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

[John McCall via cfe-commits]

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@@ -5159,16 +5156,19 @@ RValue CodeGenFunction::EmitCall(const CGFunctionInfo &CallInfo,
     } else if (!ReturnValue.isNull()) {
       SRetPtr = ReturnValue.getAddress();
     } else {
-      SRetPtr = CreateMemTemp(RetTy, "tmp", &SRetAlloca);
+      SRetPtr = CreateMemTempWithoutCast(RetTy, "tmp");
       if (HaveInsertPoint() && ReturnValue.isUnused()) {
         llvm::TypeSize size =
             CGM.getDataLayout().getTypeAllocSize(ConvertTypeForMem(RetTy));
-        UnusedReturnSizePtr = EmitLifetimeStart(size, SRetAlloca.getPointer());
+        UnusedReturnSizePtr = EmitLifetimeStart(size, SRetPtr.getBasePointer());
       }
     }
     if (IRFunctionArgs.hasSRetArg()) {
+      // If the caller allocated the return slot, it is possible that the
+      // alloca was AS casted to the default as, so we ensure the cast is
+      // stripped before binding to the sret arg, which is in the allocaAS.
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rjmccall wrote:

Sorry, what?  It seems really wrong to be blindly stripping pointer casts here.  Can you explain what code pattern is leading to us not having a pointer in the right address space?

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