[StackProtector] Fix domtree verification in NewPM

Use DTU.getDomTree() to make sure the DTU if flushed.

Author: nikic

llvm/lib/CodeGen/StackProtector.cpp

@@ -136,7 +136,8 @@ PreservedAnalyses StackProtectorPass::run(Function &F,
   bool Changed = InsertStackProtectors(TM, &F, DT ? &DTU : nullptr,
                                        Info.HasPrologue, Info.HasIRCheck);
 #ifdef EXPENSIVE_CHECKS
-  assert((!DT || DT->verify(DominatorTree::VerificationLevel::Full)) &&
+  assert((!DT ||
+          DTU.getDomTree().verify(DominatorTree::VerificationLevel::Full)) &&
          "Failed to maintain validity of domtree!");
 #endif
 

llvm/test/CodeGen/X86/stack-protector-atomicrmw-xchg.ll

@@ -1,5 +1,6 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
 ; RUN: opt -S -mtriple=x86_64-unknown-linux-gnu -passes=stack-protector < %s | FileCheck %s
+; RUN: opt -S -mtriple=x86_64-unknown-linux-gnu -passes='require<domtree>,stack-protector' < %s | FileCheck %s
 
 define void @atomicrmw_xchg(ptr %p) sspstrong {
 ; CHECK-LABEL: define void @atomicrmw_xchg(