The attached patch optimizes the atomic_exchange and
atomic_compare patterns on s390 and s390x (mostly limited to
SImode and DImode).  Among general optimizaation, the changes fix
most of the problems reported in PR 80080:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80080

Bootstrapped and regression tested on a zEC12 with s390 and s390x
biarch.

Ciao

Dominik ^_^  ^_^

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Dominik Vogt
IBM Germany