Quick: Avoid unnecessary GVN work in release builds.

In GVN's post-processing phase, compare LVNs only in debug
builds as they should be equal anyway.

Remove the Gate() from GVN cleanup pass and remove the
DCHECK() from MIRGraph::GlobalValueNumberingCleanup()
to make it a no-op if the GVN didn't run.

Bug: 16398693
Change-Id: Ia4f1e7e3ecf12d0305966c86e0e7dbae61dab0b7
4 files changed