[clang] [CIR] Function calls with aggregate arguments and return values (PR #143377)

[Andy Kaylor via cfe-commits]

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@@ -246,6 +290,44 @@ void AggExprEmitter::emitNullInitializationToLValue(mlir::Location loc,
   cgf.emitNullInitialization(loc, lv.getAddress(), lv.getType());
 }
 
+void AggExprEmitter::VisitCallExpr(const CallExpr *e) {
+  if (e->getCallReturnType(cgf.getContext())->isReferenceType()) {
+    cgf.cgm.errorNYI(e->getSourceRange(), "reference return type");
+    return;
+  }
+
+  withReturnValueSlot(
+      e, [&](ReturnValueSlot slot) { return cgf.emitCallExpr(e, slot); });
+}
+
+void AggExprEmitter::withReturnValueSlot(
+    const Expr *e, llvm::function_ref<RValue(ReturnValueSlot)> fn) {
+  QualType retTy = e->getType();
+
+  assert(!cir::MissingFeatures::aggValueSlotDestructedFlag());
+  bool requiresDestruction =
+      retTy.isDestructedType() == QualType::DK_nontrivial_c_struct;
+  if (requiresDestruction)
+    cgf.cgm.errorNYI(
+        e->getSourceRange(),
+        "withReturnValueSlot: return value requiring destruction is NYI");
+
+  // If it makes no observable difference, save a memcpy + temporary.
+  //
+  // We need to always provide our own temporary if destruction is required.
+  // Otherwise, fn will emit its own, notice that it's "unused", and end its
+  // lifetime before we have the chance to emit a proper destructor call.
+  assert(!cir::MissingFeatures::aggValueSlotAlias());
----------------
andykaylor wrote:

I'm adding a couple of these in https://github.com/llvm/llvm-project/pull/143932. We should revisit this after both PRs are merged.

https://github.com/llvm/llvm-project/pull/143377