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

[Matt Arsenault via cfe-commits]

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@@ -105,6 +105,11 @@ void AMDGPUABIInfo::computeInfo(CGFunctionInfo &FI) const {
   if (!getCXXABI().classifyReturnType(FI))
     FI.getReturnInfo() = classifyReturnType(FI.getReturnType());
 
+  // srets / indirect returns are unconditionally in the alloca AS.
+  if (FI.getReturnInfo().isIndirect())
+    FI.getReturnInfo().setIndirectAddrSpace(
+        getDataLayout().getAllocaAddrSpace());
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arsenm wrote:

It's also ok to just hardcode to AMDGPUAS::PRIVATE_ADDRESS

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