[PM] Refactor how the LoopRotation pass access the DominatorTree.

Instead of querying the pass every where we need to, do that once and
cache a pointer in the pass object. This is both simpler and I'm about
to add yet another place where we need to dig out that pointer.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@226391 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Scalar/LoopRotation.cpp

@@ -75,6 +75,7 @@ namespace {
     LoopInfo *LI;
     const TargetTransformInfo *TTI;
     AssumptionCache *AC;
+    DominatorTree *DT;
   };
 }
 
@@ -104,6 +105,8 @@ bool LoopRotate::runOnLoop(Loop *L, LPPassManager &LPM) {
   TTI = &getAnalysis<TargetTransformInfo>();
   AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(
       *L->getHeader()->getParent());
+  auto *DTWP = getAnalysisIfAvailable<DominatorTreeWrapperPass>();
+  DT = DTWP ? &DTWP->getDomTree() : nullptr;
 
   // Simplify the loop latch before attempting to rotate the header
   // upward. Rotation may not be needed if the loop tail can be folded into the
@@ -308,9 +311,8 @@ bool LoopRotate::simplifyLoopLatch(Loop *L) {
   // Nuke the Latch block.
   assert(Latch->empty() && "unable to evacuate Latch");
   LI->removeBlock(Latch);
-  if (DominatorTreeWrapperPass *DTWP =
-          getAnalysisIfAvailable<DominatorTreeWrapperPass>())
-    DTWP->getDomTree().eraseNode(Latch);
+  if (DT)
+    DT->eraseNode(Latch);
   Latch->eraseFromParent();
   return true;
 }
@@ -495,25 +497,23 @@ bool LoopRotate::rotateLoop(Loop *L, bool SimplifiedLatch) {
     // The conditional branch can't be folded, handle the general case.
     // Update DominatorTree to reflect the CFG change we just made.  Then split
     // edges as necessary to preserve LoopSimplify form.
-    if (DominatorTreeWrapperPass *DTWP =
-            getAnalysisIfAvailable<DominatorTreeWrapperPass>()) {
-      DominatorTree &DT = DTWP->getDomTree();
+    if (DT) {
       // Everything that was dominated by the old loop header is now dominated
       // by the original loop preheader. Conceptually the header was merged
       // into the preheader, even though we reuse the actual block as a new
       // loop latch.
-      DomTreeNode *OrigHeaderNode = DT.getNode(OrigHeader);
+      DomTreeNode *OrigHeaderNode = DT->getNode(OrigHeader);
       SmallVector<DomTreeNode *, 8> HeaderChildren(OrigHeaderNode->begin(),
                                                    OrigHeaderNode->end());
-      DomTreeNode *OrigPreheaderNode = DT.getNode(OrigPreheader);
+      DomTreeNode *OrigPreheaderNode = DT->getNode(OrigPreheader);
       for (unsigned I = 0, E = HeaderChildren.size(); I != E; ++I)
-        DT.changeImmediateDominator(HeaderChildren[I], OrigPreheaderNode);
+        DT->changeImmediateDominator(HeaderChildren[I], OrigPreheaderNode);
 
-      assert(DT.getNode(Exit)->getIDom() == OrigPreheaderNode);
-      assert(DT.getNode(NewHeader)->getIDom() == OrigPreheaderNode);
+      assert(DT->getNode(Exit)->getIDom() == OrigPreheaderNode);
+      assert(DT->getNode(NewHeader)->getIDom() == OrigPreheaderNode);
 
       // Update OrigHeader to be dominated by the new header block.
-      DT.changeImmediateDominator(OrigHeader, OrigLatch);
+      DT->changeImmediateDominator(OrigHeader, OrigLatch);
     }
 
     // Right now OrigPreHeader has two successors, NewHeader and ExitBlock, and
@@ -550,17 +550,15 @@ bool LoopRotate::rotateLoop(Loop *L, bool SimplifiedLatch) {
     PHBI->eraseFromParent();
 
     // With our CFG finalized, update DomTree if it is available.
-    if (DominatorTreeWrapperPass *DTWP =
-            getAnalysisIfAvailable<DominatorTreeWrapperPass>()) {
-      DominatorTree &DT = DTWP->getDomTree();
+    if (DT) {
       // Update OrigHeader to be dominated by the new header block.
-      DT.changeImmediateDominator(NewHeader, OrigPreheader);
-      DT.changeImmediateDominator(OrigHeader, OrigLatch);
+      DT->changeImmediateDominator(NewHeader, OrigPreheader);
+      DT->changeImmediateDominator(OrigHeader, OrigLatch);
 
       // Brute force incremental dominator tree update. Call
       // findNearestCommonDominator on all CFG predecessors of each child of the
       // original header.
-      DomTreeNode *OrigHeaderNode = DT.getNode(OrigHeader);
+      DomTreeNode *OrigHeaderNode = DT->getNode(OrigHeader);
       SmallVector<DomTreeNode *, 8> HeaderChildren(OrigHeaderNode->begin(),
                                                    OrigHeaderNode->end());
       bool Changed;
@@ -573,11 +571,11 @@ bool LoopRotate::rotateLoop(Loop *L, bool SimplifiedLatch) {
           pred_iterator PI = pred_begin(BB);
           BasicBlock *NearestDom = *PI;
           for (pred_iterator PE = pred_end(BB); PI != PE; ++PI)
-            NearestDom = DT.findNearestCommonDominator(NearestDom, *PI);
+            NearestDom = DT->findNearestCommonDominator(NearestDom, *PI);
 
           // Remember if this changes the DomTree.
           if (Node->getIDom()->getBlock() != NearestDom) {
-            DT.changeImmediateDominator(BB, NearestDom);
+            DT->changeImmediateDominator(BB, NearestDom);
             Changed = true;
           }
         }