[Bug target/100152] Possible 10.3 bad code generation regression from 10.2/9.3 on Mac OS 10.15.7 (Catalina)

[iains at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100152

--- Comment #22 from Iain Sandoe <iains at gcc dot gnu.org> ---
so it looks like the contents of r10 are being trashed by the call to
___UTF_8_put (the first call goes through the dylib lazy symbol resolution and
that leaves r10 with a value pointing to some mutex).

When we return from ___UTF_8_put there's a test for the loop iteration which is
expecting that to be the value in r10.  The test is for equality which fails
for the silly value now in r10 and we try a second loop iteration.

That starts with the "movl   (%rbp,%r10,4), %esi" - but r10 now has a value
that can't be used.

So .... I don't know if this is a new problem or an old problem that has been
exposed by changes in the RA .. 

.. if there's any easy way to amend the build process to attempt modifications
of the build flags to that file - this could give you a work-around in the
short term.