[clang][CodeGen] Additional fixes for #114062 (#128166)

This addresses two issues introduced by moving indirect args into an
explicit AS (please see
<https://github.com/llvm/llvm-project/pull/114062#issuecomment-2659829790>
and
<https://github.com/llvm/llvm-project/pull/114062#issuecomment-2661158477>):

1. Unconditionally stripping casts from a pre-allocated return slot was
incorrect / insufficient (this is illustrated by the
`amdgcn_sret_ctor.cpp` test);
2. Putting compiler manufactured sret args in a non default AS can lead
to a C-cast (surprisingly) requiring an AS cast (this is illustrated by
the `sret_cast_with_nonzero_alloca_as.cpp test).

The way we handle (2), by subverting CK_BitCast emission iff a sret arg
is involved, is quite naff, but I couldn't think of any other way to use
a non default indirect AS and make this case work (hopefully this is a
failure of imagination on my part).

1 files changed, 2 insertions, 9 deletions

diff --git a/clang/lib/CodeGen/CGExprAgg.cpp b/clang/lib/CodeGen/CGExprAgg.cpp
index 625ca36..200fb7f 100644
--- a/clang/lib/CodeGen/CGExprAgg.cpp
+++ b/clang/lib/CodeGen/CGExprAgg.cpp
@@ -302,15 +302,8 @@ void AggExprEmitter::withReturnValueSlot(
   llvm::Value *LifetimeSizePtr = nullptr;
   llvm::IntrinsicInst *LifetimeStartInst = nullptr;
   if (!UseTemp) {
-    // 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.
-    if (Dest.getAddress().isValid())
-      RetAddr = Dest.getAddress().withPointer(
-          Dest.getAddress().getBasePointer()->stripPointerCasts(),
-          Dest.getAddress().isKnownNonNull());
+    RetAddr = Dest.getAddress();
+    RawAddress RetAllocaAddr = RawAddress::invalid();
   } else {
     RetAddr = CGF.CreateMemTempWithoutCast(RetTy, "tmp");
     llvm::TypeSize Size =