is re-running bootstrap after a change safe?

[Martin Sebor]

On 4/5/19 3:29 PM, Jeff Law wrote:
> On 4/5/19 2:50 PM, Eric Botcazou wrote:
>>> Say if the first bootstrap succeeds and I then change a single
>>> GCC .c file and rerun make bootstrap, am I guaranteed to see
>>> the same fallout of the change as I would if I did a pristine
>>> build in a clean directory?
>>
>> No, this would imply deleting the stage2 and stage3 compilers and that isn't
>> what happens.  Instead the compiler of each stage is updated in isolation.
>>
> RIght.  Thus I always blow away stage2-* stage3-*, and stage1 target
> directories along with the "compare" stamp file.

Thanks (all of you).  It's amazing that I have been getting away
with it for all these years.

Why is this not done automatically?  I mean, what is the use case
for make bootstrap without doing these steps first?

Martin