The two requirements are different. Some codes may allow overlap or substitution in some circumstances. Others not so much.
From a pure reliability standpoint, a "system" is inherently less reliable than numerous autonomous smoke alarms because a "system" relies on many single points of failure (motherboard, power supply, alarm relay, etc). A distributed smoke alarm requirement is much less likely to fail entirely, in multiple diverse points, all at the same moment, when it matters most. Having both would be good.
If the code requirement is "smoke alarm" in each bedroom, then that's what you're required to install, unless you can point to a specific exemption in the applicable code. Whether there may also be a "fire alarm system" permitted in the code does not necessarily remove the single-station smoke alarm or multiple-station smoke alarm requirements. In other words, they may supplement each other, but the specific requirement quoted in IRC 314 is for "smoke alarms" not just a "fire alarm system".
For comparison, NFPA 1 (2009) National Fire Code specifically states
188.8.131.52.9.1.4 System smoke detectors in accordance with NFPA 72 and arranged to function in the same manner as single-station or
multiple-station smoke alarms shall be permitted in lieu of smoke
... quoting NFPA 101: 184.108.40.206.1.4
Identical wording is in NFPA 1(2015) 220.127.116.11.6, for those jurisdictions that have adopted the later version, quoting NFPA 101(2015): 18.104.22.168.6.
While we're there, NFPA 101(2015) clearly prohibits substitution of smoke alarms going "the other way":
22.214.171.124.2 Where automatic smoke detection is required by Chapters 11 through 43, smoke alarms shall not be used as a substitute.
If fire code (or life safety code) conflicts with requirements that are more strict than similar provisions in the building code, then you would generally be required to follow the more strict provisions, absent an official variance.
Also worth noting that battery-backup requirements for "fire alarm systems" may be quite different from those of "smoke alarms".
Bottom line, building code, fire code, life safety code, alarm code, and pertinent enacting statutes, are intended to be the minimum requirements for reasonable safety. Nothing prevents you from adding more layers for more safety, if the budget and schedule allow.