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

2 files changed, 13 insertions, 134 deletions

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;
 
diff --git a/llvm/test/Transforms/CodeGenPrepare/skip-merging-case-block.ll b/llvm/test/Transforms/CodeGenPrepare/skip-merging-case-block.ll
index b062e5fe734..194c86b8c04 100644
--- a/llvm/test/Transforms/CodeGenPrepare/skip-merging-case-block.ll
+++ b/llvm/test/Transforms/CodeGenPrepare/skip-merging-case-block.ll
@@ -143,107 +143,11 @@ declare void @calldefault(...) local_unnamed_addr
 !1 = !{!"branch_weights", i32 1 , i32 5, i32 1,i32 1, i32 1}
 !2 = !{!"branch_weights", i32 1 , i32 4, i32 1,i32 1, i32 1}
 
-; while.cond does not dominate return, expect to skip merging empty block
-; return.loopexit into return.
-@b = external global i32, align 4
-@a = external global i32*, align 8
-
-define void @f_switch4(i32 %i) local_unnamed_addr personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*) {
-; CHECK-LABEL: @f_switch4
-entry:
-  %0 = load i32, i32* @b, align 4
-  %cond = icmp eq i32 %0, 6
-  br i1 %cond, label %return, label %if.end
-
-if.end:                                           ; preds = %entry
-  %add = add i32 %i, 2
-  %1 = load i32*, i32** @a, align 8
-  %magicptr = ptrtoint i32* %1 to i32
-  br label %while.cond
-
-; CHECK-LABEL: while.cond:
-; CHECK: i32 0, label %return.loopexit
-; CHECK: i32 47, label %return.loopexit
-while.cond:                                       ; preds = %while.cond.backedge, %if.end
-  switch i32 %magicptr, label %while.cond.if.end10_crit_edge [
-    i32 0, label %return.loopexit
-    i32 47, label %return.loopexit
-  ]
-
-while.cond.if.end10_crit_edge:                    ; preds = %while.cond
-  br label %while.cond.backedge
-
-while.cond.backedge:                              ; preds = %while.cond.if.end10_crit_edge, %if.then9
-  br label %while.cond
-
-return.loopexit:                                  ; preds = %while.cond
-  br label %return
-
-; CHECK_LABEL: return:
-; CHECK: %{{.*}} = phi i32 [ 0, %entry ], [ %add, %return.loopexit ]
-return:                                           ; preds = %return.loopexit, %entry
-  %retval.4 = phi i32 [ 0, %entry ], [ %add, %return.loopexit ]
-  ret void
-}
-declare i32 @__gxx_personality_v0(...)
-
-; Expect to merge empty block while.cond2.loopexit into while.cond2
-define i32 @f_switch5(i32 %i) local_unnamed_addr {
-; CHECK-LABEL: @f_switch5
-entry:
-  %0 = load i32, i32* @b, align 4
-  %cond = icmp eq i32 %0, 6
-  br i1 %cond, label %while.cond.preheader, label %sw.epilog
-
-while.cond.preheader:                             ; preds = %entry
-  %1 = load i32*, i32** @a, align 8
-  %magicptr = ptrtoint i32* %1 to i64
-  %arrayidx = getelementptr inbounds i32, i32* %1, i64 1
-  br label %while.cond
-
-; CHECK-LABEL: while.cond:
-; CHECK: i64 32, label %while.cond2
-; CHECK: i64 0, label %while.cond2
-while.cond:                                       ; preds = %land.rhs, %while.cond.preheader
-  switch i64 %magicptr, label %land.rhs [
-    i64 32, label %while.cond2.loopexit
-    i64 0, label %while.cond2.loopexit
-  ]
-
-land.rhs:                                         ; preds = %while.cond
-  %2 = load i32, i32* %arrayidx, align 4
-  %tobool1 = icmp eq i32 %2, 0
-  br i1 %tobool1, label %while.cond2thread-pre-split.loopexit, label %while.cond
-
-while.cond2thread-pre-split.loopexit:             ; preds = %land.rhs
-  br label %while.cond2thread-pre-split
-
-while.cond2thread-pre-split:                      ; preds = %while.body4, %while.cond2thread-pre-split.loopexit
-  %.pr = phi i32* [ %.pr.pre, %while.body4 ], [ %1, %while.cond2thread-pre-split.loopexit ]
-  br label %while.cond2
-
-while.cond2.loopexit:                             ; preds = %while.cond, %while.cond
-  br label %while.cond2
-
-; CHECK-LABEL: while.cond2:
-; CHECK: %{{.*}} = phi i32* [ %.pr.pre, %while.body4 ], [ %1, %land.rhs ], [ %1, %while.cond ], [ %1, %while.cond ]
-while.cond2:                                      ; preds = %while.cond2.loopexit, %while.cond2thread-pre-split
-  %3 = phi i32* [ %.pr, %while.cond2thread-pre-split ], [ %1, %while.cond2.loopexit ]
-  %tobool3 = icmp eq i32* %3, null
-  br i1 %tobool3, label %sw.epilog, label %while.body4
-
-while.body4:                                      ; preds = %while.cond2
-  tail call void bitcast (void (...)* @fn2 to void ()*)()
-  %.pr.pre = load i32*, i32** @a, align 8
-  br label %while.cond2thread-pre-split
-
-sw.epilog:                                        ; preds = %while.cond2, %entry
-  ret i32 undef
-}
-
 
 ; This test that BFI/BPI is created without any assertion in isMergingEmptyBlockProfitable()
 ; in the case where empty blocks are removed before creating BFI/BPI.
+@b = common global i32 0, align 4
+@a = common global i32* null, align 8
 define i32 @should_not_assert(i32 %i) local_unnamed_addr {
 entry:
   %0 = load i32, i32* @b, align 4