[clang] [clang][CodeGen] `sret` args should always point to the `alloca` AS, so use that (PR #114062)

[Alex Voicu via cfe-commits]

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@@ -296,18 +296,25 @@ void AggExprEmitter::withReturnValueSlot(
                  (RequiresDestruction && Dest.isIgnored());
 
   Address RetAddr = Address::invalid();
-  RawAddress RetAllocaAddr = RawAddress::invalid();
 
   EHScopeStack::stable_iterator LifetimeEndBlock;
   llvm::Value *LifetimeSizePtr = nullptr;
   llvm::IntrinsicInst *LifetimeStartInst = nullptr;
   if (!UseTemp) {
-    RetAddr = Dest.getAddress();
+    // It is possible for the existing slot we are using directly to have been
+    // allocated in the correct AS for an indirect return, and then cast to
+    // the default AS (this is the behaviour of CreateMemTemp), however we know
+    // that the return address is expected to point to the uncasted AS, hence we
+    // strip possible pointer casts here.
----------------
AlexVlx wrote:

Yes, Dest could have been allocated via simple `CreateMemTemp`, which would then cast from the AllocaAS to the DefaultAS. As the code is currently structured I didn't see a way to disambiguate between allocating for a return vs allocating for a "normal" aggregate, so handling it here seemed like the only way to do it tidily.

https://github.com/llvm/llvm-project/pull/114062