[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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@@ -5390,11 +5391,19 @@ RValue CodeGenFunction::EmitCall(const CGFunctionInfo &CallInfo,
             V->getType()->isIntegerTy())
           V = Builder.CreateZExt(V, ArgInfo.getCoerceToType());
 
-        // If the argument doesn't match, perform a bitcast to coerce it.  This
-        // can happen due to trivial type mismatches.
+        // If the argument doesn't match, we are either trying to pass an
+        // alloca-ed sret argument directly, and the alloca AS does not match
+        // the default AS, case in which we AS cast it, or we have a trivial
+        // type mismatch, and thus perform a bitcast to coerce it.
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arsenm wrote:

The cast is probably unavoidable here. You need to support flat addressing for any of c++ to work anyway, so that's fine for the GPU case 

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