[Dominators] Remove misleading double-deletion test

[kuhar]

Summary

It's generally not safe to perform multiple DomTree updates without using the incremental API.

Although it is supposed to work in this particular case, the testcase is misleading/confusing, and it's better to remove it.

llvm/trunk/unittests/IR/DominatorTreeTest.cpp

while ((LastUpdate = B.applyUpdate())) {
     BasicBlock *To = B.getOrAddBlock(LastUpdate->Edge.To);
     DT.deleteEdge(From, To);
     EXPECT_TRUE(DT.verify());
     PDT.deleteEdge(From, To);
     EXPECT_TRUE(PDT.verify());
   }
 }
 
-TEST(DominatorTree, DeletionsInSubtrees) {
-  CFGHolder Holder;
-  std::vector<CFGBuilder::Arc> Arcs = {{"0", "1"}, {"1", "2"}, {"1", "3"},
-                                       {"1", "6"}, {"3", "4"}, {"2", "5"},
-                                       {"5", "2"}};
-
-  // It is possible to perform multiple deletions and inform the
-  // DominatorTree about them at the same time, if the all of the
-  // deletions happen in different subtrees.
-  std::vector<CFGBuilder::Update> Updates = {{Delete, {"1", "2"}},
-                                             {Delete, {"1", "3"}}};
-  CFGBuilder B(Holder.F, Arcs, Updates);
-  DominatorTree DT(*Holder.F);
-  EXPECT_TRUE(DT.verify());
-
-  Optional<CFGBuilder::Update> LastUpdate;
-  while ((LastUpdate = B.applyUpdate()))
-    ;
-
-  DT.deleteEdge(B.getOrAddBlock("1"), B.getOrAddBlock("2"));
-  DT.deleteEdge(B.getOrAddBlock("1"), B.getOrAddBlock("3"));
-
-  EXPECT_TRUE(DT.verify());
-  EXPECT_EQ(DT.getNode(B.getOrAddBlock("2")), nullptr);
-  EXPECT_EQ(DT.getNode(B.getOrAddBlock("3")), nullptr);
-  EXPECT_EQ(DT.getNode(B.getOrAddBlock("4")), nullptr);
-  EXPECT_EQ(DT.getNode(B.getOrAddBlock("5")), nullptr);
-  EXPECT_NE(DT.getNode(B.getOrAddBlock("6")), nullptr);
-}
-
 TEST(DominatorTree, InsertDelete) {
   std::vector<CFGBuilder::Arc> Arcs = {
       {"1", "2"}, {"2", "3"}, {"3", "4"},  {"4", "5"},  {"5", "6"},  {"5", "7"},
       {"3", "8"}, {"8", "9"}, {"9", "10"}, {"8", "11"}, {"11", "12"}};
 
   std::vector<CFGBuilder::Update> Updates = {
       {Insert, {"2", "4"}},  {Insert, {"12", "10"}}, {Insert, {"10", "9"}},
       {Insert, {"7", "6"}},  {Insert, {"7", "5"}},   {Delete, {"3", "8"}},