[PATCH] D72271: [Clang] Handle target-specific builtins returning aggregates.

[John McCall via Phabricator via cfe-commits]

rjmccall added a comment.

In D72271#1807790 <https://reviews.llvm.org/D72271#1807790>, @simon_tatham wrote:

> The current return value of `EmitTargetBuiltinExpr` will be the `llvm::Value *` corresponding to the last of a sequence of store instructions that writes the constructed aggregate into the return value slot. There's no need to actually use that `Value` for anything in this case, but we can still test that it's non-null, to find out whether `EmitTargetBuiltinExpr` has successfully recognized a builtin and generated some code, or whether we have to fall through to the `ErrorUnsupported`.


Ah, yes, good point.



================
Comment at: clang/lib/CodeGen/CGBuiltin.cpp:4350
+    llvm_unreachable("Bad evaluation kind in EmitBuiltinExpr");
+  }
 
----------------
I would just structure this as:

```
  // If the result is an aggregate, force ReturnValue to be non-null so that
  // the target-specific emission code can always just emit into it.
  TypeEvaluationKind EvalKind = getEvaluationKind(E->getType());
  if (EvalKind == TEK_Aggregate && ReturnValue.isNull()) { ... }

  // Try to emit a target builtin.
  if (Value *V = EmitTargetBuiltinExpr(BuiltinID, E, ReturnValue)) {
   // Turn the result into the appropriate kind of RValue.
   switch (EvalKind) { ... }
  }
```


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