[StructurizeCfg] Update dominator info.

In some cases StructurizeCfg updates root node, but dominator info
remains unchanges, it causes crash when expensive checks are enabled.
To cope with this problem a new method was added to DominatorTreeBase
that allows adding new root nodes, it is called in StructurizeCfg to
put dominator tree in sync.

This change fixes PR27488.

Differential Revision: https://reviews.llvm.org/D28114

llvm-svn: 291530

1 files changed, 10 insertions, 0 deletions

diff --git a/llvm/unittests/IR/DominatorTreeTest.cpp b/llvm/unittests/IR/DominatorTreeTest.cpp
index 6c49deb32d9..ae9c2684212 100644
--- a/llvm/unittests/IR/DominatorTreeTest.cpp
+++ b/llvm/unittests/IR/DominatorTreeTest.cpp
@@ -203,6 +203,16 @@ namespace llvm {
         EXPECT_EQ(DT->getNode(BB4)->getDFSNumIn(), 5UL);
         EXPECT_EQ(DT->getNode(BB4)->getDFSNumOut(), 6UL);
 
+        // Change root node
+        DT->verifyDomTree();
+        BasicBlock *NewEntry = BasicBlock::Create(F.getContext(), "new_entry",
+                                                  &F, BB0);
+        BranchInst::Create(BB0, NewEntry);
+        EXPECT_EQ(F.begin()->getName(), NewEntry->getName());
+        EXPECT_TRUE(&F.getEntryBlock() == NewEntry);
+        DT->setNewRoot(NewEntry);
+        DT->verifyDomTree();
+
         return false;
       }
       void getAnalysisUsage(AnalysisUsage &AU) const override {