RFR (sh/jdk11): C2: Always emit arraycopy barriers for Shenandoah

[Roman Kennke]

Builds for shenandoah/jdk11 are currently failing. It looks like we are
not (always) emitting arraycopy barriers. This started happening with
LRB backports, and is presumably caused by GC interface difference
between jdk13/14 and jdk11 there.

The quick fix is:
diff --git
a/src/hotspot/share/gc/shenandoah/c2/shenandoahBarrierSetC2.cpp
b/src/hotspot/share/gc/shenandoah/c2/shenandoahBarrierSetC2.cpp
--- a/src/hotspot/share/gc/shenandoah/c2/shenandoahBarrierSetC2.cpp
+++ b/src/hotspot/share/gc/shenandoah/c2/shenandoahBarrierSetC2.cpp
@@ -748,7 +748,7 @@
 }

 bool ShenandoahBarrierSetC2::array_copy_requires_gc_barriers(BasicType
type) const {
-  return false;
+  return type == T_OBJECT || type == T_ARRAY;
 }

 bool ShenandoahBarrierSetC2::clone_needs_postbarrier(ArrayCopyNode *ac,
PhaseIterGVN& igvn) {


It probably warrants some deeper investigation too, to ensure we're not
over-doing it now. I seem to remember this was a bit peculiar. But let's
fix the builds and do the correct thing first. Ok?

Roman