The new cortex-m schedule in D54142 helps performance, but can increase the amount of high-registers used. This, on average, ends up increasing the codesize by a fair amount (because less instructions are converted from T2 to T1). On cortex-m at -Oz, where we are quite size-paranoid, it is better to use the existing DAG scheduler with the RegPressure scheduling preference (at least until the issues around T2 vs T1 instructions can be improved).
I have also made sure that the Sched::RegPressure dag scheduler is always chosen for MinSize.
The test shows one case where we increase the number of registers used.