Currently the a AAPCS compliant frame record is not always created for
functions when it should. Although a consistent frame record might not
be required in some cases, there are still scenarios where applications
may want to make use of the call hierarchy made available trough it.
In order to enable the use of AAPCS compliant frame records whilst keep
backwards compatibility, this patch introduces a new command-line option
(-mframe-chain=[none|aapcs|aapcs+leaf]) for Aarch32 and Thumb backends.
The option allows users to explicitly select when to use it, and is also
useful to ensure the extra overhead introduced by the frame records is
only introduced when necessary, in particular for Thumb targets.
I guess this is related to this patch because it involves the interaction of PACBTI with -mframe_chain ? (Without this patch, PACBTI doesn't exist on any targets where the frame pointer is in r11.) I'm fine leaving it to a followup, though.