[ObjCARC] Do not move a release between a call and a
retainAutoreleasedReturnValue that retains the returned value.

This commit fixes a bug in ARC optimizer where it moves a release
between a call and a retainAutoreleasedReturnValue, causing the returned
object to be released before the retainAutoreleasedReturnValue can
retain it.

This commit accomplishes that by doing a lookahead and checking whether
the call prevents the release from moving upwards. In the long term, we
should treat the region between the retainAutoreleasedReturnValue and
the call as a critical section and disallow moving anything there
(possibly using operand bundles).

rdar://problem/20449878

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@301724 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed