[Dominators] Add DomTreeUpdater constructor from DT* and PDT*

Summary:
Previously, if a function accepts an optional DT pointer,
```
void Foo (.., DominatorTree * DT = nullptr) {
  ...
  if(DT)
    DomTreeUpdater(*DT, ...).insertEdge(A, B);
  if(DT){
    DomTreeUpdater DTU(*DT, ...);
    ... // Construct the update vector and applyUpdates
  }
  ...
  if(DT){
    DomTreeUpdater DTU(*DT, ...);
    ... // Construct the update vector and applyUpdates
  }
}
```
After this patch, it can be simplified as
```
void Foo (.., DominatorTree * DT = nullptr) {
  DomTreeUpdater DTU(DT, ...);
  ...
  DTU.insertEdge(A, B);
  if(DT){
    ... // Construct the update vector and applyUpdates
  }
  ...
  if(DT){
    ... // Construct the update vector and applyUpdates
  }
}
```
Patch by Chijun Sima <simachijun@gmail.com>.

Reviewers: kuhar, brzycki, dmgreen

Reviewed By: kuhar

Author: NutshellySima

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D48923

llvm-svn: 336294

Author: kuhar

llvm/include/llvm/IR/DomTreeUpdater.h

@@ -31,11 +31,18 @@ class DomTreeUpdater {
   explicit DomTreeUpdater(UpdateStrategy Strategy_) : Strategy(Strategy_) {}
   DomTreeUpdater(DominatorTree &DT_, UpdateStrategy Strategy_)
       : DT(&DT_), Strategy(Strategy_) {}
+  DomTreeUpdater(DominatorTree *DT_, UpdateStrategy Strategy_)
+      : DT(DT_), Strategy(Strategy_) {}
   DomTreeUpdater(PostDominatorTree &PDT_, UpdateStrategy Strategy_)
       : PDT(&PDT_), Strategy(Strategy_) {}
+  DomTreeUpdater(PostDominatorTree *PDT_, UpdateStrategy Strategy_)
+      : PDT(PDT_), Strategy(Strategy_) {}
   DomTreeUpdater(DominatorTree &DT_, PostDominatorTree &PDT_,
                  UpdateStrategy Strategy_)
       : DT(&DT_), PDT(&PDT_), Strategy(Strategy_) {}
+  DomTreeUpdater(DominatorTree *DT_, PostDominatorTree *PDT_,
+                 UpdateStrategy Strategy_)
+      : DT(DT_), PDT(PDT_), Strategy(Strategy_) {}
 
   ~DomTreeUpdater() { flush(); }
 

llvm/unittests/IR/DomTreeUpdaterTest.cpp

@@ -235,7 +235,8 @@ TEST(DomTreeUpdater, LazyUpdateDTBasicOperations) {
 
   // Make the DTU.
   DominatorTree DT(*F);
-  DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Lazy);
+  PostDominatorTree *PDT = nullptr;
+  DomTreeUpdater DTU(&DT, PDT, DomTreeUpdater::UpdateStrategy::Lazy);
   ASSERT_TRUE(DTU.hasDomTree());
   ASSERT_FALSE(DTU.hasPostDomTree());
   ASSERT_EQ(DTU.getUpdateStrategy(), DomTreeUpdater::UpdateStrategy::Lazy);
@@ -323,7 +324,8 @@ TEST(DomTreeUpdater, LazyUpdateDTInheritedPreds) {
 
   // Make the DTU.
   DominatorTree DT(*F);
-  DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Lazy);
+  PostDominatorTree *PDT = nullptr;
+  DomTreeUpdater DTU(&DT, PDT, DomTreeUpdater::UpdateStrategy::Lazy);
   ASSERT_TRUE(DTU.hasDomTree());
   ASSERT_FALSE(DTU.hasPostDomTree());
   ASSERT_EQ(DTU.getUpdateStrategy(), DomTreeUpdater::UpdateStrategy::Lazy);
@@ -449,7 +451,7 @@ TEST(DomTreeUpdater, LazyUpdateBasicOperations) {
   // Make the DTU.
   DominatorTree DT(*F);
   PostDominatorTree PDT(*F);
-  DomTreeUpdater DTU(DT, PDT, DomTreeUpdater::UpdateStrategy::Lazy);
+  DomTreeUpdater DTU(&DT, &PDT, DomTreeUpdater::UpdateStrategy::Lazy);
   ASSERT_TRUE(DTU.hasDomTree());
   ASSERT_TRUE(DTU.hasPostDomTree());
   ASSERT_EQ(DTU.getUpdateStrategy(), DomTreeUpdater::UpdateStrategy::Lazy);