OSSA: Support SimplifyCFG tryJumpThreading for testing.

This will be gated by a testing flag while tests are staged in.

Author: atrick

lib/SILOptimizer/Transforms/SimplifyCFG.cpp

@@ -1029,12 +1029,6 @@ static bool hasInjectedEnumAtEndOfBlock(SILBasicBlock *block, SILValue enumAddr)
 /// tryJumpThreading - Check to see if it looks profitable to duplicate the
 /// destination of an unconditional jump into the bottom of this block.
 bool SimplifyCFG::tryJumpThreading(BranchInst *BI) {
-  // TODO: OSSA phi support. Even if all block arguments are trivial,
-  // jump-threading may require creation of guaranteed phis, which may require
-  // creation of nested borrow scopes.
-  if (Fn.hasOwnership())
-    return false;
-
   auto *DestBB = BI->getDestBB();
   auto *SrcBB = BI->getParent();
   TermInst *destTerminator = DestBB->getTerminator();