Revert "SimplifyCFG: fix an infinite jump-threading loop."

This reverts commit fe928d5.

This causes an ASAN failure. Reverting until it can be debugged.

Author: atrick

lib/SILOptimizer/Transforms/SimplifyCFG.cpp

@@ -318,8 +318,6 @@ bool SimplifyCFG::threadEdge(const ThreadInfo &ti) {
     return false;
 
   Cloner.cloneBranchTarget(SrcTerm);
-  JumpThreadingCost[Cloner.getNewBB()] = JumpThreadingCost[SrcTerm->getDestBB()];
-
 
   // We have copied the threaded block into the edge.
   auto *clonedSrc = Cloner.getNewBB();
@@ -1133,10 +1131,6 @@ bool SimplifyCFG::tryJumpThreading(BranchInst *BI) {
   Cloner.cloneBranchTarget(BI);
   Cloner.updateSSAAfterCloning();
 
-  // Also account the costs to the cloned DestBB, so the jump threading cannot
-  // loop by cloning the cloned block again.
-  JumpThreadingCost[Cloner.getNewBB()] += copyCosts;
-
   // Once all the instructions are copied, we can nuke BI itself.  We also add
   // the threaded and edge block to the worklist now that they (likely) can be
   // simplified.
@@ -2879,8 +2873,6 @@ bool SimplifyCFG::tailDuplicateObjCMethodCallSuccessorBlocks() {
     Cloner.cloneBranchTarget(Branch);
     Cloner.updateSSAAfterCloning();
 
-    JumpThreadingCost[Cloner.getNewBB()] = JumpThreadingCost[DestBB];
-
     Changed = true;
     // Simplify the cloned block and continue tail duplicating through its new
     // successors edges.