Keil to OpenSTM32 - Code Size
If you read the release notes at https://launchpadlibrarian.net/209776344/release.txt you can see this:
Known Issues:
Thumb1 code size regression due to new register allocation:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61578
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59535
A workaround is to disable it by option -mno-lra.