Optimized IR:
/// @use-src 0:"yul_optimizer_steps_nested_brackets/input.sol"
object "C_6" {
    code {
        {
            /// @src 0:60:103  "contract C..."
            mstore(64, memoryguard(0x80))
            if callvalue()
            {
                revert_error_ca66f745a3ce8ff40e2ccaf1ad45db7774001b90d25810abd9040049be7bf4bb()
            }
            let _1 := allocate_unbounded()
            codecopy(_1, dataoffset("C_6_deployed"), datasize("C_6_deployed"))
            return(_1, datasize("C_6_deployed"))
        }
        function allocate_unbounded() -> memPtr
        {
            let memPtr_1 := mload(64)
            memPtr := memPtr_1
        }
        function revert_error_ca66f745a3ce8ff40e2ccaf1ad45db7774001b90d25810abd9040049be7bf4bb()
        { revert(0, 0) }
    }
    /// @use-src 0:"yul_optimizer_steps_nested_brackets/input.sol"
    object "C_6_deployed" {
        code {
            {
                /// @src 0:60:103  "contract C..."
                mstore(64, memoryguard(0x80))
                if iszero(lt(calldatasize(), 4))
                {
                    let selector := shift_right_unsigned(calldataload(0))
                    if eq(0x26121ff0, selector) { external_fun_f() }
                }
                revert_error_42b3090547df1d2001c96683413b8cf91c1b902ef5e3cb8d9f6f304cf7446f74()
            }
            function shift_right_unsigned(value) -> newValue
            {
                let newValue_1 := shr(224, value)
                newValue := newValue_1
            }
            function allocate_unbounded() -> memPtr
            {
                let memPtr_1 := mload(64)
                memPtr := memPtr_1
            }
            function revert_error_ca66f745a3ce8ff40e2ccaf1ad45db7774001b90d25810abd9040049be7bf4bb()
            { revert(0, 0) }
            function revert_error_dbdddcbe895c83990c08b3492a0e83918d802a52331272ac6fdb6a7c4aea3b1b()
            { revert(0, 0) }
            function abi_decode(headStart, dataEnd)
            {
                if slt(sub(dataEnd, headStart), 0)
                {
                    revert_error_dbdddcbe895c83990c08b3492a0e83918d802a52331272ac6fdb6a7c4aea3b1b()
                }
            }
            function abi_encode_tuple(headStart) -> tail
            {
                let tail_1 := add(headStart, 0)
                tail := tail_1
            }
            function external_fun_f()
            {
                if callvalue()
                {
                    revert_error_ca66f745a3ce8ff40e2ccaf1ad45db7774001b90d25810abd9040049be7bf4bb()
                }
                abi_decode(4, calldatasize())
                let memPos := allocate_unbounded()
                let memEnd := abi_encode_tuple(memPos)
                return(memPos, sub(memEnd, memPos))
            }
            function revert_error_42b3090547df1d2001c96683413b8cf91c1b902ef5e3cb8d9f6f304cf7446f74()
            { revert(0, 0) }
        }
        data ".metadata" hex"<BYTECODE REMOVED>"
    }
}