Has anybody used STM32F417IG microcontroller with 1.8V input supply?
You should read the datasheet carefully, and consider all elements in your system. Programming flash requires 2.7V min. Some of the analog-ish functions may not work as well or at all. Operation at a restricted temperature range allows a bit more voltage margin on the low side.
The core works off an internal regulator that is something like 1.2 so it is not affected.
But everything you connect to the I/O will need to work with 1.8V or have a voltage translator. Driving a blue or white LED directly becomes an issue. Not many MOSFETs are characterized for 1.8V drive. GPIO output drive current is not guaranteed for Vdd &lt; 2.7V. Maximum IO frequency such as SPI is reduced. You want guarantees at 1.7V or so to allow some tolerance on 1.8V. USB ... I don't think that part has a Vddusb pin (which would  need 2.7V).
The 12-bit ADC (and other aspects of analog functions):


VDD/VDDA minimum value of 1.7 V is obtained when the device operates in reduced temperature range, and with the use of
an external power supply supervisor (refer to Section : Internal reset OFF).


If it's only guaranteed to work at 1.8V and your 1.8V nominal regulator happens to output 1.75V then functionality is not guaranteed for some parts of the chip, so the reduced temperature range is probably a must if you're using those functions.
None of these things are necessarily show-stoppers, just a fair bit of due diligence is necessary, and only you can do that.