From 32bcb5d7fb43a4c1c81632441ec5271d94d0caf2 Mon Sep 17 00:00:00 2001
From: Balaram Makam <bmakam@codeaurora.org>
Date: Fri, 27 Oct 2017 00:35:18 +0000
Subject: Revert "[CGP] Merge empty case blocks if no extra moves are added."

This reverts commit r316711. The domtree isn't getting updated correctly.

llvm-svn: 316721
---
 llvm/lib/CodeGen/CodeGenPrepare.cpp | 47 +++++++++----------------------------
 1 file changed, 11 insertions(+), 36 deletions(-)

(limited to 'llvm/lib/CodeGen/CodeGenPrepare.cpp')

diff --git a/llvm/lib/CodeGen/CodeGenPrepare.cpp b/llvm/lib/CodeGen/CodeGenPrepare.cpp
index 9f9bde40164..1e5f15397bb 100644
--- a/llvm/lib/CodeGen/CodeGenPrepare.cpp
+++ b/llvm/lib/CodeGen/CodeGenPrepare.cpp
@@ -212,7 +212,6 @@ class TypePromotionTransaction;
     const TargetTransformInfo *TTI = nullptr;
     const TargetLibraryInfo *TLInfo;
     const LoopInfo *LI;
-    DominatorTree *DT;
     std::unique_ptr<BlockFrequencyInfo> BFI;
     std::unique_ptr<BranchProbabilityInfo> BPI;
 
@@ -263,7 +262,6 @@ class TypePromotionTransaction;
 
     void getAnalysisUsage(AnalysisUsage &AU) const override {
       // FIXME: When we can selectively preserve passes, preserve the domtree.
-      AU.addRequired<DominatorTreeWrapperPass>();
       AU.addRequired<ProfileSummaryInfoWrapperPass>();
       AU.addRequired<TargetLibraryInfoWrapperPass>();
       AU.addRequired<TargetTransformInfoWrapperPass>();
@@ -345,8 +343,6 @@ bool CodeGenPrepare::runOnFunction(Function &F) {
   TLInfo = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
   TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
   LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
-  DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
-
   OptSize = F.optForSize();
 
   if (ProfileGuidedSectionPrefix) {
@@ -759,11 +755,6 @@ bool CodeGenPrepare::isMergingEmptyBlockProfitable(BasicBlock *BB,
     return true;
 
   SmallPtrSet<BasicBlock *, 16> SameIncomingValueBBs;
-  SmallVector<PHINode *, 16> PNs;
-
-  for (auto DestBBI = DestBB->begin();
-       auto *DestPN = dyn_cast<PHINode>(&*DestBBI); ++DestBBI)
-    PNs.push_back(DestPN);
 
   // Find all other incoming blocks from which incoming values of all PHIs in
   // DestBB are the same as the ones from BB.
@@ -773,10 +764,16 @@ bool CodeGenPrepare::isMergingEmptyBlockProfitable(BasicBlock *BB,
     if (DestBBPred == BB)
       continue;
 
-    if (llvm::all_of(PNs, [&](PHINode *PN) {
-      return (PN->getIncomingValueForBlock(BB) ==
-              PN->getIncomingValueForBlock(DestBBPred));
-        }))
+    bool HasAllSameValue = true;
+    BasicBlock::const_iterator DestBBI = DestBB->begin();
+    while (const PHINode *DestPN = dyn_cast<PHINode>(DestBBI++)) {
+      if (DestPN->getIncomingValueForBlock(BB) !=
+          DestPN->getIncomingValueForBlock(DestBBPred)) {
+        HasAllSameValue = false;
+        break;
+      }
+    }
+    if (HasAllSameValue)
       SameIncomingValueBBs.insert(DestBBPred);
   }
 
@@ -786,14 +783,6 @@ bool CodeGenPrepare::isMergingEmptyBlockProfitable(BasicBlock *BB,
   if (SameIncomingValueBBs.count(Pred))
     return true;
 
-  // Check to see if none of the phis have constant incoming values for BB and
-  // Pred dominates DestBB, in such case extra COPYs are likely not added, so
-  // there is no reason to skip merging.
-  if (DT->dominates(Pred, DestBB) && llvm::none_of(PNs, [BB](PHINode *PN) {
-        return isa<Constant>(PN->getIncomingValueForBlock(BB));
-      }))
-    return true;
-
   if (!BFI) {
     Function &F = *BB->getParent();
     LoopInfo LI{DominatorTree(F)};
@@ -896,7 +885,7 @@ void CodeGenPrepare::eliminateMostlyEmptyBlock(BasicBlock *BB) {
       // Remember if SinglePred was the entry block of the function.  If so, we
       // will need to move BB back to the entry position.
       bool isEntry = SinglePred == &SinglePred->getParent()->getEntryBlock();
-      MergeBasicBlockIntoOnlyPred(DestBB, DT);
+      MergeBasicBlockIntoOnlyPred(DestBB, nullptr);
 
       if (isEntry && BB != &BB->getParent()->getEntryBlock())
         BB->moveBefore(&BB->getParent()->getEntryBlock());
@@ -937,21 +926,7 @@ void CodeGenPrepare::eliminateMostlyEmptyBlock(BasicBlock *BB) {
 
   // The PHIs are now updated, change everything that refers to BB to use
   // DestBB and remove BB.
-  SmallVector<DominatorTree::UpdateType, 3> Updates;
-  for (auto *PredBB : predecessors(BB)) {
-    if (PredBB == BB)
-      continue;
-    DominatorTree::UpdateType UT = {DominatorTree::Delete, PredBB, BB};
-    if (!is_contained(Updates, UT)) {
-      Updates.push_back(UT);
-      if (PredBB != DestBB)
-        Updates.push_back({DominatorTree::Insert, PredBB, DestBB});
-    }
-  }
   BB->replaceAllUsesWith(DestBB);
-  DT->applyUpdates(Updates);
-  BB->getTerminator()->eraseFromParent();
-  DT->deleteEdge(BB, DestBB);
   BB->eraseFromParent();
   ++NumBlocksElim;
 
-- 
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