(), false);
+      }
+    } else {
+      llvm::Value *Val = CGF.Builder.CreateLoad(writeback.Temporary);
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rjmccall wrote:

Same comment as above for the aggregate case — this should end up doing an aggregate copy, not loading an aggregate as an IR scalar.

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