Explicitly add 'sret' parameter attribute for builtins (#1438)

* Explicitly add 'sret' parameter attribute for builtins

It's required after:
commit 2182665305d90ae7d0d2b573dced9ef0ef414a9a
Author: Nikita Popov <[email protected]>
Date:   Fri Mar 11 17:30:34 2022 +0100

    [Bitcode] Don't confuse type attributes on declaration and call

    We should not be using APIs here that try to fetch the attribute
    from both the call attributes and the function attributes. Otherwise
    we'll try to upgrade a non-existent sret attribute on the call using
    the attribute on the function.

Signed-off-by: Dmitry Sidorov <[email protected]>

* Little refactoring

Signed-off-by: Dmitry Sidorov <[email protected]>

Author: MrSidims

lib/SPIRV/SPIRVUtil.cpp

@@ -1949,13 +1949,14 @@ bool postProcessBuiltinReturningStruct(Function *F) {
                     PointerType::get(F->getReturnType(), SPIRAS_Private));
       auto *NewF =
           getOrCreateFunction(M, Type::getVoidTy(*Context), ArgTys, Name);
-      NewF->addParamAttr(0, Attribute::get(*Context,
-                                           Attribute::AttrKind::StructRet,
-                                           F->getReturnType()));
+      auto SretAttr = Attribute::get(*Context, Attribute::AttrKind::StructRet,
+                                     F->getReturnType());
+      NewF->addParamAttr(0, SretAttr);
       NewF->setCallingConv(F->getCallingConv());
       auto Args = getArguments(CI);
       Args.insert(Args.begin(), ST->getPointerOperand());
       auto *NewCI = CallInst::Create(NewF, Args, CI->getName(), CI);
+      NewCI->addParamAttr(0, SretAttr);
       NewCI->setCallingConv(CI->getCallingConv());
       InstToRemove.push_back(ST);
       InstToRemove.push_back(CI);