[SILGenBuilder] NFC: Add createUncheckedForwardingCast that works with ManagedValue

(cherry picked from commit cc13060)

Author: xedin

lib/SILGen/SILGenBuilder.cpp

@@ -757,6 +757,31 @@ ManagedValue SILGenBuilder::createUncheckedBitCast(SILLocation loc,
   return cloner.clone(cast);
 }
 
+ManagedValue SILGenBuilder::createUncheckedForwardingCast(SILLocation loc,
+                                                          ManagedValue value,
+                                                          SILType type) {
+  CleanupCloner cloner(*this, value);
+  SILValue cast = createUncheckedForwardingCast(loc, value.getValue(), type);
+  
+  // Currently createUncheckedBitCast only produces these
+  // instructions. We assert here to make sure if this changes, this code is
+  // updated.
+  assert((isa<UncheckedTrivialBitCastInst>(cast) ||
+          isa<UncheckedRefCastInst>(cast) ||
+          isa<UncheckedValueCastInst>(cast) ||
+          isa<ConvertFunctionInst>(cast)) &&
+         "SILGenBuilder is out of sync with SILBuilder.");
+
+  // If we have a trivial inst, just return early.
+  if (isa<UncheckedTrivialBitCastInst>(cast))
+    return ManagedValue::forObjectRValueWithoutOwnership(cast);
+
+  // Otherwise, we forward the cleanup of the input value and place the cleanup
+  // on the cast value since unchecked_ref_cast is "forwarding".
+  value.forward(SGF);
+  return cloner.clone(cast);
+}
+
 ManagedValue SILGenBuilder::createOpenExistentialRef(SILLocation loc,
                                                      ManagedValue original,
                                                      SILType type) {

lib/SILGen/SILGenBuilder.h

@@ -340,6 +340,11 @@ class SILGenBuilder : public SILBuilder {
   ManagedValue createUncheckedBitCast(SILLocation loc, ManagedValue original,
                                       SILType type);
 
+  using SILBuilder::createUncheckedForwardingCast;
+  ManagedValue createUncheckedForwardingCast(SILLocation loc,
+                                             ManagedValue original,
+                                             SILType type);
+
   using SILBuilder::createOpenExistentialRef;
   ManagedValue createOpenExistentialRef(SILLocation loc, ManagedValue arg,
                                         SILType openedType);