A question of sstate and compilers

[Gary Thomas <gary@mlbassoc.com>]

I'm trying to isolate a problem that showed up in my builds
in the last month.  Little has changed in the sources, but
the one big change was I moved from GCC/4.9 to GCC/5.x  On
the surface, this seemed to be a non-consequence, but I have
one very subtle corner case that is now broken.  In an effort
to isolate the issue (I no longer think it was the compiler
change), I went back to GCC/4.9.  This caused my build (tree)
which has existed for many months (the same build tree started
in Feb 2016) to basically rebuild everything.

There's the rub - shouldn't the sstate-cache hold all of those
old bits and just be able to re-stage?  I'm a bit confused about
that.  Even worse, I switched back to GCC/5.x, didn't touch
anything else in my sources or build tree, and now it's off
again, [re]building the majority of my packages.

Any explanations?  Is this correct behavior?

-- 
------------------------------------------------------------
Gary Thomas                 |  Consulting for the
MLB Associates              |    Embedded world
------------------------------------------------------------