[IDF] Teach Iterated Dominance Frontier to use a snapshot CFG based on a GraphDiff.

Summary:
Create the ability to compute IDF using a CFG View.
For this, we'll need a new DT created using a list of Updates (to be refactored later to a GraphDiff), and the GraphTraits based on the same GraphDiff.

Reviewers: kuhar, george.burgess.iv, mzolotukhin

Subscribers: sanjoy, jlebar, llvm-commits

Differential Revision: https://reviews.llvm.org/D50675

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@340052 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Analysis/IteratedDominanceFrontier.h

@@ -28,6 +28,7 @@
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/CFGDiff.h"
 #include "llvm/IR/Dominators.h"
 
 namespace llvm {
@@ -45,17 +46,21 @@ namespace llvm {
 template <class NodeTy, bool IsPostDom>
 class IDFCalculator {
  public:
-  IDFCalculator(DominatorTreeBase<BasicBlock, IsPostDom> &DT)
-      : DT(DT), useLiveIn(false) {}
+   IDFCalculator(DominatorTreeBase<BasicBlock, IsPostDom> &DT)
+       : DT(DT), GD(nullptr), useLiveIn(false) {}
 
-  /// Give the IDF calculator the set of blocks in which the value is
-  /// defined.  This is equivalent to the set of starting blocks it should be
-  /// calculating the IDF for (though later gets pruned based on liveness).
-  ///
-  /// Note: This set *must* live for the entire lifetime of the IDF calculator.
-  void setDefiningBlocks(const SmallPtrSetImpl<BasicBlock *> &Blocks) {
-    DefBlocks = &Blocks;
-  }
+   IDFCalculator(DominatorTreeBase<BasicBlock, IsPostDom> &DT,
+                 GraphDiff<BasicBlock *, IsPostDom> *GD)
+       : DT(DT), GD(GD), useLiveIn(false) {}
+
+   /// Give the IDF calculator the set of blocks in which the value is
+   /// defined.  This is equivalent to the set of starting blocks it should be
+   /// calculating the IDF for (though later gets pruned based on liveness).
+   ///
+   /// Note: This set *must* live for the entire lifetime of the IDF calculator.
+   void setDefiningBlocks(const SmallPtrSetImpl<BasicBlock *> &Blocks) {
+     DefBlocks = &Blocks;
+   }
 
   /// Give the IDF calculator the set of blocks in which the value is
   /// live on entry to the block.   This is used to prune the IDF calculation to
@@ -85,6 +90,7 @@ class IDFCalculator {
 
 private:
  DominatorTreeBase<BasicBlock, IsPostDom> &DT;
+ GraphDiff<BasicBlock *, IsPostDom> *GD;
  bool useLiveIn;
  const SmallPtrSetImpl<BasicBlock *> *LiveInBlocks;
  const SmallPtrSetImpl<BasicBlock *> *DefBlocks;

lib/Analysis/IteratedDominanceFrontier.cpp

@@ -17,6 +17,7 @@
 #include <queue>
 
 namespace llvm {
+
 template <class NodeTy, bool IsPostDom>
 void IDFCalculator<NodeTy, IsPostDom>::calculate(
     SmallVectorImpl<BasicBlock *> &PHIBlocks) {
@@ -61,29 +62,39 @@ void IDFCalculator<NodeTy, IsPostDom>::calculate(
       BasicBlock *BB = Node->getBlock();
       // Succ is the successor in the direction we are calculating IDF, so it is
       // successor for IDF, and predecessor for Reverse IDF.
-      for (auto *Succ : children<NodeTy>(BB)) {
+      auto DoWork = [&](BasicBlock *Succ) {
         DomTreeNode *SuccNode = DT.getNode(Succ);
 
         // Quickly skip all CFG edges that are also dominator tree edges instead
         // of catching them below.
         if (SuccNode->getIDom() == Node)
-          continue;
+          return;
 
         const unsigned SuccLevel = SuccNode->getLevel();
         if (SuccLevel > RootLevel)
-          continue;
+          return;
 
         if (!VisitedPQ.insert(SuccNode).second)
-          continue;
+          return;
 
         BasicBlock *SuccBB = SuccNode->getBlock();
         if (useLiveIn && !LiveInBlocks->count(SuccBB))
-          continue;
+          return;
 
         PHIBlocks.emplace_back(SuccBB);
         if (!DefBlocks->count(SuccBB))
           PQ.push(std::make_pair(
               SuccNode, std::make_pair(SuccLevel, SuccNode->getDFSNumIn())));
+      };
+
+      if (GD) {
+        for (auto Pair : children<
+                 std::pair<const GraphDiff<BasicBlock *, IsPostDom> *, NodeTy>>(
+                 {GD, BB}))
+          DoWork(Pair.second);
+      } else {
+        for (auto *Succ : children<NodeTy>(BB))
+          DoWork(Succ);
       }
 
       for (auto DomChild : *Node) {