GCC default CPUs

[coypu%sdf.org@localhost]

hi port-arm,

i'm upstreaming the netbsd eabi target to gcc upstream.
a question came up about our choice of platform triplets (or is it
fourlets?:)), there are quite many.

armv4--netbsdelf-eabi
armv6--netbsdelf-eabi
armv7--netbsdelf-eabi
arm*--netbsdelf-eabi ??

also,
arm--netbsdelf, for OABI.

The first part should affect default cpu for the configuration.
In base and in upstream, given the current patch, it will be:


ISA ver		|	Base GCC		| upstream GCC
--------------------------------------------------------------------
v4		|	strongarm		| strongarm
v6		|	arm1176jzf-s		| arm1176jzf-s
v7		|	cortex-a8		| generic-armv7-a[1]
else		|	arm6 ? (not 100% sure)	| strongarm[2]

the question was: why did we make these choices?
if i had to come up with a policy, it'd be "create a target for every
time ARM decides you can break ISA compatibility, use -mcpu otherwise".

i guess armv6 exists for RPI1 alone and people did not want to
compromise for everything else?
do we want an armv8 default cpu?

i don't know what were the points ARM broke compatibility. if
anyone can fill in :-)

thanks.


The discussion is here:
https://gcc.gnu.org/ml/gcc-patches/2018-10/threads.html#01256

[1] because cortex-a8 is VFPv3-d32
this isn't a problem for base: it defaults to a certain -mfpu.
we are switching to -mfpu=auto, which detects from -mcpu.

[2] because arm6 no longer exists in upstream. strongarm is also
deprecated, but still exists.