ipainspector (command line) or IPA Injector (GUI) can quickly show compatibility data.
For iOS 7.1.2, IPAs are specifically compiled for and, in rare cases, ARMv6 (for the iPhone 3GS). This means that modern apps compiled for ARM64 (iPhone 5s and later) will not run on iOS 7.1.2. ipa files for ios 7.1.2
Automated analysis tips