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From: "iains at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/100152] Possible 10.3 bad code generation regression
 from 10.2/9.3 on Mac OS 10.15.7 (Catalina)
Date: Wed, 21 Apr 2021 20:38:23 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D100152

--- 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 whic=
h 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 be=
en
exposed by changes in the RA ..=20

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