Peter Trommler authored Nov 02, 2017 and Ben Gamari committed Nov 02, 2017

Implement AtomicRMW ops, atomic read, atomic write
in PowerPC native code generator. Also implement
branch prediction because we need it in atomic ops
anyway.

This patch improves the issue in #12537 a bit but
does not fix it entirely.

The fallback operations for atomicread and atomicwrite
in libraries/ghc-prim/cbits/atomic.c are incorrect.
This patch avoids those functions by implementing the
operations directly in the native code generator. This
is also what the x86/amd64 NCG and the LLVM backend
do.

Test Plan: validate on AIX and PowerPC (32-bit) Linux

Reviewers: erikd, hvr, austin, bgamari, simonmar

Reviewed By: hvr, bgamari

Subscribers: rwbarton, thomie

GHC Trac Issues: #12537

Differential Revision: https://phabricator.haskell.org/D3984